WO2012166122A1

WO2012166122A1 - Heat sink mount with positionable heat sinks

Info

Publication number: WO2012166122A1
Application number: PCT/US2011/038615
Authority: WO
Inventors: Zhe Hong LIU
Original assignee: Aavid Thermalloy, Llc
Priority date: 2011-05-31
Filing date: 2011-05-31
Publication date: 2012-12-06
Also published as: CN103620335A; CN103620335B

Abstract

A thermal transfer device including a thermally conductive support structure to be secured to a substrate having at least two types of heat sources. The support structure has a plurality of apertures, one for each first heat source. Each aperture accommodates an individual heat sink configured to make thermal contact with a first heat source. Each heat sink fits in its aperture, and is attached to the support structure by at least one spring mount for holding the heat sink in place. Preferably, the spring mount includes a plurality of springs disposed about the heat sink to provide a balanced downward force on the heat sink. The support structure has a bottom surface receiving a thermal transfer medium to provide thermal contact between the second heat sources and the support structure, thereby allowing for dissipation of the heat generated by the second heat sources through the support structure.

Description

HEAT SINK MOUNT WITH POSITIONABLE HEAT SINKS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a thermal transfer device having multiple heat sinks for cooling more than one major heat source and a plurality of minor heat sources, in which the positions of the heat sinks are independently adjustable.

2. Description of the Related Art

Heat sinks are used in many types of applications, especially in the field of electronics and micro-electronics. The continuing trend in these fields is for manufacturers to crowd as many processors and other electronic components as possible onto single circuit board assemblies. One side effect of crowding components onto a single assembly is that multiple components (e.g., integrated circuits - "IC's") will have different vertical displacements. These IC's generate a great deal of heat which, if not dissipated, can lead to malfunctions, and so is to be ameliorated as best as possible.

When multiple heat sources are close together and also at different vertical displacements, there is a problem with aligning multiple heat sinks in close proximity to one another and to their respective heat sources. Heat sinks function best when the surface of the heat sink aligns as closely as possible with the surface which is generating the heat, which, in this context, is the generally planar top of the heat source e.g., a computer chip or IC. That is why heat sinks for such chips have generally planar contact surfaces to make the best possible contact with the top of the chip to be cooled. However, when two or more chips are placed near one another, their planar contact surfaces (top surfaces which mate with heat sinks) may be at two different heights relative to the circuit board on which they are mounted, and further, may not be parallel to each other. This means that the top surfaces will be neither co-planar nor located in parallel planes. This can be due to differences in the dimensions of the chips, or differences in the assembly of the chips on the underlying printed circuit board ("PCB") . Having non-coplanar and/or non-parallel top surfaces means that some of the chips will not have optimal contact with the heat sink. This is because the heat sink cannot be placed in good thermal communication with these non-coplanar and / or non-parallel surfaces.

In addition, although computer chips are the largest heat sources on a printed circuit board, there are other heat-producing components as well. Conventionally, large computer chips are surrounded on a PCB by "secondary components", e.g., other electrical components, such as resistors, capacitors and smaller chips, etc., all of which generate heat, albeit in far lesser amounts than the larger computer chips. Conventionally, these smaller sources of heat are cooled either by natural convection or forced convection where air is moved over the exposed surface of the chip either by a fan, blower or other air-mover means. This is not always sufficient because of the limited exposed surface area of these secondary components. It would therefore be advantageous to place these secondary components in thermal communication with neighboring thermally conductive components to effectively add to the available surface area for cooling. Thus far, however, cooling solutions have focused on cooling the larger components, since that is where the greatest heat is generated .

One attempt to provide cooling for multiple uneven chips is disclosed in United States Patent No. 4,072,188, which teaches using a liquid-cooled heat sink with a flexible surface. The flexible surface is placed over the top of the PCB and cooling liquid is pumped behind the flexible surface to cool the tops of the chips. This approach presented problems, for example by not allowing for targeted cooling for the hottest sources of heat.

