The dominant effect of c-axis orientation in tin on the electromigration behaviors in tricrystal Sn-3.0Ag-0.5Cu solder joints

Copper atoms have a higher diffusivity along the c-axis than along the a-axis of the tin grain during electromigration (EM). The growth behavior of intermetallic compounds (IMCs) in tricrystal Sn3.0Ag0.5Cu ball grid array (BGA) solder joints under EM was investigated. The results show that the c-axis direction can significantly affect the IMCs growth behavior in a tricrystal solder joint both in the solder matrix and at the interfaces under EM. The IMCs in the solder matrix and the IMCs at the cathode grow along the electron flow direction to the c-axis direction. When the c-axis direction was along the electron flow direction to the positive direction of ND, the IMCs grew to the cross sectioned surface. However, when the c-axis direction was along the electron flow direction to the negative direction of ND, the IMCs would grow to the inner solder matrix. Moreover, it seems that, in a tricrystal solder joint, the IMCs growth behavior of one grain is not affected by the other two grains with nearly 60° misorientations.