Method and apparatus for inspecting printed wiring boards

摘要

In order that a slight positional deviation of a plated through hole such as having no substantial effect on the function of wiring should not be optically detected as a defect in a printed wiring board, the plated through hole is recognized as a part of the wiring pattern by making light representative of the plated through hole nearly equal in intensity to reflected light from the wiring pattern. This is achieved by illuminating the printed wiring board with light from the back side or by placing a reflector on the back side of the printed wiring board.