DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
Although the words “he,” “him,” and “his” are used sparingly in this course to enhance communication, they are not intended to be gender driven or to affront or discriminate against anyone.
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PREFACE By enrolling in this self-study course, you have demonstrated a desire to improve yourself and the Navy. Remember, however, this self-study course is only one part of the total Navy training program. Practical experience, schools, selected reading, and your desire to succeed are also necessary to successfully round out a fully meaningful training program.
COURSE OVERVIEW: To introduce the student to the subject of Microelectronics who needs such a background in accomplishing daily work and/or in preparing for further study.
THE COURSE: This self-study course is organized into subject matter areas, each containing learning objectives to help you determine what you should learn along with text and illustrations to help you understand the information. The subject matter reflects day-to-day requirements and experiences of personnel in the rating or skill area. It also reflects guidance provided by Enlisted Community Managers (ECMs) and other senior personnel, technical references, instructions, etc., and either the occupational or naval standards, which are listed in the Manual of Navy Enlisted Manpower Personnel Classifications and Occupational Standards, NAVPERS 18068.
THE QUESTIONS: The questions that appear in this course are designed to help you understand the material in the text.
VALUE: In completing this course, you will improve your military and professional knowledge. Importantly, it can also help you study for the Navy-wide advancement in rate examination. If you are studying and discover a reference in the text to another publication for further information, look it up.
1998 Edition Prepared by TDCS Paul H.Smith
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“I am a United States Sailor.
I will support and defend the Constitution of the United States of America and I will obey the orders of those appointed over me.
I represent the fighting spirit of the Navy and those who have gone before me to defend freedom and democracy around the world.
I proudly serve my country’s Navy combat team with honor, courage and commitment.
I am committed to excellence and the fair treatment of all.”
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1. Microelectronics ....................................................................................................... 1-1
2. Miniature/Microminiature (2M) Repair Program and High-Reliability Soldering .. 2-1
3. Miniature and Microminiature Repair Procedures ................................................... 3-1
I. Glossary.................................................................................................................. AI-1
II. Reference List......................................................................................................... AII-1
INDEX ......................................................................................................................... INDEX-1
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Many of the figures included in this edition of NEETS, Module 14, Introduction to Microelectronics, were provided by the 2M section of the Education and Training Division, Naval Air Rework Facility, Pensacola, Florida, and the Naval Undersea Warfare Engineering Center, Keyport, Washington. Their assistance is gratefully acknowledged. Permission to use the trademark “PANAVISE” by Pana Vise Products, Inc., is gratefully acknowledged. The illustrations indicated below were provided by the designated companies. Permission to use these illustrations is gratefully acknowledged:
Siliconix, Inc. 1-33 Pana Vise Products, Inc. (former company name: Harris Semiconductors)
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The Navy Electricity and Electronics Training Series (NEETS) was developed for use by personnel in many electrical- and electronic-related Navy ratings. Written by, and with the advice of, senior technicians in these ratings, this series provides beginners with fundamental electrical and electronic concepts through self-study. The presentation of this series is not oriented to any specific rating structure, but is divided into modules containing related information organized into traditional paths of instruction.
The series is designed to give small amounts of information that can be easily digested before advancing further into the more complex material. For a student just becoming acquainted with electricity or electronics, it is highly recommended that the modules be studied in their suggested sequence. While there is a listing of NEETS by module title, the following brief descriptions give a quick overview of how the individual modules flow together.
Module 1, Introduction to Matter, Energy, and Direct Current, introduces the course with a short history of electricity and electronics and proceeds into the characteristics of matter, energy, and direct current (dc). It also describes some of the general safety precautions and first-aid procedures that should be common knowledge for a person working in the field of electricity. Related safety hints are located throughout the rest of the series, as well.
Module 2, Introduction to Alternating Current and Transformers, is an introduction to alternating current (ac) and transformers, including basic ac theory and fundamentals of electromagnetism, inductance, capacitance, impedance, and transformers.
Module 3, Introduction to Circuit Protection, Control, and Measurement, encompasses circuit breakers, fuses, and current limiters used in circuit protection, as well as the theory and use of meters as electrical measuring devices.
Module 4, Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading, presents conductor usage, insulation used as wire covering, splicing, termination of wiring, soldering, and reading electrical wiring diagrams.
Module 5, Introduction to Generators and Motors, is an introduction to generators and motors, and covers the uses of ac and dc generators and motors in the conversion of electrical and mechanical energies.
Module 6, Introduction to Electronic Emission, Tubes, and Power Supplies, ties the first five modules together in an introduction to vacuum tubes and vacuum-tube power supplies.
Module 7, Introduction to Solid-State Devices and Power Supplies, is similar to module 6, but it is in reference to solid-state devices.
Module 8, Introduction to Amplifiers, covers amplifiers. Module 9, Introduction to Wave-Generation and Wave-Shaping Circuits, discusses wave generation and wave-shaping circuits.
Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas, presents the characteristics of wave propagation, transmission lines, and antennas.
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Module 11,Microwave Principles, explains microwave oscillators, amplifiers, and waveguides.
Module 12,Modulation Principles, discusses the principles of modulation.
Module 13, Introduction to Number Systems and Logic Circuits, presents the fundamental concepts of number systems, Boolean algebra, and logic circuits, all of which pertain to digital computers.
Module 14, Introduction to Microelectronics, covers microelectronics technology and miniature and microminiature circuit repair.
Module 15, Principles of Synchros, Servos, and Gyros, provides the basic principles, operations, functions, and applications of synchro, servo, and gyro mechanisms.
Module 16, Introduction to Test Equipment, is an introduction to some of the more commonly used test equipments and their applications.
Module 17, Radio-Frequency Communications Principles, presents the fundamentals of a radio- frequency communications system.
Module 18, Radar Principles, covers the fundamentals of a radar system.
Module 19, The Technician's Handbook, is a handy reference of commonly used general information, such as electrical and electronic formulas, color coding, and naval supply system data.
Module 20,Master Glossary, is the glossary of terms for the series.
Module 21, Test Methods and Practices, describes basic test methods and practices.
Module 22, Introduction to Digital Computers, is an introduction to digital computers.
Module 23,Magnetic Recording, is an introduction to the use and maintenance of magnetic recorders and the concepts of recording on magnetic tape and disks.
Module 24, Introduction to Fiber Optics, is an introduction to fiber optics.
Embedded questions are inserted throughout each module, except for modules 19 and 20, which are reference books. If you have any difficulty in answering any of the questions, restudy the applicable section.
Although an attempt has been made to use simple language, various technical words and phrases have necessarily been included. Specific terms are defined in Module 20,Master Glossary.
Considerable emphasis has been placed on illustrations to provide a maximum amount of information. In some instances, a knowledge of basic algebra may be required.
Assignments are provided for each module, with the exceptions of Module 19, The Technician's Handbook; and Module 20, Master Glossary. Course descriptions and ordering information are in NAVEDTRA 12061, Catalog of Nonresident Training Courses.
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Throughout the text of this course and while using technical manuals associated with the equipment you will be working on, you will find the below notations at the end of some paragraphs. The notations are used to emphasize that safety hazards exist and care must be taken or observed.
AN OPERATING PROCEDURE, PRACTICE, OR CONDITION, ETC., WHICH MAY RESULT IN INJURY OR DEATH IF NOT CAREFULLY OBSERVED OR FOLLOWED.
AN OPERATING PROCEDURE, PRACTICE, OR CONDITION, ETC., WHICH MAY RESULT IN DAMAGE TO EQUIPMENT IF NOT CAREFULLY OBSERVED OR FOLLOWED.
An operating procedure, practice, or condition, etc., which is essential to emphasize.
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The text pages that you are to study are listed at the beginning of each assignment. Study these pages carefully before attempting to answer the questions. Pay close attention to tables and illustrations and read the learning objectives. The learning objectives state what you should be able to do after studying the material. Answering the questions correctly helps you accomplish the objectives.
Read each question carefully, then select the BEST answer. You may refer freely to the text. The answers must be the result of your own work and decisions. You are prohibited from referring to or copying the answers of others and from giving answers to anyone else taking the course.
To have your assignments graded, you must be enrolled in the course with the Nonresident Training Course Administration Branch at the Naval Education and Training Professional Development and Technology Center (NETPDTC). Following enrollment, there are two ways of having your assignments graded: (1) use the Internet to submit your assignments as you complete them, or (2) send all the assignments at one time by mail to NETPDTC.
Grading on the Internet: Advantages to Internet grading are:
• you get your results faster; usually by the next working day (approximately 24 hours).
assignments. To submit your assignment answers via the Internet, go to:
http://courses.cnet.navy.mil
Grading by Mail: When you submit answer sheets by mail, send all of your assignments at one time. Do NOT submit individual answer sheets for grading. Mail all of your assignments in an envelope, which you either provide yourself or obtain from your nearest Educational Services Officer (ESO). Submit answer sheets to:
Answer Sheets: All courses include one “scannable” answer sheet for each assignment. These answer sheets are preprinted with your SSN, name, assignment number, and course number. Explanations for completing the answer sheets are on the answer sheet.
Do not use answer sheet reproductions: Use only the original answer sheets that we provide—reproductions will not work with our scanning equipment and cannot be processed.
Follow the instructions for marking your answers on the answer sheet. Be sure that blocks 1, 2, and 3 are filled in correctly. This information is necessary for your course to be properly processed and for you to receive credit for your work.
Courses must be completed within 12 months from the date of enrollment. This includes time required to resubmit failed assignments.
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If your overall course score is 3.2 or higher, you will pass the course and will not be required to resubmit assignments. Once your assignments have been graded you will receive course completion confirmation.
If you receive less than a 3.2 on any assignment and your overall course score is below 3.2, you will be given the opportunity to resubmit failed assignments. You may resubmit failed assignments only once. Internet students will receive notification when they have failed an assignment--they may then resubmit failed assignments on the web site. Internet students may view and print results for failed assignments from the web site. Students who submit by mail will receive a failing result letter and a new answer sheet for resubmission of each failed assignment.
After successfully completing this course, you will receive a letter of completion.
Errata are used to correct minor errors or delete obsolete information in a course. Errata may also be used to provide instructions to the student. If a course has an errata, it will be included as the first page(s) after the front cover. Errata for all courses can be accessed and viewed/downloaded at:
http://www.advancement.cnet.navy.mil
We value your suggestions, questions, and criticisms on our courses. If you would like to communicate with us regarding this course, we encourage you, if possible, to use e-mail. If you write or fax, please use a copy of the Student Comment form that follows this page.
For subject matter questions:
E-mail<EMAIL_ADDRESS>Phone: Comm:<PHONE_NUMBER>, ext. 1728
DSN: 922-1001, ext. 1728 FAX:<PHONE_NUMBER> (Do not fax answer sheets.)
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If you are a member of the Naval Reserve, you will receive retirement points if you are authorized to receive them under current directives governing retirement of Naval Reserve personnel. For Naval Reserve retirement, this course is evaluated at 4 points. (Refer to Administrative Procedures for Naval Reservists on Inactive Duty, BUPERSINST 1001.39, for more information about retirement points.)
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NAVEDTRA: 14186 Date:
We need some information about you:
Your comments, suggestions, etc.:
Privacy Act Statement: Under authority of Title 5, USC 301, information regarding your military status is requested in processing your comments and in preparing a reply. This information will not be divulged without written authorization to anyone other than those within DOD for official use in determining performance.
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Learning objectives are stated at the beginning of each topic. These learning objectives serve as a preview of the information you are expected to learn in the topic. The comprehensive check questions are based on the objectives. By successfully completing the OCC-ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below.
Upon completion of this topic, you will be able to:
1. Outline the progress made in the history of microelectronics.
2. Describe the evolution of microelectronics from point-to-point wiring through high element density state-of-the-art microelectronics.
3. List the advantages and disadvantages of point-to-point wiring and high element density state-of- the-art microelectronics.
4. Identify printed circuit boards, diodes, transistors, and the various types of integrated circuits. Describe the fabrication techniques of these components.
5. Define the terminology used in microelectronic technology including the following terms used by the Naval Systems Commands:
a. microelectronics
b. microcircuit
c. microcircuit module
d. miniature electronics
e. system packaging
f. levels of packaging (0 to IV)
g. modular assemblies
h. cordwood modules
i. micromodules
6. Describe typical packaging levels presently used for microelectronic systems.
7. Describe typical interconnections used in microelectronic systems.
8. Describe environmental considerations for microelectronics.
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In NEETS, Module 6, Introduction to Electronic Emission, Tubes, and Power Supplies, you learned that Thomas Edison's discovery of thermionic emission opened the door to electronic technology. Progress was slow in the beginning, but each year brought new and more amazing discoveries. The development of vacuum tubes soon led to the simple radio. Then came more complex systems of communications. Modern systems now allow us to communicate with other parts of the world via satellite. Data is now collected from space by probes without the presence of man because of microelectronic technology.
