Method for synthesizing carbon nanotube array-based thermal interface material for independent use

Abstract

The application provides a synthesis method of a carbon nanotube array-based thermal interface material which can be independently used, and both ends of the carbon nanotube array are welded on an ultrathin copper foil through a low-melting-point solder. On one hand, through welding, not only is the large-area and high-quality transfer of the carbon nanotube array on the original substrate achieved, but also the carbon nanotube encapsulated in the copper foil does not leak to prevent the short circuit of electronic elements when the carbon nanotube is used as a thermal interface material; on the other hand, since the intrinsic thermal conductivity of the copper foil is high, after the copper foil is welded on the carbon nanotube array, the in-plane thermal conductivity of the composite material is significantly improved, so that the problem of local overheating of electronic products is solved. The carbon nanotube-based thermal interface material prepared by the application can be directly inserted as a heat-conducting gasket, and shows great advantages in actual chip thermal management.

Description

Technical Field

[0001] This invention belongs to the field of carbon nanotube technology and relates to a synthesis strategy for carbon nanotube array-based thermal interface materials that can be used independently. Background Technology

[0002] Carbon nanotube arrays are highly sought after in the field of thermal interface materials due to their extremely high thermal conductivity and low stiffness. However, in practical applications, the growth conditions for carbon nanotube arrays are very demanding (synthesis temperatures are generally above 650℃), which is severely incompatible with electronic device packaging processes. Furthermore, the effective volume fraction of the array is small (1%-5%), resulting in fewer thermal conduction pathways. The thermal resistance between the free ends of the array and the mating surfaces is also relatively high, and the unique structure of carbon nanotube arrays leads to extremely low in-plane thermal conductivity. Therefore, all of these problems limit the practical application potential of carbon nanotube arrays in the field of thermal interface materials.

[0003] Bonding the tips of carbon nanotube arrays to the target substrate using organic materials or solders to reduce the thermal resistance between the carbon nanotube array and the mating surface is feasible. However, these techniques require the carbon nanotube arrays to be directly grown on the surface of a heat sink or radiator, which is incompatible with the synthesis process of carbon nanotube arrays. How to achieve the transfer of carbon nanotube arrays through a reasonable method while minimizing damage to their thermal conductivity and mechanical properties has become a critical scientific and technological problem that urgently needs to be solved. Therefore, it is necessary to provide a synthesis strategy for independently usable carbon nanotube array-based thermal interface materials to address the aforementioned issues. Summary of the Invention

[0004] Technical Problem: To address the shortcomings of existing technologies, this invention provides a method for synthesizing carbon nanotube array-based thermal interface materials that can be used independently, thereby solving the technical problems involved in the background metal.

[0005] Technical solution: The present invention provides a method for synthesizing a carbon nanotube array-based thermal interface material that can be used independently, comprising the following steps:

[0006] Step 1: A mixture of argon, ethylene, and hydrogen is introduced into a chemical vapor deposition system. Carbon nanotube arrays are synthesized on a silicon wafer, i.e., the growth substrate, according to the set heating conditions and time, to obtain a carbon nanotube array.

[0007] Step 2: Sputter the free ends of the obtained carbon nanotube array sequentially with layers of titanium, nickel, and gold.

[0008] Step 3: Place the free end of the carbon nanotube array with the sputtered metal layer facing down on the solder, then place the solder on the ultrathin copper foil, and perform the welding operation in the tube furnace.

[0009] Step 4: Transfer the copper foil, solder and carbon nanotube array together from the growth substrate to obtain a composite material of copper foil and carbon nanotube array.

[0010] Step 5: After the transfer, the carbon nanotube array end of the composite material consisting of copper foil and carbon nanotube array is sequentially sputtered with layers of titanium, nickel, and gold.

[0011] Step 6: Place the sputtered composite material with the carbon nanotube array end facing down on the solder, then place the solder on the ultrathin copper foil, and perform the welding operation in the tube furnace to complete the synthesis of copper-carbon nanotube array-copper.

