Method and apparatus for EMI shielding

• US 20010028558A1
• Filed: 02/28/2001
• Published: 10/11/2001
• Est. Priority Date: 02/28/2000
• Status: Active Grant

• Current Assignee: Laird Technologies Incorporated (DuPont de Nemours, Inc.)
• Original Assignee: APM SA de CV
• Inventors: McNally, Frank T., Rapp, Martin L., McFadden, Jeff
• Granted Patent: US 6,652,777 B2
• Time in Patent Office: Days
• US Class Current: 361/818
• CPC Class Codes: H05K 9/0015 Gaskets or seals
• CPC Class Codes: H05K 9/009 comprising electro-conductive fibres, e.g. metal fibres, carbon fibres, metallised textile fibres, electro-conductive mesh, woven, non-woven mat, fleece, cross-linked

Abstract

Disclosed are methods for manufacturing electromagnetic interference shields for use in nonconductive housings of electronic equipment. In one embodiment, the shield may include an electrically nonconductive substrate, such as a thermoformable film, coated with an electrically conductive element, such as an extensible ink or a combination of conductive fibers with an extensible film. In one embodiment, a compressible conductive perimeter gap gasket may be formed by using a form in place process.

Claims

1. A method of forming an EMI shield comprising the steps of:

(a) providing a thermoformable film comprising a first side and a second side;

(b) applying an extensible conductive coating to the thermoformable film;

(c) cutting the thermoformable film;

(d) thermoforming the thermoformable film into a three-dimensional shape; and

(e) applying a compressible EMI gasket to the thermoformable film, wherein steps (b) through (e) may be performed in any order.

2. The method of

claim 1

wherein the thermoformable film of step (a) is drawn from a roll.

3. The method of

claim 1

wherein the step (b) of applying an extensible conductive coating to the thermoformable film is selected from the group consisting of printing processes and film coating processes.

4. The method of

claim 3

wherein the group of printing processes and film coating processes comprise flexographic printing, screen printing, gravure printing, offset printing, letter press printing, pad printing, slot coating, flood coating, spray coating, and jet printing.

5. The method of

claim 1

wherein the step (b) of applying an extensible conductive coating to the thermoformable film comprises applying the extensible conductive coating to at least one of the first side and the second side of the thermoformable film.

6. The method of

claim 5

wherein the extensible conductive coating is applied substantially uniformly to the at least one of the first side and the second side of the thermoformable film.

7. The method of

claim 5

wherein the extensible conductive coating is applied selectively to at least one zone and not to another zone on the at least one of the first side and the second side of the thermoformable film.

8. The method of

claim 1

wherein the EMI gasket of step (d) is selected from the group consisting of conductive elastomer, fabric wrapped foam, metal fingers, polyurethane, and knitted gaskets.

9. The method of

claim 1

wherein the step (d) of applying the EMI gasket to the thermoformable film comprises the steps of:

mixing conductive particles with foamable materials to form a foam mixture with an integral network of conductive particles; and

processing the foam mixture with the integral network of conductive particles to shape the EMI gasket.

10. The method of

claim 9

wherein the foamable materials are a polyol component and an isocyonate component which form a urethane foam mixture.

11. The method of

claim 10

wherein the step of processing the urethane foam mixture with the integral network of conductive particles to shape the EMI gasket comprises moving the surface of the thermoformable film relative to a nozzle supplying the urethane foam with the integral network of conductive particles to form the EMI gasket in place.

12. The method of

claim 9

wherein the conductive particles are selected from the group consisting of silver-plated glass spheres, sintered metal particles, silver-plated copper particles, and conductive polymers.

13. The method of

claim 12

wherein the sintered metal particles have bulk resistivities below about 10⁻

5 ohm-cm.

14. The method of

claim 1

wherein the extensible conductive coating comprises conductive fibers and an extensible film.

15. A product manufactured according to the method of

claim 1

.

16. An EMI shield comprising:

(a) a thermoformable film comprising a first side and a second side, wherein the thermoformable film is thermoformed into a three-dimensional shape;

(b) an extensible conductive coating applied to the thermoformable film; and

(c) a compressible EMI gasket attached to the thermoformable film.

17. The EMI shield of

claim 16

wherein the extensible conductive coating is applied to at least one of the first side and the second side of the thermoformable film.

18. The EMI shield of

claim 17

wherein the extensible conductive coating is applied substantially uniformly to the at least one of the first side and the second side of the thermoformable film.

19. The EMI shield of

claim 17

wherein the extensible conductive coating is applied selectively to at least one zone and not another zone on the at least one of the first side and the second side of the thermoformable film.

20. The EMI shield of

claim 16

wherein the compressible EMI gasket comprises a mixture of foamable materials and conductive particles to form a foam mixture with an integral network of conductive particles.

21. The EMI shield of

claim 20

wherein the foamable materials are a polyol component and an isocyonate component which form a urethane foam mixture.

22. The EMI shield of

claim 20

wherein the conductive particles are selected from the group consisting of silver-plated glass spheres, sintered metal particles, silver-plated copper particles, and conductive polymers.

23. The EMI shield of

claim 22

wherein the sintered metal particles have bulk resistivities below about 10⁻

5 ohm-cm.

24. The EMI shield of

claim 16

wherein the extensible conductive coating comprises conductive fibers and an extensible film.

29. The EMI shield of

claim 24

, wherein the extensible film has a glass transition temperature lower than that of the thermoformable film.

25. An extensible conductive coating comprising conductive fibers and an extensible film.

26. The extensible conductive coating of

claim 25

wherein the conductive fibers are selected from the group consisting of stainless steel fibers, silver metallized fibers, silver loaded, silver/copper flake, silver/nylon fiber, silver carbon fibers, tin over copper flash, and tin.

27. The extensible conductive coating of

claim 25

wherein an outer surface of the conductive fibers are coated with a metal sufficient to produce bulk conductivity of the material per ASTM 991 to less than about 10 milliohm-cm.

28. The extensible conductive coating of

claim 25

wherein the extensible film is selected from the group consisting of polypropylene, polyethylene, polystyrene, acrylonitrile-butydiene-styrene, styrene-acrylonitrile, polycarbonate, polyester, and polyamide.