The study of interficial reaction during rapidly solidified lead-free solder Sn3.5Ag0.7Cu/Cu laser soldering

Interfacial intermetallic compound (IMC) is a necessary condition for the reliability of solder connection. In this study, the fiber lasers were used to solder rapidly-solidified lead-free solder Sn3.5Ag0.7Cu and Cu substrate, investigating the influence of laser soldering process parameters on the growth of IMC at the solid/liquid interface and finding the optimum parameters of laser soldering process. To simulate the IMC growth under actual service conditions, the solder joints under the condition p=50w, v=140mm/min were chosen to age at 150°C. Scanning electron microscopy (SEM) and EDS were used to observe IMCs morphology and analyze the composition of IMCs. The results showed that when the laser power was 50w, the thickness of IMCs formed at the interface decreased with the increase of scanning speed. And the morphology of IMCs also changed with the scanning speed. In the aging process, the thickness of the IMCs increased with the aging time, and the morphology became relatively flat. In addition, the thickness of IMCs at the rapidly-solidified Sn3.5Ag0.7Cu/Cu, which was thicker before the aging process, was thinner than that at the as-cast Sn3.5Ag0.7Cu/Cu in the subsequent aging process. The distribution of Ag₃Sn particles formed in the rapidly-solidified lead-free solders was more uniform, which suppressed the growth of Cu₆Sn₅ in the aging process better.