An ultra-small size copper nanopowder and a green and controllable synthesis method

Abstract

This invention discloses an ultra-small size copper nanoparticle powder and a green and controllable synthesis method. This invention pioneers a novel reaction pathway combining "one-step direct reduction with alkaline ascorbic acid" with three-stage programmed temperature control. By precisely controlling the reaction temperature and rate from monomer formation to nucleation and final growth stages, it achieves the green and controllable synthesis of ultra-small size copper nanoparticle powder with an average particle size of less than 80 nanometers. This invention eliminates the need for a secondary reducing agent such as ferrous sulfate, resulting in a simpler process that meets green production requirements, reduces environmental treatment costs, and offers strong controllability, making it suitable for large-scale industrial production. The prepared copper powder has a metal-based purity of ≥99.9%, high sintering activity, and a sintering temperature 30-80℃ lower than conventional copper powder. It has significant application value in high-density PCB interconnects, third-generation semiconductor packaging, high-precision 3D printing, photovoltaic pastes, flexible displays, and wearable devices.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation technology, and in particular to an ultra-small size nano-copper powder and a green and controllable synthesis method, which is especially suitable for the preparation of copper powder required in fields such as high-density PCB interconnect, third-generation semiconductor packaging, high-precision 3D printing and photovoltaic paste. Background Technology

[0002] Nano-copper powder possesses excellent electrical and thermal conductivity and sintering activity, making it valuable for applications in electronics, aerospace, and other fields. Ultra-small nano-copper powder, especially those below 80nm, is in high demand in advanced fields such as high-density PCB interconnects and microelectronic component manufacturing. Current technologies for preparing nano-copper powder mainly include mechanical ball milling, chemical vapor deposition, and chemical reduction. Mechanical ball milling is difficult to obtain nano-copper powder below 80nm and easily introduces impurities; chemical vapor deposition has high equipment costs and low yields, making industrial production difficult; while chemical reduction is lower in cost, it has the following drawbacks:

[0003] (1) The particle size is difficult to control precisely below 80nm, and the particle size distribution is wide (the coefficient of variation is usually >15%).

[0004] (2) Nano copper powder has high surface energy and is prone to agglomeration;

[0005] (3) Copper powder is easily oxidized, which affects the strength, conductivity and stability of sintered products;

[0006] (4) The reducing agents in the existing process are mostly toxic substances, which are not environmentally friendly and have high wastewater treatment costs.

[0007] To improve the aforementioned technical deficiencies, researchers mainly employ methods such as controlling the reduction process and adding surface protectants, dispersants, drag-reducing agents, or inhibitors. For example, Chinese patent CN101077529A discloses a method for preparing nano-copper powder and copper paste, including solvent replacement, primary reduction, secondary reduction, separation, and drying steps. The resulting nano-copper powder has a particle size of less than 20 nm. This method controls the reduction reaction at the water / organic interface and requires precise control of the reaction conditions of the primary and secondary reductions to inhibit the growth of the copper powder obtained from the reaction. This results in strict process control, high parameter sensitivity, and the need for multiple reaction steps, increasing the complexity of the process. CN102601381A discloses a chemical reduction method for preparing nano-copper powder. By adding drag-reducing agents and inhibitors to the copper salt solution and combining it with an aging process, the dispersibility is improved. The process is simple, but the resulting nano-copper powder particles are around 100 nm in size, with particles smaller than 80 nm accounting for less than 70%. Furthermore, the drag-reducing agents used are all toxic and environmentally unfriendly.

[0008] In summary, developing a chemical reduction method that can stably prepare copper powder below 80 nm, resulting in copper powder with good dispersibility, uniform particle size, and antioxidant properties, while simplifying the preparation process and achieving green and controllable synthesis, has significant practical significance and application value. Summary of the Invention

[0009] The purpose of this invention is to provide a chemical reduction method for the stable preparation of copper powder with a particle size below 80 nm, good dispersibility, good particle size uniformity, and strong antioxidant properties. The process is simple, green, and controllable, and is suitable for large-scale industrial application.

[0010] In a first aspect, the present invention provides a method for preparing nano-copper powder below 80 nm by chemical reduction, comprising the following steps:

[0011] 1) Pretreatment of the reaction system: Prepare a copper salt solution and a reducing agent solution, add a dispersant to the copper salt solution, adjust the reducing agent solution to alkaline, and preheat the copper salt solution and the reducing agent solution to a temperature of 55-70℃;

[0012] 2) Reduction reaction: Under stirring conditions, the preheated copper salt solution is added dropwise to the reducing agent solution. The dropwise addition process adopts a three-stage temperature control method between 55-95℃. The temperature gradually increases during the three-stage reaction process. After the dropwise addition is completed, the reaction is kept at the temperature.

