Hi Chris - do you have any pictures you can share? You may have a simple 
case of electrochemical migration (you don't need to have pretty dendrites 
to have that failure mode). Have you conducted SEM EDX on the "not 
dendritic material" to determine its composition?

Dave Hillman
Rockwell Collins
[log in to unmask]



From:   Chris Mahanna <[log in to unmask]>
To:     <[log in to unmask]>
Date:   12/17/2013 04:16 PM
Subject:        [TN] High Temperature Solder Migration/Creep
Sent by:        TechNet <[log in to unmask]>



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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