A bilayer thermally conductive material based on interlayer interconnected carbon fibers and its preparation method

Abstract

This invention discloses a bilayer thermally conductive material based on interlayer interconnected carbon fibers and its preparation method, belonging to the field of composite material preparation technology. The process includes preparing a CuCrZr / molybdenum / carbon fiber composite material by stir casting, followed by hot and cold deformation to gradually orient the carbon fibers, and then high and low temperature heat treatment under a protective atmosphere. After cutting, a copper / carbon fiber composite layer is obtained. The surface of the copper-carbon fiber composite layer is etched to expose partially exposed carbon fibers, and then carbon fibers / polymers are coated onto the etched surface using a spin-coating process. After curing, the desired bilayer thermally conductive material is obtained. This novel bilayer composite material exhibits high thermal conductivity in the heat dissipation direction. The combined addition of Cr and Zr ensures a sufficient reaction at the copper-carbon interface, resulting in low interfacial thermal resistance, high bonding strength, and minimal thermal conductivity loss after high and low temperature shocks. The preparation method employed in this invention is simple, fast, low-cost, and requires minimal equipment, making it suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, and relates to a double-layer thermally conductive material based on interlayer interconnected carbon fibers and its preparation method. Background Technology

[0002] Heat sinks are a crucial component of thermal management, primarily responsible for rapidly dissipating heat generated by chips and other heat sources to ensure the normal operation of core components. Heat sink materials must not only possess a low coefficient of thermal expansion matching the chip's plane in the direction parallel to the chip's surface, but also high thermal conductivity perpendicular to the chip's plane. AI chips are the core hardware of the artificial intelligence industry. Global AI chip development is still in its early stages. With the explosive growth of AI technology, different types of chips play a key role in AI computing, training, and inference. Each chip type has its unique advantages, thus meeting different application scenarios and needs. The rapid development of these AI chips places higher demands on the corresponding heat dissipation systems.

[0003] Thermal interface materials (TIM layers) are used during the packaging process to protect the chip and reduce gap thermal resistance. TIMs can fill small gaps or defects between surfaces, reducing thermal resistance and improving heat transfer efficiency. TIMs exist in various forms, including pastes, gaskets, liquids, and films. For example, CN114410061A, etc., TIMs are typically composed of highly thermally conductive fillers in a polymer matrix. Some common matrices include silicone grease, polyurethane, and acrylic. Each type of TIM has its advantages and disadvantages, and the optimal choice for a specific application depends on factors such as cost, thermal conductivity, ease of use, and durability. However, the thermal conductivity of TIM materials is generally much lower than that of copper-based heat sink materials (e.g., CN107057286A, CN118271853A), and because the interface between the two is not wettable, a relatively large interlayer interface thermal resistance is unavoidable. As the thermal management requirements of high-power devices such as chips become increasingly stringent, the interlayer interface thermal resistance between the TIM layer and the heat sink material is gradually becoming a bottleneck for efficient heat dissipation, greatly limiting the overall heat dissipation effect of the device.

[0004] CN112480604A discloses a high thermal conductivity carbon fiber composite material with a layered hybrid structure and its preparation method. The method involves spraying a graphene solution and a copper-containing solution onto the surface of a carbon fiber cloth layer. A sheet-like filler thermally conductive network parallel to the carbon fiber cloth layer is constructed horizontally, while a micro-nano-scale sheet-and-sphere laminated structure is constructed vertically on the surface of the carbon fiber cloth layer. The carbon fiber cloth layer is then laid up, and a polymer matrix material is injected into it, ultimately obtaining a high thermal conductivity carbon fiber composite material with a layered hybrid structure. This method is still a common approach, involving the infiltration of a matrix into the carbon fiber cloth. The finished product exhibits significant anisotropy; the horizontal direction consists of oriented carbon fiber cloth, while the vertical direction is a layer of fiber cloth and a layer of matrix stacked. Although a sheet-and-sphere laminated structure exists, its thermal conductivity is not very good. Thus, high thermal conductivity is only achieved in the direction of carbon fiber alignment, while the vertical thermal conductivity remains low. However, high vertical thermal conductivity is required in practical applications. Furthermore, when using a copper-containing solution for spraying, the copper does not bond with the carbon material; thermal conductivity relies solely on physical contact, thus not improving thermal conductivity. Fracture images show that the copper is only used to fill gaps, but most of these gaps are filled with polymer. Because there is no bonding at the interface between different phases, the material is also brittle and prone to vibration and fracture. Thermal shock can easily create a vacuum layer, further reducing thermal conductivity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a bilayer thermally conductive material based on interlayer interconnected carbon fibers and its preparation method. This bilayer composite material significantly reduces the thermal resistance between the heat sink material and the polymer-based TIM layer through vertically interconnected carbon fibers, thereby significantly improving the vertical thermal conductivity. In addition, the micro-alloying modification makes the interface between copper and carbon materials tightly bonded, which not only strengthens the mechanical properties but also improves the thermal shock resistance and thermal conductivity.

