Application of Metallic Nanoparticles and Vertically Aligned Carbon Nanotubes as Interconnect Materials for Electronics Packaging

Licentiate thesis, 2013

In the electronics industry, packaging is responsible to protect chip from atmosphere and provide the path for signal communication as well as thermal dissipation. The realization of these functions in a packaging system depends on the performance of interconnect materials. Any failure on the interconnect materials could make entire system down. Currently, one of the most popular interconnect materials is lead-free solder, which has been used for two decades instead of toxic Sn-Pb solder. The updates on processes, equipments and standards for lead-free solder have been completed. However, as continuous increase on the chip power and the miniaturization of consumer electronics, lead-free solder is facing big challenges. The disadvantages of traditional lead-free solder, such as high process temperature, grain coarsening and thermal fatigue failure, are gradually exposed. Therefore, one of the urgent needs for packaging is to develop new interconnect materials. In recent years, as the development of nanotechnology, nanostructured materials are gradually applied on the packaging. Following this tendency, two promising nanostructured interconnect materials are presented in this thesis. The first part of this thesis shows a nanocomposite material. It consists of Sn-3.0Ag-0.5Cu nanoparticles and Sn-58Bi solder matrix. Sn-58Bi solder has the advantage on low process temperature. However the inherent brittleness of Sn-58Bi limits its application. For this reason, the Sn-3.0Ag-0.5Cu nanoparticles are added into the Sn-58Bi in order to improve the mechanical properties. The result of shear test shows that the shear strength of Sn-58Bi increases by two times by the addition of Sn-3.0Ag-0.5Cu nanoparticles. The result also indicates that the nanocomposite solder has excellent thermal fatigue resistance. The demonstrated properties make nanocomposite solder can be a potential candidate for replacing Sn-Ag-Cu in future. In this thesis, we also present another kind of interconnect material based on vertically aligned carbon nanofibers. High stability and compatibility of carbon nanofibers are always attractive to the packaging industry. By using a series of processes, such as plasma-enhanced chemical vapor deposition, sputtering, transfer and bonding, the vertically aligned carbon nanofibers are successfully assembled in the packaging system. As interconnect material, vertically aligned carbon nanofibers exhibit acceptable electrical resistance and shear strength. The positive preliminary results motivate further research on the aspects of thermal fatigue resistance and stability.