Characteristics of the Sn-Pb eutectic solder bump formed via fluxless laser reflow soldering

In an attempt to develop a fluxless reflow solder bumping process, the effe cts of processing variables, which include energy input rate and time, and the shape of solder disk on the microstructure of the solder/Cu pad interfa ce and the shear strength of the joints were investigated. It was demonstra ted that a proper combination of the variables could lead to the formation of a spherical solder bump with shear strength comparable to that formed vi a the conventional reflow soldering process. In addition, the kinetics of C u pad dissolution into the solder during laser heating was modeled numerica lly to elucidate intermetallic formation mechanism at the solder/Cu pad int erface.