WO2014158339A1

WO2014158339A1 - Thermal dissipation system

Info

Publication number: WO2014158339A1
Application number: PCT/US2014/013822
Authority: WO
Inventors: Richard Allen BEYERLE II
Original assignee: Graftech International Holdings Inc.
Priority date: 2013-03-12
Filing date: 2014-01-30
Publication date: 2014-10-02

Abstract

A thermal dissipation assembly includes a substrate with a heat transfer surface. A plurality of heat transfer pins are formed by wrapping a flexible graphite sheet. The heat transfer pins extend outwardly from said heat dissipation surface where convective and/or radiative forces remove the heat therefrom. As electronic devices become more dense, the dissipation of heat becomes a critical design constraint. At the same time power increases, the devices themselves often get smaller and more compact.

Description

THERMAL DISSIPATION SYSTEM

Background

[001] As electronic devices become more dense, the dissipation of heat becomes a critical design constraint. At the same time power increases, the devices themselves often get smaller and more compact. Accordingly, there is a need in the art for improved apparatus to effectively remove heat from electronic components.

Summary

[002] According to one aspect, a thermal dissipation assembly includes a substrate having a heat transfer surface. A plurality of heat transfer pins are formed by wrapping flexible graphite sheet at least one complete revolution. The plurality of heat transfer pins extend outwardly from said heat dissipation surface.

Brief Description of the Drawings

[003] Figure 1 is an elevated view of a heat transfer pin according to the present invention;

[004] Figure 2 is an elevated view of an alternate heat transfer pin having a folded or crushed base;

[005] Figure 3 is an elevated view of a heat dissipation assembly;

[006] Figure 4 is an section view of a heat transfer pin mounted to a projection and taken along the cylindrical axis; and

[007] Figure 5 is an elevated view of an alternate heat dissipation assembly incorporating the heat transfer pins of the present invention.

Detailed Description of the Embodiments

[008] With reference now to Figs. 1 and 2, a heat transfer pin is shown and generally indicated by the numeral 10. Heat transfer pin 10 may advantageously be made of a wrapped flexible graphite sheet 12. The flexible graphite sheet 12 is relatively thin, and in one embodiment, the flexible graphite sheet 12 may be less than about 1 mm thick. In other embodiments the flexible graphite sheet 12 may be less than about 0.5 mm thick. In still other embodiments, the flexible graphite sheet 12 may be less than about 0.1 mm thick. In still other embodiments, the flexible graphite sheet 12 may be less than about 0.05 mm. According to one or more embodiments, flexible graphite sheet 12 may be from between 0.01 mm to 0.1 mm. In further embodiments, the flexible graphite sheet 12 may be from between 0.01 mm to about 0.05 mm. The flexible graphite sheets 12 may be, for example, a sheet of a compressed mass of exfoliated graphite particles, a sheet of graphitized polyimide or combinations thereof.

[009] Heat transfer pin 10 functions to conduct heat away from a heat source so that convective and/or radiative heat transfer may occur. Thus, the flexible graphite sheet 12 may have an in-plane thermal conductivity of greater than about 250 W/mK. In another embodiment, the in-plane thermal conductivity of the flexible graphite sheet 12 is at least about 400 W/mK. In yet a further embodiment, the in-plane thermal conductivity of the flexible graphite sheet 12 may be at least about 550 W/mK. In still a further embodiment, the in-plane conductivity of the flexible graphite sheet 12 may be at least about 1000 W/mK. In additional embodiments, the in-plane thermal conductivity may range from at least 1000 W/mK to about 1700 W/mK. In still further embodiments, the in-plane thermal conductivity may range from about 250 W/mK to about 700 W/mK.

