Bi On The Sn-ag-cu Lead-free Solder Alloy And Joint Structure And Performance

Legislation to limit the use of lead has been introduced in many countries because of its harmful effect to human health and environment. With the developing of the " green movement" in all the world, many people have consciousness the harm of Pb-solder. In recent years, with the development of microelectronics and Surface Mounted Technology, researching lead-free solder become one of the hot projects. Among the solders that Sn-Ag-Cu solder is recommended as the best candidate of SnPb solder. It has been indicated that addition of a mount of Bi element in Sn-Ag-Cu solder can reduce the melting point of Sn-Ag-Cu solder and increase the wettability. However, there are rare reports on the effect of Bi on Sn-Ag-Cu solder and Sn-Ag-Cu solder joints, so it is important to study the effect of Bi on Sn-Ag-Cu solder.This work choose Sn-3Ag-0.5Cu solder as experimental material, adding different amount of Bi (0-3wt%) into it. Through aging at different temperature and different time, investigation is performed on the effect of Bi on microstructures evolution and mechanical properties in Sn-3Ag-0.5Cu lead-free solder and on the microstructure evolution of Sn-3Ag-0.5Cu/Cu solder joint and the growth kinetic of IMC in solder joint. The results show that:1. The addition of Bi up to 3% increases the tensile strength and keeps a good ductibility in Sn-3Ag-0.5Cu solders, a stable mechanical properties with aging time of Bi-bearing solders is observed which may attribute to the strengthening effect of Bi from solid solution strengthening to precipitating strengthening in the solders, in SnAgCuBi system, the solubility of Bi in Sn is 1-2% in 120C, but the solubility of Bi in Sn is 3-5% in 170C.2. The morphology of IMC becomes from scallop-like to planar during aging process, and with the increase of aging time, the thickness of IMC increased in Bi-bearing soler joints, Bi accumulates at the interface with the aging temperature and aging time; 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 decreases, the activation energy of IMC in Bi-bearing solder joints is lager than SnAgCu/Cu solder joint. With the amount of Bi increases, the activation energy of IMC increases.