Method for patterned metallization of a substrate surface

• US 5,576,073 A
• Filed: 04/21/1995
• Issued: 11/19/1996
• Est. Priority Date: 04/23/1994
• Status: Expired due to Fees

• Current Assignee: LPKF Laser & Electronics AG
• Original Assignee: LPKF Cad/Cam Systeme GmbH
• Inventors: Kickelhain, Joerg
• Primary Examiner(s): Gorgos, Kathryn
• Assistant Examiner(s): Mayekar, Kishor
• Application Number:
  US08/427,093
• Time in Patent Office: 578 Days
• Field of Search: 427/98, 427/555, 427/443.1, 427/304, 427/306, 216/65
• US Class Current: 427/555
• CPC Class Codes: C23C 18/1605 by masking
• CPC Class Codes: C23C 18/206 Use of metal other than noble metals and tin, e.g. activation, sensitisation with metals sensitising with tin C23C18/285, sensitising with noble metals C23C18/30
• CPC Class Codes: C23C 18/2066 Use of organic or inorganic compounds other than metals, e.g. activation, sensitisation with polymers
• CPC Class Codes: C23C 18/30 Activating or accelerating or sensitising with palladium or other noble metal
• CPC Class Codes: H05K 2203/0709 Catalytic ink or adhesive for electroless plating catalyst filler H05K2201/0236
• CPC Class Codes: H05K 2203/107 Using laser light shaping a substrate by laser ablation H05K3/0026
• CPC Class Codes: H05K 2203/1407 Applying catalyst before applying plating resist
• CPC Class Codes: H05K 3/0017 Etching of the substrate by chemical or physical means
• CPC Class Codes: H05K 3/0023 by exposure and development of a photosensitive insulating layer
• CPC Class Codes: H05K 3/184 using masks
• CPC Class Codes: H05K 3/3452 Solder masks

Abstract

A method for patterned metallization of the surface of substrates (1), particularly circuit boards, using electromagnetic radiation (5) in which an electrically nonconducting prime coat (2) is applied full-surface to the substrate (circuit board 1); an electrically nonconducting cover coat which is easily ablated by electromagnetic irradiation (5) in the ultraviolet range is applied full-surface to the prime coating (2), the cover coat (4) being applied in a thickness that is at least equal to the thickness of the metal layer that is to be applied; the cover coat is removed from partial areas by the action of electromagnetic irradiation (5) in the ultraviolet range to form patterns (6) with sharp and steep flanks (7) and expose the prime coat (2); and in the area of the exposed patterns (6) on the prime coat (2), a metal layer is applied, guided by the flanks (7), in a reducing bath. The method facilitates patterned metallization with a very high resolution on the surface of substrates, without the need for an etching procedure.

Claims

1. A method for patterned metallization of a substrate surface, said method comprising the steps of:

applying an electrically nonconductive catalyst-containing prime coat to the full surface of the substrate;

applying an electrically nonconductive cover coat to the full surface of the prime coat, said cover layer being removable by electromagnetic radiation in the ultraviolet range and being applied in a thickness of at least 1 μ

m and approximately equal to that of a metal layer to be deposited in the metallization;

ablating partial areas of the cover coat by electromagnetic irradiation in the ultraviolet range to form a pattern having sharp and steep flanks and expose the prime coat in said partial areas; and

depositing a metal layer on the exposed prime coat in said partial areas to form electrical conductors, the deposition of the metal being effected in a reducing bath and being guided by the flanks of the cover layer pattern.

2. A method according to claim 1, wherein said substrate is a circuit board.

3. A method according to claim 1, wherein said removing step is carried out by patterned exposure of the cover coat in said partial areas to electromagnetic irradiation by an excimer laser.

4. A method according to claim 3, wherein said removing step is carried out by patterned exposure of the cover coat to radiation from a krypton fluoride excimer laser with a wavelength of 248 nm.

5. A method according to claim 1, wherein the metal layer is deposited in the partial areas of the pattern up to the level of the surface of the cover coat adjacent them.

6. A method according to claim 1, wherein the cover coat is formed of a polymer.

7. A method according to claim 6, wherein said polymer is a polyimide or a polyethylene.

8. A method according to claim 6, wherein the polymer is heat-stable under conditions of soldering.

9. A method according to claim 1, wherein the conductors formed in said partial areas have a width in the range from about 0.3 μ

m to about 1 μ

m.

10. A method according to claim 1, wherein the conductors formed in said partial areas are spaced apart a distance in the range from about 0.3 μ

m to about 1 μ

m.

11. A method according to claim 1, wherein said ablating step is carried out by exposing the cover coat through a mask.

12. A method according to claim 1, wherein said ablating step is carried out by projecting an image onto the cover coat.

13. A method according to claim 1, wherein said ablating step is performed by means of focused electromagnetic irradiation.

14. A method according to claim 1, wherein said ablating step is performed by means of a focused laser beam.

15. A method according to claim 1, wherein the prime coat contains components which exert a chemically reducing action during the subsequent metal layer depositing step.

16. A method according to claim 1, wherein the prime coat is applied to the substrate surface by brushing, spraying, printing, immersion or precipitation.