Research on the microstructure and shearing property of microbumps with one Sn grain for high density solder interconnects

In order to meet the requirement of the higher density interconnects, the volume size of the solder microbumps continues to be reduced. In the present research, the microstructure of the microbumps with a diameter of 40µm was studied using Electron Backscatter Diffraction (EBSD). When the microbumps are smaller than a Sn grain in size, only one Sn grain is found to be contained in the microbumps. Shearing tests were carried out to study the mechanical behavior and the fracture mode. The strain rate sensitivity exponent of the microbump with one Sn grain is about 0.1. And a typical sliding fracture of the Sn grain is observed at different shearing speeds, which is different from the usual microvoids accumulation fracture displayed by BGA solder joints. The research findings are useful to assess the reliability of the high density solder interconnects, such as fine pitch flip chip, 3D-TSV, copper pillar bumps, and so on.