To mount electronic parts, etc., on the opposite surfaces to each other of all boards, by exposing to the end face of the board the cross sections of a plurality of laser blind via-holes arranged in a line respectively on the front and rear surfaces of the board.

Processing by etching copper foils 3, 4 laminated on both the surfaces of an insulation board 2, first and second terminal patterns 3a, 4a are formed to form insulator layers 5, 6 by applying insulators to both the surfaces of the insulation board 2 with the formed terminal patterns 3a, 4a. Then, projecting a laser beam onto the insulator layers 5, 6 from the predetermined positions of their surface sides, bottomed holes 7 are bored in them and the first and second terminal patterns 3a, 4a are exposed to the outside to form further conductor layers 8, 9 on the surfaces of the insulator layers 5, 6 and the inner walls of the bottomed holes 7. Next, processing these conductor layers 8, 9 by etching, laser blind via-holes 10, 11 are formed, and the insulation board 2 and the insulator layers 5, 6 are cut along a line passing the centers of the via-holes 10, 11 to expose their cross sections to the end face of the insulation board 2.