At the time I posted that message, I had just finished reading a special
issue of CircuiTree magazine called "The Board Authority" Volume 4 Number 1
titled "Assembly and Solderability" which has at least three articles in it
that discuss silver plating, and the entire IPC email archives of every
post that had the word "silver" in it, and also the White Paper called "PWB
Surface Finishes" available for free at
http://www.ipc.org/html/downloads.htm
In all of those sources the ONLY drawbacks to silver that I can remember
are that it might not be reliable enough (or robust enough) for contact
switches, and that storage may be an issue. Well, I should say those are
the concerns that interested ME, there are also concerns if it comes into
contact with sulfur, different probe tips for ICT, possible incompatibility
with via plugging, stories about whiskers in the olden days, etc... but I
don't consider those as drawbacks to using it. I can't remember who stated
they should be in an airtight bag, but just for the record I have one that
was sitting on my desk exposed for weeks, and is now in a file cabinet
folder (exposed) and still seems just as solderable, but I'm no expert (I'm
a layout guy). I don't even see any evidence of tarnish. Since I can't seem
to find the exact quote that got me worried, I would like to apologize if I
misinterpreted a source and especially for using the term "most sources"
since I can't even find ONE at the moment. sorry...
good luck and best wishes,
Jack
-=original message=-
Date: Wed, 26 Jun 2002 16:34:43 +0100
From: "Reid, Lorraine" <[log in to unmask]>
Subject: Shelf life of Immersion Silver Fabs
A couple of months ago there was a discussion thread running on the merits
of immersion silver boards. One of the contributors (Jack Olson, I think)
made the comment that -
"Most sources say a silver surface will not be solderable after a month or
so unprotected. (Even in a baggie it will be okay a year later?)"
What are these "sources"? Are there published articles giving guidelines
on how fabs should be packed to maximise shelf-life?
Basically, we've just received some Immersion Silver boards from fab house
which were wrapped in tissue paper then bubble-wrap. Not in sealed bags or
anything. They claim boards should be OK, even though we won't be using
all supplied boards for a few months. They have offered to repackage if we
insist on it. I'm a little concerned, having seen how Immersion Silver
boards can easily tarnish.
I'd be interested to hear what TechNet contributors have to say on this
matter.
Thanks in advance for your replies
Lorraine Reid
Senior Electronics Engineer
Trivirix International
tel. +44 (0)28 9096 0932
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