Heat spreaders with vias

• US 20070102142A1
• Filed: 01/25/2006
• Published: 05/10/2007
• Est. Priority Date: 11/04/2005
• Status: Active Grant

• Current Assignee: NeoGraf Solutions, LLC
• Original Assignee: Graftech International Holdings Inc (Graftech International Limited)
• Inventors: Smalc, Martin, Frastaci, Michael, Skandakumaran, Prathib, Laser, Brian, Kostyak, Gary, Getz, Matthew, Reis, Bradley
• Granted Patent: US 7,303,005 B2
• Time in Patent Office: Days
• US Class Current: 165/80.300
• CPC Class Codes: F28F 13/00 Arrangements for modifying heat-transfer, e.g. increasing, decreasing F28F1/00 - F28F11/00 take precedence
• CPC Class Codes: F28F 21/02 of carbon, e.g. graphite
• CPC Class Codes: H01L 23/3677 Wire-like or pin-like cooling fins or heat sinks
• 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 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 1/0203 Cooling of mounted components H05K1/0272 takes precedence
• CPC Class Codes: H05K 1/0204 using means for thermal conduction connection in the thickness direction of the substrate H05K1/0207 takes precedence
• CPC Class Codes: H05K 1/182 associated with components mounted in the printed circuit board, e.g. insert mounted components [IMC]
• CPC Class Codes: H05K 2201/0323 Carbon
• CPC Class Codes: H05K 2201/10106 Light emitting diode [LED]
• CPC Class Codes: H05K 2201/10416 Metallic blocks or heatsinks completely inserted in a PCB metallic supports H05K3/0061

Abstract

Constructions for and methods of manufacturing graphite heat spreaders having thermal vias placed therethrough are provided. Thermal vias having one or two flanges are disclosed, as are flush thermal vias. Graphite heat spreaders having surface layers covering the graphite material are provided. Graphite heat spreaders having a layer of cladding for increased structural integrity are provided. Also disclosed are methods of co-forging a graphite heat spreader element with a metal thermal via in place therein.

Claims

1. A method of assembling a thermal management system, comprising:

(a) forming a hole through a thickness of an anisotropic graphite planar element, the planar element having first and second oppositely facing major planar surfaces, the hole having a cross-sectional shape having maximum cross-sectional dimension parallel to the plane of the planar element;

(b) providing a thermal via constructed of an isotropic material, the thermal via having a cross-sectional shape complementary to the cross-sectional shape of the hole and having a minimum cross-sectional dimension larger than the maximum cross-sectional dimension of the hole; and

(c) press fitting the thermal via into the hole of the graphite planar element, thereby creating a close fit between the thermal via and graphite planar element, so that heat from a heat source can be conducted through the via into the thickness of the planar element.

2. The method of claim 1, wherein the graphite planar element is formed by compressing particles of exfoliated graphite.

3. The method of claim 1, wherein the via is constructed from a material selected from the group consisting of gold, silver, copper, aluminum and their alloys.

4. The method of claim 1, wherein:

the cross-sectional shapes of the hole and the via are circular.

5. The method of claim 1, wherein:

in step (a), the forming of the hole comprises die-cutting the hole.

6. The method of claim 1, wherein:

in step (b), the via includes a stem and a first flange, the stem comprising the minimum cross-sectional dimension; and

in step (c), the stem is press fit into the hole until the flange engages one of the major planar surfaces of the graphite planar element.

7. The method of claim 6, further comprising:

during step (c), the graphite mushrooms up around the stem creating a mushroomed protrusion; and

forcing down the mushroomed protrusion flush with the other of the major planar surfaces of the graphite planar element opposite from the flange of the via.

8. The method of claim 6, further comprising:

tightly fitting a second flange on a free end of the stem opposite from the first flange, and compressing the graphite planar element between the first and second flanges.

9. The method of claim 6, further comprising:

pressing a press-on nut onto a free end of the stem opposite from the first flange, so that the press-on nut engages the graphite planar element to hold the via firmly in place in the hole of the graphite planar element.

10. The method of claim 1, wherein:

in step (b), the via has a thickness substantially equal to the thickness of the graphite planar element.

11. The method of claim 10, further comprising:

in step (b), the via is in the shape of a cylindrical disc having chamfered edges;

during step (c), the graphite planar element bulges adjacent the chamfered edges of the via forming peripheral bulges; and

after step (c), compressing the peripheral bulges so that the via is flush with both of the major planar surfaces of the graphite planar element.

