A method for preparing copper nanoparticles, copper nanoparticles and applications thereof

Abstract

The application provides a preparation method of copper nanoparticles, which comprises the following steps: preparing a copper source complexing agent solution; preparing a surface modifier dispersion; fully mixing a reducing agent, the copper source complexing agent solution and the surface modifier dispersion, and performing an oxidation-reduction reaction; and obtaining a copper nanoparticle mixed solution after the reaction is completed, and then performing solid-liquid separation through centrifugation to obtain the copper nanoparticles. The preparation method of the copper nanoparticles provided by the application adopts a one-step chemical synthesis method to prepare copper nanoparticles with a bimodal particle size distribution by using a combination of strong and weak reducing agents. Small copper nanoparticles are gathered around large copper nanoparticles to form composite copper nanoparticles, and the surface of the copper nanoparticles is coated with an organic ligand which is easy to desorb. The composite structure of the copper nanoparticles exhibits good low-temperature sintering performance, and the sintering structure after sintering has high compactness, thereby meeting the requirements of low-temperature sintering and high-temperature service in the application of power electronic chip interconnection.

Description

Technical Field

[0001] This application relates to the field of electronic packaging materials technology, and in particular to a method for preparing copper nanoparticles, copper nanoparticles and their applications. Background Technology

[0002] In recent years, nanoscience has provided innovative impetus for disciplines such as physics, chemistry, biology, medicine, and materials science, and has become an important source of transformative industrial manufacturing technologies, attracting widespread attention from researchers. Due to the nanoeffect, metallic nanoparticles exhibit unique physical, chemical, optical, electrical, magnetic, thermal, and biological properties, giving them enormous potential application value in multiple fields, such as sensor technology, electronic packaging, electromagnetic shielding, and flexible circuit boards.

[0003] In recent decades, the integration of power devices in power electronic equipment has trended towards miniaturization, high integration, and low loss. Compared with traditional silicon-based semiconductors, wide-bandgap (WBG) semiconductors, represented by gallium nitride and silicon carbide, have higher power density, higher breakdown voltage, and better high-temperature operating stability, making them the ideal choice for high-power semiconductor device chip materials. However, with the increase in power density of power devices, a large amount of heat energy accumulates and the junction temperature of the devices rises (greater than 200°C) during operation. In this situation, traditional tin-based solders are unsuitable as packaging interconnect materials for high-power devices because they will creep and melt under high-temperature operating conditions, causing serious reliability problems. Currently, high-temperature packaging interconnect materials used for high-power semiconductor devices mainly include: lead-containing high-melting-point solders and sintered solder pastes containing (Ag) or (Cu) fillers. Among them, sintered silver solder paste and sintered copper solder paste are considered the most promising packaging interconnect materials for high-power devices due to the high electrical and thermal conductivity of metals. However, silver is prone to electrochemical migration at high temperatures, especially in humid and oxygen-containing environments, which can lead to short-circuit failures in highly integrated high-power devices. Compared to silver, copper is cheaper and more resistant to electrochemical migration. Therefore, in recent years, many researchers have turned their attention to copper sintering technology. However, copper sintering technology also faces many challenges, such as the preparation of copper nanoparticles with good sintering properties and the oxidation of copper nanoparticles.

[0004] There are physical and chemical methods for preparing copper nanoparticles. Physical methods require sophisticated equipment, resulting in high equipment and production costs. Chemical methods mainly include electrochemical methods, sol-gel methods, and liquid-phase reduction methods. Liquid-phase reduction methods produce more uniform copper nanoparticles with a wider particle size range, enabling high packing density and improving the sintering performance of sintered copper solder paste. Furthermore, liquid-phase reduction methods offer advantages such as large-scale production and low energy consumption, making them a popular choice. Generally, liquid-phase reduction involves adding copper salts to an organic or inorganic solvent and adding a suitable reducing agent to the solution. This reduces copper ions to copper atoms, rapidly increasing the number of copper atoms in the solution. Once the concentration of copper atoms in the solvent reaches a certain value, copper atoms begin to form crystal nuclei. Newly generated copper atoms then deposit on the surface of these nuclei, eventually growing into copper particles of a specific size. Surface modifiers in the solution form an organic layer on the surface of the copper particles, maintaining good dispersion between particles and regulating their growth. Common reducing agents used in liquid-phase reduction methods include ascorbic acid, sodium borohydride, hydrazine hydrate, organic amines, polyols, glucose, and hydrogen peroxide. Common surface ligands used in liquid-phase reduction methods include polyvinylpyrrolidone, polyethylene glycol, alkyl acids, alkylamines, oleic acid, and oleylamine. Current methods for synthesizing copper nanoparticles generally suffer from difficulties in separating and purifying the synthesized nanoparticles, and often employ recalcitrant surface ligands, resulting in poor sintering properties of the prepared copper nanoparticles.

