Heat-spreading element and method for manufacturing the same

Abstract

The present invention relates to a heat-spreading element (1) for transferring heat from a heat source, such as a heat generating electronic component (110). The heat-spreading element (1) comprises a first face (10), configured to be in thermal contact with a heat source (100) and a second face (20), configured to be in thermal contact with a heat sink (200). A graphite body (30) is arranged between the first face (10) and the second face (20). The graphite body (30) comprises a graphite plane (32) that has an in-plane thermal conductivity that is higher than a cross- plane thermal conductivity of this plane, wherein the graphite plane is inclined, at least in some areas of the graphite body (30), relative to the first face (10).

Description

[0001] HEAT-SPREADING ELEMENT AND METHOD FOR MANUFACTURING THE SAME

[0002] TECHNICAL FIELD

[0003] The present invention relates to a heat spreading element, to an electronic module comprising said heat spreading element and to a method for manufacturing the heat spreading element.

[0004] BACKGROUND

[0005] Many digital and analog electronic components (e.g. semi-conductor components, such as FPGAs or ASICs) produce high power in the range of 40W or more that needs to be transported / dissipated away from the component.

[0006] Typically, a heat-spreader (or lid) is attached to the electronic component, making direct contact with the electronic component to carry the heat away from the heatsource. The heat spreading is needed to distribute the generated heat onto a heatsink, which is located further downstream. The heat sink may be part of a housing, a separate heat sink, and / or the like.

[0007] To improve the thermal and / or mechanical contact and to reduce the thermal resistance between the electronic component and the heat-spreader typically a first thermal interface material is applied between the electronic component and the heat-spreader. Generally, the first thermal interface material should have as low thermal resistance and as high thermal conductivity as possible.

[0008] Further, a second thermal interface material may be applied between the heatspreader and a heatsink. The function of second thermal interface material is twofold, namely (i) to conduct heat from heat-spreader and (ii) to improve the thermal and mechanical contact between the heat-spreader and the heat-sink.

[0009] Besides generally metallic based heat-spreaders, more complex heat spreaders, such as vapor chambers or heat-pipes are known. These more complex heat spreaders provide for a good heat dissipation, however, they are expensive and due to the higher complexity more prone to errors. Further, heat spreaders that are graphite based are known (e.g. from WO 2023 / 140 756 Al). While metallic based heat-spreaders, such as copper, CU, based heat-spreaders, are efficient in spreading the heat, in particular in a medium size range of about 30mmx30mmx2mm, they are heavy and difficult to assemble. Vapor chamber, VC, or heat-pipe heat spreaders are more complex and costly.

[0010] Further, in all heat spreaders described above, there is a coefficient of thermal expansion, CTE, mismatch between the heat-spreader and the electronic component. Thus, the electronic component is under mechanical stress when in use. To minimize the mechanical stress a relatively soft first thermal interface material can be used, that can compensate for the CTE mismatch. However, these soft first thermal interface materials have limited thermal conductivity and tend to be expensive.

[0011] SUMMARY

[0012] In view of the above, the object of the present invention is to provide a heat spreading element having a high thermal conductivity. Further, the heat spreading element's coefficient of thermal expansion can be matchable (during manufacturing). Particularly preferred is a coefficient of thermal expansion that is close to, or even meets the coefficient of thermal expansion of common semiconductors.

[0013] The objective is achieved by a heat-spreading element for transferring heat from a heat source, such as a heat generating electronic component. The heat generating electronic component may be semiconductor based, such as an ASIC or an FPGA or any type of high power semiconductor.

[0014] The heat-spreading element comprises a first face, configured to be in thermal contact with a heat source, particularly a heat generating electronic component. It is to be understood, that the first face or at least parts thereof are in direct or indirect contact for transferring heat from a heat source when the heat-spreading element is in use, i.e. placed on the heat source for transferring heat. In a particular aspect, the heat source and the first face of the heat-spreading element sandwich a first thermal interface material.

