Hi,

I am sure its some sticky residues which has not been removed by ur cleaner.
We had the same issue and when looked thru magnification and in a particular
angle we observed sticky spots. We then had to clean them with IPA. The root
cause was due to the time delay in processing between wave soldering and
cleaning process.

Thanx
Badri

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bloomquist, Ken
Sent: Friday, April 06, 2007 7:59 PM
To: [log in to unmask]
Subject: [TN] Conformal Coat Dewetting

Good afternoon all,

I've go some assemblies that are not taking conformal coating in some
areas. The boards are reflowed and then selective wave soldered with a
pallet. They us a water sol flux and run it through an inline wash using
DI. We wash them in a batch washer using a mild saponifier prior to
coating. The boards are cleanliness tested in a ROSE tester and then
coated with polyurethane.

It is only on a few boards and it appears to almost be coming from the
via's. If we try to brush coat over it it still won't coat. If we clean
it with IPA then it coats just fine.

We've ruled out silicone and finger grease.

I have a couple of photos so you can see what it looks like. One is
black light showing the void areas. The other one is where we tried to
touch up the coating around a via and you can see how it pulled back.

http://www.ema-wa.com/DSCF0845ViaContamAreas.jpg 

http://www.ema-wa.com/DSCF0840_Via_Close-up_Y1_WL.JPG 

Thanks,

KennyB

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