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