I've seen this a few times when resist overloads the developer and panels exit the developer with this "foreign body/contaminate" attached, if it is not cleaned prior to plating it inhibits copper buildup there, then during rinsing or some point after plating prior to tin plate it comes free...leaving a nice little depression in the copper.

As for where this might be mentioned within any specification, I have yet to find this particular condition so I treat it as trace reduction-height, and/or poor workmanship.

Depending upon the customers use of the board, the type signal running through the trace, and if they're in a good mood that day, this may or may not be considered a reject...but it is something that should be brought to their attention...



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