>In the Electroless Nickel-Immersion Gold process, why is the Nickel
>electroless (as opposed to electrolytic)?
>
>Thanks for the information!
>Zoila Vega

The electroless nickel/gold process is done after final etch, and sometimes
after soldermask.  At this point in the process the board is nearly, if not
completely, electrically functional.  The areas required to be nickel and
gold plated are not electrically connected to allow electroplating.
Electroless deposition is the only option open at this point in the
process, ie when there are many electctrically seperated areas.

How are contact fingers electrically plated?  They are all electrically
shorted by a trace located on the manufacturers panel, but off the edge of
the board.  This fingers are seperated from the shorting trace when the
board cut out of the manufacturing panel during the routing process.  The
fingers go to the edge of the board by design.

To get the plated nickel, the nickel and gold would have to be applied
during the plated thru hole process, and also act as a plating resist.  HP
has done this for many years.  The electrolytic gold is much thicker and
causes solder joint embrittlement.  (Although my HP calculator purchased in
1979 still works fine.)

This is the PWB 101 simple answer.  It begs the question: Why not use
nickel as a plating resist?  I will leave that for another time. (because I
am not 100% sure of the answer.)

George Franck


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