What is the laminate you are subjecting to such abuse!  This sounds like very cruel and unusual punishment.  I could see doing a test like this as part of a "what if?" potential fail-safe analysis, but can't think of any situation where you'd do that for 12 weeks.  I have recently heard of aerospace composites which can take temperatures like this, but I think they use carbon fiber, so that would create another form of the isolation problem.

If the solder mask is turning black, that is suggesting free carbon particles, which are conductive.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Tuesday, December 17, 2013 5:15 PM
To: [log in to unmask]
Subject: [TN] High Temperature Solder Migration/Creep

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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