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The thermal conductivity of an AlN-and an alumina-particulate-filled epoxy resin was investigated as a function of their volume content ratios. AlN composite exhibited thermal conductivity of 7.15W/m·K at 68.5vol% filler content but that of alumina composite was lower than 2.68W/m·K even if the filler content was as much as 63.8vol%. The thermal conductivity of the composites is strongly dependnt on that of the filler. In the AlN filler properties, the particle size of the filler used affected the thermal conductivity of composites, and composites with higher thermal conductivity could be obtained by using filler with large particle size. The thermal conductivity of composites is governed by the number of resin layers on the surface of an AlN particle. The composite thermal conductivities decreased with increasing the oxygen content of the filler. The thermal conductivity of an AlN particle depends on the oxygen content of the particle itself and the decrease of the composite thermal conductivity with the increase of the oxygen content of the filler is due to the increase of the aluminum oxide layer thickness produced on the surface of particles. In the thermal conductivity model, the measured thermal conductivity of AlN-ground-powder-filled composites disagreed with the ones calculated using Bruggeman's expression. However the measured values of aluminaspherical-powder-filled composites agreed with the calculated ones. It is considered that the results depended on the sphericity of the used powder.
Nagai et al. (Wed,) studied this question.