A method for preparing high-thermal-conductivity diamond / copper composite material based on improved salt bath plating technology

Abstract

This invention discloses a method for preparing high thermal conductivity diamond / copper composite materials based on an improved salt bath plating technique, belonging to the field of electronic packaging materials. Existing diamond surface metallization processes, such as magnetron sputtering and chemical vapor deposition, are costly and difficult to scale up; traditional salt bath plating processes easily cause thermal damage to diamond, resulting in poor coating thickness and composition uniformity, and post-processing easily introduces impurities. This invention innovatively uses elemental or multi-element pre-alloyed powders to form a unit or multi-element alloy carbide transition layer in situ on the diamond surface through an improved salt bath plating technique, effectively solving the above problems. After densification of the modified diamond and copper powder through a sintering process, the composite material exhibits strong interfacial bonding, low thermal resistance, a thermal conductivity reaching 1005 W / (m·K), and a coefficient of thermal expansion in the range of (4.5-8.5)×10⁻⁶. ‑6 K ‑1 Internally adjustable. This method features simple equipment, low cost, and easy scalability, providing a high thermal conductivity packaging material solution for heat dissipation of various high-power devices.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging materials technology, and specifically to a method for preparing high thermal conductivity diamond / copper composite materials based on salt bath plating technology. Background Technology

[0002] With the rapid development of technologies such as 5G mobile communication, artificial intelligence, and electric vehicles, the power density and integration of electronic devices are constantly increasing, making heat dissipation a core bottleneck restricting their performance and reliability. Diamond, due to its extremely high intrinsic thermal conductivity, is considered an ideal heat dissipation material. Theoretically, combining diamond with a highly thermally conductive copper matrix could yield an ideal substrate material that combines excellent thermal conductivity with an adjustable coefficient of thermal expansion. However, the intrinsic wettability between diamond and copper is extremely poor, resulting in a fragile interfacial bond and extremely high interfacial thermal resistance in the composite material, with the actual thermal conductivity far lower than the theoretical value. To improve the interface, the main technical approaches fall into two categories: 1. Matrix alloying: The process is simple, but the added active elements will seriously degrade the electrical and thermal conductivity of copper, and the interface reaction is difficult to control. 2. Diamond surface metallization: This is a more targeted approach and is currently the mainstream method. Its main methods include: (1) Magnetron sputtering and chemical vapor deposition: can obtain high-quality coatings, but the equipment is extremely expensive, the process is complex, it is difficult to process particles on a large scale, and the cost is high. (2) Powder embedding method: The process is relatively simple, but the reaction temperature is high and the time is long, which can easily lead to graphitization of the diamond surface and damage its intrinsic properties. (3) Chemical plating and electroplating: The coating and diamond are mostly physically bonded, with limited interfacial bonding strength and environmental issues. (4) Salt bath plating (molten salt method): The equipment and raw material costs are relatively low, and it is suitable for batch processing. It can form a metallurgically bonded interface layer. However, the traditional salt bath plating process is strictly controlled, which can easily cause thermal damage to diamond. It also has problems such as poor coating uniformity, complicated post-processing, and easy introduction of impurities.

[0003] In summary, existing technologies generally face the dilemma of not being able to simultaneously achieve "high performance, low cost, and scalability": either they have to bear the risk of diamond damage and high cost caused by high-temperature processes in order to obtain strong interface bonding, or they have to sacrifice interface quality and performance in pursuit of low cost.

[0004] Therefore, developing a diamond / copper composite material preparation technology that can form a strong interfacial bond under relatively mild conditions, effectively protect the properties of diamond, and is simple, low-cost, and suitable for large-scale production has important practical application value. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high thermal conductivity diamond / copper composite materials based on an improved salt bath plating technique. This improved technique directly deposits the desired elemental metal or alloy onto the surface of diamond particles, modifying the diamond surface and avoiding heat treatment, thus preventing graphitization of the diamond at its source. The diamond-copper composite material can then be prepared using one of the following methods: hot pressing sintering, spark plasma sintering, high-temperature high-pressure method, or gas pressure infiltration. The resulting diamond-copper composite material exhibits a thermal conductivity of up to 1005 W / (m·K), which not only improves the thermal conductivity of the diamond / copper composite material but also solves the problem of low-cost preparation of high thermal conductivity diamond / copper composite materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing high thermal conductivity diamond / copper composite materials based on an improved salt bath plating technique. The core of this method lies in forming a unitary or multi-element metal carbide transition layer in situ on the diamond surface using the improved salt bath plating technique, followed by composite densification through one of the above methods. The method includes at least the following steps: S1. Surface pretreatment of diamond particles; S2. Mix diamond particles, metal source powder and molten salt to obtain a mixture; S3. Under a protective atmosphere, the mixture is heated to form a carbide layer on the diamond surface; S4. Remove the basic salt of the product from S3 to obtain diamond particles with a surface coated with metal carbides. S5. Mix the diamond particles with metal carbide coating on the surface with copper powder and load them into a mold; S6. Densify the mixed powder in the mold to obtain a diamond / copper composite material; Preferably, in S1, the surface pretreatment includes sequential acid washing, alkali washing, and organic solvent cleaning; the diamond particles are single-crystal diamond or polycrystalline diamond micro powder, with a particle size range of 10μm~200μm.

[0007] Preferably, in S2, the molten salt is selected from one or more of chlorides, fluorides, carbonates, hydroxides, and oxides.

