A low-temperature copper paste suitable for high-precision 3D printing, a preparation method and application thereof

Abstract

The application relates to the field of conductive paste, in particular to a low-temperature copper paste suitable for high-precision 3D printing and a preparation method and application thereof. The low-temperature copper paste comprises nano copper particles and a dispersion preparation. The surface of the nano copper particles is coated with ligands. The dispersion preparation is composed of a binder, a protective agent and a diluent. The resistivity of the low-temperature copper paste is less than 40 mu omega cm after sintering at 200 DEG C. In the application, copper precursors are added into a ligand-containing reducing agent solution, the non-synchronous nucleation and growth of the copper precursors in the initial stage of the reaction can be controlled, and an effective coating is formed on the particle surface. According to the solubility of the ligands on the particle surface and organic solvents, the solubility of the system is adjusted to a suitable value by introducing weak polar solvents and polar solvents in sequence. Free ligands, reaction byproducts and other impurities between the particles are effectively removed, and the effective coated organic ligands on the particle surface are retained, so that the copper nanoparticles have oxidation resistance and dispersion uniformity.

Description

Technical Field

[0001] This invention relates to the field of conductive pastes, and more particularly to a low-temperature copper paste suitable for high-precision 3D printing, its preparation method, and its application. Background Technology

[0002] In recent years, fields such as printed circuits, solar cells, RFID, and displays have increasingly emphasized production costs, environmental protection, and precision improvements. Traditional etching and electroplating processes are characterized by long production cycles, high energy consumption, and severe pollution, failing to align with the principles of a green economy. Precision 3D printing technology, a globally leading advanced manufacturing technology, can achieve the fabrication of complex micro- and nano-scale three-dimensional structures through dimensional printing control, possessing immense industrial potential. Since electronic components such as PCBs and HJT batteries are not heat-resistant, the conductive pastes used must not only ensure stable output from fine nozzles but also possess excellent low-temperature sintering and high conductivity. Currently, the most common low-temperature conductive pastes on the market are silver pastes, which are prone to electron migration in continuous electric field environments, severely impacting the lifespan of electronic components. Copper, on the other hand, is significantly cheaper than silver, has better process compatibility, and, in particular, exhibits strong resistance to electron migration and high conductivity (only 6% lower than silver), making it a highly valuable substitute.

[0003] Currently, the main method for preparing low-temperature copper paste is through mixing copper particles with a dispersant. Due to the large specific surface area of ​​nano-copper particles, they are easily oxidized by oxygen in the air when not effectively coated with ligands. The resulting copper oxide coats the surface of the copper particles, leading to an increase in the sintering temperature required for the paste and a decrease in conductivity. If the residual ligand content is too high, the bonding ability between particles is weak, making it difficult to form sintering necks, resulting in a decrease in strength and conductivity.

[0004] To achieve both low-temperature sintering performance and stability in the slurry, existing technologies often use micron-sized large copper particles to prepare low-temperature copper slurry.

[0005] For example, patent CN 103021512 discloses a conductive paste composition for low-temperature sintering. This composition involves blending micron-sized flake-like, spherical, and nano-sized copper powders with a suitable dispersant to obtain a conductive copper paste that can be sintered at temperatures below 200°C. However, because the copper paste produced by this method contains more than 55% flake-like particles of 2.5μm, it is prone to layering and agglomeration. Therefore, it is only suitable for traditional printing processes with high material loss and cannot achieve precision 3D printing below 30μm, thus limiting the improvement of precision in electronic components.

[0006] Another technology improves sintering performance through particle surface modification. For example, patent CN 106928775 A discloses a low-temperature sinterable nano-copper conductive ink, its preparation method, and its printing application. This method involves treating the surface of nano-copper particles with organic acid to remove the copper oxide film, thus obtaining a low-temperature sinterable conductive ink. However, the particle surface obtained after acid etching does not contain organic ligands, resulting in poor affinity between the particles and organic solvents, leading to sedimentation problems. Furthermore, toluene is highly lipophilic and volatile; excessively high VOC concentrations have negative impacts on the atmosphere and human health, making it unsuitable for large-scale production.

[0007] Patent CN 113327721 A discloses a method for preparing low-temperature curing conductive copper paste. This method involves introducing a reducing agent and copper salt into copper powder to prepare a mixed paste. It is believed that the decomposition products of the reducing agent during sintering can remove oxides from the surface of copper particles, resulting in excellent conductivity. However, the resulting low-temperature copper paste has a solid content ≤5% and a viscosity ≤50 Pa·s. Furthermore, the copper particles are unmodified before sintering, making them prone to settling issues. This method is not suitable for designing circuits with specific aspect ratio requirements in the photovoltaic industry and is limited to the flatbed printing field. Summary of the Invention

[0008] The present invention aims to overcome the defects of existing conductive copper pastes as described above, and therefore provides a low-temperature copper paste suitable for high-precision 3D printing, its preparation method, and its application.

