Composite thermal interface material and preparation method thereof

Abstract

The invention belongs to the field of materials, and particularly relates to a composite thermal interface material and a preparation method thereof. The preparation method comprises the following steps: plating non-reactive metal, non-reactive metal carbide or non-reactive ceramic on the surface of diamond micro powder, inducing lattice defects on the surface of a plating layer and alloying a local interface by combining a mechanical force field, and defoaming to obtain the composite thermal interface material. The composite thermal interface material has high thermal conductivity and long-term stability, and the contradiction between excessive alloying of a traditional reactive coating and high interface thermal resistance of a non-reactive coating is solved. The method is particularly suitable for the field of thermal management of high-end electronic devices such as 5G chips and power modules.

Description

Technical Field

[0001] This invention belongs to the field of materials, specifically relating to a composite thermal interface material and its preparation method. Background Technology

[0002] With the continuous improvement of electronic device performance, the increasing demand for heat dissipation has become an issue that cannot be ignored. In modern electronic products, especially high-power devices, thermal management has become a crucial aspect of ensuring their stability and reliability. Therefore, the demand for high thermal conductivity interface materials is also rising to meet increasingly stringent heat dissipation requirements. However, traditional thermal interface materials mostly use polymer matrices, with thermal conductivity typically ranging from 2 to 10 W / m·K and thermal resistance from 5 to 10 mm. 2 • K / W, these performance values ​​are far from meeting the needs of high-power heat dissipation, resulting in low heat dissipation efficiency and may even affect the normal operation of the equipment.

[0003] Based on this, liquid metal, as a novel thermal interface material, exhibits unique advantages. Liquid metal possesses extremely high thermal conductivity and good fluidity, effectively filling microscopic gaps and thus significantly reducing thermal interface resistance. For example, the gallium liquid metal alloy for chip heat dissipation and its manufacturing method, invented in patent CN201611102378.8, utilizes a gallium-based alloy as a thermal interface material, demonstrating excellent heat dissipation performance and becoming a strong candidate for efficient heat dissipation solutions.

[0004] Despite the numerous advantages of liquid metals, they still face some challenges in practical applications. The surface energy of liquid metals, reaching as high as 550 mN / m, results in poor wetting of heat sinks and radiators, leading to high contact thermal resistance and the risk of leakage. Furthermore, while the intrinsic thermal conductivity of liquid metals is already quite good at approximately 26 W / m·K, there is still room for improvement in practical applications.

[0005] To address these issues, existing research (doi: 10.1038 / s41565-024-01793-0 ISSN: 2468-0230) and patent (CN202110843272.8) have proposed adding thermally conductive fillers to liquid metals to enhance their thermal conductivity and improve wettability. Among various thermally conductive fillers, diamond is considered an ideal choice due to its high thermal conductivity of up to 2000 W / m·K. However, diamond has a smooth surface and is chemically inert, resulting in minimal interaction with the substrate and poor interfacial bonding. Building on this, research (DOI: 10.1016 / j.surfin.2025.105989) has proposed improving the wettability between diamond and the liquid metal substrate by plating CuCr onto the diamond surface, thereby enhancing the thermal conductivity. This is due to the good contact ability of the CuCr alloy coating with both diamond and Ga-based liquid metals.

[0006] Besides CuCr coatings, commonly used coating materials include Al, Zn, and Cu, all of which exhibit reactivity with Ga-based liquid metals. In environments below 120°C, they can spontaneously generate R... x Ga y Alloy phases (R being the corresponding coating material) are used to enhance interfacial bonding, thereby improving the wettability of diamond fillers with liquid metal. However, with prolonged use, excessive growth occurs at the interface, which not only destroys the original interfacial structure and forms a new phase, but also, more seriously, leads to the complete dissolution of the coating. This deteriorates the contact ability between the thermally conductive filler and the liquid metal matrix, causing phase separation and loss of density in the composite material, significantly affecting its thermal conductivity. Experiments revealed that its thermal resistance deteriorates by more than 100% even at room temperature, and its cooling capacity rapidly decreases in CPU temperature control tests. In contrast, there are non-reactive coatings that are inert to Ga-based liquid metals, such as Ni, Ti metals and their corresponding carbide coatings, and some high thermal conductivity ceramic coatings. These coatings cannot spontaneously form alloy phases with Ga-based liquid metals and can maintain the integrity of the coating under long-term use. However, due to its chemical inertness, ordinary stirring and mixing are difficult to form a strong interface. The coating and the liquid metal substrate mainly rely on physical adsorption to bond, resulting in limited improvement in thermal conductivity. Therefore, there are very few application studies.

