Multi-layer composite heat-conducting sheet, preparation method and use thereof

Abstract

The present application provides a multi-layer composite thermally conductive sheet, a preparation method and a use thereof. The multilayer composite heat-conducting piece is composed of a specific metallic foil, a transition layer and a low-temperature alloy layer, has good thermal stability, solves the problems of liquid metal leakage, sagging, voids and the like, has excellent heat-conducting performance, and has a thermal conductivity coefficient of more than 25W / m·K and a thermal resistance of less than 0.025cm2·K / W.SOLUTION: The multi-layer composite heat conducting plate includes a metal foil, two transition layers disposed on two opposite surfaces of the metal foil, and two low temperature alloy layers respectively disposed on a surface of each transition layer away from the metal foil, wherein a material of the metal foil is at least one of silver, copper, zinc, and platinum, a material of the transition layer is one of indium and tin, a thickness of the transition layer is 5 to 13 μ m, and a melting point of the low temperature alloy layer is 30 to 300 °C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application belongs to the technical field of thermally conductive materials, and in particular to a multi-layer composite thermally conductive piece, its preparation method and use. [Background technology]

[0002] Liquid metal is a new thermal interface material that offers low thermal resistance and high thermal conductivity, allowing it to be used to solve heat dissipation problems in electronic devices. Liquid metal's fluidity currently poses a risk of leakage during use. While surrounding an electronic device (e.g., a chip) with a foam can reduce the risk of short circuits caused by liquid metal leakage to some extent, this method increases costs and requires a large volume. Furthermore, the gap between the foam and the chip surface makes it impossible to completely prevent liquid metal leakage. As a result, problems such as voids and drips can occur after the liquid metal undergoes a phase change and melts, significantly impacting the product's thermal conductivity.

[0003] In previous research, the liquid metal leakage problem was solved to some extent by spraying liquid metal onto the surface of the indium layer to create a multi-layer thermal conductive piece. However, the structure was generally relatively complex, and the installation of the multi-layer structure increased the contact thermal resistance, making it impossible to effectively improve the thermal conductivity performance of the entire product. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the shortcomings of the prior art, the embodiments of the present application aim to provide a multi-layer composite thermal conductive plate, its preparation method and use, which solves the problems of leakage, voids, sagging, etc. after the phase change of liquid metal, and improves the thermal conductivity performance of the thermal conductive plate. [Means for solving the problem]

[0005] In a first aspect, an embodiment of the present application provides a multi-layer composite thermally conductive plate, which includes a metal foil, two transition layers disposed on opposite surfaces of the metal foil, respectively, and two low-temperature alloy layers disposed on the transition layers' surfaces spaced apart from the metal foil, wherein the metal foil is made of at least one of silver, copper, zinc, and platinum, and the transition layers are made of indium or tin, with a thickness of 5-13 μm. According to the GB / T 9286-1998 test standard, the adhesion of the transition layers to the surface of the metal foil is grade 0, i.e., the highest level, and the melting point of the low-temperature alloy layers is 30-300°C.

[0006] This application uses a metal foil as a central substrate, a transition layer on the surface of the metal foil, and a low-temperature alloy layer on the surface of the transition layer. When the low-temperature alloy layer undergoes a phase change and melts, the transition layer quickly reacts with the liquid metal to form an alloy, thereby effectively overcoming problems such as liquid metal leakage, dripping, and voids. By controlling its composition, making its thickness relatively thin, and maximizing its adhesion, it is stably connected to the metal foil and the low-temperature alloy layer, improving the adhesion between the transition layer and the metal foil and between the transition layer and the low-temperature alloy layer, reducing the thermal contact resistance between the different material layers, and ensuring the integrity and stability of the entire structure. The simple combination of the metal foil, transition layer, and low-temperature alloy layer results in a multilayer composite thermal conductive plate with excellent thermal conductivity, with a thermal conductivity coefficient of more than 25 W / m·K and a thermal resistance of 0.025 cm. 2 ·K / W or less.

[0007] In some embodiments of the present application, the composition of the low-temperature alloy layer is, in parts by mass, 45 to 70 parts In, 20 to 40 parts Bi, 5 to 20 parts Sn, and 0 to 15 parts Ga. More preferably, the material of the low-temperature alloy layer is In. 51 Bi 30.5 Sn 15.5 It is a quaternary alloy of Ga3. In some embodiments of the present application, the thickness of the transition layer is 6-8 μm. In some examples of the present application, the thickness of the metal foil is 0.01 to 0.5 mm. In some embodiments of the present application, the low-temperature alloy layer has a thickness of 5 to 40 μm.

