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Physical Properties of the Sn-Ag-Cu-In-X (Zn,Bi) Solder alloys

With the development in microelectronic and surface mount technology, the Sn-Pb packaging materials commonly used in electronic industry will be restricted because of the lead's toxicity, the study on lead-free solders is becoming a new focus. In this article, Sn-3Ag-0.5Cu-6In-X(Zn,Bi) (x=0,1,3,5,8) packaging materials were prepared by casting method under vacuum condition. The effect of Zn and Bi elements on the physical properties of Sn-3Ag-0.5Cu-6In alloy was systematically studied, including melting temperature, electrical conductivity, thermal expansibility and wettability. Results show that proper Zn in Sn-3Ag-0.5Cu-6In alloy decreases the melting temperature and improves the electrical conduction obviously. The melting temperature is 208.7degC while Zn content is 3%, and the electric resistivity reduces about 15% while Zn content is 5%. With the addition of Zn element, the wettability decrease, but the thermal expansion coefficients didn't change clearly. Bi is an effective alloying element on decreasing the melting temperatures and improving the wettability in Sn-3Ag-0.5Cu-6In alloy, When Bi content is 8%, the melting temperature is 185.5degC, near the level of the Sn-37Pb eutectic alloy. The electrical conductivity and thermal expansion are increased when Bi content is proper, for instance, the electrical resistivity of the alloys can reduce about 10% and 20%, while the Bi content is 3% and 8%. The alloy with 5%Bi addition has the lower thermal expansion coefficient, which is better than conventional Sn-37Pb alloy.