Preparation method and application of low-viscosity copper powder in slurry

Abstract

The invention discloses a preparation method and application of low-viscosity copper powder in slurry, and relates to the technical field of copper powder preparation.The preparation method comprises the steps that S1, initial copper powder is added into a fluoride solution to obtain a mixed solution, S2, quaternary ammonium salt is added into the mixed solution to serve as an auxiliary reagent, the materials are stirred together for a reaction, and a reaction solution is obtained; and S3, the reaction liquid is subjected to sedimentation washing and low-temperature vacuum drying dewatering, and then low-viscosity copper powder in the slurry is obtained. The fluoride is R1nNH (4-n) F, wherein R1 is methyl, ethyl, propyl or butyl; and n is an integer of 0-4. According to the method for changing the viscosity of the copper powder by regulating and controlling the surface hydroxyl of the existing commercial copper powder, the viscosity of slurry directly applied by the copper powder can be effectively reduced, the viscosity of the copper powder in a reaction solution can also be reduced, the concentration of the synthesized silver-coated copper powder is improved while high dispersity is guaranteed, and the reaction activity, sintering activity and conductivity of the copper powder are not affected.

Description

Technical Field

[0001] This invention relates to the field of copper powder preparation technology, and in particular to a method for preparing low-viscosity copper powder in a slurry and its application. Background Technology

[0002] Copper powder and copper paste are important conductive materials widely used in electronics, photovoltaics, and printed circuits. Copper powder, with its high conductivity (second only to silver), low cost, and ease of processing, is often used as a conductive filler. Copper paste, composed of copper powder and an organic carrier, combines conductivity and printability, and can replace precious metal pastes in PCB circuits and photovoltaic grid electrodes, significantly reducing production costs. It shows great application potential in emerging fields such as flexible electronics and 5G devices. The viscosity of powders and pastes significantly affects their processability and usability, mainly determined by the properties of the powder itself and the paste formulation. The properties of the powder itself include interparticle van der Waals forces, electrostatic attraction, surface tension, surface wettability, and surface adsorbates (interfacial properties), as well as particle size and shape factors such as particle shape, roughness, and particle size distribution.

[0003] High viscosity affects the viscosity of copper powder when it is prepared into a suspension. In the liquid-phase preparation of silver-coated copper powder, it affects the uniform dispersion of the copper powder, causing agglomeration of the prepared silver-coated copper powder. When preparing copper paste with copper powder, the high viscosity of the copper powder affects the requirements for stirring equipment during paste preparation. More importantly, high viscosity affects the printing performance of the paste. Many factors in the paste formulation affect viscosity, but changing the paste formulation to reduce viscosity requires consideration of the compatibility with the organic system. Directly reducing the copper powder solid content in the paste or increasing the solvent will directly lead to a decline in performance. Changing particle size and shape factors such as particle shape, roughness, and particle size distribution requires control during the copper powder synthesis stage. This necessitates changes to the existing synthesis process and will directly impact subsequent applications. In addition, surface modification of copper powder is often performed to adjust its viscosity and dispersion in pastes or reaction solutions. These methods all alter the reactivity of the copper powder, affecting its performance in further applications.

[0004] Patent application CN116809921A discloses a high-photosensitive reactive slurry for pure copper photopolymerization 3D printing and its preparation method. This patent provides a high-photosensitive reactive slurry for pure copper photopolymerization 3D printing by selecting one or more acrylate monomer reactive diluents with low viscosity, such as dipropylene glycol diacrylate and cyclic trimethylolpropane formal acrylate, and compounding them with additives to obtain a low-viscosity copper powder slurry. This patent reduces the viscosity of the copper slurry by adding a large amount of reactive diluent (mass ratio 5.6%–9.4%), but the adjustable range of other components and copper powder mass (87%–92%) is narrow, with a viscosity of 1030–5890 mPa·s, limiting its application scenarios. Patent CN119786267A uses formate and organic thiols to modify copper powder to control its viscosity, reducing it to 812.7 mPa·s; however, residual modifiers, especially sulfur, severely affect electrical properties. Summary of the Invention

[0005] This invention aims to provide a method for preparing low-viscosity copper powder in slurry and its application. It addresses the existing method of regulating the surface hydroxyl groups of commercial copper powder to change the viscosity of the copper powder. This method can effectively reduce the viscosity of the slurry for direct application of copper powder, as well as the viscosity of copper powder in the reaction solution. It ensures high dispersibility while increasing the concentration of synthesized silver-coated copper powder, without affecting the reactivity, sintering activity, and conductivity of the copper powder.