[0008] In a second aspect, an embodiment of the present application provides a method for preparing the above-mentioned multi-layer composite thermally conductive piece, the method comprising: forming a transition layer on each of two opposing surfaces of a metal foil; and spraying a liquid metal onto the side of each transition layer remote from the metal foil to form a low temperature alloy layer.

[0009] In some embodiments of the present application, the step of forming a transition layer on each of the two opposite surfaces of the metal foil specifically includes: The method includes forming a transition layer on each of the two opposing surfaces of the metal foil by electroplating or magnetron sputtering.

[0010] By using electroplating or magnetron sputtering, the adhesion of the transition layer to the surface of the metal foil can be improved, the connection can be stabilized, and the transition layer can be made dense and uniform, thereby effectively reducing the interfacial thermal resistance between the transition layer and the metal foil.

[0011] In some embodiments of the present application, the electroplating step specifically includes immersing the metal foil in an electroplating solution to form a transition layer on the surface of the metal foil by electroplating, and the electroplating solution includes an anionic surfactant and a nonionic surfactant.

[0012] In a third aspect, the present application further provides a use of the above-mentioned multilayer composite thermally conductive plate. For example, the above-mentioned multilayer composite thermally conductive plate can be used for heat dissipation of electronic devices.

[0013] In order to more clearly explain the technical solutions of the embodiments of the present application, the drawings used in the embodiments will be briefly described below. The drawings described are only for illustrating some embodiments of the present application and are not intended to limit the scope. Those skilled in the art can obtain other related drawings based on these drawings without using inventive abilities. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of a multilayer composite heat-conducting plate according to the present application; [Figure 2] 1 is a diagram showing the state of the multi-layer composite thermally conductive plate according to Example 1 of the present application after a thermal resistance test. [Figure 3] 1 is a diagram showing the state of the multi-layer composite thermally conductive piece according to Example 1 of the present application after a sagging test at 125° C. for 500 hours. [Figure 4] 1 is a diagram showing the state of the multi-layer composite thermally conductive piece according to Example 1 of the present application after a sagging test at 125° C. for 1000 hours. [Figure 5] 1 is a diagram showing the results of an adhesion test in Example 1 of the present application. [Figure 6] 1 is a diagram showing the results of an adhesion test of Comparative Example 4 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to more clearly explain the objectives, technical solutions and advantages of the examples of this application, the technical solutions in the examples of this application will be clearly and completely explained. For examples where specific conditions are not specified, the experiments can be carried out under conventional conditions or under conditions recommended by the manufacturer. For reagents or equipment where the manufacturer is not specified, conventional products available on the market can be used.

[0016] The multi-layer composite thermally conductive piece according to the embodiment of the present application, its preparation method and use will be specifically described below.

[0017] Referring to Figure 1, a multilayer composite thermally conductive plate 100 according to an embodiment of the present application includes a metal foil 10, two transition layers 20 disposed on opposite surfaces of the metal foil 10, and two low-temperature alloy layers 30 disposed on the surfaces of the transition layers 20 spaced apart from the metal foil 10. The metal foil 10 is made of at least one of silver, copper, zinc, and platinum, and the transition layers 20 are made of indium or tin. The transition layers 20 have a thickness of 5-13 μm, and according to the GB / T 9286-1998 test standard, the adhesion of the transition layers to the metal foil surface is grade 0. The melting point of the low-temperature alloy layers 30 is 30-300°C.

[0018] Those skilled in the art will understand that in a multilayer composite structure, there are differences in interfacial thermal resistance between each material layer, and different materials have different thermal conductivities and phonon propagation speeds. Therefore, the more layers there are, the lower the thermal resistance will be. The multilayer composite thermal conductive piece 100 of the present application has a simple five-layer structure and includes three materials: a metal foil 10, a transition layer 20, and a low-temperature alloy layer 30. The metal foil 10 is the central base layer, which has excellent thermal conductivity, high strength, and flexibility, and can function as the framework of the product while also providing high thermal conductivity. The indium or tin layer serves as the transition layer 20, connecting the metal foil 10 and the low-temperature alloy layer 30. The transition layer 20 bonds with the molten liquid metal on its surface, quickly absorbing the liquid metal on the surface and preventing leakage. By controlling the transition layer 20 to have the highest level of adhesion and a relatively thin thickness, it is possible to ensure that the liquid metal on the surface can be completely absorbed and that it adheres firmly to the metal foil 10, thereby reducing the thermal contact resistance between different materials, preventing the layers from peeling off from each other, and ensuring the stability of the entire structure.

