Preparation method of liquid-phase in-situ self-assembly nano shell-coated micron core composite copper powder

Abstract

The invention relates to the technical field of copper powder preparation, and provides a preparation method of liquid-phase in-situ self-assembly nano-shell-coated micron-core composite copper powder, a specific inducer is introduced into a liquid-phase reduction system, copper sulfate is adopted as a copper salt, and sodium hypophosphite or VC is adopted as a reducing agent, so that one-time forming of a micron-core-nano-shell composite structure is realized; the problems of non-uniform particle size distribution, high energy consumption, low yield and the like in a traditional copper powder preparation method are effectively solved; according to the prepared composite copper powder, the low-temperature sintering driving force brought by the nanometer shell layer is obtained while the process-friendly characteristics of being easy to filter, easy to wash, easy to dry and the like of micron powder are reserved, the initial sintering temperature can be reduced to about 150 DEG C, and the machining performance of the copper powder under the low-temperature condition is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of copper powder preparation technology, and more specifically, to a method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron core composite copper powder. Background Technology

[0002] With the rapid development of electronics, electric vehicles, 5G communications, aerospace, and other fields, the demand for high-performance, reliable energy conversion and high-frequency operation is constantly increasing, making power semiconductors increasingly important in power conversion and efficient energy utilization. Traditional silicon-based semiconductor devices exhibit limitations under harsh conditions such as high temperature, high pressure, and high frequency, while third-generation semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) are gradually leading the new development of power semiconductor technology due to their superior characteristics such as high frequency, high power, high temperature resistance, and lower energy loss.

[0003] However, the emergence of third-generation semiconductor materials and devices has placed higher demands on packaging materials. Currently, commonly used chip interconnect materials mainly include high-lead alloys, gold alloys, and nano-silver pastes. However, lead is a toxic substance and does not meet environmental protection requirements; gold alloys and nano-silver pastes are mainly composed of precious metals, which are costly and not conducive to widespread application. In addition, the reliability of electronic devices using existing nano-metal solder paste materials is questioned due to the electromigration and ion migration characteristics of silver.

[0004] To address the aforementioned issues, researchers have begun to focus on copper as an alternative material. Copper has electrical and thermal conductivity similar to that of silver, and its raw material price is about one percent of that of silver, making it a promising material for applications. However, traditional methods for preparing copper powder, such as physical pulverization and gas-phase methods, often suffer from uneven particle size distribution, high energy consumption, and low yield, making it difficult to meet the market demand for high-quality nano-copper powder [6]. Therefore, developing a novel method for preparing copper powder that can achieve nanoscale particle size while maintaining micron-scale process-friendly characteristics, and also possesses good antioxidant properties and storage stability, has become a key focus and challenge in current research.

[0005] A search revealed that publication number CN117900469A discloses a method for preparing copper powder with nano-sized copper powder densely coating micron-sized copper flakes. This patent uses copper powder composed of two nano-sized copper particles, where the micron-sized copper flakes are completely and tightly coated by the two sizes of nano-copper particles, with copper particles of 5-15 nm tightly surrounding nano-copper particles of 40-100 nm. The copper powder prepared by this method is mixed with an organic solvent to form a copper paste. The resulting copper paste promotes the sintering and densification of copper particles at low temperatures, resulting in a high-strength interconnected structure. However, the particle size distribution of the copper powder in this patent's preparation method still needs further optimization to obtain a narrower particle size distribution and a more uniform particle shape.

[0006] For example, patent CN116652174A discloses a copper nanomaterial and its preparation method. This patent involves dispersing commercial copper powder in a solvent, adding acidic reagents and a coating agent, undergoing a reduction reaction, and finally washing with an alcohol solvent and vacuum drying to obtain the copper nanomaterial. The copper nanomaterial prepared by this method is stable and can be prepared in large quantities with high stability, making it suitable for the electronic packaging field. However, the preparation process of this patent still needs optimization to further improve the performance and stability of the copper nanomaterial.

