The Truth About Conformal Coating

It’s not as full-proof as you think.

Misconceptions often arise around electronic reliability—a prevalent one revolves around conformal coating and the level of protection it provides.

In case you aren’t familiar with this method, conformal coating uses a thin polymeric film that is applied to a printed circuit board assembly (PCBA). This typically works to protect the board and its components from environmental contaminants and moisture. The film (ideally) conforms and adheres to the myriad architectures and materials of the assembly, covering and protecting solder joints, the leads of electronic components, exposed traces, and other metallised areas from moisture and chemical attack.

In the end, you can find the life of the PCBA extended. But that isn’t always the case.

The phrase we often hear from those experiencing reliability issues is: “We have conformal coating—shouldn’t we be fully protected?”

Multiple factors affect the ultimate success of conformal coating and its long-term ability to effectively protect electronics.

Some issues that may impact reliability down the road:

1. The first is acknowledging that moisture intrusion is still a concern with most conformal coating types. Constant moisture/high humidity exposure will eventually permeate most coating materials.

2. The truth is, moisture typically doesn’t have to permeate the coating to cause damage, because conformal coating isn’t always uniform–unless vapor deposition is used, many irregular components (e.g., wire wound transformers) are extremely challenging to coat with a consistent thickness. Step coverage is also an area we often see lead to problems–material thin enough to coat all architectures, while thick enough to maintain good step coverage, are competing concerns.

3. Other considerations when using conformal coating:

   1. Is there adequate surface energy in your solder mask/components for good adhesion (i.e., is plasma cleaning necessary)?

   2. Are all of the other materials used in my assembly fully cured prior to coating (e.g., staking compound, underfill, silicones)?

   3. Do any of the other materials used in my assembly contain ingredients that would inhibit cure/adhesion of my chosen conformal coating?

   Ensuring electronic reliability always requires keen observation, but often it can be even more beneficial  to be aware of the pitfalls of our assumptions. Challenging these assumptions and facing our misconceptions has the potential to keep our failures to a minimum and maintain electronic reliability at its fullest potential. We’ve seen all of the other issues listed above and more–if you are experiencing conformal coating challenges, we can help.