[0012] in,

[0013] In step 1, the ratio of argon, ethylene, and hydrogen is argon: ethylene: hydrogen = (80-120) sccm: (50-100) sccm: (45-55) sccm.

[0014] In step 1, the heating conditions for synthesizing the carbon nanotube array are to heat to 780-850℃ at a rate of 15-50℃ / min, hold at that temperature for 10 minutes, and then allow it to cool naturally to room temperature.

[0015] In steps 2 and 5, the method used for sputtering the metal is electron beam evaporation.

[0016] In steps 2 and 5, the thicknesses of the sputtered metal layers are 50-60 nm for titanium, 200-250 nm for nickel, and 50-90 nm for gold, respectively.

[0017] In steps 3 and 6, the thickness of the ultrathin copper foil used is 5-15 μm.

[0018] In step 3, the solder composition used is Sn. 96.5 Ag3Cu 0.5 Its melting point is 217℃.

[0019] In step 3, the gas pressure inside the welding furnace is kept below 0.1 MPa during the welding operation; the temperature of the welding furnace is 230-3200℃ during the welding operation; and the welding time is 3-10 min.

[0020] In step 6, the solder composition used is In 97 Ag3 has a melting point of 158℃.

[0021] In step 6, the gas pressure inside the welding furnace is kept below 0.1 MPa during the welding process; the temperature of the welding furnace is 180-260℃ during the welding process; and the welding time is 3-10 min.

[0022] Beneficial Effects: This invention has significant advantages over prior art, addressing the challenge of applying carbon nanotube arrays in the field of thermal interface materials. The preparation method of this invention is simple and easy to operate, and the synthesized carbon nanotube composite material maintains the vertical orientation of the carbon nanotube array, without sacrificing the composite material's thermal conductivity. Compared with related technologies, this invention proposes a "transfer-encapsulation" strategy. By welding ultrathin copper foil to both sides of the carbon nanotube array in two steps, high-quality, large-area transfer of the carbon nanotube array from the original substrate is achieved. The encapsulated carbon nanotube array also eliminates the risk of leakage. After encapsulation, the carbon nanotube array can be used directly as an independent thermal pad within electronic products, perfectly matching the encapsulation process. Furthermore, subsequent testing and characterization confirmed that the prepared composite material possesses high thermal conductivity and a low Young's modulus. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method for synthesizing carbon nanotube array-based thermal interface materials according to the present invention;

[0024] Figure 2 This is a scanning electron microscope image of the copper-carbon nanotube array-copper of the present invention;

[0025] Figure 3 The figure shows the mechanical test results of the copper-carbon nanotube array-copper of this invention;

[0026] Figure 4 The graph shows the test results of the thermal conductivity of the copper-carbon nanotube array-copper at different temperatures in this invention.

[0027] Figure 5 The figures show the thermal resistance test results of the copper-carbon nanotube array-copper and copper-carbon nanotube array-copper@silicone grease under different pressures. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0029] The specific embodiments of the present invention are described below with reference to the accompanying drawings.

[0030] Example 1:

[0031] Figure 1 This is a flowchart of the entire synthesis strategy.

[0032] The method for synthesizing the carbon nanotube array-based thermal interface material of the present invention, which can be used independently, includes the following steps:

[0033] 1) A mixture of argon, ethylene, and hydrogen is introduced into a chemical vapor deposition system, and carbon nanotube arrays are synthesized according to the set temperature and time to obtain carbon nanotube arrays.

[0034] 2) Sputter layers of titanium, nickel, and gold onto the free ends of the carbon nanotube array;

[0035] 3) Place the sputtered carbon nanotube array with the free end facing down on the solder, then place the solder on the ultrathin copper foil, and perform the welding operation in a tube furnace;

[0036] 4) Gently peel the copper foil, solder, and carbon nanotube array together from the growth substrate using tweezers;

[0037] 5) Sputter layers of titanium, nickel, and gold onto the carbon nanotube array ends of the transferred composite material;

[0038] 6) Place the sputtered composite material with the carbon nanotube array end facing down on the solder, then place the solder on the ultrathin copper foil, and perform the welding operation in the tube furnace to complete the synthesis of copper-carbon nanotube array-copper.

