| In recent decade year, Pb-free electronic manufacture has turned into an implementary stage. It has been found by researchers that SnAgCu 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. However, the content of Ag in the Sn-Ag-Cu soler researched mostly is much higher. Due to reducing the price of existing lead-free solders, and improving its aging performance of high temperature, the development of low Ag lead-free solders plays an important part all over the world. A sort of low Ag lead-free solder Sn-0.3Ag-0.7Cu is developing now, but it has a higher melting point and a worse wettability. 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. It has been indicated that addition of a mount of Bi element in Sn-0.3Ag-0.7Cu solder can reduce the melting point and increase the wettability and the tensile strength. With the development of electronic industry electronic devices and solder joints become more and more small and buren much more than before. And the reliability of solder joints has more importance significance for the use of electronic production.This work choose Sn-0.3Ag-0.7Cu solder as experimental material,adding different amount of Bi(1-4.5wt%). Through aging at 180℃and different time, investigation is performed on the effect of Bi on microstructures evolution and mechanical properties in Sn-0.3Ag-0.7Cu lead-free solder and on the microstructure evolution of Sn-0.3Ag-0.7Cu/Cu solder joint and the growth kinetic of interfacial intermetallic compounds (IMC) in solder joint. Meanwhile, the IMC and the shear strength of Sn-0.3Ag-0.7Cu/Cu after multi-reflow are researched.It was showed by analyzing Sn-0.3Ag-0.7Cu/Cu solder joints that Cu6Sn5 informed at interface of solder and Cu substrate after soldering. The morphology of IMC changed from needle-like to planar during aging, and the Cu3Sn phase was informed between the interface of Cu6Sn5/Cu and Cu substrate. It was showed by calculating of IMC growth speed that The growth rate of IMC in SnAgCuBi/Cu solder joints was lower than SnAgCu/Cu solder joints, which numeric were 30.74, 17.87, 9.93 and 25.7(Units:10-14cm2/s).It was showed by analyzing Sn-0.3Ag-0.7Cu/Ni solder joints that (Cux Ni1-x)6Sn5 informed at interface between bulk solder and Ni substrate after soldering. The thickness of IMC was increased as the aging time prolonged. Compared with the IMC informed between bulk solder and Cu substrate, the thickness of IMC was thinner due to the Ni substrate stopping diffusing of Cu. and decreased as the amount of Bi increased.Due to the effect of solid-solution strengthening and dispersion strengthen-ing which is related to Bi, and Bi can control IMC growth. The shear strength of Sn-0.3Ag-0.7Cu-xBi solder joints are improved and increased as the amount of Bi increased. However, it was also controlled by IMC thickness, fracture positions of solder joints occurred from bulk solder to IMC partly, and fracture types changed from ductile fracture to tough-brittle fracture.After reflowing, the thickness of IMC of Sn-0.3Ag-0.7Cu/Cu solder joints increased as the number of times of multi-reflow increases. The multi-reflow promoted the growth of Cu6Sn5 in short time. And the morphology of IMC changed from needle-like to shell during aging. However, the shear strength of Sn-0.3Ag-0.7Cu-xBi/Cu joints decreased slightly after 1-4 times reflowing. And after 5 times reflowing, the shear strength decreased.
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