[0009] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0010] In a first aspect, the present invention provides a low-temperature copper paste suitable for high-precision 3D printing.

[0011] This includes copper nanoparticles and dispersing agents; among which,

[0012] The surface of the copper nanoparticles is coated with ligands;

[0013] The dispersion formulation consists of a binder, a protective agent, and a diluent;

[0014] The resistivity of the low-temperature copper paste is <40 μΩ·cm after sintering at 200℃.

[0015] In existing conductive copper pastes, the nano-copper particles are generally prepared via liquid-phase reduction, primarily by adding a reducing agent to a copper precursor solution. In this method, the reduction of the copper precursor and the nucleation and growth of nano-copper elements occur simultaneously. Due to the high concentration of the copper precursor in the initial stage of the reaction, the addition of the reducing agent easily causes localized agglomeration and growth of the elemental particles, resulting in particles that are often large in size and irregular in shape. This significantly affects the dispersibility and stability of the conductive copper paste. Furthermore, because the copper particles in the conductive copper paste are generally large, mostly at the micrometer or submicrometer level, it is only suitable for screen printing processes with low raw material utilization efficiency. However, this process is limited to printing patterns with linewidths greater than 30μm, making it difficult to achieve higher precision printing processes.

[0016] The conductive copper paste of this invention, due to the ligand coating on the surface of the copper nanoparticles, prevents the copper nanoparticles from adsorbing and agglomerating, thus maintaining their original size and shape and achieving excellent particle dispersibility and stability. Therefore, the conductive copper paste of this invention is suitable for precision 3D printing with a scale of ≥1μm, and has a higher material utilization rate than existing screen printing processes.

[0017] Meanwhile, because the surface of the nano-copper particles is coated with ligands, the elemental copper will not come into direct contact with moisture and oxygen in the air, thus effectively preventing the oxidation of the nano-copper particles. Therefore, its sintering performance will not decrease during the subsequent sintering process, and the storage stability of the slurry will not decrease significantly.

[0018] Furthermore, due to the coating of ligands, the copper nanoparticles can have good interfacial affinity with polar substrates such as glass and silicon wafers, thus exhibiting good adhesion properties after sintering.

[0019] Finally, in order to improve the stability of the conductive copper paste, the present invention also selectively introduces a protective agent into the dispersion formulation, which can further improve the stability of the nano-copper particles, thereby further improving the stability and sintering conductivity of the paste.

[0020] Preferably, the method for preparing the copper nanoparticles is as follows:

[0021] (1) Disperse the reducing agent and ligand in a solvent to form a mixed solution;

[0022] (2) The copper precursor is gradually added to the mixed solution so that the nucleation and growth of the copper precursor are asynchronous during the reduction process, and a dispersion of nano-copper particles is obtained.

[0023] (3) Add a weakly polar solvent and a polar solvent to the dispersion of nano-copper particles one after another. The solvent can be introduced in batches. After washing, separation and drying, nano-scale nano-copper particles are obtained.

[0024] Existing technologies generally prepare copper nanoparticles through liquid-phase reduction, primarily by adding a reducing agent to a copper precursor solution or by mixing the reducing agent and copper precursor solution in a single step. In this mode, the reduction of the copper precursor and the nucleation and growth of elemental copper nanoparticles occur simultaneously. Due to the high concentration of the copper precursor in the initial stage of the reaction, the addition of the reducing agent can easily cause local agglomeration and growth of elemental particles, resulting in particles that are larger in size, irregular in shape, and lack effective ligand coating protection on the surface. This significantly affects the dispersibility and stability of the conductive copper paste.

[0025] Furthermore, according to recent domestic and international literature, some technologies have been developed to prepare nanoscale conductive copper paste. However, as the particle size in the copper paste decreases, the surface free energy of the nanoscale copper particles increases rapidly, resulting in high activity. Specifically, this manifests as: 1) easy adsorption and aggregation between particles; 2) easy oxidation upon exposure to air, moisture, and oxygen, leading to a significant reduction in conductivity after sintering. This can easily reduce the storage stability of the paste and its high-precision direct-write 3D printing capabilities, limiting its development and application in the field of precision electronics.

[0026] The difference between this invention and existing technologies lies in the fact that, in the process of preparing copper nanoparticles using the liquid-phase reduction method, this invention controls the gradual addition of the copper precursor to the reducing agent solution containing ligands. This allows the nucleation and growth of the copper precursor to occur asynchronously in the early stages of the reaction, preventing local agglomeration of the copper nanoparticles during growth. This results in effectively reduced particle size, more regular shapes, and improved dispersion stability of the prepared copper nanoparticles. Therefore, it is more conducive to high-precision direct-write 3D printing, expanding its potential for development and application in the field of precision electronics.

