CN114717441A - Method for preparing diamond/copper composite material with low density and high thermal conductivity at low cost - Google Patents

Abstract

The invention provides a low-cost method for preparing a diamond/copper composite material with low density and high thermal conductivity, which comprises the following steps: pretreatment of diamond crushed material; tungsten plating on the diamond surface by DC magnetron sputtering method to prepare encapsulated elemental tungsten Thin film; annealed in a vacuum tube furnace to convert the tungsten element on the diamond surface into tungsten carbide; fully mix the tungsten carbide-wrapped diamond and copper powder in a mass ratio of 3:1 to 4:1, and press into a cylinder; then A high temperature and high pressure process is carried out by a six-sided top press to obtain a diamond/copper composite material. The invention selects diamond crushed material as raw material, which greatly reduces the cost; adopts high temperature and high pressure process to synthesize diamond composite material, which has high density, short preparation time and high efficiency; the prepared sample has low density and high thermal conductivity, and the method is simple to operate. , the production cost is low, it can be mass-produced on a large scale, and has broad industrial application prospects.

Description

A low-cost method for preparing diamond/copper composite material with low density and high thermal conductivity

technical field

The invention relates to a low-cost method for preparing a diamond/copper composite material with low density and high thermal conductivity, and belongs to the field of composite materials.

Background technique

With the rapid development of artificial intelligence technology and 5G communication technology, the integration of electronic circuits and the performance of electronic components are continuously improved, the speed of CPU processing data is getting faster and faster, the working power of high-power devices is increased, and more and more heat is generated. Transferring heat quickly and efficiently is the key to ensuring the normal operation of high-power devices. Currently, the commonly used packaging materials for heat dissipation in the market include metal-based packaging materials, polymer-based composite materials, and ceramic-based packaging materials. The preparation of ceramic packaging materials requires high-temperature sintering of powders, and it is difficult to perform secondary processing due to the brittleness of ceramics. , the high cost and difficult processing limit its large-scale application; the thermal conductivity of the polymer matrix composite material is low, and the thermal stability at high temperature is poor, absorbing moisture in the air and failing.

Metal-based materials are one of the most widely used packaging materials at the beginning. Due to the high density and high thermal expansion coefficient of traditional metal-based packaging materials such as Al, Cu, and W, their large-scale applications are limited. Diamond has a high thermal conductivity of 1000-2200W/(m·K) and a low expansion rate of 7.6-9.6×10 ^-7 K ^-1 , and has been industrially produced. Copper is the most cost-effective among all matrix materials. Combining metal copper with diamond is an ideal heat dissipation material. The diamond/copper composite material has excellent thermal conductivity and the thermal expansion coefficient matches that of Si, GaAs, GaN, SiC and other semiconductor materials. Secondly, the diamond composite material also has the advantages of excellent mechanical properties and low density, which is a new technology in the field of electronic packaging heat dissipation. Representative of a generation of thermal management materials.

Diamond has the characteristics of high hardness and high chemical stability. It does not chemically react with copper, and it is generally difficult to be wetted by alloys or metals, resulting in poor bonding between diamond and copper contact interface, which cannot give full play to the high thermal conductivity of diamond. . The interface of diamond/Cu composites was improved by optimizing the preparation process. Commonly used preparation methods of diamond/Cu composites include high temperature and high pressure sintering, spark plasma sintering, hot pressing sintering and infiltration. Among them, the diamond/Cu composites prepared by the high temperature and high pressure sintering method have high density, short time consumption and high efficiency, which make them widely used. Long-term continuous sintering, metal matrix alloying, and diamond surface metallization are used to improve the thermal conductivity of diamond/Cu composites. At present, single-crystal diamond particles are expensive, and the prepared diamond composite material has high density and low thermal conductivity. Therefore, in order to reduce the cost, reduce the density of the composite material, and improve the thermal conductivity of the composite material, it is necessary to further study a new method to improve.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the purpose of the present invention is to provide a low-cost method for preparing a diamond/copper composite material with low density and high thermal conductivity.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A low-cost method for preparing a diamond/copper composite material with low density and high thermal conductivity, comprising the following steps:

(1) Pretreatment of diamond crushed material

Recycle the defective products produced in the industrial production of diamond crystals, and obtain diamond crushed materials with a particle size of 100-120 meshes after crushing, which is used for later use;

