Abstract: Disclosed is a flexible circuit board comprising a pair of conductive films and an insulating adhesive layer sandwiched therebetween. The adhesive layer contains conductive powder in such a concentration that no leakage current occurs between the films. For the production of the flexible circuit board, the adhesive layer is first formed on at least one of the conductive layers and then the conductive layers are bonded with the adhesive layer therebetween. For the formation of a through hole portion in the board, pressure is applied at a predetermined spot on the board throughout the thickness thereof, to form recesses on both sides thereof, thereby compressing the corresponding portion of the adhesive layer. This increases the concentration of the conductive powder contained therein, which causes the adhesive layer between the recesses to be conductive and serve as a through hole portion for electrically connecting the two conductive films.

Abstract: A method of manufacturing a circuit board, comprising the steps of providing an electric conductor on one surface of a substrate made of flexible synthetic resin and selectively irradiating a laser beam onto the substrate from the other surface of the substrate so as to sublimate a portion of the substrate such that an opening is formed on the substrate, with the electric conductor traversing the opening.