Nano Cu@Sn powder, and preparation method and application thereof

Abstract

The application belongs to the technical field of nanocomposites, and particularly relates to a kind of nano Cu@Sn powder and its preparation method and application. The preparation method of the nano Cu@Sn powder comprises the following steps: S1, under nitrogen protection, ammonia is added to an aqueous solution of copper salt, then a vinylpyrrolidone-vinyl acetate copolymer is added, the temperature is raised, an aqueous solution of hydrazine hydrate is added, stirring is continued, after the stirring is completed, the product is centrifuged under nitrogen protection, washed, and dried to obtain nano copper powder; S2, a complexing agent, a complexing agent, and an antioxidant are dissolved uniformly in a eutectic ionic liquid, nano copper powder is added, stirring is performed until the nano copper powder is uniformly dispersed, a stannous chloride hydrochloride solution is added, stirring is continued, an EVA solution is added, stirring is continued, after the stirring is completed, the product is centrifuged, washed, and dried to obtain Cu@Sn powder. The solder prepared by the application has high mechanical strength of solder joints and excellent high-temperature reliability.

Description

Technical Field

[0001] This invention belongs to the field of nanocomposite materials technology, specifically relating to a nano Cu@Sn powder, its preparation method, and its application. Background Technology

[0002] In recent years, the high-speed rail, electric vehicle and aerospace fields have developed rapidly. As the core component of power control, power semiconductor devices face increasingly harsh service environments and have increasingly higher requirements for operating temperature. In particular, semiconductor devices based on third-generation wide bandgap semiconductors such as SiC and GaN require welding materials with higher temperature resistance and higher reliability, which urgently need to be developed.

[0003] Currently, the most researched high-temperature resistant soldering materials include high-melting-point alloy solders, nano-sintered silver, and transient liquid-phase diffusion soldering materials. The ability of soldering materials to assemble at lower temperatures and operate at higher temperatures is a practical requirement in manufacturing. However, high-melting-point alloy solders generally require high reflow temperatures, which may cause thermal damage to the chip and its surrounding packaging structure. While nano-sintered silver technology can be sintered at low temperatures, resulting in solder layers that can withstand higher operating temperatures, it is costly and unsuitable for industrial production. Furthermore, nano-silver solders suffer from silver migration issues, which can lead to excessively high porosity in the solder layer and reduced device reliability. Therefore, transient liquid-phase diffusion soldering materials are a very promising solution for high-temperature electronic packaging. Traditional transient liquid-phase diffusion soldering involves first melting a low-melting-point metal, which then undergoes liquid-solid interdiffusion with a high-melting-point metal to form a high-temperature resistant intermetallic compound. This method has the advantages of low cost and no environmental pollution, but it suffers from drawbacks such as incomplete interdiffusion, where residual tin melts at high temperatures, causing reliability issues, and excessively long process times.

[0004] Cu@Sn core-shell structured powder is one method to solve the problem of traditional transient liquid phase diffusion soldering. For example, Chinese patent CN103753049B discloses a Cu@Sn core-shell structured high-temperature solder and its preparation method. The core-shell structured metal powder contains only Sn and Cu elements, and has a core-shell structure with Sn coating Cu particles, with particle sizes between 1μm and 20μm. However, the solder prepared using this Cu@Sn core-shell structured metal powder can only operate at 350℃.

[0005] Chinese patent CN114043122B discloses a high-temperature solder containing Cu@Sn core-shell bimetallic powder, its preparation method, and its application. The core-shell structured metal powder contains only Sn and Cu elements, exhibiting a core-shell structure where Sn coats Cu particles with a particle size between 0.5 μm and 1.5 μm. However, the connection time for this Cu@Sn core-shell bimetallic powder high-temperature solder is relatively long, ranging from 600 s to 3600 s.

[0006] The applicant's previous research results, Chinese patent with publication number CN120438890A, also disclosed a method for preparing Cu@Sn metal powder. However, the Cu@Sn metal powder of this technical solution has poor solderability when used alone. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a nano-Cu@Sn powder, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] The first aspect of this invention provides a method for preparing nano-Cu@Sn powder, comprising the following steps:

[0010] S1. Under nitrogen protection, ammonia water was added to the aqueous solution of copper salt, followed by vinylpyrrolidone-vinyl acetate copolymer. The temperature was raised, and hydrazine hydrate aqueous solution was added. When the pH value reached 10, the addition of hydrazine hydrate aqueous solution was stopped, and stirring was continued. After stirring, the product was centrifuged under nitrogen protection, washed, and dried to obtain nano copper powder.