[0015] The first thermal interface material may be applied in a thickness of 10 pm to 500 pm, or in a thickness of 20 pm to 80 pm, or in a thickness of 40 pm to 60 pm. The first thermal interface material may have a thermal conductivity in a range from 10 Wm-1K_1to 300 Wm^K’1, or in a range from 100 Wm-1K_1to 150 Wm^K’1, or in a range from 120 Wm^K-1to 140 Wm-1K_1about 130 Wm^K’1. In a particular aspect, the first thermal interface material may have a thermal impedance of in a range from 3.3 e-7 m2KW-1to 4.0 e-7 m2KW-1, or in a range from 3,5 e-7 m2KW-1to 3.9 e-7 m2KW-1, or about 3.85 e-7 m2KW-1.

[0016] Further, the heat-spreading element comprises a second face. The second face is configured to be in thermal contact with a heat sink. This second face may at least partially be coated with a second thermal interface material to provide a good thermal contact between said second face and the heat sink. Between the first face and the second a graphite body is arranged. The graphite body comprises a graphite plane that has an in-plane thermal conductivity, kp,x-y-, that is higher than a cross-plane thermal conductivity, kp,z-, of this plane.

[0017] The characteristics of a thermal conductivity of graphite, in particular of pyrolytic graphite, are commonly described by referring to an in-plane thermal conductivity and a cross-plane thermal conductivity. The in-plane thermal conductivity is substantially larger than the cross-plane thermal conductivity. Thus, a heat conductivity in any direction along the graphite plane is larger than a heat conductivity that is not in a direction along the graphite plane. This means that the graphite plane defines a characteristic of the heat conductivity of the graphite inside the graphite body.

[0018] At least in some areas of the graphite body the graphite plane is inclined, relative to the first face, i.e. it is not parallel to the first face (at least in these respective areas). In an aspect the graphite plane is inclined over most of the graphite body or even over the entire graphite body. The inclination angle may be constant or may vary. Inclining the graphite plane leads to at least two improvements.

[0019] Firstly, as the in-plane thermal conductivity of a graphite body (x'- and y'-direc- tion) is significantly higher than the cross-plane thermal conductivity (z'-direc- tion), the thermal conductivity of the graphite body in normal direction (normal to the first face, z-direction) can be improved. This is, as due to the inclination, the high thermal conductivity of the graphite plane contributes to the thermal conductivity of the graphite body in normal direction (z-direction).

[0020] For example, the graphite body may have an in-plane thermal conductivity kp,x-y- in a range from 1400 Wm^K^ to 1800 Wm^K’1, or in a range from 1500 Wm^K-1to 1700 Wm^K’1, or about 1600 Wm^K’1. Further, the graphite body may have a cross-plane thermal conductivity kp,z- in a range from 3 Wm-1K_1to 30 Wm^K’1, or in a range from 8 Wm^K^ to 25 Wm^K’1, or about 15 Wm^K’1. The thermal conductivity of the graphite body in normal direction kb,z is about kb z= sin(a) ■ kPiX,y, + cos(a) ■ kPiZ, , wherein a denotes the inclination angle.

[0021] Secondly, as the in-plane coefficient of thermal expansion, CTEp,xy, of the graphite plane (x'- and y'-direction) is different from the cross-plane coefficient of thermal expansion, CTEP,Z- (z'-direction), the coefficient of thermal expansion of the graphite body in the plane of the first face of the heat-spreading element (x-, y-direc- tion) can be adjusted. For example, the graphite plane may have an in-plane coefficient of thermal expansion CTEp,x-y- in a range of about -0.8 ppm / °C to - 0.4 ppm / °C, particularly of about -0.5 ppm / °C , and a cross-plane coefficient of thermal expansion CTEP,Z- in a range of about 23 ppm / °C to 29 ppm / °C, particularly of about 26 ppm / °C.

[0022] The coefficient of thermal expansion of the graphite body in the plane of the first face of the heat-spreading element CTEb,xycan be adjusted by choosing an angle of inclination a according to the following formula.

[0023] CTEbiXy = cos(a) ■ CTEPiX,y, + sin(a) ■ CTEp z, ,

[0024] The coefficient of thermal expansion of the graphite body CTEb,zin a direction normal to the first face can be calculated as follows:

[0025] CTEb z= sin (a) ■ CTEp,x>y> + cos (a) ■ CTEp z> ,

[0026] Accordingly, the coefficient of thermal expansion of the graphite body in a plane of the first face of the heat-spreading element CTEb,xycan be adjusted to be in a range of about -0.5 to 3 ppm / °C, or in a range of about 2.4 ppm / °C to 2.9 ppm / °C, or 2.5 ppm / °C to 2.7 ppm / °C or of about 2.6 ppm / °C. Hence, the coefficient of thermal expansion of the graphite body in a plane of the first face of the heatspreading element CTEb,xycan be similar or even equal to the CTE of common semiconductors, such as silicon. Thus, the thermal stress between the heat spreading element and a heat source, such as a heat generating electronic component can be minimized.

