| 摘要 |
PURPOSE:To make it possible to detect with high sensitivity a defective such as a lug crack occuring at the edge part of a detected body and its circumference which could not be detected because of a light shield board, by arranging a board-edge defect detection part near an edge detector provided to the light shield board. CONSTITUTION:Of a parallel light beam from laser light source 11 having passed through collimator 12c, direct light having passed through a region where no detected body 6 resides is focused on the focal point of Fourier transform lens 13, namely, center 14a of mask 14. Further, light diffracted by edge part 6a forms a diffracted pattern, shown by 14b, on mask 14. If a defective reside at edge part 6a and its circumference, patterns of a lug crack, pin-hole, etc., appear as shown by 14c and 14d. For the purpose, light shield zone 14E is formed on mask 14 in order to disallow the direct light and edge-part pattern to pass through, so that only light diffracted by the defective will be detected by photoelectric converter 15. Board-edge defective detection unit 16 like this is provided to light shield boards 3 and 3' to attain high-sensitivity detection of the defect at the edge. |
