Comparison between bulk and particle solder alloy on the performance of low-melting solder joints

Abstract

The influence of uniformity and small size solder particles on microstructure evolution and mechanical performances of low temperature soldering joints was investigated. First, experiments were set up to obtain uniform and small-size solder particles, which were compared to bulk solder joints by using reflow at temperatures of 100 °C and 120 °C. The preparation process was carried out on the solder alloy using sono-chemical cooling process method to synthesize the uniform and small-size solder particles. Secondly, scanning electron microscopy (SEM) was utilized to obtain the morphology of solder particles, and x-ray diffraction (XRD) was used to prove that the prepared solder particles had good purity and crystallinity. We found that the size effect and uniformity of the particles would refine the morphology of the solder joints, and reduce the intermetallic compound (IMC) thickness by 17%. Thirdly, the shear strength of solder particles/Cu joints at different reflow temperatures of 100 °C and 120 °C was found to be greater than that of bulk solder. Also, the liquid solder has good flowability since the particles have extremely low surface energy, resulting in the reduction of contact angle. Furthermore, the bulk solder/Cu joints were found to fracture partially between IMC and the solder, mainly between the solder matrix, but in the solder particles/Cu joints, it fractured completely inside the solder matrix, which suggests that the uniformity of small-size particles has changed the fracture mode of the joint.