High-performance epoxy/silica coated silver nanowire composites as underfill material for electronic packaging

Silver nanowires (AgNWs), as one-dimensional nanostructured materials, possess high aspect ratio and intrinsically high thermal conductivity. However, AgNWs are difficult to disperse homogeneously in epoxy resin, and their high electrical conductivity also limits their applications for electronic packaging. Herein, silica-coated silver nanowires (AgNWs@SiO2) were synthesized by a flexible sol-gel method and then incorporated into epoxy. The less stiff silica intermediate nanolayer on AgNWs not only alleviated the mismatch between AgNWs and epoxy, but also enhanced their interfacial interaction. Hence, the thermal conductivity of an epoxy/AgNWs@SiO2 composite with 4 vol.% filler loading was increased to 1.03 W/mK from 0.19 W/mK of neat epoxy compared to 0.57 W/mK of an epoxy/AgNWs composite with identical nanowire loading. Simultaneously, the insulating silica nanolayer effectively avoided formation of an electrically conductive network of AgNWs in epoxy, leading to high electrical insulation of the composite. AgNWs@SiO2 nanowires with core-shell structure also improved the dielectric properties of epoxy. In addition, these composites possessed a viscosity suitable for the underfill process in electronic packaging.