[0006] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows: A method for preparing low-viscosity copper powder in a slurry includes the following steps: S1. Add the initial copper powder to a fluoride solution with a mass concentration of 0.1%-10% to obtain a mixed solution, wherein the mass of the fluoride solution is 2 to 20 times the mass of the initial copper powder; S2. Add quaternary ammonium salt as an auxiliary reagent to the mixture and stir together to obtain a reaction solution. The mass of quaternary ammonium salt is 0.1%-5% of the initial copper powder mass. S3. After the reaction solution is subjected to sedimentation washing and low-temperature vacuum drying to remove water, copper powder with low viscosity in the slurry is obtained.

[0007] The copper powder is prepared by three methods: PVD, atomization, and liquid phase reduction, with a particle size between 100nm and 5μm. The fluoride is R 1n NH (4-n) F, where R1 is methyl, ethyl, propyl, or butyl; n is an integer from 0 to 4; The fluoride is preferably one or more selected from ammonium fluoride, tetramethylammonium fluoride, tetraethylammonium fluoride, and tetrapropylammonium fluoride; The mass of the fluoride solution is 2 to 5 times the mass of the initial copper powder; The mass concentration of the fluoride solution is 0.1%-2%; The quaternary ammonium salt is one or both of tetramethylammonium hydroxide and tetrapropylammonium hydroxide, preferably tetramethylammonium hydroxide; The mass of the quaternary ammonium salt is 0.1%-2% of the initial copper powder mass; In step S2, the reaction temperature is 0℃-90℃; preferably, the reaction temperature is 20℃-60℃. In step S2, the reaction time is 30 minutes to 360 minutes, preferably 60 minutes to 180 minutes.

[0008] A copper powder with low viscosity in slurry is prepared by the above preparation method.

[0009] An application of low-viscosity copper powder in a slurry includes mixing the aforementioned copper powder with diethylene glycol butyl ether acetate, ethyl cellulose, phenolic resin, epoxy resin curing agent, and borosilicate bismuth glass powder to prepare a copper powder slurry.

[0010] The copper powder slurry contains: copper powder with a mass fraction of 80%-94%; diethylene glycol butyl ether acetate with a mass fraction of 0.5%-5%; ethyl cellulose with a mass fraction of 0.5%-3%; phenolic resin with a mass fraction of 2%-6%; epoxy resin curing agent with a mass fraction of 2%-43%; and borosilicate bismuth glass powder with a mass fraction of 1%-34%. An application of low-viscosity copper powder in a slurry includes preparing silver-coated copper powder through the following steps: A1. Prepare a copper suspension with a mass fraction of 5%-10% by mixing the above copper powder with pure water; A2. In a copper suspension, stir at 300 rpm for 5 minutes at room temperature, then add 10%-30% disodium tetraethylamine oxalate as a complexing agent (based on the weight of the copper powder), and stir at 300 rpm for 5 minutes at room temperature. Next, add 1.0%-3.0% silver nitrate as a sensitizer (based on the weight of the copper powder), and stir at 300 rpm for 5 minutes at room temperature. Then, add 27% citric acid (based on the weight of the copper powder), and stir at 300 rpm for 5 minutes at room temperature. Finally, add 0.1 mol / L silver ammonia solution as a coating agent, and continue stirring. The silver ammonia in the silver ammonia solution accounts for 18% of the weight of the copper powder. A3. After the reaction is complete, the silver-coated copper powder is obtained by washing with pure water and drying under low temperature vacuum.

[0011] The beneficial effects of this invention are: 1. This invention can directly adjust the viscosity of copper powder without changing the copper powder preparation process and application conditions. In synthesis and application, viscosity adjustment is limited by the formula and has a narrow adjustable range. The method used in this invention has a wide adjustable range. The method of removing hydroxyl groups by the combined action of fluoride and quaternary ammonium salt to adjust viscosity leaves no organic residue and does not affect downstream applications compared to the use of modifiers. The conditions are mild and the process is simple, making it suitable for large-scale industrial production applications.

