Heat Spreader Material

Abstract

The present invention relates to a method for manufacturing a heat spreader, comprising the following steps. i. depositing an adhesive onto a major surface of the at least one graphite layer to obtain at least one graphite layer coated with an adhesive layer; ii. placing the at least one graphite layer coated with an adhesive layer on top of one another to form a first stack of alternating graphite and adhesive layers; iii. disposing a graphite layer having a thickness of 10-200 μm on the first stack layer to form a second stack layer having the graphite layer as a top layer and a bottom layer; iv. compressing the layers of the second stack at a pressure of 7-20 MPa to form a graphite-based laminate; v. heating the graphite-based laminate to remove the solvent of the adhesive.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a graphite laminate, the graphite laminate and its use in a heat spreader device, which may be used to dissipate heat and prevent excessive temperatures in any heat generating element, such as integrated circuits, LED light sources, or semiconductor devices in various electronic products. [Background technology]

[0002] Until the early 2000s, heat spreader materials were made from aluminum and aluminum-based alloys. However, the demand for lighter and more efficient materials led to the development of graphite-based heat spreader materials. Graphite can be natural or synthetic. Natural graphite is mined, while synthetic graphite can be produced by graphitizing carbon-based materials. However, synthetic graphite differs from natural graphite in that it has a higher degree of crystallinity and fewer impurities, making it more conductive.

[0003] However, the greater the amount of heat that needs to be dissipated, the thicker the graphite-based heat spreader material becomes. Unfortunately, a rule of thumb for synthetic graphite is that the thicker the precursor film that is graphitized, the lower the crystallinity of the final graphitized film and therefore its thermal conductivity. This means that as the thickness of the precursor film increases, graphitization of the entire bulk material becomes less efficient.

[0004] Therefore, it has been common to laminate two or more graphite-based layers with an adhesive film to increase heat diffusion, but such graphite laminates result in the appearance of joints, wrinkles and bubbles, leading to yield loss. Summary of the Invention

[0005] An object of the present invention is to increase the yield of such graphite laminates. This is achieved by the manufacturing methods described in claims 1 to 11. This is also achieved by the graphite laminates described in claims 12 and 13. [Brief description of the drawings]

[0006] [Figure 1] 1 is an embodiment of the adhesive deposition step of the claimed process. [Diagram 2] 1 is an embodiment of two graphite layers coated with an adhesive layer. [Diagram 3] In one embodiment, a graphite layer is placed on the adhesive layer on top of the first stack of layers to form a second stack of layers having a graphite layer as a top layer and a bottom layer. [Figure 4] 1 is one embodiment of the compression step of the claimed process. [Diagram 5] 1 is an embodiment of the heating step of the claimed process. [Figure 6] 1 is an embodiment of a graphite laminate produced by the claimed process. [Figure 7] FIG. 7 is a plot showing the effect of pressure on the thermal conductivity of graphite laminate material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The present invention also relates to a method of manufacturing a heat spreader, comprising the steps of: i. depositing an adhesive 1 on a major surface of at least one graphite layer 2 to obtain at least one graphite layer coated with an adhesive layer, a. the adhesive layer 10 has a thickness of 0.5 to 10 μm and contains a solvent; b. the at least one graphite layer 2 has a thickness of 10-200 μm and two opposing main surfaces; ii. optionally, placing the at least one graphite layer coated with an adhesive layer on at least one further graphite layer 2 coated with an adhesive layer 10 to form a first stack of alternating graphite and adhesive layers, layer 3; iii. disposing a graphite layer 20 having a thickness of 10-200 μm on the first stack layer 3 to form a second stack layer 4 having graphite layers as top and bottom layers; iv. compressing the second stack layer 4 at a pressure of 7-20 MPa to form a graphite-based laminate 5; v. Heating the graphite based laminate 5 to remove the solvent of the adhesive.

[0008] The deposition step, step i., is shown in FIG. 1, in which an adhesive 1 is deposited on a major surface of a graphite layer 2, resulting in at least one graphite layer 2 coated with an adhesive layer 10, as shown in FIG. 2.

[0009] Preferably, in step i., the deposition is carried out by spraying. This can be done using an air spray gun fed either by gravity or by a pump. The adhesive is then sprayed manually or via automatic control, with parameters fixed according to the line of production requirements. Preferably, the air pressure is between 0.8 and 2 bar, selected depending on the opening of the needle for adhesive feeding.

[0010] Preferably, in step i., the deposition is carried out by rubbing the adhesive. This can be done using a sponge or cloth that is soaked in the adhesive and moved longitudinally relative to the film over its surface.

[0011] Alternatively, in step i., deposition can be performed by brushing and / or rolling and / or slot-die coating.

[0012] Preferably, in step i., the adhesive layer comprises an organofunctional silane and a functionalized nanoscale SiO 2 Even more preferably, in step i., the adhesive comprises an organofunctional silane and a functionalized nanoscale SiO 2 For example, the adhesive layer may be composed of organofunctional silanes and functionalized nanoscale SiO 2 It is a water-based sol-gel system composed of particles. The adhesive can be mixed with water.

