Silver can leach from the epoxy into the solderphase (if fused) or tin
phase (if unfused), leaving little silver at the epoxy surface. This
reduces conductivity.

Some epoxy catalysts react with tin, leaving cure problems at the
interface. Proper material selection can eliminate this issue.

You are also epoxying to oxides, not the metals themselves. Oxides have
little pull strength relative to the base metals.

I don't know the brightener system, so can't respond to that issue. Many
brighteners can interfere with the epoxy cure and possible "brighten"
silver particles in the epoxy.
-------------
Original Text
From: C=US/A=INTERNET/DDA=ID/TechNet(a)IPC.ORG, on 6/9/98 8:03 AM:
Ingemar writes:

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:

Electroplated, unfused, solder is not really solder.   It is a deposit of
Tin
crystals and Lead crystals sitting next to each other, unalloyed, not
dissolved in each other.  There is a strong tendency to get (galvanic)
corrosion in this type of deposit.

Although I am unfamiliar with the specific problems relating to application
adhesive to this type of deposit, it is clear that you would get corrosion
and
oxidation UNDER the adhesive, even after it was applied, and that this bond
would not have good shelf life.

This would be HELPED, maybe not cured, by fusing the solder.

Rudy Sedlak
RD Chemical Company

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