We found some PWBs that seem to have both film and liquid solder mask applied on the board. I have never encountered this before and was curious to see if this is acceptable for use.
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1\$\begingroup\$ I haven't heard of that either, unless perhaps you are referring to a conformal coating, in which case it would cover the parts on the PCB too, not just the raw PCB. Post a picture (and remember to size and crop it appropriately). \$\endgroup\$– Olin LathropCommented Aug 23, 2012 at 19:12
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1\$\begingroup\$ Was it designed for any special application? High-Voltage, high-radiation/ionization, high-temp, etc...? \$\endgroup\$– DrFriedPartsCommented Dec 13, 2012 at 11:45
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\$\begingroup\$ It's possible it was due to rework. \$\endgroup\$– Kuba hasn't forgotten MonicaCommented Apr 18, 2013 at 22:33
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1 Answer
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Recognizing that there are a lot of assumptions here about the material specifications involved...
I spoke with two of our partner factories and they both said the same thing:
This is typically a result of rework, where the original soldermask was partially removed for some reason and needed to be reapplied post-hoc.
Should still meet spec -- meaning, there are no anticipated concerns as a result of the mixed process. Some overlap between the masked areas was suggested to ensure that you maintain complete coverage over the full temperature range.
If needed for a "special" application (life/safety critical, aerospace, etc) then recertification/testing is required.
