CHARACTERIZATION AND OPTIMIZATION OF A WAVE-SOLDERING PROCESS

A case study for improving the quality of a wave-soldering process tha t produced printed circuit boards (PCB's) is presented. A mixed-level fractional factorial design was implemented in a high-volume productio n system during normal operational hours. The observed ordered-categor ical data from the bottom-side soldered leads were weighted to formula te the average, spatial uniformity, and dispersion process performance measurements. For lead classes like the integrated circuit and printe d grid array, a polynomial model was established using the least squar es method with weights provided by a dispersion function. The main-eff ect and interaction model terms were selected by forward and all-subse ts regressions. Production quotas, topside defects, presoldering board temperature, and variance models were used to set the constraints for simultaneously optimizing predictions from the average and the unifor mity models of all leads. A nonlinear optimization routine was used to determine the best and most robust settings for the continuous and di screte process variables. Results from a confirmatory experiment showe d an improvement of mean soldering quality by 33% and of uniformity by 39%.