Method for forming stacked via-holes in printed circuit boards

1. A method for forming stacked via-holes, said method comprising:

providing a printed circuit board having a conductive trace formed on a side surface thereof;

forming a first metal-clad laminate on the side surface having the conductive trace;

forming a plurality of first metal micro-vias in a metal layer of the first metal-clad laminate;

forming a second metal-clad laminate on the surface of the metal layer of the first metal-clad laminate after having formed the first metal micro-vias in such metal layer thereof;

forming a plurality of second metal micro-vias in a metal layer of the second metal-clad laminate using a first laser, each second metal micro-via being located corresponding to a location of a respective first metal micro-via, a diameter of the second metal micro-via being larger than that of the first metal micro-via; and

removing corresponding resin layer portions of the first and second metal-clad laminates using a second laser, in order to yield stacked via-holes.

2. The method as claimed in claim 1 , wherein the provided printed circuit board is a high density interconnection flexible printed circuit board.

3. The method as claimed in claim 1 , wherein the provided printed circuit board is a high density interconnection rigid printed circuit board.

4. The method as claimed in claim 1 , wherein the first metal micro-vies are formed with an etching process.

5. The method as claimed in claim 1 , wherein the resin layer portions of the first and second metal-clad laminates are removed using a laser method.

6. The method as claimed in claim 1 , wherein, in the step for forming the second metal micro-vias, a given first metal micro-via acts as a reference point that the first laser can identify.

7. The method as claimed in claim 1 , further comprising a step of metallizing an inside surface of each stacked via-hole.

8. The method as claimed in claim 1 , wherein the stacked via-holes display a high concentricity between the respective micro-via holes of which each is composed.

9. The method as claimed in claim 1 , wherein the resin layer portions wholly exposed to the first and second metal micro-vias of the first and second metal-clad laminates are removed using the second laser.

10. The method as claimed in claim 1 , wherein the first metal-clad laminate is wetted with water before forming on the side surface of the printed circuit board.

11. The method as claimed in claim 1 , wherein the first metal micro-vias are formed with a laser process.

12. The method as claimed in claim 11 , wherein the second metal micro-vias are fanned by a Nd:YAG (Neodymium:Yttrium-Aluminum-Garnet) laser.

13. The method as claimed in claim 1 , wherein the metal layer of each of the first metal-clad laminate and the second metal-clad laminate is comprised of a highly conductive, oxidation resistant metal.

14. The method as claimed in claim 13 , wherein the highly conductive, oxidation resistant metal is comprised of copper.

15. The method as claimed in claim 1 , wherein the first laser for forming the second metal micro-vias is an ultraviolet laser or an infrared laser.

16. The method as claimed in claim 15 , wherein the second metal micro-vias are formed by a fourth harmonic Nd:YAG laser.

17. The method as claimed in claim 15 , wherein the second metal micro-vias are formed by a third harmonic Nd:YAG laser.

18. The method as claimed in claim 17 , wherein the resin layer portions of the first and second metal-clad laminates are removed using a carbon dioxide laser.

19. A method for forming binary stacked via-holes, each binary stacked via hole being composed of a first micro hole and a second micro hole stacked one on another, the first micro hole being composed of a first metal micro-via and a first film micro-via, the second micro hole being composed of a second metal micro-via and a second film micro-via, said method comprising:

providing a printed circuit board having a conductive trace formed on a side surface thereof;

forming a first metal-clad laminate comprising a first metal layer and a first resin layer on the side surface having the conductive trace;

forming a plurality of first metal micro-vias in the first metal layer of the first metal-clad laminate;

forming a second metal-clad laminate comprising a second metal layer and a second resin layer on the surface of the first metal layer of the first metal-clad laminate after having formed the first metal micro-vias in the first metal layer;

forming a plurality of second metal micro-vias in the second metal layer of the second metal-clad laminate by a first laser, each second metal micro-via being located corresponding to a respective first metal micro-via, a diameter of the second metal micro-via being larger than or equal to that of the first metal micro-via; and

removing parts of the second resin layer corresponding to the second metal micro-via and parts of the first resin layer corresponding to the first metal micro-via by a second laser to obtain a plurality of first film micro-vias in the first resin layer and a plurality of second film micro-vias in the second resin layer, thereby yielding a plurality of binary stacked via-holes.

20. The method as claimed in claim 19 , wherein the parts of the second resin layer wholly exposed to the second metal micro-vies and the parts of the first resin layer wholly exposed to the first metal micro-vias are removed by the second laser to obtain the first film micro-vies in the first resin layer and the second film micro-vias in the second resin layer, respectively.