[0013] 3) Two-stage dispersion treatment: After the reaction is completed, the reaction solution is ultrasonically dispersed. After adding a surface modifier, ultrasonic dispersion is continued. After the reaction is completed, the solution is centrifuged and the precipitate is washed and dried to obtain copper powder.

[0014] Optionally, in step 1), the copper salt is one or more of copper sulfate, copper nitrate, or copper chloride; and / or,

[0015] The reducing agent is ascorbic acid; and / or,

[0016] The dispersant is one or a mixture of polyvinylpyrrolidone or sodium citrate.

[0017] Optionally, in step 1), the concentration ratio of the copper salt solution to the reducing agent solution is 0.1-1 mol / L: 0.7-3.0 mol / L, and the volume ratio is 30-60 mL: 20-200 mL.

[0018] Optionally, in step 1), the concentration ratio of the copper salt solution to the reducing agent solution is 0.4-0.5 mol / L: 2.4-2.6 mol / L, and the volume ratio is 40-50 mL: 40-50 mL.

[0019] Optionally, in step 1), the amount of dispersant added is 0.05-5% of the mass of the copper salt.

[0020] Optionally, in step 2), the copper salt solution is added to the reducing agent solution at a rate of 1-10 mL / min, and the temperature gradually increases in the three-stage reaction process as follows: the temperature is maintained at 55-70℃ in the initial stage of addition, raised to 60-75℃ in the middle stage of addition, and raised to 80-95℃ in the later stage of addition, while the copper salt solution is added at a uniform rate; after the addition is completed, the temperature for maintaining the reaction is 80-95℃, and the reaction time is 15-40 minutes.

[0021] Optionally, in step 2), the copper salt solution is added to the reducing agent solution at a rate of 2-4 mL / min, and the temperature gradually increases in the three-stage reaction process as follows: the temperature is maintained at 58-62℃ in the initial stage of addition, raised to 64-66℃ in the middle stage of addition, and raised to 88-92℃ in the later stage of addition, while the copper salt solution is added at a uniform rate; after the addition is completed, the temperature for maintaining the reaction is 88-92℃, and the reaction time is 15-35 minutes.

[0022] Optionally, in step 3), the ultrasonic dispersion treatment power is 300-1000W, the time is 5-15 minutes, and after adding the surface modifier, the ultrasonic dispersion treatment continues for 10-30 minutes; and / or,

[0023] The surface modifier is one or a mixture of malic acid, sodium dodecyl sulfonate, or lactic acid.

[0024] Secondly, the present invention provides a nano-copper powder below 80 nm, which is obtained by the aforementioned chemical reduction preparation method of nano-copper powder below 80 nm.

[0025] Optionally, the average particle size of the nano-copper powder is 60-80 nm, the coefficient of variation is less than 15%, the oxygen content is less than 1.5%, and the metal-based purity of the copper powder is above 99.9%.

[0026] In summary, the present invention has at least one of the following beneficial effects:

[0027] 1) This invention abandons the complex intermediate control process of the two-step reduction method and pioneers a new reaction path combining "one-step direct reduction with alkaline ascorbic acid" with three-stage programmed temperature control. By precisely controlling the reaction temperature and rate from monomer formation to nucleation and final growth stages, it achieves the precise synthesis of small-sized copper nanoparticles with an average particle size of less than 80 nanometers. This invention eliminates the need for a secondary reducing agent such as ferrous sulfate, resulting in a simpler process that meets green production requirements, reduces environmental treatment costs, and offers strong controllability, making it suitable for large-scale industrial production.

[0028] 2) By precisely controlling parameters such as copper salt concentration, reducing agent concentration, reaction temperature and dropping rate, this invention can stably prepare ultra-small copper powder with an average particle size between 60-80 nm, and the particle size distribution is uniform with the coefficient of variation controlled within 15%.

[0029] 3) This invention adopts a three-stage anti-agglomeration system of "dispersant pre-addition + ultrasonic dispersion + surface modification", which effectively solves the agglomeration problem of nano copper powder and the product has good dispersibility;

[0030] 4) The introduction of surface modifiers forms a protective layer on the surface of copper powder, significantly reducing the oxygen content of the copper powder to ≤1.5%;

[0031] 5) The prepared copper powder has a metal-based purity of ≥99.9%, high sintering activity, and a sintering temperature 30-80℃ lower than that of conventional copper powder. The conductive copper layer subsequently prepared has a shear strength of over 55MPa and a conductivity of 1×10⁻⁶. 7 With a shear strength of S / m or higher, it meets the application requirements of back-end power modules and PCB interconnection. Preferably, the conductive copper layer has a shear strength of over 65MPa and a conductivity of 2×10⁻⁶. 7 With a S / m or higher, it has significant application value in fields such as high-density PCB interconnection and third-generation semiconductor packaging. Attached Figure Description

[0032] Figure 1 This is an SEM image of the copper powder prepared in Example 1.

