Design of Sn-Ag-Cu-Bi solder alloy and analysis on microstructure and properties

Sn-Ag-Cu-Bi new alloy was assessed by means of theoretical calculation, and the comparison experiment with typical Sn-Ag-Cu solde was carried out.The influences of the addition of Bi to lead-free solder on the microstructure, tensile property, wettability and melting char-acteristic were inveligated.The results show that the matrix grains of Sn-Ag-Cu-Bi are smaller.Bi separates out by the simple substance form dissemination.Compared to Sn-Ag-Cu eutectic alloy, the improvement of tensile strength and wettability of Sn-Ag-Cu-Bi lead-free solder can be achieved obviouslly.Melting temperature is measured with differential scanning calorimeter (DSC), and the melting point may reduce effectively by adding small amount of Bi, which the melting point of Sn3.0Ag0.5Cu4.5Bi lead-free solder is 212℃ and reduce temperature by about 6 degree compared to Sn3.0Ag0.5Cu system.The above calculation agrees with the experimental results well.