High filler loading technique and its effects on the reliability of epoxy molding compound

A high filler loading technique was evaluated using the simplified packing model proposed by Ouchiyama and Tanaka (Ind. Eng. Chem. Fundam., vol. 23, p. 490, 1984; ibid., vol. 25, p. 125, 1986) and its effect on the reliability of epoxy molding compound (EMC) was investigated. Maximum packing fraction, φ_m, with the mixing ratio for ternary spherical filler systems was calculated, and it was found that the effect of macropores, which could exist in systems with more than 3 components of different filler size, should be considered in the calculation of φ_m in a given filler system. Based on the calculations, very low minimum melt viscosity of about 200 poise could be obtained in EMC filled with 85 vol.% of silica. As the amount of filler in EMC was increased, several properties such as coefficient of thermal expansion, moisture absorption and strength were improved. However, the adhesive strength to an alloy 42 leadframe decreased with increasing filler content. Adhesive strength was more rapidly decreased with moisture absorption. From analysis of the interface between EMC and leadframe with X-ray photoelectron spectroscopy, the principal adhesive mechanism was thought to be the hydrogen bond and thus the decrease in adhesion was attributed to hydrogen bond failure due to absorbed water. The higher adhesive strength of low level silica-filled EMC could be explained by the low viscosity and the short intermolecular spacing with the leadframe