[0011] S2. Add the ligand, complexing agent, and antioxidant to the eutectic ionic liquid and dissolve them evenly. Add the nano copper powder, stir and disperse evenly, then add the hydrochloric acid solution of stannous chloride and continue stirring. Add the EVA solution and continue stirring. After stirring, centrifuge the product, wash it, and dry it to obtain Cu@Sn powder.

[0012] Preferably, step S1 specifically involves: under nitrogen protection, adding ammonia to an aqueous solution of copper salt, stopping the addition of ammonia after the solution becomes completely clear, then adding vinylpyrrolidone-vinyl acetate copolymer, heating to 75-85°C, and adding an aqueous solution of hydrazine hydrate at 75-85°C while stirring. When the pH value reaches 10, stopping the addition of the aqueous solution of hydrazine hydrate, and continuing to stir for 0.5-1 h. After stirring, the product is centrifuged under nitrogen protection, washed three times with distilled water and then with ethanol, and dried to obtain nano-copper powder.

[0013] Preferably, the aqueous solution of the copper salt is an aqueous solution of copper sulfate.

[0014] Preferably, the molar concentration of the copper sulfate solution is 0.1-0.2 mol / L.

[0015] Preferably, the mass concentration of the ammonia water is 8-15 wt%.

[0016] Preferably, the mass concentration of the hydrazine hydrate aqueous solution is 2-3 wt%.

[0017] Preferably, the mass ratio of the copper salt to the vinylpyrrolidone-vinyl acetate copolymer is 1:1.5-2.5.

[0018] Preferably, the vinylpyrrolidone-vinyl acetate copolymer is obtained by copolymerizing 1-vinyl-2-pyrrolidone and vinyl acetate in a mass ratio of 3:2, and the K value is 25.2-30.8.

[0019] Previously, the applicant used polyvinylpyrrolidone and sodium lauryl sulfonate as dispersants to avoid agglomeration of the nano-copper powder during the preparation process. However, the inventor found that the dispersibility was not good. In solving this technical problem, the inventor unexpectedly discovered that using vinylpyrrolidone-vinyl acetate copolymer to replace polyvinylpyrrolidone and sodium lauryl sulfonate resulted in nano-copper powder with excellent dispersibility, which laid a good foundation for the subsequent tin-coated nano-copper powder. The obtained nano-Cu@Sn powder formed solder joints with high mechanical strength and good high-temperature reliability in the solder prepared.

[0020] Preferably, step S2 specifically involves: adding the ligand, complexing agent, and antioxidant to a eutectic ionic liquid and dissolving them evenly; adding nano-copper powder and stirring to disperse it evenly; adding stannous chloride hydrochloric acid solution in three batches, with each batch spaced 15-20 minutes apart; continuing to stir for 0.5-1 hour; adding EVA solution and continuing to stir for 20-30 minutes; centrifuging the product after stirring; washing it three times with distilled water and then with ethanol; and drying it to obtain Cu@Sn powder.

[0021] The above step S2 is performed at room temperature.

[0022] Preferably, the ligand is thiourea.

[0023] Preferably, the complexing agent is EDTA-2Na.

[0024] Preferably, the antioxidant is selected from at least one of hydroquinone, catechol, resorcinol, pyrogallol, and biphenyl pyrogallol.

[0025] Preferably, the mass ratio of the ligand, complexing agent, antioxidant and nano copper powder is 15-20:0.1-0.5:0.1-0.5:8-12.

[0026] Preferably, the eutectic ionic liquid is a mixture of choline chloride and thiourea in a molar ratio of 1:0.5-1.5.

[0027] Preferably, the method for preparing the eutectic ionic liquid is as follows: choline chloride and thiourea are stirred at 80℃-100℃ until they become completely colorless and transparent liquids, thus obtaining the eutectic ionic liquid.

[0028] Preferably, the mass ratio of the eutectic ionic liquid to the nano-copper powder is 20-30:1.

[0029] Preferably, the molar concentration of the stannous chloride hydrochloric acid solution is 4-6 mol / L.

