Green Light for Heat Transfer

Materials generally combine electrical and thermal conductivity or insulate against both electrical current and heat. Now the engineers at Freudenberg Sealing Technologies have developed an elastomer that merges relatively high heat capacity with electrically insulating properties by combining silicone rubber with special fillers. The innovative material will be used primarily in electric car components, since semiconductors and other current-carrying elements are never completely lossless. Any electrical energy that isn’t used for computing or switching becomes waste heat that must be dissipated into the ambient air or a cooling system. Electronic components may thus be mounted in thermally conductive aluminum housing, for example, which dissipates the heat either via cooling water or convection. The closer the circuit board is positioned to the heat sink, the more efficient is the heat transport. The heat conductivity can be reduced by roughness in material surfaces, even at levels that are invisible to the human eye.

Modified silicone

Senior Application Manager Armin Striefler explains why the experts at Freudenberg decided to use silicone – rarely used in car manufacturing – as the base material. “Our material retains its properties over a very high temperature range, from minus 50 to plus 250 degrees Centigrade, but it can be deformed with relatively low force.” When sprayed on a metal surface, it fills the tiny gaps caused by roughness, which not only improves the heat transfer but also enables adhesion without additional surface treatments. The material developed by Freudenberg has a high dielectric strength of at least 20 kilovolts per millimeter. Adding the fillers increases the heat conductivity from 0.2 to 1.6 to 2 watts per meter kelvin. As a comparison, air has a heat conductivity of 0.026 watts per meter kelvin under normal conditions. The fillers themselves are special metal compounds; knowing how to combine and process them is part of Freudenberg’s expertise.

Perspectives for electric cars

The first series application for this new material class could lie in the charging socket of electric vehicles. The new silicone-based material must be both thermally conductive and electrically insulated to ensure the safety and performance of the system. First prototypes for the charging socket with integrated sensors are already being tested by a car manufacturer.