Effects of nano-sized particles on electrical and thermal conductivities of polymer composites

Polymer composite materials, for their cost-effectiveness and design flexibility, have been widely employed in electronic packaging industry. They possess unique characteristics combining the low-temperature processability of organic polymer matrix and the various functionalities endowed by the other components in the composites. Electrically conductive adhesives (ECAs) have been explored as an environment friendly interconnection technique. While they have many potential advantages for surface mount and flip chip applications, typical ECA materials suffer from several critical issues to be used as a drop-in replacement for lead-containing solders. In an attempt to understand and improve the thermomechanical properties of ECA materials, nano-sized silver particles were introduced into the conventional ECA compositions. The influence of nano particles on bulk resistivity is reported in this paper, as maintaining an acceptable conductivity is essential for high performance and environmentally benign interconnections. It was found that the bulk resistivity of ECA formulations strongly depended on the contents of silver flake and nano particles, as well as the particle morphology and surface properties. The thermal conductivity of alumina based composite samples was also affected upon the inclusion of nano alumina particles. Both the electrical and thermal conductivities of the polymer composites containing nano particles would be determined by the contacts of microsized particles and interfaces that involve nano particles along the conduction paths.