If the boards are already built, then I agree with Wayne that a plasma
clean may be your best bet.
If the boards are not yet built, then check with the supplier to see if
they are using a post-UV bump to further cross link the mask to further
reduce ionic contamination test results. In some cases, the UV bump could
be eliminated which may improve the wetting and adhesion, while still
passing ionic testing.
Lamar Young
Specialty Coating Systems, Inc.
7645 Woodland Dr.
Indianapolis, IN 46278
(317) 244-1200 Ext. 276
www.scscoatings.com
From: Wayne Thayer <[log in to unmask]>
To: <[log in to unmask]>
Date: 02/14/2013 09:48 AM
Subject: Re: [TN] Conformal Coat Adhesion to Gloss Solder Mask
Sent by: TechNet <[log in to unmask]>
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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