Method of fabricating board having high density core layer and structure thereof

摘要

A circuit board includes a core layer substrate having a plated through hole filled with a dielectric material. The plated through hole has a sidewall coated with an inner electroless copper layer, and an electroplated metal layer plated on the inner electroless copper layer before the plated through hole is filled with the dielectric material. The outer portion of the filled plated through hole is thicker than the center portion and tapered toward the center portion to form a depressed surface on the filled plated through hole. The core layer substrate is covered with a patterned electroless copper layer and a patterned electroplated copper layer that connect with the inner electroless copper layer and electroplated metal layer of the plated through hole. The patterned electroplated copper layer forms a flat copper pad above the plated through hole.