MEASUREMENT OF THERMAL-DIFFUSIVITY OF FILLER-POLYIMIDE COMPOSITES BY FLASH RADIOMETRY

Thermal diffusivity D of filler-polyimide composites was investigated using flash radiometry. The fillers used were: diamond, alumina, boron nitride, aluminum nitride, silicon carbide, and silicon carbide whiskers. Composite films were prepared by casting a polyamic acid solution with dispersed filler on a glass plate and then annealing. The effects of filler type, size, content, and shape on D were studied. D increased with increasing average filler particle diameter and filler content. For the composite filled with fine Al2O3 whose average particle diameter is about 0.2-mu-m, aggregates of filler were observed with dimensions up to a few microns. The formation of thermal paths through this aggregate enhances thermal diffusion. For the composites filled with high thermal conductivity filler such as BN and AlN, there was a strong increase in D above a filler content of 20 vol %. D was ten times larger than that of unfilled polyimide when the BN content was 54 vol %. D of the SiC-whisker composite increased strongly up to a filler content of 18 vol %. Above this content D significantly decreased, probably because of interconnected voids formed by mold shrinkage.