Electronics > Manufacturing & Assembly

Green shmutz on trimpot screwheads

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lol what the hell the one on the left looks like corrosion but the one on the right looks like green laquer

it clearly looks like laquer when you start to chip it off and then you get the white color from the bond line breaking and air gap between the laquer and substrate

can they be trying to protect the parts from the solder process then forget to remove the protection? ingress seal of some kind

Can your CM provide samples of trimpots from the same batch used for assembly?

If the color in the extreme close-up is a varnish, it might have been applied before the pot was assembled. Or maybe it's a clear coating that sealed in corrosive contaminants.

oh yeah ultra thin conformal coats are becoming common now they might do this

Were the boards washed?  Did the CM possibly coat the pots with a sealant/masking compound for washing and missed removing it from a few units?

It's an interesting puzzle. I suspect the PCB soldering/wash, something that attacks brass. The LED holder has crusties of some residue inside it, the gold jumper pins look damaged as well. I think the board got hit with some chemical that de-zincified the brass.
You can check the trimpot date/lot codes, but a blue one got it too as well as the grey ones.


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