Thermal, electrical, and mechanical characterization of a carbon nanotube-epoxy composite

Future microelectronic circuits will need to dissipate more than 100 Watts per chip for high-performance applications, posing a thermal-management challenge for the next generation of electronic packages [1, 2]. To meet this challenge, it is imperative that all interfaces, such as those between the chip and the heat spreader and between the heat spreader and the heat sink, introduce minimal thermal resistance. We propose the use of carbon nanotube–epoxy composites to provide enhanced heat dissipation at these critical junctions. Purified single-walled carbon nanotubes (SWNTs) are considered, and the matrix selected is a typical underfill epoxy used in flip-chip packaging. Three techniques were explored to embed the carbon nanotubes (CNTs) in the epoxy matrix, namely mechanical separation, mechanical dispersion in alcohol, and ultrasonic dispersion. The distribution of the nanotubes in the epoxy as the result of each technique was qualitatively determined by field-emission scanning electron microscopy (FE-SEM). Combining ultrasonic dispersion with mechanical mixing produced the most uniform distribution among the three approaches tested. As anticipated, the resulting composites showed enhanced thermal, electrical, and mechanical properties with increased nanotube content in the matrix. However, the increase in thermal conductivity was not as significant as the changes in electrical and mechanical behavior. To enable further improvements in heat dissipation, alignment of the nanotubes in the epoxy may be required. Development of such aligned composites may enable the use of lower CNT concentrations, allowing polymer ductility and electrical isolation to be preserved while reducing additive costs.