[0019] The low-temperature alloy layer 30 according to the present application has a melting point of 30 to 300°C and is solid at room temperature. When heated (e.g., 50 to 70°C), it undergoes a phase change and melts. Part of it fills the gaps at the thermal interface, for example, filling minor irregularities and gaps between the chip and the heat dissipation unit, resulting in extremely low thermal resistance and functioning as a "thermal interface material." Another part of it quickly reacts and fuses with the transition layer 20 to form a new alloy, preventing leakage.

[0020] The metal foil, transition layer, and low-temperature alloy layer in this application cooperate with each other to ensure the integrity and stability of the multilayer composite thermal conductive plate, so that during normal operation of the device to be heat dissipated, the thermal conductive plate as a whole remains solid (without liquid), effectively solving the important defects of liquid metal such as flow and dripping, and effectively improving the thermal conductivity performance of the entire structure. The multilayer composite thermal conductive plate has a thermal conductivity coefficient of 25 W / m·K or more and a thermal resistance of 0.025 cm 2 Under favorable conditions, the multilayer composite thermally conductive piece 100 has a thermal conductivity coefficient of up to 32.5 W / m·K and a thermal resistance of 0.007 cm 2 -Can be reduced to 1000kJ / W.

[0021] The low-temperature alloy described in the present application is a low-melting-point alloy, preferably having a melting point of 30-130°C, and generally made of low-melting-point metal elements such as In, Bi, and Sn. In some embodiments, the respective components in the low-temperature alloy layer are, by mass, 50-70 parts In, 20-40 parts Bi, 5-20 parts Sn, and 0-15 parts Ga. Specifically, In 51 Bi 30.5 Sn 15.5 Ga3, In 63 Bi 20 Sn 10 Ga7, In 49 Bi 28 Sn 11 Ga 12 and quaternary alloys.

[0022] Preferably, the material of the low-temperature alloy layer is In 51 Bi 30.5 Sn 15.5 It is a quaternary alloy of Ga3, and the material of the transition layer is indium, which can ensure good bonding between the low temperature alloy layer and the indium layer.

[0023] The higher the mass part of gallium, the more corrosive, the lower the melting point of the liquid alloy formed, the more fluid it becomes, and the less stable the multilayer composite thermally conductive piece prepared becomes. In some embodiments, the thickness of the metal foil is 0.01 to 0.5 mm. Metal foils have high thermal conductivity (for example, the thermal conductivity of copper foils is as high as 400 W) and high strength, and the thinner the foil, the lower the thermal resistance. However, if the foil is too thin, the surface will not be flat due to internal residual stress (for example, copper has low plasticity).

[0024] In some embodiments, the thickness of the transition layer is 6-8 μm, and specifically may be 6 μm, 6.3 μm, 6.2 μm, 5.5 μm, etc. The thermal conductivity of the transition layer is inferior to that of the metal foil; for example, the thermal conductivity of the indium strip is only 80 W. If the thickness is too thin, it will not be able to fully absorb the liquid metal on the surface; if it is too thick, it will impair the thermal conductivity. Furthermore, the adhesive strength and uniformity of the transition layer to the metal foil also affect the thermal stability and contact thermal resistance of the entire thermal conductive strip.

[0025] In some embodiments, the thickness of the low-temperature alloy layer is 5-40 μm, and specifically may be 20 μm, 40 μm, 5 μm, etc. The low-temperature alloy layer must fill the gaps and fuse with the transition layer to form a high-melting-point alloy, thereby ensuring that the molten low-temperature alloy does not leak out. Therefore, if the low-temperature alloy layer is too thick, excess liquid molten metal will leak out, and if it is too thin, the gap filling effect will be poor and the thermal conductivity will be poor.

