Lumped parameter mathematical model of laser soldering process and comparison of different optical soldering technologies.

摘要

The ever-increasing packaging density of components on printed circuit boards, and the subsequent reduction in size continues to pose great challenges to manufacturers. With the development of low-cost, high power diode lasers, laser soldering is becoming very attractive. One of the most important advantages of laser soldering is its ability to set process parameters to suit the requirements of individual solder joints. Due to its ability to focus energy precisely on the substrate with shorter heating time and a minimal heat affected zone, an outstanding solder joint quality is achieved.; In order to evaluate the solder joint quality, predict cycle time and select process parameters, it is necessary to model the thermal dynamic response of the solder joint.; A lumped-parameter mathematical model has been developed for the laser soldering process and validated experimentally by measuring the temperature of solder preforms placed on a lead on a printed circuit board when heated with laser. This model results in four first-ordered non-linear differential equations, which can be solved with MATLAB.; Further a comparison has been made between diode laser, carbon-dioxide (CO₂) laser and Soft-Beam (xenon-arc white light) soldering with respect to the solder joint quality, cycle time and input optical energy requirements.; In addition, scanning electron microscopic studies have been done to compare the microstructure of the solder and the formation of intermetallics, when the solder is melted with laser, soft beam and a conventional soldering iron. It is found that the diode laser soldered joint has a thinner intermetallic and finer grain size resulting in a higher mechanical strength.