[0027] Further, the coefficient of thermal expansion, CTE, of the graphite body can be adjusted by metallic matrix filled holes, as described in greater detail below. In an aspect, the first face may be arranged opposite to second face, wherein the first and second faces are substantially parallel. Thus, a plate-shaped heat-spreading element can be provided. Further, the shape of the heat-spreading element can be adjusted, to be wedge shaped, and / or the like.

[0028] In a further aspect the graphite body of the heat-spreading element may include a plurality of holes, which holes may at least partially (or entirely) be filled with a matrix material. These, filled holes may include at least one of the following:

[0029] • through holes, i.e. holes that extend from the first face to the second face,

[0030] • blind holes (type I), i.e. holes that extend from the first face towards the second face (but do not reach the second face), and

[0031] • blind holes (type II), i.e. holes that extend from the second face towards the first face (but do not reach the first face).

[0032] The matrix material filled holes further improve the heat conductivity (particularly in z-direction) of the heat-spreading element. This is, as the matrix material filled holes serve as thermal vias that can transport heat from the heat source into the graphite body. In the graphite body, the heat can be transferred to the graphite body and transported towards the heat sink. Further, the matrix material filled holes can transport heat from the graphite body towards the heat sink.

[0033] In an aspect, all or some of the matrix material filled holes are arranged in an area of the heat-spreading element that is configured to be in contact with the heat source on the first face, which allows to provide a direct path for heat transport from the heat source to the heat sink in this area.

[0034] In a further aspect, the graphite plane of the graphite body s is arranged to connect one or more of the matrix material filled holes with the second face in an x' and / or y' direction. This allows that heat is transported from the first face to the second face efficiently.

[0035] Further, a distribution, density and / or size of the matrix material filled holes can be chosen to adjust the coefficient of thermal expansion and the thermal conductivity of the heat-spreading element. Thus, the inclination angle a and / or the number (respectively the distribution and / or density) and size of matrix material filled holes can be chosen to adjust the thermal properties of the heat-spreading element.

[0036] For example, the holes may have a diameter in the range from 150 pm to 1000 pm, or in a range from 200 pm to 300 pm, in a range from 220 pm to 280 pm, or in a range from 500 pm to 600 pm. Further, the holes may be distributed with 10 to 100 holes per square centimeter, or with 20 to 80 holes per square centimeter, or with 30 to 60 holes per square centimeter. Even further, a density in x-direction may differ from a density in y-direction. Even further, the holes may be distributed on the first and / or second face evenly or unevenly. In case of an uneven distribution, an area of the first face that is intended to be in thermal contact with the heat source may have a higher hole density, than an area of the first face that is not intended to be in thermal contact with the heat source.

[0037] In a further aspect, the holes may extend substantially perpendicular from the first and / or second face. The matrix material may include a metallic matrix material including at least one of gold, silver, copper, aluminum, a gold based alloy, a silver based alloy, an aluminum based alloy and / or a copper based alloy. Additionally, or alternatively the matrix material may include a non-metallic matrix material, including at least one of, graphene, aluminum nitride, silicon carbide, and / or Beryllium.

[0038] In an aspect, the graphite plane is an inclined graphite plane that enclose an angle a with the first face. The angle a may be in a range between 2° to 45°, or in a range between 4° to 20°, or in a range between 5° to 15°, or in a range between 7° and 11°. These angles have shown to result in a desired coefficient of thermal expansion and a desired thermal conductivity of the heat-spreading element.

[0039] Further, the graphite body may include at least two sections. Each section may include an inclined graphite plane, wherein an orientation of the inclined graphite plane of a first section is different than an orientation of the inclined graphite plane of a second section. In a particular example, the graphite body may include three or four sections, wherein the orientation of the inclined graphite plane differs in each section.