[0026] Accordingly, the present application further provides a method for preparing the above-mentioned multi-layer composite thermally conductive piece, the method for preparing comprising: forming a transition layer on each of two opposing surfaces of a metal foil; and spraying a liquid metal onto the side of each transition layer remote from the metal foil to form a low temperature alloy layer.

[0027] A transition layer is formed on each of the two opposing surfaces of the metal foil by electroplating or magnetron sputtering.

[0028] By using electroplating or magnetron sputtering instead of rolling or coating, the transition layer is densely and uniformly distributed on the surface of the metal foil, resulting in an extremely thin layer with zero adhesion, which reduces the thermal contact resistance at the interface between the different materials and ensures the stability of the entire structure. Because an oxide film is often present on the surface of the metal foil, the transition layer and the metal foil are not well bonded when using conventional rolling or coating methods, resulting in extremely high thermal contact resistance between the two. Furthermore, low-melting-point liquid metal alloys are intermetallic compounds, which are harder and more brittle than pure metals. If adhesion is insufficient, the transition layer will peel off from the surface of the metal foil when the liquid metal is still unmelted.

[0029] Specifically, the steps of using electroplating include: The metal foil is immersed in the electroplating solution and an electric current is passed through it for a certain period of time, forming a transition layer by electroplating on each of the two surfaces of the metal foil. The electroplating solution contains an anionic surfactant and a nonionic surfactant. The anionic surfactant is sodium lauryl sulfate, and the nonionic surfactant is ethoxylated sec-alcohol (C=11-15) (CAS: 68131-40-8). The anionic surfactant and nonionic surfactant improve the adhesion, uniformity, and purity of the plating layer to the target surface.

[0030] The electroplating solution may further include indium ions or tin ions, such as indium sulfate or tin sulfate. In some embodiments, the electroplating solution may further include sodium hydroxide, where the sodium hydroxide is for adjusting the pH. The present application also provides a use of the above-mentioned multilayer composite thermally conductive plate, which can be used for heat dissipation of an electronic device, for example, a chip or a heat sink, as an example and not a limitation. The following examples further illustrate the features and performance of the present application.

[0031] Example 1 This embodiment provides a multi-layer composite heat conducting plate, in which the metal foil is a copper plate, the transition layer is an indium layer, and the low-temperature alloy layer is In 51 Bi 30.5 Sn 15.5 The Ga3 quaternary alloy multilayer composite thermal conductive strip was prepared by the following method. (1) The copper foil was rolled into a metal foil having a thickness of 0.05 mm. (2) The above metal foil is placed in an electroplating solution to perform indium electrodeposition, and the current density is 1 A / m 2 After applying current for 2 hours, the solution is dried and a transition layer is formed on each of the two surfaces of the metal foil. The electroplating solution contains dilute sulfuric acid, indium sulfate, sodium lauryl sulfate, ethoxylated sec-alcohol (C=11-15) (CAS: 68131-40-8), and sodium hydroxide. (3) 4N pure indium particles, bismuth particles, tin particles, and gallium particles are used as raw materials for the low-temperature alloy layer, and the mass fraction ratio of indium particles, bismuth particles, tin particles, and gallium particles is 51:30.5:15.5:3. The raw materials weighed in this ratio are placed in a medium-frequency vacuum melting furnace, evacuated, heated to 400°C, and maintained for 2 hours. Then, they are removed and placed in a vacuum heating stirrer, maintained at 80°C, and stirred at a speed of 400 rad / min for 30 minutes to uniformly mix the liquid metal, resulting in In 51 Bi 30.5 Sn 15.5 A Ga3 quaternary alloy was obtained, with a melting point of 55-60°C. (4) The homogeneously mixed liquid metal was injected into a heated mechanical pump, which was then connected to a heating tube, which was then connected to a heated spray head. The overall temperature was maintained at 120°C. The mechanical pump was activated to pump the liquid metal into the spray tube for spray application. The direction of the spray head was set to spray the liquid metal onto the desired area, and the servo motor was adjusted to control the spray speed to 200mm / c. The heat dissipation unit to be sprayed was placed below the spray head, which was 30cm away from the surface to be sprayed. The liquid metal mist was sprayed evenly onto the surface of the transition layer, forming a 20μm-thick low-temperature alloy layer, which was then cooled and formed into a multilayer composite thermal conductive piece.

