Comparative study of interfacial reaction and bonding property of laser- and reflow-soldered Sn–Ag–Cu/Cu joints

Laser soldering has attracted attention as an alternative soldering process for micro-soldering that minimizes the side effects of the conventional reflow soldering. In this study, Sn-3.0Ag-0.5Cu (wt.%) solder, a widely used lead-free solder, was bonded on the organic solderability preservative-prepared Cu substrate through laser soldering and reflow soldering, respectively. After the laser and reflow soldering processes, the intermetallic compound (IMC) layer of the joints was analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Laser soldering formed a thin and flat IMC layer in a short process time. Reflow soldering formed a relatively thick and uneven IMC layer at the interface compared to laser soldering. The different morphologies of the interfacial IMC layers formed by different soldering processes caused the IMC layer to grow differently in the isothermal aging treatment. Ball shear tests were performed to evaluate the mechanical properties of the solder joint. The shear strength of laser soldering that forms a thin IMC layer and fine microstructure was the highest immediately after soldering, but fell to a similar level of reflow-soldered samples after isothermal aging treatment. As the isothermal aging time increased, the brittle fracture area of reflow soldering increased. In the laser soldering, the ductile fracture modes are observed in the whole-aging period.