[0040] For example, the sections may be arranged next to each other so that the inclined layers of the graphite body form a substantial roof shape or a substantial pyramidal shape. The graphite body itself may be substantially plate shaped. To form the graphite body, the single sections may be adhered to each other, e.g. by means of a graphite adhesive. In a further aspect, adjacent areas of the graphite body may have differently inclined graphite planes. These graphite planes of the graphite body may form a conical or bowl-shaped inner structure. The graphite body itself may be substantially plate shaped. Further, the size of the areas may be infinitesimally small, such that the in-plane thermal conductivity may follow an almost free shape, particularly said conical or bowl-shaped inner structure.

[0041] In a particular aspect, the graphite body may be a pyrolytic graphite body. The deposition of at least one graphite layer forming the graphite body may be done using a chemical vapor deposition, CVD, technique. The CVD technique involves e.g. the thermal decomposition of a hydrocarbon gas (such as methane) in a high- temperature furnace. During this process, carbon atoms are deposited on a substrate to form a thin film of pyrolytic graphite.

[0042] Further, the first and / or second face may be plated with a matrix material, particularly a metallic matrix material as specified above. Thus, the graphite body can be protected, e.g. form mechanical loads. The plating may have a thickness in a range from 1 pm to 300 pm, or from 100 pm to 150 pm. In a particular aspect, the plating metallic matrix material may be the same that is used for filling the holes. In a further aspect, the plating metallic matrix material differs from the metallic matrix material of the metallic matrix material filled holes.

[0043] The object is further achieved by an electronic module. The electronic module comprises a heat generating electronic component (e.g. a semiconductor based component, such as an ASIC or an FPGA) and a heat spreading element as described above. The heat spreading element is with its first face in thermal contact with the heat generating electronic component. Thus, heat generated by the electronic component can be effectively dissipated. Optionally a substrate for supporting the heat generating electronic component, such as a PCB, may be part of the electronic module. The PCB may provide for electrical connection points for the electronic component, such as bonding or soldering pads.

[0044] In a particular aspect, a first thermal interface material may be provided between the heat generating electronic component and the heat spreading element. Thus, a heat conductivity between the heat generating electronic component and the heat sink can be optimized. As the CTE of the heat spreading element matches the CTE of the heat generating electronic component, the first thermal interface material is not needed for balancing a CTE mismatch but can have a very high thermal conductivity.

[0045] In a further aspect, the electronic module may include a second thermal interface material. Said second thermal interface material may be provided on the second face of the heat spreading element. Optionally, a heat sink may also be provided, wherein the heat sink may be in thermal contact with the second face of the heat spreading element. In an aspect, the heat sink may be passively or actively cooled, e.g. by means of an air- or fluid flow.

[0046] The object is further achieved by a method manufacturing a heat-spreading element.

[0047] The method includes

[0048] • providing a base for depositing at least one graphite layer;

[0049] • depositing the at least one graphite layer (e.g. by CVD), wherein the graphite layer may be a pyrolytic graphite layer;

[0050] • cutting a graphite body or sections of a graphite body from the deposited graphite layer(s) and optionally assembling the sections (e.g. adhering the sections) to form a graphite bod. The cutting and / or assembling is performed such that the graphite body comprises a graphite plane that has an in-plane thermal conductivity, kp,x-y', that is higher than a cross-plane thermal conductivity, kp,z-, of this plane, and wherein the graphite plane is inclined, at least in some areas of the graphite body, relative to the first face.

[0051] Thus, a heat-spreading element can be provided that has a graphite body, which includes an inclined graphite plane. Thus, the advantages described above can be achieved.

[0052] It has to be understood, that the graphite layer can be deposited as a single layer having in-plane and cross-plane thermal properties, such as thermal conductivity and coefficient of thermal expansion, or multiple layers can be deposited. The deposited graphite may have at least the thickness of the later graphite body (i.e. after cutting and optionally assembling).

[0053] The method optionally includes drilling a plurality of holes in the graphite body, and filling at least some of the holes with a metallic matrix material. Thus, the thermal conductivity and / or the coefficient of thermal expansion can be further adjusted. In a further aspect, the method includes plating a first and / or second face of the graphite body with the metallic matrix material.

