Development of an automated X-ray inspection method for microsolder bumps

BGA, CSP, and flip-chip packages are widely used in printed circuit boards. These packages use an array of solder bumps as the electrical junction. To reduce the failures in manufacturing and after long-term use, solder bump inspection is strongly required for quality control. In this paper, we propose an automated inspection method for microsolder bumps using an X-ray image. The thickness, area, volume, and void of the solder bumps were automatically inspected by this method. We introduced some correction techniques to reduce the effects of variation in the X-ray intensity and the spatial nonuniformity in the image. In this experiment, we evaluated accuracy and repeatability. The results demonstrated that the accuracy and repeatability met the requirement for online inspection. In conclusion, our automated method for inspecting microsolder bumps may be useful in practice.