Sophisticated control systems allow us to operate equipment by remote control in hazardous situations, such as the handling of radioactive materials. We can remotely pilot aircraft from takeoff to landing. We can make course corrections to spacecraft millions of miles from Earth. Space flight, computers, and even video games would not be possible except for the advances made in microelectronics.
The most significant step in modern electronics was the development of the transistor by Bell Laboratories in 1948. This development was to solid-state electronics what the Edison Effect was to the vacuum tube. The solid-state diode and the transistor opened the door to microelectronics.
MICROELECTRONICS is defined as that area of technology associated with and applied to the realization of electronic systems made of extremely small electronic parts or elements. As discussed in topic 2 of NEETS, Module 7, Introduction to Solid-State Devices and Power Supplies, the term microelectronics is normally associated with integrated circuits (IC). Microelectronics is often thought to include only integrated circuits. However, many other types of circuits also fall into the microelectronics category. These will be discussed in greater detail under solid-state devices later in this topic.
During World War II, the need to reduce the size, weight, and power of military electronic systems became important because of the increased use of these systems. As systems became more complex, their size, weight, and power requirements rapidly increased.  These unacceptable factors were the driving force in the development of smaller, lighter, and more efficient electronic circuit components. Such requirements continue to be important factors in the development of new systems, both for military and commercial markets. Military electronic systems, for example, continue to become more highly developed as their capability, reliability, and maintainability is increased. Progress in the development of military systems and steady advances in technology point to an ever- increasing need for increased technical knowledge of microelectronics in your Navy job.
Q1. What problems were evident about military electronic systems during World War II?
Q2. What discovery opened the door to solid-state electronics?
Q3. What is microelectronics?
The earliest electronic circuits were fairly simple. They were composed of a few tubes, transformers, resistors, capacitors, and wiring. As more was learned by designers, they began to increase both the size and complexity of circuits. Component limitations were soon identified as this technology developed.
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Vacuum tubes were found to have several built-in problems. Although the tubes were lightweight, associated components and chassis were quite heavy. It was not uncommon for such chassis to weigh 40 to 50 pounds. In addition, the tubes generated a lot of heat, required a warm-up time from 1 to 2 minutes, and required hefty power supply voltages of 300 volts dc and more.
No two tubes of the same type were exactly alike in output characteristics. Therefore, designers were required to produce circuits that could work with any tube of a particular type. This meant that additional components were often required to tune the circuit to the output characteristics required for the tube used.
Figure 1-1 shows a typical vacuum-tube chassis. The actual size of the transformer is approximately 4 × 4 × 3 inches. Capacitors are approximately 1 × 3 inches. The components in the figure are very large when compared to modern microelectronics.
A circuit could be designed either as a complete system or as a functional part of a larger system. In complex systems, such as radar, many separate circuits were needed to accomplish the desired tasks. Multiple-function tubes, such as dual diodes, dual triodes, tetrodes, and others helped considerably to reduce the size of circuits. However, weight, heat, and power consumption continued to be problems that plagued designers.
Another major problem with vacuum-tube circuits was the method of wiring components referred to as POINT-TO-POINT WIRING. Figure 1-2 is an excellent example of point-to-point wiring. Not only did this wiring look like a rat's nest, but it often caused unwanted interactions between components. For example, it was not at all unusual to have inductive or capacitive effects between wires. Also, point-to- point wiring posed a safety hazard when troubleshooting was performed on energized circuits because of exposed wiring and test points. Point-to-point wiring was usually repaired with general purpose test equipment and common hand tools.
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Vacuum-tube circuits proved to be reliable under many conditions. Still, the drawbacks of large size, heavy weight, and significant power consumption made them undesirable in most situations. For example, computer systems using tubes were extremely large and difficult to maintain. ENIAC, a completely electronic computer built in 1945, contained 18,000 tubes. It often required a full day just to locate and replace faulty tubes.
In some applications, we are still limited to vacuum tubes. Cathode-ray tubes used in radar, television, and oscilloscopes do not, as yet, have solid-state counterparts.
One concept that eased the technician's job was that of MODULAR PACKAGING. Instead of building a system on one large chassis, it was built of MODULES or blocks. Each module performed a necessary function of the system. Modules could easily be removed and replaced during troubleshooting and repair. For instance, a faulty power supply could be exchanged with a good one to keep the system operational. The faulty unit could then be repaired while out of the system. This is an example of how the module concept improved the efficiency of electronic systems. Even with these advantages, vacuum tube modules still had faults. Tubes and point-to-point wiring were still used and excessive size, weight, and power consumption remained as problems to be overcome.
Vacuum tubes were the basis for electronic technology for many years and some are still with us. Still, emphasis in vacuum-tube technology is rapidly becoming a thing of the past. The emphasis of technology is in the field of microelectronics.
Q4. What discovery proved to be the foundation for the development of the vacuum tube?
Q5. Name the components which greatly increase the weight of vacuum-tube circuitry.
Q6. What are the disadvantages of point-to-point wiring?
Q7. What is a major advantage of modular construction?
Q8. When designing vacuum-tube circuits, what characteristics of tubes must be taken into consideration?
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Now would be a good time for you to review the first few pages of NEETS, Module 7, Introduction to Solid-State Devices and Power Supplies, as a refresher for solid-state devices.
The transition from vacuum tubes to solid-state devices took place rapidly. As new types of transistors and diodes were created, they were adapted to circuits. The reductions in size, weight, and power use were impressive. Circuits that earlier weighed as much as 50 pounds were reduced in weight to just a few ounces by replacing bulky components with the much lighter solid-state devices.
The earliest solid-state circuits still relied on point-to-point wiring which caused many of the disadvantages mentioned earlier. A metal chassis, similar to the type used with tubes, was required to provide physical support for the components. The solid-state chassis was still considerably smaller and lighter than the older, tube chassis. Still greater improvements in component mounting methods were yet to come.
One of the most significant developments in circuit packaging has been the PRINTED CIRCUIT BOARD (pcb), as shown in figure 1-3. The pcb is usually an epoxy board on which the circuit leads have been added by the PHOTOETCHING process. This process is similar to photography in that copper-clad boards are exposed to controlled light in the desired circuit pattern and then etched to remove the unwanted copper. This process leaves copper strips (LANDS) that are used to connect the components. In general, printed circuit boards eliminate both the heavy, metal chassis and the point-to-point wiring.
Although printed circuit boards represent a major improvement over tube technology, they are not without fault. For example, the number of components on each board is limited by the sizes and shapes of components. Also, while vacuum tubes are easily removed for testing or replacement, pcb components are soldered into place and are not as easily removed.
Normally, each pcb contains a single circuit or a subassembly of a system. All printed circuit boards within the system are routinely interconnected through CABLING HARNESSES (groups of wiring or ribbons of wiring). You may be confronted with problems in faulty harness connections that affect system reliability. Such problems are often caused by wiring errors, because of the large numbers of wires in a harness, and by damage to those wires and connectors.
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Another mounting form that has been used to increase the number of components in a given space is the CORDWOOD MODULE, shown in figure 1-4. You can see that the components are placed perpendicular to the end plates. The components are packed very closely together, appearing to be stacked like cordwood for a fireplace. The end plates are usually small printed circuit boards, but may be insulators and solid wire, as shown in the figure. Cordwood modules may or may not be ENCAPSULATED (totally imbedded in solid material) but in either case they are difficult to repair.
Q9. List the major advantages of printed circuit boards.
Q10. What is the major disadvantage of printed circuit boards?
Q11. The ability to place more components in a given space is an advantage of the _______.
Many advertisements for electronic equipment refer to integrated circuits or solid-state technology. You know the meaning of the term solid-state, but what is an INTEGRATED CIRCUIT? The accepted Navy definition for an integrated circuit is that it consists of elements inseparably associated and formed on or within a single SUBSTRATE (mounting surface). In other words, the circuit components and all interconnections are formed as a unit. You will be concerned with three types of integrated circuits: MONOLITHIC, FILM, and HYBRID.
MONOLITHIC INTEGRATED CIRCUITS are those that are formed completely within a semiconductor substrate. These integrated circuits are commonly referred to as SILICON CHIPS.
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FILM INTEGRATED CIRCUITS are broken down into two categories, THIN FILM and THICK FILM. Film components are made of either conductive or nonconductive material that is deposited in desired patterns on a ceramic or glass substrate. Film can only be used as passive circuit components, such as resistors and capacitors. Transistors and/or diodes are added to the substrate to complete the circuit. Differences in thin and thick film will be discussed later in this topic.
HYBRID INTEGRATED CIRCUITS combine two or more integrated circuit types or combine one or more integrated circuit types and DISCRETE (separate) components. Figure 1-5 is an example of a hybrid integrated circuit consisting of silicon chips and film circuitry. The two small squares are chips and the irregularly shaped gray areas are film components.
STATE-OF-THE-ART MICROELECTRONICS.
Microelectronic technology today includes thin film, thick film, hybrid, and integrated circuits and combinations of these. Such circuits are applied in DIGITAL, SWITCHING, and LINEAR (analog) circuits. Because of the current trend of producing a number of circuits on a single chip, you may look for further increases in the packaging density of electronic circuits. At the same time you may expect a reduction in the size, weight, and number of connections in individual systems. Improvements in reliability and system capability are also to be expected.
Thus, even as existing capabilities are being improved, new areas of microelectronic use are being explored. To predict where all this use of technology will lead is impossible. However, as the demand for increasingly effective electronic systems continues, improvements will continue to be made in state-of- the-art microelectronics to meet the demands.
LARGE-SCALE INTEGRATION (lsi) and VERY LARGE-SCALE INTEGRATION (vlsi) are the results of improvements in microelectronics production technology. Figure 1-6 is representative of lsi. As shown in the figure, the entire SUBSTRATE WAFER (slice of semiconductor or insulator material) is
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used instead of one that has been separated into individual circuits. In lsi and vlsi, a variety of circuits can be implanted on a wafer resulting in further size and weight reduction. ICs in modern computers, such as home computers, may contain the entire memory and processing circuits on a single substrate.
Large-scale integration is generally applied to integrated circuits consisting of from 1,000 to 2,000 logic gates or from 1,000 to 64,000 bits of memory. A logic gate, as you should recall from NEETS, Module 13, Introduction to Number Systems, Boolean Algebra, and Logic Circuits, is an electronic switching network consisting of combinations of transistors, diodes, and resistors. Very large-scale integration is used in integrated circuits containing over 2,000 logic gates or greater than 64,000 bits of memory.
Q12. Define integrated circuit.
Q13. What are the three major types of integrated circuits?
Q14. How do monolithic ICs differ from film ICs?
Q15. What is a hybrid IC?
Q16. How many logic gates could be contained in lsi?
The purpose of this section is to give you a simplified overview of the manufacture of microelectronic devices. The process is far more complex than will be described here. Still, you will be able to see that microelectronics is not magic, but a highly developed technology.
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Development of a microelectronic device begins with a demand from industry or as the result of research. A device that is needed by industry may be a simple diode network or a complex circuit consisting of thousands of components. No matter how complex the device, the basic steps of production are similar. Each type of device requires circuit design, component arrangement, preparation of a substrate, and the depositing of proper materials on the substrate.
The first consideration in the development of a new device is to determine what the device is to accomplish. Once this has been decided, engineers can design the device. During the design phase, the engineers will determine the numbers and types of components and the interconnections, needed to complete the planned circuit.
Planning the component arrangement for a microelectronic device is a very critical phase of production. Care must be taken to ensure the most efficient use of space available. With simple devices, this can be accomplished by hand. In other words, the engineers can prepare drawings of component placement. However, a computer is used to prepare the layout for complex devices. The computer is able to store the characteristics of thousands of components and can provide a printout of the most efficient component placement. Component placement is then transferred to extremely large drawings. During this step, care is taken to maintain the patterns as they will appear on the substrate. Figure 1-7 shows a fairly simple IC MASK PATTERN. If this pattern were being prepared for production, it would be drawn several hundred times the size shown and then photographed. The photo would then be reduced in size until it was the actual desired size. At that time, the pattern would be used to produce several hundred patterns that would be used on one substrate. Figure 1-8 illustrates how the patterns would be distributed to act as a WAFER MASK for manufacturing.
