TECHNET Archives

February 2013

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Glidden, Kevin" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Glidden, Kevin
Date:
Mon, 18 Feb 2013 16:43:43 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (63 lines)
Lamar,

Interesting.  So you are saying a post UV bump of the soldermask, while increasing cure (cross link), can be detrimental to conformal coating wetting and adhesion?  What is the principle behind this?  Is the UV bumped and theoretically(?) more cross-linked material simply more glossy?  It is my understanding a post UV bump typically also increases hardness and reduces VOCs.

We did run the sample test I wrote about in my last email, which was to run the PCBs through a UV curing conveyor prior to any conformal coating applied.  On this one sample, it DID seem to make a difference.  This test piece shows good wetting and adhesion.  In fact, we can't flake it off at all.

Thanks,

Kevin Glidden
Mfg Engineer
Astronics Luminescent Systems Inc.

-----Original Message-----
From: Lamar Young [mailto:[log in to unmask]] 
Sent: Thursday, February 14, 2013 9:59 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coat Adhesion to Gloss Solder Mask

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.

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2