[0006] This invention provides a double-layer thermally conductive material based on interlayer interconnected carbon fibers, comprising a copper composite layer and a polymer composite layer, wherein vertically interconnected, oriented carbon fibers are present between the copper composite layer and the polymer composite layer, the oriented carbon fibers extending from the copper composite layer into the polymer composite layer, and the oriented carbon fibers are also interconnected with the internal carbon fibers in the polymer composite layer.

[0007] Furthermore, the copper composite layer is a CuCrZr / molybdenum / carbon fiber composite material, and the polymer composite layer is a polymer / carbon fiber composite material.

[0008] Furthermore, the CuCrZr / molybdenum / carbon fiber composite material comprises molybdenum particles with a low coefficient of thermal expansion and oriented high thermal conductivity carbon fibers uniformly dispersed in a CuCrZr matrix. The addition of molybdenum particles with a low coefficient of thermal expansion adjusts the overall coefficient of thermal expansion, and alloying elements are added to the copper matrix to improve the copper-carbon interfacial affinity.

[0009] Furthermore, the high thermal conductivity carbon fiber has a diameter of 2-20 micrometers, a length of 20-200 micrometers, a volume fraction of 5%-30%, and is oriented along the vertical plane direction; the molybdenum particles have a diameter of 10-100 micrometers and a volume fraction of 40-60%.

[0010] This invention also provides a method for preparing a bilayer thermally conductive material based on interlayer interconnected carbon fibers, comprising the following steps:

[0011] (1) The CuCrZr / molybdenum / carbon fiber ingot was obtained by a non-contact stirring casting process;

[0012] (2) Carbon fibers are oriented to a certain degree through hot and cold deformation.

[0013] (3) The CuCrZr / molybdenum / carbon fiber composite material was obtained by high and low temperature heat treatments, and the copper composite layer was obtained after cutting.

[0014] (4) Prepare the polymer / carbon fiber composite material, then etch the upper surface of the copper composite layer to obtain partially exposed carbon fibers, and then use a spin coating process to coat the polymer / carbon fiber composite material onto the etched surface. After curing, the double-layer thermal conductive material is obtained.

[0015] Furthermore, in step (1), the specific steps are as follows:

[0016] 1) Pure Cu, CuCr master alloy, and CuZr master alloy are smelted and cast to obtain Cu-Cr-Zr master alloy;

[0017] 2) Under vacuum or atmosphere protection, the master alloy is remelted at a temperature of 1200-1500 degrees Celsius. The required amount of carbon fiber and molybdenum particles are added. The melt temperature is controlled at 1100-1300 degrees Celsius, and the stirring speed is controlled at 500-2500 rpm. A high-speed vortex is formed in the melt, and the carbon fiber and molybdenum particles are stirred and dispersed in the form of turbulence.

[0018] 3) After the mixture is thoroughly stirred, the melt is rapidly cooled to about 900-1000 degrees Celsius. Stirring is then stopped. A temperature gradient from top to bottom is designed to allow the bottom of the ingot to cool down slowly until it is completely cooled, thus obtaining the CuCrZr / molybdenum / carbon fiber ingot.

[0019] Furthermore, step (2) specifically involves first hot-deforming the CuCrZr / molybdenum / carbon fiber ingot at a temperature of 750–950 degrees Celsius, with a deformation amount of more than 50%, followed by cold-deforming with a deformation amount of more than 50%, to ensure the directional arrangement of the carbon fibers.

[0020] Furthermore, step (3) specifically involves performing a high-temperature heat treatment at 850–950 degrees Celsius for 4–6 hours under an atmosphere of protection, followed by rapid cooling and then a low-temperature heat treatment at 350–550 degrees Celsius for 1–5 hours, followed by furnace cooling.

[0021] Further, step (4) specifically involves preparing the polymer / carbon fiber composite material by premixing 5% to 50% carbon fiber and a certain proportion of curing agent in the polymer; etching the upper surface of the copper composite layer using concentrated nitric acid solution, adjusting the etching depth by time, and obtaining exposed carbon fiber on the upper surface after etching; then, applying the polymer / carbon fiber composite material to the etched surface using a spin coating process, designing the spin coating speed according to the required polymer layer thickness, and after spin coating, placing it in a vacuum furnace for curing according to the polymer curing requirements to obtain the double-layer thermally conductive material.

