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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
Temperature Operating Nonoperating
-
28º C to +65º
C
-
62º C to +75º C (MIL-E-16400E)
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)
RF Interference
30 Hz to 40 GHz
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