[0027] Furthermore, due to the preparation method of this invention, the nucleation and growth of the copper precursor are carried out asynchronously. After the copper particles grow to the nanoscale, their surface can be effectively coated with ligands, which further reduces the mutual adsorption between particles. In addition, the ligands can effectively separate the nano-copper particles from the moisture and oxygen in the air, effectively reducing the possibility of oxidation. This has a significant impact on the dispersibility and stability of the conductive copper paste, thereby improving its thermal sintering performance.

[0028] Furthermore, the applicant discovered that after the synthesis of copper nanoparticles, the system composition can be divided into three main parts: the copper nanoparticle-organic ligand complex, the reaction solvent, and impurities. Impurities include reaction byproducts, unreacted precursors, and free organic ligands. These impurities significantly affect the conductivity and adhesion after sintering. Therefore, some literature suggests cleaning and purifying the prepared copper nanoparticles. However, current purification techniques typically use highly polar solvents (such as water). While these strongly polar solvents can remove unbound free ligands, they also cause ligands bound to the surface of the copper nanoparticles to detach. This results in the absence of ligands on the surface of the copper nanoparticles during purification and subsequent processing, exposing elemental copper. Consequently, electrostatic adsorption easily occurs between particles, inducing localized aggregation. Simultaneously, the exposed copper atoms are easily oxidized or hydrolyzed, ultimately affecting the uniformity and stability of the slurry particle dispersion. This can easily cause needle clogging during 3D printing, making it unsuitable for 3D printing processes.

[0029] Therefore, based on the compatibility between the ligands on the particle surface and the organic solvent, this invention introduces weakly polar solvents and polar solvents (alcohol-based or amine-based solvents) in batches (purification mechanism as follows). Figure 1 As shown in the diagram, the polarity of the system is gradually adjusted to a suitable value, ensuring good compatibility among the original solvent, ligands, polar solvent, and weakly polar solvent. The nano-copper particle-organic ligand complex exhibits low solubility in the composite solvent, allowing for rapid sedimentation and protecting the ligands from detaching from the particle surface. This effectively removes free ligands during purification while retaining sufficient organic ligands on the surface of the nano-copper particles, enhancing their oxidation resistance and dispersion uniformity. This, in turn, ensures the stability of the slurry during storage and the surface density after sintering, ultimately improving the overall stability of the slurry and the electrical conductivity after sintering.

[0030] Preferably, the reducing agent in step (1) includes one or more combinations of hydrazine hydrate, hypophosphite, sodium hypophosphite, sodium borohydride, ascorbic acid, and citric acid.

[0031] Preferably, the ligand comprises one or more combinations of polyacrylic acid, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and polyether.

[0032] Preferably, in step (1), the dispersion of the reducing agent and ligand in the solvent can be achieved by one or more of ultrasonication, magnetic stirring, and mechanical stirring. In some specific embodiments of the present invention, magnetic stirring is preferred, and the stirring speed is further preferably 200-1500 r / min.

[0033] Preferably, the concentration of the copper precursor solution in step (2) is 1-7.5 mol / L;

[0034] The copper precursor solution was added at a rate of 0.2-10 ml / min.

[0035] After testing by the inventors of this application, it was found that when the copper precursor solution was added at a rate of 0.2-10 ml / min, the resulting copper nanoparticles had more uniform particle size and morphology, and the final printing accuracy was also higher.

[0036] Preferably, the copper precursor solution is added in one or more of the following methods: dropwise addition via a separatory funnel, dropwise addition via a constant-pressure dropping funnel, injection via a syringe pump, or injection via a peristaltic pump.

[0037] Preferably, the copper precursor includes one or more of copper sulfate pentahydrate, copper formate, copper acetate, copper chloride, and copper nitrate.

[0038] Preferably, the molar ratio of copper precursor to reducing agent is 1:1 to 1:6.

[0039] This invention, by controlling the molar ratio of copper precursor to reducing agent, achieves good reduction of the copper precursor while conserving the amount of reducing agent used. Furthermore, under this ratio, the generated copper nanoparticles exhibit more uniform morphology and size, which is beneficial for improving high-precision direct-write 3D printing capabilities.

[0040] Further optimization involves gradually adding the copper precursor solution to the reducing agent solution containing the ligand, followed by stirring and dispersing the solution under heating conditions to induce a redox reaction in the solution, ultimately obtaining a copper nanoparticle dispersion.

[0041] More preferably, the heating conditions can be one or more of water bath, oil bath, and electric heating plate, and the heating temperature is 60-150℃.

[0042] Preferably, the stirring and dispersing method can be one or more of magnetic stirring and mechanical stirring. In some specific embodiments of the present invention, the dispersion method is preferably magnetic stirring, and the stirring speed is further preferably 200-1500 r / min.

[0043] In step (3), the polar solvent is any one or a combination of two of the following: alcohol solvents with 1 ≤ carbon number ≤ 4 or amine solvents with 2 ≤ carbon number ≤ 6.

[0044] The weakly polar solvent is any one or a combination of esters, ketones, or alkane solvents.