[0007] In summary, the existing technology has the following drawbacks:

[0008] 1. Traditional methods for preparing copper powder, such as physical pulverization and gas-phase methods, suffer from problems such as uneven particle size distribution, high energy consumption, and low yield, making it difficult to meet the market demand for high-quality nano-copper powder;

[0009] 2. In the existing technology, the solid-liquid separation process of copper powder is difficult, and the separation and purification process of pure nano copper powder is complicated, which affects the quality and performance of the product;

[0010] 3. Current copper powder preparation methods struggle to simultaneously achieve micron-level process-friendly characteristics and nano-level performance, particularly in low-temperature sintering, making it difficult to meet the needs of different application fields;

[0011] 4. In the existing technology, the antioxidant properties and storage stability of copper powder need to be improved, which can easily lead to oxidation and performance degradation of copper powder during storage and use;

[0012] 5. Existing methods for preparing nano-copper powder still have shortcomings in optimizing process parameters, making it difficult to further improve the performance of copper powder, especially in terms of electrical conductivity and thermal stability;

[0013] To address the aforementioned issues, this application proposes a method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder. Summary of the Invention

[0014] The purpose of this invention is to provide a method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron core composite copper powder. By introducing a specific "inducer" during the liquid-phase reduction process, the "micron core-nanoshell" composite structure is formed in one step, solving problems such as uneven particle size distribution, difficulty in solid-liquid separation, insufficient driving force for low-temperature sintering, and poor antioxidant properties in the copper powder preparation process.

[0015] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder, comprising the following steps:

[0016] S1. Mix the copper source and inducer A at a mass ratio of 1:0.1 to 3, add deionized water, and stir at 20℃ to 30℃ for 30 min to 60 min to obtain a copper salt solution;

[0017] S2. Slowly add the reducing agent to the copper salt solution, so that the molar ratio of the reducing agent to the copper source is 1:0.05 to 0.95, and stir for 15 min to 30 min;

[0018] S3. Add NaOH or ammonia to adjust the pH to 9-12, and continue stirring for 20-40 minutes;

[0019] S4. Slowly add inducing agent B to the reaction solution, so that its mass ratio with copper source is 1:0.01-0.5. After stirring evenly, heat to 65-90℃, add the remaining reducing agent, so that the molar ratio of reducing agent to copper source is 1:0.3-3.5, and react for 1-4 hours.

[0020] S5. After the reaction is complete, quickly cool to room temperature, separate the solid by vacuum filtration or centrifugation, wash multiple times with ethanol or isopropanol, and finally wash with deionized water 3 to 5 times.

[0021] Preferably, the copper powder obtained in step 5 is vacuum dried at 50℃~80℃ for 4h~8h, or subjected to low-temperature inert gas drying in an inert gas burner for 3h~5h.

[0022] Preferably, after the copper powder is dried, it is lightly sieved to remove agglomerated particles and then placed in a drying oven filled with nitrogen and sealed for storage.

[0023] Preferably, the copper source in step 1 is selected from copper sulfate, copper nitrate, copper acetate or more.

[0024] Preferably, in step 1, the inducing agent A is one or more of EDTA salt, PEG, sodium hexametaphosphate, and citrate.

[0025] Preferably, the reducing agent in step 2 is one or more of ascorbic acid, hypophosphite, and hydrazine hydrate.

[0026] Preferably, in step 4, the inducing agent B is one or more of the following: nitrogen-containing / sulfur-containing ligands, quaternized polyelectrolytes, amphoteric surfactants with pyridine / imidazolium groups, and metaphosphates.

[0027] Preferably, the particle size of the micron-sized nuclei is 3μm to 10μm.

[0028] Preferably, the thickness of the nanoshell is 100 nm to 200 nm.

[0029] Preferably, the morphology of the nanoshell-enclosed micron core composite structure is spherical or polygonal.

[0030] The beneficial effects of this invention are:

[0031] 1. This invention introduces a specific inducing agent into a liquid-phase reduction system, uses copper sulfate as the copper salt and sodium hypophosphite or VC as the reducing agent, and realizes the one-time molding of a "micron core-nano shell" composite structure, effectively solving the problems of uneven particle size distribution, high energy consumption and low yield in traditional copper powder preparation methods;

[0032] 2. The composite copper powder prepared by this invention retains the process-friendly properties of micron powder, such as easy filtration, easy washing, and easy drying, while obtaining the low-temperature sintering driving force brought by the nano shell. The initial sintering temperature can be reduced to about 150°C, which significantly improves the processing performance of copper powder under low-temperature conditions.

[0033] 3. By adding composite inducers (EDTA salt, PEG, sodium hexametaphosphate, citrate, etc.), this invention achieves precise control over the in-situ surface activation, selective complexation, and nucleation barrier of micron-sized copper nuclei, effectively avoiding the phase separation and local agglomeration problems in the remixing process of micro- and nano-sized preparations, and ensuring the uniformity of the composition and morphology of copper powder.

