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May 2010

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From:
"Kinner, Phil" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kinner, Phil
Date:
Wed, 5 May 2010 15:20:20 -0400
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Ioan,

The coating seems to have pooled, which is usually due to non-planarity of the assembly.  I wonder could your assemblies be warping slightly during reflow which might explain the difference between populated and unpopulated assembly?

Excessive exhaust will exacerbate this issue, by beginning to cure the surface whilst solvent is still trapped inside the coating. 

Your issue may also be programming related, if you lay a heavier deposit in that area due to complexity (slow machine velocity) or the need to overlap in areas.

I have also seen issues where boards became charged prior to coating, and the charge was sufficient to pull the coating towards them, that was a tough one to get to the bottom of.

It is tough to see in the photo, but it looks as though there might be some coating dewetting from the thru hole area in the most affected region (unless this was a deliberate keep out area) and this might explain why the coating has pooled and gotten as thick as it has, thus leading to your issue.

Please feel free to contact me offline with more details and photos to take a closer look at what you are seeing.  

Best Regards,

Phil.

Phil Kinner
Business Director
Chase Electronic Coatings
 
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Wednesday, May 05, 2010 2:59 PM
To: [log in to unmask]
Subject: [TN] Wrinkling of conformal coating

Dear Technos,

 

Back to orange peeling, this time concerning conformal coating, please see http://ipc-technet.groupsite.com/galleries/photo/124230

 

The coating is applied with an Asymtek Century machine and is a Conap 1170 acrylic.

 

ˇ         The board is left curing in ambient temperature, no acceleration. Starting with an even coating, in about 20-30 minutes the liquid seems to move towards a certain area (no rippling at this moment). After another 10-15 minutes the rippling effect sets in.

ˇ         We thought that due to the almost 2 minutes lag between the coating of the first and last image, the drying of the coating layer is not even and the one side curing first pulls on the liquid at the other end. So we've cut the panel in 2, accelerated the machine, the problem is still there.

ˇ         The boards are laid as flat as possible, maybe not perfectly horizontal, but not worse than others with the same coating, that do not show any issue

ˇ         Just to make it more difficult: grabbed a non-populated panel from the stores, coated it, placed on the same flat surface, and guess what: no issues.

 

The PCB has Taiyo PSR 4000 MP soldermask.

 

So I would need your guidance in clarifying where is this coming from and how to fix it.

 

Thank you,

 

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer T | 450.967.7100 ext.244 E | [log in to unmask] <mailto:[log in to unmask]> W | www.digico.cc <http://www.digico.cc/> 

 
 N'imprimer que si nécessaire - Print only if you must

 


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