The Automatic Visual Inspection of Printed Circuit Boards

Printed circuit boards are scanned with a CCD linescan camera and a motorised table, under the control of a microcomputer. The camera signal is thresholded to produce a binary image of the track pattern, and this image is processed further in the microcomputer. The processing consists partly of comparisons against a stored master track pattern, and partly of an examination of the scanned track pattern alone to detect anomalies such as whiskers and broken tracks. The system will detect all defects so far presented to it, with an acceptable false alarm rate.