[0039] Example 2:

[0040] The method for synthesizing the carbon nanotube array-based thermal interface material of the present invention, which can be used independently, includes the following steps:

[0041] 1) A mixture of argon, ethylene, and hydrogen is introduced into a chemical vapor deposition system, and carbon nanotube arrays are synthesized according to the set temperature and time to obtain carbon nanotube arrays.

[0042] 2) Sputter layers of titanium, nickel, and gold onto the free ends of the carbon nanotube array;

[0043] 3) Place the sputtered carbon nanotube array with the free end facing down on the solder, then place the solder on the ultrathin copper foil, and perform the welding operation in a tube furnace;

[0044] 4) Gently peel the copper foil, solder, and carbon nanotube array together from the growth substrate using tweezers;

[0045] 5) Sputter layers of titanium, nickel, and gold onto the carbon nanotube array ends of the transferred composite material;

[0046] 6) Place the sputtered composite material with the carbon nanotube array end facing down on the solder, then place the solder on the ultrathin copper foil, and perform the welding operation in a tube furnace. Complete the synthesis of copper-carbon nanotube array-copper. Then, coat both sides of the copper-carbon nanotube array-copper with a small amount of silicone grease to complete the synthesis of copper-carbon nanotube array-copper@silicone grease.

[0047] Experimental example:

[0048] The copper-carbon nanotube array-copper synthesized in Example 1 was torn along the cross-section, and its structural morphology was observed under a scanning electron microscope.

[0049] The copper-carbon nanotube array-copper synthesized in Example 1 was adhered to a silicon wafer, and its Young's model and hardness were tested using nanoindentation testing. The nanoindentation test parameters were: maximum force 38 mN, minimum force 2 mN, load application rate 0.5 mN / s, unloading rate 0.5 mN / s, and 9 different points were tested for each sample. The same point was subjected to in-situ cyclic loading / unloading 20 times.

[0050] The copper-carbon nanotube array synthesized in Example 1, coated with graphite on both sides, was placed in a laser thermal conductivity meter for thermal conductivity testing at different temperatures (30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃). The heating rate of the laser thermal conductivity meter was 10℃ / min, and nitrogen was used as the protective gas.

[0051] The copper-carbon nanotube array-copper synthesized in Example 1 and the copper-carbon nanotube array-copper@silicone grease synthesized in Example 2 were subjected to thermal resistance tests under different pressures (0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa). The tests were conducted in accordance with the ASTM D5470 standard.

[0052] Figure 2 These are scanning electron microscope images of the copper-carbon nanotube array-copper of this invention, from... Figure 2 It can be seen that in the prepared copper-carbon nanotube array-copper, the carbon nanotube array maintains good orientation, which is beneficial to maintaining its mechanical properties and heat transfer path. Furthermore, the carbon nanotube array tip maintains a tight connection with the copper foil, demonstrating the integrity of the structure.

[0053] Figure 3 The figure shows the mechanical test results of the copper-carbon nanotube array-copper of the present invention. It can be seen that the Young's modulus of the copper-carbon nanotube array-copper is about 1 GPa, and it gradually decreases with the continuous increase of the number of cycles, showing excellent mechanical properties.

[0054] Figure 4 The graph shows the thermal conductivity test results of the copper-carbon nanotube array-copper at different temperatures. It can be seen that at room temperature, the effective thermal conductivity of the copper-carbon nanotube array-copper is 35.71 W / m². –1 K –1 .

[0055] Figure 5The figures show the thermal resistance test results of the copper-carbon nanotube array-copper and copper-carbon nanotube array-copper@silicone grease under different pressures. It can be seen that under a suitable pressure (0.5 MPa), the thermal resistance of the copper-carbon nanotube array-copper is 70.72 ± 0.27 mm. 2 KW –1 The thermal resistance of the copper-carbon nanotube array-copper@silicone grease is 13.32 ± 0.23 mm. 2 KW –1 .