[0008] Preferably, in S2, the metal source powder is selected from one or more elemental metals or alloys of multiple elemental metals selected from molybdenum, titanium, chromium, tungsten, niobium, tantalum, zirconium, and vanadium.

[0009] Preferably, in S2, the particle size of the metal source powder is less than or equal to the particle size of the diamond particles, and its mass is smaller than that of the diamond.

[0010] Preferably, in S3, the temperature of the heat treatment is 500℃~1200℃, and the holding time is 10min~120min; Preferably, in step S3, the protective atmosphere is argon, helium, or nitrogen, and the vacuum level of the reaction environment is below 10. -3 Pa.

[0011] Preferably, in step S4, the base salt is removed by washing with water, centrifugation, and drying.

[0012] Preferably, in S5, the volume ratio of the diamond particles coated with metal carbide to the copper powder is (2~8):(8~2).

[0013] Preferably, in S6, the densification process is one of the following: hot pressing sintering, spark plasma sintering, high temperature and high pressure method, and gas pressure infiltration method; wherein: (1) Hot pressing sintering method: carried out under vacuum or protective atmosphere; sintering temperature is 500℃~1100℃, heating rate is 5℃ / min~100℃ / min, sintering pressure is 10MPa~100MPa, and holding time is 0.1h~6h. (2) Spark plasma sintering: carried out under vacuum; sintering temperature is 500℃~1100℃, heating rate is 50℃ / min~150℃ / min, sintering pressure is 10MPa~100MPa, and holding time is 5min~30min. (3) High temperature and high pressure method: carried out under inert gas protection; sintering temperature is 500℃~1100℃, sintering pressure is 200MPa~600MPa, and holding time is 0.1h~6h; (4) Gas pressure infiltration method: carried out under an inert protective atmosphere; sintering temperature is 1100℃~1300℃, pressure is 1MPa~10MPa, and holding time is 10min~60min.

[0014] Compared with the prior art, the beneficial effects of the present invention are: (1) Protecting the intrinsic thermal conductivity of diamond from the source: By optimizing the molten salt system and pretreatment process, the present invention effectively avoids the risk of graphitization of diamond surface caused by high temperature and long-term reaction in traditional process, thus preserving the ultra-high thermal conductivity potential of diamond in the initial stage of interface modification. (2) Achieving a high-quality, uniform interface layer: The improved salt bath plating process overcomes the problem that traditional methods struggle to obtain a coating with uniform thickness, composition, and morphology on the diamond surface. The in-situ generated metal carbide transition layer is firmly bonded to the diamond and can effectively wet the copper substrate, significantly enhancing the interfacial bonding force and laying a structural foundation for reducing interfacial thermal resistance. (3) Stable process, low cost and easy to scale up: The process route of this invention is simple and requires conventional equipment, avoiding the dependence on expensive vacuum equipment such as magnetron sputtering and chemical vapor deposition. At the same time, the process optimization simplifies the post-processing steps and eliminates the risk of impurity introduction, so that the technology has outstanding cost advantages and large-scale production potential while ensuring high performance. (4) Achieving high thermal conductivity and a precisely matched coefficient of thermal expansion: Thanks to the strong bonding interface and low interfacial thermal resistance, the thermal conductivity of the prepared composite material is significantly improved, reaching a maximum of 1005 W / (m·K). Furthermore, by adjusting the diamond volume fraction and the interfacial structure with copper, the coefficient of thermal expansion of the composite material can be adjusted over a wide range (4.5-8.5 × 10⁻⁶). -6 K -1 Effective regulation within the package allows for good thermal matching with various semiconductor chip materials, preventing packaging failure. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is an overall flow chart of the preparation process of the present invention; Figure 2 This is a high-resolution SEM image of the surface morphology of the composite material after Mo plating in Example 1. Figure 3 This is a low-resolution SEM image of the surface morphology of the composite material after Mo plating in Example 1. Figure 4 This is an elemental distribution analysis diagram at the interface of the composite material after Mo plating in Example 1; Figure 5 This is an elemental distribution analysis diagram at the interface of the composite material after Mo plating in Example 1; Figure 6 This is a high-resolution SEM image of the surface morphology of the composite material after Ti plating in Example 2. Figure 7 This is a low-resolution SEM image of the surface morphology of the composite material after Ti plating in Example 2. Figure 8 This is an elemental distribution analysis diagram at the interface of the composite material after Ti plating in Example 2; Figure 9 This is an elemental distribution analysis diagram at the interface of the composite material after Ti plating in Example 2; Figure 10This is a high-resolution SEM image of the surface morphology of the composite material after Cr plating in Example 3. Figure 11 This is a low-resolution SEM image of the surface morphology of the composite material after Cr plating in Example 3. Figure 12 This is an elemental distribution analysis diagram at the interface of the composite material after Cr plating in Example 3; Figure 13 This is an elemental distribution analysis diagram at the interface of the composite material after Cr plating in Example 3; Figure 14 This is a high-resolution SEM image of the surface morphology of the diamond-coated composite material in Comparative Example 1. Figure 15 The image shows a low-resolution SEM image of the surface morphology of the diamond-coated composite material in Comparative Example 1. Detailed Implementation

[0017] This invention provides a method for preparing diamond-copper composite materials, comprising the following steps: S1. Surface pretreatment of diamond particles; S2. Mix diamond particles, metal source powder and molten salt to obtain a mixture; S3. Under a protective atmosphere, the mixture is heated to form a carbide layer on the diamond surface; S4. Remove the basic salt of the product from S3 to obtain diamond particles with a surface coated with metal carbides. S5. Mix the diamond particles with metal carbide coating on the surface with copper powder and load them into a mold; S6. Densify the mixed powder in the mold to obtain a diamond / copper composite material; In S1 of this invention, the surface pretreatment preferably includes: ultrasonic cleaning for 15 minutes each with concentrated hydrochloric acid, a 10% sodium hydroxide solution, and anhydrous ethanol, followed by washing with deionized water until neutral, and finally drying under vacuum at 80°C for 12 hours. The diamond particles preferably include single-crystal diamond and / or polycrystalline diamond, and the particle size of the diamond particles is preferably 20~120µm.