[0007] The above analysis reveals a trade-off between thermal conductivity and stability in diamond / liquid metal composites. Commonly used reactive coatings offer good thermal conductivity but neglect stability under long-term use, while highly stable non-reactive coatings lack high thermal conductivity due to poor contact with liquid metal under normal conditions. This contradiction has become one of the core bottlenecks restricting its practical application. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for preparing a composite thermal interface material. The preparation method includes the following steps: (1) coating the surface of diamond micropowder with at least one of a non-reactive metal, a non-reactive metal carbide, or a non-reactive ceramic to obtain coated diamond micropowder; wherein, the non-reactive metal, non-reactive metal carbide, or non-reactive ceramic refers to a metal, metal carbide, or ceramic with a thermodynamic reaction free energy ΔG > 0 with gallium-based liquid metal below 120°C; (2) mixing the coated diamond micropowder with gallium-based liquid metal by mechanical force: on the one hand, inducing lattice distortion on the surface of the coating to reduce the phonon scattering barrier at the interface and improve the phonon coupling efficiency; on the other hand, using high-energy mechanical force to break the atomic diffusion barrier on the surface of the non-reactive coating, driving Ga atoms to undergo local short-range diffusion under non-thermodynamic equilibrium conditions, forming a gradient transition layer to obtain a mixture; (3) degassing the mixture to obtain the composite thermal interface material.

[0009] Specifically, in step (1) of the above-mentioned method for preparing composite thermal interface materials, the non-reactive metal is selected from at least one of titanium (Ti), nickel (Ni), zirconium (Zr), chromium (Cr), tungsten (W), silver (Ag), and gold (Au). Nickel (Ni) is preferred. The non-reactive metal carbide is selected from at least one of titanium carbide (TiC), chromium carbide (CrC), tungsten carbide (WC), molybdenum carbide (MoC), zirconium carbide (ZrC), and tantalum carbide (TaC). Titanium carbide (TiC) is preferred. The non-reactive ceramic is selected from at least one of aluminum nitride (AlN), tungsten oxide (WO3), aluminum oxide (Al2O3), zirconium oxide (ZrO2), and silicon carbide (SiC). Aluminum nitride (AlN) is preferred.

[0010] Specifically, in step (1) of the above-mentioned method for preparing composite thermal interface materials, the particle size of the diamond micropowder is [missing information]. 10-100 μm.

[0011] Specifically, in step (1) of the above-mentioned method for preparing composite thermal interface materials, the thickness of the coating is 50 nm-5 μm.

[0012] Specifically, in step (1) of the above-mentioned method for preparing composite thermal interface materials, the coating is prepared by chemical plating, magnetron sputtering or electroplating.

[0013] Specifically, in step (2) of the above-mentioned method for preparing composite thermal interface materials, the mass ratio of coated diamond micro powder to gallium-based liquid metal is 1:10 to 10:1.

[0014] Specifically, in step (2) of the above-mentioned method for preparing composite thermal interface materials, the gallium-based liquid metal is at least one of pure gallium, gallium-indium alloy, or gallium-indium-tin alloy.

[0015] Furthermore, in step (2) of the above-mentioned method for preparing composite thermal interface material, the gallium-based liquid metal is gallium indium tin alloy (Galinstan), and its mass percentage composition is Ga 60-75%, In 15-25%, Sn 5-15%.

[0016] Specifically, in step (2) of the above-mentioned method for preparing composite thermal interface materials, the mechanical force field is obtained by ball milling, ultrasonication, or high-energy shearing.

[0017] Furthermore, in step (2) of the above-mentioned method for preparing composite thermal interface materials, the ball milling speed is 500-3000 rpm, and the ball milling time is 1-120 min.

[0018] Furthermore, in step (2) of the above-mentioned method for preparing composite thermal interface materials, the ultrasonic power is 100-500W, and the ultrasonic time is 10-60 min.

[0019] Furthermore, in step (2) of the above-mentioned method for preparing composite thermal interface materials, the high-energy shear rate is 5000-10000 rpm. The rotor-stator gap is 0.5-2 mm. The time is 1-30 min.

[0020] Specifically, in step (3) of the above-mentioned method for preparing composite thermal interface materials, the degassing treatment conditions are: vacuum degree ≤ 10. -3 Pa. Centrifugation speed: 1000-3000 rpm. Processing time: 1-30 min.

[0021] The present invention also provides a composite thermal interface material prepared by the above-described method for preparing composite thermal interface materials.

[0022] Furthermore, the aforementioned composite thermal interface material has a thermal conductivity of 80-160 W / m·K and a thermal resistance of 1.5-4 mm. 2 K / W.