[0054] In a first embodiment, the base used for depositing the at least one graphite layer may include at least one recess. The recess may have a pyramidal, conical or bowl-like shape. Thus, when depositing the graphite layer in the at least one recess a body with at least one inclined graphite plane is deposited directly. The body may include at least two sections. Each section may include an inclined graphite plane, wherein the orientation of the inclined graphite plane of a first section is different than an orientation of the inclined graphite plane of a second section. In a particular example, the graphite body may include three or four sections, wherein the orientation of the inclined graphite plane differs in each section. For example, the deposited graphite layer (and accordingly the cut body) may have inclined planes that form a substantially pyramidal shape inner structure of the layer, corresponding to the shape of the recess.

[0055] In a second embodiment, the base used for depositing the graphite layer is substantially flat. Accordingly, the graphite layer is deposited on the substantially flat base, resulting in a flat graphite plane, which is parallel to the base. In this second embodiment, sections of a graphite body are cut from the graphite layer. The cutting of the sections is performed under an angle a, which angle a corresponds to the inclination angle a of the graphite plane in the assembled graphite body. These sections may then be assembled (e.g. adhered to each other) forming the graphite body.

[0056] BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Further features and advantages will be apparent from the following description as well as the accompanying figures, to which reference is made. The figures show in detail:

[0058] Fig. 1 a schematic illustration of an electronic module according to an embodiment;

[0059] Fig. 2 a schematic illustration of a heat spreading element according to an embodiment;

[0060] Fig. 3 a schematic top view of a heat spreading element according to an embodiment; Fig. 4 a schematic illustrations of a base for depositing graphite layers;

[0061] Figs. 5A-D schematic illustrations of method steps for manufacturing a heat spreading element, e.g. shown in Fig. 2;

[0062] Figs. 6A-C a schematic illustration of method steps of a different method for manufacturing a heat spreading element, e.g. shown in Fig. 2;

[0063] Fig. 7 a more detailed view of cutting sections used for manufacturing a heat spreading element;

[0064] Fig. 8 a top view of an assembled heat spreading element, and

[0065] Fig. 9 a cut view of a base for depositing graphite layers.

[0066] DETAILED DESCRIPTION

[0067] Fig. 1 shows a schematic illustration of an electronic module 300 according to an embodiment. The electronic module 300 comprises a heat generating electronic component 110 and a heat spreading element 1. The heat spreading element 1 is explained in greater detail with respect to Fig. 2. The electronic component 110 may be semiconductor based and may be an ASIC or a FPGA.

[0068] The heat spreading element 1 includes a first face 10 that is in thermal contact with the heat generating electronic component 110. For improving the thermal conductivity, a first thermal interface material 112 may be sandwiched between the heat generating electronic component 110 and the heat spreading element 1.

[0069] As shown in Fig. 1, the heat generating electronic component 110 may be smaller in size than the heat spreading element 1. Accordingly, only a portion of the first face of the heat spreading element 1 is in thermal contact with the heat generating electronic component 110.

[0070] The electronic module 300 may further include a substrate 120 (e.g. a PCB) for supporting the heat generating electronic component 110. The heat generating electronic component 110 may be soldered or bonded to the substrate 120. Here, a soldering layer 122 is shown. The substrate 120 may be soldered (or bonded) to a further PCB 400 as indicated by soldering layer 410. In an alternative, the heat generating electronic component 110 can be mounted to the substrate 120 or the PCB 400 via a socket. Further, a second thermal interface material 212 may be provided on a second face 20, being opposite to the first face 10 of the heat spreading element 1. The second thermal interface material 212 may be sandwiched between the heat spreading element and a heat sink 200. The second thermal interface material 212 may improve the heat conductivity from the heat spreading element 1 into the heat sink 200. The heat sink may be passively or actively cooled and may have a plurality of cooling ribs or cooling fingers 210.

[0071] In Fig. 2, the heat spreading element 1 is shown in more detail. The heat spreading element 1 includes a first face 10 that is configured to be in thermal contact with a heat source 100, e.g. with a heat generating electronic component 110. Further, the heat spreading element 1 includes a second face 20, which is (at least in the embodiment shown in Fig. 2) substantially parallel to the first face 10. The second face 20 is configured to be in thermal contact with a heat sink.

