| 摘要 |
PURPOSE:To detect a defect over a non-light transmitting object with a high reliability by comparing an output of the first light detection system for detecting light from the transmission wavelength area of a substrate with an output of the second light detection system for detecting light from the absorption wavelength thereof. CONSTITUTION:A parallel light flux 5 diffuses through a printed circuit board 1 and reaches a metal plated layer 7 on the inner wall of a through hole 21 while a part thereof is leaked into a space within the hole 21 through a defect 8 and emitted outside being reflected on the wall surface of the layer 7. This leaked light in the wavelength area of a relatively small absorption is focused with a lens 3 and made incident to a photo detector 10 with a light filter 9. A part of light reflected on the surface of the substrate 1 from the light flux 5 passes through a space of the hole 21 and is incident to the lens 3. One part of the leaked light is incident to the photo detector 10 being reflected from a filter 9 while the other part thereof incident to a photo detector 11 transmitting the filter 9. Outputs of the detectors 10 and 11 are compared with a comparator 14 after amplified and then, the outputs give only the leaked light portion. |
