We have seen some interesting phenomena during TCT. We compared 0-125C to -40 - 125C. For the same package, we had no failures after 2000 cycles with the 1st profile, but had 1st failure @ 500 cycles with the 2nd profile. It appears that the
-40 C excursion is what kills the part. The most common failure we saw was substrate trace crack. The substrate was 2-2-2 build-up BT substrate. I know at -40C Young's modulus is higher. Is it a major factor? Any other factors? Why -40C would make such a big difference?
Recall there were some discussions on this topic, however, cannot find them. Any papers or on line info available?
Thanks,
Yuan
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