Patent ID: 7284323

Claim:
A method of forming conductive column in a fabrication of a circuit board, the circuit board comprising a dielectric layer formed thereon, the method comprising: forming a first blind hole in a first surface of the dielectric layer; forming a second blind hole in a second surface of the dielectric layer opposite to the first surface, a blind end of the first blind hole connecting to a blind end of the second blind hole, the first blind hole and the second blind hole constituting a through hole, wherein an inner diameter of the through hole near the first surface or the second surface is substantially larger than an inner diameter of the through hole near a middle portion of the through hole; and filling a conductive material in the through hole, wherein the conductive material fills with the through hole from a position wherein the blind ends of the first and second blind holes connect with each other and extends towards two ends of the through hole to form a conductive column.