[0045] The molar ratio of the polar solvent to the weakly polar solvent is 1:1 to 1:4.

[0046] Preferably, the separation step in step (3) can be performed by high-speed centrifugation to separate the layers, and the precipitate is obtained after filtration.

[0047] Preferably, the drying process in step (3) is as follows: the washed precipitate is dried in a nitrogen, argon or vacuum environment for ≥1h to obtain nanoscale copper elemental particles.

[0048] Preferably, the adhesive includes any one or more of alcohol-soluble epoxy resin, alcohol-soluble phenolic resin, acrylic resin, polyamide resin, and polyurethane resin;

[0049] The protective agent includes any one or more of the following: hypophosphite, ascorbic acid, formic acid, oxalic acid, thiol, primary alcohol amine with the general chemical formula OH-X-NH2, where X is 2 ≤ carbon number ≤ 6, and secondary alcohol amine with the general chemical formula NH-(Y-OH)2, where Y is 2 ≤ carbon number ≤ 6.

[0050] The diluent includes any one or more of low molecular weight alcohols with 2 ≤ carbon number ≤ 4 and mono / diepoxy reactive diluents.

[0051] Secondly, the present invention also provides a method for preparing conductive copper paste suitable for high-precision 3D printing as described above, comprising the following steps:

[0052] (S.1) Preparation of copper nanoparticles;

[0053] (S.2) The conductive copper paste is obtained by mixing the nano-copper particles with the dispersing agent.

[0054] In step (S.2), after mixing the nano-copper particles with the dispersing agent, the mixture is subjected to multiple mixing and degassing processes, and then ground using a three-roll mill to finally obtain nano-conductive copper paste.

[0055] Further preferably, the parameters for the slurry degassing treatment are set as follows: rotation speed 800-2000 rpm, and absolute pressure value of vacuum pump ≥0.2 kPa.

[0056] Thirdly, the conductive copper paste described above is also provided, or the conductive copper paste prepared by the above preparation method can achieve high-precision 3D printing at a scale of ≥1μm, thereby enabling its application in the fields of precision 3D printing, precision optics, micro-nano chips, and printed electronics.

[0057] Preferably, the substrate materials suitable for the conductive copper paste include, but are not limited to, glass, silicon wafers, PI, stainless steel, ceramics, etc.

[0058] Therefore, the present invention has the following beneficial effects:

[0059] (1) Beneficial effects: The method for preparing low-temperature conductive copper paste of the present invention adjusts the solubility of the system to a suitable value by introducing polar solvents (alcohol-based or amine-based solvents) and weakly polar solvents based on the compatibility between the ligands on the particle surface and the organic solvent. This effectively removes impurities such as free ligands and reaction byproducts between particles, while retaining the effective coating of organic ligands on the particle surface, thus enabling the copper nanoparticles to have antioxidant properties and uniform dispersion.

[0060] (2) Beneficial effects: The method for preparing low-temperature conductive copper paste of the present invention uses alcohol-soluble resin as binder and reducing agent as protective agent. The copper paste obtained has good dispersibility and stability and can be sintered at low temperature. Its resistivity after sintering at 200℃ is <40μΩ·cm, and the resistivity change range is <10% after being stored at -20℃ for 360 days.

[0061] (3) Beneficial effects: The preparation method of conductive copper paste described in this invention has a simple operation process, low cost (only 1 / 3 of silver paste), and green and environmentally friendly production process. It can replace the highly polluting acid copper electroplating process in the printed electronics industry and has extremely high replacement value.

[0062] (4) Beneficial effects: The conductive copper paste of the present invention is suitable for precision 3D printing with a scale of ≥1μm. The raw material utilization rate is higher than that of the existing screen printing process. It has good adhesion performance on flexible devices or electronic components such as HJT batteries, PCBs, and PIs, reaching 5B, and is suitable for mass production. Attached Figure Description

[0063] Figure 1 The purification mechanism of this invention;

[0064] in, Figure 1 Left: Copper nanoparticles in the reaction stock solution, with ligands coated on the surface of the copper particles. The system contains a large number of reaction byproducts and free ligands.

[0065] Figure 1 In the middle: a weakly polar solvent is introduced to initially disperse copper nanoparticles. The reaction byproducts dissolve in the solvent, but a large number of ligands remain entangled on the particle surface.

[0066] Figure 1 Right: Polar solvents are added sequentially to adjust the polarity of the system to a suitable value, so that the copper nanoparticles are coated with bound ligands and separated from the free ligands.

[0067] Figure 2 This is a SEM image of the copper paste after sintering in Example 1.

[0068] Figure 3 SEM image of copper paste after sintering in Example 2.

[0069] Figure 4SEM image of copper paste after sintering, Comparative Example 1.

