| | | Hello Netters, | | | | | | I need some info, Earl or Dave, I have a PCB that exhibits a white layer on solder side. It does not appear to be surface residues (IPA has no effect), but looks like its under solder mask. My first guess is that the LPI solder mask is uncured. I can use solder/hotair tool to heat area and it dissappears. I dug through the archives here and IPC, and found that others have had problems with TAIYO brand soldermask, " WELL Guess What!" My soldermask is also TAIYO (Z-100), which makes me wonder. I am believing that the UV cure thay are using may not provide | | | enough output (lumens) to cure mask. | | | | | | Is there a way with out a test lab to be positively certain, that soldermask is the problem?. | | | | | | Can I bake the PCB's to cure the mask or is there another solution? | | | | | | Process | | | | | | 1. Kester OA 2331-ZX flux | | | 2. Wave temp 205-215F until 490F | | | 3. Conveyor 4.5ft/min | | | 4. Wash cycle 8min at 145-160F in DI no chemical | | | 5. 3 rinse cycles, 1min at 145F | | | | | | | | | Thanks | | | | | | Tom B | | | | | Tom: Good troubleshooting!!! Sounds like your board fabricator put it to you. He should be doing back-flips to make it right by you. I'm not real excited about you trying to cure these boards. Good luck. Dave F | | | Tom: Sorry I ditz'd-out responding to you on the test you should run to test for solder mask cure. Earl chattered about MEK a while ago, but I can't find it in the archive. Anyhow: | | 1 MEK (methyl ethyl keytone) & acetone are OSHA prohibited, try hypersolve (Great Lakes Chemical) | 2 Use citrius terpine cleaners in-stead of MEK | | In truth, as I mentioned in an earlier post on this thread get your supplier involved. Your are 95%+ sure it is uncured mask, have him prove it is cure properly. | | TTYL | | Dave F | Dave,
It was methelyne chloride not methyl ethyl keytone. How some ever, that stuff might work too - just don't have any test methods for that stuff.
You're right about not being able to effect a cure once the mask is applied and the board is shipped. Molecular cross linking must take place within reasonably tight process windows.
And Tom B, I've heard about some problems with this type mask but have no details. However, those things related to fabrication process control more than the mask supplier capabilities. Also, old Dave is right about paying your local sheriff a visit to drive those outlaws out of town or make you some new boards.
Best wishes,
Earl Moon
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