[0030] Preferably, the mass ratio of stannous chloride to nano-copper powder is 0.3-0.5:1.

[0031] Preferably, the EVA solution is a mixture of EVA and toluene.

[0032] Preferably, the EVA and toluene are mixed for 10-12 hours.

[0033] Preferably, the mass concentration of the EVA solution is 2-6 wt%.

[0034] Preferably, the mass ratio of EVA to nano-copper powder is 0.05-0.1:1.

[0035] Previously, the applicant used polyethylene glycol-2000 as a dispersant and surfactant in the preparation of Cu@Sn powder to improve the dispersibility of the nano-copper powder in water. However, polyethylene glycol-2000 would remain coated on the particle surface and was not easily decomposed, affecting the subsequent welding process. To solve this technical problem, this invention creatively replaces the water reaction system with a eutectic ionic liquid system and adds an appropriate amount of EVA solution during the process. This results in a uniform and complete core-shell structure of Cu@Sn powder without affecting the subsequent welding process, and effectively improves the strength and high-temperature reliability of the solder joint. This is likely because the eutectic ionic liquid has extremely high polarity and suitable viscosity, resulting in more uniform tin deposition. The EVA molecular chain contains highly polar carbonyl groups, which can strongly interact with the surface of the nano-copper powder, inducing uniform reduction and deposition of tin ions to form a complete coating layer. At the same time, EVA is a thermoplastic polymer that melts and flows first during the welding heating process, which helps the solder wet. Subsequently, it decomposes and volatilizes at higher temperatures, avoiding the residue of organic matter, thereby improving the mechanical strength and high-temperature reliability of the solder joint.

[0036] The second aspect of the present invention provides nano-Cu@Sn powder prepared by the above-described method for preparing nano-Cu@Sn powder.

[0037] The third aspect of this invention provides the application of the above-mentioned nano-Cu@Sn powder in the preparation of conductive pastes, sintering pastes, solders, and solder pastes.

[0038] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0039] 1. This invention uses vinylpyrrolidone-vinyl acetate copolymer to replace polyvinylpyrrolidone and sodium lauryl sulfonate, resulting in nano-copper powder with excellent dispersibility, laying a good foundation for subsequent tin-coated nano-copper powder. The obtained nano-Cu@Sn powder has high mechanical strength and good high-temperature reliability in the solder joints formed by the prepared solder.

[0040] 2. This invention creatively replaces the water reaction system with a eutectic ionic liquid system and adds an appropriate amount of EVA solution during the process, which can obtain a uniform and complete core-shell structure of Cu@Sn powder without affecting the subsequent welding process, and effectively improves the strength and high-temperature reliability of the weld joint. Attached Figure Description

[0041] Figure 1 Here is a scanning electron microscope image of the nano-copper powder from Example 1;

[0042] Figure 2 This is a scanning electron microscope image of Cu@Sn powder from Example 1;

[0043] Figure 3 Here is a scanning electron microscope image of the nano-copper powder from Example 2;

[0044] Figure 4 This is a scanning electron microscope image of Cu@Sn powder from Example 2;

[0045] Figure 5 EDX image of Cu@Sn powder in Example 2;

[0046] Figure 6 This is a scanning electron microscope image of the nano-copper powder in Comparative Example 1. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Example 1

[0049] This embodiment provides a method for preparing nano-Cu@Sn powder, including the following steps:

[0050] S1. Under nitrogen protection, 10wt% ammonia solution was added to 1L of copper sulfate aqueous solution (0.15mol / L). After the solution became completely clear, the addition of ammonia solution was stopped. Then, 36g of vinylpyrrolidone-vinyl acetate copolymer was added. The temperature was raised to 80℃, and 2.5wt% hydrazine hydrate aqueous solution was added at 80℃ with stirring. When the pH value reached 10, the addition of hydrazine hydrate aqueous solution was stopped, and stirring was continued for 1h. After stirring, the product was centrifuged under nitrogen protection, washed three times with distilled water and then with ethanol, and dried to obtain nano copper powder.