Soak the diamond crushed material in aqua regia for 2.5h-3.5h to remove metal contaminants on the diamond surface; then ultrasonically use acetone, alcohol and deionized water for 8min-12min to remove organic contaminants; dry the diamonds for later use;

(2) Preparation of wrapped elemental tungsten film

The diamond surface is plated with tungsten by DC magnetron sputtering, and the thickness of the coating is 80nm-120nm;

(3) Tungsten carbide is formed on the diamond surface

The diamond wrapped with metal tungsten is annealed in a vacuum tube furnace, and the annealing condition is 900 ℃ ~ 1000 ℃ annealing for 0.5h ~ 1.5h in Ar ₂ atmosphere, so that the tungsten element on the diamond surface is converted into tungsten carbide;

(4) Preparation of diamond/copper composites

The diamond and copper powder wrapped with tungsten carbide in step (3) are fully mixed according to the mass ratio of 3:1 to 4:1, and after uniform mixing, they are pressed into a cylinder with a diameter of 10 mm × a thickness of 2 mm; then a six-sided top press is used to carry out high temperature The high-pressure process, wherein the sintering temperature is 950°C-1350°C, the pressure is 5Gpa-7Gpa, and the holding time is 8min-12min, to obtain a diamond/copper composite material.

The nitrogen content (wt%) of the diamond crushed material is 0.015%-0.020%, and the thermal conductivity is 1500W/(m·K)-2000W/(m·K).

The aqua regia contains HCl:HNO ₃ (v/v)=3:1; the volume fraction of the alcohol is 97%.

The temperature of the drying treatment was 80° C., and the drying time was 10 min.

The sputtering current of the DC magnetron sputtering method is 1A, the sputtering vacuum degree is 3×10 ⁻³ Pa, and the sputtering rate is 0.02 nm/min˜0.08 nm/min.

The purity of the copper powder is 99.9%; the particle size of the copper powder is 120-200 mesh.

The sintering temperature was 1050° C., the pressure was 6 Gpa, and the holding time was 10 min.

The diamond/copper composite material obtained by the method has a density of 3.70 g/cm ³ to 4.0 g/cm ³ .

Beneficial effects of the present invention:

The invention selects diamond crushing material as raw material, which greatly reduces the cost; adopts high temperature and high pressure process to synthesize diamond composite material, which has high density, short preparation time and high efficiency; and the prepared sample has low density and high thermal conductivity. The operation is simple, the production cost is low, the mass production can be carried out on a large scale, and the invention has broad industrial application prospects. The specific analysis is as follows:

(1) The diamond crushing material used in the present invention is obtained by crushing the defective diamond with poor crystal form produced during the industrial production of diamond. There are three advantages of using diamond crushed material. The first is low cost and easy to obtain. Secondly, because the gap between crushed material and crushed material is small, diamond crushed material is more closely combined with copper matrix than diamond with complete crystal form. The gap between the crushed materials is small, so more diamonds can be contained in the same volume, so the density of the composite material can be reduced and the thermal conductivity of the composite material can be improved by increasing the diamond content. When the volume content of diamond is more than 90%, the composite material prepared from diamond with complete crystal form will fall off due to the excessively high content of diamond and copper, and the gap between diamond crushing materials is small. When the volume content of the diamond crushed material exceeds 90%, the combination is still firm and not easy to fall off.

(2) Raw materials used in the present invention: diamond crushed material, copper powder and tungsten are all low-cost raw materials. The particle size of the diamond crushing material is 100-120 mesh. When the diamond particles are too large, the gap between diamond and diamond is relatively large, resulting in low thermal conductivity; if the diamond particles are too small, there are too many interfaces between diamond and copper, resulting in low thermal conductivity. . Therefore, the diamond particles of the present invention are 100-120 mesh, and at this time, the interface bonding is good and the thermal conductivity is high. The diamond crushed material has a larger specific surface area than the diamond with the complete crystal form. During the diamond crushing process, the crushed material will generate many unstable crystal planes, which are easier to react with the matrix and increase the matrix's holding force on the diamond; Second, the choice of copper as the substrate has higher thermal conductivity and lower cost than substrates such as silver and aluminum. In the diamond/copper composite material, diamond and copper do not wet, and the interface is not firmly bonded. Metal carbides are introduced to improve the interface state. By comparing the solubility, wetting angle, and thermal conductivity of different carbides in copper, it is found that W and WC The thermal conductivity of W is relatively higher than others, and W is insoluble in Cu, so plating W is often more advantageous to improve the thermal conductivity of composite materials.

