Method for brazing and connecting diamond and copper by adopting Ag-Cu eutectic brazing filler metal

Abstract

The invention discloses a method for brazing and connecting diamond and copper through Ag-Cu eutectic brazing filler metal. The method comprises the following steps that S1, coating treatment is conducted on diamond, and surface metallized diamond is obtained after heating activation; s2, copper to be brazed and the surface metallized diamond are subjected to brazed connection through Ag-Cu eutectic brazing filler metal; wherein in the step S1, a titanium layer, a molybdenum layer and a nickel layer are sequentially deposited on the surface of the diamond, and coating treatment of the diamond is achieved. According to the method, the residual stress of the brazed joint can be reduced, the service life of the brazed joint is prolonged, the sealing performance of the brazed joint is improved, and important reference is provided for preparation of the large-size diamond microwave window.

Description

Technical Field

[0001] The invention belongs to the field of vacuum electronic devices, and in particular relates to a method for brazing diamond and copper using Ag-Cu eutectic solder. Background Art

[0002] my country urgently needs to accelerate the development and application of clean energy technologies, improve energy efficiency, and optimize its energy structure. Against this backdrop, nuclear fusion energy, with its advantages such as abundant fuel sources, virtually zero carbon emissions, extremely low nuclear radiation pollution, high energy density, and high operational safety, is considered one of the most promising solutions to completely resolve humanity's energy crisis and has attracted international attention. The core of nuclear fusion technology lies in the effective confinement and efficient heating of high-temperature plasma. Currently, the tokamak device is the internationally recognized and most mature magnetic confinement nuclear fusion technology route. As an important heating method for the tokamak device, the electron cyclotron resonance heating system (EC&RH) heats the plasma using high-power microwaves to maintain its stable operation. As a key component of this system, the microwave window must achieve both efficient transmission of high-power microwaves and long-term stability of the vacuum environment, which is crucial to the overall performance of the nuclear fusion device. The preparation of microwave windows requires reliable connection between the diamond film and the pure copper substrate. However, due to the significant differences in the coefficient of thermal expansion (CTE), surface chemical properties and wettability between diamond and pure copper, large residual stress is easily generated during the welding process, leading to the formation of microcracks on the diamond surface, thereby significantly weakening the mechanical properties and service stability of the joint.

[0003] Furthermore, existing connection processes often rely on high-temperature brazing or alloy brazing, which not only easily triggers graphitization of diamond but also generates excessive intermetallic compounds (IMCs), further reducing the durability of microwave windows. Therefore, effectively alleviating welding residual stress and lowering the connection temperature to achieve high-quality, reliable connections between diamond and pure copper has become a key scientific issue restricting the development of microwave window fabrication and nuclear fusion engineering, and a technical bottleneck that urgently needs to be overcome in the process optimization of large-scale microwave window devices in China. Summary of the Invention

[0004] Based on the above technical problems, the present invention provides a method for brazing diamond and copper using Ag-Cu eutectic solder, which can reduce the residual stress of the brazed joint, extend the service life of the brazed joint, and improve the sealing performance of the brazed joint, providing an important reference for the preparation of large-size diamond microwave windows.

[0005] The specific scheme of the present invention is as follows:

[0006] The present invention provides a method for brazing diamond and copper using Ag-Cu eutectic solder, comprising the following steps: S1, coating the diamond, and heating and activating it to obtain a surface metallized diamond; S2, brazing the copper to be brazed and the surface metallized diamond using the Ag-Cu eutectic solder;

[0007] Among them, in S1, the diamond is coated by depositing a titanium layer, a molybdenum layer and a nickel layer on the surface of the diamond in sequence.

[0008] The present invention first coats and heats the diamond to activate the metallization process, and then uses Ag-Cu eutectic solder to braze the diamond and copper. Diamond surface metallization is a prerequisite for achieving Ag-Cu eutectic solder brazing of the diamond and copper, ensuring that the Ag-Cu eutectic solder wets the diamond surface. After the diamond surface metallization, brazing the diamond and copper using Ag-Cu eutectic solder yields a high-quality weld joint, and these two steps work in tandem.