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A wafer mask is a device used to deposit materials on a substrate. It allows material to be deposited in certain areas, but not in others. By changing the pattern of the mask, we can change the component arrangement of the circuit. Several different masks may be used to produce a simple microelectronic device. When used in proper sequence, conductor, semiconductor, or insulator materials may be applied to the substrate to form transistors, resistors, capacitors, and interconnecting leads.
As was mentioned earlier in this topic, microelectronic devices are produced on a substrate. This substrate will be of either insulator or semiconductor material, depending on the type of device. Film and hybrid ICs are normally constructed on a glass or ceramic substrate. Ceramic is usually the preferred material because of its durability.
Substrates used in monolithic ICs are of semiconductor material, usually silicon. In this type of IC, the substrate can be an active part of the IC. Glass or ceramic substrates are used only to provide support for the components.
Semiconductor substrates are produced by ARTIFICIALLY GROWING cylindrical CRYSTALS of pure silicon or germanium. Crystals are "grown" on a SEED CRYSTAL from molten material by slowly lifting and cooling the material repeatedly. This process takes place under rigidly controlled atmospheric and temperature conditions.
Figure 1-9 shows a typical CRYSTAL FURNACE. The seed crystal is lowered until it comes in contact with the molten material-silicon in this case. It is then rotated and raised very slowly. The seed crystal is at a lower temperature than the molten material. When the molten material is in contact with the seed, it solidifies around the seed as the seed is lifted. This process continues until the grown crystal is of the desired length. A typical crystal is about 2 inches in diameter and 10 to 12 inches long. Larger diameter crystals can be grown to meet the needs of the industry. The purity of the material is strictly controlled to maintain specific semiconductor properties. Depending on the need, n or p impurities are added to produce the desired characteristics. Several other methods of growing crystals exist, but the basic concept of crystal production is the same.
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The cylinder of semiconductor material that is grown is sliced into thicknesses of .010 to .020 inch in the first step of preparation, as shown in figure 1-10. These wafers are ground and polished to remove any irregularities and to provide the smoothest surface possible. Although both sides are polished, only the side that will receive the components must have a perfect finish.
Q17. What are the basic steps in manufacturing an IC?
Q18. Computer-aided layout is used to prepare _______ devices.
Q19. What purpose do masks serve?
Q20. What type of substrates are used for film and hybrid ICs?
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Q21. Describe the preparation of a silicon substrate.
Fabrication of monolithic ICs is the most complex aspect of microelectronic devices we will discuss. Therefore, in this introductory module, we will try to simplify this process as much as possible. Even though the discussion is very basic, the intent is still to increase your appreciation of the progress in microelectronics. You should, as a result of this discussion, come to realize that advances in manufacturing techniques are so rapid that staying abreast of them is extremely difficult.
Monolithic Fabrication.
Two types of monolithic fabrication will be discussed. These are the DIFFUSION METHOD and the EPITAXIAL METHOD.
DIFFUSION METHOD.—The DIFFUSION process begins with the highly polished silicon wafer being placed in an oven (figure 1-11). The oven contains a concentration impurity made up of impurity atoms which yield the desired electrical characteristics. The concentration of impurity atoms is diffused into the wafer and is controlled by controlling the temperature of the oven and the time that the silicon wafer is allowed to remain in the oven. This is called DOPING. When the wafer has been uniformly doped, the fabrication of semiconductor devices may begin. Several hundred circuits are produced simultaneously on the wafer.
The steps in the fabrication process described here, and illustrated in figure 1-12, would produce an npn, planar-diffused transistor. But, with slight variations, the technique may also be applied to the production of a complete circuit, including diodes, resistors, and capacitors. The steps are performed in the following order:
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1. An oxide coating is thermally grown over the n-type silicon starting material.
2. By means of the photolithographic process, a window is opened through the oxide layer. This is done through the use of masks, as discussed earlier.
3. The base of the transistor is formed by placing the wafer in a diffusion furnace containing a p- type impurity, such as boron. By controlling the temperature of the oven and the length of time that the wafer is in the oven, you can control the amount of boron diffused through the window (the boron will actually spread slightly beyond the window opening). A new oxide layer is then allowed to form over the area exposed by the window.
4. A new window, using a different mask much smaller than the first, is opened through the new oxide layer.
5. An n-type impurity, such as phosphorous, is diffused through the new window to form the emitter portion of the transistor. Again, the diffused material will spread slightly beyond the window opening. Still another oxide layer is then allowed to form over the window.
6. By means of precision-masking techniques, very small windows (about 0.005 inch in diameter) are opened in both the base and emitter regions of the transistor to provide access for electrical currents.
7. Aluminum is then deposited in these windows and alloyed to form the leads of the transistor or the IC.
(Note that the pn junctions are covered throughout the fabrication process by an oxide layer that prevents contamination.)
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EPITAXIAL METHOD.—The EPITAXIAL process involves depositing a very thin layer of silicon to form a uniformly doped crystalline region (epitaxial layer) on the substrate. Components are produced by diffusing appropriate materials into the epitaxial layer in the same way as the planar- diffusion method. When planar-diffusion and epitaxial techniques are combined, the component characteristics are improved because of the uniformity of doping in the epitaxial layer. A cross section of a typical planar-epitaxial transistor is shown in figure 1-13. Note that the component parts do not penetrate the substrate as they did in the planar-diffused transistor.
ISOLATION.—Because of the closeness of components in ICs, ISOLATION from each other becomes a very important factor. Isolation is the prevention of unwanted interaction or leakage between components. This leakage could cause improper operation of a circuit.
Techniques are being developed to improve isolation. The most prominent is the use of silicon oxide, which is an excellent insulator. Some manufacturers are experimenting with single-crystal silicon grown on an insulating substrate. Other processes are also used which are far too complex to go into here. With progress in isolation techniques, the reliability and efficiency of ICs will increase rapidly.
Thin film is the term used to describe a technique for depositing passive circuit elements on an insulating substrate with coating to a thickness of 0.0001 centimeter. Many methods of thin-film deposition exist, but two of the most widely used are VACUUM EVAPORATION and CATHODE SPUTTERING.
VACUUM EVAPORATION.—Vacuum evaporation is a method used to deposit many types of materials in a highly evacuated chamber in which the material is heated by electricity, as shown in figure 1-14. The material is radiated in straight lines in all directions from the source and is shadowed by any objects in its path.
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The wafers, with appropriate masks (figure 1-15), are placed above and at some distance from the material being evaporated. When the process is completed, the vacuum is released and the masks are removed from the wafers. This process leaves a thin, uniform film of the deposition material on all parts of the wafers exposed by the open portions of the mask. This process is also used to deposit interconnections (leads) between components of an IC.
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The vacuum evaporation technique is most suitable for deposition of highly reactive materials, such as aluminum, that are difficult to work with in air. The method is clean and allows a better contact between the layer of deposited material and the surface upon which it has been deposited. In addition, because evaporation beams travel in straight lines, very precise patterns may be produced.
CATHODE-SPUTTERING.—A typical cathode-sputtering system is illustrated in figure 1-16. This process is also performed in a vacuum. A potential of 2 to 5 kilovolts is applied between the anode and cathode (source material). This produces a GLOW DISCHARGE in the space between the electrodes. The rate at which atoms are SPUTTERED off the source material depends on the number of ions that strike it and the number of atoms ejected for each ion bombardment. The ejected atoms are deposited uniformly over all objects within the chamber. When the sputtering cycle is completed, the vacuum in the chamber is released and the wafers are removed. The masks are then removed from the wafers, leaving a deposit that forms the passive elements of the circuit, as shown in figure 1-17.
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Finely polished glass, glazed ceramic, and oxidized silicon have been used as substrate materials for thin films. A number of materials, including nichrome, a compound of silicon oxide and chromium cermets, tantalum, and titanium, have been used for thin-film resistors. Nichrome is the most widely used.
The process for producing thin-film capacitors involves deposition of a bottom electrode, a dielectric, and finally a top electrode. The most commonly used dielectric materials are silicon monoxide and silicon dioxide.
Thick films are produced by screening patterns of conducting and insulating materials on ceramic substrates. A thick film is a film of material with a thickness that is at least 10 times greater than the mean free path of an electron in that material, or approximately 0.001 centimeter. The technique is used to produce only passive elements, such as resistors and capacitors.
PROCEDURES.—One procedure used in fabricating a thick film is to produce a series of stencils called SCREENS. The screens are placed on the substrate and appropriate conducting or insulating materials are wiped across the screen. Once the conducting or insulating material has been applied, the screens are removed and the formulations are fired at temperatures above 600 degrees Celsius. This process forms alloys that are permanently bonded to the insulating substrate. To a limited extent, the characteristics of the film can be controlled by the firing temperature and length of firing time.
RESISTORS.—Thick-film resistance values can be held to a tolerance of ±10 percent. Closer tolerances are obtained by trimming each resistor after fabrication. Hundreds of different cermet formulations are used to produce a wide range of component parameters. For example, the material used for a 10-ohm-per-square resistor is quite different from that used for a 100-kilohm-per-square resistor.
CAPACITORS AND RESISTOR-CAPACITOR NETWORKS.—Capacitors are formed by a sequence of screenings and firings. Capacitors in this case consist of a bottom plate, intraconnections, a dielectric, and a top plate. For resistor-capacitor networks, the next step would be to deposit the resistor material through the screen. The final step is screening and firing of a glass enclosure to seal the unit.
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A hybrid microcircuit is one that is fabricated by combining two or more circuit types, such as film and semiconductor circuits, or a combination of one or more circuit types and discrete elements. The primary advantage of hybrid microcircuits is design flexibility; that is, hybrid microcircuits can be designed to provide wide use in specialized applications, such as low-volume and high-frequency circuits.
Several elements and circuits are available for hybrid applications. These include discrete components that are electrically and mechanically compatible with ICs. Such components may be used to perform functions that are supplementary to those of ICs. They can be handled, tested, and assembled with essentially the same technology and tools. A hybrid IC showing an enlarged chip is shown in figure 1-18.
Complete circuits are available in the form of UNCASED CHIPS (UNENCAPSULATED IC DICE). These chips are usually identical to those sold as part of the manufacturer's regular production line. They must be properly packaged and connected by the user if a high-quality final assembly is to be obtained. The circuits are usually sealed in a package to protect them from mechanical and environmental stresses. One-mil (0.001-inch), gold-wire leads are connected to the appropriate pins which are brought out of the package to allow external connections.
Q22. Name the two types of monolithic IC construction discussed.
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Q23. How do the two types of monolithic IC construction differ?
Q24. What is isolation?
Q25. What methods are used to deposit thin-film components on a substrate?
Q26. How are thick-film components produced?
Q27. What is a hybrid IC?
Q28. What is the primary advantage of hybrid circuits?
Once the IC has been produced, it requires a housing that will protect it from damage. This damage could result from moisture, dirt, heat, radiation, or other sources. The housing protects the device and aids in its handling and connection into the system in which the IC is used. The three most common types of packages are the modified TRANSISTOR-OUTLINE (TO) PACKAGE, the FLAT PACK, and the DUAL INLINE PACKAGE (DIP).
Transistor-Outline Package. The transistor-outline (TO) package was developed from early experience with transistors. It was a reliable package that only required increasing the number of leads to make it useful for ICs. Leads normally number between 2 and 12, with 10 being the most common for IC applications. Figure 1-19 is an exploded view of a TO-5 package. Once the IC has been attached to the header, bonding wires are used to attach the IC to the leads. The cover provides the necessary protection for the device. Figure 1-20 is an enlarged photo of an actual TO-5 with the cover removed. You can easily see that the handling of an IC without packaging would be difficult for a technician.
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The modified TO-5 package (figure 1-21) can be either plugged into [view (A)] or embedded in [view (B)] a board. The embedding method is preferred. Whether the package is plugged in or embedded, the interconnection area of the package leads must have sufficient clearance on both sides of the board. The plug-in method does not provide sufficient clearance between pads to route additional circuitry. When the packages are embedded, sufficient space exists between the pads [because of the increased diameter of the interconnection pattern, shown at the right in view (B)] for additional conductors.
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Many types of IC flat packs are being produced in various sizes and materials. These packages are available in square, rectangular, oval, and circular configurations with 10 to 60 external leads. They may be
made of metal, ceramic, epoxy, glass, or combinations of those materials. Only the ceramic flat pack will be discussed here. It is representative of all flat packs with respect to general package requirements (see figure 1-22).