[0005] my country's copper sintering technology for metal interconnects started relatively late, particularly in the production of low-temperature, easily sinterable copper nanoparticles, for which there is limited accumulation of expertise, and a mature industrialization solution is still lacking. Furthermore, academic research on the large-scale, stable preparation of copper nanoparticles for copper sintering is still in its early stages, with most research remaining at the laboratory level, lacking a green and efficient solution for large-scale industrial application.

[0006] CN113369486A discloses a method for preparing copper nanoparticles. The method involves first preparing an aqueous solution of starch and copper salt, using the pores on the surface of porous starch as a template, graphite as a reducing agent, and ammonia as a precipitant. After thorough reaction under ultrasonic conditions, the mixture is vacuum dried and calcined under N2 protection to obtain purplish-black copper nanoparticles. N2 is then continuously introduced for protection until cooling to room temperature. This patented method has a cumbersome reaction process, insufficient purity of the produced copper nanoparticles, and difficulty in maintaining a stable and controllable preparation process. In particular, the preparation process involves high energy consumption, requires protection from special gases, involves many types of reactants and reaction byproducts, and has complex post-processing, increasing production costs.

[0007] CN109822108A discloses a method for preparing copper nanoparticles with a barbed surface. In this method, the copper nanoparticles are prepared by stirring a copper sulfate aqueous solution in a 70°C water bath while simultaneously adding a hexadecyltrimethylammonium bromide ethanol solution to the copper sulfate aqueous solution to obtain a mixture. The mixture is stirred continuously, and a 6 mol / L sodium hydroxide solution is added until the pH of the mixture with added sodium hydroxide solution reaches 9–11. Then, 10–25 mL of hydrazine hydrate and 5–15 mL of ethanol are added sequentially to the mixture containing the sodium hydroxide solution, maintaining a hydrazine hydrate:ethanol ratio of 1.67–2.0:1. The mixture is stirred for 0.5–2.5 h. The copper sulfate aqueous solution, sodium hydroxide, hydrazine hydrate, and ethanol react to form a granular solid. The solid is allowed to stand for 10 min to precipitate. The solid is washed three times with water. The washed solid is then washed twice with ethanol and air-dried at room temperature to obtain copper nanoparticles with a barbed surface structure. The copper nanoparticles obtained by this method are spiky spheres, which are inconvenient to use and have less application potential than smooth-surfaced granular copper nanomaterials.

[0008] Existing chemical methods for preparing copper nanoparticles present several challenges, including cumbersome reaction steps, insufficient purity of the resulting copper nanoparticles, and difficulty in maintaining stable and controllable processes. In particular, the preparation process involves high-energy-consuming reactions, may require the protection of special gases, involves numerous reactants and byproducts, necessitates complex post-processing, high production costs, poor application prospects, and does not align with green and environmentally friendly principles. On the other hand, mechanically prepared copper nanoparticles, due to anti-oxidation treatment, have surface organic matter that is difficult to volatilize or decompose. This reduces the sintering performance of physically prepared copper nanoparticles, making sintering difficult or resulting in poor sintering characteristics at low temperatures (<300℃). Furthermore, the surface of copper nanoparticles is prone to oxidation, which also reduces sintering performance or leads to lower conductivity and mechanical properties in the resulting interconnects, thus failing to meet the application requirements of power semiconductor packaging interconnects. Summary of the Invention

[0009] Based on this, the present invention addresses the problems existing in the prior art by providing a method for preparing copper nanoparticles coated with easily desorbable organic surface ligands and exhibiting a bimodal particle size distribution, as well as their applications. To achieve the above objectives, the technical solution adopted in this application is as follows:

[0010] One of the objectives of this application is to provide a method for preparing copper nanoparticles, comprising the following steps:

[0011] Preparation of copper-based complexing agent solution;

[0012] Preparation of surface modifier dispersion;

[0013] The reducing agent, the copper source complexing agent solution, and the surface modifier dispersion are thoroughly mixed. A strong reducing agent is added dropwise to initiate the redox reaction. After the reaction is complete, a copper nanoparticle mixed solution is obtained. The copper nanoparticles are then obtained by centrifugation to separate the solid and liquid phases.