[0009] The specific functions of diamond coating are as follows: (1) the purpose of forming the titanium layer is to form a TiC reaction layer with the diamond surface during the subsequent brazing process, thereby enhancing the interface bonding strength; (2) the purpose of forming the molybdenum layer is to isolate the Ti layer from the Ni layer during the subsequent brazing process, thereby avoiding the formation of IMCs during the reaction process, which leads to a decrease in the performance of the brazed joint; (3) the purpose of forming the nickel layer is to enhance the wetting performance of the brazing material during the subsequent brazing process, thereby avoiding the accumulation of the brazing material and reducing the residual stress of the brazing joint.

[0010] Preferably, in S1, the thickness of the titanium layer is 100-300 nm, the thickness of the molybdenum layer is 300-500 nm, and the thickness of the nickel layer is 3-5 μm.

[0011] Preferably, in S1, the titanium layer and the molybdenum layer are deposited by magnetron sputtering, and the nickel layer is deposited by electroplating.

[0012] Preferably, in S1, the coated diamond is cleaned and placed in a vacuum brazing furnace for heating activation treatment, specifically including: first heating from room temperature to 690-710°C and keeping warm for 5-20 minutes; continuing to heat up to 750-800°C and keeping warm for 30-90 minutes; then cooling to 280-320°C, and finally cooling to room temperature.

[0013] Preferably, in S1, the heating rate at each stage during the heating process is independently selected from 5-15°C / min, and the cooling rate during the cooling process is 4-5°C / min.

[0014] In the present invention, the purpose of the heating activation treatment is to make each metal layer diffuse at a certain temperature to enhance the bonding strength of the coating, and then cool it down to finally obtain a surface metallized diamond with no bubbles or shedding in the film layer.

[0015] Preferably, in S2, during brazing, Ag-Cu eutectic brazing filler metal is placed between copper and surface metallized diamond to obtain a sandwich structure of the welded parts.

[0016] Preferably, in S2, the brazing temperature is 800°C-820°C, and the holding time after heating to the brazing temperature is 5-15 minutes; more preferably, the brazing temperature is 810°C.

[0017] Preferably, in S2, the specific process of brazing connection is: heating from room temperature to 280-300℃ and keeping warm for 10-30 minutes, then heating to 730-780℃ and keeping warm for 10-30 minutes; continuing to heat to the brazing temperature of 800℃-820℃, and then keeping warm at the brazing temperature for 5-15 minutes; then cooling to 280-320℃ at a rate of 4-6℃ / min, and finally cooling to room temperature with the furnace; more preferably, the heating rate in the above heating process is 5-15℃ / min.

[0018] Preferably, in S2, the mass ratio of Ag to Cu in the Ag-Cu eutectic solder is 72:28.

[0019] The beneficial effects of the present invention are:

[0020] The present invention provides a method for brazing diamond and copper using Ag-Cu eutectic solder. The diamond is first surface-metallized and then brazed using Ag-Cu eutectic solder. The combined effect of these two methods can reduce residual stress in the brazed joint, extend the service life of the brazed joint, and improve the sealing performance of the brazed joint. This method provides an important reference for the preparation of large-scale diamond microwave windows. The reasons for this are:

[0021] On the one hand, the melting point of Ag-Cu eutectic solder is significantly lower than that of traditional active solder. Since it can be completely melted at about 780°C, the brazing temperature can be significantly reduced. The lower brazing temperature not only effectively inhibits the risk of diamond to graphite conversion, but also reduces the thermal deformation and tissue damage of the copper matrix caused by high temperature, which helps to maintain the original mechanical properties of the diamond film and the copper matrix, thereby extending the service life of the microwave window assembly. The use of Ag-Cu, a solder with good antioxidant and corrosion resistance, can maintain the integrity and stability of the brazing seam for a long time under microwave irradiation and complex working conditions, thereby significantly improving the reliability and service life of the joint.

