Printed wiring board having highly reliably via hole and process for forming via hole

• US 6,280,641 B1
• Filed: 05/28/1999
• Issued: 08/28/2001
• Est. Priority Date: 06/02/1998
• Status: Expired due to Term

• Current Assignee: Mitsubishi Gas Chemical Company Incorporated (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Gas Chemical Company Incorporated (Mitsubishi Electric Corporation)
• Inventors: Ikeguchi, Nobuyuki, Tanaka, Yasuo, Gaku, Morio
• Primary Examiner(s): Gulakowski, Randy
• Assistant Examiner(s): CHAUDHRY, SAEED T
• Application Number:
  US09/321,556
• Time in Patent Office: 823 Days
• Field of Search: 216/17, 216/18, 216/65, 216/67, 216/78, 298/46, 298/47, 298/52, 219/121.61, 219/121.7, 219/121.71, 427/96, 427/97, 427/98, 427/534, 427/554, 427/555
• US Class Current: 216/17
• CPC Class Codes: B23K 26/389 of fluid openings, e.g. nozzles, jets laser machining of inkjet nozzles B41J2/1634
• CPC Class Codes: H05K 2201/0112 Absorbing light, e.g. dielectric layer with carbon filler for laser processing
• CPC Class Codes: H05K 2201/0215 Metallic fillers
• CPC Class Codes: H05K 2201/0323 Carbon
• CPC Class Codes: H05K 2201/09518 Deep blind vias, i.e. blind vias connecting the surface circuit to circuit layers deeper than the first buried circuit layer
• CPC Class Codes: H05K 2201/0969 Apertured conductors
• CPC Class Codes: H05K 2203/0315 Oxidising metal
• CPC Class Codes: H05K 2203/095 Plasma, e.g. for treating a substrate to improve adhesion with a conductor or for cleaning holes
• CPC Class Codes: H05K 2203/1383 Temporary protective insulating layer
• 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 3/0055 After-treatment, e.g. cleaning or desmearing of holes
• CPC Class Codes: H05K 3/385 by conversion of the surface of the metal, e.g. by oxidation, whether or not followed by reaction or removal of the converted layer
• CPC Class Codes: H05K 3/429 Plated through-holes specially for multilayer circuits, e.g. having connections to inner circuit layers
• CPC Class Codes: Y10T 29/49155 Manufacturing circuit on or in base
• CPC Class Codes: Y10T 29/49165 by forming conductive walled aperture in base

Abstract

Disclosed are a printed wiring board having micro-via holes highly reliable for conduction and a method of making the micro-via hole by providing a coating or sheet of an organic substance containing 3 to 97% by volume of at least one selected from a metal compound powder, a carbon powder or a metal powder having a melting point of at least 900° C. and a bond energy of at least 300 kJ/mol on a copper foil as an outermost layer of a copper-clad laminate having at least two copper layers, or providing a coating or sheet of the same after oxidizing a copper foil as an outermost layer, irradiating the coating or sheet with a carbon dioxide gas laser at an output of 20 to 60 mJ/pulse, thereby removing a micro-via-hole-forming portion of at least the copper foil as the outermost layer, then irradiating micro-via-hole-forming portions of the remaining layers with a carbon dioxide gas laser at an output of 5 to 35 mJ/pulse to make a micro-via hole which does not penetrate through the copper foil in a bottom of the micro-via hole, and electrically connecting the copper foil as the outermost layer and the copper foil in the bottom of the micro-via hole with a metal plating or an electrically conductive coating composition.

