Wiring substrate

A wiring substrate, comprising:

• a core substrate comprising a core insulating layer, a first conductor layer formed on a first surface of the core insulating layer, a second conductor layer formed on a second surface of the core insulating layer on an opposite side with respect to the first surface, a first insulating layer formed on the first surface of the core insulating layer such that the first insulating layer is covering the first conductor layer, a second insulating layer formed on the second surface of the core insulating layer such that the second insulating layer is covering the second conductor layer, a third conductor layer formed on the first insulating layer, and a fourth conductor layer formed on the second insulating layer;
• a first build-up part formed on the core substrate and comprising a third insulating layer formed on the third conductor layer of the core substrate and a fifth conductor layer formed on the third insulating layer such that the fifth conductor laver includes a fifth plane part positioned directly above the fine wirings in the third conductor layer and connected to the conductor pattern connected to the first land part in the third conductor layer;
• and
• a second build-up part formed on the core substrate and comprising a fourth insulating layer formed on the fourth conductor layer of the core substrate and a sixth conductor layer formed on the fourth insulating layer such that the sixth conductor layer includes a sixth plane part positioned directly above the fine wirings in the fourth conductor layer and connected to the conductor pattern connected to the second land part in the fourth conductor layer,
• wherein the first conductor layer includes a first land part and a first plane part, the second conductor layer includes a second land part and a second plane part, the third conductor layer includes a plurality of fine wirings and a third plane part such that the first and third plane parts are substantially overlapping with each other and have substantially a same size, the fourth conductor layer includes a plurality of fine wirings and a fourth plane part such that the second and fourth plane parts are substantially overlapping with each other and have substantially a same size, the core substrate includes a through-hole conductor formed through the core insulating layer and connecting the first land part and the second land part, a first via conductor formed through the first insulating layer and connecting the first land part and the third conductor layer, a second via conductor formed through the second insulating layer and connecting the second land part and the fourth conductor layer, a third via conductor formed through the first insulating layer and connecting the first plane part and the third plane part, and a fourth via conductor formed through the second insulating layer and connecting the second plane part and the fourth plane part, the fine wirings of the third conductor laver are formed between a conductor pattern connected to the first land part and the third plane part in the third conductor layer, the fine wirings of the fourth conductor layer are formed between a conductor pattern connected to the second land part and the fourth plane part in the fourth conductor layer, the first conductor layer includes a connection plane part connecting the first land part and the first plane part such that the connection plane part connected to the first land part is positioned directly below the fine wirings in the third conductor layer, and the second conductor layer includes a connection plane part connecting the second land part and the second plane part such that the connection plane part connected to the second land part is positioned directly below the fine wirings in the fourth conductor layer.