[0033] Figure 2 This is an SEM image of the conductive copper layer prepared in Example 1.

[0034] Figure 3 This is an SEM image of the copper powder prepared in Example 2.

[0035] Figure 4 This is an SEM image of the copper powder prepared in Example 3. Detailed Implementation

[0036] This invention provides an ultra-small size nano-copper powder and a green, controllable synthesis method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0037] Copper nanoparticles smaller than 80nm exhibit excellent conductivity and can form conductive networks when used in conductive pastes, adhesives, or inks. This makes them particularly suitable for high-density PCB interconnects, third-generation semiconductor packaging, high-precision 3D printing, and photovoltaic pastes. Furthermore, due to their high surface activity and low melting point, copper nanoparticles smaller than 80nm can be sintered to achieve density below 300℃, making them equally suitable for fabricating electronic circuits and packaging materials on flexible substrates, such as flexible displays and wearable devices. However, the chemical reduction method used in related technologies for preparing copper powder is difficult to simplify the process and achieve green and controllable synthesis. After extensive research, the inventors pioneered a novel reaction pathway combining "one-step direct reduction with alkaline ascorbic acid" with three stages of programmed temperature control. By precisely controlling the reaction temperature and rate from monomer formation to nucleation and final growth stages, this invention achieves the accurate synthesis of small-sized copper nanoparticles with an average particle size of less than 80 nanometers. This invention eliminates the need for secondary reducing agents such as ferrous sulfate, simplifying the process, meeting green production requirements, reducing environmental processing costs, and offering strong controllability suitable for large-scale industrial production. It can stably prepare ultra-small copper powder with an average particle size between 60-80 nm, exhibiting uniform particle size distribution and a coefficient of variation controlled within 15%. The prepared copper powder has a metal-based purity ≥99.9%, high sintering activity, and a sintering temperature 30-80℃ lower than conventional copper powder. The resulting conductive copper layer achieves a shear strength exceeding 55 MPa and a conductivity of 1×10⁻⁶. 7 With a shear strength of S / m or higher, it meets the application requirements of back-end power modules and PCB interconnection. Preferably, the conductive copper layer has a shear strength of over 65MPa and a conductivity of 2×10⁻⁶. 7 S / m or higher. This invention is based on this research.

[0038] In some embodiments of the present invention, a method for preparing nano-copper powder below 80 nm by chemical reduction is provided, comprising the following steps:

[0039] 1) Pretreatment of the reaction system: Prepare a copper salt solution and a reducing agent solution, add a dispersant to the copper salt solution, adjust the reducing agent solution to alkaline, and preheat the copper salt solution and the reducing agent solution to a temperature of 55-70℃, preferably 58-68℃, more preferably 58-65℃, and even more preferably 58-62℃.

[0040] 2) Reduction reaction: Under stirring conditions, the preheated copper salt solution is added dropwise to the reducing agent solution. The dropwise addition process adopts a three-stage temperature control method between 55-95℃. The temperature gradually increases during the three-stage reaction process. After the dropwise addition is completed, the reaction is kept at a constant temperature. Preferably, the dropwise addition process is between 58-92℃.

[0041] 3) Two-stage dispersion treatment: After the reaction is completed, the reaction solution is ultrasonically dispersed. After adding a surface modifier, ultrasonic dispersion is continued. After the reaction is completed, the solution is centrifuged and the precipitate is washed and dried to obtain copper powder.

[0042] In some embodiments of the present invention, in step 1), the copper salt is one or more of copper sulfate, copper nitrate, or copper chloride; and / or, the reducing agent is ascorbic acid; and / or, the dispersant is one or more of polyvinylpyrrolidone or sodium citrate.

[0043] In some embodiments of the present invention, in step 1), the concentration ratio of the copper salt solution to the reducing agent solution is 0.1-1 mol / L: 0.7-3.0 mol / L, and the volume ratio is 30-60 mL: 20-200 mL; preferably, the concentration ratio is 0.15-0.5 mol / L: 1.0-3.0 mol / L, and the volume ratio is 30-60 mL: 20-120 mL; more preferably, the concentration ratio is 0.2-0.5 mol / L: 1.1-2.6 mol / L, and the volume ratio is 30-60 mL: 30-60 mL; even more preferably, the concentration ratio is 0.4-0.5 mol / L: 2.4-2.6 mol / L, and the volume ratio is 40-50 mL: 40-50 mL.

[0044] In some embodiments of the present invention, the amount of dispersant added is 0.05-5% of the mass of copper salt, preferably 2-4%.

