Microsoldering with short-pulsed IR laser

A theoretical and experimental study investigates the minimum obtainable volume of soft soldered contacts to be made with an IR laser source. The parameters include the heat transfer and the surface energy of the liquid solder pool. The process is separated into a preheating step for the flux activation in the fine-grained solder paste, and into a melting and an overheating step. After switching-off the laser power a constitutional undercooling with the formation of intermetallics takes place. The optimization scheme considers the sensitivity of the calculated solder geometry with respect to the thermodynamic parameters for the state of equilibrium between power input, heat conduction and reflection of radiation.