A Union of Opposites: Heat-Conductive and Electrically Insulating

Predestined for complex applications

“TThis project was right up our alley, because our material is predestined for a wide range of complex electrical applications. With its numerous qualities, it provides the right answers,” says Armin Striefler, Product and Process Developer at Freudenberg Sealing Technologies. “An important advantage for efficient series processes: The elastomer material can be processed through injection molding. This also makes its use very flexible, since nearly all three-dimensional geometries are possible and, thanks to its the material properties, always adhere optimally to the substrate – whether plastic or metal. It can be sprayed on directly and doesn’t need primer."

Like all plastics, silicone is inherently thermally insulating. For the new material, it is mixed with inorganic fillers that make it thermally conductive. These fillers are special non-conductive metal compounds.

Top values for important key figures

A few key figures for the innovative thermal interface material: Thermal conductivity is 1.7 to two watts per meter-Kelvin. For comparison, the thermal conductivity of air is 0.026. The manufacturing process makes thin-walled components possible. According to the heat equation from Fourier equation, this is good for thermal conductivity. In the above-mentioned project, the elastomer below the temperature sensor has a thickness of only 0.8 millimeters. “We have had very good experiences with thicknesses between 0.8 and three millimeters,” reports Striefler. “For physical reasons, heat transfer decreases when the walls are thicker.” The material achieves a CTI value of 600, placing it in the best possible protection class for tracking resistance. The dielectric strength is more than 10 kilovolts per millimeter. This means that the common test voltages of 2.4 to 4 kilovolts won’t pose any particular challenges for the material. Its hardness is around 35 Shore A.

Being able to use an injection molding processes is a definite plus. The specific production process prevents trapped air both in the elastomer and on the contact surfaces with other materials. This might otherwise lead to electrical problems, such as voltage breakdowns – which are certainly not welcome, of course. The material is fire-resistant in accordance with UL94 with classification V0, which puts it at the highest possible safety level.