Adhesion Problems with Conformal Coating

We have a large RF back plane that is gold plated on the operational side. We are having intermittent adhesion issues with the conformal coating. Our vendor wants us to change to a new coating.

We are being told that in general conformal coating has a very difficult time adhering to gold surfaces. And the cracks or lifting in the coating is caused by stress in the back plane where it is fastened to the card guides.

What can we do to eliminate the adhesion problem?

T.A.

Expert Panel Responses

Goingto a Silicone based conformal coating could help with the cracking. As far as adhesion goes, making sure the surface is very, very clean is critical, as well as making sure the material you are using isn't expired, or mixed incorrectly.Is it possible to conformal coat it after the card guides are on? That may help as well.

T.J. Hughes
Manufacturing Engineer
Esterline Interface Technologies

Mr. Hughes has been in the electronics manufacturing field for 20 years. Operating the processes and as a manufacturing engineer for the last 14 years. He is also a CIT as well as an SMTA Certified Process Engineer.

To address the issue with the conformal coating adhering to large gold surfaces we would suggest using a plasma surface treatment to roughen up the surface to improve the bonding energy.

Terry Munson
President/Senior Technical Consultant
Foresite

Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.

For your review and consideration:
Plasma Treatment Improves Conformal Coating Adhesion from Nordson March

Robert "Bob" Lazzara
President
Circuit Connect, Inc.

Bob has been in PCB design and fabrication since 1976. He has held elected positions with the SMTA, is a member of the MSD Council, has served as a committee member for various IPC standards and is a Certified IPC Trainer.

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