THERMALLY CONDUCTING POLYMER-MATRIX COMPOSITES CONTAINING BOTH ALN PARTICLES AND SIC WHISKERS

Aluminum nitride particles (size 4 mum) and silicon carbide whiskers (diameter 1.4 mum, length 18.6 mum) were used as filters in a polyimide polymer matrix. Aluminum nitride in the amount of 50 vol.% decreased the coefficient of thermal expansion from 81 x 10(-6) to 11.3 x 10(-6)/degrees-C and increased the thermal conductivity from 0.128 up to 1.76 W/(m.-degrees-C). Silicon carbide in the amount of 50 vol.% decreased the coefficient of thermal expansion from 81 x 10(-6) to 18.1 x 10(-6)/degrees-C and increased the thermal conductivity from 0. 128 up to 1.26 W/(m.-degrees-C). When both SiC whiskers and AlN particles in the 1:3 volume ratio and in the total amount of 50 vol.% were added to the polymer, the thermal conductivity increased from 0.128 to 2.23 W/(m.-degrees-C). These effects are attributed to the large aspect ratio of the SiC whiskers, which tended to bridge adjacent AlN particles and also act as a reinforcement to improve the toughness of the composite. On the other hand, the SiC whiskers in the mixed fillers also enhanced the toughness of the composites. The composite containing 50 vol.% AlN particles alone had a lower dielectric constant (7.1 at 100 kHz) than the composite containing 50 vol.% SiC whiskers alone (15.9 at 100 kHz). The composites containing a mixture of AlN particles and SiC whiskers at different ratios and in the total amount of 50 vol.% had lower values of the dielectric constant than the composite containing SiC whiskers alone.