[0014] In some embodiments, the step of preparing the copper source complexing agent solution specifically includes the following steps: mixing a dispersion of copper source and a complexing agent to generate a copper source complexing agent solution.

[0015] In some embodiments, the molar ratio of the copper source to the complexing agent is 1:0.001 to 1:1000.

[0016] In some embodiments, the copper source is a copper oxide, a copper complex, an inorganic or organic copper source.

[0017] In some embodiments, the copper source is any one or a combination of at least two of copper oxide, cuprous oxide, copper chloride, copper nitrate, copper sulfate, copper formate, copper acetate, copper carbonate, and copper hydroxide.

[0018] In some embodiments, the complexing agent is any one or a combination of at least two of the following: ethylenediamine, propylamine, dipropylamine, isopropylamine, cyclopropylamine, cyclopentylamine, hydroxylamine, 2-ethanolamine, methoxyethylamine, 2-hydroxypropylamine, methoxypropylamine, cyanoethylamine, ethoxyamine, n-butoxyamine, tripropylamine, 1,2-propanediamine, 2-propenylamine, isopropanolamine, n-butylamine, di-n-butylamine, isobutylamine, sec-butylamine, 1,4-butanediamine, tert-butylamine, isopentylamine, and triethanolamine.

[0019] In some embodiments, in the step of preparing the surface modifier dispersion, the surface modifier includes polyvinylpyrrolidone, oleylamine, oleic acid, polyacrylamide, polyallylamine, polyethyleneimine, and fatty acid C1-C. 18 Fatty amines: any one or a combination of at least two of the following: hexylamine, 2-ethylhexylamine, hexanediamine, trioctylamine, n-octylamine, decylamine, 1,10-decanediamine, dodecaneamine, hexadecaneamine, tetradecaneamine, octadecaneamine, docosylamine, 2-hexoxyamine, methoxyethoxyethylamine, methoxyethoxyethoxyethylamine, hexamethyleneimine, 2,2-(ethylenedioxy)diethylamine, etc.; polyethylene glycol; gum arabic; hexadecyl ammonium bromide; sodium dodecylbenzenesulfonate; triethanolamine; or ethanolamine.

[0020] In some embodiments, the step of thoroughly mixing a strong reducing agent, a weak reducing agent, the copper source complexing agent solution, and the surface modifier dispersion, then adding a strong reducing agent dropwise to induce a redox reaction, and obtaining a copper nanoparticle mixed solution after the reaction is complete, followed by centrifugal solid-liquid separation to obtain the copper nanoparticles, specifically includes the following steps:

[0021] The weak reducing agent, the copper source complexing agent solution, and the surface modifier dispersion are thoroughly mixed. The mixed solution is heated to 60℃~180℃ for reaction. A strong reducing agent is added dropwise, and a redox reaction occurs in the reaction solution to prepare copper nanoparticles. After the reaction is completed, the solution is cooled to room temperature.

[0022] An alcohol solvent was added to the cooled reaction solution, and the mixture was then centrifuged, washed, separated, and dried to obtain the copper nanomaterial structure.

[0023] In some embodiments, the mass ratio of copper source to reducing agent is 1:0.001 to 1:1000.

[0024] In some embodiments, the strong reducing agent includes any one or a combination of at least two of the following: stannous chloride, oxalic acid, sodium borohydride, sodium hypophosphite, citric acid, sodium citrate, disodium citrate, ascorbic acid, sodium ascorbate, glucose, hydrazine hydrate, phenylhydrazine, hydroxylamine, ethanolamine, 2-ethanolamine, methoxyethylamine, 2-hydroxypropylamine, methoxypropylamine, n-butoxyamine, ethylenediamine, propylenediamine, diethylamine, dipropylamine, isopropanolamine, aniline, and adipamide.