[0018] In S2 of this invention, the metal or its alloy is preferably selected from one or more elements or alloys of molybdenum (Mo), titanium (Ti), chromium (Cr), tungsten (W), niobium (Nb), tantalum (Ta), zirconium (Zr), and vanadium (V). The molten salt is preferably selected from one or more mixtures of chlorides, fluorides, carbonates, hydroxides, and oxides; wherein the chloride preferably includes sodium chloride and / or potassium chloride, the fluoride preferably includes sodium fluoride, and the carbonate preferably includes sodium carbonate. When the molten salt is a mixture of two salts, the molar ratio is preferably (0~1):1. The mass ratio of the diamond particles, metal or its alloy powder to the molten salt is preferably (5~12):(0.8~1.2):(8~25), wherein the mass of the metal or its alloy powder is less than the mass of the diamond particles. The reaction vessel is preferably designed with a multi-layer crucible.

[0019] In S3 of the present invention, the heat treatment conditions preferably include: heating to 500~1200°C at a rate of 5°C / min under a protective atmosphere (such as argon, helium or nitrogen), holding at that temperature for 10~120min, and preferably having a vacuum degree of less than 10 kJ / min in the reaction environment. - 3 Pa.

[0020] In S4 of the present invention, the preferred method for removing the molten salt is water washing, centrifugal separation, followed by drying.

[0021] In S5 of the present invention, the volume ratio of the diamond particles coated with metal carbides to the copper powder is preferably (2~8):(8~2), and the sum of the volume percentages of the two is 100%.

[0022] In S6 of this invention, the densification process is one of the following: hot pressing sintering, spark plasma sintering, high temperature and high pressure method, and gas pressure infiltration method; wherein: (1) Hot pressing sintering method: carried out under vacuum or protective atmosphere; sintering temperature is 500℃~1100℃, heating rate is 5℃ / min~100℃ / min, sintering pressure is 10MPa~100MPa, and holding time is 0.1h~6h. (2) Spark plasma sintering: carried out under vacuum; sintering temperature is 500℃~1100℃, heating rate is 50℃ / min~150℃ / min, sintering pressure is 10MPa~100MPa, and holding time is 5min~30min. (3) High temperature and high pressure method: carried out under inert gas protection; sintering temperature is 500℃~1100℃, sintering pressure is 200MPa~600MPa, and holding time is 0.1h~6h; (4) Gas pressure infiltration method: carried out under an inert protective atmosphere; sintering temperature is 1100℃~1300℃, pressure is 1MPa~10MPa, and holding time is 10min~60min.

[0023] The present invention also provides a diamond-copper composite material prepared by the preparation method described above, wherein the composite material is preferably in the form of a disc, for example, with a diameter of 20 mm and a thickness of 5 mm.

[0024] The present invention also provides the application of the diamond-copper composite material described above in the preparation of high thermal conductivity devices, particularly for improving the thermal conductivity of the composite material.

[0025] To further illustrate the present invention, the present invention will be described in detail below with reference to embodiments, but these embodiments should not be construed as limiting the scope of protection of the present invention.

[0026] Example 1: Diamond / copper composite materials with molybdenum (Mo) coated on the diamond surface were prepared by hot pressing sintering using a chloride-based mixed salt system. S1: Select 100g of single-crystal diamond particles with a particle size of 50μm. Clean them sequentially with concentrated hydrochloric acid (acid washing), 10% sodium hydroxide solution (alkali washing), and anhydrous ethanol (organic solvent cleaning) for 15 minutes each. After each cleaning, wash thoroughly with deionized water until neutral. Finally, dry in a vacuum oven at 80℃ for 12 hours.

[0027] S2: Grind the NaCl and KCl mixed salts in a molar ratio of 1:1 until homogeneous. Take 10g of pretreated diamond particles and mix them with 1g of molybdenum (Mo) powder with a particle size ≤45μm (mass ratio 10:1), then grind them together with 15g of mixed salt for 10 minutes to ensure thorough mixing.

[0028] S3: Place the mixture into a cleaned crucible and then into a quartz tube. Connect the quartz tube to a vacuum system and slowly evacuate until the pressure is below 10. -3 After Pa, high-purity argon gas is introduced to atmospheric pressure, and this operation is repeated 3 times to fully replace the air. Finally, the quartz tube is sealed with an oxyhydrogen flame under an argon atmosphere. The sealed tube is placed in a tube furnace and heated to 1100°C at a rate of 5°C / min, held at that temperature for 120 minutes, and then cooled with the furnace.

[0029] S4: After cooling, the product is removed and placed in deionized water and boiled to dissolve the salt. After multiple centrifugations, washing, and drying at 80°C, the product is passed through a 200-mesh sieve to obtain diamond particles coated with molybdenum carbide (Mo2C).

[0030] S5: Mix the diamond to be plated with copper powder in a volume ratio of 4:6 and grind it in a quartz bowl for 20 minutes to ensure thorough mixing. Then, put the ground powder into a cylindrical graphite mold lined with graphite paper (to prevent the powder from sticking to the mold during sintering) and seal the holes with graphite paper.

