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Date: | Fri, 14 Mar 97 12:02:00 mst |
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I'm not sure this is the correct forum for this topic, but here is my two
cents worth. As I understand it, there is a trend in much of the military
industry to use parts which have not been screened to military standards and
which may not even necessarily meet the required military temperature range.
This requires two things: 1) the supplier of the parts must be certified by
you or someone you trust to supply commercial parts which will "survive" the
environment for your product, and 2) you "may" need to relax some of the
specified parameters to compensate for the expanded temperature range over
which the part must operate.
A group who has done extensive work in this area is the CALCE Electronic
Packaging Research Center at the University of Maryland. They claim that
many parts are designed to operate over a wider temperature range than
specified and they may be willing to tell you what their internal design
temperature rule are. They will probably not be willing to guarantee these
parameters, however, because they are not tested over temperature. The
CALCE Electronic Packaging Research Center cites a test case of a Motorola
MC68332 32-bit microprocessor in a 132 lead PQFP package specified to run
from -40 to 85 degrees C. 10 of 10 devices tested passed parametric testing
to -70 degrees. One device stopped operating properly at -90 degrees until
its temperature was raised. 20 out of 25 devices passed functional testing
at -150 degrees. Later qualification tests to -65 degrees found 0 out of
720 devices tested! They also commented that even though the parts were
rated for 16MHz (suggesting that they were the units that failed to pass as
20MHz parts), the devices tested at the high end temperatures operated at
16MHz all the way up to 170 degrees C!
A web location you might want to look at is: http://www.calce.umd.edu
John
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