Tin-Nickel alloy plating is a unique metal that is just about
uncorrodable. We used it at Hewlett-Packard for about 23 years
(1965-1988). First as a final finish (but in those days we had acid
fluxes in the wave solder) than as a barrier metal under bright tin and
then gold. You can read about it in Coomb's PC Handbook 4th Ed. (pp.
19.42-19.44) or earlier. It is not in the new 5th Ed. I don't know if
it is being used anymore in the San Francisco Bay Area like in the earlier
days of pcb growth. It is a non-proprietary plating bath that has no
organic additives. It can be difficult to control and its plating can be
very stressed. But it has a number of unique metallurgical properties--It
is non-magnetic--Gold WILL NOT DIFFUSE INTO IT--It will not corrode unless
you use concentrated aqua-regia. Stanford Univ once did a project to
understand how the alloy worked because the properties were SO MUCH
different from either nickel or tin. The report was fascinating,
especially for a metallurgist because the alloy was truly unique.
Morton Adler of Bell Labs did a lot of research on it because 5
microinches of gold on tin-nickel out performed their 100 microinches of
gold on nickel for switch contacts.
I think Electrochemicals developed a proprietary tin-nickel that had an
organic stress reducer in it and did not require hydrofluoric acid to
control the pH. The Metal Finishing Handbook had the bath formulation in
it. I know personally that it made a great finish for sail boat
parts--never a sign of salt water corrosion in 20 years and we helped some
artists in Estes Park, COL plate a bronze statue so it would look good
forever.
Happy Holden
Westwood Associates
375 Morgan Lane, #206
West Haven, CT 06516
"Crepeau, Phil" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
05/21/2003 05:52 PM
Please respond to "TechNet E-Mail Forum."; Please respond to "Crepeau,
Phil"
To: [log in to unmask]
cc:
Subject: Re: [TN] PCB plating
hi,
i think, but am not certain, that i understand your question.
first of all, i interpret nickel/tin plating to be 'pure' nickel with
'pure' tin deposited on top of it. if this is the case, you haven't
gotten rid of the magnetic nickel.
second, nickel-only is not a good finish to solder to to say the least
third, specifically, what do you mean by reliability?
phil
-----Original Message-----
From: Stolar, Paul W [mailto:[log in to unmask]]
Sent: Wednesday, May 21, 2003 1:33 PM
To: [log in to unmask]
Subject: [TN] PCB plating
Does anyone have any knowledge about Ni versus Ni/Sn plating as it
relates to reliability? We cannot use pure Ni since it is magnetic.
Any ideas about how thicker Pd will affect reliability?
Paul Stolar
Materials Engineer
Houston Technology Center
Baker Atlas
713-625-5376
713-625-4949 (fax)
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