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.