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Will solder mask stick to aluminium?

PeeCeeBee

Apr 20, 2021
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I have designed an aluminium single-sided PCB, but since the bottom aluminium surface is visible to the user, I would like to have the aluminium surface coated with the same solder mask as the component side to improve its appearance.

Will solder mask stick to the bottom aluminium surface?
 

Harald Kapp

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Nov 17, 2011
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Ask the manufacturer of the aluminium carrier. He knows which material he uses and whether it sticks to the aluminium or not. If not, you can always apply spray paint to give the bare aluminium any color you wish.
 

PeeCeeBee

Apr 20, 2021
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Ask the manufacturer of the aluminium carrier. He knows which material he uses and whether it sticks to the aluminium or not. If not, you can always apply spray paint to give the bare aluminium any color you wish.
Thanks Harald. I already did and his answer was "Make it double-sided and put a couple of dummy pads on the underside, then we can apply the solder mask", which didn't really answer my question.
It would also make the PCB more expensive than it might need to be.
If it were only one or two boards involved, then spray painting would be fine, but painting 300 boards, each 350x390 mm is a chore I'd rather avoid.
Solder mask also has a very consistent, even finish that I would struggle to achieve with spray painting.
 

Harald Kapp

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If your manufacturer is not cooperative, maybe try another manufacturer.
For one it seems, judging from his answer, that he isn't able to apply solder stop to the underside at all if there are no pads, for whatever reason.
Secondly we don't know what he uses as solder stop, so we cannot judge whether it will stick well to bare aluminium.

Imho solder stop is not suitable for a visible finish. It is not designed to withstand the possible mistreatment by people that come in touch with the surface. There are other coatings e.g. in various colors that are (hopefully) more resistant to abuse. If your manufacturer does not offer this option, another reason to chose another one.
 
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