Characterization of Nanomaterials for Interconnect and Thermal Management in Electronic Packaging

Doktorsavhandling, 2015

Electronic packaging, protecting the fragile chip from atmosphere and providing the paths for signal transmission as well as heat dissipation, is one of the most important parts in electronic devices. The cost, dimensions, performance, and reliability of an electronic device therefore strongly depend on its packaging structures and materials. In recent years, the miniaturization and diversification of electrical devices, having increased packaging and power density, pose a serious challenge to the reliability of traditional packaging materials. To address this challenge, several nanomaterials were thus fabricated and used for either interconnection or heat dissipation in the electronic packaging. For interconnection, vertically aligned carbon nanotubes (VACNT) grown with thermal chemical vapor deposition (TCVD) method were used as filling materials of through silicon vias (TSV). Meanwhile, vertically aligned carbon nanofibers (VACNF) fabricated with plasma enhanced chemical vapor deposition (PECVD) method were used as not only the bump material for chips, but also for the reinforcement material for solder joints. By using these carbon nanomaterials, some failure modes, such as burnout, electromigration, and coarseness, can be avoided. Besides carbon, alloy and semiconductor nanomaterials were also fabricated in this thesis for interconnection. Sn3.0Ag0.5Cu (SAC305) alloy and Bi2Te3 semiconductor nanopowders were mixed with traditional Sn58Bi and SAC305 lead free solders respectively in order to improve the shear strength and thermal fatigue resistance of solder joints. The dislocation movement and crack propagation can be effectively delayed by uniformly distributed nanoparticles in the solder matrix. However, it always shows a performance degradation when the content of nanoparticles passes a threshold. This phenomenon could be caused by increased voids and the agglomeration of nanoparticles in the solder matrix with increased content of nanoparticles. For heat dissipation, a polyimide (PI) network enhanced indium thermal interface material (TIM) was developed as a passive heat dissipation solution, and meanwhile a nanostructured bulk thermoelectric (TE) material constructed of Ag and Bi2Te3 nanopowders is presented as an active heat dissipation solution. The mechanical properties of pure indium TIM can be improved by the PI network without any degradation of heat dissipation ability. This is attributed to the Ag-coated PI fibers which formed solid bonding with the indium matrix and constrained the crack propagation. For the TE material, the thermal conductivity of nanostructured Bi2Te3 samples was much lower than that of raw materials due to the increased phonon scattering at the grain boundaries, which consequently led to a higher figure of merit (ZT value).