[0045] In some embodiments of the present invention, in step 1), the pH value of the reducing agent solution is adjusted to 9-13, preferably 11-12.5, using a pH adjuster. The pH adjuster may be a potassium hydroxide or sodium hydroxide solution.

[0046] In some embodiments of the present invention, in step 2), the copper salt solution is added dropwise to the reducing agent solution at a rate of 1-10 mL / min; preferably, the copper salt solution is added dropwise to the reducing agent solution at a rate of 1-5 mL / min, and more preferably, the copper salt solution is added dropwise to the reducing agent solution at a rate of 2-4 mL / min. Preferably, the stirring speed in step 2) is 200-1000 rpm, more preferably 300-900 rpm.

[0047] In some embodiments of the present invention, in step 2), the temperature gradually increases during the three-stage reaction process as follows: The temperature is maintained at 55-70°C in the initial stage of addition, raised to 60-75°C in the middle stage, and raised to 80-95°C in the later stage; preferably, the temperature is maintained at 58-68°C in the initial stage, raised to 64-72°C in the middle stage, and raised to 83-95°C in the later stage; preferably, the temperature is maintained at 58-62°C in the initial stage, raised to 64-66°C in the middle stage, and raised to 88-92°C in the later stage. Preferably, the copper salt solution is added at a uniform rate. After the addition is completed, the temperature for maintaining the reaction is 80-95°C, preferably 85-95°C, more preferably 88-92°C, and the reaction time is 15-40 minutes, preferably 18-35 minutes, more preferably 18-32 minutes.

[0048] In some embodiments of the present invention, in step 3), the ultrasonic dispersion power is 300-1000W, the time is 5-15 minutes, and after adding the surface modifier, the ultrasonic dispersion continues for 10-30 minutes. Preferably, the ultrasonic dispersion power is 300-900W. Preferably, the surface modifier is one or a mixture of malic acid, sodium dodecyl sulfonate (SDS), or lactic acid. Preferably, the amount of surface modifier added is 5-20% of the theoretical yield of copper powder. Preferably, the centrifugation speed is 8000-15000 rpm, the time is 10-20 minutes, the precipitate is collected; the precipitate is washed 2-3 times with deionized water, and then washed 1-2 times with anhydrous ethanol.

[0049] In some embodiments of the present invention, a copper nanoparticle with a wavelength of less than 80 nm is provided, which is obtained by the aforementioned chemical reduction preparation method of copper nanoparticles with a wavelength of less than 80 nm.

[0050] In some embodiments of the present invention, the average particle size of the nano-copper powder is 60-80 nm, preferably 60-70 nm; the coefficient of variation is less than 15%, preferably 9-11%; the oxygen content is less than 1.5%, preferably less than 1.3%; and the metal-based purity of the copper powder is 99.9% or higher.

[0051] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials used in this embodiment are all commercially available.

[0052] Example 1

[0053] This embodiment provides a chemical reduction preparation method for ultra-small size nano-copper powder, including the following steps:

[0054] 1) Pretreatment of the reaction system: Dissolve 5.0 g of copper sulfate (copper sulfate pentahydrate, 99.9%, Aladdin) in 45 mL of deionized water to prepare a copper sulfate solution with a concentration of 0.45 mol / L; add 0.15 g of polyvinylpyrrolidone (PVP, K30, Aladdin) to the copper sulfate solution and stir until completely dissolved to obtain a copper salt solution; preheat the copper salt solution to 60℃; dissolve 20.0 g of ascorbic acid (99.5%, Aladdin) in 45 mL of deionized water to prepare a reducing agent solution with a concentration of 2.52 mol / L; adjust the pH of the reducing agent solution to 11.5 with 1 mol / L sodium hydroxide solution; preheat the reducing agent solution to 60℃.

[0055] 2) Reduction reaction: Under stirring conditions, the stirring speed was 400 rpm, and the copper salt solution was added dropwise to the reducing agent solution at a rate of 3 mL / min; a three-stage temperature control was adopted. In the initial stage of addition (0-5 minutes), the temperature was maintained at 60℃ to ensure the formation of a large number of monomers and reach the critical nucleation concentration; in the middle stage of addition (5-10 minutes), the temperature was increased to 65℃ to ensure the uniformity of nanoparticle nucleation; in the later stage of addition (10-15 minutes), the temperature was increased to 90℃ to shorten the reaction time of the growth stage; after the addition was completed, the reaction was continued at 90℃ for 20 minutes.

[0056] 3) Two-stage dispersion treatment: After the reaction is completed, the reaction solution is ultrasonically dispersed at 400W for 10 minutes. Then, 0.1g of malic acid (99%, Aladdin) is added, and ultrasonic stirring is continued for 15 minutes. After that, centrifugation is performed at 10,000 rpm for 15 minutes. The precipitate is collected, washed twice with deionized water, and then washed once with anhydrous ethanol. It is then dried at 30℃ and 0.08MPa vacuum for 4 hours to obtain copper powder product.