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After the external leads are sealed to the mounting base, the rectangular area on the inside bottom of the base is treated with metal slurry to provide a surface suitable for bonding the monolithic die to the base. The lead and the metalized area in the bottom of the package are plated with gold. The die is then attached by gold-silicon bonding.
The die-bonding step is followed by bonding gold or aluminum wires between the bonding islands on the IC die and on the inner portions of the package leads. Next, a glass-soldered preformed frame is placed on top of the mounting base. One surface of the ceramic cover is coated with Pyroceram glass, and the cover is placed on top of the mounting base. The entire assembly is placed in an oven at 450 degrees Celsius. This causes the glass solder and Pyroceram to fuse and seal the cover to the mounting base. A ceramic flat pack is shown in figure 1-23. It has been opened so that you can see the chip and bonding wires.
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The dual inline package (DIP) was designed primarily to overcome the difficulties associated with handling and inserting packages into mounting boards. DIPs are easily inserted by hand or machine and require no spreaders, spacers, insulators, or lead-forming tools. Standard hand tools and soldering irons can be used to field-service the devices. Plastic DIPs are finding wide use in commercial applications, and a number of military systems are incorporating ceramic DIPS.
The progressive stages in the assembly of a ceramic DIP are illustrated in figure 1-24, views (A) through (E). The integrated-circuit die is sandwiched between the two ceramic elements, as shown in view (A). The element on the left of view (A) is the bottom half of the sandwich and will hold the integrated-circuit die. The ceramic section on the right is the top of the sandwich. The large well in view (B) protects the IC die from mechanical stress during sealing operations. Each of the ceramic elements is coated with glass which has a low melting temperature for subsequent joining and sealing. View (B) shows the Kovar lead frame stamped and bent into its final shape. The excess material is intended to preserve pin alignment. The holes at each end are for the keying jig used in the final sealing operation. The lower half of the ceramic package is inserted into the lead frame shown in view (C). The die is mounted in the well and leads are attached. The top ceramic elements are bonded to the bottom element shown in view (D) and the excess material is removed from the package. View (E) is the final product.
Ceramic DIPs are processed individually while plastic DIPs are processed in quantities of two or more (in chain fashion). After processing, the packages are sawed apart. The plastic package also uses a Kovar lead frame, but the leads are not bent until the package is completed. Because molded plastic is
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used to encapsulate the IC die, no void will exist between the cover and die, as is the case with ceramic packaging.
At present, ceramic DIPs are the most common of the two package types to be found in Navy microelectronic systems. Figure 1-25 shows a DIP which has been opened.
Considerable effort has been devoted to eliminating the fine wires used to connect ICs to Kovar leads. The omission of these wires reduces the cost of integrated circuits by eliminating the costs associated with the bonding process. Further, omission of the wires improves reliability by eliminating a common cause of circuit failure.
 These patterns connect the external leads to bonding pads on the inside surface of the die. The pads are then bonded to appropriate pedestals on the package that correspond to those of the bonding pads on the die (figure 1-26).
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wafer, as shown in figure 1-27. This type of structure imposes no electrical difficulty, and parasitic capacitance (under 0.05 picofarad per lead) is equivalent to that of a wire-bonded and brazed-chip assembly. In addition, the electrodes may be tapered to allow for lower inductance, impedance matching, and better heat conductance. The beam-lead technique is easily accomplished and does not have the disadvantages of chip brazing and wire bonding. The feasibility of this technique has been demonstrated in a variety of digital, linear, and thin-film circuits.
Another advance in packaging is that of increasing the size of DIPs. General purpose DIPs have from 4 to 16 pins. Because of lsi and vlsi, manufacturers are producing DIPs with up to 64 pins. Although size is increased considerably, all the advantages of the DIP are retained. DIPs are normally designed to a particular specification set by the user.
Q29. What is the purpose of the IC package?
Q30. What are the three most common types of packages?
Q31. What two methods of manufacture are being used to eliminate bonding wires?
At the beginning of this topic, we discussed many applications of microelectronics. You should understand that these applications cover all areas of modern electronics technology. Microelectronic ICs are produced that can be used in many of these varying circuit applications to satisfy the needs of modern technology. This section will introduce you to some of these applications and will show you some EQUIVALENT CIRCUIT comparisons of discrete components and integrated circuits.
Integrated circuits can be produced that combine all the elements of a complete electronic circuit. This can be done with either a single chip of silicon or a single chip of silicon in combination with film components. The importance of this new production method in the evolution of microelectronics can be demonstrated by comparing a conventional J-K flip-flop circuit incorporating solid-state discrete devices and the same type of circuit employing integrated circuitry. (A J-K flip-flop is a circuit used primarily in computers.)
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You should recall from NEETS, Module 13, Introduction to Number Systems, Boolean Algebra, and Logic Circuits, that a basic flip-flop is a device having two stable states and two input terminals (or types of input signals), each of which corresponds to one of the two states. The flip-flop remains in one state until caused to change to the other state by application of an input voltage pulse.
A J-K flip-flop differs from the basic flip-flop because it has a third input terminal. A clock pulse, or trigger, is usually applied to this input to ensure proper timing in the circuit. An input signal must occur at the same time as the clock pulse to change the state of the flip-flop. The conventional J-K flip-flop circuit in figure 1-28 requires approximately 40 discrete components, 200 connections, and 300 processing operations. Each of these 300 operations (seals and connections) represents a possible source of failure. If all the elements of this circuit are integrated into one chip of silicon, the number of connections drops to approximately 14. This is because all circuit elements are intraconnected inside the package and the 300 processing operations are reduced to approximately 30. Figure 1-29 represents a size comparison of a discrete J-K circuit and an integrated circuit of the same type.
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When you look at an IC package you should notice that the IC could be connected incorrectly into a circuit. Such improper replacement of a component would likely result in damage to the equipment. For this reason, each IC has a REFERENCE MARK to align the component for placement. The dual inline package (both plastic and ceramic) and the flat pack have a notch, dot, or impression on the package. When the package is viewed from the top, pin 1 will be the first pin in the counterclockwise direction next to the reference mark. Pin 1 may also be marked directly by a hole or notch or by a tab on it (in this case pin 1 is the counting reference). When the package is viewed from the top, all other pins are numbered consecutively in a counterclockwise direction from pin 1, as shown in figure 1-30, views (A) and (B).
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The TO-5 can has a tab for the reference mark. When numbering the leads, you must view the TO-5 can from the bottom. Pin 1 will be the first pin in a clockwise direction from the tab. All other pins will be numbered consecutively in a clockwise direction from pin 1, as shown in figure 1-31.
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As mentioned earlier, integrated circuits are designed and manufactured for hundreds of different uses. Logic circuits, clock circuits, amplifiers, television games, transmitters, receivers, and musical instruments are just a few of these applications.
In schematic drawings, ICs are usually represented by one of the schematic symbols shown in figure 1-32. The IC is identified according to its use by the numbers printed on or near the symbol. That series of numbers and letters is also stamped on the case of the device and can be used along with the data sheet, as shown in the data sheet in figure 1-33, by circuit designers and maintenance personnel. This data sheet is provided by the manufacturer. It provides a schematic diagram and describes the type of device, its electrical characteristics, and typical applications. The data sheet may also show the pin configurations with all pins labeled. If the pin configurations are not shown, there may be a schematic diagram showing pin functions. Some data sheets give both pin configurations and schematic diagrams, as shown in figure 1-34. This figure illustrates a manufacturer's data sheet with all of the pin functions shown.
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Q32. On DIP and flat-pack ICs viewed from the top, pin 1 is located on which side of the reference mark?
Q33. DIP and flat-pack pins are numbered consecutively in what direction?
Q34. DIP and flat-pack pins are numbered consecutively in what direction?
Q35. Viewed from the bottom, TO-5 pins are counted in what direction?
Q36. The numbers and letters on ICs and schematics serve what purpose?
You should understand the terminology used in microelectronics to become an effective and knowledgeable technician. You should be familiar with packaging concepts from a maintenance standpoint and be able to recognize the different types of assemblies. You should also know the electrical and environmental factors that can affect microelectronic circuits. In the next section of this topic we will define and discuss each of these areas.
As in any special electronics field, microelectronics terms and definitions are used to clarify communications. This is done so that everyone involved in microelectronics work has the same knowledge of the field. You can imagine how much trouble you would have remembering 10 or more different names and definitions for a resistor. If standardization didn't exist for the new terminology, you would have far more trouble understanding microelectronics. To standardize terminology in microelectronics, the Navy has adopted several definitions with which you should become familiar. These definitions will be presented in this section.
Microelectronics is that area of electronics technology associated with electronics systems built from extremely small electronic parts or elements. Most of today's computers, weapons systems, navigation systems, communications systems, and radar systems make extensive use of microelectronics technology.
A microcircuit is not what the old-time technician would recognize as an electronic circuit. The old- timer would no longer see the familiar discrete parts (individual resistors, capacitors, inductors, transistors, and so forth). Microelectronic circuits, as discussed earlier, are complete circuits mounted on a substrate (integrated circuit). The process of fabricating microelectronic circuits is essentially one of building discrete component characteristics either into or onto a single substrate. This is far different from soldering resistors, capacitors, transistors, inductors, and other discrete components into place with wires and lugs. The component characteristics built into microcircuits are referred to as ELEMENTS rather than discrete components. Microcircuits have a high number of these elements per substrate compared to a circuit with discrete components of the same relative size. As a matter of fact, microelectronic circuits often contain thousands of times the number of discrete components. The term HIGH EQUIVALENT CIRCUIT DENSITY is a description of this element-to-discrete part relationship. For example, suppose you have a circuit with 1,000 discrete components mounted on a chassis which is 8 × 10 × 2 inches. The equivalent circuit in microelectronics might be built into or onto a single substrate which is only 3/8 × 1 × 1/4 inch. The 1,000 elements of the microcircuit would be very close to each other (high density) by
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comparison to the distance between discrete components mounted on the large chassis. The elements within the substrate are interconnected on the single substrate itself to perform an electronic function. A microcircuit does not have any discrete components mounted on it as do printed circuit boards, circuit card assemblies, and modules composed exclusively of discrete component parts.
Microcircuits may be used in combination with discrete components. An assembly of microcircuits or a combination of microcircuits and discrete conventional electronic components that performs one or more distinct functions is a microcircuit module. The module is constructed as an independently packaged, replaceable unit. Examples of microcircuit modules are printed circuit boards and circuit card assemblies. Figure 1-35 is a photograph of a typical microcircuit module.
Miniature electronics includes miniature electronic components and packages. Some examples are printed circuit boards, printed wiring boards, circuit card assemblies, and modules composed exclusively of discrete electronic parts and components (excluding microelectronic packages) mounted on boards, assemblies, or modules. MOTHER BOARDS, large printed circuit boards with plug-in modules, are considered miniature electronics. Cordwood modules also fall into this category. Miniature motors, synchros, switches, relays, timers, and so forth, are also classified as miniature electronics.
Recall that microelectronic components contain integrated circuits. Miniature electronics contain discrete elements or parts. You will notice that printed circuit boards and circuit card assemblies are mentioned in more than one definition. To identify the class (microminiature or miniature) of the unit, you must first determine the types of components used.
Q37. Standardized terms improve what action between individuals?
Q38. Microcircuit refers to any component containing what types of elements?
Q39. Components made up exclusively of discrete elements are classified as what type of electronics?
When a new electronics system is developed, several areas of planning require special attention. An area of great concern is that of ensuring that the system performs properly. The designer must take into
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account all environmental and electrical factors that may affect the system. This includes temperature, humidity, vibration, and electrical interference. The design factor that has the greatest impact on you, as the technician, is the MAINTAINABILITY of the system. The designer must take into account how well you will be able to locate problems, identify the faulty components, and make the necessary repairs. If a system cannot be maintained easily, then it is not an efficient system. PACKAGING, the method of enclosing and mounting components, is of primary importance in system maintainability.
For the benefit of the technician, system packaging is usually broken down to five levels (0 to IV). These levels are shown in figure 1-36.
LEVEL 0.—Level 0 packaging identifies nonrepairable parts, such as integrated circuits, transistors, resistors, and so forth. This is the lowest level at which you can perform maintenance. You are limited to simply replacing the faulty element or part. Depending on the type of part, repair might be as simple as plugging in a new relay. If the faulty part is an IC, special training and equipment will be required to accomplish the repair. This will be discussed in topic 2.