[0056] In summary, the preparation method of this invention is simple and easy to operate, and the synthesized carbon nanotube composite material maintains the vertical orientation of the carbon nanotube array without sacrificing the thermal conductivity of the composite material. Compared with related technologies, this invention proposes a "transfer-encapsulation" strategy, which achieves high-quality, large-area transfer of the carbon nanotube array from the original substrate by welding ultrathin copper foil on both sides of the carbon nanotube array in two steps. The encapsulated carbon nanotube array also eliminates the risk of leakage. After encapsulation, the carbon nanotube array can be used directly as an independent thermal pad in electronic products, perfectly matching the encapsulation process. Furthermore, subsequent testing and characterization have confirmed that the prepared composite material has high thermal conductivity and low Young's modulus.

[0057] It will be understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing a carbon nanotube array-based thermal interface material that can be used independently, characterized in that, The method includes the following steps: Step 1: A mixture of argon, ethylene, and hydrogen is introduced into a chemical vapor deposition system. Carbon nanotube arrays are synthesized on a silicon wafer (the growth substrate) according to the set heating conditions and time. The heating conditions for synthesizing the carbon nanotube arrays are: heating at 15-50℃ / min to 780-850℃, holding at that temperature for 10 min, and then allowing it to cool naturally to room temperature. Step 2: The free ends of the obtained carbon nanotube array are sequentially sputtered with layers of titanium, nickel, and gold; the sputtering method used is electron beam evaporation. Step 3: Place the free end of the carbon nanotube array with the sputtered metal layer facing down on the solder, then place the solder on the ultrathin copper foil, and perform the welding operation in a tube furnace; during the welding operation, keep the gas pressure in the welding furnace below 0.1 MPa; the temperature of the welding furnace during the welding operation is 230 - 3200℃; the welding time is 3 - 10 min. Step 4: Transfer the copper foil, solder and carbon nanotube array together from the growth substrate to obtain a composite material of copper foil and carbon nanotube array. Step 5: After transfer, the carbon nanotube array end of the composite material consisting of copper foil and carbon nanotube array is sequentially sputtered with layers of titanium, nickel, and gold; the sputtering method used is electron beam evaporation. Step 6: Place the sputtered composite material with the carbon nanotube array end facing down on the solder, then place the solder on the ultrathin copper foil, and perform the welding operation in a tube furnace to complete the synthesis of copper-carbon nanotube array-copper; during the welding process, keep the gas pressure in the welding furnace below 0.1MPa; the temperature of the welding furnace during the welding process is 180-260℃; the welding time is 3-10min.

2. The method for synthesizing a carbon nanotube array-based thermal interface material that can be used independently, as described in claim 1, is characterized in that... In step 1, the ratio of argon, ethylene, and hydrogen is argon: ethylene: hydrogen = (80 - 120) sccm: (50 - 100) sccm: (45 - 55) sccm.

3. The method for synthesizing a carbon nanotube array-based thermal interface material that can be used independently, as described in claim 1, is characterized in that... In steps 2 and 5, the thicknesses of the sputtered metal layers are 50-60 nm for titanium, 200-250 nm for nickel, and 50-90 nm for gold.

4. The method for synthesizing a carbon nanotube array-based thermal interface material that can be used independently, as described in claim 1, is characterized in that... In steps 3 and 6, the thickness of the ultrathin copper foil used is 5-15 μm.

5. The method for synthesizing a carbon nanotube array-based thermal interface material that can be used independently, as described in claim 1, is characterized in that... In step 3, the solder composition used is Sn. 96.5 Ag3Cu 0.5 Its melting point is 217℃.

6. The method for synthesizing a carbon nanotube array-based thermal interface material that can be used independently, as described in claim 1, is characterized in that... In step 6, the solder composition used is In 97 Ag3 has a melting point of 158℃.

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