The influence of strengthening and recrystallization to the cracking behavior of Ni, Sb, Bi alloyed SnAgCu solder during thermal cycling

The explosion of high density and high temperature electronic devices is intensifying the desire for high temperature Pb-free solders. Alloying high melting point elements with conventional solders is one of the most potential solutions drawing attention. In this paper, the relationship between cracking and microstructure evolution of SnAgCu and Ni, Sb, Bi alloyed SnAgCu solders during thermal cycling was systematically studied and compared by ultrasonic C-scanning, SEM, EDX, EBSD, etc. It turned out that alloying Ni, Sb, Bi with SnAgCu solder offered better crack resistance by strengthening and recrystallization energy consumption before ~600 cycles. However, its failure dramatically accelerated after those cycles because of the large amount of grain boundaries caused by severe early recrystallization, the coarsened IMCs, and the decrease of Schmid Factor as SnAgCu were softened, while SnAgCuNiSbBi can be excessively hardened by thermal cycles.