GuitarBud wrote:

> I recently received immersion gold finished boards from a PCB supplier where
> some of the edges of the traces were black.  The gold was flaking or had a
> bubbled appearance in areas as well.

> snip---------------------------------------------------------------------------

Sounds like you have substandard plating.  If the gold is bubbled, it probably won't pass a tape
test.  (You might try performing one on the boards.  See any IPC board spec or TM650.)  There is
no reason that properly applied nickel/gold, either electrolytic or ENIG, should exhibit the
characteristics mentioned.  As stated by other responders, flakes and bubbles indicate poor
adhesion of the plating to the substrate.  Since nickel doesn't dissolve appreciably during
soldering, do you want to solder to nickel that doesn't adhere to the copper?  If the gold
bubbled from the nickel, you won't be able to form a reliable solder joint to the passivated
nickel under the bubbles.

The black material sounds like residual tin or tin/lead.  If those contaminates are present in
quantities that are visible, the intregrity of both the nickel and gold is suspect.  As an aside,
I've seen electroless nickel seperate under a tape test when a supplier attempted some rework
because all of the pads didn't initiate on the first try.  When the gold flakes were examined
under magnification, the back sides had nickel coloration and there was nickel on the board at
the failure sites.

In any case, send the boards back.

Don Vischulis

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