A tiered-color illumination approach for machine inspection of solder joints

An experimental color vision inspection system for the detection of solder joint flaws on printed circuit boards is described. A tiered lighting arrangement is used to generate color contours on the solder joint for the detection and classification of defects including no solder, insufficient or excess solder, poor wetting of component leads or solder pad, and faults due to improper insertion of component leads. Each type of defect gives rise to a characteristic pattern of color contours which are processed using binary image techniques on each color plane of the image. Geometric descriptors measuring the shape of the color contours and the color level intensities of the solder joint images are used to identify each defect class. Statistical distributions are determined for each of the good and defective joint classes, from which a flaw detection and classification tree is derived. The performance of the system was tested on samples of commercially manufactured, wave-soldered circuit boards