Why Parylene is the Preferred Coating Over Acrylic

Posted by Jake Hinojoza on Oct 10, 2017 9:00:00 AM
Jake Hinojoza

Parylene and acrylic coatings are two widely used substances for coating products like circuit boards, medical devices, and many other devices. While acrylic is a bit more expensive, and a very popular option, it hasn't quite stood up to the quality and range of uses Parylene offers. So what are some of the major differences between these two coatings?

Acrylic Coating

Acrylic coating has earned some popularity through the years. AR, or acrylic resin can be applied in the following three ways:

  • brushing the resin onto a given object
  • spraying the resin
  • (or, in the case of larger jobs) an object can be dipped into the resin

While acrylic coating does its job when it comes to moisture resistance and good protection against electrical interference, the most popular forms only withstand 125 degrees Celsius. The unfortunate characteristics of an acrylic coating are that it is removed easily by solvents. This may sound like a plus, being that you could easily remove and reapply, but when something as common as rubbing alcohol could completely remove a coating, it stops being beneficial.

Parylene Coating

With excellent moisture resistance, chemical resistance, and a great dielectric, parylene boasts some impressive characteristics. The unfortunate truth is, parylene can't be applied quite as easily, making it more expensive.

How exactly is parylene applied? The object being coated is first deposited in a vapor chamber, and the parylene is heated and vaporized. Anywhere air can touch, the parylene is thinly and uniformly deposited onto the object.

A characteristic shared by both acrylic and parylene coatings is their tolerance for heat. Parylene does well around 80 degrees Celsius; handily heat spikes up to 125. While parylene isn't too friendly with the sun, it can also withstand things like gamma rays and electron beams.

Parylene is hard to one-up when it comes to its chemical resistance. It withstands against all manner of corrosive solvents, acids, salts, etc. This is why it is often the first choice for coating implants. 

There are many fascinating aspects of parylene that can be studied to further appreciate the countless applications and numerous benefits of this unique coating, but one element that should never be overlooked is the deposition process. This process is crucial to the longevity and reliability of parylene, and, as you'll see, it is just as much an art as a science.

The Science

The artful part of the parylene deposition process must be built on a sturdy foundation of science. This unique process begins when specialized equipment is used to heat the raw material "dimer" to vaporization when it becomes a dimeric gas. This gas then undergoes more molecular-level processes; wherein it is reduced to a monomeric form that allows it to be placed with precision and confidence. At this point, both the monomer gas and the surface in need of coating are placed into a temperature-controlled chamber, and the gas is deposited in the malleable, pinhole-free polymer coating that is parylene's most recognizable identity. This process is crucial in giving parylene its reliability and longevity; because it is applied as a gas, parylene can coat even the most challenging corners and crevices with a wide variety of thicknesses.

The Art

Our parylene coating experts know that, while "the science side" of the deposition process is important, there is a necessary artistic touch that's just as crucial. Here's a quick look!

  • Substrates. Each unique substrate material to which parylene can be applied--including metal, plastic, paper, and more--has its own specific needs. Although parylene can cater to all of these needs, it often requires a bit of help in the form of A-174 silane applied before coating. Experts have perfected the art of deposition to the point where any substrate material can be coated with all the reliability and precision expected of parylene coatings.
  • Cleanliness. The artistic side of parylene's deposition process demands a high level of cleanliness. Anything that is not part of the substrate--from human oils to dust particles--can interrupt the deposition and impact the performance and safety of the parylene. As a result, there are countless standards in place to ensure purity.
  • Preparation. Parylene is a strong and reliable coating, but it can be a bit too strong when it's applied to anything but the substrate material--which is why experts know that the art of preparation is crucial. The inside of the temperature-controlled chamber must be carefully prepared before deposition to protect from an accidental application.

Interested in more info on the deposition process? Looking for experts in parylene coatings? Contact us today!

Topics: Parylene Conformal Coating