In conformal coating there are many common failure mechanisms in conformal coating including capillary flow (scavenging), delamination (loss of adhesion), cracking, de-wetting, orange peel, pin holes, bubbles and foam. This article briefly looks at reasons each of the defects occur in processing with potential solutions to avoid them in the future.
“It can be as basic as the coating just will not stick to the PCB or it runs away from areas on the PCB. At other times, it’s interpreting just how well the coating is stuck and determining if it’s good enough for the customer? Normally, this cannot be answered instantly and leads to some serious thinking!”
The biggest single cause of de-wetting (a lack of adhesion) of conformal coating on a printed circuit board is silicone contamination accidently introduced in the production line. The silicones can come from many areas including RTVs on the bench and lubricants for machines.