Hi Mason! There are a number of different surface reactions which could be
present (silver sulfide, silver chloride, silver oxide, etc.). I use my
SERA test unit with a borate buffer solution to nondestructively analyze
the immersion silver surface to determine who is present. You also could
use  Auger spectroscopy too but that would require a destructive analysis.

Dave Hillman
Rockwell Collins
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Mason Hu <[log in to unmask]>@IPC.ORG> on 05/30/2001 05:56:25 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
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Subject:  Re: [TN] Immersion silver boards tarnish


I recently ran a few test assemblies (with immersion Ag finish, of course)
through thermal cycling (for 2nd level reliability).  At the end of the
test, some of the non-soldered metal area (EMI contact) got the yellow
tarnish.  When probed with a multimeter I measured significant increase in
contact resistance.

I read a lot of comments on the presence of sulfur and chlorine (or their
ionic counterparts) as being the possible root cause.  My question is: what
is the chemical reaction(s) here?  Are those agents attacking the Ag or the
organic co-deposited with the Ag?  Does anybody know what the yellow stuff
is?

Mason Hu

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