Thermally conducting aluminum nitride polymer-matrix composites

Thermally conducting, but electrically insulating, polymer-matrix composite s that exhibit low values of the dielectric constant and the coefficient of thermal expansion (CTE) are needed for electronic packaging. For developin g such composites, this work used aluminum nitride whiskers (and/or particl es) and/or silicon carbide whiskers as fillers(s) and polyvinylidene fluori de (PVDF) or epoxy as matrix. The highest thermal conductivity of 11.5 W/(m K) was attained by using PVDF, AlN whiskers and AlN particles (7 mum), suc h that the total filler volume fraction was 60% and the AlN whisker-particl e ratio was 1:25.7. When AlN particles were used as the sole filler, the th ermal conductivity was highest for the largest AlN particle size (115 Lm), but the porosity increased with increasing AlN particle size. The thermal c onductivity of AlN particle epoxy-matrix composite was increased by up to 9 7% by silane surface treatment of the particles prior to composite fabricat ion. The increase in thermal conductivity is due to decrease in the filler- matrix thermal contact resistance through the improvement of the interface between matrix and particles. At 60 vol.% silane-treated AlN particles only , the thermal conductivity of epoxy-matrix composite reached 11.0 W/(m K). The dielectric constant was quite high (up to 10 at 2 MHz) for the PVDF com posites. The change of the filler from AlN to SiC greatly increased the die lectric constant. Combined use of whiskers and particles in an appropriate ratio gave composites with higher thermal conductivity and low CTE than the use of whiskers alone or particles alone. However, AlN addition caused the tensile strength, modulus and ductility to decrease from the values of the neat polymer, and caused degradation after water immersion. (C) 2001 Publi shed by Elsevier Science Ltd.