US Patent 7183491 Printed wiring board with improved impedance matching

To provide a printed wiring board where the impedance between pads through which differential signals pass has been set to a predetermined standard value. The printed wiring board includes a first conductor layer extending over an area excluding a hole formed for each pad group and filled with a dielectric, and a second conductor layer extending over an area containing areas facing the hole. The hole encompasses a plurality of areas facing predetermined respective pads which are adjacent to each other and which form the pad group from among the plurality of pads.