(3) The present invention adopts the magnetron sputtering process to complete the coating of the diamond crushed material, and the thickness of the coated metal by the magnetron sputtering can be relatively accurately controlled by a film thickness meter. Moreover, the metal thickness of magnetron sputtering is flat and uniform, and there is no leakage plating area, which can complete the wrapping of a large number of diamonds at one time. The preparation of diamond/copper composite material adopts high temperature and high pressure process. The composite material sample prepared by high temperature and high pressure has high density, high thermal conductivity, short preparation time and high efficiency. Among them, if the sintering time is too long, the metal tungsten on the diamond surface will be precipitated into the copper matrix, which will cause the thermal conductivity of the copper matrix to decrease. If the sintering time is too short, the copper cannot fully flow into the gap between the diamond and the diamond. The sintering time was 10min, and it was found that the thermal conductivity was the highest when the sintering temperature was 1050℃.

(4) According to the calculation formula of the thermal conductivity of the composite material: γ=ρ·Cρ·α where γ is the thermal conductivity; ρ is the density of the sample; Cρ is the specific heat capacity of the sample at constant pressure; α is the thermal diffusivity. It can be seen that the higher the thermal conductivity of the prepared composite material, the better, and the lower the density of the composite material, the better. In general, the density of the composite is reduced by increasing the diamond content, but the decrease in density also leads to a decrease in thermal conductivity. Therefore, in general, the thermal diffusivity is increased by reducing the interface thermal resistance between diamond and copper to increase the thermal conductivity. The invention adopts tungsten plating of diamond crushing material to improve the interface and reduce the thermal resistance of the interface. Among them, when the volume content of the diamond crushed material reaches 90%, it is still firmly bonded. The 90% diamond content leads to the density of the samples being lower than 4g/cm ³ , and the solid bonding between the diamond and copper interface leads to a high thermal diffusivity (331mm ^-2 ·s). ^-1 ) and high thermal conductivity (655.2002W·m ^-1 ·k ^-1 ).

(5) The density of the diamond/copper composite material sample obtained by the present invention is calculated to be 3.7～4.0g/cm ³ , the specific heat capacity at constant pressure is 0.50～0.51kJ/(kg·°C), and the thermal diffusivity is 188～331mm ^{− 2} ·s ^-1 , the thermal conductivity is 360～656W·m ^-1 ·k ^-1 .

Description of drawings

Fig. 1, the diamond crushing material before magnetron sputtering among the embodiment 1;

Fig. 2, the tungsten-plated diamond crushing material before annealing after magnetron sputtering in Example 1;

Fig. 3, the tungsten-plated diamond crushed material after annealing in embodiment 1;

Fig. 4, the scanning electron microscope picture of the tungsten-coated diamond before annealing in embodiment 1;

Fig. 5, the scanning electron microscope picture of the tungsten-plated diamond after annealing in Example 1;

Figure 6, the X-ray diffractogram of the tungsten-plated diamond before annealing in Example 1;

Figure 7, the X-ray diffractogram of the tungsten-plated diamond after annealing in Example 1;

Fig. 8, the scanning electron microscope picture of the diamond/copper composite material prepared in embodiment 1;

Fig. 9, the scanning electron microscope picture of the diamond/copper composite material prepared in embodiment 2;

Fig. 10, the scanning electron microscope picture of the diamond/copper composite material prepared in embodiment 3;

Fig. 11, the scanning electron microscope picture of the diamond/copper composite material prepared in embodiment 4;

Fig. 12, the scanning electron microscope picture of the diamond/copper composite material prepared in embodiment 5;

Figure 13. Thermal diffusivity of diamond/copper composites prepared in Examples 1-5;

Figure 14. Thermal conductivity of diamond/copper composites prepared in Examples 1-5.

Detailed ways

The specific embodiments of the present invention will be further described in detail below with reference to the examples. Unless otherwise specified, the instruments and equipment involved in the examples are all conventional instruments and equipment; the involved reagents are all commercially available conventional reagents; and the involved test methods are all conventional methods.

