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January 14, 2026 - Updated August 13, 2014 - Originally Posted 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.
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All of the experts have spoken well, but in addition to needing a very clean and somewhat etched surface, it also must be extremely DRY! Do not allow the cleaned assemblies any time to sit out and collect moisture from humidity in the air. Bake for a minimum of 4 hours at 105 deg. C, then coat immediately after baking or place them in a drybox at less than 10%RH until they can be coated. Tip: a slightly heated DR Storage drybox is best! They make excellent dryboxes. Richard D. Stadem Advanced Engineer/Scientist, General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.
Another point to consider (irrespective of the actual coating), is to ensure that the CTE of the coating is well matches to that of the PCB. That, in conjunction with a suitably cleaned and roughened surface as advised by other panel members, will give you the best outcome.
Technical Sales Manager, Fineline VAR Ltd
40 Years in PCBs. Large and small companies in the UK and the US. Experienced Process Engineer, DFM, Materials, Impedance Control, Surface Finishes, etc. Working with Fineline now across the portfolio of manufacturers covering rigid, flex, rigid flex, ATE, Load Boards, MSAP, and other existing and emerging technologies.
For your review and consideration:Plasma Treatment Improves Conformal Coating Adhesion from Nordson March
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.
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.
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.
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.
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.
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