[0070] Figure 5 The image shown is a SEM image of the copper paste after sintering, as shown in Comparative Example 2. Detailed Implementation

[0071] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0072] Example 1

[0073] (1) Dissolve 0.48 mol of hydrazine hydrate and 0.3 mmol of polyvinylpyrrolidone (K30) in 60 ml of deionized water and stir at 800 r / min with a mechanical stirrer at room temperature until the particles are completely dissolved.

[0074] (2) Dissolve 20g of copper sulfate pentahydrate in 60ml of water, adjust the pH value to 9-10 with ammonia, and after mixing evenly, slowly inject it into the above solution at a flow rate of 2ml / min using a syringe pump. Stir the reaction with magnetic force at 1500r / min for 3h, and then keep stirring and heat at 60℃ for 1h with an electric heating plate to obtain a nano copper dispersion.

[0075] (3) Add 250 ml of ethyl acetate to the nano-copper dispersion and stir magnetically at 500 r / min for 5 min. Then add 100 ml of ethanol solution in 5 portions, stirring magnetically at 500 r / min for 10 min and let stand for 60 min. Remove the supernatant, transfer the precipitate to a centrifuge tube and centrifuge at 9000 rpm in a Beckman high-speed centrifuge for 10 min. Dry in an argon atmosphere at 50℃ for 1 h to obtain copper elemental particles with a particle size of 80-130 nm.

[0076] (4) A dispersion formulation composed of 70 wt% alcohol-soluble epoxy resin, 10 wt% ascorbic acid and 20 wt% butyl glycidyl ether was prepared. The dispersion formulation was added to the nano-copper particles at a ratio of 2:3. The mixture was degassed and stirred for 8 min at 1500 rpm and 0.8 kPa vacuum using a Thinky planetary mixer. After thorough grinding and dispersion by a three-roll mill, a conductive copper paste with a viscosity of 10 Pa·s was obtained.

[0077] Example 2:

[0078] (1) Dissolve 0.08 mol anhydrous citric acid, 0.15 mol hypophosphoric acid and 0.4 mmol polyvinylpyrrolidone (K23-27) in 100 ml of deionized water and stir at 200 r / min with a magnetic stirrer at room temperature until the particles are completely dissolved.

[0079] (2) A 1.875 mol / L copper hydroxide solution was slowly added to the above solution at a flow rate of 0.5 ml / min using a constant pressure dropping funnel. The mixture was then stirred magnetically at 1200 r / min for 3 h and heated in an oil bath at 60 °C for 1 h to obtain a nano copper dispersion.

[0080] (3) Add 200 ml of n-hexane to the nano copper dispersion and stir magnetically at 500 r / min for 5 min. Then add 150 ml of methanol solution in 5 portions, stirring magnetically at 500 r / min for 10 min and let stand for 60 min. Remove the supernatant, transfer the precipitate to a centrifuge tube and centrifuge at 9000 rpm in a Beckman high-speed centrifuge for 10 min. Dry in an argon atmosphere at 50 °C for 1 h to obtain copper elemental particles with a particle size of 50-120 nm.

[0081] (4) Prepare a dispersion formulation consisting of 60 wt% alcohol-soluble phenolic resin, 30 wt% ethylene glycol, and 10 wt% ascorbic acid. Add the dispersion formulation to the nano-copper particles at a ratio of 1:9. Defoam and stir for 10 min using a Thinky planetary mixer at 800 rpm and 0.4 kPa vacuum. After thorough grinding and dispersion using a three-roll mill, a conductive copper paste with a viscosity of 1000 Pa·s is obtained.

[0082] Example 3:

[0083] (1) Dissolve 0.48 mol of hydrazine hydrate and 0.3 mmol of polyvinylpyrrolidone (K30) in 60 ml of deionized water and stir at 800 r / min with a mechanical stirrer at room temperature until the particles are completely dissolved.

[0084] (2) Dissolve 20g of copper sulfate pentahydrate in 80ml of water, adjust the pH value to 9-10 with ammonia, and after mixing evenly, slowly inject it into the above solution at a flow rate of 10ml / min using a syringe pump. Stir the reaction with magnetic force at 1500r / min for 3h, and then keep stirring and heat at 60℃ for 1h with an electric heating plate to obtain a nano copper dispersion.

[0085] (3) Add 250 ml of ethyl acetate to the nano-copper dispersion and stir magnetically at 500 r / min for 5 min. Then add 100 ml of isopropanol solution in 5 portions, and stir magnetically at 500 r / min for 10 min. Let stand for 60 min. Remove the supernatant, take the precipitate into a centrifuge tube and centrifuge at 9000 rpm in a Beckman high-speed centrifuge for 10 min. Dry in an argon atmosphere at 50℃ for 1 h to obtain copper elemental particles with a particle size of 80-130 nm.

[0086] (4) A dispersion formulation composed of 70 wt% alcohol-soluble epoxy resin, 12.5 wt% oxalic acid and 17.5 wt% propylene glycidyl ether was prepared. The dispersion formulation was added to the nano-copper particles at a ratio of 2:3. The mixture was degassed and stirred for 8 min at 1500 rpm and 0.8 kPa vacuum using a Thinky planetary mixer. After thorough grinding and dispersion by a three-roll mill, a conductive copper paste with a viscosity of 10 Pa·s was obtained.

