I've never heard of migration associated with 10/88/2 or similar alloys, but
that's not to say it's never happened. That alloy starts to melt around 270C
giving soldering temps of 300 plus. At that sort of temperature everything
organic is pretty friable and likely to come unstuck/delaminated/thermally
degraded into ???.  Including conventional rosin/resin fluxes which will
probably be caramelising. Certainly, if you're doing it, post solder
cleaning is difficult and likely to be compromised. Therefore I think the
cause is more likely to originate in those areas rather than directly from
the solder. An area to go on to your investigate list anyway. It would be
useful to know what the assembly process and material types are.

Regards 
 
Mike 
BS&P
M: +44 [0] 7810 526 317 
T: +44 [0] 1865 522 663

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Tuesday, December 17, 2013 10:15 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





______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________



______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________