Comparison of Joint Characteristics of Micro Solder Balls for Semiconductor Packaging by Laser-Assisted Bonding and Reflow Processes

In this study, the bonding characteristics of 100 μm diameter micro solder balls were comparatively analyzed according to the bonding process. Laser-assisted bonding (LAB) and vacuum reflow were applied, and an additional reflow process was conducted to simulate actual package assembly conditions. Accordingly, four bonding conditions were evaluated: LAB, LAB followed by reflow, vacuum reflow, and reflow followed by reflow. Cross-sectional microstructures were observed, and the thickness of intermetallic compounds (IMCs) was analyzed. In addition, shear strength measurements and fracture surface analyses were performed. The IMC thicknesses were 0.7, 2.3, 2.5, and 3.0 μm for LAB, LAB followed by reflow, vacuum reflow, and reflow followed by reflow, respectively. The shear strengths were 536.0, 520.3, 504.7, and 512.2 mN for the respective bonding conditions, showing no significant difference. Fracture analysis revealed that failure occurred within the solder matrix in all samples, indicating that the mechanical properties of the solder dominated rather than the interfacial strength. These results confirm that the LAB process is suitable for micro solder ball bonding applications and that it can effectively suppress IMC growth under multiple reflow conditions.