I was recently at a customers facility examining their production process.They had issues with conformal coating de-wetting on their board.
The defect was occurring just after the spray application of the coating. The system being used was a selective robot applying an acrylic solvent based conformal coating.
So far so good. Nothing complex in the process. But, the de-wetting was occurring all over the circuit.
I asked if the problem had always been there?
The answer was no, it had just started to occur in the last 2-3 weeks. Hence, my being there.
So, we dug a little deeper into the process. Without going into all the details it turns out that they had changed the solder resist and this was the root cause of the problem.
The original solder resist was fine. The conformal coating wet the surface perfectly.
However, the new solder resist had a lower surface energy and now the conformal coating was de-wetting all over the surface.
Well, the company had originally matched the material and process to the circuit board. They were compatible. They had applied a holistic approach to the process.
But, someone decided to change a material part of the circuit board. The failure came in not applying the holistic approach to check for compatibility of the three parts, the material, process and board.
This resulted in lots of scrap circuits, a defective conformal coating process and a company discussing whether to scrap a lot of bare laminates or whether they could salvage them.
How to avoid conformal coating problems?
If you are going to use a conformal coating check that all the parts are compatible. That is the material, process and board.
If you are going to change a part of the process, repeat the tests. Don’t assume the process is instantly drop in regardless of what you are told.
Need further help?
If further information on these topics and the key question you can go to our free eBook by clicking the conformal coating holistic approach now.
If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page.
Dr Lee Hitchens is the author of the Nexus conformal coating website and eBook.
Send me an email at firstname.lastname@example.org and let me know what you think?