[0022] On the other hand, a titanium layer, a molybdenum layer and a nickel layer are sequentially deposited on the diamond surface. The Ti layer reacts in situ with the diamond surface under high temperature conditions to form a dense TiC transition layer, forming a strong chemical bond at the interface. At the same time, the Mo layer is located on it, effectively isolating the Ti layer from the outer Ni layer, preventing the two from directly reacting to form excessive intermetallic compounds during subsequent heat treatment or brazing. The effective isolation effect of the Mo layer not only inhibits the precipitation of large-scale intermetallic compounds that may be produced between the Ti layer and the Ni layer at high temperatures, but also ensures that the Ni layer can fully play its wetting promotion role during subsequent brazing. With the help of the Ni layer, the molten Ag-Cu eutectic solder can uniformly wet the metallized diamond and the copper substrate surface, and form a continuous and tight brazing seam structure after thermal activation treatment, without visible holes or cracks, so that the joint has extremely high density and excellent airtightness under long-term vacuum conditions, fully meeting the use requirements of the microwave window in a long-term stable vacuum environment.

[0023] On this basis, the Ag-Cu eutectic solder only needs to melt at around 800°C to achieve sufficient wetting, so that the molten solder Mo layer and the copper matrix are evenly diffused and tightly filled, and no solder corners are formed on the diamond. Therefore, it can significantly alleviate the local stress concentration caused by the mismatch of thermal expansion coefficients between diamond and copper matrix, reduce the risk of interface cracks and delamination, and thus significantly reduce the residual stress of the brazed joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The diamond obtained after coating treatment in Example 1;

[0025] Figure 2 The surface metallized diamond obtained in Example 1;

[0026] Figure 3 This is the appearance of the brazed joint obtained in Example 1;

[0027] Figure 4 is a cross-sectional view of the brazed joint obtained in Example 1;

[0028] Figure 5 2 is a cross-sectional view of the brazed joint obtained in Comparative Example 1;

[0029] Figure 6 This is the backscattered microstructure morphology of the brazed joint obtained in Example 1;

[0030] Figure 7 This is an EDS surface scan of the brazed joint obtained in Example 1;

[0031] Figure 8 The following are the comparison data of equivalent stress between Example 1 and Comparative Example 1 through Ansys finite element simulation. DETAILED DESCRIPTION

[0032] The present invention provides a method for brazing diamond and copper using Ag-Cu eutectic solder, comprising the following steps: S1, coating the diamond, and heating and activating it to obtain a surface metallized diamond; S2, brazing the copper to be brazed and the surface metallized diamond using the Ag-Cu eutectic solder;

[0033] Among them, in S1, the diamond is coated by depositing a titanium layer, a molybdenum layer and a nickel layer on the surface of the diamond in sequence.

[0034] The present invention first coats the diamond and then heats and activates it to obtain surface metallized diamond. The coating process produces three layers of Ti / Mo / Ni thin films, each of which performs key functions in the brazing process:

[0035] First, the Ti layer reacts with the diamond surface under high temperature conditions to form a dense and continuous TiC transition layer. This transition layer not only eliminates the chemical inertness of the diamond itself, but also significantly improves the bonding strength between the diamond and subsequent coatings, providing a solid interface foundation for the entire brazing system.

[0036] Secondly, the Mo layer coated on the Ti layer has excellent thermal stability and anti-diffusion ability. Its primary function is to isolate the Ti layer from the outer Ni layer, preventing the two from directly reacting at high temperatures to form excessive intermetallic compounds (IMCs). On the other hand, it ensures that the coating system can still maintain a stable structure at a brazing temperature of around 800°C, thereby avoiding the formation of interfacial brittle phases.

[0037] Finally, the outermost Ni electroplating layer significantly improves the wettability of the solder during brazing, allowing the Ag-Cu eutectic solder to evenly diffuse and tightly cover between the metallized diamond and the copper matrix after being heated and melted, achieving a high-density brazing seam, thereby improving the airtightness and bonding reliability of the joint.

