Reaction kinetics between SnPb eutectic solder and Au/Ni/Cu pad during laser reflow

The laser reflow is a potential technique in bumping SnPb eutectic solder in an electronic packaging area. Scanning electron microscopy (SEM) was used to analyze the interfacial reaction between 63Sn37Pb and Au/Ni/Cu pad during the laser reflow. In addition, the kinetics of Au layer dissolution and diffusion into the solder during laser heating was modeled numerically to elucidate the formation mechanism of the intermetallic phase at the solder/Au pad interface. Results showed that the 63Sn37Pb solder reacted with the Au layer in the Au/Ni/Cu pad to form Au-Sn intermetallics soon after the solder was melted by the laser, and the morphology and the distribution of intermetallic compounds at the interface were strongly influenced by laser input energy. With the increase of laser input energy, the Au-Sn intermetallics changed from the continuous layer into needle-like articles. Finally, AuSn₄ disappeared at the interface, and the even distribution of small particles.