Method of manufacturing a printed circuit board

摘要

In a method of manufacturing a printed circuit board, a photoresist layer is formed on a three-dimensionally molded substrate through a conductive layer. A planar photomask which is provided with a mask pattern and a light-transmissive pattern is placed in front of the photoresist layer. A parallel light beam is radiated to the photomask in order to give to the photoresist layer an exposed pattern of an intended width "L" in correspondence to the light-transmissive pattern. In the present invention, the light-transmissive pattern is configured so as to satisfy the following relations: when D=0, W/L=1, when D>0, W/L<1, wherein "W" is a width of the light-transmissive pattern for forming the exposed pattern of the intended width "L", and "D" is a distance between the light-transmissive pattern and the photoresist layer. The photoresist layer of the exposed or an non-exposed pattern is removed to leave a patterned area of the conductive layer without the photoresist layer. A circuit pattern is formed on the substrate in accordance with the patterned area of the conductive layer. Since the light-transmissive pattern of the photomask is configured so as to reduce the influence of diffraction of the parallel light beam at the light-transmissive pattern, the circuit pattern can be precisely formed on the substrate.