Ultraviolet laser system and method for forming vias in multi-layered targets

• US 5,593,606 A
• Filed: 07/18/1994
• Issued: 01/14/1997
• Est. Priority Date: 07/18/1994
• Status: Expired due to Term

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Inventors: Owen, Mark D., O'Brien, James N.
• Primary Examiner(s): Walberg, Teresa J.
• Assistant Examiner(s): Mills, Gregory L.
• Application Number:
  US08/276,797
• Time in Patent Office: 911 Days
• Field of Search: 219/121.61, 219/121.69, 219/121.71, 219/121.78, 219/121.8, 219/121.85, 219/121.7, 216/65, 216/66, 216/94, 427/554, 427/555, 427/556, 437/173, 264/400
• US Class Current: 219/121.71
• CPC Class Codes: B23K 2103/08 Non-ferrous metals or alloys
• CPC Class Codes: B23K 2103/10 Aluminium or alloys thereof
• CPC Class Codes: B23K 2103/12 Copper or alloys thereof
• CPC Class Codes: B23K 2103/14 Titanium or alloys thereof
• CPC Class Codes: B23K 2103/172 wherein at least one of the layers is non-metallic
• CPC Class Codes: B23K 2103/26 Alloys of Nickel and Cobalt and Chromium
• CPC Class Codes: B23K 2103/40 Paper
• CPC Class Codes: B23K 2103/42 Plastics B23K2103/16 takes precedence
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 2103/52 Ceramics
• CPC Class Codes: B23K 2103/54 Glass
• CPC Class Codes: B23K 26/384 of specially shaped holes
• CPC Class Codes: B23K 26/389 of fluid openings, e.g. nozzles, jets laser machining of inkjet nozzles B41J2/1634
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved
• CPC Class Codes: C23C 14/046 Coating cavities or hollow spaces, e.g. interior of tubes; Infiltration of porous substrates
• CPC Class Codes: C23C 14/048 using irradiation by energy or particles
• CPC Class Codes: C23C 14/28 by wave energy or particle radiation C23C14/32 - C23C14/48 take precedence
• CPC Class Codes: H05K 2203/107 Using laser light
• CPC Class Codes: H05K 2203/108 Using a plurality of lasers or laser light with a plurality of wavelengths
• CPC Class Codes: H05K 3/0035 of blind holes, i.e. having a metal layer at the bottom
• CPC Class Codes: H05K 3/0038 : combined with laser drilling through a metal layer
• CPC Class Codes: H05K 3/027 : the conductive material being removed by irradiation, e.g. by photons, alpha or beta particles
• CPC Class Codes: H05K 3/4076 : by thin-film techniques
• CPC Class Codes: H05K 3/427 : initial plating of through-holes in metal-clad substrates

Abstract

The output of a continuously pumped, Q-switched, Nd:YAG laser (10) is frequency converted to provide ultraviolet light (62) for forming vias (72, 74) in multi-layered targets (40). The parameters of the output pulses (62) are selected to facilitate substantially clean, simultaneous or sequential drilling or via formation in a wide variety of materials such as metals, organic dielectrics, and reinforcement materials having different thermal absorption characteristics in response to ultraviolet light. These parameters typically include at least two of the following criteria: high average power of greater than about 100 milliwatts measured over the beam spot area, a temporal pulse width shorter than about 100 nanoseconds, a spot diameter of less than about 50 microns, and a repetition rate of greater than about one kilohertz. The laser system (10) and method circumvent conventional depth of cut saturation limitations and can achieve an increased depth of cut per pulse in a target (40) formed of either single- or multi-layered material.

Claims

1. A method for laser processing a multi-layered target including at least two layers having different chemical compositions, comprising:

generating, from a non-excimer laser at a repetition rate of greater than about 1 kHz, high power ultraviolet laser output pulses having a predetermined spatial spot size, a wavelength shorter than about 400 nm, a temporal pulse width shorter than about 100 ns, and an average output power of greater than about 100 mW measured over the spatial spot size; and

applying the laser output pulses to the target so that the laser output pulses cleanly remove at least two layers within the spatial spot size.

2. The method of claim 1 in which the layers comprise any combination of at least two of the following chemical compositions:

organic dielectric material, reinforcement material, or metal or combination of metals.

3. The method of claim 2 in which the organic dielectric material comprises PTFE, polyimides, epoxies, BT, phenolics, cyanate esters, paper, cardboard, or combinations thereof;

the reinforcement material comprises glass, aramid fibers, KEVLAR, ceramics, or combinations thereof; and

the metal comprises aluminum, titanium, nickel, copper, tungsten, platinum, gold, molybdenum, palladium, silver, or combinations thereof.

