Hi Doug,
No, a thin silver coating does not improve solderability--it may however give
a false indication of good wetting.  Solderability will solely depend on the
surface and material that you want to solder to; the silver will facilitate
the easy spreading of the liquid solder on this surface because of the high
solubility of Ag in tin.  If the underlying surface is solderable, than Ag
may improve wetting because of the somewhat faster spreading of the liquid
solder; if the surface is not solderable, the Ag may still facilitate the
spreading of the liquid solder without changing the non-solderable nature of
the underlying surface.  Thus, you may get the appearance of a properly
wetted solder joint, but not have good wetting.  
If you have too much Ag in your solder joints, you can get into real trouble.
 The effect of Ag-Sn intermetallics was amply demonstrated in 1983 when
Ag-plated PLCC-J leads from TI fell off circuit boards made by IBM-Austin as
the result of the brittle and weak Ag3Sn intermetallic compounds. This event
caused the formation of the IEEE Compliant Lead Task Group with 23 competing
companies participating to investigate this occurrence and to gain
understanding in the reliability achieved with compliant leads.

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]  

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