Aren't plasma parameters very important if mass production? We used
Oxygen/Argon which gives a combination of ashing and etching, but as far as
I remember it was not easy to decide the parameters because the urethane
surface seemed to vary a lot from lot to lot, and where the urethane was
thin, the plasma attacked the epoxy.  We abandoned the method as nobody was
enough interested to dig.  Will be interesting to see what comes up.

Inge

On 14 February 2013 06:58, Lamar Young <[log in to unmask]> wrote:

> 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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