Printed wiring board

A printed wiring board, comprising:

• a substrate;
• a first conductor layer formed on a first surface of the substrate;
• a second conductor layer formed on a second surface of the substrate;
• a through-hole conductor penetrating through the substrate such that the through-hole conductor is connecting the first conductor layer and the second conductor layer;
• a build-up layer formed on the second surface of the substrate and comprising a plurality of conductor layers and a plurality of insulating layers;
• and
• a first insulating layer formed on the first surface of the substrate such that the first insulating layer is covering the first conductor layer on the first surface of the substrate,
• wherein the substrate has a cavity penetrating through the first insulating layer and the substrate such that the cavity is exposing the build-up layer laminated on the second surface of the substrate, and the substrate and the insulating layers in the build-up layer are formed such that a difference between a thermal expansion coefficient of the substrate and a thermal expansion coefficient of the insulating layers in the build-up layer is set in a range of 15 ppm or less.