The Effect Of Bi On The Microstructure And Shear Strength Of Sn-3Ag-0.5Cu/Cu Solder Joints

Legislation to limit the use of lead in electronic production in many countries because of its harmful to human health an environment, so it is a tendency to develop lead-free solders for electronic assembles, and to research viable alternative lead-free solders become one of important projects which faced in. solder industry. In recent decade year research it has. been found that Sn-Ag-Cu eutectic alloy is the best candidate of SnPb solder among the lead-free solders for its good performances, such as mechanical property, weldability, heat fatigue resistance and so on. It has been indicated that addition of a mount of Bi element in Sn-Ag-Cu solder Can reduce the melting point and increase the wettability. With the development of electronic industry electronic devices and solder joints become more and more small and burden much more than before. And the reliability of solder joints has more importance significance for the use of electronic production. However, there are rare reports on the effect of Bi onSn-3Ag-0.5Cu/Cu solder joints, so it is importance to study it.This work choose Sn-3Ag-0.5Cu lead-free solderas experimental material, adding different amount of Bi(0-3wt%) into it. Through aging at different temperature and different times, investigation is performed on the effect of Bi on the microstructure evolution and the growth kinetic of IMC in Sn-3Ag-0.5Cu/Cu solder joints and shear strength of solder joints. The results show that:1. Cu₆Sn₅ IMC is formed at interface of solder and Cu after soldering, The morphology of IMC changes from needle-like to planar during aging, and when the aging temperature is higher, the time spent in this process is shorter. The growth rate of IMC in Bi-bearing solder joints is lower than SnAgCu/Cu solder joints. With the amount of Bi increases, the growth rate of IMC deceases. This is because Bi aggregates at the interface and decrease IMC growth during aging.2. By the control of IMC thickness, fracture positions of solder joints change from solder to IMC, and fracture types change from ductile fracture to brittle fracture. Shear strength of Bi-bearing solder joints are improved by the effect of solution strength and dispersion strength that is relate to Bi, as well as by Bi can decrease IMC growth.