[0051] S2. Dissolve 18g thiourea, 0.3g EDTA-2Na, and 0.3g hydroquinone in 190g eutectic ionic liquid until homogeneous. Add 10g of nano copper powder and stir to disperse evenly. Then, add 5.27mL of stannous chloride hydrochloric acid solution in three batches, 20min apart, and continue stirring for 1h. Add 20g of 5wt% EVA solution and continue stirring for 30min. After stirring, centrifuge the product and wash it three times with distilled water and then with ethanol. Dry the product to obtain Cu@Sn powder.

[0052] The vinylpyrrolidone-vinyl acetate copolymer is obtained by copolymerizing 1-vinyl-2-pyrrolidone and vinyl acetate in a mass ratio of 3:2, with a K value of 25.2-30.8. (Yuang Technology Co., Ltd., Product Name: VP / VA64 Powder)

[0053] The eutectic ionic liquid is obtained by stirring choline chloride and thiourea at a molar ratio of 1:1 at 90°C until they become a colorless and transparent liquid.

[0054] The EVA solution was prepared by mixing EVA and toluene for 12 hours.

[0055] The scanning electron microscope image of the nano-copper powder in this embodiment is as follows: Figure 1 As shown, the scanning electron microscope image of Cu@Sn powder is as follows. Figure 2 As shown.

[0056] Example 2

[0057] This embodiment provides a method for preparing nano-Cu@Sn powder, including the following steps:

[0058] S1. Under nitrogen protection, 10 wt% ammonia solution was added to 1 L of copper sulfate aqueous solution (0.15 mol / L). After the solution became completely clear, the addition of ammonia solution was stopped. Then, 48 g of vinylpyrrolidone-vinyl acetate copolymer was added. The temperature was raised to 80 °C, and 2.5 wt% hydrazine hydrate aqueous solution was added at 80 °C with stirring. When the pH value reached 10, the addition of hydrazine hydrate aqueous solution was stopped, and stirring was continued for 1 h. After stirring, the product was centrifuged under nitrogen protection, washed three times with distilled water and then with ethanol, and dried to obtain nano copper powder.

[0059] S2. Dissolve 18g thiourea, 0.3g EDTA-2Na, and 0.3g hydroquinone in 190g eutectic ionic liquid until homogeneous. Add 10g of nano copper powder and stir to disperse evenly. Then, add 5.27mL of stannous chloride hydrochloric acid solution in three batches, 20min apart, and continue stirring for 1h. Add 20g of 5wt% EVA solution and continue stirring for 30min. After stirring, centrifuge the product and wash it three times with distilled water and then with ethanol. Dry the product to obtain Cu@Sn powder.

[0060] The vinylpyrrolidone-vinyl acetate copolymer is obtained by copolymerizing 1-vinyl-2-pyrrolidone and vinyl acetate in a mass ratio of 3:2, with a K value of 25.2-30.8. (Yuang Technology Co., Ltd., Product Name: VP / VA64 Powder)

[0061] The eutectic ionic liquid is obtained by stirring choline chloride and thiourea at a molar ratio of 1:1 at 90°C until they become a colorless and transparent liquid.

[0062] The EVA solution was prepared by mixing EVA and toluene for 12 hours.

[0063] The scanning electron microscope image of the nano-copper powder in this embodiment is as follows: Figure 3 As shown, the scanning electron microscope image of Cu@Sn powder is as follows. Figure 4 As shown, the EDX plot of Cu@Sn powder is as follows: Figure 5 As shown.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 2 is as follows: 1 L of copper sulfate aqueous solution (0.15 mol / L) was taken, and 10.0 wt% ammonia solution was slowly added under a nitrogen atmosphere. After the solution became completely clear, the addition of ammonia solution was stopped. Then, 40 g of polyvinylpyrrolidone and 0.5 g of sodium lauryl sulfonate were added, and the temperature was raised to 80°C. Then, under stirring, 2.5 wt% hydrazine hydrate aqueous solution at 80°C was added. When the pH value reached 10, the addition of hydrazine hydrate aqueous solution was stopped, and stirring was continued for 1 hour. Centrifugation was performed under a nitrogen atmosphere, and the obtained solid was washed three times with distilled water and then with ethanol, respectively, and dried to obtain nano copper powder; the rest were the same.

