US Patent 7781681 Multilayer printed wiring board

A multilayer printed wiring board includes a core substrate and a built-up wiring layer formed by alternately layering conductor circuits and insulating resin layers. The built-up wiring layer includes a first surface provided in contact with the core substrate and a second surface opposing the first surface and including a mounting area on which at least one semiconductor device is to be mounted. A first plurality of through-hole conductors is formed in a first portion of the core substrate which corresponds to the mounting area of the second surface, and a second plurality of through-hole conductors formed in a second portion of the core substrate which corresponds to another area of the second surface other than the mounting area. A pitch between the first plurality of through-hole conductors is smaller than a pitch between the second plurality of through-hole conductors. In one aspect, a ratio of pads to through holes directly below a processor core section of the semiconductor device is less that a number of pads to through holes in an area outside the processor core.