[0012] 2. After oxidation, copper powder undergoes high-temperature acid and alkali washing, which activates its relatively inert surface and introduces hydroxyl groups. The hydrogen bonding energy between hydroxyl groups is higher than the energy of the electrostatic and van der Waals forces between copper powder particles, leading to increased powder viscosity. This increased viscosity results in high paste viscosity, which is detrimental to printability, causing uneven printing, difficulty in demolding, and other problems. This invention utilizes the highly electronegative fluoride ions in fluorides to activate the hydroxyl groups on the metal surface. During activation, the quaternary ammonium salt can simultaneously interact with multiple activated copper hydroxyl groups. Due to the strong electronegativity of fluoride ions and their ability to activate hydroxyl groups, as well as the quaternary ammonium salt-assisted dehydration reaction between the activated hydroxyl groups, two hydroxyl groups can be dehydrated at relatively low temperatures, achieving the goal of eliminating hydroxyl groups and thus reducing the viscosity of the copper powder in the paste. Attached Figure Description

[0013] Figure 1 This is a schematic flowchart of the method for preparing low-viscosity copper powder in a slurry according to the present invention.

[0014] Figure 2 This is a scanning electron microscope image of the silver-coated copper powder prepared from copper powder in Example 1 of the present invention.

[0015] Figure 3 This is a scanning electron microscope image of the silver-coated copper powder prepared from the copper powder in Comparative Example 1 of this invention.

[0016] Figure 4 This is a scanning electron microscope image of the silver-coated copper powder prepared from the copper powder in Comparative Example 6 of this invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0018] Example 1 This embodiment provides a low-viscosity copper powder in a slurry. In this embodiment, such as... Figure 1 As shown, low-viscosity copper powder in the slurry is prepared through the following steps: S1. Add 50 g of initial 3.0 μm PVD copper powder to twice its mass of a 1% fluoride solution to obtain a mixture. S2. Add 2% of the initial copper powder mass of quaternary ammonium salt as an auxiliary reagent to the mixture, and stir together at 60℃ for 100 min to obtain the reaction solution. S3. After the reaction solution is washed by sedimentation and dried under low temperature vacuum to remove water, copper powder with hydroxyl groups removed is obtained.

[0019] In this embodiment, the fluoride is ammonium fluoride; The quaternary ammonium salt is tetramethylammonium hydroxide.

[0020] Example 2 The difference between this embodiment and Embodiment 1 is that, in this embodiment, In step S1, the fluoride is tetra-n-butyldihydrotrifluoride; the fluoride mass concentration is 1%; and the mass of the fluoride solution is 5 times the mass of the initial copper powder. In step S2, the quaternary ammonium salt is tetrapropylammonium hydroxide; the mass of the quaternary ammonium salt is 0.2% of the initial copper powder mass; in step S2, the reaction temperature is 20°C; the reaction time is 60 minutes; and the remaining conditions are the same as in Example 1.

[0021] Example 3 Compared with Example 1, the difference in this embodiment is that, in step S1, the fluoride is tetrabutylammonium fluoride; the mass concentration of the fluoride is 2%; and the mass of the fluoride solution is 3 times the mass of the initial copper powder. In step S2, the quaternary ammonium salt is a mixture of tetramethylammonium hydroxide and tetrapropylammonium hydroxide in a mass ratio of 1:1; the mass of the quaternary ammonium salt is 0.1% of the initial copper powder mass; the reaction temperature is 20°C; the reaction time is 90 minutes; and the remaining conditions are the same as in Example 1.

[0022] Example 4 Compared with Example 1, the difference in this embodiment is that, in step S1, the fluoride is tetramethylammonium fluoride; the mass concentration of the fluoride is 10%; and the mass of the fluoride solution is twice the mass of the initial copper powder. In step S2, the quaternary ammonium salt is tetramethylammonium hydroxide; the mass of the quaternary ammonium salt is 5% of the initial copper powder mass; the reaction temperature is 90°C; the reaction time is 30 minutes; and the remaining conditions are the same as in Example 1.

