Why Uneven Conformal Coating?

Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting. Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes

Phil Zarrow With over 50 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes. Jim Hall A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

Transcript

Phil
And welcome to Board Talk with Jim Hall and Phil Zarrow, the Assembly Brothers, who by day go as ITM Consulting. We are here at Board Talk to help you solve your various process problems and dilemmas concerning components, materials, equipment, procedures, and all sorts of things.

Jim, today's question is with regard to conformal coating. R.H. writes, we are experiencing an issue with our conformal coating process. We chemically wash prior to coating and spray the material in two coats.

On matte finish boards the conformal coating is vibrating away from some others and building up in others. We are getting coverage, but this causing our boards to look like a topographical map with hills and valleys.

We don't have an issue with adhesion just uneven finish. Any help on this would be greatly appreciated.

Jim
Well, fortunately my brother is a world-known expert in conformal coating. What do you think Phil?

Phil
No, I'm not.

I think there are a lot of unknowns in this particular case with regard to materials. It could be a number of things. It could be the way your equipment is set-up, the way you are spraying it.

I think most likely it is the material itself, the way you are prepping the material. If it has been mixed properly, if it is stored properly, if it is within expiration date. What kind of humidity has it been exposed to? If it has been titrated properly.

So there is a lot of gray area.

Jim
Phil, they say we chemically wash prior to coating. Could there be some residues from the washing process?

Phil
Yeah, depending what kind of chemicals you are using, there could be residues that way. I am assuming the boards are dry.

Really the best place to defer this question is to the supplier of your material. It is their materials that is acting kind of funny.

I would advise you to contact your conformal coating manufacturer and your applications people and explain what is going on. Perhaps they can give you some insight.

Jim
Better than us?

Phil
Yeah, so called expert.

We hope that helps R.H., sends you in the right direction. Definitely talk to the manufacturer of the conformal coating. Who knows, maybe you have a bad batch.

You didn't say where you are doing this operation, and I am not just talking facility wise with humidity. That is obviously going to affect it.

This sounds obtuse, but we have seen it happen, make sure you have the real material. There are certain countries abroad where we have seen cases of counterfeit materials. They were packaged under the names of well-known, recognized, validated conformal coating manufacturers.

Sometimes when they mix them up, with the open air, things can get contaminated, overexposed to humidity and things like that. Make sure you have good, pure material. Counterfeiting does extend to materials, as well as components. Been there, done that, and own the stained t-shirt.

I hope that sets R.H. in the right direction.

Remember, whether your board is going to be conformally coated or not when you go to solder, please don't solder like my brother.

Jim
And don't solder like my brother.

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