[0072] Between the first and the second faces 10, 20 a graphite body 30 is arranged. The graphite body 30 is substantially plate shaped. The graphite body 30 comprises a graphite plane 32 that has an in-plane thermal conductivity that is higher than a cross-plane thermal conductivity of this plane. Thus, heat is transported better in a direction along the plane 32 (x', y' direction) than in any other direction. To illustrate the primary direction of a heat transport that results from the characteristics of the thermal conductivity of the graphite body 30, the figures are illustrating multiple graphite planes 32, wherein a heat transport is primarily along these graphite planes 32. As can be seen from Figure 2, the graphite planes32 are inclined, relative to the first face 10. The inclination angle is a about 9° in the embodiment shown. As outlined above, the inclination angle a can be chosen to adjust the thermal conductivity and the coefficient of thermal expansion.

[0073] As the in-plane thermal conductivity, kp,xy, of the graphite planes 32 (x'- and y'- direction) is significantly higher than the cross-plane thermal conductivity, kp,z-, (i.e. in the z'-direction), the thermal conductivity of the graphite body 30 in normal direction (normal to the first face 10, z-direction) can be improved.

[0074] Further, as the in-plane coefficient of thermal expansion, CTEp,x-y-, of a graphite plane 32 (x'- and y'-direction differs from the cross-plane coefficient of thermal expansion CTE,P,Z- (z'-direction), the coefficient of thermal expansion of the graphite body 30 in the plane of the first face of the heat-spreading element (x-, y-direction) can be adjusted.

[0075] Even further, to improve the heat transfer into (or out of) the graphite body 30, a plurality of holes 34 can be provided. The holes 34 are at least partially filled with a metallic matrix material 40. The holes 34 may be through holes (as shown) or blind holes, extending from the first and / or second face 10, 20.

[0076] In Fig. 2, the graphite body 30 includes at least two sections 36a, 36c. Both sections 36a, 36c include inclined graphite planes 32, however, the orientation of the graphite planes 32 differs in the sections 36a, 36c.

[0077] In Fig. 3 a schematic top view of a heat spreading element 1 according to an embodiment is shown. The heat spreading element 1 includes a plate shaped graphite body 30 that includes four sections 36a, 36b, 36c, 36d. These sections include inclined graphite planes 32, wherein the orientation of the graphite planes 32 differs in each of the sections 36a, 36b, 36c, 36d. The sections may be adhered to each other to form the graphite body 30. Further, a plurality of metal matrix filled holes 34 is shown. In a central area 35, the areal density of the holes is higher than in a peripheral area. A heat source may be located in the central area 35 allowing generated heat to be transferred into the graphite body 30 and then to a heat sink.

[0078] Fig. 4 shows a schematic illustrations of a base 600 for depositing at least one graphite layer 33. The base 600 includes at least one recess 630. Here, for illustrative purposes, three recesses 630 are shown. The recesses 630 have a substantially pyramidal form. Hence, on each pyramid surface, a graphite layer 33 with inclined graphite planes 32 is deposited. From the deposited layer 32, a graphite body can be cut.

[0079] In Fig. 5A, a sectional view of the base 600 is shown. The pyramid surfaces are inclined with an angle a. Accordingly, the graphite planes 32 of the graphite layer 32 that is deposited, have an inclination angle a. As shown, the orientation of the inclined graphite planes 32 of the graphite layer 33 is different in sections 36a, 36c.

[0080] In Fig. 5B, the entire graphite layer 33 is deposited. As next step, the graphite body 30 can be cut from the deposited graphite layer 33. In Fig. 5C an exemplary cutting line 640 is shown. After being cut, a graphite body 30 is obtained (cf. Fig. 5D). This graphite body 30 includes inclined graphite planes 32 and a central area 35. At least in the central area, holes 34 can be drilled. The holes 34 can be filled with a metallic matrix material as shown in Fig. 2.

[0081] Figs. 6A-C illustrate a different method for manufacturing the heat spreading element 1 shown in Fig. 2. As shown in Fig. 6A, a graphite layer 33 is deposited on a substantially flat base 650. The graphite layer 33 has multiple graphite planes 32. After having deposited the graphite layer 33, the deposited graphite layer can be cut under an angle a, which corresponds to the inclination angle a, to obtain sections 36a. In Fig. 6B a corresponding cutting line 645 is shown. The cut sections 36a, 36c can be adhered to from a graphite body 30. This graphite body 30 includes inclined graphite planes 32 and a central area 35. At least in the central area, holes 34 can be drilled. The holes 34 can be filled with a metallic matrix material as shown in Fig. 2.

