Hi everyone ... I have been looking at solder joint failures for quite a
while and have stumbled on something new to me.  I hope someone has seen
this and can give me some insights.  Here it is ...

*  the failures occur on a number of different component types including
SOICs, QFPs, SMT caps (not chip caps)
*  the failure is complete interfacial failure of the mounting pad at
the copper/IMC interface (i.e the solder, Cu6Sn5 and Cu3Sn layers stay
with the component lead)
*  the board finish was HASL and the IMC layer appears normal (i.e. ~
1-2 microns total thickness)
*  the copper is heavily oxidized.  However, I believe this is because
the crack existed for a long period of time (perhaps?)
*  I see no convincing evidence of contamination at the failed interface

*  the failure does not appear to be related to an electroplated copper
interface

Based on past experience, this type of thing seems to be caused by gross
thermal shock!?!  Have any of you seen the type of failure I have
described?  If so, what was the conclusion as to cause?

Best regards,
Ed Hare
VP SEM Lab, Inc.

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