[0087] Example 4:

[0088] (1) Dissolve 0.48 mol of hydrazine hydrate and 0.1 mmol of polyacrylic acid (Mw=50,000) in 80 ml of ethylene glycol and stir at 1200 r / min with a magnetic stirrer at room temperature until the particles are completely dissolved.

[0089] (2) Add ammonia to 30g of 60wt% copper acetate solution to adjust the pH value to 9-10. After mixing evenly, use a peristaltic pump to slowly inject the solution into the above solution at a flow rate of 2ml / min. Stir the reaction with magnetic force at 500r / min for 3h and then keep stirring. Heat in a water bath at 150℃ for 30min to obtain a nano copper dispersion.

[0090] (3) Add 250 ml of ethyl acetate to the nano-copper dispersion and stir magnetically at 500 r / min for 5 min. Then add 150 ml of dimethylformamide solution in 5 portions, and stir magnetically at 500 r / min for 10 min. Let stand for 60 min. Remove the supernatant, take the precipitate into a centrifuge tube and centrifuge at 9000 rpm in a Beckman high-speed centrifuge for 10 min. Dry in an argon atmosphere at 50℃ for 1 h to obtain copper elemental particles with a particle size of 400-500 nm.

[0091] (4) A dispersion formulation composed of 30 wt% acrylic resin, 65 wt% ethylene glycol monomethyl ether and 5 wt% formic acid was prepared. The dispersion formulation was added to the nano-copper particles at a ratio of 3:7. The mixture was degassed and stirred for 5 min at 2000 rpm and 1.0 kPa vacuum using a Thinky planetary mixer. After thorough grinding and dispersion using a three-roll mill, a conductive copper paste with a viscosity of 400 Pa·s was obtained.

[0092] Comparative Example 1

[0093] (1) Dissolve 0.48 mol of hydrazine hydrate and 0.3 mmol of polyvinylpyrrolidone (K30) in 60 ml of deionized water and stir at 800 r / min with a mechanical stirrer at room temperature until the particles are completely dissolved.

[0094] (2) Dissolve 20g of copper sulfate pentahydrate in 60ml of water, adjust the pH value to 9-10 with ammonia, and after mixing evenly, slowly inject it into the above solution at a flow rate of 2ml / min using a syringe pump. Stir the reaction with magnetic force at 1500r / min for 3h, and then keep stirring and heat at 60℃ for 1h with an electric heating plate to obtain a nano copper dispersion.

[0095] (3) Add 350 ml of ethyl acetate to the nano copper dispersion and stir magnetically at 500 r / min for 15 min, then let stand for 60 min. Remove the supernatant, take the precipitate into a centrifuge tube and centrifuge at 9000 rpm in a Beckman high-speed centrifuge for 10 min. Dry in an argon atmosphere at 50℃ for 1 h to obtain copper elemental particles with a particle size of 80-130 nm;

[0096] (4) A dispersion formulation composed of 70 wt% alcohol-soluble epoxy resin, 10 wt% ascorbic acid and 20 wt% butyl glycidyl ether was prepared. The dispersion formulation was added to the nano-copper particles at a ratio of 2:3. The mixture was degassed and stirred for 8 min at 1500 rpm and 0.8 kPa vacuum using a Thinky planetary mixer. After thorough grinding and dispersion by a three-roll mill, a conductive copper paste with a viscosity of 10 Pa·s was obtained.

[0097] Comparative Example 2

[0098] (1) Dissolve 0.48 mol of hydrazine hydrate and 0.3 mmol of polyvinylpyrrolidone (K30) in 60 ml of deionized water and stir at 800 r / min with a mechanical stirrer at room temperature until the particles are completely dissolved.

[0099] (2) Dissolve 20g of copper sulfate pentahydrate in 60ml of water, adjust the pH value to 9-10 with ammonia, and after mixing evenly, slowly inject it into the above solution at a flow rate of 2ml / min using a syringe pump. Stir the reaction with magnetic force at 1500r / min for 3h, and then keep stirring and heat at 60℃ for 1h with an electric heating plate to obtain a nano copper dispersion.

[0100] (3) Add 350 ml of ethanol to the nano copper dispersion and stir magnetically at 500 r / min for 15 min, then let it stand for 60 min. Remove the supernatant, take the precipitate into a centrifuge tube and centrifuge at 9000 rpm in a Beckman high-speed centrifuge for 10 min. Dry it at 50℃ in an argon atmosphere for 1 h to obtain copper elemental particles with a particle size of 80-130 nm.