Another attempt to address the problem is disclosed in United States Patent No. 6,966,361, wherein a unitary heat sink having fixed surfaces of differing heights is provided. This, however, only was of use if the exact differences in height of the heat sources could be predicted, and if the relative orientations of the top surfaces of the chips were parallel. Otherwise, one or more of the top surfaces of the chips would still be in less than optimal contact with the heat sinks.

United States Patent No. 6,367,541 provided one solution for the problem of cooling multiple chips of different heights mounted on a common circuit board by providing a unitary heat sink that was deformable, so that it could be bent slightly to conform to differences in the levels and orientation of nearby chips . However, such a solution has limited applicability, in that there is a limit to how much such a heat sink may be deformed to accommodate differences in height of adjacent chips, and the bending itself causes stress to the heat sink, thereby increasing the chance of fatigue for the heat sink and shortening the life of the heat sink. Another solution is shown in United States Patent No. 7,269,018, which teaches a holder for a plurality of individually movable heat sinks, in which each heat sink is held between a pair of flexible opposed arms, and urged downward by a resilient spring member when attached to a PCB, so that the spring member urges an individual heat sink into contact with the top surface of a respective chip. The independent mounting of the heat sinks allows each heat sink to contact the top of its respective chip regardless of the orientation of any adjacent chip. This structure, however, still has some drawbacks. For example, there is no restriction on the movement of the individual heat sinks within the space between the flexible arms. This permits the heat sinks to move to any side, or even to tilt. This may be disadvantageous in some applications. Such devices are also difficult to implement if the chips are assembled otherwise than in a linear array, such as in a rectangular array.

A common drawback to all of these solutions is that they do not address the different cooling needs of the secondary components which are arrayed around the large chips.

There is thus a need in the art for improved heat sink mountings for cooling pluralities of different heat sources which have different capacities for generating heat, and top surfaces that are not co- planar . SUMMARY OF THE INVENTION

Embodiments of the invention may be realized by a thermal transfer device having a support structure or frame capable of being secured to a substrate having at least two types of heat sources. The support structure is formed of a heat conductive material, such as aluminum, copper or an alloy of steel. The first type of heat source includes objects capable of generating a relatively large amount of heat, and the second type of heat source includes objects capable of generating lesser amounts of heat relative to the first type of objects. The support structure includes a plurality of apertures, with each being sized to accommodate an individual heat sink configured to make thermal contact with a respective one of the first type of heat sources. Each individual heat sink is sized to fit in its aperture, and is attached to the support structure by a mount. Preferably, the mount is a spring mount having a plurality of springs about the periphery of the heat sink to provide a balanced downward force on the periphery of the heat sink.

The support structure has a bottom surface which faces the tops of the second type of heat sources, and may receive a thermal transfer medium, such as a paste or gap pad, to provide for thermal contact between the second types of heat sources and the bottom surface of the support structure, thereby allowing for dissipation of the heat generated by the second type of heat sources through the support structure itself. Used in this manner the support structure effectively provides additional cooling surface area for the second types of heat sources . In one embodiment, the thermal transfer device includes a conduit for transporting a thermal transfer fluid into thermal contact with the heat sinks, thereby- allowing for improved cooling of the individual first type of heat sources. It is most preferred if the fluid conduit is ductile, allowing for some small deformation of the conduit when the heat sinks are independently affixed to the support structure and urged into thermal contact with their respective heat sources.

Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims . It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further description of the invention, reference is made to the exemplary embodiments shown in the drawings, in which like numerals refer to like parts .

Fig. 1 is cross-section of an embodiment of the thermal transfer device mounted to a substrate; and

Fig. 2 is a partially exploded, perspective view of the thermal transfer device of Fig. 1. DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED

EMBODIMENTS

With reference to Figs. 1 and 2, a thermal transfer device 10 is shown and includes a support structure, or frame, 12 attached to a substrate 14, such as a printed circuit board ("PCB"), to which a plurality of primary heat sources, such as large computer chips 16, 18, is affixed. Secondary components such as secondary heat sources 20, 22, 24, are for example, electrical components such as resistors, capacitors or smaller chips, which are also affixed to substrate 14. For clarity of illustration in Fig. 1, computer chips 16, 18 and electrical components 20, 22, 24 are shown schematically, with no connections or exact dimensioning illustrated.