[0031] S6: Place the mold into a vacuum hot pressing sintering furnace. Evacuate to 5×10⁻⁶. -3 After reaching 950℃ and 60MPa, the temperature was increased at a rate of 50℃ / min. The temperature was then held for 3 hours at 950℃ and 60MPa. Afterward, the furnace was cooled to room temperature, yielding a composite material disc with a diameter of 20mm and a thickness of approximately 5mm.

[0032] Results Explanation: like Figure 2 and Figure 3 As shown, the transition layer is dense (relative density can reach over 99%) and well bonded to both sides, with obvious element diffusion; Figure 4 and Figure 5 The existence of the Mo element is confirmed.

[0033] Using a mixed salt of sodium chloride (NaCl) and potassium chloride (KCl) (molar ratio 1:1) as the molten salt medium, a highly fluid melt can be formed at 1100℃. This chloride molten salt system is a mature and inexpensive process, which is beneficial for the transport of molybdenum (Mo) ions and their reaction with carbon atoms on the diamond surface. Therefore, a uniform, continuous, and firmly bonded molybdenum carbide (Mo2C) transition layer can be formed on the diamond surface. After subsequent mixing with copper powder and hot-pressing and sintering at 950℃ / 60MPa for 3 hours, the resulting composite material achieves good densification and interfacial bonding.

[0034] Due to the formation of an effective Mo2C interface layer, the composite material achieves a high level of thermal conductivity in the vertical direction (e.g., comparable to the results of Example 1, with the potential to reach even higher levels). The coefficient of thermal expansion can be controlled within the target range (e.g., (4.5-8.5) × 10⁻⁶). -6 K -1 ).

[0035] Example 2: Diamond / copper composite materials with titanium (Ti) coating on diamond surfaces were prepared by spark plasma sintering using a fluoride-based mixed salt system. S1: Select 100g of single-crystal diamond particles with a particle size of 50μm. Clean them sequentially with concentrated hydrochloric acid (acid washing), 10% sodium hydroxide solution (alkali washing), and anhydrous ethanol (organic solvent cleaning) for 15 minutes each. After each cleaning, wash thoroughly with deionized water until neutral. Finally, dry in a vacuum oven at 80℃ for 12 hours.

[0036] S2: Grind a mixture of lithium fluoride (LiF) and potassium fluoride (KF) salts in a molar ratio of 1:1 until homogeneous. Take 10g of pretreated diamond particles and mix them with 1g of titanium (Ti) powder with a particle size ≤45μm (mass ratio 10:1), then grind them together with 15g of the mixed salt for 10 minutes to ensure thorough mixing.

[0037] S3: Place the mixture into a cleaned crucible and then into a quartz tube. Connect the quartz tube to a vacuum system and slowly evacuate until the pressure is below 10. -3 After Pa, high-purity argon gas is introduced to atmospheric pressure, and this operation is repeated 3 times to fully replace the air. Finally, the quartz tube is sealed with an oxyhydrogen flame under an argon atmosphere. The sealed tube is placed in a tube furnace and heated to 1150°C at a rate of 5°C / min, held at that temperature for 180 minutes, and then cooled with the furnace.

[0038] S4: After cooling, the product is removed and placed in deionized water and boiled to dissolve the salt. After multiple centrifugations, washing, and drying at 80°C, the product is passed through a 200-mesh sieve to obtain diamond particles coated with titanium carbide (TiC).

[0039] S5: Mix the diamond to be plated with copper powder at a volume ratio of 4:6, and grind in a mortar for twenty minutes to ensure thorough mixing. Then, load the ground mixture into a cylindrical graphite mold whose inner wall is coated with a boron nitride release agent.

[0040] S6: Place the mold into the vacuum chamber of the spark plasma sintering furnace. Evacuate to 5×10⁻⁶. -3 After Pa, axial pressure is applied and the temperature is increased by electricity. The sintering process is as follows: the temperature is increased to 1000℃ at a rate of 150℃ / min, while an axial pressure of 30MPa is applied. After reaching the temperature, it is held for 5 minutes. After the process is completed, it is cooled in the furnace to obtain a dense composite material disc.

[0041] Results Explanation: 1. A well-flowing melt was formed at 1150 °C using a mixed salt of lithium fluoride (LiF) and potassium fluoride (KF) (molar ratio 1:1) as the molten salt medium. This fluoride system has a low melting point and high ionic conductivity, which effectively promotes the transport of titanium (Ti) ions and their reaction with carbon atoms on the diamond surface, thereby generating a uniform, continuous, and firmly bonded titanium carbide (TiC) transition layer in situ on the diamond surface.

[0042] 2. After mixing with S5, densification was carried out using spark plasma sintering. The synergistic effect of pulsed current and pressure enabled rapid sintering and diffusion bonding between particles, resulting in a high-density (>99%) composite material.

[0043] 3. For example Figure 6 and Figure 7As shown, the prepared composite material exhibits good interfacial bonding and significant element diffusion. Figure 8 and Figure 9 The presence of Ti at the interface was confirmed. The formation of a strongly bonded titanium carbide interface layer effectively reduced the interfacial thermal resistance, resulting in a maximum thermal conductivity of 613.5 W / (m·K) in the vertical direction for the composite material. Furthermore, its coefficient of thermal expansion can be adjusted by changing the diamond volume fraction, within the range of (4.5-8.5)×10⁻⁶. -6 K -1 The control is adjusted within the target range to meet the matching requirements of different semiconductor materials.