[0038] Compared with traditional active solders that require higher temperatures, the Ag-Cu (72:28 mass ratio) eutectic solder has a lower melting point and can be completely melted and welded at only about 780°C. This not only significantly reduces the risk of diamond graphitization, but also reduces thermal damage to the copper substrate. At the same time, the dense brazing seam formed after the Ag-Cu alloy is melted has excellent thermal conductivity, which can quickly transfer the local heat generated at the weld to the heat dissipation structure, alleviate the temperature gradient and thermal stress concentration, and ensure structural stability. In addition, the intermetallic compounds in the brazing seam are finely and evenly distributed, which can give the solder joints excellent mechanical strength and airtightness, so that the connection between the metallized diamond and the copper substrate maintains long-term heat resistance, corrosion resistance and structural integrity under high vacuum environment and high-power microwave irradiation conditions, fully meeting the requirements of large-size diamond microwave windows for high reliability and long life of the joints under harsh working conditions such as nuclear fusion devices.

[0039] Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration only and are not to be construed as limiting the scope of the present invention.

[0040] In the following examples, optical-grade CVD single-crystal diamond (5*5*0.5 mm) was purchased from Advanced Crystal Technology Co., Ltd. Ag-Cu eutectic solder was purchased from Zhejiang Yatong New Materials Co., Ltd. Oxygen-free copper TU1 was purchased from Dongguan Hetianxia Metal Materials Co., Ltd.

[0041] Example 1

[0042] A method for brazing diamond and copper using Ag-Cu eutectic solder, comprising the following steps:

[0043] S1. Preparation of surface metallized diamond

[0044] 1) Diamond coating

[0045] Use silicone-tipped tweezers to place an optical-grade CVD diamond sheet into a beaker containing acetone solution. Place the beaker in an ultrasonic cleaner filled with water and clean it for 15 minutes. Dry it and place it in a clean sample bag for later use.

[0046] The diamond sheet treated in the steps is placed in a fully automatic magnetron sputtering coating machine and loaded with Ti and Mo targets. A 200 nm Ti layer and a 400 nm Mo layer are magnetron sputtered on the surface of the diamond sheet. After cooling to room temperature, the sheet is taken out and sealed for storage. The obtained Ti and Mo layer metallized diamond sheet is placed in a Ni plating solution for electroplating Ni 5 μm. After completion, the optical-grade CVD diamond sheet is transferred to a beaker with an acetone solution using silicone-tipped tweezers. The beaker is placed in a water ultrasonic cleaner for cleaning for 15 minutes and dried to obtain the coated diamond, which is sealed and stored for storage.

[0047] The diamond obtained after the coating treatment in this embodiment is as follows Figure 1 As shown, it can be seen that the surface film layer is well adhered without any shedding or bubbles.

[0048] 2) The diamond after coating is subjected to heating activation treatment, specifically including:

[0049] The coated diamond sheet was placed into a mold and transferred to a vacuum brazing furnace. The vacuum degree of the vacuum brazing furnace was first controlled at 2×10 -3 Pa, heat up to 700℃ at a rate of 10℃ / min and keep warm for 10min, continue to heat up to 750℃ at a rate of 10℃ / min and keep warm for 60min, then cool down to 300℃ at a rate of 4℃ / min, finally cool to room temperature with the furnace, take out the sample, and obtain surface metallized diamond.

[0050] The surface metallized diamond obtained in this embodiment is as follows Figure 2 As shown, it can be seen that the interface is well bonded and no peeling or bulging is observed.

[0051] S2. Use Ag-Cu eutectic solder for brazing connection

[0052] 1) Pretreatment

[0053] Cut the Ag-Cu solder flakes into 5*5mm pieces by wire-cutting with electric sparks. After removing them, polish them with sandpaper from 1000# to 1500# to remove all oxide films on the surface. Then clean them with an ultrasonic cleaner filled with acetone and put them into a clean sample bag for later use.