Support structure 12 includes apertures 26, 28 (aperture 28 is best seen in Fig. 2), and a plurality of mounts 30. Each mount 30 preferably has an interior thread. Support structure 12 is formed of a thermally conductive . material, preferably a metal such as aluminum, copper or an alloy of steel. In use, a thermally conductive medium 32, such as a thermally conductive paste or gap pads, is affixed to the bottom surface of support structure 12 and positioned to contact the tops of secondary heat sources 20, 22, 24, to provide thermal coupling between the secondary heat sources 20, 22, 24 and the support structure 12. Support structure 12 also includes standoffs 34 for mounting support structure 12 above substrate 14 and secondary heat sources 20, 22, 24.

Thermal transfer device 10 further includes a plurality of independently mounted heat sinks 36, 38. Each heat sink 36, 38 is sized to fit into a respective aperture 26, 28, and has a bottom surface configured to contact the top of its respective primary heat source, 16 , 18 to maximize the thermal contact therebetween. In this example, all surfaces are generally planar. Each heat sink 36 , 38 includes a plurality of spring mounts 40 {Fig. 2), positioned on a flange 42 on the periphery of heat sinks 36 , 38 and configured to screw into mounts 30 on support structure 12 .

Preferably, thermal transfer device 10 includes a conduit 44 for conducting a thermal transfer fluid through heats sinks 36 , 38 to permit even cooling thereof. To accommodate some relative movement between heat sinks 36 and 38 , it is preferred that conduit 44 be formed of a ductile material, such as copper.

In use, thermal transfer device 10 is positioned on top of an already assembled substrate 14 having heat sources 16 , 18 , 20 , 22 , 24 affixed thereto. Thermally conductive medium 32 is affixed to the bottom of support structure 12 . Support structure 12 is then positioned on substrate 14 by standoffs 34 , which are affixed thereto by any suitable means, such as screws 46 . This causes thermally conductive medium 32 to contact the tops of secondary heat sources 20 , 22 , 24 . Heat sinks 36 , 38 which have been previously mounted in apertures 26 , 28 and secured to the support structure 12 by spring mounts 40 aligned with mounts 30 , and fastened, such as by screwing screws 48 into the internal threads of mounts 30 , are positioned such that the bottoms of heat sinks 36 , 38 are located opposite the tops of primary heat sources 16 , 18 , respectively. Preferably, spring mounts 40 include springs 50 for exerting a downward force on heat sinks 36 , 38 , depending on the axial position of the screws 48 in the mounts 30 , so that heat sinks 36 , 38 have an optimum thermal contact with their respective primary heat sources 16 , 18 .

As an alternative to mounting the heat sinks to the support structure before attaching the support structure to substrate 14 , the heat sinks can be positioned in apertures 26 , 28 after the connection of the support structure to the substrate. In either case, the relative positions of the heat sinks can be adjusted via spring mounts 40 .

By spacing a plurality of spring mounts 40 on the peripheries of heat sinks 36 , 38 , a gimbal effect is produced so that support structure 12 may be affixed securely and squarely to substrate 14 and heat sinks 36 , 38 may be independently and securely positioned on the tops of their respective primary heat sources 16 , 18 , regardless of the relative orientation of the tops of primary heat sources 16 , 18 , even if the tops are not co-planar or precisely parallel to the planes of either support structure 12 or substrate 14 .

The use of ductile fluid conduit 44 allows for a balancing of the heat dissipation available to the primary heat sources . An example of such a ductile fluid conduit is commonly known as a heat pipe. A heat pipe, based on a well understood system of internal boiling and condensing of fluid, will naturally move heat from a higher temperature region of its outer surface to a lower temperature region of its outer surface. This in turn means that if one of the primary heat sources 16 , 18 is operating at a higher temperature than the other, some of the heat will be conveyed to the heat sink { 36 or 38 ) associated with the other (cooler) primary heat source. Also, the provision of thermally conductive medium 32 and forming support structure 12 of a thermally conductive material allows for additional dissipation of heat from secondary heat sources 20 , 22 , 24 , rendering thermal transfer device 10 more efficient than known thermal transfer devices.

