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April 2006

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Subject:
Re: Shelf life of circuit board plating
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
(Leadfree Electronics Assembly Forum)
Date:
Fri, 28 Apr 2006 14:03:58 EDT
Content-Type:
text/plain
Parts/Attachments:
text/plain (23 lines) 
Hi Phil,
No the Au does not tarnish, but the issue is not the Au, but the underlying 
Ni it is supposed to protect. imAu is porous--you need to balance imAu 
thickness between sufficient thickness for reduced porosity and too thick for 
Au-embrittlement.   [also, imAu is at least to some degree, self-limiting in plating 
thickness].
imSn and imAg are also porous, so protecting the underlying Cu may be limited 
in time also.
Vacuum sealing is a goood idea.
And no, you are NOT going to see solderability problems at 6 months or before 
from Cu-Sn intermetallics with imSn—you may see it with thin HASL layers, 
however. In that time-frame other problems may develop for thin layers, but IMC 
is not one of them.
Werner

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