Microstructure, IMCs layer and reliability of Sn-58Bi solder joint reinforced by Mo nanoparticles during thermal cycling

Highlights: • The microstructure is coarsened with increasing thermal cycling times and it is refined by adding Mo nanoparticles. • The IMCs layer thickness is increased with increasing thermal cycling times and fewer voids are found by adding Mo. • The mechanical strength is decreased with increasing thermal cycling times and it is improved by adding Mo. • The fracture mode by adding Mo is mixed with ductile and brittle fracture and becomes brittle fracture after thermal cycling. -- Abstract: The microstructure, IMCs layer and reliability of Sn-58Bi and Sn-58Bi-0.25Mo solder joints during thermal cycling were investigated. The results showed that the microstructure of Sn-58Bi and Sn-58Bi-0.25Mo solder joints is coarsened with increasing thermal cycling times and it is refined by adding Mo nanoparticles. The IMCs morphologies of Sn-58Bi and Sn-58Bi-0.25Mo solder joints are both changed to be flat and thick with increasing thermal cycling times and fewer voids are found in the IMCs layer of Sn-58Bi-0.25Mo solder joint than that of Sn-58Bi solder joint. The IMCs layer thickness of Sn-58Bi and Sn-58Bi-0.25Mo solder joints is increased with increasing thermal cycling times due to the formation of Cu₆Sn₅ and Cu₃Sn compounds, and slow IMCs layer growth is obtained by Mo-reinforced solder joint during thermal cycling. The shear and tensile strength of Sn-58Bi-xMo (x = 0, 0.25) solder joints are both decreased with increasing thermal cycling times and the mechanical properties of Sn-58Bi solder joint are improved by adding Mo nanoparticles. The fracture mode of Mo contained composite solder joint is mixed with ductile and brittle fracture with lots of dimples, and it is changed to brittle fracture after 1200 thermal cycles with the reduction in dimples.