[0057] The microstructure of the copper powder prepared in Example 1 was characterized using scanning electron microscopy (SEM). The test results are as follows: Figure 1 As shown, by Figure 1 As can be seen, the prepared copper nanoparticles are spherical particles with good dispersibility, concentrated particle size distribution, and small differences. The particle size of 200 copper powder particles was randomly counted using the Nano Measure method, and the average particle size was calculated. The average particle size of the copper powder was found to be 60 nm. The coefficient of variation (CV) was used to measure the uniformity of the copper powder particle size distribution. The formula for calculating the coefficient of variation (CV) is: CV = σ / μ × 100%, where σ is the standard deviation, reflecting the dispersion of particle size, and μ is the arithmetic mean of particle size. The calculated coefficient of variation of the copper powder particle size was 10.12%.

[0058] The purity of the copper powder prepared in Example 1 was determined by inductively coupled plasma mass spectrometry (ICP-MS), and the purity of the copper powder in Example 1 was found to be 99.93%. The oxygen content of the copper powder prepared in Example 1 was determined by an oxygen analyzer, and the oxygen content of the copper powder in Example 1 was found to be 1.25%.

[0059] The nano-copper powder prepared in Example 1 was added as a conductive phase to an electronic paste. The electronic paste was then coated onto a ceramic substrate, and sintered under a nitrogen atmosphere at 210°C and 15 MPa for 10 minutes to obtain a conductive copper layer. Figure 2 It can be seen that the conductive copper layer prepared by sintering has good density, with a porosity of less than 7%. The measured shear strength of the conductive copper layer can reach 67.17 MPa, and the conductivity can reach 2.09 × 10⁻⁶ MPa. 7 S / m meets the application requirements of back-end power modules and PCB interconnection.

[0060] Example 2

[0061] This embodiment provides a chemical reduction preparation method for ultra-small size nano-copper powder, including the following steps:

[0062] 1) Pretreatment of the reaction system: Dissolve 1.53g of copper chloride (copper chloride dihydrate, 99.9%, Aladdin) in 45mL of deionized water to prepare a copper chloride solution with a concentration of 0.2mol / L; add 0.05g of sodium citrate (HOC(COONa)(CH2COONa)2·2H2O, 99%, Bailingwei) to the copper chloride solution and stir until completely dissolved to obtain a copper salt solution. Preheat the copper salt solution to 60℃; dissolve 10g of ascorbic acid (99.5%, Aladdin) in 45mL of deionized water to prepare a reducing agent solution with a concentration of 1.26mol / L. Adjust the pH of the reducing agent solution to 12 with 1mol / L sodium hydroxide solution and preheat the reducing agent solution to 60℃.

[0063] 2) Reduction reaction: Under stirring conditions, the stirring speed was 800 rpm, and the copper salt solution was added dropwise to the reducing agent solution at a rate of 3 mL / min; a three-stage temperature control was adopted. In the initial stage of addition (0-5 minutes), the temperature was maintained at 60℃ to ensure the formation of a large number of monomers and reach the critical nucleation concentration; in the middle stage of addition (5-10 minutes), the temperature was increased to 65℃ to ensure the uniformity of nanoparticle nucleation; in the later stage of addition (10-15 minutes), the temperature was increased to 90℃ to shorten the reaction time of the growth stage; after the addition was completed, the reaction was continued at 90℃ for 30 minutes.

[0064] 3) Two-stage dispersion treatment: After the reaction is completed, the reaction solution is ultrasonically dispersed at 800W for 10 minutes. Then, 0.1g of sodium dodecyl sulfate (SDS, 99%, Aladdin) is added, and ultrasonic stirring is continued for 20 minutes. After that, centrifugation is performed at 12,000 rpm for 15 minutes. The precipitate is collected, washed twice with deionized water, and then washed once with anhydrous ethanol. It is then dried at 30℃ and 0.09MPa vacuum for 3 hours to obtain copper powder product.

[0065] The microstructure of the copper powder prepared in Example 2 was characterized using the same testing methods as in Example 1. The test results are as follows: Figure 3 As shown, from Figure 3 As can be seen from the results, the copper powder prepared in Example 2 consists of spherical particles with good dispersibility and a concentrated particle size distribution with minimal variation. Using the same statistical method as in Example 1, the average particle size of the copper powder was calculated to be 63.72 nm, and the coefficient of variation for the copper powder particle size was 9.16%.

[0066] The purity of the copper powder prepared in Example 2 was 99.91% and the oxygen content was 1.23%, which was determined using the same testing method as in Example 1.

