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

High filler loading technique was evaluated using the simplified packing model proposed by Ouchiyama and Tanaka 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 be existed in the 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 calculation very low minimum melt viscosity of about 200 poise could be obtained in EMC filled with 85 volume percent of silica. As the amount of filler in EMC was increased, several properties such as coefficients of thermal expansion, moisture absorption and strength were improved. However, the adhesive strength to alloy 42 leadframe was decreased with the content of filler. The adhesive strength was more rapidly decreased with the moisture absorption. From the 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 of the adhesion was attributed to the failure of the hydrogen bond by the absorbed water. The higher adhesive strength of low amount of silica-filled EMC could be explained as the low viscosity and the short intermolecular spacing with the leadframe.