[0054] Cut the Cu plate into 10*10*4mm Cu blocks and polish the Cu blocks with sandpaper from 600# to 1500# to remove the cutting marks and oxide film on all sides and surfaces of the slices. Then clean them with an ultrasonic cleaner filled with acetone and put them into a clean sample bag for later use.

[0055] 2) Brazing treatment

[0056] The treated Cu, Ag-Cu eutectic solder, and surface metallized diamond are stacked in a graphite mold to form a welded assembly (the Ag-Cu eutectic solder, surface metallized diamond, and Cu block are glued together using 502 glue during assembly). A 5g molybdenum block is then placed on the welded assembly as a counterweight to ensure close contact between the Ag-Cu flake solder and the surface metallized diamond and Cu, respectively. The assembly is then transferred to a vacuum brazing furnace.

[0057] The vacuum degree of the vacuum brazing furnace is controlled at 2×10 -3Pa, heat from room temperature to 300℃ and keep warm for 30min to make the glue fully volatilize, then heat to 750℃ and keep warm for 15min to make the mold and brazing material evenly heated, then heat to brazing temperature 810℃, then keep warm at brazing temperature for 10min to melt the brazing material and complete welding, then cool to 300℃ at a rate of 5℃ / min, finally cool to room temperature with the furnace and take out the sample to finally obtain the brazing joint.

[0058] The appearance of the brazed joint obtained in this embodiment is as follows: Figure 3 As shown, it can be seen that the interface is well bonded and no cracks or falling off are seen.

[0059] Example 2

[0060] A method for brazing diamond and copper using Ag-Cu eutectic solder, comprising the following steps:

[0061] S1. Preparation of surface metallized diamond

[0062] 1) Diamond coating

[0063] The optical-grade CVD diamond was pre-treated using the method of Example 1;

[0064] The pre-treated diamond sheet was placed in a fully automatic magnetron sputtering coating machine and loaded with Ti and Mo targets. A 100nm Ti layer and a 300nm Mo layer were magnetron sputtered on the surface of the diamond sheet. After cooling to room temperature, the sheet was taken out and sealed for storage. The obtained Ti and Mo layer metallized diamond sheet was placed in a Ni plating solution for electroplating Ni 5μm. After completion, the optical-grade CVD diamond sheet was carefully transferred to a beaker with acetone solution using silicone-tipped tweezers. The beaker was placed in a water ultrasonic cleaner for cleaning for 10 minutes and dried to obtain the coated diamond, which was sealed and stored for later use.

[0065] 2) The diamond after coating is subjected to heating activation treatment, specifically including:

[0066] The coated diamond sheet was placed in a mold and transferred to a vacuum brazing furnace. The vacuum degree of the vacuum brazing furnace was first controlled at 2×10 -3 Pa, heat up to 710℃ at a rate of 8℃ / min and keep warm for 15min, continue to heat up to 780℃ at a rate of 8℃ / min and keep warm for 70min, then cool down to 280℃ at a rate of 5℃ / min, finally cool to room temperature with the furnace, take out the sample, and obtain surface metallized diamond.

[0067] S2. Use Ag-Cu eutectic solder for brazing connection

[0068] 1) Pre-treating the Ag-Cu flake solder and the Cu plate according to the method of Example 1;

[0069] 2) Brazing treatment

[0070] The assembly to be welded was assembled according to the method of Example 1, and then the assembly to be welded was transferred to a vacuum brazing furnace;

[0071] The vacuum degree of the vacuum brazing furnace is controlled at 2×10 -3 Pa, heat from room temperature to 300℃ and keep it for 10 minutes, then heat to 780℃ and keep it for 10 minutes, then heat to brazing temperature 800℃, then keep it at brazing temperature for 15 minutes, then cool to 280℃ at a rate of 6℃ / min, finally cool to room temperature with the furnace and take out the sample to finally obtain the brazed joint.

