Liquid immersion cooling device

Abstract

The purpose of the present invention is to provide a liquid immersion cooling device having an ability to improve cooling performance. A liquid immersion cooling device (1) includes an electronic device (10) and a cooling medium (20). An electronic device (10) includes a circuit board (11), a heat generator (20) mounted on the circuit board (11), a heat sink (13), and a thermally conductive sheet (14) disposed between the heat generator (12) and the heat sink (13). The cooling medium (14) is arranged to at least partially submerge the electronic device (10). At least a portion of the thermally conductive sheet (14) is made of a porous material.

Description

Technical Field

[0001] The present invention relates to a liquid immersion cooling device, and more particularly to a liquid immersion cooling device including an electronic device and a cooling medium. Background Art

[0002] WO2006 / 049768A1 discloses a liquid immersion cooling device for cooling a heat sink. The liquid immersion cooling device includes a heat transfer fluid held in an airtight sealed container. In the liquid immersion cooling device, a thermal interface material is disposed between a heat generator and a heat sink. For example, an indium sheet can be used as the thermal interface material. Summary of the invention

[0003] Technical issues

[0004] There is still room for improvement in the cooling performance of existing liquid immersion cooling devices.

[0005] An object of the present invention is to provide a liquid immersion cooling device having the capability of improving cooling performance.

[0006] Problem Solution

[0007] A liquid immersion cooling device according to one aspect of the present invention includes an electronic device and a cooling medium. The electronic device includes a circuit board, a heat generator mounted on the circuit board, a heat sink, and a heat conductive sheet inserted between the heat generator and the heat sink. The cooling medium is arranged to at least partially immerse the electronic device. At least a portion of the heat conductive sheet is made of a porous material.

[0008] A liquid immersion cooling device according to another aspect of the present invention includes an electronic device and a cooling medium. The electronic device includes a circuit board, a heat generator mounted on the circuit board, a heat sink, and a heat conductive sheet inserted between the heat generator and the heat sink. The cooling medium is arranged to at least partially immerse the electronic device. The heat conductive sheet has at least one selected from the group consisting of concave-convex, slits, grooves, and pores.

[0009] A liquid immersion cooling device according to another aspect of the present invention includes an electronic device and a cooling medium. The electronic device includes a circuit board, a heat generator mounted on the circuit board, a heat sink, and a heat conductive sheet inserted between the heat generator and the heat sink. The cooling medium is arranged to at least partially immerse the electronic device. The heat conductive sheet is made of graphite.

[0010] Advantageous Effects of the Invention

[0011] The present invention provides a liquid immersion cooling device having the capability of improving cooling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1is a schematic cross-sectional view showing a liquid immersion cooling device according to an exemplary embodiment of the present invention; and

[0013] Figure 2 is a schematic diagram showing a liquid immersion cooling device according to another embodiment of the present invention. DETAILED DESCRIPTION

[0014] 1. Overview

[0015] A liquid immersion cooling device 1 according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiments to be described below are merely exemplary embodiments of various embodiments of the present invention and should not be construed as limiting. More specifically, the exemplary embodiments can be easily modified in various ways according to design choices or any other factors without departing from the true spirit and scope of the present invention. The drawings referred to in the following description of the embodiments are all schematic diagrams. Therefore, the ratios of the sizes (including thicknesses) of the corresponding constituent elements shown in the drawings do not always reflect their actual size ratios.

[0016] In the above-mentioned known liquid immersion cooling device, for example, an indium sheet is used as a thermal interface material provided between the heat generator and the heat sink. The indium sheet is not compressible and therefore cannot fully fill the gap between the heat generator and the heat sink. The inventors have conducted extensive research and development to overcome such problems in the prior art. As a result, the inventors have found that by using a member having specific physical properties as a heat conductive sheet 14 between the heat generator 12 and the heat sink 13 in the liquid immersion cooling device 1, the cooling performance of the liquid immersion cooling device will be improved, thereby conceiving the concept of the present invention.

