The tensile properties, shear properties and creep properties of newly developd Pb-free Sn-based solder alloys, whick are Sn-6.9Bi-3.1Ag and Sn-8Bi-5In-3Ag, were investigated at temperature ranged from room temperature to 120℃. The Sn-6.9Bi-3.1Ag and Sn-8Bi-5In-3Ag Lead-free alloys were designed by computer calculations based on equilibrium thermodynamics and were prepared by induction melting. The tensile tests were performed using bulk specimens in as-cast condition. The shear tests and creep tests were performed using modified double-lap joint specimens. The tensile tests, shear tests and creep tests of Pb-Sn eutectic solder were also performed in order to compare with the mechanical properties of lead-free solders. The microstructure of Sn-6.9Bi-3.1Ag and Sn-8Bi-5In-3Ag alloys are consisted of Bi-rich phase and $Ag_3Sn$ precipitate in β-Sn matrix phase. The tensile strengths of Sn-6.9Bi-3.1Ag and Sn-8Bi-5In-3Ag are higher than that of 60Sn-40Pb alloy due to the precipitation hardening effect of Bi-rich phase, $Ag_3Sn$ precipitate and solid solution hardening of Bi, In atom while the tensile elongation is lower than that of 60Sn-40Pb alloy due to birttle Bi-rich phase in β-Sn matrix. The shear strength of Sn-6.9Bi-3.1Ag and Sn-8Bi-5In-5Ag alloys in solder joint part is higher that of 60Sn-40Pb alloy, and the shear strain of these alloys is lower than that of 60Sn-40Pb alloy. The shear strain of Sn-6.9Bi-3.1Ag and 60Sn-40Pb alloy drastically decreased with increasing temperature from 100℃ to 120℃, because the interfacial bond strength between solder and intermetallic phase decreased with increasing temperature. The creep behavior of Sn-6.9BI-3.1Ag solder represented the inverse primary creep behavior at all test conditions. It is suggested that the inverse primary creep behavior is induced from Bi solute atoms in Sn-matrix. The creep activation energy of Sn-6.9Bi-3.1Ag alloy changed from 27.7kcal/mole above 100+Y to 16.1kcal/mole below 100+Y. The creep resistance of Sn-6.9Bi-3.1Ag alloy is better than that of 60Sn-40Pb alloy at all test conditions. This reason is that creep rate decrease by viscous dislocation glide controlled creep due to the presence of Bi-solute atoms in Sn-6.9Bi-3.1Ag alloy.