[0034] 4. The composite copper powder prepared by this invention significantly improves the antioxidant properties and storage stability of copper powder through selective complexation by an inducing agent and dense coating of a nanoshell, effectively solving the problems of easy oxidation and performance degradation of copper powder during storage and use in the prior art;

[0035] 5. This invention can be achieved using aqueous phase reduction, normal pressure conditions, and common equipment. The process parameters are easy to optimize and control, and it has good scalability and mass production prospects. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the state of copper powder in Example 1;

[0038] Figure 2 This is a schematic diagram of the state of copper powder in Example 2;

[0039] Figure 3 This is a schematic diagram of the state of copper powder in Example 3;

[0040] Figure 4 This is a TMA thermomechanical analysis diagram. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0042] Example 1

[0043] This embodiment provides a method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder, including the following steps:

[0044] S1. Mix 0.5 mol copper sulfate and 0.15 mol sodium hexametaphosphate, add 500 ml deionized water, and stir at 25 °C for 45 min to obtain a copper salt solution;

[0045] S2. Slowly add 0.15 mol of ascorbic acid to the copper salt solution to make the molar ratio of ascorbic acid to copper sulfate 1:0.3, and stir for 20 min;

[0046] S3. Add 10ml of ammonia water to adjust the pH to 10, and continue stirring for 30 minutes;

[0047] S4. Add inducing agent: Slowly add 0.02 mol of ethylene glycol monobutyl ether ketone (ODH) to the reaction solution, stir until homogeneous, heat to 75°C, add the remaining ascorbic acid to make the molar ratio of ascorbic acid to copper sulfate 1:1.2, and react for 2 hours;

[0048] S5. Termination and solid-liquid separation: After the reaction is complete, rapidly cool to room temperature, separate the solid by centrifugation, wash three times with ethanol, and finally wash four times with deionized water;

[0049] S6. The obtained solid was dried under vacuum at 60°C for 6 hours;

[0050] S7. After drying, the product is sieved through a 200-mesh sieve to remove agglomerated particles, and then placed in a drying oven and sealed with nitrogen.

[0051] The resulting composite copper powder, such as Figure 1 As shown, the particle size distribution is in the range of 7-10 μm, and the thickness of the nanoshell is 800-1000 nm.

[0052] Scanning electron microscopy revealed that the nanoshells were uniformly coated on the surface of the micron core, with a tight interface between them.

[0053] Example 2

[0054] This embodiment provides a method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder, including the following steps:

[0055] S1. Mix 1 mol of copper nitrate with 0.3 mol of triethanolamine, add 1000 ml of ethylene glycol, and stir for 30 min to obtain a copper salt solution;

[0056] S2. Slowly add 0.3 mol of sodium hypophosphite to the copper salt solution to make the molar ratio of sodium hypophosphite to copper nitrate 1:0.9, and stir for 25 min;

[0057] S3. Add 15 ml of sodium hydroxide solution to adjust the pH to 11, and continue stirring for 35 min;

[0058] S4. Slowly add 0.03 mol of diethylenetriamine (DETDA) to the reaction solution, stir until homogeneous, heat to 80°C, add the remaining sodium hypophosphite, making the molar ratio of sodium hypophosphite to copper nitrate 1:1.5, and react for 3 hours;

[0059] S5. After the reaction is complete, rapidly cool to room temperature, separate the solid by vacuum filtration, wash twice with isopropanol, and finally wash five times with deionized water;

[0060] S6. The obtained solid was dried under vacuum at 70°C for 7 hours;

[0061] S7. After drying, the product is sieved through a 150-mesh sieve to remove agglomerated particles, and then placed in a drying oven and sealed with nitrogen.

[0062] The resulting composite copper powder, such as Figure 2 As shown, the particle size distribution is in the range of 6-9 μm, and the thickness of the nanoshell is 110-190 nm.

[0063] Scanning electron microscopy revealed that the nanoshells uniformly coated the surface of the micron-sized core, with a tight interface between them; Figure 4 The test data shown indicates that the composite copper powder begins to sinter at 150℃, and the nano-copper powder on the surface plays a good role in sintering.

[0064] Example 3

[0065] This embodiment provides a method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder, including the following steps:

[0066] S1. Mix 2 mol of copper acetate with 0.6 mol of sodium metaphosphate, add 800 ml of anhydrous ethanol, and stir for 50 min to obtain a copper salt solution;

[0067] S2. Slowly add 0.6 mol of hydrazine hydrate to the copper salt solution to make the molar ratio of hydrazine hydrate to copper acetate 1:0.3, and stir for 20 min;

[0068] S3. Add 20ml of hydrochloric acid to adjust the pH to 9.5, and continue stirring for 25 minutes;

[0069] S4. Slowly add 0.04 mol of ethanolamine (MEA) to the reaction solution, stir until homogeneous, heat to 70°C, add the remaining hydrazine hydrate to make the molar ratio of hydrazine hydrate to copper acetate 1:1.8, and react for 2.5 h;

[0070] S5. After the reaction is complete, rapidly cool to room temperature, separate the solid by centrifugation, wash three times with ethanol, and finally wash three times with deionized water;

[0071] S6. The obtained solid was dried under vacuum at 65°C for 5 hours;

[0072] S7. After drying, the product is sieved through a 180-mesh sieve to remove agglomerated particles, and then placed in a drying oven and sealed with nitrogen.