Claims

1. The method of making a micro-via hole for electrically connecting a first copper foil as an outermost layer of a printed wiring board to a copper foil in a bottom of the micro-via hole with a carbon dioxide gas laser, the method comprising providing a coating or sheet of an organic substance containing 3 to 97% by volume of at least one member selected from the group having a melting point of at least 900°

C. and a bond energy of at least 300 kJ/mol, a carbon powder and a metal powder on a copper foil as an outermost layer of a copper-clad laminate having at least two copper layers, irradiating the coating or sheet with a carbon dioxide gas laser at an output of 20 to 60 mJ/pulse, thereby removing a micro-via-hole-forming portion of at least the copper foil as the outermost layer, then irradiating micro-via-hole-forming portions of a resin layer or a resin layer and a copper layer with a carbon dioxide gas laser at an output of 5 to 35 mJ/pulse to make a micro-via hole which does not penetrate through the copper foil in a bottom of the micro-via hole, and electrically connecting the copper foil as the outermost layer and the copper foil in the bottom of the micro-via hole with a metal plating or an electrically conductive coating composition, wherein the coating or sheet of the organic substance is a coating formed of a coating composition containing a mixture of at least one of a metal compound powder, a carbon powder or a metal powder with a water-soluble resin, or a sheet which is formed by applying the coating composition on one surface of a thermoplastic film and has a total thickness of 30 to 200 μ

m.

2. The method according to claim 1, wherein the first copper foil layer of the copper-clad laminate is oxidized, the coating or sheet of the organic substance is placed on the oxidized first copper foil surface as required, and the micro-via hole is made with a carbon dioxide gas laser.

3. The method according to claim 1, wherein, after the removal of the micro-via-hole-forming portion of the copper foil as the outermost layer with the carbon dioxide gas laser, the copper foil positioned below a copper foil as an outermost layer is removed partly in the thickness direction thereof with the carbon dioxide gas laser at an output of 20 to 35 mJ/pulse.

4. The method according to claim 1, wherein the first copper foil as the outermost layer, the copper foil in the bottom of the micro-via hole and a copper foil exposed on a wall surface of the micro-via hole are electrically connected through the micro-via hole.

5. The method according to claim 1, wherein a first copper foil as the outermost layer is surface-etched to remove the first copper foil partly in the thickness direction of the first copper foil and at the same time to remove a copper foil burr after making a micro via hole and removing the organic coating or sheet.

6. The method according to claim 5, wherein the first copper foil as the outermost layer is etched until it has a thickness of 3 to 7 μ

m.

7. The method according to claim 1, wherein the copper-clad laminate is a double-side copper-clad laminate or a multi-layered laminate.

8. The method according to claim 7, wherein the double-side copper-clad laminate comprises a substrate formed by impregnating an inorganic or organic woven or non-woven fabric with a thermosetting resin composition, either a dye or a pigment, and an inorganic insulating filler.

9. The method according to claim 8, wherein the thermosetting resin composition contains at lest one resin selected from the group consisting of an epoxy resin, a polyfunctional cyanate ester resin, a polyfunctional maleimide-cyanate ester resin, a polyfunctional maleimide resin, and an unsaturated-group-containing polyphenylene ether resin.

10. The method according to claim 1, wherein part of the copper foil surface in the bottom of the micro-via hole is removed and then an inside of the micro-via hole is treated in a gaseous phase to remove remaining resin layer, followed by wetting treatment.

11. The method according to claim 10, wherein the remaining resin is removed by the treatment in a gaseous phase and the wetting treatment.

12. The method according to claim 10, wherein the first copper foil as the outermost layer is etched before the treatment in a gaseous phase.

13. The method according to claim 10, wherein the treatment in a gaseous phase is plasma treatment or low-pressure ultraviolet light treatment.

14. The method according to claim 1, wherein the first copper foil and the copper foil layer in the bottom of the micro-via hole are electrically connected by filling at least 80% by volume of the micro-via hole with a copper plating.

15. The method according to claim 4, wherein the sheet of the organic substance is laminated on a first copper foil as the outermost layer under heat and under pressure.

16. The method according to claim 4, wherein the sheet of the organic substance is wetted 3 μ

m or less deep before the sheet is laminated on a first copper foil.