I thank you all so far for your input including those emailing me personally
and those on this forum.
This is a fast moving thing and should be wrapped up early next week
depending on DOE implementation and results. Right now, I'm leaning heavily
toward thermally induced failure causing "melt down" and subsequent, and
very fast, catostrophic electrical failures.
1) Using acoustic microscopy, in accordance with MIL-STD-883 test method
2030, I have seen die attach eutectic (AuSn) bonding material voiding in
exceeding minimum requirements in as received parts. This equates to poor
thermal transfer, for one thing, and that the supplier missed the boat on
this testing.
2) We are not using thermal compound between the device base and the heat
sink thus not allowing adequate thermal dissipation/transfer. Also, we are
using preliminary/prototype castings with inconsistent voiding. Again,
thermal transfer is compromised.
3) As so many other tests, including liquid crystal analysis for ESD damage
detection, particle impact noise detection, leak detection, RGA, various
contamination/surface analysis testing, and others, have turned up negative,
the thermal theory is highest on my list.
4) Other random possibilities exist, though not yet verified, as solder
balls, mis-handling events, and the normal/abnormal assembly "techniques"
but seem unlikely to cause such failures as found.
I'll keep you all posted when all the raw data is converted to useful
information.
Earl Moon
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