[0032] Example 2 The preparation method of this example was basically the same as that of Example 1, except that the thickness of the metal foil in step (1) was 0.1 mm.

[0033] Example 3 The preparation method of this example was basically the same as that of Example 1, except that the thickness of the metal foil in step (1) was 0.2 mm.

[0034] Example 4 The preparation method of this example was basically the same as that of Example 1, except that the thickness of the metal foil in step (1) was 0.01 mm.

[0035] Example 5 This example is basically the same as the preparation method of Example 1. The liquid metal in step (3) is made from 4N pure indium particles, bismuth particles, tin particles, and gallium particles, with a mass fraction ratio of 63:20:10:7. 63 Bi 20 Sn 10 The only difference was that the melting point of the Ga7 quaternary alloy was 45-50℃.

[0036] Example 6 This example is basically the same as the preparation method of Example 1. The liquid metal in step (3) is made from 4N pure indium particles, bismuth particles, tin particles, and gallium particles, with a mass fraction ratio of 49:28:11:12. 49 Bi 28 Sn 11 Ga 12 The only difference was that the melting points of the quaternary alloys were 40-45°C.

[0037] Example 7 The preparation method of this example was basically the same as that of Example 1, except that the thickness of the low-temperature alloy layer sprayed in step (4) was 5 μm.

[0038] Example 8 The preparation method of this example was basically the same as that of Example 1, except that the thickness of the low-temperature alloy layer sprayed in step (4) was 40 μm.

[0039] Example 9 The preparation method of this example was basically the same as that of Example 1, except that the current application time in step (2) was 4 hours.

[0040] Comparative Example 1 The preparation method of this comparative example was basically the same as that of Example 1, except that the current application time in step (2) was 5 hours.

[0041] Comparative Example 2 The preparation method of this comparative example was basically the same as that of Example 1, except that the current application time in step (2) was 0.5 hours.

[0042] Comparative Example 3 The preparation method of this comparative example was basically the same as that of Example 1, except that in step (2), the indium piece was rolled into a metal foil to obtain a transition layer with a thickness of 6 μm.

[0043] Comparative Example 4 The preparation method of this comparative example was basically the same as that of Example 1, except that in step (2), a layer of molten indium was applied to the surface of the metal foil, and after drying, a 6 μm-thick indium layer was obtained. The multi-layer composite heat-conducting pieces prepared in Examples 1 to 9 and Comparative Examples 1 to 4 were subjected to performance tests, and the methods of each performance test were as follows: (1) Thermal conductivity / thermal resistance: The test was carried out using a Taiwan Swiss thermal conductivity testing device (model: Longwin 9389), and the test parameters were 50 psi, 80°C, and 20 minutes. (2) Sagging: The multilayer composite heat-conducting piece was left standing in an oven at 125°C for 500 hours and 1000 hours. (3) Adhesion: After forming the transition layer on the metal foil, the samples were selected and tested for the adhesion of the transition layer on the metal foil according to the GBT9286-1998 test standard. Based on the test results, the adhesion was classified into six grades from grade 0 to grade 5, and the corresponding evaluation criteria for each grade were as follows:

[0044] Grade 0: The cutting edge is completely smooth and there is no missing lattice. Grade 1: A small amount of coating has fallen off at the intersection of the cut ends, but the affected area of ​​the cross cut does not significantly exceed 5%. Grade 2: Missing coating at the intersection of the cuts and / or along the edges of the cuts, with the affected area of ​​the intersecting cuts clearly exceeding 5% and not exceeding 15%. Grade 3: The coating has broken off in pieces partially or completely along the cut edge and / or partially or completely in different parts of the grid, with the cross-cut area affected clearly exceeding 15% and not clearly exceeding 35%. Grade 4: The coating has flaked off in large pieces along the cut edge and / or some grids have partially or completely flaked off, with the affected cross-cut area clearly exceeding 35% and not clearly exceeding 65%. Grade 5: The degree of peeling exceeds Grade 4.

