Effect of reflow temperature on the mechanical drop performance of Sn-Bi solder joint

Abstract

The effect of reflow peak temperatures from 160°C to 180°C on the mechanical drop performance of Sn-58Bi solder joint was studied. The mechanical drop performance was evaluated through the three point dynamic bending test in which the strain of PCB was step increased until the failure of daisy chain circuit was detected with 50 kHz sampling rate. The wetting behaviour of Sn-58Bi on Cu was investigated by wetting balance tests at various pot temperatures from 150°C to 190°C. The dynamic bending behaviour of solder joint decreased significantly with the decrease of temperatures from 170°C to 160°C. Microstructural observation and ball shear test results revealed that the decrease of joint area on Cu pad affected the deterioration of mechanical drop performance. From wetting balance tests at various pot temperatures, it was considered that the abrupt change in wetting activation energy at temperatures between 165°C and 170°C was responsible for the wetting behaviour on Cu pad and resultantly the mechanical drop performance of Sn-58Bi solder. It was also considered that the change of wetting activation energy was caused from the change of interface reaction mechanism which was due to the change in IMC formation behaviour with reflow peak temperature.