Multilayer wiring substrate, and method of manufacturing the same

A multilayer wiring substrate comprising a laminate structure in which a plurality of resin insulation layers made primarily of a same resin insulation material, and a plurality of conductive layers are laminated alternately in multilayer arrangement, a plurality of first-main-surface-side connection terminals being disposed on a first main surface side of the laminate structure, a plurality of second-main-surface-side connection terminals being disposed on a second main surface side of the laminate structure, the plurality of conductive layers being formed in the plurality of resin insulation layers and interconnected by means of via conductors whose diameters increase toward the first main surface side of the laminate structure or the second main surface side of the laminate structure, wherein:

• the plurality of resin insulation layers are formed of a hardened resin insulation material that is not photocurable;
• a plurality of first openings are formed in an outermost resin insulation layer on the first main surface side of the laminate structure;
• the plurality of first-main-surface-side connection terminals include terminal outer surfaces and are disposed to correspond to the plurality of first openings, and peripheral portions of the terminal outer surfaces are covered by the outermost resin insulation layer on the first main surface side of the laminate structure;
• a plurality of second openings are formed in an outermost resin insulation layer on the second main surface side of the laminate structure;
• the plurality of second-main-surface-side connection terminals are disposed to correspond to the plurality of second openings and include terminal inner surfaces and terminal outer surfaces, the terminal inner surfaces including a peripheral edge that is rounded and peripheral portions of the terminal outer surfaces are covered by the outermost resin insulation layer on the second main surface side of the laminate structure;
• each of the plurality of second-main-surface-side connection terminals includes a copper layer having a concave portion that extends across the entire portion of the terminal outer surfaces that are exposed from the plurality of second opening;
• and
• a plating layer covering the concave portion of the copper layer.