Printed Circuit Board Through-Hole Inspection Using Video Camera
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Through-holes of multilayer printed circuit boards are inspected for epoxy smears by a video camera with its optical axis slanted with respect to the vertical axis. With the camera oriented in this manner, the through-hole is sensed as an elliptical image. To facilitate image processing, the elliptical image is coordinate-translated to a rectangular image. Fig. 1 shows the inspection arrangement. The printed circuit board to be inspected is placed on a frosted glass support plate illuminated from below. The optical axis of the video camera is oriented at an angle of 15o-45o with respect to vertical axis. Fig. 2A shows an elliptical through-hole image as viewed from the camera. As shown in Fig.