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Parylene Dielectric Properties: Designing for High Voltages

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Mallory McGuinness | September 11, 2020

For decades, product designers have used polymer coatings, such as Parylene, to protect PCBAs from contaminants, moisture, and other common threats. Coatings used in electronic circuits fulfill critical functions, including electrical insulation, reducing PCB conductor spacing. Understanding Parylene dielectric properties is an important requisite for protecting a product’s long term function.

What Is Dielectric Strength?

Dielectric strength is defined as the maximum voltage at or below which no breakdown occurs. This property quantifies how strong a conformal coating’s insulation is, with a higher number signifying the insulating material’s high resistance to dielectric breakdown. In other words, the measurement calculates the maximum voltage the insulating material can withstand before it goes into a breakdown and loses its insulative properties.

Maintaining dielectric resistance is critical for impedance and signal integrity concerns, as the insulating material must keep the circuit working correctly. 

Why Increasing Dielectric Strength Is Important

Increasing dielectric strength offers several benefits. Enhancing dielectric strength protects the circuit board’s long-term function. The safety and effectiveness of a device with a circuit board rely on the device having an entirely closed system, so insulation with high dielectric resistance is critical.

Another consideration is that PCB designs can be more compact when they feature a coating with increased dielectric strength. Integrating more capability into smaller form factors in the demanding electronics industry is crucial to staying ahead of the curve.

Finally, coatings should be able to withstand an applied voltage without breakdown. At the breakdown voltage, the coating fails to provide the intended benefit. The insulative properties left (if any) are negligible at this point. Therefore, an essential electrical property is the 

At both high and low voltages, dielectric considerations are particularly important for the reliability of electronic circuits.

Dielectric Constant and Dissipation Factor

Ideal electrical insulating coatings have low dielectric constants and low dissipation factors and the ability to retain these low values over a wide temperature and humidity range.

Parylene for Dielectric Strength

Parylene’s electrical properties make it the best conformal coating to protect against dielectric Strength. The figure below illustrates the breakdown voltage as a function of film thickness:

Chart of Parylene Dielectric Properties
Chart of Parylene C and N Dielectric Properties

Coating Materials for Electronic Applications, James Licari

Dielectric considerations are particularly important for the reliability of electronic circuits.

 

As you can see, each Parylene type has different dielectric properties, so there is a suitable Parylene for virtually any application. Additionally, the insulating properties of the Parylene coating increase with thickness, creating the possibility to fine-tune electricity-blocking properties.

Better Dielectrics Come from Better Processes

As a general rule, a polymer’s dielectric strength decreases as impurities or imperfections in the coating increase. Clean, dry coatings may exhibit high insulation resistances but have inadequate dielectric breakdown voltages because of pinholes or voids.

For this reason, Parylene’s chemical vapor deposition (CVD) process contributes to the coating’s excellent dielectric properties. With the CVD process, the dimer is heated into a vapor that deposits deep into the crevices of printed circuit board assemblies, providing consistent, even 3D coverage free of pinholes and imperfections.

Since every surface on a product is coated with uniform thickness, Parylene is an excellent choice to supplement other forms of insulation.

HZO Coatings Improve Dielectric Strength

We commonly use Parylene to protect a circuit board’s complex internal components. Parylene deposits onto the application surface molecule by molecule, creating a comprehensive protective coating for your PCBs. We apply Parylene with a uniform coating thickness so that you can use it as a supplement to other forms of insulation.

Learn More About our Parylene Coatings

Contact us today to learn more or talk to one of our experts about how to design a better product. Making a small investment of your time now could yield decades of reliability.

Learn More About How to Choose a Parylene Coating Company

To learn more or talk to one of our experts about how to design a better product, contact us today. Making a small investment of your time now could yield decades of reliability.

There is a suitable Parylene for virtually any application.

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.

Ryan 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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