Method for forming stacked via-holes in a multilayer printed circuit board

1. A method for forming stacked via-holes in a multilayer printed circuit board, comprising the steps of:

providing a base circuit board having conductive traces;

attaching a first copper-coated-substrate having a first substrate and a first copper layer thereon and a second copper-coated-substrate having a second substrate and a second copper layer thereon onto the base circuit board in a manner such that the first substrate is brought into contact with the base circuit board and the second substrate is brought into contact with the first copper layer;

forming at least one first window in the second copper layer thereby yielding a residual second copper layer;

forming a protective layer on the residual second copper layer;

making at least one first hole in the second substrate through the at least one first window using a first laser treatment;

forming at least one second window in the first copper layer through the at least first hole;

removing the protective layer;

making at least one second hole in the first substrate through the at least one second window using a second laser treatment, thus allowing the at least first window, the at least first hole, the at least second window and the at least second hole to cooperatively form at least one part-finished stacked via-hole; and

plating a metal layer on an inner surface of the at least one part-finished stacked via-hole thereby forming at least one stacked via-hole.

2. The method as claimed in claim 1 , wherein the base circuit board is a single-layer circuit board.

3. The method as claimed in claim 1 , wherein the base circuit board is a multilayer circuit board.

4. The method as claimed in claim 1 , wherein the first copper-coated-substrate and the second copper-coated-substrate are each selected from a group consisting of resin coated copper foil and prepreg copper-clad foil.

5. The method as claimed in claim 1 , wherein the protective layer is comprised of a material selected from a group consisting of metal and resin.

6. The method as claimed in claim 5 , wherein the protective layer is comprised of a material selected from a group consisting of tin, nickel, tin-lead and inert metal.

7. The method as claimed in claim 1 , wherein the at least one first window is formed using a photolithographic process.

8. The method as claimed in claim 1 , wherein the at least one second window is formed using an etching process.

9. The method as claimed in claim 1 , wherein a diameter of the at least one first hole is equal to a diameter of the at least one first window.

10. The method as claimed in claim 1 , wherein a diameter of the at least one first hole is less than a diameter of the at least one first window.

11. The method as claimed in claim 10 , wherein the at least one first hole and the at least one first window are substantially concentric.

12. The method as claimed in claim 1 , wherein a diameter of the at least one second window is equal to a diameter of the at least one first hole.

13. The method as claimed in claim 1 , wherein the first laser treatment and the second laser treatment are performed using a carbon dioxide laser.

14. The method as claimed in claim 1 , wherein the stacked via-hole is a via-hole selected from a group consisting of blind vias, buried vias and through-hole vias.

15. The method as claimed in claim 1 , wherein the stacked via-hole is formed with at least two stepped structures therein.