[0044] Example 3: Diamond / copper composite materials with chromium (Cr) plating on the diamond surface were prepared by high temperature and high pressure method using a carbonate system mixed salt. S1: Select 100g of single-crystal diamond particles with a particle size of 50μm. Clean them sequentially with concentrated hydrochloric acid (acid washing), 10% sodium hydroxide solution (alkali washing), and anhydrous ethanol (organic solvent cleaning) for 15 minutes each. After each cleaning, wash thoroughly with deionized water until neutral. Finally, dry in a vacuum oven at 80℃ for 12 hours.

[0045] S2: Grind a mixture of potassium carbonate (K2CO3) and sodium carbonate (Na2CO3) in a molar ratio of 1:1 until homogeneous. Take 10g of pretreated diamond particles and mix them with 1g of chromium (Cr) powder with a particle size ≤45μm (mass ratio 10:1), then grind them together with 15g of the mixed salt for 10 minutes to ensure thorough mixing.

[0046] S3: Place the mixture into a cleaned crucible and then into a quartz tube. Connect the quartz tube to a vacuum system and slowly evacuate until the pressure is below 10. -3 After Pa, high-purity argon gas is introduced to atmospheric pressure, and this operation is repeated 3 times to fully replace the air. Finally, the quartz tube is sealed with an oxyhydrogen flame under an argon atmosphere. The sealed tube is placed in a tube furnace and heated to 700°C at a rate of 5°C / min, held at that temperature for 240 minutes, and then cooled with the furnace.

[0047] S4: After cooling, the product is removed and placed in deionized water and boiled to dissolve the salt. After multiple centrifugations, washing, and drying at 80°C, the product is passed through a 200-mesh sieve to obtain diamond particles coated with carbon chromium (Cr3C2).

[0048] S5: Mix the diamond to be coated with copper powder at a volume ratio of 4:6, and grind it in a mortar for 20 minutes to ensure thorough mixing. Place the mixed powder into a cylindrical sample chamber inside a dedicated high-pressure chamber (such as a pyrophyllite sealing block).

[0049] S6: Place the assembled high-pressure chamber into the six-sided top press. Start the equipment and simultaneously apply pressure and heat. The sintering process is as follows: heat to 1100℃ while applying a pressure of 1GPa, and hold at that temperature for 6 minutes after reaching the set value. After completion, depressurize and cool, remove the sample, and obtain a dense composite material block.

[0050] Results Explanation: 1. Feasibility Verification of the Carbonate Molten Salt System: Using a mixed salt of potassium carbonate (K₂CO₃) and sodium carbonate (Na₂CO₃) (molar ratio 1:1) as the molten salt medium, the feasibility of using the carbonate system for salt bath plating was verified. Under strict argon gas sealing protection at 700℃, this system can provide the necessary liquid phase environment for the carbon reaction between chromium (Cr) powder and the diamond surface, successfully suppressing the potential oxidizing effect of carbonates, thereby generating a chromium carbide transition layer in situ.

[0051] 2. Rapid Densification Achieved by High Temperature and High Pressure: As described in S6, densification is achieved using a high temperature and high pressure method. Simultaneous pressurization and heating are performed in a six-sided press with the following process parameters: temperature rises to 1100℃, pressure is applied simultaneously at 200MPa, and the temperature is held for 6 minutes. The high-pressure environment promotes particle rearrangement and plastic flow, achieving rapid and ultra-high densification of the composite material (relative density >99%).

[0052] 3. Achieve a good interface and performance: such as Figure 10 and Figure 11 As shown, the prepared composite material exhibits dense interfacial bonding and significant element diffusion. Figure 12 and Figure 13 The enrichment of Cr at the interface was confirmed. Thanks to the strongly bonded chromium carbide interfacial layer, the composite material exhibits low interfacial thermal resistance. Due to the differences in the physicochemical properties (such as viscosity and ion mobility) between carbonate molten salts and chloride or fluoride systems, the precise control of the microstructure of the interfacial transition layer is somewhat unique, yet the composite material still achieves high thermal conductivity. Furthermore, its coefficient of thermal expansion can be controlled within a wide range through design.

[0053] Example 4: Preparation of diamond / copper composite materials with tungsten (W) coated on diamond surfaces by pressure infiltration method using a hydroxide-oxide molten salt system. S1: Select 100g of single-crystal diamond particles with a particle size of 50μm. Clean them sequentially with concentrated hydrochloric acid (acid washing), 10% sodium hydroxide solution (alkali washing), and anhydrous ethanol (organic solvent cleaning) for 15 minutes each. After each cleaning, wash thoroughly with deionized water until neutral. Finally, dry in a vacuum oven at 80℃ for 12 hours.

[0054] S2: Mix sodium hydroxide (NaOH), potassium hydroxide (KOH), and boron oxide (B2O3) in a molar ratio of 2:2:1 and grind them evenly. Take 10g of pretreated diamond particles and mix them with 1g of tungsten (W) powder with a particle size ≤45μm (mass ratio 10:1), and then grind them together with 15g of the above molten salt medium for 10 minutes to ensure that the three are fully mixed.

[0055] S3: Place the mixture into a cleaned crucible and then into a quartz tube. Connect the quartz tube to a vacuum system and slowly evacuate until the pressure is below 10. -3 After Pa, high-purity argon gas is introduced to atmospheric pressure, and this operation is repeated 3 times to fully replace the air. Finally, the quartz tube is sealed with an oxyhydrogen flame under an argon atmosphere. The sealed tube is placed in a tube furnace and heated to 550°C at a rate of 5°C / min, held at that temperature for 180 minutes, and then cooled with the furnace.