Example 1

A low-cost method for preparing a diamond/copper composite material with low density and high thermal conductivity, comprising the following steps:

(1) Pretreatment of diamond crushed material

Recycle the defective products produced in the industrial production of diamond crystals, and carry out crushing treatment to obtain diamond crushed materials with a particle size of 100-120 meshes, the nitrogen content (wt%) of which is 0.015%-0.020%, and the thermal conductivity is 1500-2000W/(m ·K), spare;

Soak the diamond crushed material in aqua regia (HCl:HNO ₃ (v/v)=3:1) for 3h to remove the metal contaminants on the diamond surface; then use acetone, 97% (v/v) alcohol, remove Ionized water was sonicated for 10 minutes to remove organic pollutants; finally, the treated diamond was dried at 80°C for 10 minutes for use (as shown in Figure 1, the diamond was in the form of yellow powder);

(2) Preparation of wrapped elemental tungsten film

The diamond treated in step (1) is placed on a magnetron sputtering sample stage with ultrasonic, vibration and tumbling functions, and tungsten is plated on the diamond surface by DC magnetron sputtering; the sputtering current is 1A, and the sputtering vacuum The temperature was 3×10 ^-3 Pa, and the sputtering rate was 0.02-0.08 nm/min; finally, 100 nm thick metal tungsten was deposited on the diamond surface (as shown in Fig. 2).

(3) Tungsten carbide is formed on the diamond surface

The diamond wrapped with metal tungsten was annealed in a vacuum tube furnace. The annealing condition was annealing at 950 ° C for 1 h in an Ar ₂ atmosphere, so that the tungsten element on the diamond surface was converted into tungsten carbide (the conversion rate was greater than 80%), and the obtained diamond sample was from The original silver-white color becomes gray-black (as shown in Figure 3).

Phase analysis and evaluation: The tungsten-coated diamond before and after annealing was analyzed by scanning electron microscope (as shown in Figures 4 and 5). The SEM test results showed that the tungsten carbide coating on the diamond surface was uniform and dense, and there was almost no surface after annealing. The metal falls off, indicating that the magnetron sputtering technology can make the material tightly bonded to the deposited material, which has a better bonding effect than thermal evaporation. Before and after annealing, some changes have taken place in the micro-morphology of the diamond surface. For example, after annealing, the metal on the surface of the sample changes from flat to ravine, which is more likely to form a tight bond with copper, which is beneficial to reduce the interface thermal resistance and improve the thermal conductivity.

X-ray diffraction analysis was performed on the tungsten-coated diamond before and after annealing (as shown in Figures 6 and 7). The XRD test results showed that the metal tungsten on the diamond surface was converted into tungsten carbide by annealing.

(4) Preparation of diamond/copper composites

The diamond and pure copper powder (purity of 99.9%, copper powder particle size of 120-200 mesh) wrapped with tungsten carbide in step (2) are fully mixed according to the mass ratio of 3.54:1, and the fully automatic cutter head press is used after uniform mixing. Press into a cylinder of Φ10mm×2mm, and finally place the sample in the hot high pressure assembly cavity of a domestic hinged six-sided top press (UDS650);

The high-pressure equipment used in the high-temperature and high-pressure process is a domestic hinged six-sided top press. In the experiment, the graphite tube was heated to reach the required temperature. The sintering temperature was 950°C, the pressure was 6Gpa, and the holding time was 10min. The diamond/copper composite material was obtained. .

Thermoelectric performance evaluation: The SEM test results show that diamond and copper are tightly bonded through the tungsten carbide interface (Figure 8). The density of the diamond/copper composite sample is calculated to be 3.787682g/cm ³ , the specific heat capacity at constant pressure is 0.505522kJ/(kg·℃), the thermal diffusivity is 188mm ^-2 ·s ^-1 , and the thermal conductivity is 360.5966W· m ^-1 ·k ^-1 .

Example 2

The sintering temperature in the high temperature and high pressure process in step (3) in Example 1 was changed to 1050° C., and other method steps were the same as those in Example 1, to obtain a diamond/copper composite material.

Thermoelectric performance evaluation: The SEM test results show that diamond and copper are tightly bonded through the tungsten carbide interface (Figure 9). The density of the diamond/copper composite sample is calculated to be 3.941599g/cm ³ , the specific heat capacity at constant pressure is 0.502196kJ/(kg·℃), the thermal diffusivity is 331mm ^-2 ·s ^-1 , and the thermal conductivity is 655.2002W· m ^-1 ·k ^-1 .

Example 3

The sintering temperature in the high-temperature and high-pressure process in step (3) of Example 1 was changed to 1150° C., and other method steps were the same as those of Example 1 to obtain a diamond/copper composite material.

