US Patent 7737368 Circuit board and method of manufacturing circuit board

A circuit board includes: a plurality of wiring layers; an insulating layer which insulates the plurality of wiring layers, the insulating layer containing a fibrous filler and a resin; and a conductor part formed on a sidewall of a via piercing through the insulating layer. The fibrous filler protrudes from the sidewall and is covered with the conductor part, with a length greater than the thickness of the conductor layer.