[0056] S4: After cooling, the product is removed and placed in deionized water and boiled to dissolve the salt. After multiple centrifugations, washing, and drying at 80°C, the product is passed through a 200-mesh sieve to obtain diamond particles coated with tungsten carbide (WC / W2C).

[0057] S5: The diamond particles to be plated are loaded into a graphite mold and vibrated to compact them, forming a porous diamond preform. The preform and a measured amount of copper block are placed together in the crucible of a pneumatic impregnation furnace, with the copper block positioned above the preform.

[0058] S6: Evacuate the system to 5×10⁻⁶ -3 After Pa, an inert protective gas (such as argon) is introduced. The crucible is heated to 1150°C (above the melting point of copper) to completely melt the copper block. Then, a high-pressure inert gas (5 MPa) is introduced into the system and held at that pressure for 30 minutes, forcing the molten copper to penetrate into the pores of the diamond preform under pressure. After cooling, a near-net-shape, dense composite material is obtained.

[0059] Results Explanation: 1. The feasibility of the hydroxide-oxide molten salt system was verified: a NaOH-KOH-B₂O₃ mixture was used as the molten salt medium. NaOH and KOH form a eutectic mixture, significantly lowering the system's melting point and providing an effective liquid-phase reaction environment at a relatively low temperature of 550℃, which helps reduce energy consumption and thermal damage to diamond. B₂O₃, as the oxide component, can adjust the molten salt viscosity and enhance the wettability to the diamond surface in the molten state, and may participate in interfacial reactions. Under sealed argon protection, the reaction between tungsten powder and carbon atoms on the diamond surface was successfully induced, resulting in the in-situ formation of a tungsten carbide (WC / W₂C) transition layer.

[0060] 2. An effective combination of gas pressure infiltration and salt bath plating modification was achieved: As described in S5-S6, the diamond particles coated on the surface were made into a preform and densified using gas pressure infiltration. Copper was melted at 1150℃, and a gas pressure of 5MPa was applied to drive the molten copper to fully penetrate the pores of the preform. This process achieved perfect filling of the complex porous structure by the melt, resulting in a high-density, near-net-shape composite material, and avoiding thermomechanical damage to the coating or diamond that may be caused during sintering.

[0061] 3. Obtaining materials with excellent interface and comprehensive properties: The synergistic effect of the lower salt bath plating temperature and the unique molten salt composition results in an interfacial transition layer that may differ in morphology and fine structure from the high-temperature system. Combined with the subsequent gas pressure infiltration process, the prepared composite material exhibits good interfacial bonding and is complete and dense. Due to the formation of an effective WC / W2C interfacial layer, the composite material possesses low interfacial thermal resistance and good thermal conductivity, and its coefficient of thermal expansion can also be controlled through design, verifying the feasibility of the combined process route of "low-temperature salt bath plating + gas pressure infiltration".

[0062] Example 5: (Mo 0.9 Ti 0.1 Diamond / copper composite material prepared by hot pressing sintering of alloy powder (using a chloride system mixed salt) to produce diamond. S1: Select 50g of single-crystal diamond particles with a particle size of 100μm. Clean them sequentially with concentrated hydrochloric acid (acid washing), 10% sodium hydroxide solution (alkali washing), and anhydrous ethanol (organic solvent cleaning) for 15 minutes each. After each cleaning, wash thoroughly with deionized water until neutral. Finally, dry in a vacuum oven at 80℃ for 12 hours.

[0063] S2: Grind a 1:1 mixture of sodium chloride (NaCl) and potassium chloride (KCl) until homogeneous. Take 5g of pretreated diamond particles and 0.5g of molybdenum-titanium alloy powder (Mo). 0.9 Ti 0.1 Mix (Mo mass fraction 90%, Ti mass fraction 10%, particle size ≤45μm) and then grind together with 7.5g of the above mixed salt for 10 minutes to ensure thorough mixing of the three.

[0064] S3: Place the mixture into a cleaned crucible and then into a quartz tube. Connect the quartz tube to a vacuum system and slowly evacuate until the pressure is below 10. -3 After Pa, high-purity argon gas is introduced to atmospheric pressure, and this operation is repeated 3 times to fully replace the air. Finally, the quartz tube is sealed with an oxyhydrogen flame under an argon atmosphere. The sealed tube is placed in a tube furnace and heated to 950°C at a rate of 5°C / min, held at that temperature for 90 minutes, and then cooled with the furnace.

[0065] S4: After cooling, the product is removed and placed in deionized water and boiled to dissolve the salt. After multiple centrifugations, washing, and drying at 80°C, diamond particles coated with a molybdenum-titanium composite carbide layer are obtained by passing them through a 200-mesh sieve.

[0066] S5: Mix the diamond to be plated with copper powder in a volume ratio of 4:6 and grind it in a quartz bowl for 20 minutes to ensure thorough mixing. Then, put the ground powder into a cylindrical graphite mold lined with graphite paper (to prevent the powder from sticking to the mold during sintering) and seal the holes with graphite paper.

[0067] S6: Place the mold into a vacuum hot pressing sintering furnace. Evacuate to 5×10⁻⁶. -2 After reaching 900℃ and 60MPa, the temperature was increased at a rate of 30℃ / min. Holding was then initiated at 900℃ and 60MPa for 2 hours. Afterward, the furnace was cooled to room temperature, yielding a composite material disc with a diameter of 25mm and a thickness of approximately 15mm.