[010] The flexible graphite sheet 12 is thermally anisotropic and accordingly the thru-plane conductivity is significantly less than the in-plane conductivity. Preferably the anisotropic ratio of the sheet is greater than at least about 40, other examples of suitable anisotropic ratios include at least about 75, at least about 100, and at least about 150. Anisotropic ratio is used herein to mean the in-plane thermal conductivity divided by the thru-plane thermal conductivity. In one embodiment, the thru-plane thermal conductivity of the flexible graphite sheet may be from between about 1 W/mK and about 20 W/mK. In this or other embodiments, the thru-plane thermal conductivity is from between about 2 W/mK and about 6 W/mK. In these or other embodiments, the thru-plane thermal conductivity may be less than about 20 W/mK. In further embodiments, the thru-plane thermal conductivity may be less than about 10 W/mK. Any combination of the above in-plane and thru -plane thermal conductivities may be practiced. [011] In an optional embodiment, the flexible graphite sheet 12 may be resin reinforced prior to, or after the flexible graphite sheet 12 is rolled into pin form. The resin may be used, for example, to improve the rigidity of the flexible graphite sheet 12. In combination with resin reinforcement, or in the alternative, one or more flexible graphite layers may include carbon fiber and/or graphite fiber reinforcement.

[012] The flexible graphite sheet 12 is a more conformable material than conventional materials used in heat sink pin fin configuration (ex. aluminum or copper). Use of flexible graphite sheet offers a reduction in interfacial thermal heat transfer resistance between the heat transfer pin 10 and the thermal substrate or electric component or non-electric heat source for the transfer of heat. Further, many graphite sheet materials such as many graphitized polyimide and some compressed exfoliated graphite sheets have greater thermal conductivities than materials such as aluminum and even copper. Likewise, it is the conformable nature of flexible graphite sheets that allows the sheet to be rolled in accordance with the present invention.

[013] In one embodiment, the heat transfer pin 10 has a generally c-shaped cross section made of a flexible graphite sheet 12 wrapped at least a half revolution. With reference to Fig. 1 , in a more advantageous embodiment, the heat transfer pin is a generally cylindrical shape and is formed by wrapping the flexible graphite sheet 12 at least one complete revolution. In still other embodiments, the heat transfer pin may be formed by wrapping the flexible graphite sheet 12 in a spiral pattern multiple times to form the heat transfer pin 10. Thus, in one embodiment, the flexible graphite sheet 12 may be wrapped at least 1.5 revolutions and in further embodiments, at least 2 revolutions.

[014] With reference to Fig. 2, according to a further embodiment, the pin 10 may be formed by wrapping as generally described above, and thereafter, compressed in the direction indicated by arrow A. This may create a crushed area 13 that may advantageously improve thermal contact with the mounting surface (such as the substrate to be described herein below), whether a flat surface, a raised projection or a bore hole (as will be discussed further herein below). In this embodiment, the pin 10 is compressed to less than 95 percent of the original length, in other embodiments less than 75 percent of the original length, and still further embodiments, less than 50 percent of the original length. In this or other embodiments, the pin 10 may be compressed to from between 25 percent and 95 percent of the original length. [015] In one embodiment, the heat transfer pin 10 may be from between about 5 mm and about 25 mm in length. In other embodiments the pin 10 may be from between about 10 mm and about 20 mm in length. In still other embodiments, the pin 10 may be less than about 50 mm in length. In other embodiments, the pin 10 may be less than about 25 mm in length. In still other embodiments, the pin 10 may be less than 10 mm in length. The heat transfer pin 10 diameter is advantageously from between 50 μιη and about 3,000 μιη. In further embodiments, the pin 10 diameter may be from between 100 μιη and about 2,000 μιη. In still further embodiments, the pin 10 diameter may be from between about 300 μιη and about 1,000 μιη. In these or other embodiments, the pin 10 diameter may be less than about 3,000 μιη. In other embodiments, the pin 10 diameter may be less than about 1,000 μιη. In still further embodiments, the pin 10 diameter may be less than about 500 μιη.

[016] Advantageously, the flexible graphite sheet is rolled tightly so that overlapping layer(s) of flexible graphite sheet 12 form a substantially solid outer wall. In other words, advantageously, no gaps are formed between adjacent layer(s) of flexible graphite sheet 12. In this manner, an internal open volume 14 may thus be formed. Pin 10 advantageously includes an average internal diameter d and an average external diameter D. In this or other embodiments, the ratio of d/D is from between 0.9 and about 0.4. In other embodiments, the ratio of d/D is from between about 0.8 and about 0.5. In this or other embodiments, the ratio of d/D is at least 0.4. In other embodiments, the ratio of d/D is at least about 0.6. In still further embodiments, the ratio of d/D is at least about 0.75.