4. The method of claim 3 in which the two layers comprise an organic dielectric material layer and a metal layer.

5. The method of claim 1 in which the wavelength of the laser output pulses is within a range of about 180-400 nm.

6. The method of claim 1 in which the target comprises at least three layers having different chemical compositions and optical absorption characteristics, and the laser output pulses sequentially remove all three layers.

7. The method of claim 1 in which the spatial spot size is less than about 50 μ

m across its surface diameter.

8. The method of claim 1 in which several pulses are employed to remove a spatial region of the target that is greater than 25 μ

m in diameter.

9. The method of claim 1 in which the laser output is generated by a solid-state laser.

10. The method of claim 9 in which the solid-state laser is selected from the group of Nd:

YAG, Nd;

YLF, Nd;

YAP, and Nd;

YVO₄.

11. The method of claim 9 in which the laser comprises YAG doped with holmium or erbium.

12. The method of claim 1 in which the layers have a combined depth of greater than 25 μ

m.

13. The method of claim 1 in which the spatial spot size defines a spot area that is smaller than and lies within a spatial region of the target, the method further comprising:

directing the laser output pulses sequentially to multiple positions associated with the spatial region to remove multiple amounts of target material corresponding to the spot areas.

14. The method of claim 13 in which the spatial region has a periphery and the multiple positions to which the laser output pulses are directed define a contiguous set of spot areas along the periphery of the spatial region to remove the target material within the spatial region and thereby produce a hole through the target material.

15. The method of claim 14 in which the target comprises at least an organic dielectric material, a reinforcement material, and a metal;

and in which the organic dielectric material comprises PTFE, polyimides, epoxies, BT, phenolics, cyanate esters, paper, cardboard, or combinations thereof;

the reinforcement material comprises glass, aramid fibers, Kevlar™

, ceramics, or combinations thereof; and

the metal comprises aluminum, titanium, nickel, copper, tungsten, platinum, gold, molybdenum, palladium, silver, or combinations thereof.

16. The method of claim 15 in which the spatial spot size is less than about 50 μ

m in diameter and the layers have a combined depth of greater than about 25 μ

m.

17. The method of claim 15 in which the target comprises a circuit board.

18. The method of claim 13 in which the spatial region has a periphery and a central portion and in which the multiple positions to which the laser output pulses are directed define a contiguous set of spot areas extending outwardly from the central portion along a path to the periphery of the spatial region to remove the target material from the spatial region and thereby produce a blind via in the target material.

19. The method of claim 18 in which the path is generally of spiral shape.

20. The method of claim 1 in which a single pulse cleanly removes material from at least two layers within the spatial spot size.

21. The method of claim 1 further comprising creating a blind via having a depth:

diameter aspect ratio that is greater than 1.

22. The method of claim 1 further comprising creating a via having a depth:

diameter aspect ratio that is greater than 2.

23. The method of claim 22 in which the via is a through hole.

24. The method of claim 1 in which the target comprises a circuit board.

25. The method of claim 1 further comprising:

forming a via having a depth of greater than 25 μ

m and having a diameter greater than that of the spatial spot size and smaller than about 300 μ

m.

26. The method of claim 1 in which the layers comprise any combination of at least two of the following chemical compositions:

inorganic reinforcement material, or metal or combination of metals, or organic dielectric material with or without organic reinforcement material.

27. A method for laser processing a multi-layered target including at least two layers having different chemical compositions, comprising:

generating high power ultraviolet laser output pulses having a predetermined spatial spot size, a wavelength shorter than about 400 nm, a temporal pulse width shorter than about 100 ns, and an average output power of greater than about 100 mW measured over the spatial spot size; and

applying the laser output pulses to the target so that at least one of the laser output pulses simultaneously removes material from at least two layers within the spatial spot size and the laser output pulses cleanly remove at least two layers within the spatial spot size.

28. The method of claim 27 further comprising:

forming a via having a diameter greater than that of the spatial spot size and smaller than about 300 μ

m, the via also having a depth of greater than 25 μ

m and the laser output pulses being generated at a repetition rate of greater than about 1 kHz.

29. The method of claim 28 in which the layers comprise any combination of at least two of the following chemical compositions:

inorganic reinforcement material, or metal or combination of metals, or organic dielectric material with or without organic reinforcement material.

30. The method of claim 29 in which the spatial spot size is less than about 50 μ

m in diameter.