[0022] Furthermore, based on the interfacial area of ​​the carbon material, appropriate amounts of Cr and Zr elements are added to the copper matrix, with the Cr element content ranging from 0.2 to 2 wt.% and the Zr element content ranging from 0.2 to 4 wt.%.

[0023] Before spin coating, the polymer is premixed with carbon fiber of 10% to 25% by volume and a certain proportion of curing agent.

[0024] The total carbon fiber volume fraction in the polymer composite layer is 5% to 50%.

[0025] The polymer surface can be directly bonded to the low-expansion-coefficient chip, serving as a TIM material.

[0026] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0027] (1) The resulting bilayer composite material exhibits high thermal conductivity in the vertical direction. Directionally aligned high thermal conductivity carbon fibers are introduced into the copper matrix. These carbon fibers are oriented towards the heat dissipation direction, forming a highly efficient thermally conductive network. More importantly, the carbon fibers extend from the copper matrix into the polymer matrix and connect with the internal carbon fibers of the polymer matrix, achieving interlayer continuity of the carbon fiber network. This significantly reduces interlayer thermal resistance and effectively improves the heat dissipation capacity of the bilayer composite material. Experimental results show that the bilayer composite material has high thermal conductivity in the orientation direction, reaching approximately 600–1000 W / (m·K). Furthermore, by adjusting the carbon fiber content, the thermal conductivity, coefficient of thermal expansion, and polymer flexibility of the resulting composite material can be effectively adjusted.

[0028] (2) The copper-carbon interface reaction is sufficient, resulting in low interfacial thermal resistance, high bonding strength, and minimal thermal conductivity loss after high and low temperature shocks. The novel composite material utilizes the combined addition of Cr and Zr to achieve the connection at the copper-carbon interface. Cr and Zr elements react with the surface carbon atoms of the carbon fibers during the infiltration process and high-temperature heat treatment, forming a carbide layer of a certain thickness on the carbon material surface. This transition layer significantly improves the bonding strength of the copper-carbon interface and also facilitates phonon conduction. The combined addition of Cr and Zr promotes copper-carbon interfacial bonding, and the thickness and uniformity of this interfacial layer can be controlled, thus achieving a series of advantages such as low interfacial thermal resistance, high interfacial bonding strength, and resistance to high and low temperature shocks.

[0029] (3) The stirring casting process used involves stirring in the high-viscosity region of the molten copper alloy. During stirring, interfacial reactions occur between Cr and Zr elements and carbon materials. Combined with the turbulence generated during stirring, this effectively promotes the uniform dispersion of carbon materials and molybdenum particles of different sizes within the copper molten metal. Combined with initial rapid solidification and subsequent directional solidification, a composite material ingot with uniform dispersion of carbon materials and molybdenum particles and good alloy casting quality can be obtained. A oriented carbon fiber network can be obtained using conventional deformation methods, thus providing good thermal conductivity in the heat dissipation direction. The subsequent etching and spin-coating processes are also relatively simple and can effectively construct a continuous interlayer thermally conductive network. By adjusting the molybdenum content in the copper matrix, and the carbon fiber content and orientation degree in the copper matrix and polymer, a better combination of thermal conductivity and expansion coefficient can be obtained. The preparation method used in this invention is simple, efficient, low-cost, and requires minimal equipment, making it suitable for large-scale production. Attached Figure Description

[0030] Figure 1 This is a SEM image of the original carbon fiber powder described in this invention.

[0031] Figure 2 The microstructure and elemental energy spectrum of the CuCrZr / molybdenum / carbon fiber ingot described in this invention.

[0032] Figure 3 This is a microstructure diagram (SEM image) of the CuCrZr / molybdenum / carbon fiber ingot described in this invention.

[0033] Figure 4 This is a microstructure (SEM image) of the etched copper / carbon fiber composite layer described in this invention. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] Example 1 and Comparative Example 1

[0036] This invention relates to a bilayer thermally conductive material based on interlayer interconnected carbon fibers and its preparation method, comprising the following steps:

[0037] First, CuCrZr / molybdenum / carbon fiber ingots were prepared using a stirred casting process.