[0025] In some embodiments, the weak reducing agent can also be prepared by the following preparation method:

[0026] Collect and obtain plant biomass raw materials; the plant biomass raw materials are selected from one or more of the roots, stems, branches, leaves, flowers, fruits and seeds of evergreen trees, and the evergreen trees include at least one of the following: Korean pine, Chinese pine, Scots pine, Masson pine, slash pine, Chinese fir, spruce, oriental arborvitae, Chinese juniper, prickly juniper, bamboo cypress, dragon juniper, podocarpus, large-leaved privet, Chinese pistache, southern magnolia, white magnolia, Elaeocarpus decipiens, Albizia julibrissin, banyan, camphor tree, laurel, osmanthus, longan, litchi and loquat;

[0027] The plant biomass raw material is baked at 40℃~90℃ to obtain dried plant biomass.

[0028] The dried plant biomass is soaked in an alcohol solution to obtain a plant biomass extract, wherein the reducing agent includes any one or a combination of at least two of the plant biomass extracts.

[0029] In some embodiments, the alcohol solvent is an organic molecule containing at least one hydroxyl group, and the alcohol solvent is at least one selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, middle butanol, tert-butanol, n-pentanol, n-hexanol, n-octanol, and terpineol.

[0030] The second objective of this application is to provide copper nanoparticles prepared by any of the preparation methods described herein.

[0031] The third objective of this application is to provide an application of the aforementioned copper nanoparticles in power chip packaging.

[0032] The present application adopts the above technical solution, and its beneficial effects are as follows:

[0033] The method for preparing copper nanoparticles provided in this application involves preparing a copper-based complexing agent solution; preparing a surface-modifying agent dispersion; thoroughly mixing a weak reducing agent, the copper-based complexing agent solution, and the surface-modifying agent dispersion; adding a strong reducing agent dropwise to induce a redox reaction; and obtaining a copper nanoparticle mixed solution after complete reaction. The copper nanoparticles are then obtained through centrifugal solid-liquid separation. This method employs a one-step chemical synthesis to prepare copper nanoparticles with a bimodal particle size distribution. Smaller copper nanoparticles aggregate around larger ones to form composite copper nanoparticles, and the surface of these nanoparticles is coated with easily desorbable organic ligands. These composite copper nanoparticles exhibit excellent low-temperature sintering properties and high density after sintering, thus meeting the requirements for low-temperature sintering and high-temperature service in power electronic chip interconnect applications. Furthermore, the above-mentioned process for preparing copper nanoparticles is environmentally friendly, simple, energy-efficient, and has mild and controllable preparation conditions, resulting in low cost and suitability for mass production.

[0034] The copper nanoparticles provided in this application have a bimodal particle size distribution, which is beneficial to improving their initial packing density. In addition, the surface of the copper nanoparticles is coated with easily desorbable organic ligands, which makes them easy to sinter. Therefore, the copper nanoparticles can be sintered at low temperature while ensuring the good compactness of the resulting sintered microstructure. As a result, the sintered interconnect copper joints exhibit good mechanical properties and can provide an easy-to-sinter and inexpensive nano solder paste raw material for electronic packaging materials. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a process flow diagram of the preparation method of the copper nanomaterial structure in the embodiments of the present invention;

[0037] Figure 2 This is the XRD pattern of sample 1 in Embodiment 1 of the present invention;

[0038] Figure 3 This is a SEM image of sample 1 in Embodiment 1 of the present invention;

[0039] Figure 4 This is a SEM image of sample 2 in Example 1 of the present invention;

[0040] Figure 5 This is a SEM image of sample 3 in Example 1 of the present invention;

[0041] Figure 6 This is an SEM image of sample 4 in Example 2 of the present invention;

[0042] Figure 7 This is a SEM image of sample 5 in Example 2 of the present invention;

[0043] Figure 8 This is an SEM image of sample 6 in Example 2 of the present invention. Detailed Implementation

[0044] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0045] In the description of this application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0047] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0048] Please see Figure 1 The following is a flowchart of a method for preparing copper nanoparticles according to an embodiment of this application, including steps S110 to S130. The implementation of each step is described in detail below.

[0049] Step S110: Prepare copper source complexing agent solution.

[0050] In some embodiments, the step of preparing the copper source complexing agent solution specifically includes the following steps: mixing a dispersion of copper source and a complexing agent to generate a copper source complexing agent solution.

[0051] In some embodiments, the molar ratio of the copper source to the complexing agent is 1:0.001 to 1:1000.

[0052] In some embodiments, the copper source is a copper oxide, a copper complex, an inorganic or organic copper source.

[0053] In some embodiments, the copper source is any one or a combination of at least two of copper oxide, cuprous oxide, copper chloride, copper nitrate, copper sulfate, copper formate, copper acetate, copper carbonate, and copper hydroxide.

