Thermal management device and method of making such a device

• US 6,514,616 B1
• Filed: 03/05/2001
• Issued: 02/04/2003
• Est. Priority Date: 07/08/1998
• Status: Expired due to Fees

• Current Assignee: Queen Mary & Westfield College University of London
• Original Assignee: Queen Mary & Westfield College University of London
• Inventors: De Oliveira, Rui, Gandi, Angelo, Carter, Anthony Arthur
• Primary Examiner(s): Jones, Deborah
• Assistant Examiner(s): Bahta, Abraham
• Application Number:
  US09/719,478
• Time in Patent Office: 701 Days
• Field of Search: 428/408, 428/901, 428/594, 361/704, 361/705, 361/679
• US Class Current: 428/408
• CPC Class Codes: H01L 23/373 Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
• CPC Class Codes: H01L 23/3732 Diamonds
• CPC Class Codes: H01L 23/3733 having a heterogeneous or anisotropic structure, e.g. powder or fibres in a matrix, wire mesh, porous structures H01L23/3732, H01L23/3737 take precedence
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H05K 1/056 the metal substrate being covered by an organic insulating layer
• CPC Class Codes: H05K 2201/0323 Carbon
• CPC Class Codes: H05K 2201/09609 Via grid, i.e. two-dimensional array of vias or holes in a single plane
• CPC Class Codes: H05K 3/445 having insulated holes or insulated via connections through the metal core
• CPC Class Codes: H05K 3/4644 by building the multilayer layer by layer, i.e. build-up multilayer circuits making via holes in the insulating layers H05K3/0011; special circuit boards as base or core whereon the multilayer is built H05K3/4602
• CPC Class Codes: Y10S 428/901 Printed circuit
• CPC Class Codes: Y10T 428/12347 Plural layers discontinuously bonded [e.g., spot-weld, mechanical fastener, etc.]
• CPC Class Codes: Y10T 428/30 Self-sustaining carbon mass or layer with impregnant or other layer

Abstract

A thermal management device includes an isotropic carbon encapsulated in an encapsulating material that improves the strength of the carbon. The encapsulating material may be e.g. polyimide, epoxy resin, acrylic, polyurethane, polyester, or any other suitable polymer.

Claims

1. A thermal management device comprising anisotropic carbon encapsulated in an encapsulating material that is applied directly to the anisotropic carbon, wherein the anisotropic carbon is pyrolytic graphite or thermalized pyrolytic graphite.

2. A thermal management device as claimed in claim 1, wherein the encapsulating material is polyimide or epoxy resin or acrylic or polyurethane or polyester.

3. A thermal management device as claimed in claim 1, wherein the anisotropic carbon has mosaic or full ordering.

4. A thermal management device as claimed in claim 1, wherein the thermalized pyrolytic graphite has an in plane thermal conductivity in the range of 1550-1850 W/mK at room temperature.

5. A thermal management device as claimed in claim 4, wherein the thermalized pyrolytic graphite has a low value of tensile strength in the orthogonal direction.

6. A thermal management device as claimed in claim 1, wherein the pyrolytic graphite is in an “

as deposited”

or partially ordered form.

7. A thermal management device as claimed in claim 6, wherein the conductivity of the pyrolytic graphite is in the range of 300-420 W/mK in one plane.

8. A thermal management device as claimed in claim 1, wherein the tensile strength of the anisotropic carbon is 1.5 Ksi in the orthogonal plane.

9. A thermal management device as claimed in claim 1, wherein the anisotropic carbon is a plate.

10. A thermal management device as claimed in claim 9, wherein the carbon plate has a thickness in the range 100-500 μ

m.

11. A thermal management device as claimed in claim 1 wherein the material encapsulating the carbon has a low thermal expansion coefficient and high degradation temperature.

12. A thermal management device as claimed in claim 1, wherein the encapsulating material has a thickness in the range from 8 microns to 30 microns.

13. A thermal management device as claimed in claim 1, wherein multiple layers of encapsulating material are deposited on the carbon in order to build up a desired thickness.

14. A thermal management device as claimed in claim 1, wherein a matrix of fine holes is formed through the carbon.

15. A thermal management device as claimed in claim 14, wherein the holes are filled during encapsulation of the plate.

47. A thermal management device as claimed in claim 9, wherein the carbon plate has a thickness in the range 200-250 μ

m.

48. A thermal management device as claimed in claim 9, wherein the carbon plate has a thickness in the range 250-300 μ

m.

49. A thermal management device as claimed in claim 9, wherein the carbon plate has a thickness in the range 300-350 μ

m.

50. A thermal management device as claimed in claim 9, wherein the carbon plate has a thickness in the range 350-400 μ

m.

51. A thermal management device as claimed in claim 9, wherein the carbon plate has a thickness in the range 400-450 μ

m.

52. A thermal management device as claimed in claim 9, wherein the carbon plate has a thickness in the range 450-500 μ

m.

53. A thermal management device as claimed in claim 14, wherein each hole has a diameter of 200 μ

m.

62. A thermal management device as claimed in claim 1, wherein the encapsulating material has a thickness of 15 microns.

63. A thermal management device as claimed in claim 1, wherein the encapsulating material has a thickness in the range from two microns to ninety microns.

64. A thermal management device as claimed in claim 1, wherein the anisotropic carbon is completely encapsulated in the encapsulating material.

65. A thermal management device as claimed in claim 64, wherein the encapsulating material is a single encapsulating material.

66. A thermal management device as claimed in claim 1, wherein the encapsulating material is applied directly to all surfaces and edges of the anisotropic carbon.