[0045] The test results for the above performance are shown in Table 1. [Table 1]

[0046] As can be seen from the comparison of the performance test results in Table 1, all of the multilayer composite thermally conductive pieces prepared in Examples 1 to 9 have a thermal conductivity coefficient of 25 W / m·K or more and a thermal resistance of 0.025 cm 22, 3, and 4, the product had no sagging, deformation, or leakage. Comparing the test results of Comparative Examples 1 and 2 with those of Example 1, it can be seen that if the transition layer was too thick or too thin, the thermal conductivity performance of the final thermal conductive piece was impaired and the adhesive strength rating was also reduced. Comparing the test results between Comparative Examples 3 and 4 and Example 1, it can be seen that in Example 1, the transition layer was formed by electroplating. As can be seen from the adhesion test results shown in Figure 5, the cut surface of the transition layer was smooth, no lattice fell off after peeling off the adhesive tape, the adhesion grade was 0, the corresponding thermal conductivity was 32.5 W / m K higher, and the thermal resistance was 0.007 cm 2 .K / W. In Comparative Examples 3 and 4, the transition layer formed by rolling or coating was not uniform, resulting in a significant decrease in adhesion of the transition layer to the surface of the metal foil. As can be seen from the phase diagram of Comparative Example 4 after the adhesion test shown in Figure 6, the marked area in the diagram fell off. Furthermore, due to the lack of adhesion, an oxide layer formed on the surface of the metal foil, affecting the heat conduction path (the heat conduction performance of the oxide layer is ten or even several tens of times lower than that of pure metal), thereby reducing the heat conduction performance of the entire heat conductive piece.

[0047] The above examples are only some of the examples of the present application, but not all of the examples. The detailed description of the examples of the present application does not limit the scope of the application to be protected, but is only selected examples of the present application. All other examples that a person skilled in the art can obtain based on the examples in the present application without using his or her inventive ability also fall within the scope of protection of the present application. [Explanation of symbols]

[0048] 10 Metal foil 20 Transient layer 30 Low-temperature alloy layer 100 Multilayer composite heat conductive sheet

Claims

1. The invention comprises a metal foil, two transition layers provided on two opposite surfaces of the metal foil, and two low-temperature alloy layers provided on the surfaces of the transition layers spaced apart from the metal foil, the material of the metal foil is at least one of silver, copper, zinc, and platinum; the transition layer is made of one of indium and tin, the transition layer has a thickness of 5 to 13 μm, and when tested according to GB / T 9286-1998 standard, the transition layer has an adhesion of grade 0 on the surface of the metal foil; The melting point of the low-temperature alloy layer is 30 to 300°C. A multilayer composite thermally conductive piece characterized by:

2. The composition of each of the low-temperature alloy layers is, in parts by mass, 45 to 70 parts of In, 20 to 40 parts of Bi, 5 to 20 parts of Sn, and 0 to 15 parts of Ga. The multi-layer composite thermally conductive plate according to claim 1 .

3. The material of the low-temperature alloy layer is In ５１ Bi ３０．５ Sn １５．５ Ga ３ is a quaternary alloy of The multi-layer composite heat-conducting plate according to claim 2 .

4. The thickness of the transition layer is 6 to 8 μm. The multi-layer composite thermally conductive plate according to claim 1 .

5. The thickness of the metal foil is 0.01 to 0.5 mm. The multi-layer composite thermally conductive plate according to claim 1 .

6. The thickness of the low-temperature alloy layer is 5 to 40 μm. The multi-layer composite thermally conductive plate according to claim 1 .

7. A method for preparing the multilayer composite thermally conductive piece according to any one of claims 1 to 6, comprising the steps of: forming the transition layer on each of two opposite surfaces of the metal foil; and spraying a liquid metal onto the side of the transition layer remote from the metal foil to form the low-temperature alloy layer. A method for preparing a multilayer composite thermally conductive piece, comprising:

8. The step of forming the transition layer on each of the two opposite surfaces of the metal foil includes: forming the transition layer on each of the two opposite surfaces of the metal foil by electroplating or magnetron sputtering; 8. The method of claim 7.

9. The electroplating step includes: immersing the metal foil in an electroplating solution to form the transition layer by electroplating on each of the two opposite surfaces of the metal foil; The electroplating solution contains an anionic surfactant and a nonionic surfactant.

9. The method of claim 8.

10. Use of the multilayer composite heat-conducting piece according to any one of claims 1 to 6, The multi-layer composite thermal conductive plate is used for heat dissipation of electronic devices.

1. Use of a multilayer composite heat-conducting piece, characterized in that:

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