[0054] In some embodiments, the complexing agent is any one or a combination of at least two of the following: ethylenediamine, propylamine, dipropylamine, isopropylamine, cyclopropylamine, cyclopentylamine, hydroxylamine, 2-ethanolamine, methoxyethylamine, 2-hydroxypropylamine, methoxypropylamine, cyanoethylamine, ethoxyamine, n-butoxyamine, tripropylamine, 1,2-propanediamine, 2-propenylamine, isopropanolamine, n-butylamine, di-n-butylamine, isobutylamine, sec-butylamine, 1,4-butanediamine, tert-butylamine, isopentylamine, and triethanolamine.

[0055] Step S120: Prepare a surface modifier dispersion.

[0056] In some embodiments, the surface modifier includes polyvinylpyrrolidone, oleylamine, oleic acid, polyacrylamide, polyallylamine, polyethyleneimine, and fatty acid C1-C. 18 Fatty amines: any one or a combination of at least two of the following: hexylamine, 2-ethylhexylamine, hexanediamine, trioctylamine, n-octylamine, decylamine, 1,10-decanediamine, dodecaneamine, hexadecaneamine, tetradecaneamine, octadecaneamine, docosylamine, 2-hexoxyamine, methoxyethoxyethylamine, methoxyethoxyethoxyethylamine, hexamethyleneimine, 2,2-(ethylenedioxy)diethylamine, etc.; polyethylene glycol; gum arabic; hexadecyl ammonium bromide; sodium dodecylbenzenesulfonate; triethanolamine; or ethanolamine.

[0057] Step S130: The weak reducing agent, the copper source complexing agent solution and the surface modifier dispersion are thoroughly mixed, a strong reducing agent is added, and a redox reaction occurs. After the reaction is fully completed, a copper nanoparticle mixed solution is obtained, and then the copper nanoparticles are obtained by centrifugation solid-liquid separation.

[0058] It is understood that, in preparing the above-mentioned mixed reaction solution, the concentration of the complexing agent is controlled to a certain value, and the particle size of the copper nanomaterial is finally obtained by adjusting the amount of copper source, thermal decomposition temperature, reaction time, amount and type of strong and weak reducing agent, amount and type of surfactant, and molar ratio of reducing agent to copper source.

[0059] Furthermore, the molar ratio of the copper source to the reducing agent is set to 1:0.001 to 1:1000, resulting in a copper nanomaterial particle size distribution range of 0-5 μm.

[0060] Furthermore, when preparing the mixed reaction solution, the concentration of the reducing agent is controlled to a certain value, and the morphology of the finally obtained copper nanomaterial is controlled by adjusting the type of the complexing agent.

[0061] In some embodiments, the process of thoroughly mixing the reducing agent, the copper source complexing agent solution, and the surface modifier dispersion to undergo a redox reaction, obtaining a copper nanoparticle mixed solution after the reaction is complete, and then obtaining the copper nanoparticles by centrifugal solid-liquid separation specifically includes the following steps S131 to S132. The implementation of each step is described in detail below.

[0062] Step S131: Thoroughly mix the reducing agent, the copper source complexing agent solution, and the surface modifier dispersion. Heat the mixed solution to 60℃~180℃ for reaction, and further add the reducing agent. After the reaction is complete, cool to room temperature.

[0063] Specifically, the strong reducing agent, the weak reducing agent, the copper source complexing agent solution, and the surface modifier dispersion are thoroughly mixed. The mixed reaction solution is placed in a reaction vessel and heated to a temperature range of 60–180°C. The reducing agent dispersion is independently injected into the additive at a rate of 1–20 mL / min for mixing. The reaction is carried out at 60–180°C for 0.1–3 h under stirring conditions, and the reaction is maintained at this temperature for 5–50 min. After the reaction is completed, the mixture is allowed to cool naturally to room temperature.

[0064] It is understood that the appropriate introduction of a combination of strong and weak reducing agents can effectively promote the nucleation and growth of copper particles. The preferred strong reducing agents are at least one of stannous chloride, oxalic acid, sodium borohydride, sodium hypophosphite, citric acid, sodium citrate, disodium citrate, ascorbic acid, sodium ascorbate, glucose, hydrazine hydrate, phenylhydrazine, hydroxylamine, ethanolamine, 2-ethanolamine, methoxyethylamine, 2-hydroxypropylamine, methoxypropylamine, n-butoxyamine, ethylenediamine, propylenediamine, diethylamine, dipropylamine, isopropanolamine, aniline, and adipamide. The preferred weak reducing agents are at least one of the extracts of biomass raw materials from evergreen trees.

