Patent ID: 7250355

Claim:
A method of producing a multi-layered circuit substrate for a semiconductor device, said process comprising: forming connecting pads on a metal plate; successively laminating a plurality of resin layers, on which conductive patterns are formed, on said metal plate, so that each said resin layer is provided with respective vias for electrically, mutually connecting the conductive patterns on the resin layers and also electrically connecting the conductive patterns with said connecting pads, to form a multi-layered circuit substrate body having first and second surfaces, said first surface thereof attached to said metal plate, said first surface defining a semiconductor element mounting surface, and each said via having a bottom thereof at a side of said first surface and being open toward a side of said second surface; attaching a plate member, a rigidity thereof being higher than that of said multi-layered circuit substrate body, to said second surface thereof; and removing said metal plate so that said semiconductor element mounting surface is exposed.