Wiring board

A wiring board comprising:

• a plurality of first insulating layers;
• a plurality of first wiring layers alternately formed in the plurality of first insulating layers;
• a plurality of first via wirings formed by filling metal in via holes formed in the plurality of first insulating layers, respectively;
• a plurality of second insulating layers formed on a first surface of an uppermost first insulating layer of the plurality of first insulating layers;
• a plurality of second wiring layers alternately formed in the plurality of second insulating layers at the first surface of the uppermost first insulating layer;
• a plurality of second via wirings formed by filling metal in via holes in the plurality of second insulating layers, respectively;
• and
• a solder resist layer formed on a second surface of a lowermost first insulating layer of the plurality of first insulating layers,
• wherein the plurality of first insulating layers are composed of non-photosensitive resin,
• wherein the plurality of second insulating layers, and the solder resist layer are composed of photosensitive resin, respectively,
• wherein a lowermost second wiring layer has a stacked structure of a seed layer and an electrolytic plating layer stacked on the seed layer, the seed layer being a stacked body of two different metals,
• wherein a first end surface of an uppermost first via wiring of the plurality of first via wirings embedded in the uppermost first insulating layer is exposed from the first surface of the uppermost first insulating layer and is directly connected to the seed layer of the lowermost second wiring layer, the lowermost second wiring layer in the plurality of second wiring layers being formed on the first surface of the uppermost first insulating layer and the first end surface of the uppermost first via wiring,
• wherein the first surface of the uppermost first insulating layer and the first end surface of the uppermost first via wiring are polished surfaces,
• wherein the first end surface of the uppermost first via wiring is flush with the first surface of the uppermost first insulating layer, and
• wherein the wiring density of the plurality of second wiring layers is higher than the wiring density of the plurality of first wiring layers,
• wherein the roughness of the first surface of the uppermost first insulating layer, on which the lowermost second wiring layer is directly formed, is smaller than the roughness of a surface of another first insulating layer of the plurality of first insulating layers on which one of the first wiring layers is directly formed,
• wherein the wiring board is a coreless substrate,
• wherein the thickness of the lowermost second wiring layer is thinner than that of an uppermost first wiring layer, and
• wherein the thickness a lowermost second insulating layer is thinner than the thickness of the uppermost first insulating layer.