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Three Proven Facts You Should Know About Corrosion-Resistant Coatings

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February 4, 2021

According to NACE, corrosion is directly responsible for $2.5 trillion in costs every year, excluding damage incurred in the electronics and telecommunications industries. Corrosion is a devastating phenomenon that can be prevented, and it pays to do so. Corrosion prevention best practices could save $375 – $875 billion in costs worldwide. Among these best practices is the utilization of anti-corrosion coatings to protect electronics from unexpected failure.

View a webinar about proven corrosion resistant methods delivered by Dr. Sean Clancy, Director of Coating Technology at HZO & Anti-Corrosion Expert

What is Anti-Corrosion Coating?

Corrosion-resistant coatings, including conformal coatings, are applied to electronics to protect the printed circuit board, component, or device from degradation due to oxidation, moisture, chemicals, or exposure to harmful elements found throughout operating environments in a range of industries. These coatings act as a barrier to inhibit contact between susceptible surfaces and corrosive materials. Specific coatings provide added protection, including electrical properties such as high dielectric strength and low dielectric constant.

This post will discuss three facts you should know about corrosion-resistant conformal coatings, specifically noting Parylene’s properties as an example. Parylene coatings are polymeric films with physical properties that hinder the effects of corrosion, including water vapor transmission rate (WVTR), water absorption rate, and resistance to harmful gases. Parylene exhibits superior performance when it comes to these properties. Combined with a repeatable, reliable application method, Parylene is the gold standard for corrosion resistance.

1. Water Vapor Transmission Rate is a Key Coating Property to Bear in Mind

Crucially, conformal coatings protect electronics from moisture and humidity damage that leads to corrosion, and the water vapor transmission rate (WVTR) of the coating is an indicator of this ability. This rate can be defined as the mass of water vapor that passes through an area of material, tested at a specific humidity and temperature over a period. Lower values represent better protection from moisture vapor.

Property

Parylene C
Parylene F
Parylene N
Epoxy
Urethane

WVTR (g·mil)/(100in²·day)

0.21
0.32
1.5
6.6
20.2

Of all the conformal coatings, WVTR is the lowest.

2. The Lower the Water Absortption Rate, the Better

In addition to WVTR, the water absorption rate is a critical anti-corrosion property that should be evaluated when selecting a corrosion-resistant coating. In this test, the material is emerged in water at agreed-upon conditions, often 23°C for 24 hours or until equilibrium. The specimens are removed, patted dry with a lint-free cloth, and weighed to determine how much water has been absorbed. Once again, the lower the water absorption rate, the better likely a coating is to resist corrosion.

Material

FR-4
Polyester
Polyimide
Parylene C
Parylene F
Parylene N

Water Absorption

< 0.1% (0.125")
< 0.8%
0.8% to 2.9%
< 0.1%
< 0.1%
< 0.1%
Water absorption of materials after 24 hours.

Combined with a repeatable, reliable application method, Parylene is the gold standard for corrosion resistance.

3. Resistance to Harmful Gases is a Critical Consideration

Corrosive conditions often come from air pollution and can have a serious impact on vulnerable surfaces. The following are just some of the threats posed to PCBAs, components, or products themselves.

  • Hydrogen sulfide is released into the air from processing from forest products (such as pulp and paper processing), clay processing, rubber, wastewater, and oil and gas, as well as geothermal regions.
  • Ammonia is produced from agricultural regions, fertilizer manufacturing, food and beverage cleaning agents, and wastewater processing.

  • Sulfur dioxide is produced from the processing of cement, metals, oil, and gas, and power generation, and tire manufacturing.
  • Chlorine is produced from food and beverage cleaning agents, pulp and paper processing, and water processing.

Salt Fog, Flowers-of-Sulfur (FoS), and Mixed Flowing Gases (MFG) tests are performed to gauge a coating’s resiliency against these corrosive.

  • Salt Fog simulates a severe marine environment.
  • FoS simulates sulfurous atmospheres from air pollution.
  • MFG simulates and amplifies the types of gases that may be found in some industrial environments.

Picture Courtesy of CALCE, University of Maryland

Parylene exceeds these testing conditions. The image above shows examples of electronics before and after being exposed to MFG. The non-coated and acrylic-coated (AR1) samples show signs of corrosion, while the Parylene-coated sample doesn’t.

Corrosion Protection Coating Services at HZO

Corrosion protection is a critical requirement for many electronics projects, and HZO is a leading supplier for top-tier companies across industries. Our tech team and domain experts have spent countless hours perfecting the Parylene coating process (chemical vapor deposition, or CVD) and built our optimized coating chambers from the ground up to meet scalability and cost considerations. We are so confident in our technology that we guarantee results. Reach out to one of our SMEs today to find out more about our Parylene or corrosion-resistant nanocoatings.

Corrosive conditions often come from air pollution and can have a serious impact on vulnerable surfaces. lution.

Ryan MooreRyan Moore

Ryan is a 9-year veteran to the world of protecting electronics from harsh environments and a lover of all things technology.

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