[0013] Alternatively, in step i., the adhesive layer may include an amino-functional silane that is hydrolyzed prior to application.

[0014] Preferably, in step i, the adhesive layer has a thickness of 0.5 to 5 μm. Preferably, in step i, the adhesive layer has a thickness of 1 μm to 5 μm.

[0015] The at least one graphite layer can be any graphite in sheet or foil form that exhibits anisotropic thermal conductivity.

[0016] Preferably, in step i., the at least one graphite layer is made from compressed exfoliated natural graphite, pyrolytic graphite or heat-treated graphitizable polymer. Even more preferably, the at least one graphite layer is made from heat-treated polyimide. Even more preferably, the at least one graphite layer is made from graphene oxide. The formation process of such graphite layers is well known to those skilled in the art.

[0017] Preferably, in step i., the at least one graphite layer has a thickness of 15 to 200 μm. Such a thicker graphite layer increases the mechanical resistance and thus limits the risk of breakage during compression in step iv.

[0018] Preferably, in step i., the at least one graphite layer has a thermal conductivity of at least 400 W.mK. -1 , more advantageously at least 1000 W.mK -1 , and even more advantageously at least 1400 W.mK -1 It has an in-plane thermal conductivity of

[0019] In another embodiment, in step i., the at least one graphite layer has a thermal conductivity of 400 to 2500 W.mK -1 It has an in-plane thermal conductivity of

[0020] Preferably, in step i., the at least one graphite layer is composed of one film. Thus, each graphite layer is composed of one film.

[0021] Alternatively, in step i., the at least one graphite layer is composed of 2 to 6 films. Thus, each graphite layer is composed of 2 to 6 films.

[0022] Preferably, in step i, the adhesive layer is deposited on one graphite layer. Preferably, in step i, the adhesive layer is deposited on 2 to 7 graphite layers.

[0023] In step i., if adhesive is deposited on only one graphite layer, step ii. can be omitted since the coated graphite layer forms the first stack of layers.

[0024] In an optional step ii., the at least one graphite layer coated with an adhesive layer obtained in step i. is disposed on at least one further graphite layer coated with an adhesive layer. For example, the at least one graphite layer obtained with an adhesive layer can be disposed on two graphite layers coated with adhesive layers.

[0025] In step iii., a graphite layer 20 is placed on top of layer 3 of the first stack, as shown in Figure 3. The graphite layer is placed on the adhesive layer to form a stack of the following layers: - alternating graphite layers with adhesive layers; and - It has graphite layers as top and bottom layers.

[0026] Step iv. is embodied in FIG. 4, in which the second stack, layer 4, is compressed by a press P.

[0027] Preferably, in step iv., the compression is carried out at a pressure of 10 to 16 MPa.

[0028] Preferably, in step iv., the compacting is carried out by means of a press, preferably a hydraulic press.

[0029] Preferably, in step iv., the compression is performed by rollers.

[0030] Step v., aimed at removing the solvent, is well known to those skilled in the art.

[0031] Preferably, in step v., the heating is carried out at a temperature of 50° C. to 150° C. More preferably, in step iv., the heating is carried out at a temperature of 70° C. to 130° C.

[0032] Preferably, in step v, the heating is carried out for 20 to 120 minutes. Even more preferably, in step iv, the heating is carried out for 30 to 60 minutes.

[0033] The present invention relates to a graphite laminate 6 manufactured as described above, as shown in FIG. 6, which includes at least two graphite layers 200 having a thickness of 5-100 μm and at least one adhesive layer 100 having a thickness of 1-5 μm, - the at least two graphite layers 200 and the at least one adhesive layer 100 are arranged alternately on top of each other; - the top layer 7 and the bottom layer 8 of the graphite laminate are graphite layers; It also relates to graphite laminates.

[0034] Thus, the graphite layers 200 and the adhesive layers 100 are interleaved to form alternating graphite and adhesive layers. This is shown in Figure 6, where the graphite stack comprises five layers, namely three graphite layers and two adhesive layers, a graphite layer on top of an adhesive layer on top of a graphite layer on top of an adhesive layer on top of a graphite layer.

[0035] Preferably, the graphite laminate comprises 2 to 7 graphite layers.

[0036] Preferably, the at least two graphite layers are made from compressed exfoliated natural graphite, pyrolytic graphite or a heat-treated graphitizable polymer.

[0037] Preferably, the at least two graphite layers have a thickness of 15 to 100 μm.

[0038] Preferably, the at least two graphite layers have a thermal conductivity of 400 to 2500 W.mK. -1 It has an in-plane thermal conductivity of

[0039] The thickness of the adhesive layer of the graphite laminate is different from the thickness of the coated adhesive layer in step i. of the process due to the heating step (step v.) where the adhesive solvent is removed. Preferably, said at least one adhesive layer 100 has a thickness of 1-3 μm.