[0023] Example 5 Compared with Example 1, the difference in this embodiment is that, in step S1, the fluoride is tetraethylammonium fluoride; the mass concentration of the fluoride is 5%; and the mass of the fluoride solution is 10 times the mass of the initial copper powder. In step S2, the quaternary ammonium salt is tetramethylammonium hydroxide; the mass of the quaternary ammonium salt is 4% of the initial copper powder mass; the reaction temperature is 0°C; the reaction time is 360 minutes; and the remaining conditions are the same as in Example 1. Example 6 Compared with Example 1, the difference in this embodiment is that, in step S1, the fluoride is tetrapropylammonium fluoride; the mass concentration of the fluoride is 2%; and the mass of the fluoride solution is 20 times the mass of the initial copper powder. In step S2, the quaternary ammonium salt is tetramethylammonium hydroxide; the mass of the quaternary ammonium salt is 2% of the initial copper powder mass; the reaction temperature is 50°C; the reaction time is 180 minutes; and the remaining conditions are the same as in Example 1. Example 7 The difference between this embodiment and Embodiment 1 is that, in this embodiment, in step S1, the fluoride is a mixture of ammonium fluoride and tetramethylammonium fluoride in a mass ratio of 1:1; the mass concentration of the fluoride is 0.1%; and the mass of the fluoride solution is 8 times the mass of the initial copper powder. In step S2, the quaternary ammonium salt is tetramethylammonium hydroxide; the mass of the quaternary ammonium salt is 3% of the initial copper powder mass; the reaction temperature is 10°C; the reaction time is 50 minutes; and the remaining conditions are the same as in Example 1. Example 8 The difference between this embodiment and Embodiment 1 is that the copper powder used in this embodiment is 100nm PVD copper powder, while the other conditions are the same as in Embodiment 1.

[0024] Example 9 The difference between this embodiment and Embodiment 1 is that the copper powder used in this embodiment is 4μm atomized copper powder, while the other conditions are the same as in Embodiment 1.

[0025] Example 10 The difference between this embodiment and Example 1 is that the copper powder used in this embodiment is 1.5μm liquid-phase reduction copper powder, while the other conditions are the same as in Example 1.

[0026] Comparative Example 1 The difference between this comparative example and Example 1 is that no fluoride was added in this comparative example, while the other conditions are the same as in Example 1.

[0027] Comparative Example 2 The difference between this comparative example and Example 1 is that no quaternary ammonium salt was added in this comparative example, while the other conditions are the same as in Example 1.

[0028] Comparative Example 3 The difference between this comparative example and Example 1 is that the mass of fluoride added was changed, and the mass of the fluoride solution was 30 times the mass of the initial copper powder; the other conditions were the same as in Example 1.

[0029] Comparative Example 4 The difference between this comparative example and Example 1 is that the mass of fluoride added was changed, and the mass concentration of the fluoride was 0.05%; the mass of the fluoride solution was 1.5 times the mass of the initial copper powder; the other conditions were the same as in Example 1.

[0030] Comparative Example 5 The difference between this comparative example and Example 1 is that the mass of the added quaternary ammonium salt was changed, and the mass of the quaternary ammonium salt was 10% of the initial copper powder mass; the other conditions were the same as in Example 1.

[0031] Comparative Example 6 The difference between this comparative example and Example 1 is that the mass of the added quaternary ammonium salt was changed, and the mass of the quaternary ammonium salt was 0.05% of the initial copper powder mass; the other conditions were the same as in Example 1.

[0032] Application Example 1 This application example provides an application of low-viscosity copper powder in a slurry, comprising mixing copper powder obtained in Examples 1-10 and Comparative Examples 1-6 with diethylene glycol butyl ether acetate, ethyl cellulose, phenolic resin, epoxy resin curing agent, and borosilicate bismuth glass powder to prepare a copper powder slurry.

[0033] The copper powder slurry contains 80% copper powder by mass; 5% diethylene glycol butyl ether acetate by mass; 3% ethyl cellulose by mass; 6% phenolic resin by mass; 3% epoxy resin curing agent by mass; and 3% borosilicate bismuth glass powder by mass.

[0034] Application Example 2 This application example provides an example of the use of low-viscosity copper powder in a slurry, including the preparation of silver-coated copper powder through the following steps: A1. The copper powder obtained in Examples 1-10 and Comparative Examples 1-6 was prepared into a copper suspension with a mass fraction of 5%-10% using pure water. A2. Select PVD copper powder with an average particle size of 3 μm and a maximum particle size of 8.3 μm. Stir the powder in a copper suspension at 300 rpm for 5 minutes at room temperature. Then add 10% disodium tetraethylamine oxalate (based on the weight of the copper powder) as a complexing agent and stir at 300 rpm for 5 minutes at room temperature. Next, add 1.0% silver nitrate (based on the weight of the copper powder) as a sensitizer and stir at 300 rpm for 5 minutes at room temperature. Then add 27% citric acid (based on the weight of the copper powder) and stir at 300 rpm for 5 minutes at room temperature. Finally, add 0.1 mol / L silver ammonia solution as a coating agent and continue stirring. The silver ammonia in the silver ammonia solution accounts for 18% of the copper powder's weight. A3. After the reaction is complete, the silver-coated copper powder is obtained by washing with pure water and drying under low temperature vacuum.