Thermoelectric performance evaluation: The SEM test results show that diamond and copper are tightly bonded through the tungsten carbide interface (Figure 10). The density of the diamond/copper composite sample is calculated to be 3.988798g/cm ³ , the specific heat capacity at constant pressure is 0.50103kJ/(kg·℃), the thermal diffusivity is 262.53mm ^-2 ·s ^-1 , and the thermal conductivity is 524.6684W. ·m ⁻¹ ·k ⁻¹ .

Example 4

The sintering temperature in the high-temperature and high-pressure process in step (3) of Example 1 was changed to 1250° C., and other method steps were the same as those of Example 1 to obtain a diamond/copper composite material.

Thermoelectric performance evaluation: SEM test results show that diamond and copper are tightly bonded through the tungsten carbide interface (Figure 11). The density of the diamond/copper composite sample is calculated to be 3.997079g/cm ³ , the specific heat capacity at constant pressure is 0.500918kJ/(kg·℃), the thermal diffusivity is 233.999mm ^-2 ·s ^-1 , and the thermal conductivity is 468.5152W. ·m ⁻¹ ·k ⁻¹ .

Example 5

The sintering temperature in the high temperature and high pressure process in step (3) of Example 1 was changed to 1350° C., and other method steps were the same as those of Example 1, to obtain a diamond/copper composite material.

Thermoelectric performance evaluation: SEM test results show that diamond and copper are tightly bonded through the tungsten carbide interface (Figure 12). The density of the diamond/copper composite sample is calculated to be 3.9905g/cm ³ , the specific heat capacity at constant pressure is 0.500678kJ/(kg·℃), the thermal diffusivity is 227.401mm ^-2 ·s ^-1 , and the thermal conductivity is 456.133W. ·m ⁻¹ ·k ⁻¹ .

Claims (8)

1. A method for preparing a diamond/copper composite material with low density and high thermal conductivity at low cost is characterized by comprising the following steps:

(1) pretreatment of diamond crushing material

Recovering defective products generated in the industrial production of diamond crystals, and crushing to obtain a diamond crushed material with the granularity of 100-120 meshes for later use;

soaking the diamond crushed material in aqua regia for 2.5-3.5 h to remove metal pollutants on the surface of the diamond; then, respectively using acetone, alcohol and deionized water to carry out ultrasonic treatment for 8-12 min, and removing organic pollutants; drying the diamond for later use;

(2) preparing a film wrapping elemental tungsten

Plating tungsten on the surface of the diamond by a direct-current magnetron sputtering method, wherein the thickness of a plating layer is 80-120 nm;

(3) forming tungsten carbide on the surface of diamond

Annealing the diamond coated with the metal tungsten in a vacuum tube furnace under the condition of Ar₂900-10 ℃ in atmosphereAnnealing at 00 ℃ for 0.5-1.5 h to convert the tungsten simple substance on the surface of the diamond into tungsten carbide;

(4) preparation of diamond/copper composite Material

And (3) coating the diamond and the copper powder coated with the tungsten carbide in the step (3) according to the weight ratio of 3: 1-4: 1, uniformly mixing, and pressing into a cylinder with the diameter of 10mm multiplied by the thickness of 2 mm; and then, carrying out a high-temperature high-pressure process by using a cubic press, wherein the sintering temperature is 950-1350 ℃, the pressure is 5-7 Gpa, and the heat preservation time is 8-12 min, so as to obtain the diamond/copper composite material.

2. The method of claim 1, wherein the diamond compact has a nitrogen content (wt%) of 0.015% to 0.020% and a thermal conductivity of 1500W/(m-K) to 2000W/(m-K).

3. The method of claim 1, wherein the aqua regia is HCl: HNO₃(v/v) ═ 3: 1; the volume fraction of the alcohol is 97%.

4. The method according to claim 1, wherein the drying process is carried out at a temperature of 80 ℃ for a drying time of 10 min.

5. The method of claim 1, wherein the sputtering current of the DC magnetron sputtering method is 1A, and the sputtering vacuum degree is 3 x 10^-3Pa, sputtering rate of 0.02 nm/min-0.08 nm/min.

6. The method of claim 1 wherein said copper powder has a purity of 99.9%; the granularity of the copper powder is 120-200 meshes.

7. The method of claim 1, wherein the sintering temperature is 1050 ℃, the pressure is 6Gpa, and the holding time is 10 min.

8. The method of claim 1, wherein the method produces a diamond/copper compositeThe density of the composite material is 3.7g/cm³～4.0g/cm³。

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