[017] With reference now to Fig. 3, a heat dissipation assembly is shown and generally indicated by the numeral 16. Heat dissipation assembly 16 includes a substrate 18 which includes a heat dissipation surface 20. A plurality of heat transfer pins 10 are secured to surface 20. As shown in Fig. 3, surface 20 may include a plurality of bore holes 22 arranged in a repeating pattern such as a matrix including rows and columns. In other embodiments, the plurality of bore holes 22 may be arranged in a random pattern. Bore holes 22 may advantageously extend inwardly by a depth of at least 5 percent of the length of the inserted heat transfer pin 10. In other embodiments, the bore holes 22 extend inwardly at least 10 percent of the length of the inserted heat transfer pin 10. In still further embodiments, the bore holes 22 extend inwardly at least 25 percent of the length of the inserted heat transfer pin 10. Bore holes 22 are advantageously spaced a distance apart from between about 5 times the diameter D of the inserted pins 10 to about 1 times the diameter D of the inserted pins 10. In other embodiments bore holes 22 are spaced a distance apart of from between about 2 times the diameter D of the inserted pins 10 to about 1 times the diameter D of the inserted pins 10. In still further embodiments, bore holes 22 are spaced a distance apart of less than about 5 times the diameter D of the inserted pins 10. In still further embodiments, bore holes 22 are spaced a distance apart of less than about 2 times the diameter D of the inserted pins 10. It should be appreciated that the above disclosure related to spacing and arrangement of bore holes 22 is also applicable to other attachment arrangements, such as, for example, the spacing and arrangement of an outwardly extending projection (discussed later in greater detail) that receives the pin 10 thereon.

[018] With reference now to Fig. 4, an alternate mounting arrangement is shown, wherein the substrate 16 includes an outwardly extending projection 30. As can be seen, the projection 30 is sized to fit inside internal volume 14. Pins 10 may be secured in bore holes 22 or on projections 30 by friction fit, adhesive and/or other mechanical fastening techniques. For example, pin 10 may include a retaining cap 32 positioned on the end of pin 10 opposed from surface 18. A fastener 34 may extend from retaining cap 32, through internal volume 14 and be secured to outwardly extending projection 30. In this manner pin 10 may be secured to substrate 20 by compression between retaining cap 32 and surface 20. Further, though securing pins 10 in bore holes 22 or on outwardly extending projections 30 is particularly advantageous, other methods of securing pins to surface 20 without the use of bore holes or projections may be employed, such as, for example, adhesives and particularly high thermal conductivity adhesives. [019] With reference now to Fig. 5, a heat dissipation assembly 40 includes a substrate 42 which is generally cylindrical in shape. As can be seen, substrate 42 includes a radial outer heat dissipation surface 44. A plurality of heat transfer pins 10 are secured to surface 44. As shown in Fig. 5, surface 44 may include a plurality of bore holes 46 (or alternately outwardly extending projections) arranged in a repeating or random pattern having spacing as described herein above. Bore holes 46 may advantageously extend inwardly by a depth of at least 5 percent of the length of the inserted heat transfer pin 10. In other embodiments, the bore holes 46 extend inwardly at least 10 percent of the length of the inserted heat transfer pin 10. In still further embodiments, the bore holes 46 extend inwardly at least 25 percent of the length of the inserted heat transfer pin 10. Pins 10 may be secured in bore holes 46 by friction fit, adhesive or other mechanical fastening techniques. Further, though securing pins 10 in bore holes 46 is particularly advantageous, other methods of securing pins to surface 44 without the use of bore holes 46 may be employed, such as, for example, adhesives and particularly high thermal conductivity adhesives. Further, pins 10 may be secured to substrate 42 according to the pattern, spacing and arrangement described herein above.