[0082] As best seen in Fig. 7, a plurality of section 36a, 36b, 36c, 36d can be cut from the deposited layer 33 in staggered fashion, thereby minimizing offcut material. The cut sections 36a, 36b, 36c, 36d may have an angled form (cf. Fig. 8) and can be assembled (e.g. adhered) to form a graphite body 30.

[0083] In Fig. 9 a further base 680 is shown, which has a bowl-like shaped recess 630. Hence, adjacent areas (which may be infinitesimally small) of the surface of said bowl-like shaped recess 630 have different inclination angles. In a graphite layer 33 is deposited into the recess 630, the graphite layer 33 will have planes 32, which form a bowl-shaped inner structure. The graphite body itself may be substantially plate shaped (after cutting).

[0084] Some of the embodiments contemplated herein are described more fully with reference to the accompanying figures. Other embodiments, however, are contained within the scope of the subject matter disclosed herein. The disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0085] The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

[0086] LIST OF REFERENCE SIGNS

[0087] 1 heat spreading element

[0088] 10 first face

[0089] 20 second face

[0090] 30 graphite body

[0091] 32 graphite plane

[0092] 33 graphite layer

[0093] 34 hole

[0094] 35 central area

[0095] 36a-d section

[0096] 40 metallic matrix material

[0097] 100 a heat source

[0098] 110 electronic component

[0099] 112 first thermal interface material

[0100] 120 substrate

[0101] 122 soldering layer

[0102] 200 heat sink

[0103] 210 cooling finger

[0104] 212 second thermal interface material

[0105] 300 electronic module

[0106] 400 PCB

[0107] 410 soldering layer

[0108] 600 base

[0109] 630 recess

[0110] 640 cutting line

[0111] 645 cutting line

[0112] 650 base

[0113] 680 base a inclination angle

Claims

CLAIMS1. A heat-spreading element (1) for transferring heat from a heat source (100), such as a heat generating electronic component (110), the heat-spreading element (1) comprising a first face (10), configured to be in thermal contact with a heat source (100); and a second face (20), configured to be in thermal contact with a heat sink (200), wherein a graphite body (30) is arranged between the first face (10) and the second face (20) wherein the graphite body (30) comprises a graphite plane (32) that has an inplane thermal conductivity, kp,x-y-, that is higher than a cross-plane thermal conductivity, kp,z-, of this plane, wherein the graphite plane (32) is inclined, at least in some areas of the graphite body (30), relative to the first face (10).

2. The heat-spreading element (1) according to claim 1, wherein the first face (10) is arranged opposite to second face (20), and wherein the first and second faces (10, 20) are substantially parallel.

3. The heat-spreading element (1) according to claim 1 or claim 2, wherein the graphite body (30), includes a plurality of holes extending from the first face (10) towards the second face (20), wherein the holes are at least partially filled with a matrix material (40), and / or a plurality of holes extending from the second face (20) towards the first face (10), wherein the holes are at least partially filled with a matrix material (40); and / or a plurality of holes (34) extending from the first face (10) to the second face (20), wherein the holes (34) are at least partially filled with a matrix material (40).

4. The heat-spreading element (1) according to any one of claims 1 to 3, wherein the holes (34) extend substantially perpendicular from the first and / or second face (10, 20), and / or whereinthe holes (34) have a diameter in the range from 150 m to 1000 pm, or in a range from 200 pm to 300 pm, or in a range from 220 pm to 280 pm.

5. The heat-spreading element (1) according to any one of claims 1 to 4, wherein the matrix material (40) includes a metallic matrix material including at least one of gold, silver, copper, aluminum, a gold based alloy, a silver based alloy, an aluminum based alloy and / or a copper based alloy, and / or wherein the matrix material includes a non-metallic matrix material, including at least one of, graphene, aluminum nitride, silicon carbide, and / or Beryllium.

6. The heat-spreading element (1) according to any one of claims 1 to 5, wherein the graphite plane (32) is an inclined graphite plane that encloses an angle a with the first face (10), wherein the angle a is in a range between 2° to 45°, or in a range between 4° to 20°, or in a range between 5° to 15°, or in a range between 7° and 11°.

