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This section details the reliability performance,
time, and operating conditions for microcircuits and recommends microcircuit
prediction guidance. Part reliability is defined in the Scope section. Use this
section to select reliability requirements for microcircuit usage.
Defining a microcircuit’s performance in today’s
military is extremely critical. Historically, the military microcircuit industry
overstated what was satisfactory operation for the performance of microcircuits
used in military applications. In addition, the military mandated the use of
military qualified parts. Today consumer microcircuits are being used beside
military parts in many applications. This freedom presents a potential risk to
the application and makes defining satisfactory operation more difficult than in
the past. To assist in developing performance criteria for microcircuits,
performance specification MIL-PRF-38535 should be used.
Microcircuits qualified to MIL-PRF-38535 and listed
in QML-38535 are designed to last up to 20 years. On the other hand,
non-military microcircuits are designed to last from 12 months up to 5 years.
The microcircuit’s package has a significant effect on the part’s life. Packages
that dissipate heat effectively and/or protect the internal circuitry from the
environment allow the Microcircuit to last longer. The environmental categories
detailed in the Scope section of this document/database establish timed-based
requirements for microcircuit usage.
Microcircuit Operating Conditions
With the inclusion of non-military microcircuit usage
into military applications, this element of reliability has become more critical
then in the past. PEMs, which are not hermetically sealed, are susceptible to
humidity (moisture) contamination. In addition, PEMs packaging is more
restrictive to heat dissipating out than is ceramic or metal hermetic packages.
Plastic packages by design raise the temperature of the microcircuit higher than
if in a hermetic package. The environmental categories detailed in the Scope
section of this document/database establish operating condition requirements for
Microcircuit Reliability Prediction -
The Reliability Prediction of Electronic Equipment
Handbook, MIL-HDBK-217F notice 2, is used as a guideline to establish and
maintain probability for microcircuits. An area of some current disagreement in
the MIL-HDBK-217F notice 2 is with the Quality Factor for commercial/consumer
microcircuits. The handbook lists the Quality Factor (pQ)
as 10. This was established prior to 1991. Through review with industry, the
Quality Factor for consumer plastic encapsulated microcircuits (PEMs) used in
NAVSEA systems, is being reduced to a Quality Factor (pQ)
of 4.0. In addition, for PEMs used in NAVSEA systems, the Environmental
Factor in the MIL-HDBK-217F notice 2 should be modified to the
a. For microcircuits used in the Protected
Environment, the Environmental Factor (pE)
b. For microcircuits used in the Normal Environment,
the Environmental Factor (pE)
In addition to the MIL-HDBK-217F, notice 2 there are
other methods used to predict microcircuit reliability. The MIL-HDBK-217F,
notice 2 is the preferred method until a suitable replacement is developed.