PCB overmolding

[Sukhram]

PCB Overmolding is required. In Past, we had used PA678 material with low pressure molding provision. But it attracts moisture through cables inside PCB. What should be the best alternative to avoid moistures. Now we are looking similar low pressure molding but need to avoid moisture inside. Please advise!

 

[Sukhram]

Can parylene coating be done before overmolding? will it work?

 

[btrueblood]

Yes. We had similar problems with moisture intrusion along hardware seams and wire strands. Parylene coating over the fully assembled and soldered boards, prior to overmolding, got us around it. We tested by immersing the overmolded boards in water; previously overmolded boards failed due to water intrusion in about 24-48 hours. I think the latest coated boards went well past 2 months. Talk to a parylene coater about which of the varieties of parylene you want, some are more water resistant than others.