Failure analysis on SAC305 large-size BGA components attached with SnPb solder

Defect of SAC305 large-size BGA components attached with SnPb solder was analyzed by metallographic examination, and the faulty welded joint was found at the center position of the component. In order to explain the failure mode, reflow process simulation on assembled PCB board was carried out by ANSYS, and the temperature distribution was deeply studied. It is shown that there a obvious difference between solder temperature and environment temperature. Also, the temperature at the center position is lower than that at the corner, and the time above liquidus at the center position is only 16s. Microstructure on the bonding interface was observed, and the reaction products were given at different position of solder balls. It is shown that an IMC layer with acceptable thickness is generated when the reflow process time is reasonable, otherwise a faulty welded joint occurs when the reflow process time is not enough. In the future, extending the reflow process time in an acceptable range should be considered to avoid the defects.