[0068] Results Explanation: Successfully formed transition layer: Molybdenum-titanium alloy powder Mo 0.9 Ti 0.1 Using alloy powder as a metal source, under the salt bath plating process conditions described in this invention, molybdenum (Mo) and titanium (Ti) atoms in the alloy react simultaneously with carbon atoms on the diamond surface in the molten salt medium. Scanning electron microscopy (SEM) and corresponding elemental mapping analysis show that a uniform and continuous composite carbide (Ti,Mo)C transition layer is formed in situ on the diamond surface.

[0069] Excellent interfacial bonding and performance: The composite carbide layer of this composition achieves strong covalent bonding between TiC and diamond, and maintains good physical compatibility with the copper matrix through Mo2C, realizing a progressive matching of the interfacial phonon spectrum and thermal expansion coefficient. After the hot-pressing sintering process, the composite material has high density (>99%) and strong interfacial bonding.

[0070] Superior thermophysical properties: Due to the significantly optimized phonon transport path and reduced interfacial thermal resistance achieved by the transition layer, the prepared composite material exhibits comprehensive performance surpassing that of a single metal coating system. Tests show a significant improvement in its vertical thermal conductivity, reaching 1005 W / (m·K). Simultaneously, the composite material's coefficient of thermal expansion is 5.8 × 10⁻⁶. -6 K -1 It achieves excellent compatibility with the vast majority of semiconductor chip materials.

[0071] Comparative Example 1 Preparation of uncoated diamond / copper composite materials Specifically, the steps for preparing the diamond / copper composite material in this comparative example are as follows: S1: Select 100g of single-crystal diamond particles with a particle size of 50μm. Clean them sequentially with concentrated hydrochloric acid (acid washing), 10% sodium hydroxide solution (alkali washing), and anhydrous ethanol (organic solvent cleaning) for 15 minutes each. After each cleaning, wash thoroughly with deionized water until neutral. Finally, dry in a vacuum oven at 80℃ for 12 hours.

[0072] S2: First, soak the crucible in aqua regia for cleaning. Then, place the crucible in a clean beaker and add alcohol to the beaker until the alcohol completely covers the crucible. Place the beaker in an ultrasonic cleaner and ultrasonically clean for five minutes. Pour out the alcohol and wipe the crucible with a test tube brush and rinse it with alcohol. Repeat this process three times to obtain a clean crucible.

[0073] S3: Mix the uncoated diamond and copper powder in a volume ratio of 4:6 in a quartz bowl and grind for 20 minutes to ensure thorough mixing. Then, put the ground powder into a cylindrical graphite mold lined with graphite paper (to prevent the powder from sticking to the mold during sintering) and seal the holes with graphite paper.

[0074] S4: Place the mold into a vacuum hot pressing sintering furnace. Evacuate to 5×10⁻⁶. -3 After reaching 950℃ and 60MPa, the temperature was increased at a rate of 50℃ / min. Holding was then initiated at 950℃ and 60MPa for 3 hours. Afterward, the furnace was cooled to room temperature, yielding a composite material disc with a diameter of 20mm and a thickness of approximately 5mm.

[0075] This comparative example prepared diamond / copper composite material according to the method in Example 1, the only difference from Example 1 being that steps S3 to S5 of Example 1 were not performed. The rest of the process was the same as in Example 1.

[0076] The results indicate that due to the extremely poor wettability and lack of chemical bonding between diamond and copper, the resulting composite material exhibits weak interfacial bonding and numerous pores. Its thermal conductivity and mechanical properties (such as flexural strength) are significantly lower than those of all previous embodiments, with poor bonding on both sides of the interface and minimal element diffusion.

[0077] Comparative Example 2 Preparation of diamond / copper composite material coated with (using non-preferred metals) This comparative example prepared a diamond / copper composite material according to the method in Example 1, the only difference being that in S3, the metal powder was replaced with nickel (Ni) powder. All other processes were the same as in Example 1.

[0078] The results show that although Ni can react with carbon, the resulting nickel carbide (such as Ni3C) has a much lower thermodynamic stability than molybdenum carbide and titanium carbide. Furthermore, it decomposes at the subsequent copper sintering temperature or forms a low-melting-point eutectic with copper. The transition layer is discontinuous, unstable, or poorly bonded to the matrix, resulting in high interfacial thermal resistance of the composite material, limited performance improvement, and low thermal conductivity.

[0079] Comparative Example 3 Preparation of diamond / copper coated composite materials (outside the preferred process range) This comparative example prepared diamond / copper composite materials according to the method in Example 1, with the only difference from Example 1 being a significant change in two key parameters: 1. In Example 1, the reaction temperature in S4 (salt bath plating) is increased to 1300°C (exceeding the preferred range of 500-1200°C).

[0080] 2. In Example 1, the sintering pressure in S7 (hot pressing sintering) is increased to 120 MPa (exceeding the preferred range of 10-100 MPa).

[0081] The remaining processes are the same as in Example 1.

[0082] The results show that excessively high salt bath temperatures lead to severe graphitization of the diamond surface, compromising its intrinsic thermal conductivity. Excessive sintering pressure causes the diamond particles to be crushed, introducing numerous microcracks. Both of these factors severely degrade the final properties of the composite material.

