Isothermal aging and shear creep behavior of a novel lead-free solder joint with small additions of Bi, Sb and Ni

In this paper, we investigate the effects of isothermal aging on the microstructure and creep properties of a novel lead-free SAC387-3Bi-1.5Sb-0.15Ni (InnoLot)/Cu solder joints. Single-lap shear solder joints of the InnoLot solder were aged up to 1 year at 100 °C, and then loaded to failure in shear creep tests under different applied shear stresses and testing temperatures. The findings show that both aging time and temperature lead to the global increase of the interfacial IMC thickness significantly, but the growth of the Sn-rich IMC layer during aging remains limited in comparison with other solder materials due to the Ni content. In addition, shear creep tests reveal that the shear creep strength of the aged solder joint decreases initially before remaining dramatically stable in the long term. In terms of failure modes, shear creep tests at room and elevated temperatures show distinct rupture features. While rupture within the bulk solder happens at higher temperatures, rupture through the interface occurs at lower temperatures. When the specimens are exposed to isothermal aging, creep deformation becomes more predominant. The aged microstructure exhibits a brittle-to-ductile transition with occurrence of intergranular fracture due to the dynamic recrystallization inside the solder matrix. It is observed that the mechanical factor is of first-order importance in the formation of the new grain structure of the solder.