[0023] This invention utilizes a synergistic effect of non-reactive coating design and mechanochemical interface activation. On one hand, it induces lattice distortion on the coating surface, improving interfacial phonon coupling efficiency; on the other hand, it employs high-energy mechanochemical activation to locally activate the short-range diffusion of Ga atoms into the coating, forming a transition interface. The resulting composite thermal interface material achieves an overall thermal conductivity of 80-160 W / m·K and an interfacial thermal resistance as low as 1.5-4 mm. 2The K / W ratio is reduced by more than 70% compared to ordinary polymer mixing solutions. The increase in interfacial thermal resistance after prolonged resting and operation is less than 5%. Its thixotropic coefficient (yield stress) is ≤300 KPa, and there is no liquid metal leakage within the operating temperature range. In aging tests, the material of this invention exhibits excellent long-term stability, significantly superior to commonly used active coating solutions, successfully solving the technical challenge of achieving both enhanced wettability and interfacial stability in existing technologies, providing a revolutionary solution for thermal management of high-power electronic devices. Attached Figure Description

[0024] Figure 1 The process flow diagram for preparing the diamond / liquid metal composite thermal interface material of this invention.

[0025] Figure 2 LAMMPS simulation of mechanically induced Ni-diamond / Ga penetration interface formation.

[0026] Figure 3 Comparison of thermal resistance and stability between mechanically induced non-reactive coated diamond / liquid metal composites and ordinary reactive coated diamond / liquid metal composites.

[0027] Figure 4 Comparison of CPU heat dissipation capacity and stability between mechanically induced non-reactive coated diamond / liquid metal composite materials and ordinary reactive coated diamond / liquid metal composite materials. Detailed Implementation

[0028] This invention addresses the core problems of high interfacial thermal resistance, uncontrollable binder layer thickness (BLT), and poor long-term stability in liquid metal / diamond composite materials. It proposes a liquid metal / diamond composite thermal interface material based on a mechanochemical activation mechanism and its preparation method. Through the synergistic effect of non-reactive coating design and mechanochemical interface activation, it overcomes the bottlenecks of high interfacial thermal resistance, uncontrollable binder layer thickness (BLT), and poor long-term stability in traditional technologies.

[0029] The present invention discloses a method for preparing a liquid metal-diamond composite thermal interface material, comprising the following steps: (1) Diamond surface coating treatment: Diamond micro powder is surface coated and modified. The coating material is selected from metals, metal carbides or ceramic materials that do not spontaneously react with gallium-based liquid metals within the operating temperature range of electronic devices (20-120℃). (2) Mechanochemical interface activation: The modified coated diamond micro powder and gallium-based liquid metal are mixed in a certain mass ratio and mechanical force is applied to perform mechanochemical activation; during this process, the strong mechanical force causes the Ga-based liquid metal to penetrate into the lattice of the coating material to form coordination bonds, thereby strengthening the degree of interfacial bonding. (3) Degassing treatment: The modified coated diamond-liquid metal composite material is placed in a degassing device to remove the bubbles generated during the mixing process, and finally the composite thermal interface material is obtained.

[0030] In this invention, the coating material is selected from materials that do not spontaneously react with gallium-based liquid metals below 120°C. Such materials have a thermodynamic reaction free energy ΔG > 0 with Ga-based liquid metals below 120°C, ensuring that the coating does not spontaneously consume under static conditions. For example, metals, metal carbides, or ceramics are selected. The metal is selected from at least one of titanium (Ti), nickel (Ni), zirconium (Zr), chromium (Cr), tungsten (W), silver (Ag), and gold (Au). Nickel (Ni) is preferred. The metal carbide is selected from at least one of titanium carbide (TiC), chromium carbide (CrC), tungsten carbide (WC), molybdenum carbide (MoC), zirconium carbide (ZrC), and tantalum carbide (TaC). Titanium carbide (TiC) is preferred. The ceramic is selected from at least one of aluminum nitride (AlN), tungsten oxide (WO3), aluminum oxide (Al2O3), zirconium oxide (ZrO2), and silicon carbide (SiC). Aluminum nitride (AlN) is preferred.

[0031] In this invention, nickel (Ni), a stable metal with a high thermal conductivity, is preferentially selected as the coating material. Ni does not miscible with gallium-based liquid metals below 250°C, ensuring the long-term stability of the intermediate coating under the operating temperature conditions of electronic devices.

[0032] In this invention, a suitable coating method is selected based on the chosen coating material. For example, metal and metal carbide coatings are coated using magnetron sputtering, physical vapor deposition, or chemical vapor deposition; ceramic coatings are coated using magnetron sputtering, sol-gel method, or precursor hydrolysis-condensation process.

