Atomic diffusion of Zn in Sn-Zn based solder joints subjected to high temperature aging

The diffusion behavior of Zn in Sn-8Zn-3Bi solder joints was investigated during long-time aging at 160 °C. Intermetallic compounds (IMCs) were formed at the interface, which were identified as Ni-Zn. Thickness of the IMCs layer increased whereas the growth rate decreased with time. It was found that the growth kinetic of the IMCs was diffusion control. A diffusion model was thus proposed to describe the diffusion behavior of Zn during long-term aging, which appeared to provide a good agreement with the microstructure evolution.