[0017] Figure 1 is a cross-sectional view showing an exemplary liquid immersion cooling device 1 according to the present embodiment. Figure 1 The illustrated liquid immersion cooling device 1 includes an electronic device 10 and a cooling medium 20. The electronic device 10 includes a circuit board 11, a heat generator 12 mounted on the circuit board 11, a heat sink 13, and a heat conductive sheet 14 interposed between the heat generator 12 and the heat sink 13. The cooling medium 20 is arranged to at least partially immerse the electronic device 10.

[0018] Figure 2 The liquid immersion cooling device 1 shown includes a plurality of (e.g. Figure 2 In the example shown, there are five electronic devices 10, all of which are immersed in the cooling medium 20. In addition, Figure 1 The illustrated immersion cooling device 1 further comprises a heat exchanger 30. The cooling medium 20 is supplied to the heat exchanger 30 by a pump (not shown), cooled by the heat exchanger 30, and then fed back to its original place.

[0019] In the liquid immersion cooling device 1 according to this embodiment, the heat conductive sheet 14 is characterized by: (1) being at least partially made of a porous material; (2) having at least one selected from the group consisting of concavoconvexity, slits, grooves and pores; or (3) being made of graphite.

[0020] The liquid immersion cooling device 1 according to this embodiment improves cooling performance. The reason why the liquid immersion cooling device 1 achieves this advantage by using one of these configurations can be inferred, for example, as follows. Specifically, the heat conductive sheet 14 having any one of the three features (1) to (3) can be easily folded into a specific shape, which makes it easier to fill the gap between the heat generator 12 and the heat sink 13. In addition, wetting the heat conductive sheet 14 with the cooling medium 20 also allows the air gap of the heat conductive sheet 14 to be filled. In addition, allowing the cooling medium 20 thus wetted to move inside the heat conductive sheet 14 and move to the surface of the heat conductive sheet 14 allows the heat conductive sheet 14 to be in close contact with the heat generator 12 and the heat sink 13. Therefore, this reduces the thermal resistance between the heat generator 12 and the heat sink 13. In addition, the cooling medium 20 is allowed to enter and leave the heat conductive sheet 14, and the heat generator 12 is repeatedly heated and cooled. Through such a mechanism, the cooling performance of the liquid immersion cooling device 1 will be improved.

[0021] Therefore, the liquid immersion cooling device 1 according to this embodiment can improve the cooling performance.

[0022] 2. Details

[0023] <Liquid Immersion Cooling Device>

[0024] Next, the liquid immersion cooling device 1 according to this embodiment will be described in detail.

[0025] [First embodiment]

[0026] The liquid immersion cooling device 1 comprises an electronic device 10 and a cooling medium 20. In the liquid immersion cooling device 1 according to the first embodiment, at least a portion of the heat conducting sheet 14 is made of a porous material.

[0027] The respective constituent elements of the immersion cooling device 1 will now be described one by one.

[0028] [Electronic devices]

[0029] The electronic device 10 includes a circuit board 11, a heat generator 12, a heat sink 13 and a heat conducting sheet 14. The liquid immersion cooling device 1 may include one electronic device 10 or a plurality of electronic devices 10, whichever is appropriate.

[0030] Examples of the electronic device 10 include an HDD, a DVD player, a mobile phone, a smart phone, a tablet computer, an electronic control unit (ECU) of an automobile, a power control unit (PCU), a display device (such as a liquid crystal display), an organic EL lamp, a solar cell, a touch screen, a camera module, an inverter, a converter, and a blade server that houses these devices and components (such as a memory and a central processing unit (CPU)) in a small housing.

[0031] (Circuit Board)

[0032] The circuit board 11 is a board including various circuits (such as an inverter circuit and a motor drive circuit) for starting the electronic device 10. The electronic device 10 may include only one circuit board 11 or a plurality of circuit boards 11, whichever is appropriate. The circuit board 11 may be a single-layer board or a multi-layer board, whichever is appropriate.