LEVEL I.—This level is normally associated with small modules or submodules that are attached to circuit cards or mother boards. The analog-to-digital (A/D) converter module is a device that converts a signal that is a function of a continuous variable (like a sine wave) into a representative number sequence in digital form. The A/D converter in figure 1-37 is a typical Level I component. At this level of
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maintenance you can replace the faulty module with a good one. The faulty module can then be repaired at a later time or discarded. This concept significantly reduces the time equipment is inoperable.
LEVEL II.—Level II packaging is composed of large printed circuit boards and/or cards (mother boards). Typical units of this level are shown in figures 1-37 and 1-38. In figure 1-38 the card measures 15 × 5.25 inches. The large dual inline packages (DIPs) are 2.25 inches x 0.75 inch. Other DIPs on the pcb are much smaller. Interconnections are shown between DIPs. You should also be able to locate a few discrete components. Repair consists of removing the faulty DIP or discrete component from the pcb and replacing it with a new part. Then the pcb is placed back into service. The removed part may be a level 0 or I part and would be handled as described in those sections. In some cases, the entire pcb should be replaced.
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LEVEL III.—Drawers or pull-out chassis are level III units, as shown in figure 1-36. These are designed for accessibility and ease of maintenance. Normally, circuit cards associated with a particular subsystem will be grouped together in a drawer. This not only makes for an orderly arrangement of subsystems but also eliminates many long wiring harnesses. Defective cards are removed from such drawers and defective components are repaired as described in level II.
LEVEL IV.—Level IV is the highest level of packaging. It includes the cabinets, racks, and wiring harnesses necessary to interconnect all of the other levels. Other pieces of equipment of the same system classified as level IV, such as radar antennas, are broken down into levels 0 to III in the same manner.
During component troubleshooting procedures, you progress from level IV to III to II and on to level 0 where you identify the faulty component. As you become more familiar with a system, you should be able to go right to the drawer or module causing the problem.
Q40. Resistors, capacitors, transistors, and the like, are what level of packaging?
Q41. Modules or submodules attached to a mother board are what packaging level?
Q42. What is the packaging level of a pcb?
As electronic systems become more complex, interconnections between components also becomes more complex. As more components are added to a given space, the requirements for interconnections become extremely complicated. The selection of conductor materials, insulator materials, and component physical size can greatly affect the performance of the circuit. Poor choices of these materials can contribute to poor signals, circuit noise, and unwanted electrical interaction between components. The three most common methods of interconnection are the conventional pcb, the multilayer pcb, and the modular assembly. Each of these will be discussed in the following sections.
Printed circuit boards were discussed earlier in topic 1. You should recall that a conventional pcb consists of glass-epoxy insulating base on which the interconnecting pattern has been etched. The board may be single- or double-sided, depending on the number of components mounted on it. Figures 1-37 and 1-38 are examples of conventional printed circuit boards.
Multilayer Printed Circuit Board.
The multilayer printed circuit board is emerging as the solution is interconnection problems associated with high-density packaging. Multilayer boards are used to:
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Figure 1-39 illustrates how individual boards are mated to form the multilayer unit. Although all multilayer boards are similarly constructed, various methods can be used to interconnect the circuitry from layer to layer. Three proven processes are the clearance-hole, plated-through hole, and layer build- up methods.
CLEARANCE-HOLE METHOD.—In the CLEARANCE-HOLE method, a hole is drilled in the copper island (terminating end) of the appropriate conductor on the top layer. This provides access to a conductor on the second layer as shown by hole A in figure 1-40.  Usually, the hole is drilled through the entire assembly at the connection site. This small hole is necessary for the SOLDER-FLOW PROCESS used with this interconnection method.
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Conductors located several layers below the top are connected by using a STEPPED-DOWN HOLE PROCESS. Before assembly of a three-level board, a clearance hole is drilled down to the first layer to be interconnected. The first layer to be interconnected is predrilled with a hole smaller than those drilled in layers 1 and 2; succeeding layers to be connected have progressively smaller clearance holes. After assembly, the exposed portion of the conductors are interconnected by filling the stepped-down holes with solder, as shown by hole B in figure 1-40. The larger the number of interconnections required at one point, the larger must be the diameter of the clearance holes on the top layer. Large clearance holes on the top layer allow less space for components and reduce packaging density.
PLATED-THROUGH-HOLE METHOD.—The PLATED-THROUGH-HOLE method of interconnecting conductors is illustrated in figure 1-41. The first step is to temporarily assemble all the layers into their final form. Holes corresponding to required connections are drilled through the entire assembly and then the unit is disassembled. The internal walls of those holes to be interconnected are plated with metal which is 0.001 inch thick. This, in effect, connects the conductor on the board surface through the hole itself. This process is identical to that used for standard printed circuit boards. The boards are then reassembled and permanently bonded together with heat and pressure. All the holes are plated through with metal.
LAYER BUILD-UP METHOD.—With the LAYER BUILD-UP method, conductors and insulation layers are alternately deposited on a backing material, as shown in figure 1-42. This method produces copper interconnections between layers and minimizes the thermal expansion effects of dissimilar materials. However, reworking the internal connections in built-up layers is usually difficult, if not impossible.
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Some of the advantages and disadvantages of printed circuit boards were discussed earlier in this topic. They are strong, lightweight, and eliminate point-to-point wiring. Multilayer printed circuit boards allow more components per card. Entire circuits or even subsystems may be placed on the same card. However, these cards do have some drawbacks. For example, all components are wired into place, repair of cards requires special training and/or special equipment, and some cards cannot be economically repaired because of their complexity (these are referred to as THROWAWAYS).
The MODULAR-ASSEMBLY (nonrepairable item) approach was devised to achieve ultra-high density packaging. The evolution of this concept, from discrete components to microelectronics, has progressed through various stages. These stages began with cordwood assemblies and functional blocks and led to complete subsystems in a single package. Examples of these configurations are shown in figure 1-43, view (A), view (B), and view (C).
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Cordwood Modules.
The cordwood assembly, shown in view (A) of figure 1-43, was designed and fabricated in various forms and sizes, depending on user requirements. This design was used to reduce the physical size and increase the component density and complexity of circuits through the use of discrete devices. However, the use of the technique was somewhat limited by the size of available discrete components used.
The next generation assembly was the micromodule. Designers tried to achieve maximum density in this design by using discrete components, thick- and thin-film technologies, and the insulator substrate principle. The method used in this construction technique allowed for the efficient use of space and also provided the mechanical strength necessary to withstand shock and vibration.
Semiconductor technology was then improved further with the introduction of the integrated circuit. The flat-pack IC form, shown in view (C), emphasizes the density and complexity that exists with this technique. This technology provides the means of reducing the size of circuits. It also allows the reduction of the size of systems through the advent of the lsi circuits that are now available and vlsi circuits that are being developed by various IC manufacturers.
Continuation of this trend toward microminiaturization will result in system forms that will require maintenance personnel to be specially trained in maintenance techniques to perform testing, fault isolation, and repair of systems containing complex miniature and microminiature circuits.
Q43. What are the three most common methods of interconnections?
Q44. Name the three methods of interconnecting components in multilayer printed circuit boards.
Q45. What is one of the major disadvantages of multilayer printed circuit boards?
Q46. What was the earliest form of micromodule?
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The environmental requirements of each system design are defined in the PROCUREMENT SPECIFICATION. Typical environmental requirements for an IC, for example, are shown in table 1-1. After these system requirements have been established, components, applications, and packaging forms are considered. This then leads to the most effective system form.
Table 1-1.—Environmental Requirements
Humidity 95 percent plus condensation (MIL-E-16400E) Shock 250 to 600 g (MIL-S-901C) Vibration 5 to 15 Hz, 0.060 DA 16 to 25 Hz, 0.040 DA 26 to
33 Hz, 0.020 DA Resonance test in three mutual perpendicular planes. (MIL-STD-167)
In the example in table 1-1, the environmental requirements are set forth as MILITARY STANDARDS for performance. The actual standard for a particular factor is in parentheses. To meet each of these standards, the equipment or component must perform adequately within the test guidelines. For example, to pass the shock test, the component must withstand a shock of 250 to 600 Gs (force of gravity). During vibration testing, the component must withstand vibrations of 5 to 15 cycles per second for 0.06 day, or about 1 1/2 hours; 16 to 25 cycles for 1 hour; and 26 to 33 cycles for 1/2 hour. Rf interference between 30 hertz and 40 gigahertz must not affect the performance of the component. Temperature and humidity factors are self-explanatory.
When selecting the most useful packaging technique, the system designer must consider not only the environmental and electrical performance requirements of the system, but the maintainability aspects as well. The system design will, therefore, reflect performance requirements of maintenance and repair personnel.
The electrical characteristics of a component can sometimes be adversely affected when it is placed in a given system. This effect can show up as signal distortion, an improper timing sequence, a frequency shift, or numerous other types of unwanted interactions. Techniques designed to minimize the effects of system packaging on component performance are incorporated into system design by planners. These techniques should not be altered during your maintenance. Several of the techniques used by planners are discussed in the following sections.
Ground Planes and Shielding.
At packaging levels I and II, COPPER PLANES with voids, where feed-through is required, can be placed anywhere within the multilayer board. These planes tend to minimize interference between circuits and from external sources.
At other system levels, CROSS TALK (one signal interfering with another), rf generation within the system, and external interference are suppressed through the use of various techniques. These techniques
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are shown in figure 1-44. As shown in the figure, rf shielding is used on the mating surfaces of the package, cabling is shielded, and heat sinks are provided.
To meet the high-frequency characteristics and propagation timing required by present and future systems, the device package must not have excessive distributed capacitance and/or inductance. This type of packaging is accomplished in the design of systems using ICs and other microelectronic devices by using shorter leads internal to the package and by careful spacing of complex circuits on printed circuit boards. To take advantage of the inherent speed of the integrated circuit, you must keep the signal propagation time between circuits to a minimum. The signal is delayed approximately 1 nanosecond per foot, so reducing the distance between circuits as much as possible is necessary. This requires the use of structures, such as high-density digital systems with an emphasis on large-scale integration, for systems in the future. Also, maintenance personnel should be especially concerned with the spacing of circuits, lead dress, and surface cleanliness. These factors affect the performance of high-speed digital and analog circuits.
Q47. In what publication are environmental requirements for equipment defined?
Q48. In what publication would you find guidelines for performance of military electronic parts?
Q49. Who is responsible for meeting environmental and electrical requirements of a system?
Q50. What methods are used to prevent unwanted component interaction?
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This topic has presented information on the development and manufacture of microelectronic devices. The information that follows summarizes the important points of this topic.
VACUUM-TUBE CIRCUITS in most modern military equipment are unacceptable because of size, weight, and power use.
Discovery of the transistor in 1948 marked the beginning of MICROELECTRONICS.
The PRINTED CIRCUIT BOARD (pcb) reduces weight and eliminates point-to-point wiring.
The INTEGRATED CIRCUITS (IC) consist of elements inseparably associated and formed on or within a single SUBSTRATE.
ICs are classified as three types: MONOLITHIC, FILM, and HYBRID.
The MONOLITHIC IC, called a chip or die, contains both active and passive elements.
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FILM COMPONENTS are passive elements, either resistors or capacitors.
HYBRID ICs are combinations of monolithic and film or of film and discrete components, or any combination thereof. They allow flexibility in circuits.
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Rapid development has resulted in increased reliability and availability, reduced cost, and higher element density.
LARGE-SCALE (lsi) and VERY LARGE-SCALE INTEGRATION (vlsi) allow thousands of elements in a single chip.
MONOLITHIC ICs are produced by the diffusion or epitaxial methods.
DIFFUSED elements penetrate the substrate, EPITAXIAL do not.
ISOLATION is a production method to prevent unwanted interaction between elements within a chip.
THIN-FILM ELEMENTS are produced through EVAPORATION or CATHODE SPUTTERING techniques.
THICK-FILM ELEMENTS are screened onto the substrate.
The most common types of packages for ICs are TO, FLAT PACK, and DUAL INLINE.
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FLIP CHIPS and BEAM-LEAD CHIPS are techniques being developed to eliminate bonding wires and to improve packaging.
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Large DIPs are being used to package lsi and vlsi. They can be produced with up to 64 pins and are designed to fulfill a specific need.
Viewed from the tops, DIPS and FLAT-PACK LEADS are numbered counterclockwise from the reference mark.
Viewed from the bottom, TO-5 LEADS are numbered clockwise from the tab.
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Numbers and letters on schematics and ICs identify the TYPE OF IC.
Knowledge of TERMINOLOGY used in microelectronics and of packaging concepts will aid you in becoming an effective technician.
STANDARD TERMINOLOGY has been adopted by the Navy to ease communication.
