Study On Microstructure And Properties Of SnAgBi-XSm Solder

In order to adapt to electronic packaging, consumer electrical products, automotive and other industries to meet the demand of the Ro HS and WEEE directive, urgently need to be developed a new lead-free solder. Research new lead-free solder needs to consider its physical properties, microstructure, reliability of solder joints, etc. Thus to start a new solder research has important value. This paper systematically studied the rare earth element samarium(Sm) of Sn-3.5Ag-1.5Bi lead-free solder alloy melting point, wettability, the evolution of the solder joint interface intermetallic compound, shear strength and fracture morphology influences.This paper studies the Sn-3.5Ag-1.5Bi-XSm(X=0?0.025?0.05?0.1? 0.2 wt %) lead-free solder melting point. The results show that adding trace rare earth Sm on Sn3.5Ag1.5Bi has a little influence on the melting point of solder alloy, when Sm content is 0.2 %, the lowest melting point can reach 217.48 ?.The wettability of Sn-3.5Ag-1.5Bi-XSm solder alloy were investigated by the test method of solder spreading area. The results show that adding trace rare earth Sm, can improve Sn3.5Ag1.5Bi solder alloy on the copper pad spreading area, significantly improves the solder wettability. When Sm content is 0.1 %, the largest spreading area is 56.74 mm2. Rare earth Sm has stronger oxygen affinity, mainly enrichment in the interface, reducing the interfacial tension between the solder pads and the liquid is reduced, thereby improving the wettability of solder.With aging time respectively 0 h, 24 h, 96 h and 360 h of isothermal aging test, studied the Sm content changes before and after aging for Sn3.5Ag1.5Bi solder morphology and thickness of intermetallic compounds. The study found that before aging Sm content of 0.025 % and a thickness of IMC layer is thinnest 3.46 ?m. After aging, the interface to flatten evenly, the same composition Sn-3.5Ag-1.5Bi-XSm/Cu solder joints, with the time of aging, the thickness of the IMC layer showed an increasing trend. After 360 h aging, the IMC layer thickness of containing Sm solder below did not add Sm solder matrix, Sm for solder joint interface of the IMC layer have been suppressed, can improve the reliability of solder joints.Solder joint shear test results show that before aging, when Sm content is 0.025 %, the largest shear strength and the dimples distributed more uniform. After aging, with the extension of aging time, five-component solder joint shear strength decreased. Aging time for 360 h, the shear strength of containing Sm solder are greater than not add Sm solder matrix. The study found that the holes in the shear fracture after aging, when the hole in the solder alloy and Cu substrate interface, the combination of the welded joint strength is reduced.