[0083] Comparative Example 4 Preparation of diamond / copper composite material coated with metal source powder (using non-preferred molar ratios) This comparative example prepared diamond / copper composite material according to the method in Example 1, the only difference being that the mixed salt was replaced with NaCl and KCl in a molar ratio of 10:1 (i.e., NaCl was much more abundant than KCl). The rest of the process was the same as in Example 1.

[0084] The results show that changing the molar ratio of the mixed salt from the optimized (1-9):1 to 10:1 significantly alters the eutectic point, viscosity, ionic activity, and solubility and mass transfer capacity of the molten salt system. The decreased uniformity and stability of the salt bath leads to uneven transport of metal atoms (Mo) to the diamond surface. The altered reaction kinetics result in a less dense, less uniform, or partially uncovered molybdenum carbide (Mo2C) coating. The interfacial bonding quality between the diamond and copper matrix in the composite material is lower than in Example 1, leading to increased interfacial thermal resistance and a noticeable decrease in overall thermal conductivity and mechanical properties.

[0085] Comparative Example 5 Preparation of diamond / copper composite material coated (without protective atmosphere) This comparative example prepared diamond / copper composite material according to the method in Example 1. The only difference from Example 1 is that in S3, after the quartz tube was evacuated, it was not filled with argon gas or sealed. Instead, it was kept at 900°C in a flowing air atmosphere. All other processes were the same as in Example 1.

[0086] The results show that the metal powder (Mo powder) and the diamond surface at high temperatures will be severely oxidized. The metal oxide cannot form an effective carbide transition layer with carbon, and may even introduce impurity phases. Ultimately, the composite material exhibits poor interfacial bonding and low performance.

[0087] Comparative Example 6 Preparation of diamond / copper coated composite material (due to improper ratio of diamond to metal powder particle size) It is basically the same as Example 1, but in S3, fine molybdenum powder with a particle size of 5 μm (much smaller than diamond with a particle size of 50 μm) is used.

[0088] The results show that excessively fine metal powders agglomerate severely during mixing and reaction, failing to uniformly coat the diamond surface. This results in an uneven and discontinuous carbide layer, significantly reducing the interface improvement effect.

[0089] Table 1. Effects of different salt bath plating systems and process parameters on the properties of diamond / copper composite materials.

[0090] The above examples demonstrate that the method provided by the present invention, which combines salt bath plating with hot pressing sintering, spark plasma sintering, high temperature and high pressure, and gas pressure infiltration, can effectively prepare diamond / copper composite materials with good interfacial bonding and high thermal conductivity, and the process has cost advantages.

[0091] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing high thermal conductivity diamond / copper composite materials based on an improved salt bath plating technique, characterized in that, Includes the following steps: S1. Surface pretreatment of diamond particles; S2. Mix diamond particles, metal source powder and molten salt to obtain a mixture; S3. Under a protective atmosphere, the mixture is heated to form a carbide layer on the diamond surface; S4. Remove the basic salt of the product from S3 to obtain diamond particles with a surface coated with metal carbides. S5. Mix the diamond particles with metal carbide coating on the surface with copper powder and load them into a mold; S6. Densify the mixed powder in the mold to obtain a diamond / copper composite material.

2. The preparation method according to claim 1, characterized in that, In S1, the surface pretreatment includes sequential acid washing, alkali washing, and organic solvent cleaning; the diamond particles are single-crystal diamond or polycrystalline diamond micro powder, with a particle size range of 10μm~200μm.

3. The preparation method according to claim 1, characterized in that, In S2, the molten salt is selected from one or more of chlorides, fluorides, carbonates, hydroxides, and oxides.

4. The method as described in claim 1, characterized in that, In S2, the metal source powder is selected from one or more elemental metals or alloys of multiple elemental metals selected from molybdenum, titanium, chromium, tungsten, niobium, tantalum, zirconium, and vanadium.

5. The preparation method according to claim 1, characterized in that, In S2, the particle size of the metal source powder is less than or equal to the particle size of the diamond particles, and its mass is smaller than that of the diamond.

6. The preparation method according to claim 1, characterized in that, In S3, the temperature of the heat treatment is 500℃~1200℃, and the holding time is 10min~120min.

7. The preparation method according to claim 1, characterized in that, In S3, the protective atmosphere is argon, helium, or nitrogen, and the vacuum level of the reaction environment is below 10. -3 Pa.

8. The preparation method according to claim 1, characterized in that, In step S4, the base salt is removed by washing with water, centrifugation, and drying.

9. The preparation method according to claim 1, characterized in that, In S5, the volume ratio of diamond particles coated with metal carbides to copper powder is (2~8):(8~2).

10. The preparation method according to claim 1, characterized in that, In S6, the densification process is one of the following: hot pressing sintering, spark plasma sintering, high temperature and high pressure method, and gas pressure infiltration method; wherein: (1) Hot pressing sintering method: carried out under vacuum or protective atmosphere; sintering temperature is 500℃~1100℃, heating rate is 5℃ / min~100℃ / min, sintering pressure is 10MPa~100MPa, and holding time is 0.1h~6h. (2) Spark plasma sintering: carried out under vacuum; sintering temperature is 500℃~1100℃, heating rate is 50℃ / min~150℃ / min, sintering pressure is 10MPa~100MPa, and holding time is 5min~30min. (3) High temperature and high pressure method: carried out under inert gas protection; sintering temperature is 500℃~1100℃, sintering pressure is 200MPa~5GPa, and holding time is 0.1h~6h; (4) Gas pressure infiltration method: carried out under an inert protective atmosphere; sintering temperature is 1100℃~1300℃, pressure is 1MPa~10MPa, and holding time is 10min~60min.

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