Study Of Melting, Wetting And Interface Of SnAgCuGe Solder

Lead and its compounds are harmful to environment and human health. In recent years, with the development of microelectronic and Surface Mounted Technology, developing new green solders to replace tin lead solder is becoming one of the most important subjects. After ten years study, researcher found that among all of the lead free solders, SnAgCu solder is the most possible solder to replace tin lead solder.As our research about lead free solder is latter, we have a great gap compared with abroad. This work choose the most popular solder (Sn-Ag-Cu lead free solder) as experimentl material, adding a small mount of Ge into in, to study the effect of Ge to its microstructure,melting characteristic and spreading wettability, and how Ge effect the interface of Sn-Ag-Cu/Cu, and its effect on Sn-Ag-Cu/Cu joint after aging.The result shows that, there is no low-melting eutectic substance formed in the Sn-Ag-Cu alloy, because there is no low-melting eutectic peak in all the alloys. This can form reliable spot weld. Ge has small effect on Sn-Ag-Cu solder's melting temperature. Its melting temperature is between 217.642℃and 218.622℃. According to measure the spreading area: when adding 0.5% Ge, the solder has lager spreading area and smaller wetting angle.After adding Ge into the solder, the Ag3Sn phase and Cu6Sn5 phase are refined, and their distribution become homogeneous, and the arrangement of intermetallic compounds become more regulation.Studied the interface of Sn-Ag-Cu-Ge solder and Cu plate. When the amount of Ge is 1.0%, the interface has the smallest thickness(2.165μm), and the interface is flattest. When the amount of Ge is 0.5%, the interface's thickness is between 2.37~3.75μm, and the interface is unflat.Studied the soldering joint after aging 100 hours at 150℃in drying cabinet, the intermetallic compounds in the three solders are all growed up. Sn-2.5Ag-0.7Cu-1.0Ge/Cu has the thinnest interface (3.94μm). Sn-2.5Ag-0.7Cu-0.5Ge/Cu has the thickest interface (4.71μm). Generally speaking, the speed of Cu atom from the basic body to the Cu-Sn boundary layer is higher than the speed of Cu atom from boundary layer to the solder, that makes the boundary layer grow up,when aging 100 hours.