[0035] like Figure 2 The image shown is a scanning electron microscope image of the silver-coated copper powder prepared from copper powder in Example 1 of the present invention.

[0036] like Figure 3 The image shown is a scanning electron microscope (SEM) image of the silver-coated copper powder prepared from the copper powder in Comparative Example 1 of this invention.

[0037] like Figure 4 The image shown is a scanning electron microscope (SEM) image of the silver-coated copper powder prepared from the copper powder in Comparative Example 6 of this invention.

[0038] The copper powder slurry and silver-coated copper powder prepared in Application Examples 1 and 2 were subjected to performance tests, and the test methods included: Copper powder slurry viscosity test: The viscosity of the slurry was tested using a rotational viscometer at a temperature of about 25°C in a three-stage constant shear rate test mode (3ITT) of low-high-low.

[0039] The morphology and dispersibility of the silver-coated copper powder were detected using SEM, and the particle size and particle size distribution of the silver-coated copper powder were detected using a wet laser particle size analyzer. The performance parameters of the copper powders obtained in Examples 1-10 and Comparative Examples 1-6, as well as the copper powder slurries and silver-coated copper powders prepared from them, are shown in Table 1. Table 1 Performance parameters of copper powder and its prepared copper powder slurry and silver-coated copper powder

[0040] Examples 1-7 and Comparative Examples 1-6 reveal that the type, concentration, and amount of fluoride, as well as the type and amount of quaternary ammonium salt, uniformly affect the elimination of hydroxyl groups and the regulation of viscosity. Analysis of Example 1 and Comparative Examples 1-4 shows that... Figure 2 and Figure 3It is known that silver-coated copper powder without the addition of quaternary ammonium salt exhibits particle adhesion and agglomeration, and the silver layer is rougher. The type, concentration, and amount of fluoride directly affect its removal effect on the hydroxyl groups on the copper powder surface, thus affecting the viscosity of the copper powder and the morphology of the finished silver-coated copper powder. Quaternary ammonium salt, as an auxiliary reagent, also plays an important role in the regulation of copper powder viscosity and is crucial for the synergistic dehydration of hydroxyl groups. In Example 1, tetramethylammonium hydroxide was used, with a viscosity of 707 mPa·s; in Example 3, a mixture of tetramethylammonium hydroxide and tetrapropylammonium hydroxide was used, with a viscosity of 1371 mPa·s, indicating that different quaternary ammonium salts or their mixtures may produce different auxiliary effects. This is mainly due to the strength of the interaction between the spatial structure of the quaternary ammonium salt molecules and the hydroxyl groups on the copper powder surface. The temperature and time of copper powder treatment mainly affect hydroxyl removal from thermodynamic and kinetic factors. In Comparative Examples 5 and 6, both excessive and insufficient addition of quaternary ammonium salts affected the viscosity control. Excessive quaternary ammonium salts significantly increased the alkalinity of the copper powder reaction solution, which, under strongly alkaline conditions, could corrode the copper powder, resulting in poor treatment performance and high viscosity. Figure 2 and Figure 4 It can be seen that, compared with Example 1, the silver-coated copper powder in Comparative Example 6 exhibits slight agglomeration, with a uniform overall silver layer growth and the presence of smaller, coarse silver particles. In Examples 8-10, different types and particle sizes of copper powder were used. Due to the influence of copper powder type and particle size, testing the particle size and particle size distribution of the silver-coated copper powder is not very meaningful, and the viscosity of the copper powder in the slurry also varies, but is higher than that in Example 1. The intrinsic particle size and surface morphology of copper powder both affect viscosity, indicating that the preparation method of the present invention has certain applicability to different types and particle sizes of copper powder, but the optimal conditions may vary depending on the characteristics of the copper powder.

[0041] The above analysis shows that the type, concentration, and amount of fluoride, the type and amount of quaternary ammonium salt, and the reaction temperature and time all significantly affect the viscosity of copper powder. This invention, by precisely controlling these factors, achieves effective regulation of copper powder viscosity, providing a reliable method for preparing low-viscosity copper powder and its application in slurries.