[0065] In some embodiments, the weak reducing agent can also be prepared by the following preparation method:

[0066] Step S210: Collect and obtain plant biomass raw materials; the plant biomass raw materials are selected from one or more of the roots, stems, branches, leaves, flowers, fruits and seeds of evergreen trees, and the evergreen trees include at least one of the following: Korean pine, Chinese pine, Scots pine, Masson pine, slash pine, Chinese fir, spruce, arborvitae, juniper, prickly juniper, bamboo cypress, dragon juniper, podocarpus, large-leaved privet, Chinese pistache, southern magnolia, white magnolia, Elaeocarpus decipiens, Albizia julibrissin, banyan, camphor tree, laurel, osmanthus, longan, litchi and loquat;

[0067] Step S220: The plant biomass raw material is baked at 40℃~90℃ to obtain dried plant biomass;

[0068] Step S230: The dried plant biomass is soaked in an alcohol solution to obtain a plant biomass extract, wherein the reducing agent includes any one or a combination of at least two of the plant biomass extracts.

[0069] It is understood that the method for preparing and synthesizing small-sized nanoparticles using plant biomass extract as a reducing agent in this embodiment is green and environmentally friendly.

[0070] Step S132: Add alcohol solvent to the cooled reaction solution, and then perform centrifugation, washing, separation, and drying in sequence to obtain the copper nanomaterial structure.

[0071] Specifically, an alcohol solvent is added to the cooled reaction solution, centrifuged, washed 3 to 8 times, and then dried to obtain the copper nanoparticles.

[0072] In some embodiments, the alcohol solvent is an organic molecule containing at least one hydroxyl group, preferably at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, middle butanol, tert-butanol, n-pentanol, n-hexanol, n-octanol, and terpineol.

[0073] The method for preparing copper nanoparticles provided in the above embodiments of this application uses a one-step chemical synthesis method to prepare copper nanoparticles with multi-scale distribution. This allows small-sized copper particles to be uniformly distributed around large-sized copper particles. In addition to increasing the density of the sintered structure, it can also reduce the sintering temperature of these copper nanoparticles, thereby meeting the requirement that the sintering process temperature in power electronic chip packaging interconnect applications is generally required to be below 300°C. Moreover, the above-mentioned process for preparing copper nanoparticles is green and environmentally friendly, with simple preparation methods, low energy consumption, mild and controllable preparation conditions, low cost, and can be promoted for mass production.

[0074] The copper nanoparticles provided in this application have the advantage of a bimodal particle size distribution, which is characterized by high initial packing density and easy sintering surface properties. They can be sintered at low temperatures while ensuring the compactness of the resulting structure, thus enabling the joint to exhibit good mechanical properties after sintering. This provides a reliable, easy-to-sinter, and inexpensive nano-soldering paste raw material for electronic packaging materials.

[0075] Example 1

[0076] In this embodiment, copper sulfate is selected as the copper source, methanol is selected as the solvent, ethylenediamine is selected as the complexing agent, lactic acid is selected as the surface modifier, ascorbic acid alcohol turbidity is selected as the strong reducing agent and litchi biomass raw material extract is selected as the weak reducing agent, and the molar ratio of strong and weak reducing agents to copper source is 1:0.001 to 1:1000.

[0077] The method for preparing copper nanomaterials provided in this embodiment includes the following steps:

[0078] (1) Prepare a methanol solution of copper sulfate; at room temperature, add a certain amount of dipropylamine and lactic acid mixed solution to the methanol solution of copper sulfate and mix them together, add a certain amount of litchi biomass extract to obtain a uniform reaction solution.

[0079] (2) Place the mixed reaction solution in a reaction vessel, keep the entire solution at a constant temperature of 80°C, add an appropriate amount of ascorbic acid alcohol turbidity, keep the reaction at the temperature for 15 minutes, and let it cool naturally to room temperature after the reaction is completed.

[0080] (3) After centrifuging the cooled reaction solution, add ethanol solution and centrifuge, wash and separate in sequence. Then dry in a low-temperature vacuum oven to obtain copper nanoparticles.