16. An electrical system comprising a thermal management device that includes anisotropic carbon encapsulated in an encapsulating material that is applied directly to the anisotropic carbon, wherein the anisotropic carbon is pyrolytic graphite or thermalized pyrolytic graphite, and electrical contacts and/or devices are provided on the surface of the thermal management device.

17. An electrical system as claimed in claim 16, wherein the electrical contacts and/or devices are deposited directly on the surface of the thermal management device or are glued thereto.

18. An electrical system as claimed in claim 16, wherein the devices are encapsulated in polyimide or epoxy resin or acrylic or polyurethane or polyester.

19. An electrical system as claimed in claim 16, wherein a plurality of layers of electrical components are provided.

20. An electrical system as claimed in claim 19, wherein each layer of electrical components is spaced apart by layers of encapsulating material.

21. An electrical system as claimed in claim 16, wherein the electrical contacts are made of thin film metal.

54. An electrical system as claimed in claim 17, wherein the electrical contacts and/or devices are glued to the surface of the thermal management device using a thin layer of liquid glue.

55. An electrical system as claimed in claim 20, wherein the encapsulating material is polyimide.

56. An electrical system as claimed in claim 21, wherein the thin film metal is aluminium.

67. An electrical system as claimed in claim 16, wherein the anisotropic carbon is completely encapsulated in the encapsulating material.

68. An electrical system as claimed in claim 16, wherein the thermal management device is adapted to provide direct electrical interconnection between opposing sides of the thermal management device.

22. A method of fabricating a thermal management device comprising:

cleaning a surface of pyrolytic graphite or thermalized pyrolytic graphite;

applying a coat of encapsulating material directly to the cleaned surface; and

repeating the step of applying until the graphite is encapsulated.

23. A method as claimed in claim 22, wherein the encapsulating material is one of polyimide or epoxy resin or acrylic or polyurethane or polyester.

24. A method as claimed in claim 23 that further involves curing the encapsulating material.

25. A method as claimed in claim 22, wherein the step of applying involves brushing or rolling or dipping or spraying or spinning or stamping or screen-printing.

26. A method as claimed in claim 25, wherein for polyimide, which consists of a single-component, the step of applying the coat involves brushing the polyimide onto the surface or applying it using a roller.

27. A method as claimed in claim 23, wherein for solid phase application a cast is used.

28. A method as claimed in claim 27, wherein the carbon and cast are pressed together within a vacuum and at high temperature.

29. A method as claimed in claim 23, wherein multiple layers of encapsulating material are applied until a desired thickness is reached.

30. A method as claimed in claim 22, wherein the step of cleaning involves using pumice powder under water to remove loose materials, followed by drying.

31. A method as claimed in claim 22, wherein the step of drying involves drying the carbon by baking the carbon surface to remove moisture.

32. A method as claimed in claims 31, wherein the step of drying involves baking the carbon at 100 C for one hour.

33. A method as claimed in claim 22, wherein the step of cleaning involves degreasing the surface of the pyrolytic graphite or thermalized pyrolytic graphite.

34. A method as claimed in claim 24, wherein when polyimide is used, the step of curing involves heating the carbon to substantially 150 C and subsequently temperature cycling the carbon to 150 C for 30 minutes, 250 C for 30 minutes and finally 300 C for 30 minutes.

35. A method as claimed in claim 22, further comprising drilling the carbon with at least one hole prior to application of the encapsulating material.

36. A method as claimed in claim 35, wherein the at least one hole is infilled with encapsulating material.

37. A method as claimed in claim 35, wherein the holes are infilled with encapsulating material that is mixed with glass fiber spheres.

38. A method as claimed in claim 36, wherein the infilled holes are drilled thereby to provide through passages that are electrically isolated from the carbon.

39. A method as claimed in claim 38, wherein a layer of a conducting material is applied to the at least one through passage to produce electrical connections, thereby to enable electrical connections through the carbon.

40. A method as claimed in claim 39, wherein the conducting material is a metal.

41. A method as claimed in claim 35, comprising coating edges that define the at least one hole with the encapsulating material in such a way as to maintain a passage through the carbon.

42. A method as claimed in claim 22, wherein the pyrolytic graphite or thermalized pyrolytic graphite is a plate, the method further involving forming a matrix of fine holes through the plate.

43. A method of fabricating an electrical component comprising the method as defined in claim 22, additionally comprising the steps of forming electrical contacts on at least one surface of the carbon and/or depositing electrical devices thereon.

44. A method as claimed in claim 43, wherein the step of depositing involves fabricating the devices directly on the surface or forming the devices or a thin film multi-layer circuit containing the devices separately from the carbon surface and fixing them to that surface.

45. A method as claimed in claim 44, wherein the step of fixing involves applying epoxy glue to the devices or the circuit or the carbon surface and pressing the devices or circuit and the surface together at room temperature and at low vacuum.

46. A method as claimed in claim 43, wherein the electrical contacts are applied using thin film processing techniques.

57. A method as claimed in claim 33, wherein the step of cleaning involves degreasing the surface of the pyrolytic graphite or thermalized pyrolytic graphite by rinsing it with acetone.

58. A method as claimed in claim 34, wherein the step of curing involves heating the carbon to substantially 150 C for one hour.

59. A method as claimed in claim 36, wherein the holes are infilled with encapsulating material that is mixed glass fiber spheres, each sphere having a diameter of 30 μ

m.

60. A method as claimed in claim 40, wherein the conducting material is thin film aluminum.

61. A method as claimed in claim 46, wherein the electrical contacts are applied using thin film processing techniques using aluminum.

69. A method as claimed in claim 22, wherein the applying step is repeated until the graphite is completely encapsulated.