PURPOSE: To improve the adhering state of a via to a pattern (pad) so as to improve the mechanically and electrically joined quality by reheating the junction face between the pattern (pad) and a conductive metal constituting the via by means of a heating means of a specific temperature after the via is filled with the metal.

CONSTITUTION: A semi-solidified green sheet 1 is formed by prebaking an unbaked green sheet with no wiring pattern formed on both surfaces and a fine hole is formed through the sheet 1 at a prescribed point where a via 2 is formed by using a laser beam or drill. The hole is filled with the powder of a conductive metal, for example, copper powder, and a wiring pattern 3 or patterns are formed on one surface or both surfaces of the sheet 2 where the via 2 is formed by a prescribed process. Then the junction face of the pattern (pad) 3 and filler is heated by using a non-contact type heating means, for example, a laser beam, etc., having a prescribed temperature from the surface of the pattern (pad) 3. Therefore, the adhered state is improved, the quality of mechanical and electrical joint is improved, and, accordingly, the reliability is improved.