The staining can be analysed relatively simply and cheaply using an SEM with
EDXA (note these instruments aren't particularly inexpensive but there are
companies or institutions who will do the work for you for a fee) this will
give you a an elemental map. You'll find gold, maybe some nickel and then
potentially carbon and/or oxygen perhaps some other elements. From that a
chemist or perhaps a metallurgist, knowledgeable in the industry could
speculate fairly accurately the nature of your stain and the possibly the
source. You can then take it from there.
As to contamination vs. solderability, I doubt very much whether any really
useful information could be gathered from such a study, since staining is a
relatively random occurrence i.e. it doesn't happen to everyone's products
at the same time, for the same reasons. Over and above that there isn't that
much information on the very diverse flux systems used and their reaction
with the 'stain'. A simple study might be available or could be carried out
but it would be very, very, specific and of very limited use to anyone other
than perhaps a flux formulation chemist looking to develop an understanding
of flux activation, over a number of years.
I don't know about the effects on keypad performance.
Best regards,
Andrew Hoggan
www.bba-associates.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Bev Christian
Sent: Thursday, July 12, 2001 11:37
To: [log in to unmask]
Subject: [TN] Staining on Gold
TechNetters,
I have checked the archives and have not been successful in finding
sufficient info on the titled subject. Either I have not done a diligent
enough search or the info is not there. So, here are my questions.
1) If you were presented with varying amounts of what looks like water
stains on immersion gold pads how would you determine its composition? No
guesses now, I can do that. I want to know how people have actually done
it! Also, I am not referring to "purple plague" but just slightly off color
gold.
2) Has anyone ever been able to correlate amount of staining to
solderability issues? Or is it a non-issue?
3) Has anyone seen staining cause problems with respect to keypad electrical
continuity?
regards,
Bev Christian
Research in Motion
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