Patent ID: 7838779

Claim:
A wiring board comprising: a board-insulating film which has a thickness of 20 to 100 μm and in which a concave portion is formed on one face thereof; first wiring formed in said concave portion of said board-insulating film; second wiring formed on the other face of said board-insulating film; a via hole for connecting said second wiring and said first wiring formed on said board- insulating film to each other; the cross-section of said via hole in the thickness direction of said board-insulating film has a shape wherein widths of the shape on each end of the via hole are less than a width of the shape in a central portion of said via hole; and a 0.5 to 10 μm stepped portion being formed between an outer surface of said first wiring and the one face of said board-insulating film.