You can try silver nitrate, I have used it to determine if there is resist left at the foot of
a developed trace.  Keep it off your hands, it will stain them and it is used to cauterize
wounds.

Brown, Matthew wrote:

> Does anybody know of a chemical that can be used to detect mono-layers
> of organic resist on top of copper?
> We've had issues in the past with resist residues left after develop
> causing plating problems. A fellow engineer
> mentioned that he had heard of a stain that would leave any contaminated
> areas on the Cu a different color. He
> did not know what it was however...
>
> Matthew Brown
> Metal Plating Engineer
> International Flex Technologies
> Phone: (607) 658-5032
> Pager: (607) 778-4554
>
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