An experimental vision system for SMD component placement inspection

An experimental system for automatic visual measurement of surface mount device (SMD) placement on printed circuit boards is described. Infrared illumination is used to aid in segmentation of component lead and solder pad images from the background. Best-fit lines through centroids of the lead and soldering pad images are calculated, from which the displacement and the angular orientation of the component relative to the pads is computed. Measurements are derived from a combination of slope and mean centroids from opposite sides of a device to reduce the effects of sensor resolution, missing pads, or missing leads. Experimental results of testing the accuracy of the system are reported. The results compare favorably with manufacturer's placement tolerance specification and with measurements made manually.<<ETX>>

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