We are looking for experiences with a problem that apparently manifests
during the immersion nickel/gold process.

As I understand it (pardon lack of technical expertise) the narrower fine
pitch pads have less nickel surface than larger pads and during the
nickel/gold exchange, there is some chemical process that results in
entrapment between the remaining nickel and gold surface.

This is not visible to the naked eye.  It survives the "tape test" at
incoming inspection, it is not lot specific, it does not manifest as
"blackened pads" until being exposed to the flux/reflow/cleaning process.

These pads are "reworkable", but the rework requires component removal,
slight abrasion, "retinning" of the pad, etc.

We have seen this across our PWB supplier base (providing the Ni/Au
immersion boards).  It is apparently inherent in the chemistries involved in
the process.

This is a relatively new problem for us.  Does anyone out there have any
long term experience with this?  What about reliability issues?  Latent
failures?  Have you determined when a board should be reworked or scrapped?


Our major issue is that we cannot get recovery from some suppliers when this
problem manifests.  Retooling charges for various boards is prohibitive.  We
are exploring OSP as an alternative.

Janice M. Pelchat
SR Quality Engineer
Benchmark Electronics
Hudson Division

Email:  [log in to unmask]
Voice:  603-879-7000 ext 2412
Fax:     603-879-7157

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