MICROELECTRONICS is that area of technology associated with electronic systems designed with extremely small parts or elements.
A MICROCIRCUIT is a small circuit which is considered as a single part composed of elements on or within a single substrate.
A MICROCIRCUIT MODULE is an assembly of microcircuits or a combination of microcircuits and discrete components packaged as a replaceable unit.
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MINIATURE ELECTRONICS are card assemblies and modules composed exclusively of discrete electronic components.
SYSTEM PACKAGING refers to the design of a system, taking into account environmental and electronic characteristics, access, and maintainability.
PACKAGING LEVELS 0 to IV are used to identify assemblies within a system. Packaging levels are as follows:
LEVEL 0-Nonrepairable parts (resistors, diodes, and so forth.)
LEVEL I -Submodules attached to circuit cards.
LEVEL II -Circuit cards and MOTHER BOARDS.
LEVEL III - Drawers.
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LEVEL IV - Cabinets.
The most common METHODS OF INTERCONNECTION are the conventional pcb, the multilayer pcb, and modular assemblies.
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Three methods of interconnecting circuitry in multilayer printed circuit boards are the CLEARANCE-HOLE, the PLATED-THROUGH-HOLE, and LAYER BUILD-UP.
MODULAR ASSEMBLIES were devised to achieve high circuit density.
Modular assemblies have progressed from CORDWOOD MODULES through MICROMODULES. Micromodules consist of film components and discrete components to integrated and hybrid circuitry.
ENVIRONMENTAL FACTORS to be considered are temperature, humidity, shock, vibration, and rf interference.
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ELECTRICAL FACTORS are overcome by using shielding and ground planes and by careful placement of components.
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ANSWERS TO QUESTIONS Q1. THROUGH Q50.
A1. Size, weight, and power consumption.
A2. The transistor and solid-state diode.
A3. Technology of electronic systems made of extremely small electronic parts or elements.
A4. The Edison Effect.
A5. Transformers, capacitors, and resistors.
A6. "Rat's nest" appearance and unwanted interaction, such as capacitive and inductive effects.
A7. Rapid repair of systems and improved efficiency.
A8. Differences in performance of tubes of the same type.
A9. Eliminate heavy chassis and point-to-point wiring.
A10. Components soldered in place.
A11. Cordwood module.
A12. Elements inseparably associated and formed in or on a single substrate.
A13. Monolithic, film, and hybrid.
A14. Monolithic ICs contain active and passive elements. Film ICs contain only passive elements.
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A15. Combination of monolithic ICs and film components.
A16. 1,000 to 2,000.
A17. Circuit design, component placement, suitable substrate, and depositing proper materials on substrate.
A18. Complex.
A19. Control patterns of materials on substrates.
A20. Glass or ceramic.
A21. Crystal is sliced into wafers. Then ground and polished to remove any surface defect.
A22. Diffusion; epitaxial growth.
A23. Diffusion penetrates substrate; epitaxial does not.
A24. Electrical separation of elements.
A25. Evaporation and cathode sputtering.
A26. Screening.
A27. Combination of monolithic and film elements.
A28. Circuit flexibility.
A29. Protect the IC from damage; make handling easier.
A30. TO, flat pack, DIP.
A31. Flip-chip, beam lead.
A32. Left.
A33. Counterclockwise.
A34. Reference mark.
A35. Clockwise.
A36. Identify the type of IC.
A37. Communication.
A38. Integrated circuits.
A39. Miniature.
A40. Level 0.
A41. Level I.
A42. Level II.
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A43. Conventional printed circuit boards, multilayer printed circuit boards and modular assemblies.
A44. Clearance hole, plated-through hole, and layer build-up.
A45. Difficulty of repair of internal connections.
A46. Cordwood modules.
A47. Procurement specifications.
A48. Military Standards.
A49. Equipment designers (planners).
A50. Ground planes, shielding, component placement.
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Upon completion of this topic, the student will be able to:
1. State the purpose and need for training and certification of 2M repair technicians.
2. Explain the maintenance levels at which maintenance is performed.
3. Identify the specialized and general test equipment used in fault isolation.
4. Recognize the specialized types of tools used and the importance of repair facilities.
5. Explain the principles of high-reliability soldering.
As mentioned in topic 1, advances in the field of microelectronics are impressive. With every step forward in production development, a corresponding step forward must be made in maintenance and repair techniques.
This topic will teach you how the Navy is coping with the new technology and how personnel are trained to carry out the maintenance and repair of complex equipment. The program discussed in this topic is up to date at this time, but as industry advances, so must the capabilities of the technician.
Training requirements for miniature and microminiature repair personnel were developed under guidelines established by the Chief of Naval Operations. The Naval Sea Systems Command (NAVSEA) developed a program which provides for the proper training in miniature and microminiature repair. This program, NAVSEA Miniature/Microminiature (2M) Electronic Repair, authorizes and provides proper tools and equipment and establishes a personnel certification program to maintain quality repair.
The Naval Air Systems Command has developed a similar program specifically for the aviation community. The two programs are patterned after the National Aeronautics and Space Administration (NASA) high-reliability soldering studies and have few differences other than the administrative chain of command. For purposes of this topic, we will use the NAVSEA manual for reference.
The 2M program covers all phases of miniature and microminiature repair. It establishes the training curriculum for repair personnel, outlines standards of workmanship, and provides guidelines for specific repairs to equipment, including the types of tools to use. This part of the program ensures high-reliability repairs by qualified technicians.
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Upon satisfactory completion of a 2M training course, a technician will be CERTIFIED to perform repairs. The CERTIFICATION is issued at the level at which the technician qualifies and specifies what type of repairs the technician is permitted to perform. The two levels of qualification for technicians are MINIATURE COMPONENT REPAIR and MICROMINIATURE COMPONENT REPAIR. Miniature component repair is limited to discrete components and single- and double-sided printed circuit boards, including removal and installation of most integrated circuit devices. Microminiature component repair consists of repairs to highly complex, densely packaged, multilayer printed circuit boards. Sophisticated repair equipment is used that may include a binocular microscope.
To ensure that a technician is maintaining the required qualification level, periodic evaluations are conducted. By inspecting and evaluating the technician's work, certification teams ensure that the minimum standards for the technician's level of qualification are met. If the standards are met, the technician is recertified; if not, the certification is withheld pending retraining and requalification. This portion of the program ensures the high-quality, high-reliability repairs needed to meet operational requirements.
Q1. Training requirements for (2M) repair personnel were developed under guidelines established by what organization?
Q2. What agencies provide training, tools, equipment, and certification of the 2M system?
Q3. To perform microminiature component repair, a 2M technician must be currently certified in what area?
Q4. Multilayer printed circuit board repair is the responsibility of what 2M repair technician?
Effective maintenance and repair of microelectronic devices require one of three levels of maintenance. Level-of-repair designations called SOURCE, MAINTENANCE, and RECOVERABILITY CODES (SM&R) have been developed and are assigned by the Chief of Naval Material. These codes are D for DEPOT LEVEL, I for INTERMEDIATE LEVEL, and O for ORGANIZATIONAL LEVEL.
DEPOT-LEVEL MAINTENANCE.
SM&R Code D maintenance is the responsibility of maintenance activities designated by the systems command (NAVSEA, NAVAIR, NAVELEX). This code augments stocks of serviceable material. It also supports codes I and O activities by providing more extensive shop facilities and equipment and more highly skilled technicians. Code D maintenance includes repair, modification, alteration, modernization, and overhaul as well as reclamation or reconstruction of parts, assemblies, subassemblies, and components. Finally, it includes emergency manufacture of nonavailable parts. Code D maintenance also provides technical assistance to user activities and to code I maintenance organizations. Code D maintenance is performed in shops, located in shipyards and shore-based facilities, including contractor maintenance organizations.
SM&R code I maintenance, performed at mobile shops, tenders or shore-based repair facilities (SIMAS) provides direct support to user organizations. Code I maintenance includes calibration, repair, or replacement of damaged or unserviceable parts, components, or assemblies, and emergency manufacture of nonavailable parts. It also provides technical assistance to ships and stations.
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SM&R code O maintenance is the responsibility of the activity who owns the equipment. Code O maintenance consists of inspecting, servicing, lubricating, adjusting, and replacing parts, minor assemblies, and subassemblies.
An INTEGRATED LOGISTICS SUPPORT PLAN (ILSP) determines the maintenance level for electronic assemblies, modules, and boards for each equipment assigned to an activity. The ILSP codes the items according to the normal maintenance capabilities of that activity. This results in two additional repair-level categories - NORMAL and EMERGENCY.
Generally, 2M repairs are performed at the level set forth in the maintenance plan and specified by the appropriate SM&R coding for each board or module. Therefore, normal repairs include all repairs except organizational-level repair of D- and I-coded items and intermediate-level repair of D-coded items.
In the NAVSEA 2M Electronic Repair Program, emergent/emergency repairs are those arising unexpectedly. They may require prompt repair action to restore a system or piece of equipment to operating condition where normal repairs are not authorized. These Code O repairs on boards or modules are normally SM&R-coded for Code D repairs. Emergent/emergency 2M repairs may be performed only to meet an urgent operational commitment as directed by the operational commander.
The Allowance Parts List (APL) is a technical document prepared by the Navy for specific equipment/system support. This document lists the repair parts requirements for a ship having the exact equipment/component. To determine the availability of repair parts, the 2M technician must be familiar with these documents. SM&R codes, found in APLs, determine where repair parts can be obtained, who is authorized to make the repair, and at what maintenance level the item may be recovered or condemned.
Q5. What are the three levels of maintenance?
Q6. Maintenance performed by the user activity is what maintenance level?
Microelectronic developments have had a great impact on the test equipment, tools, and facilities necessary to maintain systems using this technology. This section discusses, in general terms, the importance of these developments.
Early electronic systems could be completely checked-out with general-purpose electronic test equipment (GPETE), such as multimeters, oscilloscopes, and signal generators. Using this equipment to individually test the microelectronics components in one of today's very complex electronic systems would be extremely difficult if not impossible. Therefore, improvements in system testing procedures have been necessary.
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One such improvement in system testing is the design of a method that can test systems at various functional levels. This allows groups of components to be tested as a whole and reduces the time required to test components individually. One advantage of this method is that complete test plans can be written to provide the best sequencing of tests for wave shape or voltage outputs for each functional level. This method of testing has led to the development of special test sets, called AUTOMATED TEST EQUIPMENT (ATE). These test sets are capable of simulating actual operating conditions of the system being tested. Appropriate signal voltages are applied by the test set to the various functional levels of the system, and the output of each level is monitored. Testing sequences are prewritten and steps may be switched-in manually or automatically. The limits for each functional level are preprogrammed to give either a "go/no-go" indication or diagnose a fault to a component. A go/no-go indication means that a functional level either meets the test specifications (go) or fails to meet the specifications (no-go).
If a no-go indication is observed for a given function, the area of the system in which it occurs is then further tested. You can test the trouble area by using general purpose electronic test equipment and the troubleshooting manual for the system. General purpose electronic test equipment (GPETE) will be discussed later in this topic. (Effective fault isolation at this point depends on the experience of the technician and the quality of the troubleshooting manual.) After the fault is located, the defective part is then replaced or repaired, depending on the nature of the defect. At this stage, the defective part is usually a circuit card, a module, or a discrete part, such as a switch, relay, transistor, or resistor.
One type of fault isolation that can be either on-line or off-line is BUILT-IN TEST EQUIPMENT (BITE). BITE is any device that is permanently mounted in the prime equipment (system); it is used only for testing the equipment or system in which it is installed either independently or in association with external test equipment. The specific types of BITE are too varied to discuss here, but may be as simple as a set of meters and switches or as complex as a computer-controlled diagnostic system.
Functional-level testing and modular design have been successfully applied to most electronic systems in use today; however, the trend toward increasing the number of subassemblies within a module by incorporating microelectronics will make this method of testing less and less effective.
The increased circuit density and packaging possible with microelectronic components makes troubleshooting and fault location difficult or, in some cases, impossible. The technician's efforts must be aided if timely repairs to microelectronic systems are to be achieved. These repairs are particularly significant when considered in the light of the very stringent availability requirements for today's systems. This dilemma has led to the present trend of developing both ON-LINE and OFF-LINE automatic test systems. The on-line systems are designed to continuously monitor performance and to automatically isolate faults to removable assemblies. Off-line systems automatically check removable assemblies and isolate faults to the component level.
