Papers by Author: Yao Li Wang

Abstract: The morphology and growing behavior of Cu₆Sn₅ intermetallic compound (IMC) of low Ag content Sn-2.5Ag-0.7Cu-0.1RE/Cu solder joint interface are investigated by adopting the X-ray diffraction, JSM-5610LV scanning electronic microscope and energy spectrum analysis. The results show that the cross-section morphology Cu₆Sn₅ of the solder joint interface is scallop-like and its section morphology is circle-like grain. With the aging time increasing, the cross-section Cu₆Sn₅ morphology of the solder joint interface can be changed from the scallop-like to the shape-layer, and the growing kinetics is coincidence with the law of parabola and its growing behavior is controlled by diffusion. With adding a small amount of rare earth elements in the Sn-2.5Ag-0.7Cu solder alloy, the growing rate of the Cu₆Sn₅ can be reduced.

Abstract: The interfacial microstructures and kinetics of low Ag content Sn2.5Ag0.7Cu/Cu solder joint were investigated by the X-ray diffraction, scanning electronic microscope and energy spectrum analysis during the isothermal aging. The results show that the interfacial microstructures of the Sn2.5Ag0.7Cu/Cu solder joint are composed of Cu₃Sn and Cu₆Sn₅ after soldering. With the aging time increasing, the intermetallic compound (IMC) pattern of the solder joint interface can be changed from the scallop-like to the shape-layer, and the growing dynamics is coincidence with the law of parabola and its growing behavior is controlled by diffusion. The growing activation energies values of Cu₃Sn and Cu₆Sn₅ layer at the Sn2.5Ag0.7Cu/Cu solder joint are 82.4kJ/mol and 69.6kJ/mol respectively.

Abstract: Creep property is one of the most important factors to affect the reliability of soldered joints. The effect of rare earth(RE) on the creep rupture life of Sn2.5Ag0.7Cu solder joints were investigated under constant temperature and stress using creep specimens with a 1mm² cross sectional area. The results show that adding tiny RE in Sn2.5Ag0.7Cu solder alloy can effectually affect the size and configuration of the intermetallic compound (IMC) of interfacial layer. The IMC of Sn2.5Ag0.7Cu interfacial layer is thinner and its thickness is homogeneous with adding 0.1% RE, and the creep rupture life of solder joints is longest, which is apparently superior to that of Sn2.5Ag0.7Cu and commercial used Sn3.8Ag0.7Cu solder alloy.

Abstract: Taking 1.4%C and 1.6%C ultrahigh carbon steels (UHCSs) with ultra-fine structures developed through thermo-mechanical processing as research objects, the influences of superplastic deformation conditions and electric field on compression superplasticity were conducted without electric field and with electric field. The experimental results indicate that 1.4%C and 1.6%C UHCSs have respectively superplasticity or electro-superplasticity under the conditions of deformation temperature of 800°C, the initial strain rate of 0.75-3.75×10-4 s-1 and deformation temperature of 780 °C, the initial strain rate of 0.5-5.0×10-4 s-1 and the suitable external electric field. Its strain rate sensitivity are respectively 0.32 and 0.46.When the electric field intensity of 3 kV/cm in the manner of the specimen connected to positive terminal, the steady flow stress of 1.6%C UHCS decreases more than 10.5% as compared with electric field intensity of 0 kV/cm.

Abstract: Effect of rare earth content on microstructure and interfacial reactions of low Ag content SnAgCu solder is researched by adopting the X-ray diffraction, JSM-5610LV scanning electronic microscope, energy spectrum analysis and JEM2100 ultrahigh resolution electron microscopy. The results show that proper quantities of rare earth (0.1%) can refine the eutectic microstructure of the solder alloy; and petal-like rare earth compound can be found in the solder alloy while the rare earth addition is 0.5%. The growing rate of the interfacial intermetallic compound can be reduced during the soldering with adding 0.1% rare earth in the Sn2.5Ag0.7Cu solder alloy.