[0066] The scanning electron microscope image of the comparative example of nano-copper powder is shown below. Figure 6 As shown.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 2 is as follows: 18g of thiourea, 0.3g of EDTA-2Na, and 0.3g of hydroquinone were added to 190g of eutectic ionic liquid and dissolved evenly. 10g of nano copper powder was added, and after stirring and dispersing evenly, 5.27mL of stannous chloride hydrochloric acid solution was added in three batches, with an interval of 20min each time. Stirring was continued for 1h. After stirring, the product was centrifuged and washed three times with distilled water and then with ethanol, respectively. After drying, Cu@Sn powder was obtained. All other steps were the same.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 2 is as follows: 18g of thiourea, 0.3g of EDTA-2Na, and 0.3g of hydroquinone were dissolved in 190g of water and then added. 10g of nano-copper powder was added and stirred until evenly dispersed. Then, 5.27mL of stannous chloride hydrochloric acid solution was added in three batches, with an interval of 20min each time. The mixture was stirred for 1h. Then, 20g of 5wt% EVA solution was added and the mixture was stirred for 30min. After stirring, the product was centrifuged and washed three times with distilled water and then with ethanol. The product was then dried to obtain Cu@Sn powder. All other steps were the same.

[0071] Comparative Example 4

[0072] The difference between this comparative example and Example 2 is that the eutectic ionic liquid was obtained by stirring choline chloride and anhydrous ethylene glycol at a molar ratio of 1:1 at 90°C until it became a colorless and transparent liquid.

[0073] Comparative Example 5

[0074] The difference between this comparative example and Example 2 is that the eutectic ionic liquid was obtained by stirring choline chloride and glycerol at a molar ratio of 1:1 at 90°C until it became a colorless and transparent liquid.

[0075] Comparative Example 6

[0076] The difference between this comparative example and Example 2 is as follows: 180 mL of deionized water was placed in a beaker and heated to 80 °C. Then, 18 g of thiourea, 5 g of polyethylene glycol-2000, 0.3 g of EDTA-2Na, and 0.3 g of hydroquinone were added to the beaker in sequence. The stirring speed was maintained at 80 rpm until the solution became clear and transparent. After cooling to room temperature, 9.5 g of nano copper powder was added and stirred to disperse evenly to obtain a mixed solution. Under stirring, 10 mL of stannous chloride hydrochloric acid aqueous solution (5 mol / L) was added in three portions (each 20 min apart, with about 3.3 mL added each time). After the addition was completed, the reaction was stirred for 1 h. The resulting mixture was placed in a funnel and filtered. The obtained solid was washed three times with distilled water and then with ethanol, and dried to obtain Cu@Sn powder.

[0077] Performance testing:

[0078] The above Cu@Sn powder is mixed with an organic carrier at a mass ratio of 3:1 to prepare a solder. The organic carrier includes 1% succinic acid, 1% salicylic acid, 1% cetyltrimethylammonium bromide, 1% fumed silica, 1% bentonite, 25% hydrogenated rosin, 20% ethylene glycol butyl ether, 30% ethylene glycol, and 20% triethylene glycol butyl ether.

[0079] (1) The above solder and Cu substrate were soldered under the process parameters of preheating at 120°C for 40s, holding at 180°C for 80s, and reflowing at 250°C for 120s. The shear strength of the solder joint was measured when it was sheared at 25°C at a rate of 0.1mm / min.

[0080] (2) The above solder and Cu substrate were soldered under the process parameters of preheating at 120°C for 40s, holding at 180°C for 80s, and reflowing at 250°C for 120s. After being placed at 400°C for 360h, the shear strength of the solder joint was measured when it was sheared at a high temperature of 0.1mm / min.

[0081] Test Results

[0082] Table 1

[0083] Shear strength at room temperature (MPa) High-temperature shear strength (MPa) Example 1 39.6 33.3 Example 2 40.2 33.8 Comparative Example 1 32.5 27.2 Comparative Example 2 25.5 19.5 Comparative Example 3 28.3 22.7 Comparative Example 4 31.9 25.4 Comparative Example 5 30.3 24.3 Comparative Example 6 21.9 16.6

[0084] Results Analysis: Figures 1-6 It can be seen that using vinylpyrrolidone-vinyl acetate copolymer as a dispersant can yield uniformly sized nano-copper powder, and using the eutectic ionic liquid and EVA solution specific to this invention can yield uniformly sized Cu@Sn powder.