[0033] In this invention, the coating thickness is controlled to be between 50 nm and 5 μm to optimize the interfacial bonding performance and thermal conductivity.

[0034] In this invention, the gallium-based liquid metal is a gallium-based alloy with a melting point below 60°C. Examples include pure gallium, gallium-indium alloys, and gallium-indium-tin alloys. Gallium-indium-tin alloys are preferred, with a mass percentage composition of Ga 60-75%, In 15-25%, and Sn 5-15%.

[0035] In this invention, a mechanical force field mixing method is employed to ensure thorough mixing of the modified coated diamond and gallium-based liquid metal. The presence of mechanical force fields such as ball milling, ultrasonication, and shearing induces interactions between the surface coating and the gallium-based liquid metal, forming a stable intermediate layer. Specifically, the energy of the mechanical force field activates a mechanochemical reaction between the coating atoms and the liquid metal, causing the non-reactive coating atoms to alloy with the gallium-based liquid metal. By forming a stable alloy phase, the interfacial interaction and thermodynamic compatibility between the two are enhanced. This mechanochemical reaction not only significantly improves the thermal conductivity between the interfaces but also enhances the thixotropy and stability of the composite material, effectively reducing thermal resistance. Finally, by utilizing the normal non-reactive nature of the selected coating material and the instantaneous and terminateable nature of the mechanical force, precise control of the reaction process is achieved. The interfacial reaction immediately stops upon removal of the external force, completely avoiding the over-alloying problem of traditional reactive coatings and contributing to maintaining the long-term stability and reliability of the material.

[0036] In this invention, a mechanical force field causes the atoms on the coating surface to permeate with gallium-based liquid metal, forming a micro-nano scale gradient heterogeneous diffusion interface alloy phase layer, such as a nickel-gallium alloy (Ni). x Ga y Titanium gallium alloy (Ti) x Ga y It can be a titanium carbide-gallium composite phase or an aluminum nitride-gallium composite phase, with a crystal structure that is nanocrystalline or amorphous, and forms a continuous chemical bonding interface with the diamond coating and the liquid metal substrate.

[0037] In this invention, after sufficient mechanochemical action, the final step is to perform degassing treatment to remove bubbles that may be generated during the mixing process, thereby further improving the density and thermal conductivity of the composite material.

[0038] This invention takes pure Ga liquid metal and Ni-plated diamond as an example, and uses LAMMPS software to calculate the heat transfer resistance between diamond and liquid metal, verifying the effect of the transition structure formed by mechanical force on improving heat transfer performance. Figure 1 This is a process flow diagram for the preparation of diamond / liquid metal composite thermal interface materials.

[0039] Example 1 The raw materials consist of diamond with a particle size of 50 μm and gallium (Ga)-based liquid metal, with a mass ratio of coated diamond: liquid metal = 1:2. The specific preparation method is as follows: (1) Preparation of Ni alloy coating by magnetron sputtering A Ni alloy coating with a thickness of 100 nm was deposited on the surface of diamond using magnetron sputtering technology.

[0040] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond was mixed with Ga-based liquid metal in a specific ratio and then processed using a ball mill. The ball milling time was set to 5 min at a speed of 2000 rpm. Afterward, a degassing treatment was performed by centrifugation at 1000 rpm for 1 min to ensure the material's density. The diamond / liquid metal composite material obtained through the above steps in this embodiment has excellent thermal conductivity and good thixotropic properties.

[0041] Example 2 The raw materials consist of diamond with a particle size of 50 μm and Ga-based liquid metal, with a mass ratio of coated diamond to liquid metal of 1:2. The specific preparation method is as follows: (1) Preparation of TiC coating by vapor deposition A TiC coating with a thickness of 100 nm was deposited on the surface of diamond using physical vapor deposition (PVD) technology.

[0042] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond was mixed with liquid metal in a specific ratio and then processed using a ball mill. The ball milling time was set to 5 min at a speed of 2000 rpm. Afterward, degassing was performed by centrifugation at 1000 rpm for 1 min.

[0043] Example 3 The raw materials consist of diamond with a particle size of 50 μm and Ga-based liquid metal, with a mass ratio of coated diamond to liquid metal of 1:2. The specific preparation method is as follows: (1) Preparation of AlN ceramic coating by magnetron sputtering An AlN ceramic coating with a thickness of 100 nm was deposited on the surface of diamond using magnetron sputtering technology.

