| dc.description.abstract |
Due to the miniaturization of electronic devices, the reliability of electromigration (EM) has become a major concern issue when shrinking the solder dimensions in flip-chip joints. Fast reaction between solders and electrodes causes intermetallic compounds (IMCs) to form, which grow rapidly and occupy entire joints when solder volumes reduced. It reveals a different failure mechanisms between the traditional large solder bumps and the microbump which occupied by IMCs, due to the distinct electrical and mechanism properties. In this study, U-grooves were fabricated on Si chips as test vehicles. An electrode-solder-electrode sandwich structure was fabricated by using lithography and electroplating. Gaps exhibiting well-defined dimensions were filled with Sn3.5Ag solders. The gaps between the copper or nickel electrodes in the test sample were limited to less than 15 μm to simulate microbumps. The samples of Cu/Sn3.5Ag/Cu and Ni/Sn3.5Ag/Ni were stressed at various current densities at 100, 125, and 150 oC. The morphological changes of the IMCs were observed, and the dimensions of the IMCs were measured to determine the kinetic growth of IMCs. Therefore, in the first part of this study focused on the influence of back stress caused by microstructural evolution in microbumps.
Besides, the high anisotropic diffusivity in white Sn (β-Sn) grain is particularly significant, especially in the limited Sn-based solders, which had a strong effect on the growth kinetics of the interfacial IMCs. Electron Backscatter Diffraction (EBSD), which possess the high resolution and non-destruction, is a good candidate to monitor the evolution of grain growth under in-situ electromigration as the minute size of solder was whole occupied by IMCs. Hence, in the second part of this study succeed in analyzing the correlation between the grain orientation of Sn and Ni3Sn4 and the current flow direction in Ni/Sn3.5Ag/Ni solder lines. The merging effect of Ni3Sn4 grains was also investigated by the mass fluxes during electromigration to provide the reliability mode in the evaluation of electronic packaging. | en_US |