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November 1998

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Subject:
From:
WILLIAM G KENYON 302-652-4272 <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 20 Nov 1998 23:26:00 -0500
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TEXT/PLAIN
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TEXT/PLAIN (41 lines)
Have been following the various postings/answers to the problem
of gold tarnish and how to get rid of it, etc. There is a better
way that was developed in the early '80s. To prevent scratching
of gold fingers with metal protective clips used to prevent
solder pick-up during wave solder, as well as contamination from
synthetic rubber finger protectors used for the same purpose, a
solvent soluble organic coating was invented.  The material
contained a UV fluorescing dye, so it could be quickly painted
onto gold surfaces, inspected under black light for coverage,
then run through the soldering and cleaning processes.  The
temporary gold protection and flux residues were removed at the
same time during defluxing. Rockwell published excellent data on
this use at Nepcon West '81, paper by G. J. Engelland.
Interestingly, Rockwell found the contact resistance of the gold
fingers was significantly lower after this process, meaning that
the yield of cards meeting the contact resistance requirements
was much higher. Why? the temporary protective coating pulled out
the co-deposited organics and other contaminants from the gold
finger plating process.
This method might be much preferred to using abrasive erasers
which could leave other contaminants on the surface. I believe
the coating is still commercially available, but like many other
things, this "trick of the trade" has been forgotten by the
present generation of soldering folks.

-Bill Kenyon
Global Centre for Process Change, Inc.
Tel/Fax: 302-652-4272/-5701  email: [log in to unmask]

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