Method of manufacturing printed circuit board

The invention relates to a method of manufacturing a printed circuit board. The method comprises a step of forming bump pads on the surface of the substrate corresponding to a cavity zone, covering the whole surface with a second insulating layer (such as an insulating layer etched by a sand spraying process, for example, resin free of glass fibers), forming a copper barrier for protecting the second insulating layer on the surface of a second insulating layer corresponding to the cavity zone, forming a third insulating layer on the whole upper surface of the copper barrier, and forming a copper foil electrical circuit on the third insulating layer. A mask is formed on the copper foil electrical circuit in the way that only the region for a cavity is exposed. The cavity is formed by laser-drilling only the surface-exposed area of the third insulating layer. The copper layer is disposed at the bottom so as to protect the second insulating layer and bump pads underneath from laser damages. The copper barrier is