Paul,

The Blsck Pad occurrence was very low to begin with. However when a problem
occurred it had very high visibility.

Thanks to this visibility the process is now taken seriously by suppliers and
fabricators. ENIG is the most complex process in a PCB manufacturing shop.

You have to ensure that the incomming part is defect free, a clean copper
surface with the proper topograph, free of any residual tin and most important
free of soldermask residues.
You then go thru surface prep and microetching online. This is followed by
catalyzation, before going into the electroless nickel bath.

The electroless nickel bath runs at high temperature with an approximate
dwell of 20 minute. The Ni is plated out of the bath and must be continuous
replenished with Ni, reducer and stabilizer, in addition the pH must remain constant
thoughout the plating cycle.

Unlike th electroless copper process where this is the last process step , in
ENIG the electroless nickel is follwed by immersion gold which by nature is a
corrosion reaction.

With this understanding of the complexity of the process and the following
the new IPC guidelines of only 2 - 4 uins of gold; the production of ENIG
finished boards continues to grow and the Black Pad is quickly becoming a thing of
the past.

George Milad
National Accounts Manager for technology
Uyemura International Corporation
Southington CT
(516) 901 3874 mobile

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