You may not have an incompatibility issue between the conformal coating and the flux residue. What you may have could be outgassing of moisture from inside the pwb around the vias and pads that is causing the conformal coating to delaminate, or to not adhere properly in the first place.  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Juan T. Marugán
Sent: Tuesday, September 30, 2008 11:20 AM
To: [log in to unmask]
Subject: Re: [TN] Big problem when coating with Parylene C.

Well, we have now two problems, but I don't want to open a forum about the expiration date for the use of 141-b.

Let me re-center the problem. Brian, I agree with you. We should be using 141-b MGX, but why we have obtained good results in other boards (diferent P/N and different manufacturer, but polyimide boards also) conformal coated at the same time that the other one? If we used the same solder paste, the same cleaning solvent, the same outgassing, the same thermal cycling after coating... the results should be the same.

One of the trials we did was cleaning a couple of boards with plasma. The results were also bad.

For that reson we are looking for some incompatibility between Parylene C and our polyimide laminate.

Is there anybody out there that experienced a problem of non-compatibility of materials when coated a board with Parylene C?

Anyway, thank you Brian for your help.

Juan

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