Module 14 - Introduction to Microelectronics
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3-41, Index
![Manufacturer's Data Sheet - RF Cafe](images/14131img11.gif)
Figure 1-34. - Manufacturer's Data Sheet.
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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?
MICROELECTRONIC System DESIGN CONCEPTS
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.
Terminology
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 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. Microcircuit
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 x 10 x 2 inches. The equivalent circuit in microelectronics might be built into or onto a single substrate which
is only 3/8 x 1 x 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. Microcircuit Module
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.
![Microcircuit module - RF Cafe](images/14131img13.gif)
Figure 1-35. - Microcircuit module.
Miniature Electronics 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?
System PACKAGING 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. Levels of Packaging 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.
![Packaging levels - RF Cafe](images/14131img15.gif)
Figure 1-36. - Packaging levels.
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.
![Printed circuit board (pcb) - RF Cafe](images/14131img17.gif)
Figure 1-37. - Printed circuit board (pcb).
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 x
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.
![Printed circuit board (pcb) - RF Cafe](images/14131img19.gif)
Figure 1-38. - Printed circuit board (PCB).
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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?
INTERCONNECTIONS IN PRINTED Circuit BOARDS 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. Conventional Printed Circuit
Board
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:
· reduce weight · conserve space in interconnecting circuit modules
· eliminate costly and complicated wiring harnesses · provide shielding for a
large number of conductors · provide uniformity in conductor impedance for high-speed
switching systems
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· allow greater wiring density on boards
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.
![Multilayer pcb - RF Cafe](images/14131img1B.gif)
Figure 1-39. - Multilayer PCB.
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. The clearance hole is filled with solder to complete the connection.
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.
![Clearance-hole interconnection - RF Cafe](images/14131img1D.gif)
Figure 1-40. - Clearance-hole interconnection.
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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.
![Plated through-hole interconnection - RF Cafe](images/14131img1F.gif)
Figure 1-41. - Plated through-hole interconnection.
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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![Layer build-up technique - RF Cafe](images/14131img21.gif)
Figure 1-42. - Layer build-up technique.
Advantages and Disadvantages of Printed Circuit Boards 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).
MODULAR ASSEMBLIES
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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![Evolution of modular assemblies. CORDWOOD - RF Cafe](images/14131img23.gif)
Figure 1-43A. - Evolution of modular assemblies. CORDWOOD.
![Evolution of modular assemblies. MICROMODULE - RF Cafe](images/14131img25.gif)
Figure 1-43B. - Evolution of modular assemblies. MICROMODULE.
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- |
Matter, Energy,
and Direct Current |
- |
Alternating Current and Transformers |
- |
Circuit Protection, Control, and Measurement |
- |
Electrical Conductors, Wiring Techniques,
and Schematic Reading |
- |
Generators and Motors |
- |
Electronic Emission, Tubes, and Power Supplies |
- |
Solid-State Devices and Power Supplies |
- |
Amplifiers |
- |
Wave-Generation and Wave-Shaping Circuits |
- |
Wave Propagation, Transmission Lines, and
Antennas |
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Microwave Principles |
- |
Modulation Principles |
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Introduction to Number Systems and Logic Circuits |
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- Introduction to Microelectronics |
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Principles of Synchros, Servos, and Gyros |
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Introduction to Test Equipment |
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Radio-Frequency Communications Principles |
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Radar Principles |
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The Technician's Handbook, Master Glossary |
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Test Methods and Practices |
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Introduction to Digital Computers |
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Magnetic Recording |
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Introduction to Fiber Optics |
Note: Navy Electricity and Electronics Training
Series (NEETS) content is U.S. Navy property in the public domain. |
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