한국주조공학회

Microstructure and mechanical properties of Sn-3. 1 wt?/c-Ag-6.9 wt.%Bi system solders on Cu-substrate were studied. The Sn- 3.l wt.%Ag-6.9 wt.%Bi alloy was designed by phase diagram and chemical properties and was prepared by melting in argon atmosphere. The mechanical properties of solder/Cu joints were examined by shear strength test, and also creep test. The micro- structure of Sn-3.1 wt.%Ag-6.9 wt.%Bi alloy consists of Bi-rich phase and Ag3Sn precipitate in [3-Sn matrix phase. The shear strength of the joint was decreased with aging treatment. Crack path under shear test was through the solder. Similar crack path change mode was observed at the creep test of solder/Cu joint. The creep behavior of Sn-3.l wt.%Ag-6.9 wt.%Bi alloy repre- sented the inverse primary creep behavior at all test condition. It is suggested that the inverse primary creep behavior is induced from Bi solute atoms in Sn-matrix. The creep resistance of Sn-3.lAg-6.9Bi alloy is better than that of Sn-3.5 wt.%Ag alloy at all test conditions.

Sn-3.5Ag, Pb-free solder, Creep, Shear strength