[0044] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond was mixed with liquid metal in a specific ratio and then processed using a ball mill. The ball milling time was set to 5 min at a speed of 2000 rpm. Afterward, degassing was performed by centrifugation at 1000 rpm for 1 min.

[0045] Example 4 The raw materials consist of diamond with a particle size of 50 μm and gallium (Ga)-based liquid metal, with a mass ratio of coated diamond: liquid metal = 1:2. The specific preparation method is as follows: (1) Preparation of Ni alloy coating by magnetron sputtering A Ni alloy coating with a thickness of 100 nm was deposited on the surface of diamond using magnetron sputtering technology.

[0046] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond was mixed with Ga-based liquid metal in a specific ratio and then treated with ultrasound. The ultrasound power was set to 300 W and the ultrasound time was 20 min. After that, degassing was performed by centrifugation at 1000 rpm for 1 min. Example 5 The raw materials consist of diamond with a particle size of 50 μm and gallium (Ga)-based liquid metal, with a mass ratio of coated diamond: liquid metal = 1:2. The specific preparation method is as follows: (1) Preparation of Ni alloy coating by magnetron sputtering A Ni alloy coating with a thickness of 100 nm was deposited on the surface of diamond using magnetron sputtering technology.

[0047] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond was mixed with Ga-based liquid metal in a specific ratio and treated using a high-shear rotor-stator mixer. The shear intensity was 6000 rpm, the rotor-stator gap was 1 mm, and the shearing time was 2 min. Afterward, degassing was performed by centrifugation at 1000 rpm for 1 min.

[0048] Comparative Example 1 The raw materials consist of diamond with a particle size of 50 μm and Ga-based liquid metal, with a mass ratio of coated diamond to liquid metal of 1:2. The specific preparation method is as follows: (1) Preparation of Ni alloy coating by magnetron sputtering A Ni alloy coating with a thickness of 100 nm was deposited on the surface of diamond using magnetron sputtering technology.

[0049] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond and liquid metal were mixed in a specific ratio using a standard stirring apparatus, a process devoid of mechanochemical interaction. The stirring time was 20 min at 1000 rpm. Following this, degassing was performed by centrifugation at 1000 rpm for 1 min. Comparative Example 2 The composite material preparation method proposed in this comparative example is similar to that in Example 1, except that: In this comparative example, no surface modification treatment was performed on the diamond. Instead, the diamond was directly ball-milled with liquid metal, without any surface coating. The remaining steps are the same as in Example 1, including ball milling and degassing.

[0050] Comparative Example 3 The raw materials consist of diamond with a particle size of 50 μm and gallium (Ga)-based liquid metal, with a mass ratio of coated diamond: liquid metal = 1:2. The specific preparation method is as follows: (1) Preparation of Ni alloy coating by magnetron sputtering A Ni alloy coating with a thickness of 100 nm was deposited on the surface of diamond using magnetron sputtering technology.

[0051] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond was mixed with Ga-based liquid metal in a specific ratio and then processed using a ball mill. The milling time was set to 5 min, and the rotation speed was 2000 rpm. No degassing treatment was performed. Comparative Example 4 The raw materials consist of diamond with a particle size of 50 μm and Ga-based liquid metal, with a mass ratio of coated diamond to liquid metal of 1:3. The specific preparation method is as follows: (1) Preparation of Al alloy coating by salt bath plating: A reactive Al alloy coating with a thickness of 200 nm was deposited on the surface of diamond using a salt bath Al plating technique.

[0052] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond and liquid metal were mixed in a specific ratio and processed using a standard stirring apparatus. The stirring time was set to 20 min at a speed of 1000 rpm. Afterward, degassing was performed by centrifugation at 1000 rpm for 1 min.

[0053] Comparative Example 5 The raw materials consist of diamond with a particle size of 50 μm and Ga-based liquid metal, with a mass ratio of coated diamond to liquid metal of 1:3. The specific preparation method is as follows: (1) Preparation of molten salt CuCr alloy coating A reactive CuCr alloy coating with a thickness of 200 nm was deposited on the surface of diamond using molten salt synthesis technology.

[0054] (2) Mixing of diamond and Ga-based liquid metal 50 μm diamond was mixed with liquid metal in a specific ratio and then processed using a ball mill. The ball milling time was set to 5 min at a speed of 1000 rpm. Afterward, degassing was performed by centrifugation at 1000 rpm for 1 min.

[0055] Comparative Example 6 The composite material preparation method proposed in this comparative example is similar to that in Example 1, except that: In this comparative example, the Ni alloy coating deposited on the diamond surface using magnetron sputtering technology has a thickness of 20 nm. The remaining steps are the same as in Example 1, including ball milling and degassing.