[0081] In this embodiment, referring to the above process steps (1) to (2), different copper nanoparticle samples are prepared by changing the ratio of copper source, complexing agent, and reducing agent, as well as the reaction temperature and time in step (1). Specifically, as follows:

[0082] Sample 1 was prepared by changing the molar ratio of copper source and strong reducing agent in the reaction solution to 2:1.

[0083] Sample 2 was prepared by changing the molar ratio of copper source and strong reducing agent in the reaction solution to 1:1.

[0084] Sample 3 was prepared by changing the molar ratio of copper source and strong reducing agent in the reaction solution to 1:2.

[0085] Figure 2 This is the XRD pattern of sample 1. Figure 3 This is the SEM image of sample 1, from... Figure 2 As can be seen, the copper nanomaterial sample prepared in this embodiment, from Figure 3As can be seen, the sample 1 prepared in this embodiment is a near-spherical copper nanomaterial structure with a particle size distribution range of 50nm to 500nm.

[0086] Figure 4 This is the SEM image of sample 2, from... Figure 4 It can be seen that the sample 2 prepared in this embodiment is a near-spherical copper nanomaterial structure with a particle size distribution range of 50nm to 400nm.

[0087] Figure 5 This is the SEM image of sample 3, from... Figure 4 It can be seen that the sample 3 prepared in this embodiment is a near-spherical copper nanomaterial structure with a particle size distribution range of 50nm to 400nm.

[0088] Combining the schemes of samples 1 to 3, it can be seen that as the amount of strong reducing agent gradually increases, the number of small particles gradually increases, the particle size of the prepared copper nanoparticles decreases, and at the same time, the aggregation phenomenon becomes more and more obvious.

[0089] Example 2

[0090] In this embodiment, copper hydroxide is selected as the copper source, ethylene glycol is selected as the solvent, n-hexylamine is selected as the complexing agent, formic acid is selected as the surface modifier, glucosyl alcohol turbidity is selected as the strong reducing agent, and longan biomass raw material leaching solution is selected as the weak reducing agent. The molar ratio of strong and weak reducing agents to copper source is 1:0.001 to 1:1000.

[0091] The method for preparing copper nanomaterials provided in this embodiment includes the following steps:

[0092] (1) Prepare a methanol solution of copper hydroxide; at room temperature, add a certain amount of a mixed solution of n-hexylamine and formic acid to the methanol solution of copper hydroxide and mix them together, add a certain amount of a weak reducing agent, and obtain a homogeneous reaction solution.

[0093] (2) Place the mixed reaction solution in a reaction vessel, keep the entire solution at a constant temperature of 90°C, add an appropriate amount of glucose alcohol turbidity, maintain the reaction for 10 minutes, and allow it to cool naturally to room temperature after the reaction is complete.

[0094] (3) After centrifuging the cooled reaction solution, add ethanol solution and centrifuge, wash and separate in sequence. Then dry in a low-temperature vacuum oven to obtain copper nanoparticles.

[0095] In this embodiment, referring to the above process steps (1) to (2), different copper nanoparticle samples are prepared by changing the ratio of copper source, complexing agent, and reducing agent, as well as the reaction temperature and time in step (1). Specifically, as follows:

[0096] The reaction temperature was controlled at 60℃ to prepare sample 4.

[0097] The reaction temperature was controlled at 90℃ to prepare sample 5.

[0098] The reaction temperature was controlled at 120℃ to prepare sample 6.

[0099] Figure 6 This is the SEM image of sample 4. Sample 4 prepared in this embodiment is a near-spherical copper nanomaterial structure with a particle size distribution range of 50 nm to 400 nm.

[0100] Figure 7 This is the SEM image of sample 5, from... Figure 7 It can be seen that the sample 5 prepared in this embodiment is a near-spherical copper nanomaterial structure with a particle size distribution range of 50nm to 400nm.

[0101] Figure 7 This is the SEM image of sample 6, from... Figure 7 It can be seen that the sample 6 prepared in this embodiment is a near-spherical copper nanomaterial structure with a particle size distribution range of 50nm to 400nm.

[0102] Combining the methods used for samples 4 to 6, it can be seen that the particle size increases with increasing reaction temperature. This is likely because higher reaction temperatures accelerate the growth and nucleation of copper nanoparticles, making aggregation more pronounced.