[0067] A conductive copper layer was prepared using the copper powder obtained in Example 2, following the same preparation method as in Example 1. The shear strength of the conductive copper layer was measured to be greater than 60 MPa, and the conductivity was not less than 1 × 10⁻⁶. 7 S / m meets the application requirements of back-end power modules and PCB interconnection.

[0068] Example 3

[0069] This embodiment provides a chemical reduction preparation method for ultra-small size nano-copper powder, including the following steps:

[0070] 1) Pretreatment of the reaction system: Dissolve 2g of copper chloride (copper chloride dihydrate, 99.9%, Aladdin) in 45mL of deionized water to prepare a copper chloride solution with a concentration of 0.26mol / L; add 0.06g of sodium citrate (HOC(COONa)(CH2COONa)2·2H2O, 99%, Bailingwei) to the copper chloride solution and stir until completely dissolved to obtain a copper salt solution. Preheat the copper salt solution to 65℃; dissolve 9g of ascorbic acid (99.5%, Aladdin) in 45mL of deionized water to prepare a reducing agent solution with a concentration of 1.14mol / L. Adjust the pH of the reducing agent solution to 12 with 1mol / L sodium hydroxide solution and preheat the reducing agent solution to 65℃.

[0071] 2) Reduction reaction: Under stirring conditions, the stirring speed was 800 rpm, and the copper salt solution was added dropwise to the reducing agent solution at a rate of 3 mL / min; a three-stage temperature control was adopted. In the initial stage of addition (0-5 minutes), the temperature was maintained at 65℃ to ensure the formation of a large number of monomers and reach the critical nucleation concentration; in the middle stage of addition (5-10 minutes), the temperature was increased to 70℃ to ensure the uniformity of nanoparticle nucleation; in the later stage of addition (10-15 minutes), the temperature was increased to 85℃ to shorten the reaction time of the growth stage; after the addition was completed, the reaction was continued at 85℃ for 30 minutes.

[0072] 3) Two-stage dispersion treatment: After the reaction is completed, the reaction solution is ultrasonically dispersed at 800W for 10 minutes. Then, 0.15g of lactic acid (95%, Aladdin) is added, and ultrasonic stirring is continued for 20 minutes. After that, centrifugation is performed at 12,000 rpm for 15 minutes. The precipitate is collected, washed twice with deionized water, and then washed once with anhydrous ethanol. It is then dried at 35℃ and 0.09MPa vacuum for 3 hours to obtain copper powder product.

[0073] The microstructure of the copper powder prepared in Example 3 was characterized using the same testing methods as in Example 1. The test results are as follows: Figure 4 As shown, from Figure 4 As can be seen from Example 3, the copper powder prepared in Example 3 consists of spherical particles with good dispersibility, a concentrated particle size distribution, and minimal variation. Using the same statistical method as in Example 1, the average particle size of the copper powder was calculated to be 75 nm, and the coefficient of variation of the copper powder particle size was 9.82%.

[0074] The purity of the copper powder prepared in Example 3 was 99.90% and the oxygen content was 1.18%, as determined by the same testing method as in Example 1.

[0075] A conductive copper layer was prepared using the same preparation method as in Example 1, employing the copper powder from Example 3. The shear strength of the conductive copper layer was measured to be greater than 60 MPa, and the conductivity was not less than 1 × 10⁻⁶ MPa. 7 S / m meets the application requirements of back-end power modules and PCB interconnection.

[0076] Example 4

[0077] This embodiment provides a chemical reduction preparation method for ultra-small size nano-copper powder, including the following steps:

[0078] 1) Pretreatment of the reaction system: Dissolve 1.53g of copper chloride (copper chloride dihydrate, 99.9%, Aladdin) in 45mL of deionized water to prepare a copper chloride solution with a concentration of 0.2mol / L; add 0.05g of sodium citrate (HOC(COONa)(CH2COONa)2·2H2O, 99%, Bailingwei) to the copper chloride solution and stir until completely dissolved to obtain a copper salt solution. Preheat the copper salt solution to 60℃; dissolve 10g of ascorbic acid (99.5%, Aladdin) in 45mL of deionized water to prepare a reducing agent solution with a concentration of 1.26mol / L. Adjust the pH of the reducing agent solution to 12 with 1mol / L sodium hydroxide solution and preheat the reducing agent solution to 60℃.

[0079] 2) Reduction reaction: Under stirring conditions, the stirring speed is 800 rpm, and the copper salt solution is added dropwise to the reducing agent solution at a rate of 10 mL / min; a three-stage temperature control program is used: the temperature is maintained at 60℃ in the initial stage of addition (0-1.5 minutes); the temperature is increased to 65℃ in the middle stage of addition (1.5-3 minutes); the temperature is increased to 90℃ in the later stage of addition (3-4.5 minutes); after the addition is completed, the reaction is continued at 90℃ for 30 minutes.

