Investigation of tin atomic migration of tin-based solders with cluster model and DV-Xα method in electromigration

The continual accumulations of Sri atom near anode and of vacancy near cathode in electromigration of tin-based solder related to the detail of Sri atomic migration. In this research, ab initio molecular orbital calculations for variation of electronic state with movement of tin atom in tin-based solder alloys were conducted by using the discrete-variational (DV)-X alpha cluster method. In the results, we confirmed anisotropism of vacancy diffusion from the viewpoint of the covalent interaction. Furthermore, it is found that the net charge of the moving Sri atom changed from negative to positive with the movement. These results would be helpful to further the fundamental knowledge on diffusion process with vacancies in the case of electromigration.