Characterization of Carbon Nanotube Array Based Thermal Interface Material After Bonding Process

Vertically Aligned Carbon Nanotube (CNT) Arrays are promising to use as advanced thermal interface material. While possessing high thermal conductivity for an individual tube, carbon nanotube array based thermal interface materials (TIMs) fell short of expectations due to poor CNTs-target surface contacts. Investigations suggested that the overall resistance can be potentially reduced to less than 1 m²-K/MW by increasing the number of tubes to target surface contacts. This paper use chromium/gold/indium assisted thermal pressure-bonding to enhance contacts. A CNT array with 12.7% areal density was bonded to an experimental glass surface with 2-μm indium bonding layer and 10 nm-chromium/150 nm-gold adhesion layers under pressure of 196 KPa and temperature of 350 °C. Phase sensitive photothermal reflectance method was used for thermal measurement. The overall resistance, including CNTs-glass contact resistance and effective CNT array thermal resistance, is 1.1 m²-K/MW ± 27%. Although the contact resistance was reduced to 0.39 m²-K/MW ± 15%, the effective thermal conductivity of the post-bonded 80 μm long CNTs was 114 W/m-K ± 22%, which was lower than the expected lower bound of the thermal conductivity of 12.7% filled CNT array. It was suggested that the deformation of CNT array after mechanical bonding reduced its performance.