Ioan

As a follow-up to your issue, you say that you had no problem with the non-populated board fresh from stores. Have you got silicone anywhere in the process, release agents and the like?

Be aware that Taiyo PSR 4000 has been problematic in regard to acrylic coating adhesion and wetting for the past 15+ years. This resist is available in around 1500+ variations, "tweaked" to suit the customer. Try a pre-bake and see if this makes a difference?

Puddling and pooling are obvious characteristics to avoid, I would also check the coating rheological behaviour if you were to try different thinners. You might experiment with different coating thicknesses until you see the recurrence of the problem on the "bare boards" if you have enough to work with - maybe some panels from your board supplier?

Hope this helps
 
Regards

Graham Naisbitt - KBO

Email: [log in to unmask]
Phone: +44 (0)12 5252 1500
Web: www.gen3systems.com

On 5 May 2010, at 20:20, Ioan Tempea wrote:

> Graham,
> 
> This is a new product, unsuccessful from the beginning. Thickness OK, but the customer rejects due to the rippling.
> 
> Will try tomorrow the thinner coating, we only do one pass. Will also try more/less viscous liquid.
> 
> Thanks,
> 
> Ioan Tempea, ing.
> Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
> T | 450.967.7100 ext.244
> E | [log in to unmask] 
> W | www.digico.cc
> 
> N'imprimer que si nécessaire - Print only if you must
> 
> -----Message d'origine-----
> De : [log in to unmask] [mailto:[log in to unmask]] 
> Envoyé : May-05-10 3:13 PM
> À : TechNet E-Mail Forum; Ioan Tempea
> Objet : RE: [TN] Wrinkling of conformal coating
> 
> For my guess I'll go with either too thick, or contamination on the panel making it try to dewet.
> 
> Questions: is this a new problem on a product you have been successfully coating until now?  Have you measured the thickness to ensure it is within normal range?
> 
> Suggestion: Could you do two thinner coats and let it flash off a bit between coats?
> 
> regards, 
>   
> Graham Collins 
> Halifax Production Engineering 
> L-3 communications Electronic Systems 
> (902) 873-2000 ext. 6215 
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
> Sent: Wednesday, May 05, 2010 3:59 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.
> 
> 
> 
> ·         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.
> 
> ·         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.
> 
> ·         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
> 
> ·         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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