7. The heat-spreading element (1) according to any one of claims 1 to 6, wherein the graphite plane (32) has an in-plane coefficient of thermal expansion, CTEp.xv, in a range of about -0.8 ppm / °C to - 0.4 ppm / °C, particularly of about -0.5 ppm / °C , and a cross-plane coefficient of thermal expansion, CTEP,Z-, in a range of about 23 ppm / °C to 29 ppm / °C, particularly of about 26 ppm / °C, and wherein the inclination angle a and / or the number and size of metallic matrix material (40) filled holes (34) may be chosen to achieve a coefficient of thermal expansion, CTEb,xy, in the plane of the first face (10) of the heat-spreading element (1) in a range of 2.4 ppm / °C to 2.9 ppm / °C, or 2.5 ppm / °C to 2.7 ppm / °C or of about 2.6 ppm / °C.

8. The heat-spreading element (1) according to any one of claims 1 to 7, wherein the graphite body (30) includes at least two sections (36a-d), each section including an inclined graphite plane (32), wherein an orientation of the inclined graphite plane (32) of a first section is different than an orientation of the inclined graphite plane (32) of a second section, whereinwhere the sections (36a-d) are optionally arranged next to each other so that the inclined planes (32) of the graphite body (30) form a substantial roof shape or a substantial pyramidal shape.

9. The heat-spreading element (1) according to any one of claims 1 to 8, wherein adjacent areas of the graphite body (30) include differently inclined graphite planes, wherein these graphite planes may form a conical or bowlshaped inner structure.

10. The heat-spreading element (1) according to any one of claims 1 to 9, wherein the graphite body (30) is a pyrolytic graphite body.

11. The heat-spreading element (1) according to any one of claims 1 to 10, wherein the first and / or second face (10, 20) are plated with a matrix material, the plating may have a thickness from 1 pm to 300 pm, or from 10 pm to 200 pm, or from 50 to 180 pm, or from 100 to 150 pm.

12. An electronic module (300) comprising a heat generating electronic component (110) and a heat spreading element (1) according to any one of claims 1 to 11, the heat spreading element (1) being on its first face (10) in thermal contact with the heat generating electronic component (110); optionally a substrate (120) for supporting the heat generating electronic component (110), and further optionally a first thermal interface material (112), being provided between the heat generating electronic component (110) and the heat spreading element (1).

13. The electronic module (300) of claim 12, further comprising a second thermal interface material (212), being provided on the second face (20) of the heat spreading element (1), and optionally a heat sink (200), the heat sink being in thermal contact with the second face (20) of the heat spreading element (1), wherein the heat sink (200) is configured to be air and / or fluid cooled.

14. Method for manufacturing a heat-spreading element (1) according to any one of claims 1 to 11, the method comprisingproviding a base (600; 650; 680) for depositing at least one graphite layer (33), depositing the at least one graphite layer (33) onto the base (600; 50; 680), wherein the graphite layer (33) may be a pyrolytic graphite layer; cutting a graphite body (30) or sections (36a-d) of a graphite body from the deposited graphite layer (33) and optionally assembling the sections (36a-d) to form a graphite body (30), wherein the cutting and / or assembling is performed such that the graphite body (30) comprises a graphite plane (32) that has an in-plane thermal conductivity, kp,x-y-, that is higher than a cross-plane thermal conductivity, kp,z-, of this plane, and wherein the graphite plane (32) is inclined, at least in some areas of the graphite body (30), relative to the first face (10).

15. The method of claim 14, the method further comprising: drilling a plurality of holes (34) in the graphite body (30), and filling at least some of the holes (34) with a metallic matrix material (40).

16. The method of claim 14 or 15, the method further comprising plating a first and / or second face (10, 20) of the graphite body (30) with the metallic matrix material (40).

17. The method of any one of claims 14 to 16, wherein the base (660, 680) includes at least one recess (630), the recess having a pyramidal, conical or bowl-like shape, and wherein the graphite layer (33) is deposited in the at least one recess (630).

18. The method of any one of claims 14 to 16, wherein the base is substantially flat, wherein the graphite layer (33) is deposited on the substantially flat base, and wherein cutting of the sections (36a-d) of a graphite body is performed under an angle a, which angle a corresponds to the inclination angle a of the graphite plane (32).

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