The reliability of a solder ball joint with a Sn-Ag-Cu-Ni-Ge lead-free alloy, which is expected to be an advanced lead-free solder, was investigated under heat exposure conditions. Solder ball joints with a eutectic Sn-Ag alloy and a ternary Sn-Ag-Cu alloy were also prepared to compare with that of the Sn-Ag-Cu-Ni-Ge alloy. Microstructual observations of the cross sections of the solder ball joints were conducted to investigate microstructural evolutions in the solders and the growth kinetics of reaction layers formed at joint interfaces. The influence of heat exposure treatment on joint strength was investigated by ball shear test. Moreover, the influence of surface treatment of a Cu pad on the reliability of the solder joint was also investigated.

An influence of content of Ni and Ag in a Sn-Ag-Cu-Ni-Ge lead-free solder has been investigated on microstructure and joint strength of the soldered joint under heat exposure conditions. The growth kinetics of the reaction layer formed at the joint interface has been investigated, and the apparent activation energy of the reaction layer growth has been also examined. Moreover, the soldered joints with Sn-Ag and Sn-Ag-Cu solders were prepared and were compared with the joints with the Sn-Ag-Cu-Ni-Ge solders.