Hi Ed,
Your real problem is the testing requirement. While, for automotive
applications cycling of -40C to +140C with 30 minute dwell times makes sense,
the10 sec transition most likely does not (where in an automobile to you get a
temperature ramp of 18C/sec—even reflow soldering ramps are limited to
2C/sec). It is this T-shock condition of 1080 C/minute that is killing your
assemblies. You are setting up hugh transient warpages in both components and
substrate putting the solder joints in tension. When I was still at Bell Labs,
we once soldered two ceramic components together (to assure that there was
absolutely no CTE-mismatch) and T-shocked them. Our results were similar to
yours; both solder joints as well as metallizations failed. Your problem is
neither solder related nor process related; it comes from your sales people
accepting a job with a real crazy requirement.
On the other hand, I really would not want a car with some electronics that
could withstand only 1000 cycles.
From a design point-of-view, your only possible solution is to put leads
onthese components that are very compliant in the z-direction. Not a very
practical solution, not to speak of the cost.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]


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