Module 14 - Introduction to Microelectronics
Navy Electricity and Electronics Training Series (NEETS)
Chapter 1:  Pages 1-41 through 1-50

Figure 1-43C. - Evolution of modular assemblies. INTEGRATED-Circuit.

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.

Micromodules

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?

1-41

ENVIRONMENTAL Considerations

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

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.

ELECTRICAL Considerations

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

1-42

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.

Figure 1-44. - Ground planes and shielding.

Interconnection and Intraconnections

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?

1-43

Summary

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.

1-44

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.

1-45

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.

1-46

FLIP CHIPS and BEAM-LEAD CHIPS are techniques being developed to eliminate bonding wires and to improve packaging.

1-47

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.

1-48

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.

1-49

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.

1-50