Wiring substrate

A wiring substrate, comprising

• a first build-up part comprising a plurality of first insulating layers, a plurality of first conductor layers and a plurality of first via conductors formed in the first insulating layers and connecting the first conductor layers;
• a second build-up part laminated to the first build-up part and comprising a plurality of second insulating layers, a plurality of second conductor layers and a plurality of second via conductors formed in the second insulating layers and connecting the second conductor layers;
• and
• a third build-up part laminated on the second build-up part on an opposite side with respect to the first build-up part and comprising a third insulating layer, a third conductor layer formed on the third insulating layer, and a plurality of third via conductors formed in the third insulating layer and connecting the third conductor layer and one of the second conductor layers in the second build-up part such that the second build-up part includes a greater number of conductor layers than the third build-up part,
• wherein the plurality of first conductor layers in the first build-up part and the plurality of second conductor layers in the second build-up part include a plurality of wirings such that a wiring width and an inter-wiring distance of the wirings in the first conductor layers are smaller than a wiring width and an inter-wiring distance of the wirings in the second conductor layers, an aspect ratio of the wirings in the first conductor layers is in a range of 2.0 to 4.0, the wiring width of the wirings in the first conductor layers is 3 μm or less, and the inter-wiring distance of the wirings in the first conductor layers is 3 μm or less, and the second and third build-up parts are formed such that the third insulating layer has a thickness that is greater than a thickness of each of the second insulating layers in the second build-up part and that the third conductor layer has a thickness that is greater than a thickness of each of the second conductor layers in the second build-up part.