[0042] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for preparing low-viscosity copper powder in a slurry, characterized in that: Includes the following steps: S1. Add the initial copper powder to a fluoride solution with a mass concentration of 0.1%-10% to obtain a mixed solution, wherein the mass of the fluoride solution is 2 to 20 times the mass of the initial copper powder; S2. Add quaternary ammonium salt as an auxiliary reagent to the mixture and stir together to obtain a reaction solution. The mass of quaternary ammonium salt is 0.1%-5% of the initial copper powder mass. S3. After the reaction solution is washed by sedimentation and dried under low temperature vacuum to remove water, copper powder with low viscosity in the slurry is obtained. The fluoride is R 1n NH (4-n) F, where: R1 is methyl, ethyl, propyl or butyl; n is an integer from 0 to 4.

2. The method for preparing low-viscosity copper powder in a slurry according to claim 1, characterized in that: The fluoride is one or more of ammonium fluoride, tetramethylammonium fluoride, tetraethylammonium fluoride, and tetrapropylammonium fluoride.

3. The method for preparing low-viscosity copper powder in a slurry according to claim 1, characterized in that: The mass of the fluoride solution is 2 to 5 times the mass of the initial copper powder.

4. The method for preparing low-viscosity copper powder in a slurry according to claim 1, characterized in that: The mass concentration of the fluoride solution is 0.1%-2%.

5. The method for preparing low-viscosity copper powder in a slurry according to claim 1, characterized in that: The quaternary ammonium salt is one or both of tetramethylammonium hydroxide and tetrapropylammonium hydroxide.

6. The method for preparing low-viscosity copper powder in a slurry according to claim 5, characterized in that: The quaternary ammonium salt is tetramethylammonium hydroxide.

7. The method for preparing low-viscosity copper powder in a slurry according to claim 1, characterized in that: The mass of the quaternary ammonium salt is 0.1%-2% of the initial copper powder mass.

8. The method for preparing low-viscosity copper powder in a slurry according to claim 1, characterized in that: In step S2, the reaction temperature is 0℃-90℃.

9. The method for preparing low-viscosity copper powder in a slurry according to claim 8, characterized in that: In step S2, the reaction temperature is 20℃-40℃.

10. The method for preparing low-viscosity copper powder in a slurry according to claim 1, characterized in that: In step S2, the reaction time is 30 minutes to 360 minutes.

11. The method for preparing low-viscosity copper powder in a slurry according to claim 10, characterized in that: In step S2, the reaction time is 60-180 minutes.

12. An application of low-viscosity copper powder in a slurry, characterized in that: The method includes mixing copper powder obtained by any one of claims 1-11 with diethylene glycol butyl ether acetate, ethyl cellulose, phenolic resin, epoxy resin curing agent, and borosilicate bismuth glass powder to prepare a copper powder slurry; wherein the copper powder slurry has a mass fraction of 80%-94%; a mass fraction of diethylene glycol butyl ether acetate of 0.5%-5%; a mass fraction of ethyl cellulose of 0.5%-3%; a mass fraction of phenolic resin of 2%-6%; a mass fraction of epoxy resin curing agent of 2%-4%; and a mass fraction of borosilicate bismuth glass powder of 1%-4%.

13. An application of low-viscosity copper powder in a slurry, characterized in that: The silver-coated copper powder is prepared through the following steps: A1. The copper powder obtained by any one of claims 1-11 is prepared into a copper suspension with a mass fraction of 5%-10% by pure water. A2. In a copper suspension, stir at 300 rpm for 5 minutes at room temperature, then add 10%-30% disodium tetraethylamine oxalate as a complexing agent (based on the weight of the copper powder), and stir at 300 rpm for 5 minutes at room temperature. Next, add 1.0%-3.0% silver nitrate as a sensitizer (based on the weight of the copper powder), and stir at 300 rpm for 5 minutes at room temperature. Then, add 27% citric acid (based on the weight of the copper powder), and stir at 300 rpm for 5 minutes at room temperature. Finally, add 0.1 mol / L silver ammonia solution as a coating agent, and continue stirring. The silver ammonia in the silver ammonia solution accounts for 18% of the weight of the copper powder. A3. After the reaction is complete, the silver-coated copper powder is obtained by washing with pure water and drying under low temperature vacuum.

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