[0038] 1) Pure Cu, CuCr master alloy, and CuZr master alloy are smelted and cast to obtain Cu-0.5Cr-1Zr master alloy;

[0039] 2) Under vacuum or atmospheric protection, the obtained master alloy is remelted at a remelting temperature of 1400 degrees Celsius, and 10 vol.% carbon fiber (such as...) is added. Figure 1 As shown, the carbon fiber has an average diameter of 10 micrometers and a length of 200 micrometers, and the molybdenum particles (average size of 20 micrometers) contain 30 vol.% of the material. The melt temperature is 1250 degrees Celsius, and the stirring speed is 2500 rpm. A high-speed vortex is formed in the melt, and the melt disperses the carbon fiber and molybdenum particles in a turbulent manner.

[0040] 3) After thorough stirring, rapidly cool the melt to 1100 degrees Celsius, stop stirring, and allow the bottom of the ingot to cool slowly until completely cooled, yielding a CuCrZr / molybdenum / carbon fiber ingot (e.g. Figure 2 , 3 (As shown).

[0041] The ingot is then subjected to hot extrusion with a deformation of 75% at a temperature of 900 degrees Celsius, followed by cold forging with a deformation of 80%.

[0042] Argon-protected rapid heating and cooling furnace is used for high and low temperature heat treatment. The deformed ingot is heated to 900 degrees Celsius for 5 hours and then rapidly cooled. It is then heated to 400 degrees Celsius and held for 2 hours, then cooled in the furnace and cut to obtain the required copper carbon fiber composite layer.

[0043] Finally, concentrated nitric acid solution was used to etch the surface of the copper-carbon fiber composite layer. The etching depth was adjusted by time, with an etching time of 25 seconds. The etched surface is shown below. Figure 4As shown. The carbon fiber / polymer is then spin-coated onto the etched surface at 1000 rpm. Before spin-coating, the polymer is premixed with 10% carbon fiber and a curing agent by volume. After spin-coating, the material is placed in a vacuum furnace for curing to obtain the final desired double-layer thermally conductive material, with a polymer layer thickness of 50 micrometers.

[0044] Its performance data is shown in Table 1.

[0045] Table 1 Performance data of the bilayer composite material in Example 1

[0046]

[0047] In contrast, carbon fiber / polymer was directly coated onto the surface of the copper carbon fiber composite layer without surface etching, and its performance data are shown in Table 2.

[0048] Table 2 shows the performance data of the bilayer composite material in Comparative Example 1.

[0049]

[0050] Example 2 and Comparative Example 2

[0051] This invention relates to a bilayer thermally conductive material based on interlayer interconnected carbon fibers and its preparation method, comprising the following steps:

[0052] First, CuCrZr / molybdenum / carbon fiber ingots were prepared using a stirred casting process.

[0053] 1) Pure Cu, CuCr master alloy, and CuZr master alloy are smelted and cast to obtain Cu-0.7Cr-1.4Zr master alloy;

[0054] 2) Under vacuum or atmosphere protection, the obtained master alloy is remelted at a remelting temperature of 1400 degrees Celsius. 25 vol.% carbon fiber and 50 vol.% molybdenum particles are added. The melt temperature is 1250 degrees Celsius and the stirring speed is 2500 rpm. A high-speed vortex is formed in the melt, and the carbon fiber and molybdenum particles are stirred and dispersed in the form of turbulence.

[0055] 3) After the mixture has been stirred thoroughly, the melt is rapidly cooled to 1100 degrees Celsius. Stirring is stopped, and the bottom of the ingot is allowed to cool down slowly until it is completely cooled to obtain a CuCrZr / molybdenum / carbon fiber ingot.

[0056] Subsequently, the ingot was hot-extruded with 80% deformation at a temperature of 900 degrees Celsius, followed by cold forging with 80% deformation. A rapid heating and cooling furnace under argon protection was used for high and low temperature heat treatment. The deformed ingot was heated to 900 degrees Celsius for 5 hours, rapidly cooled, then heated to 400 degrees Celsius and held for 2 hours before being cooled in the furnace. After cutting, the desired copper-carbon fiber composite layer was obtained.

[0057] Finally, concentrated nitric acid solution was used to etch the surface of the copper-carbon fiber composite layer. The etching depth was adjusted by time, with an etching time of 20 seconds. Then, carbon fiber / polymer was spin-coated onto the etched surface at 1500 rpm. Before spin-coating, the polymer was premixed with 20% carbon fiber and a curing agent by volume. After spin-coating, the material was placed in a vacuum furnace for curing to obtain the final desired double-layer thermally conductive material, with a polymer layer thickness of 48 micrometers.

[0058] Its performance data is shown in Table 3.

[0059] Table 3 Performance data of the bilayer composite material in Example 2

[0060]

[0061] In contrast, carbon fiber / polymer was directly coated onto the surface of the copper carbon fiber composite layer without surface etching, and its performance data are shown in Table 4.

