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Reply To: | TechNet E-Mail Forum. |
Date: | Wed, 6 Jun 2001 11:34:02 -0500 |
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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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