Silicone Modified Epoxy Thermally Conductive Adhesive

Current trends in encapsulating heating dissipating electronic components with epoxy resins have stimulated interest in the thermal conductivity of particulate-filled epoxy resins. By the careful selection of filler, the thermal properties of the epoxy system can be influenced. It is important also in many of these applications that the fillers chosen exhibit a high electrical resistance in order to maintain low leakage currents and high dielectric strength. When developing such epoxy system ,it is equally important that the processing ability and mechanical end properties be given high consideration.A copolymer was synthesized through the copolycondensation of a hydroxyl terminated polydimethylsiloxane(PDMS), bisphenol A epoxy resin(EP). The copolymerization of polysiloxane and EP was confirmed by the decrease of the hydroxyl group absorption at 3500 cm-1 and the appearance of the absorption of Si-O-C and Si-O-Si at 806 cm-1, 1090-1020 cm-1. The effect of reaction conditions and the quantity of catalyst and organosilicon has been explored. As a result, the best conditions for copolymerization of organosilicon and EP are 120℃ -150℃/4-6h, with W-3 as catalyst. A stable dispersion of polysiloxane particles in an epoxy resin matrix was achieved. The copolymer was characterized by IR, DSC, TEM. Upon cure the glass transition temperature is 119℃. A "sea-island" structure ("island" of silicon rubber dispersed in the "sea" of an epoxy resin) was observed in cured rubber-modified epoxy networks via SEM.With the modified epoxy resin as the matrix, different fillers (Al powder AIN A1203 BeO SiC) are presented. The results showed that adhesive filled with Al powder shows very low electrical resistance. The effects of particle size and distribution, temperature on thermal conductivity were studied. The thermal conductivities increased from 223K to 373K. A thermal conductivity of 0.80 W/m.K is achieved for SiC at its loading of 75% by weight with an average size of ca.lum, 1.0 W/m-K with an average size of ca.10um and 1.2 W/m-K with an average size ofca. 76um.The adhesive is employed for long time at -60-350℃.and the shear strength could reach over 13 MPa, flexural strengths at room temperature are 82 MPa. Upon cure the adhesive exhibit a high electrical resistance.