Wiring board and manufacturing method for the same

A manufacturing method for a wiring board, the manufacturing method comprising:

• forming a groove and a recessed portion having a width wider than the groove, at an upper surface of an insulation layer;
• forming an underlying metal layer at the upper surface of the insulation layer, an inner surface of the groove, and an inner surface of the recessed portion;
• forming at least one plating resist having a width narrower than the width of the recessed portion, on the underlying metal layer in the recessed portion;
• forming a first electrolytic plating layer on the underlying metal layer exposed from the plating resist;
• removing the plating resist from on top of the underlying metal layer;
• forming a second electrolytic plating layer on the first electrolytic plating layer and on the underlying metal layer;
• and
• removing portions of the first electrolytic plating layer, the second electrolytic plating layer, and the underlying metal layer to form a first wiring conductor that fills the groove and is made of a first electrolytic plating metal derived from the first electrolytic plating layer or a second electrolytic plating metal derived from the second electrolytic plating layer, and a second wiring conductor that fills the recessed portion and is made of the first electrolytic plating metal derived from the first electrolytic plating layer and the second electrolytic plating metal derived from the second electrolytic plating layer, wherein the second wiring conductor comprises a first portion and a second portion located adjacent to and integrally with the first portion, and a plurality of voids each having a maximum length in a range from 50 nm to 1 μm are located at a boundary between the first portion and the second portion.