Abstract: 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.

Abstract: A method for forming a conducting metal layer on an inorganic substrate is to heat the inorganic substrate accommodated in a vacuum vessel of sputtering device in which a high degree of vacuum is attained, to lead into the vacuum vessel a discharge gas as regulated to be at a predetermined pressure, to apply a high frequency power with the inorganic substrate made as a target, to interrupt the power to regulate the discharge gas to be at a predetermined pressure relatively low, and to apply DC power with a conductive metal member made as a target for thereby forming the conducting metal layer on the inorganic substrate. The metal layer formation on the inorganic substrate is thereby simplified enough for improving the producibility in industrial scale and is still capable of attaining a satisfactory bonding strength between the metal layer and the substrate.

Abstract: Superior polyimide prepolymers particularly suitable for fabrication of multi-layer printed boards are produced by reacting unsaturated bisimides with diamines to consist essentially of 41-55% of unreacted reactants, 39-54% of components having a molecular weight of between 400 and 15,000, and 3.0-6.8% of components having a molecular weight of more than 15,000. The resulting prepolymers enable the preparation of their solution having enough working life for successfully impregnating a given substrate therewith in the preparation of prepregs.