Our epoxy vendors have given two reasons for not using silver filled
adhesives with tin lead solder:

1.  The conductive epoxy adhesion to solder is poor.
2.  The curing process may result in an oxide formation on the solder
surface, resulting in increased contact resistance.  This may not be
evident at first, but can increase over time.  The epoxy is not hermetic,
and oxygen can migrate to the interface, resulting in latent failures.

For components, a silver-palladium or gold end termination is recommended.
For substrates gold over nickel should work well.

Dave Anderson
Medtronic, Inc.


"Opinions may or may not reflect those of my employer"


>>> <[log in to unmask]> 06/09/98 04:34am >>>
Salve TechNet.
What happens when you try to use silverepoxy on Sn60/Pb40? Especially if
the electrolytically applied solder is greenish because of surface
acting brightners (nanometers or less). Adhesives on solders are not
recommended, but why? What happens chemically in the interface that can
give you a weak bond or no bond at all? Will the epoxy's curing media be
defect by som interference with the solder? Or will the epoxy start
oxydizing of the Lead? Or something with the surface energies? Or
what....? /
                             Ingemar @ Ericsson Microwave Systems

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