Two on-line systems, the TEST EVALUATION AND MONITORING SYSTEM (TEAMS) and the CENTRALIZED AUTOMATIC TEST SYSTEM (CATS), are presently in production or under development by the Navy.
TEAMS is an on-line system that continuously monitors the performance of electronic systems and isolates faults to a removable assembly. This system is controlled by a computer using a test program on perforated or magnetic tape, cassettes, or disks. Displays are used to present the status of the equipment and to provide data with instructions for fault localization. Lights, usually an LED, are used to indicate
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which equipments are being tested and also which equipments are in an out-of-tolerance condition. A printer provides a read out copy of the test results. These results are used by maintenance personnel to isolate the fault in a removable assembly to a replaceable part.
CATS is an on-line system that continuously monitors the performance of electronic systems, predicts system performance trends, and isolates faults to removable assemblies. CATS, however, is computer controlled and the instructions are preprogrammed in the computer memory. The status of the electronic system being monitored by CATS is presented in various forms. Information concerning a failed module is presented on a status- and fault-isolation indicator to alert the maintenance technician of the need for a replacement module. If equipment design does not permit module replacement, complete electrical schematics and fault-isolation procedures will be made available to the maintenance technician.
The Navy has under development an advanced assembly tester designated Naval Electronics Laboratory Assembly Tester (NELAT). This tester is an off-line, general-purpose test system designed to check-out and isolate faults in electronic plug-in assemblies, modules, and printed circuit boards. Equipped with a complete range of instrumentation, the system allows testing to be accomplished automatically, semiautomatically, or manually. In the automatic mode, a complete range of stimuli generators and monitors are connected and switched by means of a microfilmed test program.
The NELAT incorporates modular electronic assemblies that will facilitate updating of the system. The system is designed for use aboard ship. When put into service, this tester will greatly improve the technician's capability in the checkout and fault isolation of microelectronic assemblies.
Another important system for off-line testing is the Versatile Avionic Shop Test System (VAST). VAST is used in the aviation community for fault isolation in aviation electronics (avionics) equipment on ships and shore commands with aircraft INTERMEDIATE MAINTENANCE DEPARTMENTS (AIMDs). It is an automatic, high-speed, computer controlled, general-purpose test set that will isolate faults to the component level.
When no automatic means of accomplishing fault isolation is available, general-purpose electronic test equipment and good troubleshooting procedures is used; however, such fault diagnosis should be attempted only by experienced technicians. Misuse of electrical probes and test equipment may permanently damage boards or microelectronic devices attached to them. The proximity of leads to one another and the effects of interconnecting the wiring make the testing of boards extremely difficult; these factors also make drift or current leakage measurements practically impossible.
Boards that have been conformally coated are difficult to probe because the coating is often too thick to penetrate for a good electrical contact. These boards must be removed for electrical probe testing. Many boards, however, are designed with test points that can be monitored either with special test sets or general-purpose test equipment. Another method of obtaining access to a greater number of test points is to use extender cards or cables. The use of extender cards or cables makes these test points easier to check.
Special care should be exercised when probing integrated circuits; they are easily damaged by excessive voltages or currents, and component leads may be physically damaged. Precautions concerning the use of test equipment for troubleshooting equipments containing integrated circuits are similar to
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those that should be observed when troubleshooting equipment containing semiconductor or other voltage and current-sensitive devices.
Voltage and resistance tests of resistors, transistors, inductors, and so forth, are usually effective in locating complete failures or defects that exhibit large changes from normal circuit characteristics; however, these methods are time-consuming and sometimes unsuccessful. The suspect device often must be desoldered, removed from the circuit, and then retested to verify the fault. If the defect is not verified, the device must be resoldered to the board again. If this procedure has to be repeated several times, or if the board is conformally coated, the defect may never be located. In fact, the circuit may be further damaged by the attempt to locate the fault. For these reasons, the device should never be desoldered until all possible in-circuit tests are performed and the defect verified.
Q7. List the three groups of test equipment used for fault isolation in 2M repair.
Q8. What test equipment continuously monitors electronic systems?
Q9. NELAT and VAST are examples of what type of test equipment?
In addition to the requirements for special skills, the repair of 2M electronic circuits also requires special tools. Because these tools are delicate and expensive, they are distributed only to trained and certified 2M repair technicians.
2M repair stations are equipped with electrical and mechanical units, tools, and general repair materials. Such equipments are needed to make reliable repairs to miniature and microminiature component circuit boards.
Although most of the tools and equipments are common to both miniature and microminiature repair stations, several pieces of equipment are used solely with microminiature repair. Precision drill presses and stereoscopic-zoom microscopes are examples of microminiature repair equipment normally not found in a miniature repair station. A brief description of some of the tools and equipments and their uses will broaden your knowledge and understanding of 2M repair.
The 2M repair set consists of special electrical units, tools, and materials necessary to make high- reliability repairs to component circuitry. The basic repair set is made up of a repair station power unit, magnifier/light system, card holder, a high-intensity light, a Pana Vise, and a tool chest with specialized tools and materials. As mentioned previously, stations that have microminiature repair capabilities will include a stereoscopic-zoom microscope and precision drill press.
The repair station power unit is a standardized system that provides controlled soldering and desoldering of all types of solder joint configurations. The unit is shown in figure 2-1. Included in the control unit's capabilities are:
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• "Spike free" power switching for attached electrical hand tools to eliminate damage to electrostatic discharge components.
• Abrading, milling, drilling, grinding, and cutting using a flexible shaft, rotary-drive machine. This allows the technician to remove conformal coatings, oxides, eyelets, rivets, damaged board material, and damaged platings from assemblies.
• Lap flow solder connections and thermal removal of conformal coatings.
• Resistive and conductive tweezer heating for connector soldering applications.
• Thermal wire stripping for removing polyvinyl chloride (PVC) and other synethetic wire coverings.
The basic unit houses the power supply, power level indicator, motor control switch, hand tool temperature controls, air pressure and vacuum controls with quick connect fittings, positive ground terminal, the mechanical power-drive for the rotary-drive machine, and a vacuum/pressure pump. A two- position foot pedal, to the left of the power unit in the illustration, allows hand-free operation for all ancillary (additional) handpieces. The first detent on the pedal provides power to the voltage heating outputs. The second detent activates the motor drive or vacuum/pressure pump.
The handpieces used with the power unit are shown in figures 2-2 and 2-3. The lap flow handpiece, view (A) of figure 2-2, is used with the variable low-voltage power source. This handpiece allows removal of conformal coatings, release of sweat joints, and lap flow soldering capability. (Lap flow soldering will be discussed in topic 3.) The thermal wire stripper in view (B) is used to remove insulation from various sizes of wire easily and cleanly.
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The resistive tweezers, shown in view (C), are used for soldering components. Two sizes [views (C) and (D)] are provided to meet the needs of the technician. Both the thermal stripper and the resistive tweezers are used with the low-voltage power supply.
The solder extractor, shown in view (A) of figure 2-3, is connected to the variable high-voltage outlet. This handpiece allows airflow application (at controlled temperatures) of a vacuum or pressure to the selected area. Five sizes of extractor tips are provided, as shown in view (B). You can determine the one to be used by matching the tip with the circuit pad and the component being desoldered.
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A soldering iron is shown in figure 2-4. This is connected to the 115-volt ac variable outlet of the power unit. You control the temperature by adjusting the voltage. The iron has replaceable tips. Chosen for their long life and good heat conductivity, soldering iron tips are high quality with iron-clad over copper construction. The tip shape and size and the heat range used are determined by the area and mass to be soldered.
This variable-speed, rotary power drive adapts to standard diameter shank drill bits, ball mills, wheels, disks, brushes, and mandrels for most drilling and abrasive removal techniques (figure 2-5).
The accessories used with the rotary-drive tool are shown in views (A) through (F) of figure 2-6. Abrasive ball mills, wheels, discs, and brushes are either premounted on mandrels or can be mounted by the technician on the mandrels provided. These attachments are used for sanding and smoothing repaired areas, drilling holes, removing conformal coatings, and repairing burned or damaged areas. A chuck- equipped handpiece allows it to accept rotary tools with varying shank sizes.
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The circuit card holder is an adjustable, rotatable holder for virtually any size circuit card. Figure 2-7 shows the circuit card holder [view (A)] and the magnifier unit [view (B)]. The magnifier unit provides magnification when detail provided by a microscope is not required. The special lens allows the technician to view a rectangular area of over 14 square inches with low distortion, fine resolution, and excellent depth of field. The magnifier unit, which includes high intensity lamps, adapts to the vertical shaft of the circuit card holder.
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The high-intensity light provides a variable, high-intensity, portable light source over the work area. The two flexible arms permit both front and back lighting of the workpiece and provide a balanced light that eliminates shadows (figure 2-8).
The high-intensity light uses 115-volt, 60-hertz input power. One brightness knob controls a flood- type bulb, and the other knob controls a spot-type bulb.
This nylon-jawed, multiposition vise can rotate and tilt. With this flexibility the technician can achieve any compound angle for holding a workpiece during assembly, modification, or repair (figure 2-9).
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Figure 2-10, views (A) through (C), shows some representative types of hand tools used in 2M repair procedures.
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In view (A), the figure shows the pliers preferred for 2M repair procedures. These precision pliers have a long and useful life if handled and cared for properly. The flush-cutting pliers are used to cut various sizes of wire and component leads. The needlenose, roundnose, and flatnose pliers are used for forming, looping, and bending wires and component leads. They are also used for gripping components and leads during removal or installation.
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View (B) shows tweezers contained in the 2M repair set. The top two pairs of tweezers are used to hold small components during installation and repair procedures. The other pairs are anti-wicking tweezers used to tin and solder stranded wire leads.
View (C) shows some of the dental tools contained in the 2M repair set. They are used for picking, chipping, abrading, mixing, and smoothing various conformal coatings used on printed circuit boards and other general pcb repair techniques.
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Among the repair procedures required of the 2M repair technician is the replacement of eyelets. Eyelets must sometimes be replaced because of the damage caused by incorrect repair procedures or complete failure of a printed circuit board. Figure 2-11 illustrates the tools used to replace these eyelets. Eyelets will be discussed in topic 3.
An assortment of some of the miscellaneous items used in 2M repair are shown in figure 2-12. A variety of brushes, files, scissors, thermal shunts, and consumables, such as solder wick, are included.
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Even though all the items are not used in every repair procedure, it is extremely important that they be available for use should the need arise.
The nature of 2M repair requires items to be included in the tool kit for the personal safety of the technicians. The goggles and respirator illustrated in figure 2-13 have been approved for use by the technician. These should be worn at all times where dust, chips, fumes, and other hazardous substances are generated as a result of drilling, grinding, or other repair procedures.
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The stereoscopic-zoom microscope provides a versatile optical viewing system. This viewing system is used in the fault detection, fault isolation, and repair of complex microminiature circuit boards and components. Figure 2-14 shows the microscope mounted on an adjustable stand. The microscope has a minimum of 3.5X and a maximum of 30X magnification to detect hairline cracks in conductor runs and stress cracks in solder joints.
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The tool chest (not shown), provides storage space for the electronic repair hand tools, dental tools, abrasive wheels, solder and solder wicks, eyelets, abrasive disks, ball mills, various burrs, and other consumables used with the repair procedures. The chest is portable, lockable, and has variously sized drawers for convenience.
Replacement parts are provided with the 2M repair set to ensure the technician has the capability to maintain the equipment properly. Actual preventive and corrective maintenance procedures, as well as data on additional spare parts and ordering information, are found in the technical manual for the 2M repair set equipment.
To be effective, 2M electronic component repair must be performed under proper environmental conditions. Repair facility requirements, whether afloat or ashore, include adequate lighting, ventilation, noise considerations, work surface area, ESD (electrostatic discharge) protection, and adequate power availability. The recommended environmental conditions are discussed below. With the exception of requirements imposed by the Naval Environmental Health Center and other authorities for ship and shore work conditions, each activity tailors the requirements to meet local needs.
The recommended lighting for a work surface is 100 footcandles from a direct lighting source. Light- colored overheads and bulkheads and off-white or pastel workbench tops are used to complement the lighting provided.
Fumes from burning flux, coating materials, grinding dust, and cleaning solvents require adequate ventilation. The use of toxic, flammable substances, solvents, and coating compounds requires a duct system that vents gasses and vapors. This type of system must be used to prevent contamination often
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found in closed ventilation systems. This need is particularly important aboard ship. Vented hoods, ducts, or installations that are vented outside generally meet the minimum standards set by the Naval Environmental Health Center.