[020] Substrate 18/42 may be a thermal interface material in contact with a heat generating electronic component. In this or other embodiments, the interface material may be relatively high thermal conductivity metal such as aluminum or copper for example. In other embodiments, the interface material may be anisotropic graphite material. For example, the thermal interface material may be one or more layers of compressed exfoliated natural graphite. In still further embodiments, the substrate 26/42 may be integral with the heat generating component and thus, the heat transfer pins 10 may be directly engaged with the heat generating component. In this embodiment, bore holes or projections might be made in the outer housing or outer surface of the heat generating component or, as discussed above, the pins might be simply adhered to and extend outwardly from, the outer housing or outer surface of the heat generating component. In another embodiment, the substrate 26/42 may be a printed circuit board, a metal cladded printed circuit board, a sheet of copper, a sheet of silicon or combinations thereof. Substrate 26/42 may further include the housings or exterior surfaces or heat radiating surfaces of battery-backed or powered sensors located near heat sources such as industrial equipment, testers, power generators or converters. Indeed, substrate 26/42 may include any heat-generating or warm block that permits holes drilled in its surface to a depth adequate to hold the fin or to enable the formation of a projection thereon.

[021] The various embodiments disclosed herein may be practiced in any combination thereof. The above description is intended to enable the person skilled in the art to practice the invention. It is not intended to detail all of the possible variations and modifications that will become apparent to the skilled worker upon reading the description. It is intended, however, that all such modifications and variations be included within the scope of the invention that is defined by the following claims. The claims are intended to cover the indicated elements and steps in any arrangement or sequence that is effective to meet the objectives intended for the invention, unless the context specifically indicates the contrary.

Claims

Claims We claim:

1. A thermal dissipation assembly comprising:

a. a substrate having a heat transfer surface;

b. a plurality of heat transfer pins formed by wrapping flexible graphite sheet at least one complete revolution; and

c. wherein said plurality of heat transfer pins extend outwardly from said heat dissipation surface.

2. The thermal dissipation assembly according to claim 1 wherein said flexible graphite sheet comprises a sheet of a compressed mass of exfoliated natural graphite particles.

3. The thermal dissipation assembly according to claim 1 wherein said flexible graphite sheet comprises a sheet of graphitized polyimide.

4. The thermal dissipation assembly according to claim 1 wherein said flexible graphite sheet has an anisotropic ratio of at least 40.

5. The thermal dissipation assembly according to claim 1 wherein said flexible graphite sheet has an anisotropic ratio of at least 75.

6. The thermal dissipation assembly according to claim 1 wherein said substrate comprises a thermal interface material in thermal contact with a heat source.

7. The thermal dissipation assembly according to claim 6 wherein said thermal interface material comprises one or more layers of compressed exfoliated natural graphite.

8. The thermal dissipation assembly according to claim 6 wherein said thermal interface material comprises an isotropic metal selected from the group consisting of copper, aluminum and alloys thereof.

9. The thermal dissipation assembly according to claim 1 wherein said heat transfer surface includes a plurality of bores and one of said heat transfer pins are received in each of said bores.

10. The thermal dissipation assembly according to claim 9 wherein said heat transfer surface is generally cylindrical.

11. The thermal dissipation assembly according to claim 9 wherein said heat transfer surface is generally flat.

12. The thermal dissipation assembly according to claim 1 wherein said heat transfer pin is a flexible graphite sheet wrapped at least 1.5 revolution.

13. The thermal dissipation assembly according to claim 1 wherein said heat transfer pin is a flexible graphite sheet wrapped at least 2 revolutions.

14. The thermal dissipation assembly according to claim 1 wherein said heat transfer pin includes an open internal volume.

15. The thermal dissipation assembly according to claim 1 wherein said substrate comprises one of a printed circuit board, a metal cladded printed circuit board, or housings or exterior surfaces or heat radiating surfaces of battery-backed or powered sensors.

16. The thermal dissipation assembly according to claim 1 wherein said heat transfer pin includes a crushed portion proximate to said substrate.

17. The thermal dissipation assembly according to claim 1 wherein said substrate includes at least one outwardly extending projection, said outwardly extending projection having a heat transfer pin mounted thereon.

18. The thermal dissipation assembly according to claim 17 wherein said heat transfer pin defines an internal volume and further comprises a retaining cap positioned on the end of said heat transfer pin opposed from said heat dissipation surface and a fastener, said fastener extending from said retaining cap to said heat dissipation surface within said internal volume

19. The thermal dissipation assembly according to claim 1 wherein said plurality of heat transfer pins have an outer diameter and are arranged in a pattern and are each spaced a distance apart from between about 5 times said diameter to about 1 times said diameter D.