Process for forming a bump structure and bump structure

A method for forming a bump structure and a bump structure for conductive interconnection with another element having at least one of microelectronic devices or wiring thereon, used as an electric connection in an electronic circuit, includes the steps of forming a mandrel by steps including forming at least one opening extending through a bump-forming die body in the thickness direction thereof and positioning a bump-forming die lid on a surface of the bump-forming die body so as to cover one end of the opening and to thereby define a bump-forming recess. The bump-forming die body may be comprised of a metal sheet. A metal layer is formed at least on an inner surface of the bump-forming die lid exposed within the bump-forming recess. The mandrel is removed so as to expose the metal layer and form a bump structure.