It will be appreciated by those of ordinary skill in the art that the inventive concept may be applied to thermal transfer devices having more than two primary heat sources and therefore more than two heat sinks . The invention also applies where a plurality of heat sinks are arranged non-linearly, such as in a rectangular array, or even irregularly, so long as their respective apertures are disposed in locations allowing access to the primary heat sources mounted on the substrate .

Thus, while there have shown and described and pointed out fundamental novel features of the invention s applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements shown and/or described herein may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

CLAIMS What is claimed is:

1. A thermal transfer device for cooling objects mounted to a substrate, the objects including at least first and second primary objects each having a top surface and being capable of producing heat, and at least one secondary object having a top surface and being capable of producing heat, said thermal transfer device comprising:

a thermally conductive support structure configured to be mounted to the substrate, the support structure having

a bottom surface oriented to face the top surface of the at least one secondary object, said bottom surface also being adapted to receive a thermal transfer medium for transferring heat from the top surface of the at least one secondary object to said bottom surface of said support structure and thereby facilitate the dissipation of heat from the at least one secondary object;

a first mount; and

a second mount;

a first heat sink mounted at said first mount to said support structure for transferring heat from the top surface of the first primary object to said first heat sink when said support structure is mounted to the substrate; and

a second heat sink mounted at said second mount to said support structure for transferring heat from the top surface of the second primary object to said second heat sink when said support structure is mounted to the substrate ; whereby said first and second mounts permit independent positioning of said first and second heat sinks with respect to their respective primary objects; and

whereby said first mount permits said first heat sink to be thermally coupled to the top surface of the first primary object and said second mount permits said second heat sink to be thermally coupled to the top surface of the second primary object even if the top surfaces of the first and second primary objects are not co-planar .

2. The thermal transfer device of claim 1, wherein said support structure is made of metal.

3. The thermal transfer device of claim 2, wherein said metal is selected from the group consisting of aluminum, copper and an alloy of steel.

4. The thermal transfer device of claim 1, wherein said, first mount constrains transverse movement of said first heat sink with respect to the first primary object.

5. The thermal transfer device of claim 4, wherein said second mount constrains transverse movement of said second heat sink with respect to the second primary object.

6. The thermal transfer device of claim 4, wherein said first mount is resilient.

7. The thermal transfer device of claim 6, wherein said first mount includes a spring.

8. The thermal transfer device of claim 7, wherein said spring includes a plurality of springs mounted on said support structure about a periphery of said first heat sink.

9. The thermal transfer device of claim 8, wherein said plurality of springs permits said first heat sink to be positioned atop said first primary object at substantially any orientation within the limits of said first mount, thereby permitting optimal thermal contact between said first heat sink and the first primary object.

10. The thermal transfer device of claim 1, further comprising a fluid conduit for conducting a thermal transfer fluid to at least one of said first and second heat sinks.

11. The thermal transfer device of claim 10, wherein said fluid conduit conducts thermal transfer fluid to both of said first and second heat sinks.

12. The thermal transfer device of claim 11, wherein said fluid conduit is formed to accommodate the expected relative positions of said first and second heat sinks.

13. The thermal transfer device of claim 12, wherein said fluid conduit is ductile, and can therefore deform slightly to accommodate the relative movements of said first and second heat sinks while they are independently affixed to said support structure and urged into thermal contact with said primary objects.

14. The thermal transfer device of claim 1, wherein said support structure comprises at least a first aperture sized to permit said first heat sink to pass therethrough to contact the top of the first primary object.

15. The thermal transfer device of claim 14, wherein said support structure comprises at least a second aperture sized to permit said second heat sink to pass therethrough to contact the top of the second primary object.

16. The thermal transfer device of claim 1, wherein said thermal transfer medium is a thermal transfer paste.

17. The thermal transfer device of claim 1, wherein said thermal transfer medium is a gap pad.

18. The thermal transfer device of claim 1, wherein said first heat sink is configured for optimum thermal contact with the first primary object.

19. The thermal transfer device of claim 18, wherein the top of the first primary object is substantially planar, and said first heat sink has a substantially planar surface for contacting the top of the first primary object.