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Unlike traditionally packaged electronic components,
the Hybrid or MCM thermal environment for each application must be considered
separately on its own merit. Package density/mounting determines the thermal
rise peculiar to the individual package design. Failure rates, an exponential
function of temperature for all electronic components, makes an accurate thermal
analysis the essential element to the integrity of predicted reliability
figures. Recommend that derating of MCMs and hybrid devices are accomplished by
considering the most reliability-limiting element contained within the packaged
device. All passive and active devices need to be considered separately.
Recommend the user refer to the individual part chapters in this manual when
attempting to derate a MCM or hybrid device, as shown in Table 1.
When passive structures are used in microwave
applications, properly designed transmission lines and other passive microwave
components should not require power derating. In cases of poor design or
fabrication, transmission lines can fail as a result of electrical over stress
(EOS), resulting in an open circuit. Poor design can also limit the reliability
of other passive structures; however, normally it is the active device elements,
which pose the primary reliability threat for microwave structures.
Table 1. Recommended Derating Guidelines
for Hybrid and MCM Devices
1. For repetitive pulse applications, the average
power is determined by dividing pulse duration by duty cycle, and multiplying
the result by the peak power.
2. Voltages must never be applied in reverse of the
normal polarization of a polarized capacitor.
3. Maximum junction temperature ratings for all
semiconductors and integrated circuits are assumed greater than or equal to the
maximum operating temperature required of the device.
4. Derating values for thick film resistors is taken
from IPC-MC-790, “Guidelines for Multichip Module Technology Utilization”;