Method for producing wiring substrate

A method for producing a wiring substrate provided with bumps protruding from a surface of the substrate, the method comprising:

• covering one side of a metallic base with an electrical insulating film and forming open holes in the insulating film so as to expose, at the bottoms thereof, the base;
• etching the base using the insulating film, having the open holes formed therein as a mask, to form concavities in the base;
• electroplating the interior face of each of the concavities, using the base as a plating power supply layer, with a first metal material, different from the material of the base, to form a barrier metal film on the interior face of each of the concavities;
• completely filling the concavities with a second, bump metal material different from said first metal material, by electroplating, using the base as a plating power supply layer;
• forming a barrier layer of a third metal material, different from said second metal material, on the surface of the bump material in each concavity, using the base as a plating power supply layer;
• forming a stack of a predetermined number of wiring patterns on the insulating film, the adjacent wiring patterns in the stack being separated from each other by an intervening insulating layer and being electrically connected to each other through vias formed in the intervening insulating layer and to the bump material in the concavities;
• and
• removing the base from the stack of wiring patterns having bumps, each bump having the barrier metal film thereon, and removing the barrier metal film from each of the bumps, thereby producing the wiring substrate.