ASSY: GEN: Popcorning during reflow

Gary Peterson (gdpeter@sandia.gov)
Wed, 30 Oct 1996 14:44:06 -0700

Has anyone else observed the following?

We have a CMOS PQFP that was "popcorned" during reflow soldering. Cross
sectioning clearly shows that the die, along with its mounting epoxy, has
separated from the leadframe by approximately .002" (2-mils). There were
no visible cracks in the plastic overmold material at 500X magnification.

The problem is...some parts don't fail until after a few thermal cycles
of 0 to 50 degrees C during live circuit testing at-speed. And...we can
make them recover after failing by merely baking the entire board from
1.5 to 24 hours at 125 degrees C. The baking fix is not permanent and the
parts eventually fail again. Some parts don't work initially but do work
after the above baking treatment (we discovered, quite by accident, that baking
"fixes" the parts).

My question is...is the popcorning likely to be the only problem with
these parts?

Has anyone else been able to anneal a part so that it will recover from
popcorning? Doesn't sound likely to me!

Gary P.

---
                                  Gary D. Peterson
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