Right out of resist strip before etch an dTin/lead strip, the gold stains are very noticeable. Galvanic reaction theories had been thrown around here to explain the phenomena.
Lourdes

>>> Dave Hoover <[log in to unmask]> 02/18 7:28 AM >>>
Is it coming from the etcher?
Or is it coming from another process like Tin Lead Strip?
Chase it down.
Remember, galvanic (stray currents....or whatever you may call
them...<gremlins>)
leaves some trend or pattern that may be repeatable between PCB's.
Are you seeing that?

Groovy

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