High solids loading of aluminum nitride powder in epoxy resin: Dispersion and thermal conductivity

Most semiconductor devices are now packaged in an epoxy polymer composite, which includes a silica powder filler for reducing the thermal expansion coefficient. However, increased heat output from near-future semiconductors will require higher thermal conductivity fillers such as aluminum nitride powder, instead of silica. This thesis research is intended to apply improved dispersant chemistry, in order to achieve a high volume percentage of AlN powder in epoxy, increasing the thermal conductivity of the composite without causing excessive viscosity before the epoxy monomer is crosslinked.; In initial experiments, the dispersibility of aluminum oxide in epoxy monomer resin was better than that of AlN, because of the weaker basicity of oxide surfaces compared with nitride. To improve the dispersibility of AlN, its surface was modified by pretreatment with silane coupling agents. Silane molecules with different head groups were investigated. In those experiments, methylsilane gave lower viscosities than chloro- or methoxysilane, while pretreatments using organic acids increased the viscosity of the AlN dispersion. The viscosity changes and FTIR peak intensity trends suggested that the silane molecules could be adsorbed on AlN surfaces in the form of a monolayer during optimization experiments, and the best silane monolayer coverage on the AlN powder surfaces was achieved with 2 wt% amounts in a 3 hour treatment.; A particular phosphate ester was a good second layer dispersant for the AlN-plus-epoxy system. When that dispersant was added onto the silane-treated filler surfaces, the degree of viscosity reduction was dependent on the types of silane coupling agent functional groups. In the optimized results, silane pretreatment followed by dispersant addition was better than either alone.; High solids loading, up to 57 vol.%, was achieved with a wide particle size distribution of powder, and the viscosity of that dispersion was 60,000 to 90,000 cps, which easily flowed by gravity alone at room temperature. The highest thermal conductivity of the composites measured by the hot disc method was 3.39 W/mK, which had been increased up to 15 times higher than for pure epoxy. The Agari and Uno model was a good fit to the experimental data. Electronic I-V curves obtained after encapsulation of testing devices indicated that the highly AlN-filled epoxy slip appeared to be feasible for use in the encapsulation of IC chips.