Hardness Characteristics of Au Cone-Shaped Bumps Targeted for 3-D Packaging Applications

Three-dimensional large scale integration (3D-LSI) packaging is crucial toward obtaining increased circuit density within a small footprint. In a 3D-LSI package, chip-to-chip interconnection is typically obtained using through-silicon vias and microbumps. In particular, microbumps realized by nanoparticle deposition (NPD) are promising to obtain high-density interconnections. However, the effect of temperature on the mechanical properties (i.e., hardness) of NPD bumps is little understood. This paper seeks to investigate the influence of temperature on the hardness of NPD bumps, with reference to NPD films. The results obtained suggest a significant reduction in the NPD bump hardness from room temperature to 200 °C. In particular, the hardness was observed to be mainly dependent on temperature rather than grain size, as the grain microstructures obtained at room temperature and 200 °C are similar. Overall, these results suggest a simple approach to control the NPD bump compression during flip-chip bonding, where the hardness-temperature data for the NPD bumps suffices to estimate for the bump compression during flip-chip bonding.