Noise in the work area during normal work periods must be no greater than the acceptable level approved for each activity involved. Because the work is tedious and tiring, noise levels should be as low as possible. Ear protectors are required to be worn when a noise level exceeds 85 dB. Ear protectors should also be worn anytime the technician feels distracted by, or uncomfortable with, the noise level.
Work stations should have a minimum work surface of at least 60-inches wide and 30-inches deep. Standard Navy desks are excellent for this purpose. Standard shipboard workbenches are acceptable; however, off-white or pastel-colored heat-resistant tops should be installed on the workbenches. Chairs should be the type with backs and without arms. They should be comfortably padded and of the proper height to match the work surface height. Drawers or other suitable tool storage areas are usually provided.
A 2M work station should be capable of becoming a static-free work station. This is specified in the Department of Defense Standard, Electrostatic DISCHARGE Control Program for Protection of Electrical and Electronic Parts, Assemblies, and Equipment. ESD will be discussed in greater detail in topic 3.
No special power source or equipment mounting is required. The 2M repair equipment operates on 115-volt, 60-hertz power. A 15-ampere circuit is sufficient and six individual power receptacles should be available.
The most common types of miniature and microminiature repair involve the removal and replacement of circuit components. The key to these repairs is a firm knowledge of solder and high- reliability soldering techniques.
Solder is a metal alloy used to join two or more metals with a metallic bond. The bonding occurs when molten solder dissolves a small amount of the metals and then cools to form a solid connection. The solder most commonly used in electronic assemblies is an alloy of tin and lead. Tin-lead alloys are identified by their percentage in the solder; the tin content is given first. Solder marked 60/40 is an alloy of 60 percent tin and 40 percent lead. The two most common alloys used in electronics are 60/40 and 63/37.
The melting temperature of tin-lead solder varies depending on the percentage of each metal. Lead melts at a temperature of 621 degrees Fahrenheit, and tin melts at 450 degrees Fahrenheit. Combinations of the two metals melt into a liquid at different temperatures. The 63/37 combination melts into a liquid at 361 degrees Fahrenheit. At this temperature, the alloy changes from a solid directly to a liquid with no plastic or semiliquid state. An alloy with such a sharp changing point is called a EUTECTIC ALLOY.
As the percentages of tin and lead are varied, the melting temperature increases. Alloy of 60/40 melts at 370 degrees Fahrenheit, and alloy of 70/30 melts at approximately 380 degrees Fahrenheit. Alloys,
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other than eutectic, go through a plastic or semiliquid state in their heating and cooling stages. Solder joints that are disturbed (moved) during the plastic state will result in damaged connections. For this reason, 63/37 solder is the best alloy for electronic work. Solder with 60/40 alloy is also acceptable, but it goes into a plastic state between 361 and 370 degrees Fahrenheit. When soldering joints with 60/40 alloy, you must exercise extreme care to prevent movement of the component during cooling.
Reliable solder connections can only be accomplished with clean surfaces. Using solvents and abrasives to clean the surfaces to be soldered is essential if you are to achieve good solder connections. In almost all cases, however, this cleaning process is insufficient because oxides form rapidly on heated metal surfaces. The rapid formation of oxides creates a nonmetallic film that prevents solder from contacting the metal. Good metal-to-metal contact must be obtained before good soldering joints may take place. Flux removes these surface oxides from metals to be soldered and keeps them removed during the soldering operation. Flux chemically breaks down surface oxides and causes the oxide film to loosen and break free from the metals being soldered.
Soldering fluxes are divided into three classifications or groups: CHLORIDE FLUX (commonly called ACID), ORGANIC FLUX, and ROSIN FLUX. Each flux has characteristics specific to its own group. Chloride fluxes are the most active of the three groups. They are effective on all common metals except aluminum and magnesium. Chloride fluxes, however, are NOT suitable for electronic soldering because they are highly corrosive, electrically conductive, and are difficult to remove from the soldered joint.
Organic fluxes are nearly as active as chloride fluxes, yet are less corrosive and easier to remove than chloride fluxes. Also, these fluxes are NOT satisfactory for electronic soldering because they must be removed completely to prevent corrosion.
Rosin fluxes ARE ideally suited to electronic soldering because of their molecular structure. The most common flux used in electronic soldering is a solution of pure rosin dissolved in suitable solvent. This solution works well with the tin- or solder-dipped metals commonly used for wires, lugs, and connectors. While inert at normal temperatures, rosin fluxes break down and become highly active at soldering temperatures. In addition, rosin is nonconductive.
Most electronic solder, in wire form, is made with one or more cores of rosin flux. When the joint or connection is heated and the wire solder is applied to the joint (not the iron), the flux flows onto the surface of the joint and removes the oxide. This process aids the wetting action of the solder. With enough heat the solder flows and replaces the flux. Insufficient heat results in a poor connection because the solder does not replace the flux.
Q10. Stereoscopic-zoom microscopes and precision drill presses are normally associated with what type of repair station?
Q11. Solder used in electronic repair is normally an alloy of what two elements?
Q12. In soldering, what alloy changes directly from a solid state to a liquid state?
Q13. Flux aids in soldering by removing what from surfaces to be soldered?
Q14. What type(s) of flux should never be used on electronic equipment?
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This topic has presented information on the Miniature and Microminiature 2M Repair Program and high-reliability soldering. The information that follows summarizes the important points of this topic.
The MINIATURE/MICROMINIATURE (2M) REPAIR PROGRAM provides training, tools and equipment, and certification for 2M repair personnel.
CERTIFICATION of technicians ensures the capability of high-quality, high-reliability repairs.
The three SM&R codes for maintenance of electronic devices are: DEPOT (D), INTERMEDIATE (I), and ORGANIZATIONAL (O).
SM&R CODE D MAINTENANCE is characterized by extensive facilities and highly trained personnel. Code D activities are capable of the most complex type repairs.
CODE I activities provide direct support for user activities. This includes calibration, repair, and emergency manufacture of nonavailable parts.
CODE O maintenance is the responsibility of the user activity. It includes preventive maintenance and minor repairs.
ON-LINE TEST EQUIPMENT continuously monitors system performance and isolates faults to removable assemblies.
OFF-LINE TEST EQUIPMENT evaluates removable assemblies outside of the equipment and isolates faults to the component level.
FAULT ISOLATION USING GENERAL-PURPOSE ELECTRONIC TEST EQUIPMENT (GPETE) should only be attempted by experienced technicians.
2M REPAIR STATIONS are equipped according to the level of repairs to be accomplished.
ALLOYS, such as solder, which change directly from a solid state to a liquid are called eutectic alloys.
SOLDER with a tin/lead ratio of 63/37 is preferred for electronic work. A ratio of 60/40 is also acceptable.
ROSIN or RESIN FLUXES are the only fluxes to be used in electronic work.
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ANSWERS TO QUESTIONS Q1. THROUGH Q14.
A1. Chief of Naval Operations (CNO).
A2. Naval Sea Systems Command (NAVSEASYSCOM) and Naval Air Systems Command (NAVAIRSYSCOM).
A3. Microminiature component repair.
A4. Microminiature repair technician.
A5. Depot, Intermediate, and Organizational.
A6. Organizational.
A7. On-line, off-line, and General Purpose Electronic Test Equipment (GPETE).
A8. On-line.
A9. Off-line.
A10. Microminiature repair station.
A11. Tin and lead.
A12. Eutectic.
A13. Oxides.
A14. Chloride or (acid) and organic.
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Upon completion of this topic, the student will be able to:
1. Explain the purpose of conformal coatings and the methods used for removal and replacement of these coatings.
2. Explain the methods and practices for the removal and replacement of discrete components on printed circuit boards.
3. Identify types of damage to printed circuit boards, and describe the repair procedures for each type of repair.
4. Describe the removal and replacement of the dual-in-line integrated circuit.
5. Describe the removal and replacement of the TO-5 integrated circuit.
6. Describe the removal and replacement of the flat-pack integrated circuit.
7. Describe the types of damage to which many microelectronic components are susceptible and methods of preventing damage.
8. Explain safety precautions as they relate to 2M repair.
As you progress in your training as a technician, you will find that the skill and knowledge levels required to maintain electronic systems become more demanding. The increased use of miniature and microminiature electronic circuits, circuit complexity, and new manufacturing techniques will make your job more challenging. To maintain and repair equipment effectively, you will have to duplicate with limited facilities what was accomplished in the factory with extensive facilities. Printed circuit boards that were manufactured completely by machine will have to be repaired by hand.
To meet the needs for repairing the full range of electronic equipment, you must be properly trained. You must be capable of performing high-quality, reliable repairs to the latest circuitry.
As mentioned at the beginning of topic 2, 2M repair personnel must undergo specialized training. They are trained for a particular level of repair and must be certified at that level. Also, recertification is required to ensure the continued high-quality repair ability of these technicians.
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THIS SECTION IS NOT, IN ANY WAY, TO BE USED BY YOU AS AUTHORIZATION TO ATTEMPT THESE TYPES OF REPAIRS WITHOUT OFFICIAL 2M CERTIFICATION.
In the following sections, you will study the general procedures used in the repair, removal, and replacement of specific types of electronic components. By studying these procedures, you will become familiar with some of the more common types of repair work. Before repair work can be performed on a miniature or microminiature assembly, the technician must consider the type of specialized coating that usually covers the assembly. These coatings are referred to as CONFORMAL COATINGS.
Conformal coatings are protective material applied to electronic assemblies to prevent damage from corrosion, moisture, and stress. These coatings include epoxy, parylene, silicone, polyurethane, varnish, and lacquer. Coatings are applied in a liquid form; when dry, they exhibit characteristics that improve reliability. These characteristics are:
Because of the characteristics that conformal coatings exhibit, they must be removed before any work can be done on printed circuit boards. The coating must be removed from all lead and pad/eyelet areas of the component. It should also be removed to or below the widest point of the component body. Complete removal of the coating from the board is not done.
Methods of coating removal are thermal, mechanical, and chemical. The method of removal depends on the type of coating used. Table 3-1 shows suggested methods of removal of some types. Note that most of the methods are variations of mechanical removal.
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The coating material can best be identified through proper documentation; for example, technical manuals and engineering drawings. If this information is not available, the experienced technician can usually determine the type of material by testing the, hardness, transparency, thickness, and solvent solubility of the coating. The thermal (heat) properties may also be tested to determine the ease of removal of the coating by heat. The methods of removal discussed here describe the basic concept, but not the step-by-step "how to" procedures.
THERMAL REMOVAL.—Thermal removal consists of using controlled heat through specially shaped tips attached to a handpiece. Soldering irons should never be used for coating removal because the high temperatures will cause the coatings to char, possibly damaging the board materials. Modified tips or cutting blades heated by soldering irons also are not used; they may not have proper heat capacity or allow the hand control necessary for effective removal. Also, the thin plating of the circuit may be damaged by scraping.
The thermal parting tool, used with the variable power supply, has interchangeable tips, as shown in figure 3-1, that allow for efficient coating removal. These thin, blade-like instruments act as heat generators and will maintain the heat levels necessary to accomplish the work. Tips can be changed easily to suit the configuration of the workpiece. These tips cool quickly after removal of power because their small thermal mass and special alloy material easily give up residual heat.
The softening or breakdown point of different coatings vary, which is a concern when you are using this method. Ideally, the softening, point is below the solder melting temperature. However, when the softening point is equal to or above the solder melting point, you must take care in applying heat at the solder joint or in component areas. The work must be performed rapidly to limit the heating of the area involved and to prevent damage to the board and other components.
HOT-AIR JET REMOVAL.—In principle, the hot-air jet method of coating removal uses controlled, temperature-regulated air to soften or break down the coating, as shown in figure 3-2. By controlling the temperature, flow rate, and shape of the jet, you may remove coatings from almost any workpiece configuration without causing any damage. When you use the hot-air jet, you do not allow it to
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physically contact the workpiece surface. Delicate work handled in this manner permits you to observe the removal process.
POWER-TOOL REMOVAL DESCRIPTION.—Power-tool removal is the use of abrasive grinding or cutting to mechanically remove coatings. Abrasive grinding/rubbing techniques are effective on thin coatings (less than 0.025 inch) while abrasive cutting methods are effective on coatings greater than 0.025 inch. This method permits consistent and precise removal of coatings without mechanical damage or dangerous heating to electronic components. A variable-speed mechanical drive handpiece permits fingertip-control and proper speed and torque to ease the handling of gum-type coatings. A variety of rotary abrasive materials and cutting tools is required for removal of the various coating types. These specially designed tools include BALL MILLS, BURRS, and ROTARY BRUSHES.