[0056] Comparative Example 7 The composite material preparation method proposed in this comparative example is similar to that in Example 1, except that: In this comparative example, the Ni alloy coating deposited on the diamond surface using magnetron sputtering technology has a thickness of 10 μm. The remaining steps are the same as in Example 1, including ball milling and degassing.

[0057] Comparative Example 8 This comparative example is similar to Example 1, except that: In this comparative example, the mass ratio of coated diamond to liquid metal was 1:15, which means that the diamond content was significantly reduced.

[0058] The remaining steps are the same as in Example 1, including the deposition of the diamond magnetron sputtered Ni alloy coating, ball milling, and degassing treatment.

[0059] Comparative Example 9 This comparative example is similar to Example 1, except that: In this comparative example, the mass ratio of coated diamond to liquid metal is 11:1, which means that the diamond content is increased.

[0060] The remaining steps are the same as in Example 1, including the deposition of the diamond magnetron sputtered Ni alloy coating, ball milling, and degassing treatment.

[0061] Comparative Example 10 This comparative example is similar to Example 1, except that: In this comparative example, the mass ratio of coated diamond to liquid metal is 15:1, meaning the diamond content is further increased.

[0062] The remaining steps are the same as in Example 1, including the deposition of the diamond magnetron sputtered Ni alloy coating, ball milling, and degassing treatment.

[0063] Comparative Example 11 This comparative example is similar to Example 1, except that: In this comparative example, the grinding speed is 300 rpm, which reduces the mechanical force.

[0064] The remaining steps are the same as in Example 1, including the deposition of the diamond magnetron sputtering Ni alloy coating, ball milling time, and degassing treatment.

[0065] Comparative Example 12 This comparative example is similar to Example 1, except that: In this comparative example, the grinding speed is 4000 rpm, which enhances the mechanical force.

[0066] The remaining steps are the same as in Example 1, including the deposition of the diamond magnetron sputtering Ni alloy coating, ball milling time, and degassing treatment.

[0067] Comparative Example 13 This comparative example is similar to Example 1, except that: In this comparative example, the grinding time was 0.5 min, which means the time for mechanochemical action was reduced.

[0068] The remaining steps are the same as in Example 1, including the deposition of the diamond magnetron sputtering Ni alloy coating, the ball milling speed, and the degassing treatment.

[0069] Comparative Example 14 This comparative example is similar to Example 1, except that: In this comparative example, the grinding time was 180 min, which means the mechanochemical reaction time was extended.

[0070] The remaining steps are the same as in Example 1, including the deposition of the diamond magnetron sputtering Ni alloy coating, the ball milling speed, and the degassing treatment.

[0071] In practical applications of thermal interface materials, thermal conductivity determines the material's heat transfer capability; a higher value indicates higher heat transfer efficiency. Secondly, thermal resistance determines the overall obstacle to heat transfer, while bond thickness represents the average thickness of the thermal interface material in application, i.e., the length of the heat transfer path. Reducing the yield stress of the material can improve its thixotropic properties, making it easier to deform, flow, and fill gaps, thereby reducing contact thermal resistance and bond thickness. Therefore, the lower the thermal resistance, bond thickness, and yield stress, the smaller the heat transfer obstacle. Thermal conductivity, thermal resistance, and bond thickness of the diamond / liquid metal composites prepared in the examples and comparative examples were tested using a thermal resistance meter under a compression condition of 40 Psi, and the testing standard was ASTM D5470. Yield stress of the composites was tested using a rheometer at room temperature. The test results are shown in Table 1.

[0072] As shown in Table 1, compared to ordinary polymer-based thermal interface materials (thermal conductivity 2-10 W / m·K, thermal resistance 5-10 mm),... 2 Liquid metal composites filled with diamond microparticles (·K / W) exhibit high thermal conductivity and low thermal resistance. The lower bond thickness and yield stress also indicate improved thixotropic properties of the composites.

[0073] Examples 2 and 3 respectively selected TiC, a metal carbide inert to Ga-based liquid metals, and AlN, a ceramic material. The introduction of TiC coating and AlN ceramic coating improved the thermal conductivity of the composite material to a certain extent. Its thermal conductivity, thermal resistance, and bonding thickness all reached the expected levels, proving that the preparation method is applicable to a variety of non-reactive coating fillers.

[0074] Examples 4 and 5 selected ultrasonic and high-energy shearing devices, respectively, and obtained results similar to those in Example 1, proving that the mechanochemical activation interface process in this scheme can be achieved by various mechanical force fields, and ultimately a thermal interface material with good thermal properties can be obtained.

