Effects Of Trace Amounts Of Element On The Properties And Microstructure Of Snagcu Lead-Free Solder Alloy

With the development of surface mount technology (SMT), electronic products are being developed into models of minimization, digitization and multifunction. The electrical current density and the thermal storage in per unite solder joint were increased, because the solder joint take on the function of electrical connection and mechanical connection. Thus, how to improve the solder joint reliability becomes extremely important. SnAgCu lead-free solder alloy, as the suitable alternative alloy in the SMT fields, has been more concerns. Adding trace amounts of elements are important method to improve the technological properties of solder and the service probability of the solder joints. The first purpose of this study is to investigate the effect of trace amounts of elemental additions on the processing property, mechanical property and microstructure of Sn_3.0Ag0.5Cu solder alloy. Secondly,the effect of Ag content on the microstructure and properties of SnAgCu solder alloy was studied. A cost-effective low-Ag lead-free solder was developed. Finally, Solidification cracks in SnAgCu lead free solder joints were investigated because it influences on the solder joint reliability.Adding only Ni, P or Ce has little effect on the melting temperature of Sn0.5AgCu lead free solder, which is able to keep the excellent low-temperature performance for solder alloy. Ni or Ce elemental additions can depress the decreasing of shear strength of the solder joint due to high–temperature aging. Adding P can improve the wettability and the oxidation resistance of solder alloy; however, adding trace amounts of Ce makes oxidation resistance of the solder worsened. Adding all the 0.1wt%Ni, 0.001wt%P and 0.05wt%Ce can improve the wettability, oxidation resistance, and the shear strength of solder joints at as-reflowed and after aging state.Reducing Ag content can decrease the cost of solder alloy in the SnAgCu alloy, but it affacts the properties of solder alloy. That is, melting temperature was increased; wettability and shear strength of solder joint were decreased. Adding all the Ni, P and Ce into low-Ag SnAgCu solder alloy can depress the decreasing of the properties of solder alloy when decreasing Ag content to a certain extent. To consider the costs and the comprehensive performance of SnAgCu solder alloy, Sn_1.0Ag0.7CuX has the best properties in all solder alloys tested, and Sn0.7Ag0.7Cu solder alloy also has great further research value.Solidification cracks exist in significant numbers in the miniature Sn_3.0Ag0.5Cu solder joints on the tested PCB. Test method II can simulate the solidification crack formation and regenerate the solidification cracks in lead free solder joints. Solidification crack susceptibility of the solder was evaluated using the total crack length of the solder joint. Adding trace amounts of Ni or Ce can depress the solidification crack formation of the solder joints,especially for Ni additions. P addition aggravated the solidification crack formation of Sn_3.0Ag_0.5Cu solder joints, which is not conducive to improve the reliability of solder joints.