We have an FA project that appears to be migration of 10Sn/88Pb/2Ag solder across a 0.024 inch antipad to ground plane on the surface of the polyimide board.
It is not dendritic in appearance.  Looks more like Ag creep corrosion.
Failure occurred under dry heat testing at our lab.
Bias is 48 volts
The test temperatures are 200-250C over 12 weeks
Ran at atmosphere, no added moisture
The failure coincides with the loss of solder mask adhesion, under which the metal can be seen...sort of, as mask is just about charcoal now.
There is also some evidence of flux residue, which would likely be very corrosive, but don't we need moisture?

Literature searches get swamped by Ag migration/creep.  Anyone got an idea?  Keywords?  Tests for differential diagnosis.

Chris

Chris Mahanna
Robisan Lab





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