Study on the solid-solid interfacial reaction behavior of solder micro bump prepared by laser assisted bonding

The laser assisted bonding (LAB) technology has become a replaceable soldering method for 3D packaging technology through which the side effects of traditional reflow soldering are minimized. In this study, Sn-3.0Ag-0.5Cu (wt.%) solder, a widely used lead-free solder, was soldered on the Ni-P substrate through LAB with two laser energies (6.5 mJ, 7.5 mJ) and reflow soldering, respectively. The average thickness of interfacial IMC in Ni-P/SAC305 micro bumps after LAB at 7.5mJ is 0.33 µm, which is higher than that (0.26 µm) in Ni-P/SAC305 micro bumps after LAB at 6.5mJ. Reflow soldering formed an uneven and a thick IMCs layer (1.53 µm) at the Ni-P/SAC305 interface compared to LAB. Subsequently, three types of micro bumps experienced solid-solid interfacial reaction. With the solid-solid interfacial reaction time increasing, the thickness of interfacial IMCs became thicker in three types micro bumps. After aging at 150 °C for 400 h, the interfacial IMCs in Ni-P/SAC305 (100 µm) micro bumps soldered by reflowing (2.22 μm) was significantly thicker than those in the in Ni-P/SAC305 (100 µm) micro bumps soldered by LAB with 6.5 mJ (0.75 μm), and 7.5 mJ (1.15 μm). Therefore, the laser assisted bonding (LAB) technology can effectively reduce the initial thickness of interfacial IMCs and improve the mechanical reliability of solder micro bumps after aging.