What type of primer process are you using? Silane bath, in-chamber vacuum, plasma? Most of the loss of adhesion appears around the solder joints in the pics you sent...
From http://www.devicelink.com/mpb/archive/96/03/004.html
"Clean metal surfaces are inorganic. Parylene monomers are organic, and do not bind readily to the electron-rich metallic surface. The organic silane has both inorganic and organic molecular surfaces. During the priming operation, the inorganic surface of the A-174 binds permanently to the inorganic metal, presenting an organic face to the incoming para-chloro-xylylene monomers."
Mike
-----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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