[0080] 3) Two-stage dispersion treatment: After the reaction is completed, the reaction solution is ultrasonically dispersed at 800W for 10 minutes. Then, 0.1g of sodium dodecyl sulfate (SDS, 99%, Aladdin) is added, and ultrasonic stirring is continued for 20 minutes. After that, centrifugation is performed at 12,000 rpm for 15 minutes. The precipitate is collected, washed twice with deionized water, and then washed once with anhydrous ethanol. It is then dried at 30℃ and 0.09MPa vacuum for 3 hours to obtain copper powder product.

[0081] The microstructure of the copper powder prepared in Example 4 was characterized using the same testing method as in Example 1. The average particle size of the copper powder was calculated to be 78 nm, and the coefficient of variation of the copper powder particle size was 13.9%.

[0082] The purity of the copper powder prepared in Example 4 was 99.90% and the oxygen content was 1.19%, which was determined using the same testing method as in Example 1.

[0083] A conductive copper layer was prepared using the same preparation method as in Example 1, employing the copper powder from Example 4. The shear strength of the conductive copper layer was measured to be greater than 55 MPa, and the conductivity was not less than 1 × 10⁻⁶. 7 S / m meets the application requirements of back-end power modules and PCB interconnection.

[0084] As can be seen from Examples 1-4, the chemical reduction preparation method provided in this invention can prepare copper nanoparticles with an average particle size of less than 80 nanometers. Specifically, the average particle size prepared in Examples 1 and 2 is 60-65 nm with a coefficient of variation of 9.1-10.2%, and the average particle size prepared in Examples 3 and 4 is 75-80 nm with a coefficient of variation of 9.8-13.9%. The oxygen content is less than 1.25%, and the metal-based purity of the copper powder is above 99.9%. Compared to Example 4, the dropping rates in Examples 1-3 were moderate, and combined with specific three-stage temperature control, the prepared copper nanoparticles had smaller average particle sizes, smaller coefficients of variation, and better particle size distribution uniformity. The prepared conductive copper layers had better shear strength. Compared to Example 3, the initial and middle reaction temperatures in the three-stage temperature control of Examples 1 and 2 were lower, while the later reaction temperature was higher. This ensured uniform nucleation and growth, resulting in copper nanoparticles with smaller average particle sizes and better distribution uniformity. In particular, in Example 1, the copper salt and reducing agent had optimal reaction concentrations. Therefore, the prepared copper nanoparticles and conductive copper layers had optimal particle size distribution, mechanical properties, and electrical conductivity.

[0085] Comparative Example 1

[0086] The difference between Comparative Example 1 and Example 3 is that in Comparative Example 1, step 2) of the reduction reaction was not temperature-controlled; the reaction was carried out at 85°C for 45 minutes. The remaining preparation steps were the same as in Example 3, and copper powder was obtained.

[0087] Using the same testing method as in Example 3, the average particle size of the copper powder in Comparative Example 1 was measured to be 95 nm, the coefficient of variation was 18.53%, and the oxygen content was 1.21%.

[0088] Comparative Example 2

[0089] The difference between Comparative Example 2 and Example 3 is that in Comparative Example 2, step 2) of the reduction reaction is carried out using a two-stage temperature control program. The reaction is carried out at 65°C for 15 minutes in the initial stage of addition and at 85°C for 30 minutes in the later stage. The remaining preparation steps are the same as in Example 3, and copper powder is obtained.

[0090] Using the same testing method as in Example 3, the average particle size of the copper powder in Comparative Example 2 was measured to be 83 nm, the coefficient of variation was 15.21%, and the oxygen content was 1.19%.

[0091] Comparative Example 3

[0092] The difference between Comparative Example 3 and Example 3 is that in step 1) of the reaction system pretreatment in Comparative Example 3, the copper salt solution and reducing agent solution were not preheated. The remaining preparation steps were the same as in Example 3, and copper powder was obtained.

[0093] Using the same testing method as in Example 3, the average particle size of the copper powder in Comparative Example 3 was measured to be 86 nm, the coefficient of variation was 16.33%, and the oxygen content was 1.17%.

[0094] Comparative Example 4

[0095] The difference between Comparative Example 4 and Example 3 is that in step 2) of the reduction reaction in Comparative Example 4, the reducing agent solution was added dropwise to the copper salt solution at a rate of 3 mL / min, using a three-stage temperature program: the temperature was maintained at 65°C during the initial stage of addition (0-5 minutes); the temperature was increased to 70°C during the middle stage of addition (5-10 minutes); and the temperature was increased to 85°C during the later stage of addition (10-15 minutes). After the addition was completed, the reaction was continued at 85°C for 30 minutes. The remaining preparation steps were the same as in Example 3, and copper powder was obtained.