[0072] Comparative Example 1

[0073] A method for brazing diamond and copper, comprising:

[0074] S1. Use silicone-tipped tweezers to place an optical-grade CVD diamond sheet into a beaker containing acetone solution. Place the beaker in an ultrasonic cleaner filled with water and clean it for 15 minutes. Dry it and place it in a clean sample bag for later use.

[0075] S2, using Ag-Cu-Sn-Ti alloy solder for brazing connection, wherein the pre-treatment of the Ag-Cu-Sn-Ti alloy solder and the Cu plate is the same as that in Example 1;

[0076] Brazing treatment: The vacuum degree of the vacuum brazing furnace is controlled at 2×10 -3 Pa, heat from room temperature to 300℃ and keep warm for 30min to make the glue fully volatilize, then heat to 670℃ and keep warm for 15min to make the mold and brazing material evenly heated, then heat to brazing temperature 750℃, then keep warm at brazing temperature for 10min to melt the brazing material and complete welding, then cool to 300℃ at a rate of 5℃ / min, finally cool to room temperature with the furnace and take out the sample to finally obtain the brazing joint.

[0077] The brazing joints obtained in Example 1 and Comparative Example 1 were tested as follows:

[0078] (1) The brazed joint obtained in this example was cut in the middle with a laser, and the surface of the brazed joint weld was polished in sequence with diamond grinding discs with a roughness of 600# to 2000#. Then, the joint was placed on a polishing machine and polished with a diamond suspension with a particle size of 1 μm until the brazing surface was free of marks. The polished sample was carefully placed in a beaker with acetone solution using tweezers, and the beaker was placed in a water ultrasonic cleaner for cleaning for 10-20 minutes. After drying, it was placed in a clean sample bag for later use.

[0079] Figure 4 This is a cross-sectional view of the brazed joint obtained in Example 1 cut by laser; Figure 5 Cross-sectional view of the brazed joint obtained in Comparative Example 1.

[0080] It can be seen that the brazing filler metal of the brazed joint obtained by the method of the embodiment of the present application does not adhere to the side surface of the diamond.

[0081] (2) Backscattered microstructure of the joint after brazing Figure 6 shown.

[0082] It can be seen that the weld interface is free of holes and cracks, and the microstructure is uniform. Combined with EDS characterization, it is determined that the joint is composed of Ag(s,s) and Cu(s,s) phases, with no other IMCs formed.

[0083] (3) The brazed joint formed in this embodiment is further enlarged by the EDS surface scan as shown below: Figure 7 shown.

[0084] It can be seen that the Ti layer and the Mo layer are intact and clearly separated, and the Ni layer reacts well with the Ag-Cu solder and has a uniform structure.

[0085] (4) The results of the comparison between Example 1 and Comparative Example 1 by Ansys finite element simulation are as follows Figure 8 shown.

[0086] Depend on Figure 8 It can be seen that the maximum equivalent stress on the diamond side of the brazed joint obtained in Example 1 is 346.72 MPa and the minimum is 196.68 MPa. The maximum equivalent stress on the diamond side of the brazed joint obtained in Comparative Example 1 is 1311.3 MPa and the minimum is 540.68 MPa.

[0087] This paper proposes a method for brazing surface-metallized diamond and copper using an Ag-Cu eutectic solder. The structure of the Ti / Mo / Ni coating was studied, clarifying the formation and evolution mechanism of the joint. As the temperature gradually increases, the Ag-Cu eutectic solder begins to melt and transform into a molten liquid at approximately 780°C. Simultaneously, the Ti layer reacts with the diamond surface to form a TiC transition layer. The Mo layer acts as a barrier, preventing direct reaction between the Ti and Ni, while the Ni layer enhances the solder's wettability, allowing the molten solder to diffuse evenly at the interface between the metallized diamond and the copper substrate.

