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Best Conformal Coating for Humidity Protection

humidity written in a humid window

Mallory McGuinness | July 7, 2020

How to Protect Electronic Devices from Humidity

Conformal coatings protect electronic devices from a variety of environments, providing some level of moisture resistance. However, highly humid environments where moisture is ubiquitous can be more challenging when it comes to reliable performance. Every electronic application is different and serves different purposes; therefore, you should determine how to protect electronic devices from humidity on a case by case basis.

Conformal Coating Humidity Questions to Consider

The following questions can help determine the best way to offer conformal coating humidity protection:

What are the Attributes of the Board?

Some boards are highly sensitive to moisture than other boards that may require less humidity protection. What is the voltage? Are there several pins located closely? Take these variables into consideration when you are thinking about how to protect your product from humidity.

What is the Coating Application Process?

Defects such as de-wetting can leave parts of a substrate exposed, opening the possibility for failure, which is why you should select the most appropriate application process for your coating selection. Ensure the board has proper coverage in the areas that need protection.

What is the Curing Process?

Be sure to cure the coating using the coating manufacturers’ recommended schedule to ensure adequate protection.

Orientation of board

Consider board orientation. If the board is mounted horizontally, water may sit on the substrate for long stretches if condensation appears. This moisture could begin to penetrate through certain coatings, causing failure. If a board is in a vertical position, water can run off of the surface and may require less protection.

Best Conformal coating for Humidity Protection

In humid environments, moisture is pervasive, so the conformal coating you choose can’t merely protect against water ingress. The protection solution must completely seal the coated substrate. Because of this necessity, the best conformal coating for humidity protection will either be silicone or Parylene.

The material that comprises silicone coating is hydrophobic, making it an ideal candidate for humility protection. Because of this, silicone seals humid areas, including bathrooms and kitchens. Unfortunately, due to its softness, silicone can easily be scratched or rubbed away, rendering it unsuitable for protecting components subject to abrasion or other physical threats. Additionally, silicone needs to be applied with a thick coat to reduce the likelihood of gaps in the seal or pinholes, which may make it an unfeasible choice if your application involves smaller, complex components.

a protective circuit board getting wet from humid environments

Parylene Conformal Coating for Humidity Resistance

If you have decided that silicone is not a suitable protection method, Parylene is the best alternative method. Parylene can be applied with a coat as small as 1/100th the thickness of silicone, allowing you to provide your product with substantial humidity resistance without increasing weight or bulk. Parylene is also hard enough to weather scratches, abrasions, or knocks that would ordinarily break down silicone.

Unlike other conformal coatings that are dipped, brushed, or sprayed, Parylene deposits using a method called chemical vapor deposition (CVD). During this process, Parylene dimer is heated into a vapor, allowing it to penetrate every crevice of a substrate, creating a truly conformal coating.

At HZO, we have perfected the CVD process, constructing capital equipment from the ground up optimized to increase efficiency and throughput. If you are considering using Parylene conformal coating protection, Parylene engineers for a quote.

Mallory McGuinness

Mallory is an electronics protection evangelist who writes content for HZO. In her free time she is reading non-fiction, and hanging out with her beta fish, King Awesome.

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