[0096] Using the same testing method as in Example 3, the average particle size of the copper powder in Comparative Example 4 was measured to be 156 nm, the coefficient of variation was 35%, and the oxygen content was 1.15%.

[0097] Comparative Example 5

[0098] The difference between Comparative Example 5 and Example 3 is that step 3) of Comparative Example 5 did not employ a two-stage dispersion treatment. After the reaction was complete, 0.15 g of lactic acid (95%, Aladdin) was added, and the mixture was ultrasonically stirred for 30 minutes. Then, it was centrifuged at 12,000 rpm for 15 minutes. The precipitate was collected, washed twice with deionized water, and then once with anhydrous ethanol. It was then dried at 35°C and a vacuum of 0.09 MPa for 3 hours to obtain copper powder. The remaining preparation steps were the same as in Example 3, and copper powder was obtained.

[0099] Using the same test method as in Example 3, the oxygen content of copper powder in Comparative Example 5 was measured to be 1.53%.

[0100] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing nano-copper powder below 80 nm by chemical reduction, characterized in that, Includes the following steps: 1) Pretreatment of the reaction system: Prepare a copper salt solution and a reducing agent solution. Add a dispersant to the copper salt solution. The reducing agent is ascorbic acid. Adjust the reducing agent solution to alkaline. The concentration of the copper salt solution is 0.2-0.5 mol / L and the volume is 30-60 mL. The concentration of the reducing agent solution is 1.1-2.6 mol / L and the volume is 30-60 mL. Preheat the copper salt solution and the reducing agent solution to a temperature of 55-70℃. 2) Reduction reaction: Under stirring conditions, the preheated copper salt solution is added dropwise to the reducing agent solution at a rate of 2-4 mL / min. The addition process is carried out using a three-stage temperature control method between 55-95℃, with the temperature gradually increasing during each stage. After the addition is completed, the reaction is maintained at this temperature for 15-40 minutes. Specifically, the temperature is maintained at 55-70℃ in the initial stage, increased to 60-75℃ in the middle stage, and increased to 80-95℃ in the later stage, while the copper salt solution is added at a uniform rate. After the addition is completed, the reaction is maintained at 80-95℃ for 15-40 minutes. 3) Two-stage dispersion treatment: After the reaction is completed, the reaction solution is ultrasonically dispersed. After adding a surface modifier, ultrasonic dispersion is continued. After the reaction is completed, the solution is centrifuged and the precipitate is washed and dried to prepare nano copper powder. The average particle size of the nano-copper powder is 60-80 nm, the particle size variation coefficient is 9-11%, the oxygen content is below 1.5%, and the metal-based purity of the copper powder is above 99.9%.

2. The chemical reduction preparation method for 80nm and below nano-copper powder according to claim 1, characterized in that, In step 1), the copper salt is one or more of copper sulfate, copper nitrate, or copper chloride; and / or, The dispersant is one or a mixture of polyvinylpyrrolidone or sodium citrate.

3. The chemical reduction preparation method for 80nm and below nano-copper powder according to claim 1, characterized in that, In step 1), the concentration of the copper salt solution is 0.4-0.5 mol / L and the volume is 40-50 mL, and the concentration of the reducing agent solution is 2.4-2.6 mol / L and the volume is 40-50 mL.

4. The chemical reduction preparation method for 80nm and below nano-copper powder according to claim 1, characterized in that, In step 1), the amount of dispersant added is 0.05-5% of the mass of the copper salt.

5. The chemical reduction preparation method of copper nanoparticles below 80 nm according to any one of claims 1 to 4, characterized in that, In step 2), the temperature gradually increases in the three stages of the reaction process as follows: the temperature is maintained at 58-62℃ in the initial stage of the drop addition, raised to 64-66℃ in the middle stage of the drop addition, and raised to 88-92℃ in the later stage of the drop addition, while the copper salt solution is added at a uniform rate; after the drop addition is completed, the temperature for the reaction is maintained at 88-92℃ for 15-35 minutes.

6. The chemical reduction preparation method of copper nanoparticles below 80 nm according to any one of claims 1 to 4, characterized in that, In step 3), the ultrasonic dispersion treatment power is 300-1000W, the time is 5-15 minutes, and after adding the surface modifier, the ultrasonic dispersion treatment continues for 10-30 minutes; and / or, The surface modifier is one or a mixture of malic acid, sodium dodecyl sulfonate, or lactic acid.

7. A nano-copper powder with a wavelength of less than 80 nm, obtained by the chemical reduction preparation method of the nano-copper powder with a wavelength of less than 80 nm according to any one of claims 1 to 6.

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