Doug,
We've suffered through similar frustrations. One thing we found that might be of some help is uur supplier, unbeknownst to us, was outsourcing their immersion gold. Their supplier apparently lost control of their process for a period of a few months. As best as I can tell it was for the weeks of of 52/99 - 7/00. I've pasted below one of the email responses from our supplier:
"Once the boards in question were received back, it was quite obvious that the boards had a black pad issue. You are correct, it did take additional time to determine "why" it happened. The returned boards were sent to [our supplier] for SEM analysis. It was noted on the report that the boards did in fact have issues with the nickel plating (manifesting in "black pad"). I believe this to be isolated to the date codes from 5299 to 0700 as the supplier has not seen issues other then this time frame, and has review both bath make-up and controls."
They said something about Phosphorous being the cause, but I lost the details, maybe Dave F. can shed some light on this.
We couldn't live with the risks of black pad disease (we saw it from 2 vendors), so we switched to Immersion Tin and have not had any problems so far (in 3 months).
Our board vendor claimed that their immersion gold supplier was the largest in Southern CA and lots of board shops outsource their immersion gold to them. If that's the case, lots of people have had black pad problems from the date codes listed above.
Years ago, we had a vendor "accidentally" run our boards down their gold plate line instead of their immersion gold line and we ended up with 30+ u in. of gold. But they 'fessed up to it when we sent them back and they checked the thickness.
Steve Schrader
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