[0033] (Heat generator)

[0034] The heat generator 12 is a component that generates heat. The heat generator 12 is mounted on the circuit board 11. The heat generator 12 may be, for example, a semiconductor component. Examples of semiconductor components include, but are not limited to, transistors, central processing units (CPUs), microprocessing units (MPUs), driver ICs, and memories. The heat generator 12 may be composed of, for example, a heat spreader and a chip fixed on the heat spreader. The heat spreader may be, for example, a plate member made of metal. The chip may be, for example, a semiconductor package. In this case, the chip may be mounted on the heat spreader except for the peripheral portion of the heat spreader. The peripheral portion may have a plurality of screw holes at corresponding positions corresponding to the plurality of screw holes passing through the heat spreader.

[0035] (heat sink)

[0036] The heat sink 13 is a member to which the heat generated by the heat generator 12 is transferred. The heat can be dissipated from the heat sink 13. The heat sink 13 can be, for example, a heat sink. If the heat sink 13 is a plate-shaped heat sink, the heat sink 13 can also include heat dissipation fins. The heat sink 13 can have, for example, a plurality of screw holes at corresponding positions corresponding to the plurality of screw holes of the heat generator 12 described above.

[0037] (Thermal conductive sheet)

[0038] The heat conducting sheet 14 is a member for transferring heat from the heat generator 12 to the radiator 13. In the liquid immersion cooling device 1 according to the first embodiment, at least a portion of the heat conducting sheet 14 is made of a porous material. As used herein, "porous material" refers to a solid having internal pores (or air gaps). As used herein, "air gaps" refer to the corresponding portion of the constituent material of the heat conducting sheet 14 where there is no heat conducting sheet. The pores of the porous material may be connected holes or independent holes, either of which is suitable. The pores may or may not be connected to the surface of the heat conducting sheet 14. The pores are preferably connected to the connected holes connected to the surface. This makes it easier for the cooling medium 20 to infiltrate the heat conducting sheet 14. The air gap ratio of the heat conducting sheet 14 is preferably greater than or equal to 30% by volume and less than or equal to 95% by volume, and more preferably greater than or equal to 50% by volume and less than or equal to 90% by volume. As used herein, the air gap ratio (volume %) is calculated by [1-the apparent specific gravity of the heat conducting sheet / the true specific gravity of the constituent material of the heat conducting sheet] × 100. The apparent specific gravity of the thermally conductive sheet can be calculated based on the volume and mass obtained from the external dimensions of the thermally conductive sheet. Preferably, more than 50% by mass of the thermally conductive sheet 14 is a porous material. More preferably, more than 90% by mass of the thermally conductive sheet 14 is a porous material. Even 100% by mass of the thermally conductive sheet 14 can be a porous material.

[0039] As can be seen, the heat conducting sheet 14 has air gaps. In the liquid immersion cooling device 1, at least some of the air gaps are preferably wetted by the cooling medium 20. In this case, the cooling medium 20 wetted thereby can further reduce the thermal resistance of the heat conducting sheet 14.

[0040] The thermally conductive sheet 14 preferably has at least one structure selected from the group consisting of sponge, honeycomb structure, fiber and laminate. As used herein, "sponge" refers to a structure with countless internal pores, which can be connected pores or independent pores, whichever is suitable. As used herein, "honeycomb structure" refers to a structure as a bundle of multiple linear pores, which are separated from each other by thin boundary walls. The cross-section of each of these linear pores can have a hexagonal shape or any other suitable shape. As used herein, "fiber" refers to a structure in which each constituent material of the thermally conductive sheet has a fiber shape (for example, a ratio of its length to diameter is equal to or greater than 3). As used herein, "laminate" refers to a plurality of layered structures superimposed on each other.

[0041] The heat conductive sheet 14 having any of these structures may collapse easily when compressed, thereby more easily filling the gap between the heat generator 12 and the heat sink 13, and thus the thermal resistance may be further reduced.

