Freudenberg Sealing's latest thermal insulating material ideal for EVs

WEINHEIM, Germany—Freudenberg Sealing Technologies has developed a "union of opposites" with its new thermal interface material for the electric vehicle industry.

The heat-conductive and electrically-insulating silicone material already has garnered interest from several OEMs for its wide-ranging applications.

"The new (thermal insulating material) ... combines seemingly incompatible properties by being both thermally conductive and electrically insulating at the same time," Freudenberg said in a June 27 release.

The TIM adheres to many of the substrates found in EVs, including plastics, aluminum and copper.

And the material can be applied to rough areas, filling in gaps and smoothing the surface of the substrate.

"This project was right up our alley, because our material is predestined for a wide range of complex electrical applications," said Armin Striefler, product and process developer at FST. "With its numerous qualities, it provides the right answers."

The new material was developed with versatility in mind, even for projects that feature great complexity.

"An important advantage for efficient series processes is that this elastomer material can be processed through injection molding," Striefler said. "This makes its use very flexible, since nearly all three-dimensional geometries are possible and, thanks to its material properties, it always adheres optimally to the substrate, whether plastic or metal."

The material can be sprayed on, Streifler said, and it does not require a primer.

The charging port of an EV has many complex considerations in a very small space.

Behind the charging port cover on the body of the vehicle, there is a multi-pin connector for the charging cable, embedded in a plain plastic front. Behind this frontage is equipment whose interaction is essential for thermal management and the charging process.

There is a circuit board with temperature sensors and measurement, and control electronics for charging management. All of it is secured in a three-dimensional housing about the size of a fist.

With Freudenberg's new silicone material, thermal conductivity and electrical insulation is ensured for the area between the housing and sensors.

"The material picks up the heat flow through the copper wires connected to the battery and passes it on to the temperature sensors, promoting the rapid build-up of charging control, including the continuous thermal management of the vehicle battery," Freudenberg said.

The electronics portion is essentially clipped into the housing with snap connections, and the new TIM keeps the board (essentially a firewall), which can easily be bent, in place.

With a charging force of up to 800 volts, Freudenberg has designed a material that shields the sensitive electronics to electrical pressure.

FST manufactures the housing with the injected elastomer, and provides this as a package to automotive supplier customers.

The customers, in turn, produce the full module for the OEM.

The material supports precise contact, but its contradictory nature of being thermally conductive and electrically insulative comes from inorganic, non-conductive metal compounds—since silicone is inherently thermally insulating.

"We have had very good experiences with thicknesses between .8 and 3 millimeters," said Striefler. "For physical reasons, heat transfer decreases when the walls are thicker."

The dielectric strength of the new material is more than 10 kilovolts per millimeter.

"This means that the common test voltages of 2.4 to 4 kilovolts won't pose any challenges for the material," Striefler said.

The material's durometer is around 35 Shore A.

Typically, the material is used in conjunction with injection molding, as this process prevents trapped air in the elastomer itself as well as on the contact surface with other materials, Freudenberg said.

The material also is fire-resistant in accordance with UL94 with classification V0, which puts it "at the highest possible safety level," according to Freudenberg.

Outside of the charging port, effective heat dissipation is needed in other electrical applications, especially where "considerable computing power is required," Freudenberg said.

Examples include cooled busbars in traction batteries, which can heat up "with intensity," Freudenberg said.

"The range of applications is vast. But we welcome tricky challenges," Striefler said. "Because that's exactly where this material is in its element."

Not yet released, Freudenberg Sealing also is developing an oil-resistant TIM—a material that has the potential to go even further in similar applications.