US Patent 7284323 Process of fabricating conductive column

A fabrication process of a conductive column suitable for a fabrication of a circuit board. The circuit board comprises a dielectric layer. A first blind hole is formed in the dielectric layer from a second surface opposite to the first surface, wherein the blind end of the first blind hole connects to the blind end of the second blind hole. The first blind hole and the second blind hole constitute a through hole. The through hole is formed in an hourglass shape such that an inner diameter of the through hole near the first or the second surface is substantially larger than an inner diameter of the through hole near a middle portion of the through hole. A conductive material is filled in the though hole to form a conductive column.