[0062] Table 4 Performance data of the bilayer composite material in Comparative Example 2

[0063]

Claims

1. A bilayer thermally conductive material based on interlayer interconnected carbon fibers, characterized in that, The material comprises a copper composite layer and a polymer composite layer, with vertically connected, oriented carbon fibers in two layers between the copper and polymer composite layers. These connecting carbon fibers extend from the copper composite layer into the polymer composite layer and are also interconnected with the internal carbon fibers within the polymer composite layer. The copper composite layer is a CuCrZr / molybdenum / carbon fiber composite material, and the polymer composite layer is a polymer / carbon fiber composite material. The CuCrZr / molybdenum / carbon fiber composite material consists of uniformly dispersed molybdenum particles with a low coefficient of thermal expansion and oriented, highly thermally conductive carbon fibers within a CuCrZr matrix. The highly thermally conductive carbon fibers have a diameter of 2–20 micrometers, a length of 20–200 micrometers, a volume fraction of 5%–30%, and are oriented vertically. The molybdenum particles have a diameter of 10–100 micrometers and a volume fraction of 40–60%.

2. The method for preparing a bilayer thermally conductive material based on interlayer interconnected carbon fibers according to claim 1, characterized in that, Includes the following steps: (1) The CuCrZr / molybdenum / carbon fiber ingot is obtained by non-contact stirring casting process; (2) The carbon fibers are oriented to be arranged by hot and cold deformation; (3) The CuCrZr / molybdenum / carbon fiber composite material is obtained by high and low temperature heat treatment, and the copper composite layer is obtained after cutting; (4) The polymer / carbon fiber composite material is prepared, and then the upper surface of the copper composite layer is etched to obtain partially exposed carbon fibers. The polymer / carbon fiber composite material is then coated onto the etched surface by spin coating process, and the double-layer thermally conductive material is obtained after curing.

3. The method for preparing the double-layer thermally conductive material according to claim 2, characterized in that, In step (1), the specific steps are as follows: 1) Melt pure Cu, CuCr master alloy, and CuZr master alloy to obtain Cu-Cr-Zr master alloy; 2) Under vacuum or atmosphere protection, remelt the master alloy at a remelting temperature of 1200-1500 degrees Celsius, add the required amount of carbon fiber and molybdenum particles, control the melt temperature at 1100-1300 degrees Celsius, and control the stirring speed at 500-2500 rpm to form a high-speed vortex in the melt, and disperse the carbon fiber and molybdenum particles in the form of turbulence; 3) After sufficient stirring, rapidly cool the melt to 900-1000 degrees Celsius, stop stirring, and then design a temperature gradient from top to bottom to allow the bottom of the ingot to cool down slowly first until it is completely cooled to obtain the CuCrZr / molybdenum / carbon fiber ingot.

4. The method for preparing the double-layer thermally conductive material according to claim 2, characterized in that, The specific step (2) involves first hot-deforming the CuCrZr / molybdenum / carbon fiber ingot at a temperature of 750 to 950 degrees Celsius, with a deformation amount of more than 50%, and then cold-deforming it with a deformation amount of more than 50% to ensure the directional arrangement of the carbon fibers.

5. The method for preparing the double-layer thermally conductive material according to claim 2, characterized in that, The specific steps (3) are as follows: a high-temperature heat treatment of 850-950 degrees Celsius for 4-6 hours is carried out under atmosphere protection, followed by rapid cooling and a low-temperature heat treatment of 350-550 degrees Celsius for 1-5 hours, and then cooling with the furnace.

6. The method for preparing the double-layer thermally conductive material according to claim 2, characterized in that, Specifically, step (4) involves preparing the polymer / carbon fiber composite material by premixing 5% to 50% carbon fiber and a certain proportion of curing agent in the polymer; etching the upper surface of the copper composite layer using concentrated nitric acid solution, adjusting the etching depth by time, and obtaining exposed carbon fiber on the upper surface after etching; then, applying the polymer / carbon fiber composite material to the etched surface using a spin coating process, designing the spin coating speed according to the required polymer layer thickness, and after spin coating, placing it in a vacuum furnace for curing according to the polymer curing requirements to obtain the double-layer thermally conductive material.

7. The method for preparing the double-layer thermally conductive material according to claim 3, characterized in that, Based on the interfacial area of ​​the carbon material, appropriate amounts of Cr and Zr elements are added to the copper matrix, with the Cr content ranging from 0.2 to 2 wt.% and the Zr content ranging from 0.2 to 4 wt.%.

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