Xinhe Tang

Carbon nanotube enhanced thermally and electrically conductive adhesive for advanced packaging

A comprehensive investigation has been carried out to develop nano-adhesive by studying the influences of post-treatment of carbon nanotue (CNT), dispersing parameter, CNT content and matrix on the adhesive performance. It has been found that both thermal resistance (Rth) and volume resistance reduced greatly by incorporating CNT into the epoxy. The uniform distribution of CNT has been achieved by optimizing the dispersion parameter. It has been demonstrated that the Rth decreased with increasing the CNT content. The formation of the network of CNTs in the matrix, the loading grade of the filler, the manufacture process and the properties of the matrix exert an important influence on the thermal, electrical and mechanical properties of the adhesive. The adhesive made of post-treated CNT showed lower thermal resistance than any other non-treated CNT. The low thermal resistance, 3.5Kmm2/W at bondline thickness 10µm was achieved. TGA study gave the degradation temperature from 330°C to 470°C, depending on the matrices used. The thermal shock cycling was performed at temperature from −55°C to 150°C and no delamination was observed. The volume resistance, 4.51×10−3 Ohm-cm has been measured and post-curing further decreased the resistance. In addition, viscosity, glass transition temperature and screen printability have been studied. The glass transition temperature was evaluated to be higher than the unloaded epoxy resin. The highest glass transition temperature, 270°C was achieved by finding out the desirable composition where the CNTs and epoxy were well incorporated. Screen printability is another important property of adhesive. The adhesive could be screen printed onto substrate and the uniform dispersion of CNT made it possible to print the adhesive either on large area or in fine structure for different application. The pot life has been determined by measuring the change of the viscosity with the exposing time in air. In order to study the adherence strength, a copper foil was bonded with ceramic substrate using the newly developed adhesive and then peeled off. The adhesive remained on both sides of Cu and ceramic, showing strong adhesion to metal and ceramic as well. A constant peeling strength along the length direction, 4N/mm has been measured. The new application of the CNT-enhanced adhesive has been studied too.