[0042] The heat conductive sheet 14 preferably does not react with the cooling medium 20 , nor does it dissolve in the cooling medium 20 .

[0043] The compression rate of the thermally conductive sheet 14 when compressed in the thickness direction under the applied pressure of 200 kPa is preferably equal to or higher than 5% and equal to or lower than 95%. This allows the gaps between the thermally conductive sheet 14, the heat generator 12 and the heat sink 13 to be more fully filled, thereby further reducing the thermal resistance. The compression rate of the thermally conductive sheet 14 is more preferably equal to or higher than 20% and equal to or lower than 95%, and even more preferably equal to or higher than 30% and equal to or lower than 95%. As used herein, the "compression rate" of the thermally conductive sheet 14 refers to the percentage representation of 1-T1 / T0, where T0 is the initial thickness of the thermally conductive sheet 14, and T1 is the thickness of the thermally conductive sheet 14 after applying a pressure of 200 kPa.

[0044] The average thickness of the thermally conductive sheet 14 may be, for example, equal to or higher than 30 μm and equal to or lower than 500 μm, and preferably equal to or higher than 50 μm and equal to or lower than 200 μm. As used herein, “average thickness” refers to the arithmetic mean of thicknesses measured at a plurality of points (e.g., any 10 points) of the thermally conductive sheet 14.

[0045] [Cooling medium]

[0046] The cooling medium 20 is a medium for cooling the electronic device 10 (particularly its heat sink 13). The cooling medium 20 is generally held in, for example, a container, and is used by immersing the electronic device 10 in the cooling medium 20. For example, an insulating liquid having excellent electrical insulating properties can be used as the cooling medium 20.

[0047] Examples of the cooling medium 20 include hydrocarbon-based oils (such as hydrocarbons and polyalphaolefins (PAO)); fluorine-containing oils (such as perfluorocarbons, hydrofluorocarbons, hydrofluoroethers, and perfluoroketones); hydrocarbons (such as silicone oils, alkylbenzenes, alkylnaphthalenes, and alkyldiphenylalkanes); and medicinal oils (such as mineral oil). The cooling medium 20 preferably contains at least one of hydrocarbon-based oils or fluorine-containing oils.

[0048] [Heat exchanger]

[0049] The immersion cooling device 1 generally includes a heat exchanger 30. The heat exchanger 30 performs heat exchange between the cooling medium 20 supplied by a pump (not shown) and the cooling water supplied by a cooling unit (not shown), for example. This allows the temperature of the cooling medium 20 to be controlled, thereby further improving the cooling performance of the immersion cooling device 1.

[0050] [Second embodiment]

[0051] In the liquid immersion cooling device 1 according to the second embodiment, the heat conductive sheet 14 has at least one item selected from the group consisting of concavo-convex, slits, grooves and pores. Except for the heat conductive sheet 14, the liquid immersion cooling device 1 according to the second embodiment has the same configuration as the liquid immersion cooling device 1 according to the first embodiment.

[0052] The thermally conductive sheet 14 according to the second embodiment has at least one item selected from the group consisting of concavoconvex, slit, groove and pore. As used herein, the phrase "having concavoconvex" refers not only to the case where both concave and convex are provided, but also to the case where only concave or only convex is provided. "Slit" as used herein refers to a cut or cut with a narrow width that penetrates the thermally conductive sheet. "Groove" as used herein refers to a linear or curved opening that does not penetrate the thermally conductive sheet. "Porosity" as used herein refers to an orifice that does not penetrate the thermally conductive sheet and a through hole that penetrates the thermally conductive sheet.

[0053] In the liquid immersion cooling device 1 , the heat conducting sheet 14 having such a structure can be appropriately compressed, and the thermal resistance between the heat generator 12 and the heat sink 13 can be further reduced, thereby further improving the cooling performance of the liquid immersion cooling device 1 .