[0040] Preferably, the adhesive layer comprises an organofunctional silane and a functionalized nanoscale SiO 2Even more preferentially, said adhesive layer comprises organofunctional silanes and functionalized nanoscale SiO 2 It is composed of particles.

[0041] The present invention also relates to the use of said graphite laminate for a heat spreader device, which can be used in an electronic device, for example a mobile phone or a motherboard. EXAMPLES

[0042] Experimental Results Experimental tests were carried out to evaluate the effect of the value of the net pressure during step iii. of the claimed process.

[0043] For all trials, a 50 μm thick polyimide film was graphitized. To do so, the polyimide film was heated with N 2 The film was carbonized by heat treatment at 1000 °C for 60 min in an inert atmosphere of Ar to remove all non-carbon groups of the polymer. The carbonized film was then placed in a graphitization furnace in an inert atmosphere of Ar and heat treated up to 2800 °C to rearrange the carbon atoms in the graphite crystal lattice to obtain a graphite film of about 40 μm. The graphite film was then rolled to reduce the porosity and increase the thermal conductivity. The resulting film had a thermal conductivity of about 900-1000 W.mK. -1 and a thickness on the order of 25 μm.

[0044] For all trials, an adhesive layer of approximately 1 μm was deposited by spray coating on the first side of the graphite film, as shown in FIG.

[0045] The stack of layers was then pressed by a hydraulic press to form a compressed stack of layers as shown in Figure 4. Different pressure values ​​were tested for different stacks of layers to determine the best range.

[0046] The compressed stack of layers was then placed in an oven at a temperature of 70° C. for 30 minutes to remove the adhesive solvent, as shown in FIG.

[0047] Finally, the in-plane thermal conductivity was measured using the “Thermal Bridge Method” described in Yifeng Fu et al. 2020 2D Mater7 012001.

[0048] The results of the experiment are plotted in Figure 7, which plots the in-plane thermal conductivity as a function of the pressure applied to the compressed stack of layers.

[0049] It is evident that the value of pressure affects the in-plane conductivity of the graphite stack, and the best range is for pressure values ​​between 7 and 20 MPa.

Claims

1. A method of manufacturing a heat spreader, comprising the steps of: i. depositing an adhesive 1 on a main surface of at least one graphite layer 2 to obtain at least one graphite layer 2 coated with an adhesive layer 10, a. the adhesive layer 10 has a thickness of 0.5 to 10 μm and contains a solvent; b. the at least one graphite layer 2 has a thickness of 10-200 μm and has two opposing major surfaces; ii. Optionally, placing the at least one graphite layer coated with the adhesive layer on at least one further graphite layer 2 coated with an adhesive layer 10 to form a first stack of alternating graphite and adhesive layers, layer 3; iii. disposing a graphite layer 20 having a thickness of 10-200 μm on the first stack, layer 3, to form a second stack, layer 4, having graphite layers as top and bottom layers; iv. compressing the second stack of layers 4 at a pressure of 7-20 MPa to form a graphite-based laminate 5; v. Heating the graphite based laminate 5 to remove the solvent of the adhesive.

2. 2. The method of claim 1, wherein in step i., the depositing is performed by spraying the adhesive.

3. 2. The method of claim 1, wherein in step i., the depositing is performed by rubbing the adhesive.

4. In step i., the adhesive layer is formed by mixing organofunctional silane and functionalized nanoscale SiO ２ The method of claim 1 comprising particles.

5. 2. The method of claim 1, wherein in step i., the adhesive layer has a thickness of 1 to 5 μm.

6. 2. The method according to claim 1, wherein in step i., the at least one graphite layer 2 is made from compressed exfoliated natural graphite, pyrolytic graphite or a heat-treated graphitizable polymer.

7. In step i., the at least one graphite layer 2 is - has a thickness of between 15 and 200 μm, and / or - have an in-plane thermal conductivity of 400 to 2500 W.mK -1 The method of claim 1.

8. 2. The method of claim 1, wherein in step iv., the compacting is performed by a roller.

9. 2. The method of claim 1, wherein in step iv., the compressing is performed by a hydraulic press.

10. 2. The method of claim 1, wherein in step iv., the compression is carried out at a pressure of 10 to 16 MPa.

11. A graphite laminate 6 manufactured according to any one of claims 1 to 10, comprising at least two graphite layers 200 having a thickness of 5 to 100 μm and at least one adhesive layer 100 having a thickness of 1 to 5 μm, the at least two graphite layers 200 and the at least one adhesive layer 100 are arranged alternately on top of each other; a graphite stack, the top layer 7 and the bottom layer 8 of the graphite stack being graphite layers.

12. Graphite stack according to claim 11, wherein the graphite stack 6 comprises 2 to 7 graphite layers.

13. 12. Use of the graphite laminate of claim 11 in a heat spreader device.

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