[0088] When the brazing temperature is raised to 810°C and maintained, a TiC transition layer persists and stabilizes at the interface. Ag and Cu elements fully wet and fill the interface. The Mo layer effectively suppresses the formation of excessive intermetallic compounds, while the Ni layer promotes fusion between the brazing filler metal and the copper substrate. During cooling, the Ag-Cu alloy solidifies and forms a dense microstructure dominated by Ag(s,s) and Cu(s,s). No coarse IMCs form at the interface. Compared to traditional high-temperature active brazing processes, this significantly reduces the risk of diamond graphitization and mitigates thermal deformation of the copper substrate.

[0089] Based on the above analysis, the brazed joint obtained by the present invention can achieve highly dense contact between the metallized diamond and the copper substrate due to the good melt wettability of the Ag-Cu eutectic solder; the formation of the TiC transition layer significantly enhances the interfacial bonding strength between the diamond and the coating; the effective isolation of Ti and Ni by the Mo layer reduces the precipitation of brittle phases, ensuring a uniform and fine microstructure within the weld; the wetting-promoting effect of the Ni layer can reduce residual stress and improve the airtightness and mechanical strength of the joint. In addition, the Ag-Cu solder itself has excellent electrical and thermal conductivity, which can reduce the thermal resistance of the joint and maintain good antioxidant and corrosion resistance under high vacuum and high-power microwave irradiation conditions, thereby extending the service life of the diamond microwave window assembly. This research provides important theoretical and technological support for the reliable connection of diamond and copper in high vacuum, high-power nuclear fusion microwave windows.

[0090] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for brazing diamond and copper using Ag-Cu eutectic solder, characterized in that: The method comprises the following steps: S1, coating the diamond, and heating and activating the diamond to obtain a surface metallized diamond; S2, brazing the copper to be brazed and the surface metallized diamond using Ag-Cu eutectic brazing material; Among them, in S1, the diamond is coated by depositing a titanium layer, a molybdenum layer and a nickel layer on the surface of the diamond in sequence.

2. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 1, characterized in that: In S1, the thickness of the titanium layer is 100-300 nm, the thickness of the molybdenum layer is 300-500 nm, and the thickness of the nickel layer is 3-5 μm.

3. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 1 or 2, characterized in that: In S1, the titanium layer and the molybdenum layer are deposited by magnetron sputtering, and the nickel layer is deposited by electroplating.

4. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 1 or 2, characterized in that: In S1, the coated diamond is cleaned and placed in a vacuum brazing furnace for heating activation treatment, specifically including: first heating from room temperature to 690-710°C and keeping it at this temperature for 5-20 minutes; then heating to 750-800°C and keeping it at this temperature for 30-90 minutes; then cooling to 280-320°C, and finally cooling to room temperature.

5. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 4, characterized in that: In S1, the heating rate of each stage in the heating process is independently selected from 5-15°C / min, and the cooling rate in the cooling process is 4-5°C / min.

6. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 1 or 2, characterized in that: In S2, during brazing, Ag-Cu eutectic brazing filler metal is placed between copper and surface metallized diamond to obtain a sandwich structure of the welded parts.

7. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 1 or 2, characterized in that: In S2, the brazing temperature is 800°C-820°C, and the holding time after heating to the brazing temperature is 5-15 minutes.

8. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 1 or 2, characterized in that: In S2, the specific process of brazing connection is: heating from room temperature to 280-300℃ and keeping warm for 10-30 minutes, then heating to 730-780℃ and keeping warm for 10-30 minutes; continuing to heat to brazing temperature 800-820℃, then keeping warm at brazing temperature for 5-15 minutes; then cooling to 280-320℃ at a rate of 4-6℃ / min, and finally cooling to room temperature with the furnace.

9. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 8, characterized in that: During brazing connection, the heating rate during the heating process is 5-15°C / min.

10. The method for brazing diamond and copper using Ag-Cu eutectic solder according to claim 1 or 2, characterized in that: In S2, the mass ratio of Ag to Cu in the Ag-Cu eutectic solder is 72:28.

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