Effect of Sn crystallographic orientation on solder electromigration and Ni diffusion in Cu/Ni plating/Sn–0.7Cu joint at low current density

Abstract

Electromigration (EM) in solder joints has recently been recognized as a serious reliability issue in the field of car electronics. EM in power modules is also of concern for next-generation environmentally-friendly vehicles. The current density of 10 kA/cm2 is well-known as the threshold for EM failure. Few researches have studied the EM behavior of solders at realistic current densities lower than 10 kA/cm2. In the present study, EM in a Cu/Ni plating/Sn–0.7Cu joint was investigated at low current densities of 2.5 and 5.0 kA/cm². It was found that even at a low current density of 2.5 kA/cm2, severe EM damage can be induced depending on Sn crystallographic orientation. When the c-axis of Sn crystals was parallel to the direction of electron flow, the solder detached at the cathode of the joint operated at 2.5 kA/cm2 for 2520 h. Conversely, when the c-axis of Sn crystals was perpendicular to the direction of electron flow, the solder did not detach in the joint until after a much longer time of 8200 h. Thus, it was clarified that the EM lifetime in a Cu/Ni plating/Sn–0.7Cu joint when the c-axis of Sn crystals was parallel to the direction of electron flow at a low current density of 2.5 kA/cm2 was about one-third that of the perpendicular orientation.