Vibration Fracture Behavior of Sn-Bi Solder Alloys with Various Bi Contents

Abstract

This study investigated the resonant vibration properties of Sn-Bi solders with hypoeutectic (Sn-10 mass%Bi and Sn-30 mass%Bi, referred to as 10Bi and 30Bi respectively) and eutectic (Sn-58 mass%Bi, referred to as 58Bi) compositions. Results show that the damping capacity of the 58Bi specimen with continuous distributed eutectic Bi phase was higher than Sn-30Bi, and higher than Sn-10Bi with isolated Bi precipitates. Also, the specimens with higher damping capacity possessed greater vibration fracture resistance under a fixed vibration force. When the vibration was conducted with a constant initial deflection, the vibration fracture resistance decreased in the order of 30Bi, 10Bi and 58Bi. Interfriction at eutectic Sn/Bi phase boundaries can be regarded as an effective mechanism in absorbing vibration energy. In the case of 58Bi and 30Bi, the crack propagated mainly along eutectic-Bi/Sn interfaces and occasionally through the eutectic Bi. As for the 10Bi specimen, the crack propagation path was mainly intergranular and this can be attributed to fast crack linking by Bi precipitates on the eutectic cell boundaries. In addition, microstructural coarseness caused by artificial aging reduced the area and continuity of eutectic Sn/Bi interfaces and thus decrease damping capacity and change the crack propagation morphology.