Printed wiring board

A printed wiring board, comprising:

• a core substrate comprising a core layer, a first conductor layer formed on a first surface of the core layer, a second conductor layer formed on a second surface of the core layer on an opposite side with respect to the first surface, and a plurality of through-hole conductors penetrating through the core layer and connecting the first conductor layer and the second conductor layer;
• a first build-up layer comprising a first resin insulating layer formed on a first surface side of the core substrate, an inner side first conductor layer formed on the first resin insulating layer, a plurality of first via conductors penetrating through the first resin insulating layer and electrically connecting the first conductor layer and the inner side first conductor layer, an outermost first resin insulating layer formed on the inner side first conductor layer, an outermost first conductor layer formed on the outermost first resin insulating layer, and a plurality of outermost first via conductors penetrating through the outermost first resin insulating layer and electrically connecting the inner side first conductor layer and the outermost first conductor layer;
• and
• a second build-up layer comprising a second resin insulating layer formed on a second surface side of the core substrate on an opposite side with respect to the first surface side of the core substrate, an inner side second conductor layer formed on the second resin insulating layer, a plurality of second via conductors penetrating through the second resin insulating layer and electrically connecting the second conductor layer and the inner side second conductor layer, an outermost second resin insulating layer formed on the inner side second conductor layer, an outermost second conductor layer formed on the outermost second resin insulating layer, and a plurality of outermost second via conductors penetrating through the outermost second resin insulating layer and electrically connecting the inner side second conductor layer and the outermost second conductor layer,
• wherein the core substrate and the first and second build-up layers are formed such that each of the first and second conductor layers, the inner side first and second conductor layers, and the outermost first and second conductor layers comprises a metal foil, a seed layer formed on the metal foil, and an electrolytic plating film formed on the seed layer, that the plurality of first via conductors comprises the electrolytic plating film of the inner side first conductor layer, that the plurality of second via conductors comprises the electrolytic plating film of the inner side second conductor layer, that the plurality of outermost first via conductors comprises the electrolytic plating film of the outermost first conductor layer, that the plurality of outermost second via conductors comprises the electrolytic plating film of the outermost second conductor layer, and that a ratio t1/T1 is smaller than 1, a ratio t2/T2 is smaller than 1, a ratio u1/U1 is smaller than 1, a ratio u2/U2 is smaller than 1, a ratio s1/S1 is larger than 1, and a ratio s2/S2 is larger than 1, where t1 is a thickness of the electrolytic plating film of the first conductor layer, T1 is a thickness of the metal foil of the first conductor layer, t2 is a thickness of the electrolytic plating film of the second conductor layer, T2 is a thickness of the metal foil of the second conductor layer, u1 is a thickness of the electrolytic plating film of the outermost first conductor layer, U1 is a thickness of the metal foil of the outermost first conductor layer, u2 is a thickness of the electrolytic plating film of the outermost second conductor layer, U2 is a thickness of the metal foil of the outermost second conductor layer, s1 is a thickness of the electrolytic plating film of the inner side first conductor layer, S1 is a thickness of the metal foil of the inner side first conductor layer, s2 is a thickness of the electrolytic plating film of the inner side second conductor layer, and S2 is a thickness of the metal foil of the inner side second conductor layer.