What is Parylene technology?

November 23, 2020

Enhancing reliability of e-mobility through Parylene Technology.

Rakesh Kumar Ph.D. at SCS Coatings explains.

As we move towards e-mobility due to environmental friendliness, economic considerations and social forces, scientific and engineering communities have focused their efforts on creating motors/engines that receive their energy from the power grid or energy storage sources. These motors and engines support many types of vehicles, including ships, hover boats, planes, helicopters, drones, unmanned aerial vehicles, etc., and their long-term success heavily relies on the development of reliable electronic systems and energy storage systems (electric, hybrid and fuel cell technologies).

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public transport, modern city tram, approaching the bus stop Moscow, Russia.

Today, electronic systems no longer work as independent components, but as fully integrated systems that use sensors, MEMS and radar to control various autonomous functions. The reliability of electronic components and systems can be compromised, at best, or fail completely, worst case, due to their exposure to harsh environments, which causes the corrosion of components due to water, salt and other stress factors.

Parylene technologies enhance the reliability of electronic systems and components by not only offering solutions to eliminate such catastrophic reliability failures, but they also enable the development of innovative electronic systems and components for e-mobility. Electronic systems and components can either be coated with Parylene for their protection from environmental degradation, and/or Parylene can be used as a structural material to make such components and systems.

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What are Parylene technologies?

Parylene is the name for a unique series of polymeric organic coating materials that are polycrystalline and linear in nature, possess excellent dielectric and barrier properties per unit thickness, and are chemically inert. Of the commercially available Parylene variants, Parylene C, Parylene HT® and ParyFree® are the most suitable for e-mobility applications. In addition to electrical insulation at ultra-thin levels, Parylenes provide outstanding moisture, chemical and dielectric barrier capabilities. Parylene HT also offers increased thermal and UV stability. Parylenes are RoHS and REACH compliant and have been proven to provide metallic whisker mitigation in lead-free solder applications. Parylenes are ideal for protecting electrical components, wires, PCBs and sensors – any component that require reliable, long-life performance in harsh environments, including those in electric power drivetrains.

What differentiates Parylenes from other conformal coatings

Rather than dispensing, spraying, brushing or dipping, Parylene coatings are applied using a vapor deposition process. The Parylene process is carried out in a closed system under a controlled vacuum, with the deposition chamber remaining at room temperature throughout the process. No solvents, catalysts or plasticizers are used in the coating process. The molecular “growth” of Parylene coatings ensures not only an even, conformal coating at specified thicknesses, but because Parylenes are formed from a gas, they conforms to all surfaces, edges and crevices of a substrate, including the interiors of multi-layer electronic packages. Parylenes provide a superior pinhole-free shield to protect against corrosive liquids, fluids, gasses and chemicals, even at elevated temperatures (up to 350°C long-term). Parylenes are typically applied in thicknesses ranging from 500 angstroms to 75 microns. A 25 micron coating of ParyFree, for example, will have a dielectric capability in excess of 6,900 volts. No other coating material can be applied as thin as Parylene coatings and still provide the same level of protection, which is why manufacturers have used Parylenes in the automotive and transportation industries for over 4 decades.

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In markets such as e-mobility, where many electronic systems, RF devices and sensors are used, it is critical that such devices and systems are well protected for long-term reliability, without the loss of any signal or communication. To avoid signal degradation of high frequency devices when they are protected with a conformal coating, it is important that loss tangent of the conformal coating does not adversely change over the operating frequencies. The loss tangent and low dielectric constant of Parylenes are very stable up to 70 GHz, as tested, but expected to be stable up to 100 GHz as well, which help advance next generation high frequency devices.

Harsh Environments

Parylenes have also been used to provide moisture and chemical barrier properties to a wide array of components, including sensors and circuit boards, providing protection from the most corrosive chemicals such as nitric and sulfuric acids and common automotive fluids like brake fluid, power steering fluid, and windshield washer fluid. For example, fuel cells operate in the midst of corrosive chemicals at elevated temperatures, a very harsh environment for electronics. Parylene HT provides superior protection for these fuel cell components due to its moisture and chemical barrier properties and high temperature stability.

The operating system environment of vehicles can range from -40°C to more than 300°C, making coating stability imperative to the trouble-free life of vehicle electronics. As stated, Parylene HT provides long-term thermal stability up to 350°C, with intermittent exposures up to 450°C. The coating also offers UV stability (more than 2,000 hours of highly accelerated UV exposure, per ASTM G154), providing protection from degradation and discoloration.

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Electronics Parylene Chart

With electronic systems increasingly replacing mechanical control systems, tight package protection is needed to keep moisture and chemicals from causing shorts. At the same time, this protection must not add dimension to the control electronics, and the coating must be dielectrically compatible to ensure that signals are not blocked. Parylene coatings are lightweight, do not add significant mass or dimension and do not block communication signals.

Even as vehicle monitoring and conditioning has moved to electronic systems, traditional printed circuit boards and sensors are also being replaced with MEMS technologies in this next generation of vehicle design. The use of MEMS reduces overall package size while putting more capabilities into one tiny microelectronic package. Due to their properties and gas-phase deposition process, which results in ultra-thin, conformal coatings, Parylenes are able to effectively protect MEMS packages against wear, moisture and corrosive fluids.

The prevalence of complex and integrated electrical systems shows no signs of slowing down. Pressures to lower costs, migrate offshore production and consolidate abound in the electric vehicle industry. At the same time, OEMs feel pressures to bring better, faster and cheaper components and systems to the market. Adding Parylene technologies to the component manufacturing process enhances the reliability of electric driven vehicles’ electronics and components, regardless of the type of vehicle or operating system. The level of protection Parylenes afford manufacturers is one that reduces costly maintenance and warranty issues for the life of the vehicle. The good news is that as components become more complex and are exposed to new and increasingly extreme environments, new Parylene technologies and services are being developed and deployed to parallel this growth.

Headquartered in Indianapolis, IN, SCS is the worldwide leader in Parylene conformal coating services, systems, and materials. SCS has over 35 years of application experience and expertise in the medical device, electronics, automotive, and military industries. With nine coating facilities throughout the Americas, Europe, and Asia, SCS leverages its worldwide Parylene coating resources in order to meet its customers’ needs on a global basis. The Company also offers industry-leading liquid coating systems including spray, spin and dip coating systems and ionic contamination test systems. To find out more about SCS and its industry-leading product lines, visit the company’s website at www.scscoatings.com.

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