Abstract: A step of forming bump pads on the surface of the substrate corresponding to the cavity region, and covering the whole surface with a second insulating layer, forming a copper barrier on the surface of a second insulating layer corresponding to the cavity region for protection of the second insulating layer, forming a third insulating layer, and forming a copper layer for electrical circuit. A mask is formed on the copper later of the external circuit so that only the cavity region is exposed. The cavity is formed by laser-drilling only the surface-exposed area of the third insulating layer. The bottom copper layer protects the second insulating layer and bump pads underneath from laser damages. The copper barrier is removed by chemical etch after the laser drill. The second insulating layer with the bottom surface exposed will be removed via sand blast process, exposing the bump pads fabricated.

Abstract: The present invention comprises a step of forming bump pads on the surface of the substrate, covering the whole surface with a second insulating layer, forming a copper barrier on the surface of a second insulating layer, forming a third insulating layer, and forming a copper layer for an electrical circuit. A mask is formed on the copper layer of the external circuit in such a way that only the region for the cavity is exposed. The cavity is formed by laser-drilling only the surface-exposed area of the third insulating layer. The copper layer at the bottom protects the second insulating layer and bump pads underneath from laser damages. The copper barrier is removed by chemical etch once the laser drill is over. The second insulating layer will be removed via sand blast process, exposing the bump pads which were fabricated in the earlier steps.