[0054] [Third embodiment]

[0055] In the liquid immersion cooling device 1 according to the third embodiment, the heat conductive sheet 14 is made of graphite. Except for the heat conductive sheet 14, the liquid immersion cooling device 1 according to the third embodiment has the same configuration as the liquid immersion cooling devices 1 according to the first and second embodiments.

[0056] The heat conductive sheet 14 according to the third embodiment is made of graphite. As used herein, "graphite" refers to black lead, which is one of the allotropes of carbon and is also called "plumbago". Graphite has a structure formed by stacking and combining a plurality of layers (graphene layers) in the thickness direction by van der Waals force, in each of which carbon atoms are arranged in the form of sp 2 The bonding is arranged in a hexagonal honeycomb grid shape. The graphite may also be, for example, a stack of multiple graphite layers (multilayer graphite).

[0057] In the liquid immersion cooling device 1, the heat conducting sheet 14 is made of graphite having such a structure, and therefore has a moderate air gap and can be moderately compressed, thereby further reducing the thermal resistance between the heat generator 12 and the heat sink 13. Therefore, this helps to further improve the cooling performance of the liquid immersion cooling device 1.

[0058] (Restate the main points)

[0059] As can be seen from the above description, the present invention has the following aspects. In the following description, reference numerals are added in parentheses of corresponding components only to clarify the corresponding relationship between the following aspects of the present invention and the above exemplary embodiments.

[0060] A liquid immersion cooling device (1) according to a first aspect comprises an electronic device (10) and a cooling medium (20). The electronic device (10) comprises a circuit board (11), a heat generator (12) mounted on the circuit board (11), a heat sink (13), and a heat conductive sheet (14) interposed between the heat generator (12) and the heat sink (13). The cooling medium (20) is arranged to at least partially immerse the electronic device (10). At least a portion of the heat conductive sheet (14) is made of a porous material.

[0061] According to a second aspect, a liquid immersion cooling device (1) comprises an electronic device (10) and a cooling medium (20). The electronic device (10) comprises a circuit board (11), a heat generator (12) mounted on the circuit board (11), a heat sink (13), and a heat conductive sheet (14) interposed between the heat generator (12) and the heat sink (13). The cooling medium (20) is arranged to at least partially immerse the electronic device (10). The heat conductive sheet (14) has at least one item selected from the group consisting of concave-convex, slits, grooves, and pores.

[0062] A liquid immersion cooling device (1) according to a third aspect comprises an electronic device (10) and a cooling medium (20). The electronic device (10) comprises a circuit board (11), a heat generator (12) mounted on the circuit board (11), a heat sink (13), and a heat conductive sheet (14) interposed between the heat generator (12) and the heat sink (13). The cooling medium (20) is arranged to at least partially immerse the electronic device (10). The heat conductive sheet (14) is made of graphite.

[0063] The first aspect, the second aspect and the third aspect can reduce the thermal resistance between the heat generator (12) and the heat sink (13), thereby improving the cooling performance of the liquid immersion cooling device (1).

[0064] In the liquid immersion cooling device (1) according to the fourth aspect which can be implemented in combination with any one of the first to third aspects, the heat conducting sheet (14) has an air gap, and at least a portion of the air gap is soaked in the cooling medium (20).

[0065] In a fourth aspect, the thermal resistance can be further reduced by providing the heat conducting sheet (14) with an air gap at least partially wetted by the cooling medium (20), thereby further improving the cooling performance of the liquid immersion cooling device (1).

[0066] In the liquid immersion cooling device (1) according to the fifth aspect which can be implemented in combination with any one of the first to fourth aspects, the heat conductive sheet (14) has at least one structure selected from the group consisting of sponge, honeycomb structure, fiber and laminate.

[0067] In the fifth aspect, the heat conducting sheet (14) can be formed by using at least one of these structures to reduce thermal resistance, thereby further improving the cooling performance of the liquid immersion cooling device (1).

