The use of conformal coatings began in the 1960s, as manufacturers sought to protect printed circuit boards from extreme environments.
Coatings like acrylic, urethane, epoxy, and silicone added valuable characteristics to electronics components, including chemical resistance, adhesion, and shielding from stress.
One polymer invented in the 1940s, Parylene, has been used increasingly in the electronics, medical, and aerospace industry. The thin film, for example, has provided moisture and dielectric-barrier protection on technologies ranging from surgical tools to NASA's JunoCam.
The thin, optically clear "poly(p-xylylene)" is a non-line-of-sight coating, meaning that the polymer goes everywhere on a part.
But once it's on there, then what? Can Parylene be removed? How do you know if Parylene is properly sterilized for medical use?
In a recent Tech Briefs webinar titled Enhance Product Design and Dependability with Advanced Coating Technologies, readers had plenty of questions about the material. Here are two from the conclusion of the presentation, posed to Lamar Young, Technical Manager at the Indianapolis, IN-based Specialty Coating Systems.
Read Young's edited responses below.
Can Parylene be removed for component rework?
Lamar Young: Yes. If you’re looking at just removing Parylene over a specific component, there are different ways to accomplish that. It really depends on the component.
Probably one of the harder examples is a ball grid array, because the coating gets underneath and coats all the balls. But you can use heat to soften the Parylene, and to pull it off, and then there’s going to be some clean-up in that area; then, you can go back and recoat it.
Parylene is not going to be like an acrylic, where you can just dunk the whole thing in xylene, strip it off, replace it, and then run it through the process again. It’s going to be a little bit different, but Parylene has been repaired and recoated; that’s nothing new. It really depends on the component, and that kind of pushes you in one direction or another as far as how you rework it.
Can Parylene coated components be sterilized?
There are a whole host of sterilization methods because Parylene is used in the medical industry.
The steam autoclave is a common process. The autoclave itself does not hurt or damage or change the Parylene coating, but it does stress the adhesion interface between the Parylene and the substrate. Obviously, if your part is going to have to be autoclaved, you want to evaluate that you have good adhesion, and that there’s no residue or contamination present that would impact that interface bond.
There are other methods that people use, like gamma radiation and ethylene oxide. Of course, like with radiation, there is a cumulative effect, depending on the dose rate and the number of sterilization cycles that the part has to go through.
What are your Parylene questions? Submit them in the comments section below.