[0101] (4) A dispersion formulation composed of 70 wt% alcohol-soluble epoxy resin, 10 wt% ascorbic acid and 20 wt% butyl glycidyl ether was prepared. The dispersion formulation was added to the nano-copper particles at a ratio of 2:3. The mixture was degassed and stirred for 8 min at 1500 rpm and 0.8 kPa vacuum using a Thinky planetary mixer. After thorough grinding and dispersion by a three-roll mill, a conductive copper paste with a viscosity of 10 Pa·s was obtained.

[0102] Comparative Example 3

[0103] (1) Dissolve 0.3 mmol of polyvinylpyrrolidone (K30) in 70 ml of deionized water, then add 20 g of copper sulfate pentahydrate, adjust the pH value to 9-10 with ammonia, and stir with a mechanical stirrer at 800 r / min at room temperature until the particles are completely dissolved.

[0104] (2) Dissolve 0.48 mol of hydrazine hydrate in 50 ml of water and add it directly to the above solution. Stir the mixture magnetically at 200 r / min for 3 h and then heat it in an oil bath at 150 °C for 1 h while maintaining the stirring state. After the reaction is completed, cool it to obtain a nano copper dispersion.

[0105] (3) Add 250 ml of ethyl acetate to the nano-copper dispersion and stir magnetically at 500 r / min for 5 min. Then add 100 ml of ethanol solution in 5 portions, stirring magnetically at 500 r / min for 10 min each time, and let stand for 60 min. Remove the supernatant, transfer the precipitate to a centrifuge tube, centrifuge at 9000 rpm in a Beckman high-speed centrifuge for 10 min, and dry in an argon atmosphere at 50℃ for 1 h to obtain copper elemental particles with a particle size of 500-800 nm.

[0106] (4) A dispersion formulation composed of 70 wt% alcohol-soluble epoxy resin, 10 wt% ascorbic acid and 20 wt% butyl glycidyl ether was prepared. The dispersion formulation was added to the nano-copper particles at a ratio of 2:3. The mixture was degassed and stirred for 8 min at 1500 rpm and 0.8 kPa vacuum using a Thinky planetary mixer. After thorough grinding and dispersion by a three-roll mill, a conductive copper paste with a viscosity of 100 Pa·s was obtained.

[0107] Comparative Example 4

[0108] Preparation methods (1)-(3) are the same as in Example 1.

[0109] (4) A dispersion formulation composed of 70 wt% oily epoxy resin, 10 wt% ascorbic acid and 20 wt% butyl glycidyl ether was prepared. The dispersion formulation was added to the nano-copper particles at a ratio of 2:3. The mixture was degassed and stirred for 8 min at 1500 rpm and 0.8 kPa vacuum using a Thinky planetary mixer. After thorough grinding and dispersion by a three-roll mill, a conductive copper paste with a viscosity of 10 Pa·s was obtained.

[0110] [Performance Testing]

[0111] The detection method is as follows:

[0112] (1) Particle size observation: The size and morphology of copper nanoparticles were characterized using a Phenom scanning electron microscope.

[0113] The specific method is as follows: ① Take a small amount of copper paste and dilute it in deionized water or organic solvent at a ratio of 1:1000; ② Disperse the diluted solution thoroughly, take a small amount with a dropper and add it to the surface of the carrier, and heat it to remove excess solvent; ③ After preparing the sample and spraying it with gold, send the sample for observation to obtain image information on the size and morphology of copper nanoparticles.

[0114] (2) Resistivity test: The resistivity of copper paste was measured using the Ruikeweiye FT-340 four-probe square resistance tester.

[0115] The specific method is as follows: ① The prepared conductive copper paste is coated onto the glass substrate using a coating machine and sintered at 300℃ for 60 minutes under a nitrogen atmosphere to obtain a conductive copper film; ② The thickness of the copper film sample after high-temperature sintering is measured using a step meter; ③ The corresponding parameters are set in the sheet resistance meter, and the four probes are adjusted to be above the sample to be tested and then pressed down vertically to touch it; ④ After the readings stabilize, the sheet resistance, resistivity and other data are recorded.

[0116] (3) Viscosity test: The viscosity of copper paste was measured using a Brookfield DVNextCP cone-plate viscometer.

[0117] The specific steps are as follows: ① Zero the torque and adjust the cone-plate spacing to 0.0005 inches; ② Place 0.5 ml of conductive copper paste in the center of the sample cup, set the rotation speed and test time, with the rotation speed set to 0.5 rpm; ③ Start the test to obtain and record the material viscosity information.

[0118] (4) Adhesion test

[0119] ① The prepared conductive copper paste is coated onto the glass substrate using a coating machine and sintered at 200°C for 60 min under a nitrogen atmosphere to obtain a conductive copper film;

[0120] ② Using ASTM D3359-2017 as the test standard, use a cross-cutting tool to cut the surface of the test piece at a cutting speed of 20-50 mm / s;

[0121] ③ Rotate the specimen 90° and repeat the above operation on the cut to form a grid pattern;

[0122] ④ Use a soft brush to brush the diagonals on both sides of the grid pattern, brushing lightly 5 times each way.

