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Wed, 06 Sep 95 10:41:18 EST
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I manage a captive PWB shop that produces 4,000 square feet per week of
double sided plated thru hole product from .062 FR-4 copper laminate.  Our
product is a bit uncommon in that it has about .0004 inch hard nickel plated
over the copper traces.  Thru testing, we find a VERY thin layer (maybe 150
angstroms) of some contaminate that affects the surface conductivity when it
is used as a switch half with a stainless steel snap dome.  Using a
Scotchbrite pad to burnish the surface provides a solution, but I would like
to know the source of the substance and how to prevent it in the original
process.  Any ideas on the subject?


Have it analyized. Try Auget (OJ) testing. You'll probably find that one of
your post Ni Plate processes is depositing the film and producing the 
contaminate. Nickel is also prone to passivation when it's alone and left
exposed for some time or exposed to thermal excursions. (eg, high temp bakes)


                   Hadco Printed Circuits
                Tech Center Two / Watsonville                


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                Dave Hoover              (408) 728-6677
                Senior Process Engineer  (408) 728-1728 Fax
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