Abstract
This paper describes an automatic solder joint inspection system by X-ray imaging. The following were developed for highly reliable inspection of J-lead and gull-wing lead solder joints : (1) An automatic inspection method for double side-mounted PCBs (Printed Circuit Boards) by micro-focus X-ray imaging and board tilting, (2) Enhancement of X-ray image of solder joints by logarithmic transformation of a detected image, (3) Fillet judgement by comparison between a detected image and a number of typical nondefective images selected by a clustering procedure, (4) Bridge determination by multi-step thresholding and comparison between pattern frequency distribution of a detected image and that of a nondefective image. The inspection system developed with these technologies had a defect detection rate of 100% with the smallest detectable defect being 50 μm.
