A light plasma clean will make this problem go away.  Test wetting with water drop test before and after.  You should see a dramatic difference even if the surface looks unaffected.

Wayne

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Thursday, February 14, 2013 9:30 AM
To: [log in to unmask]
Subject: [TN] Conformal Coat Adhesion to Gloss Solder Mask

Hi everyone,
We have a PCB that is using a gloss soldermask, and we are having extreme difficulty getting urethane conformal coating to adhere.   We use this same soldermask on many PCBs, but only this one particular PCB gives us issues.  It has occurred for some time, across multiple lots of PCBs. We do pre-clean all PCBs with IPA and DI water just prior to coating.  This is just a light surface clean just to remove any fingerprints or whatever contaminants might be introduced between post solder cleaning, through e-test, and then masking.  I think much of the issue for this particular PCB is due to geometry.  The PCB is small and has large masked areas- a few dots and all around the perimeter.  When the masking is removed, all the coating flakes off.  Ultimately, converting this PCB to matte finish is my goal, but I have many PCBs in stock to use up.  HDBK-830 states no primer is known to be needed for urethanes.  Is anyone out there using primers for urethanes, and would you care to recommend one?  What about alternate methods to roughen the gloss surface?  I am thinking perhaps if the PCB supplier could somehow dull the finish with an acid etch, or possibly light grit-blast internally?
Just looking for ideas.
Thanks,
Kevin Glidden
Mfg Engineer
Astronics Luminescent Systems Inc.

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