[0123] ⑤ Use 3M 600-1PK test tape to perform a peel test and evaluate the material's adhesion performance.

[0124] Characterization of experimental results:

[0125] The prepared conductive copper paste was sealed and stored at 0-5℃, and its sintering stability was monitored during the 360-day storage period. The SEM images of the copper pastes prepared in Examples 1, 2, 1, and 2 after sintering are shown below. Figures 2-5 As shown in Table 1, the particle morphology and resistivity changes after sintering of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.

[0126] Table 1. Particle morphology and resistivity changes after sintering in Examples 1-4 and Comparative Examples 1-4

[0127] .

[0128] According to Table 1 and Figure 2-5 Experimental test results show that the conductive copper paste obtained by the preparation method described in this invention has high particle morphology uniformity, strong interparticle compatibility after sintering, and low resistivity of only 9.8 μΩ·cm. At the same time, it maintains a resistivity change of <10% after being stored at 0~-5℃ for 1 year.

[0129] Table 2 Adhesion of slurries from Examples 1-4 and Comparative Examples 1-4 after sintering in different media

[0130] .

[0131] According to the experimental test results in Table 2, the conductive copper paste obtained by the preparation method of the present invention has sintering adhesion performance on substrates such as glass, silicon wafers, PI, ceramics, and stainless steel that meets the ASTM D3359-2017 test standard 5B performance and is superior to the schemes in Comparative Examples 1-4.

Claims

1. A low-temperature copper paste suitable for high-precision 3D printing, characterized in that, This includes copper nanoparticles and dispersing agents; among which, The surface of the copper nanoparticles is coated with ligands; The dispersion formulation consists of a binder, a protective agent, and a diluent; The resistivity of the low-temperature copper paste is <40μΩ·cm after sintering at 200℃; The adhesive is any one or more of alcohol-soluble epoxy resin, alcohol-soluble phenolic resin, and acrylic resin; The protective agent is any one or more of hypophosphite, ascorbic acid, formic acid, oxalic acid, thiols, primary alcoholamines, and secondary alcoholamines; wherein, the general chemical formula of primary alcoholamines is OH-X-NH2, where X is 2 ≤ carbon number ≤ 6; and the general chemical formula of secondary alcoholamines is NH-(Y-OH)2, where Y is 2 ≤ carbon number ≤ 6. The ligand is one or more of polyacrylic acid, polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol; The method for preparing the copper nanoparticles is as follows: (1) Disperse the reducing agent and ligand in a solvent to form a mixed solution; (2) The copper precursor solution is gradually added to the mixed solution so that the nucleation and growth of the copper precursor are asynchronous during the reduction process, and a dispersion of nano-copper particles is obtained. (3) First, add a weakly polar solvent to the dispersion of nano-copper particles and stir to disperse. Then, add a polar solvent in batches, stir and let stand, remove the supernatant, take the precipitate and dry it to obtain nano-scale nano-copper particles. In step (3), the polar solvent is any one or a combination of two of the following: alcohol solvents with 1 ≤ carbon number ≤ 4 or amine solvents with 2 ≤ carbon number ≤ 6. The weakly polar solvent is any one or a combination of esters, ketones, or alkane solvents; The molar ratio of the polar solvent to the weakly polar solvent is 1:1 to 1:

4.

2. The low-temperature copper paste suitable for high-precision 3D printing according to claim 1, characterized in that, In step (1), the reducing agent is one or more of the following: hydrazine hydrate, hypophosphite, sodium hypophosphite, sodium borohydride, ascorbic acid, and citric acid.

3. The low-temperature copper paste suitable for high-precision 3D printing according to claim 1, characterized in that, In step (2), the concentration of the copper precursor solution is 1-7.5 mol / L; The copper precursor solution was added at a rate of 0.2-10 ml / min.

4. A low-temperature copper paste suitable for high-precision 3D printing according to claim 1 or 3, characterized in that, The copper precursor is one or more of copper sulfate pentahydrate, copper formate, copper acetate, copper chloride, and copper nitrate.

5. The low-temperature copper paste suitable for high-precision 3D printing according to claim 1, characterized in that, The diluent is any one or more of low molecular weight alcohols with 2 ≤ carbon number ≤ 4 and mono / diepoxy reactive diluents.

6. The method for preparing low-temperature copper paste suitable for high-precision 3D printing as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (S.1) Preparation of copper nanoparticles; (S.2) The low-temperature copper paste is obtained by mixing the nano-copper particles with the dispersing agent.

7. The low-temperature copper paste suitable for high-precision 3D printing as described in any one of claims 1 to 5, or the low-temperature copper paste suitable for high-precision 3D printing prepared by the preparation method described in claim 6, can achieve high-precision 3D printing at a scale of ≥1μm, and has applications in the fields of precision 3D printing, precision optics, micro-nano chips, and printed electronics.

Images