12. The method of claim 11, further comprising:

during said compressing step, co-forging both the via and the graphite planar element thereby creating simultaneous plastic deformation of both the via and the graphite planar element.

13. The method of claim 11, further comprising:

after said compressing step, cladding one of the major planar surfaces and covering the via with the cladding.

14. A thermal management system, comprising:

an anisotropic graphite planar element having first and second opposed major planar surfaces; and

a thermal via, constructed of an isotropic material, the via being embedded in the graphite planar element and having first and second exposed ends flush with the first and second opposed major planar surfaces, respectively, of the graphite planar element, the via having a recess defined thereon and the graphite planar element overlapping the recess.

15. The system of claim 14, wherein the anisotropic graphite planar element comprises compressed particles of exfoliated graphite.

16. The system of claim 14, wherein the via is constructed from a material selected from the group consisting of gold, silver, copper, aluminum and their alloys.

17. The system of claim 14, wherein:

the recess comprises a peripheral chamfer on each of the first and second ends of the via.

18. The system of claim 14, wherein the overlapping of the graphite planar element and the recess of the via enhances heat transfer between the graphite planar element and the via.

19. The system of claim 14, wherein the overlapping of the graphite planar element and the recess of the via provides a mechanical bond between the via and the graphite.

20. The system of claim 14, wherein the via is cylindrical in shape.

21. The system of claim 14, further comprising:

a surface layer thinner than a thickness of the graphite planar element and covering the opposed major planar surfaces of the graphite planar element, the first and second exposed ends of the via being flush with the surface layer.

22. The system of claim 14, further comprising:

a cladding layer adhered to the first major planar surface and covering the first end of thermal via.

23. The system of claim 22, further comprising a mounting screw hole extending through the cladding layer and the graphite planar element.

24. A thermal management system, comprising:

an anisotropic graphite planar element having first and second oppositely facing major planar surfaces and having a thickness defined between the planar surfaces, the planar element having a relatively high thermal conductivity parallel to the planar surfaces and having a relatively low thermal conductivity across the thickness, the planar element having a cavity defined therethrough between the planar surfaces, the cavity being defined by an inner cavity wall; and

a thermal via having;

a stem extending through the cavity and closely engaging the inner cavity wall;

a flange extending laterally from the stem and closely engaging one of the planar surfaces of the planar element; and

the via being constructed of an isotropic material so that heat from a heat source can be conducted through the via into the thickness of the planar element.

25. The system of claim 24, wherein the anisotropic graphite planar element comprises compressed particles of exfoliated graphite.

26. The system of claim 24, wherein the via is constructed from a material selected from the group consisting of gold, silver, copper, aluminum, and their alloys.

27. The system of claim 24, further comprising:

a push-on nut, received over and frictionally engaging the stem, the nut snugly engaging the other of the planar surfaces other than the one of the planar surfaces engaged by the flange, so that the planar element is sandwiched between the flange and the nut.

28. The system of claim 27, wherein the nut is made from a different material than the via.

29. The system of claim 27, further comprising:

a heat source having a heat conducting contact area defined thereon in contact with an end of the stem opposite from the flange, the contact area being less than an area of the end of the stem.

30. The system of claim 27, wherein the stem has a free end opposite from the flange, the free end extending entirely through and past the push-on nut.

31. The system of claim 27, further comprising:

a washer loosely received about the stem and clamped between the push-on nut and the graphite planar element.

32. The system of claim 24, further comprising:

a second flange attached to the stem adjacent an end of the stem opposite from the first flange, the second flange having an inner bore closely received about the stem; and

the graphite planar element having an annular portion surrounding the cavity compressed between the first and second flanges so that both the first and second flanges are in intimate heat conducting engagement with the graphite planar element.

33. The system of claim 32, wherein the second flange is press fit upon the stem.

34. The system of claim 32, wherein:

the stem has a stem shoulder defined thereon and facing away from the first flange; and

the inner bore of the second flange has a flange shoulder defined thereon complementary to and abutting the stem shoulder of the stem.

35. The system of claim 32, wherein:

the stem has a straight cylindrical outer surface of constant diameter and the inner bore of the second flange is a straight cylindrical inner bore; and

the second flange is flush with the end of the stem opposite from the first flange.