[0075] Compared to Example 1, Comparative Example 1 lacks mechanical force. Due to the poor contact between Ni and Ga-based liquid metal, ordinary stirring cannot induce a good interaction between the filler and the matrix, resulting in lower thermal conductivity, higher thermal resistance, and poorer thixotropy in Comparative Example 1. Example 1, on the other hand, activates the interface through mechanochemical action, improving thermal conductivity and demonstrating the role of mechanical force in this embodiment. Comparative Example 2 lacks a coating. Although the uncoated high thermal conductivity diamond filler brings higher thermal conductivity to the composite material, it also significantly affects the contact between the filler and the matrix, leading to increased yield stress and extremely high interfacial thermal resistance and bonding thickness. See Appendix for further details. Figure 2 Three models were constructed by comparing the theoretical thermal conduction behavior of Example 1, Comparative Example 1 (without mechanical force), and Comparative Example 2 (uncoated). For the gradient interface formed by sufficient mechanochemical interaction between coated diamond and liquid metal, the interfacial thermal resistance was reduced by an order of magnitude compared to the sharp interfaces of liquid metal / diamond and liquid metal / diamond coating. Comparative Example 3, which did not undergo degassing treatment, showed a significant decrease in both thermal conductivity and thixotropic properties, demonstrating the importance of air removal and maintaining a dense internal structure for thermally conductive materials.

[0076] Comparative Examples 4 and 5 selected materials reactive with Ga-based liquid metals as coatings, with... Figure 3 The changes in thermal resistance of different coating materials over time were recorded, as shown in Table 1 and Appendix. Figure 3The following conclusions can be drawn. The thermal resistance of Examples 1, 2, and 3 changed by less than 5% within 10 days, demonstrating that the presence of the non-reactive coating provides good interfacial stability for the composite material, and that this preparation method is universally applicable to metal, metal carbide, and high thermal conductivity ceramic coating materials. Comparative Example 2 lacked an intermediate coating, resulting in an excessively large surface energy difference between the diamond filler and the liquid metal, making phase separation highly likely and leading to a rapid deterioration in thermal conductivity. The thermal resistance of Comparative Example 4 increased significantly over time. Although the Al coating has the best contact with the liquid metal, and a composite material with good interfacial contact can be obtained simply by stirring and mixing, it is also the most likely to miscible with the matrix to form an alloy phase. Below 50°C, Ga can rapidly penetrate the Al lattice, causing metal embrittlement and greatly increasing the interfacial contact thermal resistance. Comparative Example 5 also showed performance deterioration, demonstrating that the CuCr coating has relatively moderate stability with the liquid metal, and a stable and good contact interface can be formed in a short time through ball milling. However, under long-term medium-high temperature environments, the Cu lattice is still easily penetrated by Ga to form a new alloy phase, resulting in a decrease in thermal conductivity.

[0077] Furthermore, attached Figure 4 The temperature performance of Examples 1, 2, 3, Comparative Example 4, and Comparative Example 5 in practical applications was compared. Figure 4 It can be seen that with prolonged use, the CPU temperatures of Comparative Examples 4 and 5 rose rapidly, indicating a certain degree of decline in thermal management effectiveness. This proves that the coatings in Comparative Examples 4 and 5 reacted with the Ga-based liquid metal, leading to a deterioration in thermal conductivity. In contrast, the CPU temperatures of Examples 1, 2, and 3 remained stable, demonstrating that the non-reactive coated diamond / liquid metal composite material subjected to mechanochemical action has efficient and stable application value.

[0078] Furthermore, Comparative Examples 6 and 7 adjusted the coating thickness on the diamond surface. Compared to Comparative Example 2 without a coating, Comparative Example 6 exhibited a higher thermal conductivity, significantly reduced thermal resistance, and reduced bonding thickness after introducing a 20 nm thick coating, demonstrating that the metal coating deposited on the diamond surface can promote the interaction between the liquid metal and diamond, thereby improving thermal conductivity. However, the thermal conductivity of Comparative Example 6 was not as good as that of Example 1, because a thin coating may result in problems such as incomplete coating or incomplete coverage. Further increasing the coating thickness led to a deterioration in thermal conductivity in Comparative Example 7, because the intrinsic thermal conductivity of the coating is lower than that of diamond, and its increased thickness leads to a decrease in overall heat transfer capacity. Therefore, it is necessary to minimize the thickness while fully covering the diamond surface to effectively improve the thermal conductivity of the composite material. Thus, this approach controls the thickness of the surface coating at the micro-nano level to optimize interfacial bonding performance and thermal conductivity efficiency.