[0073] The resulting composite copper powder, such as Figure 3 As shown, the particle size distribution is in the range of 5-8 μm, and the thickness of the nanoshell is 190-280 nm.

[0074] Scanning electron microscopy revealed that the nanoshells were uniformly coated on the surface of the micron core, with a tight interface between them.

[0075] Combination Figure 4 As shown, the self-assembled nanoshell-encapsulated micron-core composite copper powder of this application (composed of a 5-7 micron copper core and a 100-300 nanometer copper particle layer) exhibits significant two-stage sintering characteristics. The curves of dimensional change rate (dL / L0) and thermal expansion coefficient change rate (T.α) in the figure clearly show two key shrinkage stages:

[0076] The first-stage shrinkage peak appears around 150℃, which is attributed to the low-temperature surface activation and sintering neck formation induced by the high surface energy of the outer layer nano-copper particles, thus achieving the initial conductive connection of the material at a lower temperature.

[0077] The second-stage main shrinkage peak appears in the 300℃ to 350℃ range, corresponding to the micron-level nuclear rearrangement and overall synergistic densification process assisted by nanolayers.

[0078] The test results confirm that the core-shell structure design adopted in this application not only effectively reduces the initial sintering temperature of copper materials, but also controls the shrinkage rate throughout the process to a low level of about 6%, which is significantly better than traditional pure nano copper paste. This effectively overcomes technical defects such as excessive volume shrinkage and coating cracking during the sintering process, and has both excellent low-temperature sintering activity and high-temperature dimensional stability.

[0079] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; it should be understood that the terms "opening", "upper", "lower", "thickness", "top", "middle", "length", "inner", "around", etc., which indicate orientation or positional relationship, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0080] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder, characterized in that, Includes the following steps: S1. Mix the copper source and inducer A at a mass ratio of 1:0.1 to 3, add deionized water, and stir at 20℃ to 30℃ for 30 min to 60 min to obtain a copper salt solution; S2. Slowly add the reducing agent to the copper salt solution, so that the molar ratio of the reducing agent to the copper source is 1:0.05 to 0.95, and stir for 15 min to 30 min; S3. Add NaOH or ammonia to adjust the pH to 9-12, and continue stirring for 20-40 minutes; S4. Slowly add inducing agent B to the reaction solution, so that its mass ratio with copper source is 1:0.01-0.

5. After stirring evenly, heat to 65-90℃, add the remaining reducing agent, so that the molar ratio of reducing agent to copper source is 1:0.3-3.5, and react for 1-4 hours. S5. After the reaction is complete, quickly cool to room temperature, separate the solid by vacuum filtration or centrifugation, wash multiple times with ethanol or isopropanol, and finally wash with deionized water 3 to 5 times.

2. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 1, characterized in that: The copper powder obtained in step S5 is vacuum dried at 50℃~80℃ for 4h~8h, or dried at low temperature in an inert gas burner for 3h~5h.

3. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 2, characterized in that: After the copper powder is dried, it is sieved through an 80-300 mesh screen to remove agglomerated particles, and then stored in a drying oven filled with nitrogen and sealed.

4. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 1, characterized in that: In step 1, the copper source is selected from copper sulfate, copper nitrate, copper acetate, or a combination thereof.

5. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 1, characterized in that: In step 1, inducer A is one or more of EDTA salt, PEG, sodium hexametaphosphate, and citrate.

6. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 1, characterized in that: In step 2, the reducing agent is one or more of ascorbic acid, hypophosphite, and hydrazine hydrate.

7. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 1 or 5, characterized in that: In step 4, inducer B is one or more of the following: nitrogen- or sulfur-containing ligands, quaternized polyelectrolytes, amphoteric surfactants with pyridine / imidazolium groups, and metaphosphates.

8. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 1, characterized in that: The particle size of the micron nucleus ranges from 3 μm to 10 μm.

9. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 1, characterized in that: The thickness of the nanoshell is 100nm to 300nm.

10. The method for preparing liquid-phase in-situ self-assembled nanoshell-encapsulated micron-core composite copper powder according to claim 1, characterized in that: The morphology of the nanoshell-enclosed micron core composite structure is spherical or polygonal.

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