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Long ago, I worked at a place (in Texas) that would conformally coat all the circuit boards used in their navigation equipment assemblies' due to the expected service environment.
As a QA tech, 8 different boards used in that unit were tested on vacuum-contact jigs (specifying rework if needed) BEFORE they were sent to another station to be "potted" before assembly into a unit. When testing the assembled units, an occasional soldering-related repair needed done on a board, so MEK (methyl ethyl chloride) was used to dissolve that coating so repairs could be performed. Then it was patch-potted, showing an obvious repair.
I rarely see solder masking fail unless it has worn or scraped off. The picture looks as if corrosion crept in from the sides of that trace, like rust on a car, and the masking failed. RCA seemed to flow solder on all the traces, others like Philco, GE and Sylvania used something coating the entire board except where solder connections are made.
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"When resistors increase in value, they're worthless"
-Dave G
Last edited by DavGoodlin; 04-08-2022 at 09:37 AM.
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