[0079] Furthermore, Comparative Examples 8, 9, and 10 varied the ratio of diamond filler to Ga-based liquid metal. The low diamond content in Comparative Example 8 resulted in a very low thermal conductivity, as diamond is the main contributor to thermal conductivity in the composite system; insufficient diamond content significantly reduces thermal conductivity. Comparative Example 9, with its increased diamond content compared to Example 1, showed improved thermal conductivity, but a slight deterioration in thermal resistance, bond thickness, and yield stress. Comparative Example 10, with its further increased diamond content, exhibited a significant deterioration in thermal conductivity. This phenomenon demonstrates that excessive diamond content leads to a decrease in the thermal conductivity of the composite material. The reason can be derived from the difference in the magnitude of changes in thermal conductivity and other properties: diamond itself has a high thermal conductivity, contributing significantly to the thermal conductivity of the composite material. However, diamond's high rigidity and excessive addition severely reduce the thixotropic properties of the composite material, increasing its viscosity and modulus, reflected in a significant increase in bond thickness and yield stress. This change severely impedes the material's flowability, greatly affecting the effectiveness of the heat conduction path, thus leading to a decrease in thermal conductivity and an increase in thermal resistance. In addition, the increased number of contact points between diamond particles, coupled with their brittleness and hardness, can lead to poor local thermal contact between particles, further increasing thermal resistance.

[0080] Comparative Examples 11 and 12 adjusted the intensity of the mechanical force, while Comparative Examples 13 and 14 varied the duration of the mechanochemical reaction. The table shows that weak and short-duration mechanochemical reactions are insufficient to allow sufficient penetration of liquid metal atoms into the Ni layer lattice, resulting in low thermal conductivity in Comparative Examples 11 and 13. Conversely, excessively strong or prolonged mechanochemical reactions cause severe oxidation of the liquid metal, resulting in extremely low thermal conductivity and extremely high thermal resistance in Comparative Examples 12 and 14, rendering them unusable.

[0081] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a composite thermal interface material, characterized in that: Includes the following steps: (1) Coating the surface of diamond micro powder with at least one of non-reactive metal, non-reactive metal carbide or non-reactive ceramic to obtain coated diamond micro powder; wherein, the non-reactive metal, non-reactive metal carbide or non-reactive ceramic refers to a metal, metal carbide or ceramic with a thermodynamic reaction free energy ΔG > 0 with gallium-based liquid metal below 120°C; (2) Mixing coated diamond micro powder with gallium-based liquid metal using a mechanical force field to obtain a mixture; (3) Degassing the mixture to obtain the composite thermal interface material.

2. The method for preparing the composite thermal interface material according to claim 1, characterized in that: In step (1), the non-reactive metal is selected from at least one of Ti, Ni, Zr, Cr, W, Ag and Au; the non-reactive metal carbide is selected from at least one of TiC, CrC, WC, MoC, ZrC and TaC; and the non-reactive ceramic is selected from at least one of AlN, WO3, Al2O3, ZrO2 and SiC.

3. The method for preparing the composite thermal interface material according to claim 1 or 2, characterized in that: In step (1), the particle size of the diamond powder is 10-100 μm.

4. The method for preparing the composite thermal interface material according to claim 1 or 2, characterized in that: In step (1), the thickness of the coating is 50 nm-5 μm.

5. The method for preparing the composite thermal interface material according to claim 1 or 2, characterized in that: In step (2), the mass ratio of the coated diamond micro powder to the gallium-based liquid metal is 1:10 to 10:

1.

6. The method for preparing the composite thermal interface material according to claim 1 or 2, characterized in that: In step (2), the gallium-based liquid metal is at least one of pure gallium, gallium-indium alloy, or gallium-indium-tin alloy.

7. The method for preparing the composite thermal interface material according to claim 1 or 2, characterized in that: In step (2), the mechanical force field is obtained by ball milling, ultrasound or high-energy shearing.

8. The method for preparing the composite thermal interface material according to claim 7, characterized in that: In step (2), the ball milling speed is 500-3000 rpm and the ball milling time is 1-120 min; the ultrasonic power is 100-500 W and the ultrasonic time is 10-60 min; the high-energy shear rate is 5000-10000 rpm, the rotor-stator gap is 0.5-2 mm, and the time is 1-30 min.

9. The method for preparing the composite thermal interface material according to claim 1 or 2, characterized in that: In step (3), the degassing treatment conditions are: vacuum degree ≤ 10. -3 The centrifugation speed is 1000-3000 rpm, and the processing time is 1-30 min.

10. A composite thermal interface material prepared by the method for preparing composite thermal interface material according to any one of claims 1-9.

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