Effects of Heating Factors on Brittle Fractures of Solder Joints by High Speed Shear Test

During the solder process, the components, distribution and thickness of intermetallic compound (IMC) between solder and pad can strongly affect the strength of solder joints, which eventually determine the brittleness of joints. In this paper, the influence of heating factor (Q_eta), defined as the integral of the measured temperature over the dwell time above liquids in the reflow profile on impact toughness of solder joints was evaluated quantitatively by means of high speed shear test (HSST) and conventional static shear test (SST), in which the shear rate was 1.5m/s and 8times10^-5m/s respectively. The results of high speed shear testing indicate that with heating factor increasing, the impact toughness of solder joints increases to a peak and then decreases. Therefore, it is obvious that Q_eta= 600~1200 sdegC is an optimal heating factor range for Sn96Ag3.5Cu0.5, in which the assembly exhibits the greatest impact toughness under HSST. The results also show that the failure mode and position of solder joints in these two tests are quite different, and the results of HSST appears more susceptible to the reflow process than that of SST.