[0068] In the liquid immersion cooling device (1) according to the sixth aspect which can be implemented in combination with any one of the first to fifth aspects, the heat conductive sheet (14) neither reacts with the cooling medium (20) nor dissolves in the cooling medium (20).

[0069] The sixth aspect allows the liquid immersion cooling device (1) to maintain sufficient cooling performance.

[0070] In the liquid immersion cooling device (1) according to the seventh aspect which can be implemented in combination with any one of the first to sixth aspects, when compressed in the thickness direction under an applied pressure of 200 kPa, the compression rate of the heat conductive sheet (14) is equal to or higher than 5% and equal to or lower than 95%.

[0071] The seventh aspect can also reduce the thermal resistance by setting the compression rate of the heat conductive sheet (14) to a value falling within the range, thereby further improving the cooling performance of the liquid immersion cooling device (1).

[0072] In the liquid immersion cooling device (1) according to the eighth aspect which can be implemented in combination with any one of the first to seventh aspects, the heat conductive sheet (14) contains graphite.

[0073] The eighth aspect can further reduce the thermal resistance of the heat conducting sheet (14), thereby further improving the cooling performance of the liquid immersion cooling device (1).

[0074] According to the liquid immersion cooling device (1) of the ninth aspect which can be implemented in combination with any one of the first to eighth aspects, the liquid immersion cooling device (1) further comprises a heat exchanger (30) for cooling the cooling medium (20).

[0075] In the ninth aspect, by providing a heat exchanger (30) for the liquid immersion cooling device (1), the liquid immersion cooling device (1) is allowed to control the temperature of the cooling medium (20), thereby further improving the cooling performance of the liquid immersion cooling device (1).

[0076] List of Reference Numerals

[0077] 1Liquid immersion cooling device

[0078] 10 Electronic devices

[0079] 11 Circuit Board

[0080] 12 Heat generator

[0081] 13 Radiator

[0082] 14 Heat conducting sheet

[0083] 20 Cooling medium

[0084] 30 heat exchangers.

Claims

1. A liquid immersion cooling device, comprising: An electronic device comprising a circuit board, a heat generator mounted on the circuit board, a heat sink, and a heat conducting sheet interposed between the heat generator and the heat sink; as well as a cooling medium arranged to at least partially immerse the electronic device, At least a portion of the heat conductive sheet is made of porous material.

2. A liquid immersion cooling device, comprising: An electronic device comprising a circuit board, a heat generator mounted on the circuit board, a heat sink, and a heat conducting sheet interposed between the heat generator and the heat sink; as well as a cooling medium arranged to at least partially immerse the electronic device, The thermally conductive sheet has at least one item selected from the group consisting of concavo-convex, slits, grooves and pores.

3. A liquid immersion cooling device, comprising: An electronic device comprising a circuit board, a heat generator mounted on the circuit board, a heat sink, and a heat conducting sheet interposed between the heat generator and the heat sink; as well as a cooling medium arranged to at least partially immerse the electronic device, The heat conducting sheet is made of graphite.

4. The liquid immersion cooling device according to any one of claims 1 to 3, wherein: The heat conductive sheet has an air gap, and At least a portion of the air gap is wetted by the cooling medium.

5. The liquid immersion cooling device according to any one of claims 1 to 3, wherein: The thermally conductive sheet has at least one structure selected from the group consisting of sponge, honeycomb structure, fiber and laminate.

6. The liquid immersion cooling device according to any one of claims 1 to 3, wherein: The heat conductive sheet neither reacts with the cooling medium nor dissolves in the cooling medium.

7. The liquid immersion cooling device according to any one of claims 1 to 3, wherein: The thermally conductive sheet has a compression rate when compressed in a thickness direction under an applied pressure of 200 kPa that is equal to or higher than 5% and equal to or lower than 95%.

8. The liquid immersion cooling device according to claim 1 or 2, wherein: The thermally conductive sheet contains graphite.

9. The liquid immersion cooling device according to any one of claims 1 to 3, further comprising a heat exchanger configured to cool the cooling medium.

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