Protecting Sensors and Systems in Electric Motors

18.5.2016

The use of electric motors in vehicles continues to grow in response to ongoing concerns surrounding fossil fuels and the environment. With this industry growth comes the development of powerful, intelligent electric motors and integral systems. Sensor technologies follow suit, becoming more sophisticated as they are relied upon to keep up with expanding needs.

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Left: Parylene coatings have protected automotive components for over 40 years. Right: The electric motor market is a fast-growing industry.

In sophisticated systems, the generation, distribution and control of electric energy needs to be constantly monitored and controlled within vehicles. To provide accurate system control, sensors and sensor systems must reliably receive and transmit information that keeps vehicle systems operational and safe.

To do this, they need to be highly accurate and have extremely fast response times in order to correct system issues. They must also have high noise immunity and be able to survive harsh environments. Sensors, in all their forms, keep electric engines in continual sync with the entire vehicle system.

In order to survive such conditions and operate reliably, many sensors require an added level of protection. Parylene conformal coatings ensure a long and reliable life, enabling sensors to accumulate and transmit data accurately for the life of the motor.

Making Sense of Sensor Protection

Sensors, and all other electronic components that are integral to electric motors and their associated systems, require specific protection that can withstand the hostile environments in which these units operate. Simultaneously, protection must not add significant weight or thickness to components and cannot interfere with signal transmissions.

Parylene conformal coatings provide a highly reliable solution for the protection of sensors and other electronics, those which are internal to engines and those externally that make up the electronic chain of signals.

Parylenes are a unique series of polymeric organic coating materials that are polycrystalline and linear in nature and possess useful dielectric and barrier properties per unit thickness. They are chemically inert, ultra-thin, pinhole free and truly conform to components due to their molecular-level polymerization – basically growing on the deposition surface one molecule at a time.

The coatings are applied using a vapour deposition process. The parts to be coated are placed in the deposition chamber and the powdered raw material, known as dimer, is placed in the vaporizer at the opposite end of the deposition system.

The dimer is heated, causing it to sublimate to a vapour, then heated again to break it into a monomeric vapour. This vapour is then transferred into the ambient temperature chamber where it spontaneously polymerizes onto the substrates to be coated, forming the thin Parylene film.

The 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.

Because there is no liquid phase in this deposition process, there are no subsequent meniscus, pooling or bridging effects as often seen in the application of liquid coatings, thus dielectric properties are never compromised.

The molecular growth of coatings also ensures not only an even, conformal coating at the thickness specified by the manufacturer, but because Parylene is formed from a gas, it also penetrates into every crevice, regardless of how seemingly inaccessible, and completely encapsulates substrates without blocking small openings.

The coatings are extremely lightweight, offering excellent pinhole-free barrier properties without adding dimension or significant mass to delicate components. Parylene is typically applied in thicknesses ranging from 500 angstroms to 75 microns.

A 25-micron coating, for example, will have a dielectric capability of 7,000 volts. Simply, no other coating material can be applied as thinly as this and still provide the same level of protection, making it an ideal option for components used in an extremely wide range of sensor system configurations.

Parylene variants

The family of conformal coatings (Parylenes N, C and D) has been trusted as a reliable protection solution for a wide range of applications for over 45 years. These coatings provide excellent barriers to moisture, chemicals and biological agents.

They are also RoHS compliant and have been proven effective to mitigate metallic whisker growth in lead-free solder applications. Parylene HT®, which more recently became commercially available, offers additional protective capabilities for end users. It was developed by replacing the alpha hydrogen atom of the Parylene N dimer with fluorine.

The resulting Parylene film possesses increased dielectric capabilities and superior thermal and UV stability, making it ideal for electronics that need reliable, long-life performance in harsh environments, including oil and gas drilling operations, surface mining, forest products and chemical plants.

- Parylene N is a primary dielectric, exhibiting a very low dissipation factor, high dielectric strength, and a low dielectric constant invariant with frequency.

- Parylene C has a useful combination of electrical and physical properties, plus a very low permeability to moisture and corrosive gases.

- Parylene D has properties similar to Parylene C with the added ability to withstand temperatures up to 100 °C short-term, 120 °C continuous.

- Parylene HT is useful in high temperature applications (short-term exposures up to 450 °C, continuous up to 350 °C) and those in which UV stability is required. It also has an extremely low dielectric constant and dissipation factor, enabling it to provide small, tight packages with dielectric insulation via a thin coating. Its extremely small molecular structure allows the coating to ingress deeper through open areas on the top or bottom of any package, regardless of the size or complexity of integrated devices.

Electric Motor System Examples

The electric motor market is a fast-growing industry. High-quality sensor systems are introduced with every new motor design.

Sensors provide electric motors with a method to measure currents and voltages, from ignition to the battery system, drive train and everything connected to vehicle operation and safety. Control system sensors receive the measured signals and, subsequently, manage systems throughout the vehicle.

There are several types of electric and hybrid vehicles in the market today: Electric-only vehicles (EV) that run solely on electrical battery power; Extended range electric vehicles (ER-EV) are a cross between a plug-in hybrid and a battery vehicle; and Hybrid Electric vehicles (HEV) have both a gasoline and electrical/battery motor for improved fuel economy.

Following suit with the automotive industry, larger Class 8 trucks are also beginning to incorporate hybrid and electric vehicle technologies, utilizing both diesel and electric/battery motors for improved fuel economy. More recently, the industry has introduced hybrid electric drive systems for in-city delivery trucks. These systems have motors at each wheel for propulsion, and since they are used in a city environment, recharging is relatively convenient. Parylene conformal coatings provide motors and other electronic components within these systems protection to ensure reliable operation and long life.

Parylene protection has been proven over decades of use in all types of sensor devices and applications. As electric motors become power generators for all types of systems, what has been learned in decades of use to protect electronic systems and components is now moving into leading-edge electric motor designs. Parylene’s moisture, chemical and dielectric barrier properties, combined with its innate thermal and UV stability, protect motors and associated sensors, ensuring long life, greatly reducing failures and the occurrences of costly maintenance.

Hardy_Alan_SCS

Alan Hardy

Electronics Market Manager, Specialty Coating Systems,

ahardy(at)scscoatings.com

www.scscoatings.com

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