Copper Nanowire-Filled Soft Elastomer Composites for Applications as Thermal Interface Materials

Efficient heat dissipation is a critical requirement for sustained performance and failure prevention of microelectronic components. Thermal interface materials are used to fill the voids at the solid interface between the device and the heat sink to create a thermally conducting pathway for heat dissipation. This work reports flexible elastomer composite embedded copper nanowires with high aspect ratios (2500-5000), leading to a thermal percolation network at very low volume filler loading fractions of approximate to 0.009 phi. In order to achieve a high thermal conductivity at ultralow filler fractions, the copper nanowires are freeze-casted into a monolithic sponge, to create an interconnected network. The composites formed by subsequently embedding the nanowire sponge in elastomer matrix exhibit a thermal conductivity of 3.1 +/- 0.2 W mK(-1), a 19-fold enhancement over the pristine matrix, in a temperature range between 20 and 80 degrees C. The effect of thermal contact resistance at nanowire junctions is substantially reduced by in situ microwave welding of the nanowires. The use of Ecoflex, an ultrasoft silicone elastomer as the matrix, along with very low filler loadings of copper nanowire networks, keeps the elastic modulus <250 kPa, retaining the high compliance of the composites.