Thermo-magnetic properties of dual functional sheet made of core shell type composite powder

Thermo-magnetic properties of dual functional sheet made of core shell type composite powder
composite powder; core-shell powder; heat conduction; heat dissipation; Thermo-magnetic properties; dual functional sheet
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In this study, thermo-magnetic properties of dual functional sheet made of core shell structured filler and liquid silicone rubber were investigated. Recently, as the mobile digital devices become thinner and multi-functional, heat dissipation and EMI (Electro-Magnetic Interference) problems became more serious for circuit designers. So requests for higher performance materials to solve the thermal and EMI problems simultaneously are increasing so much [1-3]. However, general commercialized thermo-magnetic hybrid sheets have weak point for breakdown voltage because it contains ferrous alloy metal powder. So we suggested a solution to improve breakdown voltage of dual functional sheet by using ceramic coated metal powder. Core materials can be soft magnetic ferrous alloy powders such as Fe-Cr, Fe-Si, Fe- Si-Cr, etc. And shell materials can be high thermally conductive ceramic powders such as Al2O3, BN, etc. In this study, we tested Fe-Cr powder and Al2O3 powder which have big size difference. The average particle size(D50) of Fe-Cr powder is 50 μm and Al2O3 powder is 0.2 μm. High speed super mixer was used to form homogeneous shell layer on the surface of core particles. The coating thickness and continuity were investigated by EDS mapping method and confirmed that coating thickness was about 3 μm and microstructure of coating layer was homogeneous. And finally we checked the thermal conductivity, power loss [4] and electrical property after making the dual functional sheet. The maximum value of thermal conductivity was 3.1 W/mK, power loss at 1 GHz was 34% and breakdown voltage was 2.4 kV. Specially, the breakdown voltage increased ten-times higher than that of the commercialized products and this result can be very useful for many future applications of dual functional sheet.
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