At 01:43 PM 1/9/97 EST, you wrote:
>	I am working on a program that uses Plastic Encapsulated Modules (PEM).
>
>The system  operating temperature range is from -55 to +90 DegC. Does
>
>anyone have or know of a source for any information on reliability data,
>
>including long-term storage for PEM devices? Reliability numbers need to
>
>be calculated for this system and valid data for PEMs is hard to come by.

Mike,

If you are looking for a reliability prediction source for PEMs, I do not
recommend using MIL-HDBK-217.  The failure rates that it predicts for PEMs
are much higher than actual field performance results.  The Bellcore
reliability predictions model yield more accurate results.  (A reliability
prediction procedure written by General Electric referenced field results
which corresponded well with the Bellcore models while the MIL-HDBK-217
models yielded failure rates about 3.5 times too high.)  The latest version
of the Bellcore publication is "Reliability Prediction for Electronic
Equipment", TR-332, Issue 5, December 1995.

The problem with using the Bellcore models is that they only use three
ground environments (benign, fixed, and mobile).  What I have done before is
used the environmental pi-factor tables from MIL-HDBK-217 to modify the
Bellcore failure rates for an environment not covered in the Bellcore model.
This is by no means a procedure "approved" by Bellcore.  However, you need
to use your own engineering judgement.  Reliability predictions after all
are just that -- predictions.  It is important to keep that in mind and
allow sufficient reliability design margins.

I hope this helps...


Brian Hyde

--------------------------------------------
Brian P. Hyde
Reliability Engineer
Lockheed Martin Advanced Recorders
E-Mail: [log in to unmask]
--------------------------------------------

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