Cleaning process development and optimization in the surface mount assembly line of power modules

Abstract

The cleaning process in the surface mount assembly line of power modules had been found to insufficiently remove solder flux residue from printed circuit board (PCB) assemblies after the process of reflow soldering. This thesis details the development of an optimized cleaning process that effectively removes solder flux residue from PCB assemblies. The first stage of this study involves the experimental validation of root cause of process ineffectiveness. A novel visual inspection based grading scale is developed to quantify the amount of residue present. Using the grading scale optimal process parameters were identified and studied. The study finds that power modules are most effectively cleaned in a saponifier based cleaning solution using ultrasonic agitation. Power modules are completely cleaned when washed in an ultrasonic bath at 60°C for 7 minutes, in a saponifier based cleaning solution that is 5% concentration by volume.