[0085] As can be seen from Table 1, the solder obtained by using Cu@Sn powder prepared in this invention can improve the mechanical strength of the solder joint while having excellent high-temperature reliability.

[0086] Due to poor dispersion of nano-copper powder in Comparative Example 1, due to lack of EVA in Comparative Example 2, due to the use of water instead of ionic liquid in Comparative Example 3, due to the replacement of ionic liquid components in Comparative Examples 4-5, and due to the absence of both ionic liquid and EVA in Comparative Example 6, the mechanical strength and high-temperature reliability of the solder joints formed by the Cu@Sn powder used in the preparation of the solder decreased.

[0087] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing nano-Cu@Sn powder, characterized in that, Includes the following steps: S1. Under nitrogen protection, ammonia water was added to the aqueous solution of copper salt, followed by vinylpyrrolidone-vinyl acetate copolymer. The temperature was raised, and hydrazine hydrate aqueous solution was added. When the pH value reached 10, the addition of hydrazine hydrate aqueous solution was stopped, and stirring was continued. After stirring, the product was centrifuged under nitrogen protection, washed, and dried to obtain nano copper powder. S2. Add the ligand, complexing agent, and antioxidant to the eutectic ionic liquid and dissolve them evenly. Add the nano copper powder, stir and disperse it evenly. Then add the hydrochloric acid solution of stannous chloride and continue stirring. Add the EVA solution and continue stirring. After stirring, centrifuge the product, wash it, and dry it to obtain Cu@Sn powder. The eutectic ionic liquid is a mixture of choline chloride and thiourea in a molar ratio of 1:0.5-1.

5.

2. The method for preparing nano-Cu@Sn powder according to claim 1, characterized in that, Step S1 is as follows: Under nitrogen protection, ammonia is added to the aqueous solution of copper salt. After the solution becomes completely clear, the addition of ammonia is stopped. Then, vinylpyrrolidone-vinyl acetate copolymer is added, and the temperature is raised to 75-85℃. Under stirring, hydrazine hydrate aqueous solution at a temperature of 75-85℃ is added. When the pH value reaches 10, the addition of hydrazine hydrate aqueous solution is stopped, and stirring is continued for 0.5-1h. After stirring, the product is centrifuged under nitrogen protection, washed three times with distilled water and then with ethanol, and dried to obtain nano copper powder.

3. The method for preparing nano-Cu@Sn powder according to claim 2, characterized in that, The vinylpyrrolidone-vinyl acetate copolymer is obtained by copolymerizing 1-vinyl-2-pyrrolidone and vinyl acetate in a mass ratio of 3:2, with a K value of 25.2-30.

8.

4. The method for preparing nano-Cu@Sn powder according to claim 3, characterized in that, Step S2 is as follows: The ligand, complexing agent, and antioxidant are added to the eutectic ionic liquid and dissolved evenly. Nano copper powder is added and stirred and dispersed evenly. Then, stannous chloride hydrochloric acid solution is added in three batches, with an interval of 15-20 minutes between each batch. Stirring is continued for 0.5-1 hour. EVA solution is added and stirring is continued for 20-30 minutes. After stirring, the product is centrifuged and washed three times with distilled water and then with ethanol. The product is then dried to obtain Cu@Sn powder.

5. The method for preparing nano-Cu@Sn powder according to claim 4, characterized in that, The mass ratio of the ligand, complexing agent, antioxidant and nano copper powder is 15-20:0.1-0.5:0.1-0.5:8-12.

6. The method for preparing nano-Cu@Sn powder according to claim 5, characterized in that, The mass ratio of the eutectic ionic liquid to the nano-copper powder is 20-30:1; the mass ratio of the stannous chloride to the nano-copper powder is 0.3-0.5:

1.

7. The method for preparing nano-Cu@Sn powder according to claim 6, characterized in that, The EVA solution is a mixture of EVA and toluene; the mass concentration of the EVA solution is 2-6 wt%.

8. A nano-Cu@Sn powder, characterized in that, It is prepared by the method for preparing nano-Cu@Sn powder according to any one of claims 1-7.

9. The application of nano-Cu@Sn powder in the preparation of conductive pastes, sintering pastes, or solders, characterized in that, The nano-Cu@Sn powder is prepared by the method for preparing nano-Cu@Sn powder according to any one of claims 1-7.

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