[0103] Example 3:

[0104] This implementation example prepares copper nanoparticles according to the following method:

[0105] (1) Dissolve 4.0g of sodium borohydride in 20mL of ethanol to obtain sodium borohydride alcohol solution, and disperse 2.0g of oxalic acid and cinnamon extract in 20mL of ethanol to obtain a dispersion solution containing oxalic acid.

[0106] (2) Disperse copper oxalate and 2 mL of ethylenediamine in 20 mL of ethanol to obtain a copper-amine complex solution. Then heat the solution to 80 °C and inject the sodium borohydride dispersion obtained in step (1) and the mixture containing oxalic acid dispersion into the heated copper-amine complex solution at a rate of 10 mL / min. React at 80 °C for 20 min, centrifuge and wash 3 times, and dry under vacuum to obtain copper nanoparticle powder.

[0107] In this example, the mass ratio of copper oxalate to sodium borohydride in step (2) is 3:5.

[0108] Example 4:

[0109] This implementation example prepares copper nanoparticles according to the following method:

[0110] (1) Dissolve 2.0g of sodium oxalate in 20mL of ethanol to obtain sodium oxalate alcohol solution, and disperse 2.0g of oxalic acid and a certain amount of banyan biomass raw material extract in 20mL of ethanol to obtain a dispersion solution containing oxalic acid.

[0111] (2) Disperse copper oxalate and 2 mL of ethylenediamine in 20 mL of ethanol to obtain a copper-amine complex solution. Then heat the solution to 85 °C and inject the sodium oxalate dispersion obtained in step (1) and the mixture containing oxalic acid dispersion into the heated copper-amine complex solution at a rate of 10 mL / min. React at 85 °C for 20 min, centrifuge and wash 3 times, and dry under vacuum to obtain copper nanoparticle powder.

[0112] In this example, the mass ratio of copper oxalate to sodium borohydride in step (2) is 3:5.

[0113] Example 5:

[0114] This implementation example prepares copper nanoparticles according to the following method:

[0115] (1) Dissolve 2.0g of sodium oxalate in 20mL of ethanol to obtain sodium oxalate alcohol solution, and disperse 2.0g of lactic acid and a certain amount of litchi biomass raw material extract in 20mL of ethanol to obtain a dispersion solution containing lactic acid.

[0116] (2) Disperse copper hydroxide and 2 mL of ethylenediamine in 20 mL of ethanol to obtain a copper-amine complex solution. Then heat the solution to 85 °C and inject the sodium oxalate dispersion obtained in step (1) and the mixture containing lactic acid dispersion into the heated copper-amine complex solution at a rate of 10 mL / min. React at 85 °C for 20 min, centrifuge and wash 3 times, and dry under vacuum to obtain copper nanoparticle powder.

[0117] In this example, the mass ratio of copper hydroxide to sodium acetate in step (2) is 1:2.

[0118] Example 6:

[0119] This implementation example prepares copper nanoparticles according to the following method:

[0120] (1) Dissolve 2.0g of glucose in 20mL of ethanol to obtain an alcoholic solution of glucose. Disperse 2.0g of polyvinylpyrrolidone and a certain amount of longan biomass raw material extract in 20mL of ethanol to obtain a dispersion solution containing lactic acid.

[0121] (2) Disperse copper hydroxide and 2 mL of ethylenediamine in 20 mL of ethanol to obtain a copper-amine complex solution. Then heat the solution to 85 °C and inject the glucose dispersion obtained in step (1) and the mixture containing polyvinylpyrrolidone dispersion into the heated copper-amine complex solution at a rate of 10 mL / min. React at 85 °C for 20 min, centrifuge and wash 3 times, and dry under vacuum to obtain copper nanoparticle powder.

[0122] In this example, the mass ratio of copper hydroxide to lactic acid in step (2) is 1:2, and the mass ratio of copper hydroxide to glucose is 1:2.

[0123] Example 7:

[0124] This implementation example prepares copper nanoparticles according to the following method:

[0125] (3) Dissolve 2.0g of sodium acetate in 20mL of ethanol to obtain an alcoholic solution of glucose. Disperse 2.0g of lactic acid and a certain amount of spruce biomass extract in 20mL of ethanol to obtain a dispersion solution containing lactic acid.

[0126] (4) Disperse copper hydroxide and 2 mL of isopropanolamine in 20 mL of ethanol to obtain a copper amine complex solution. Then heat the solution to 85 °C and inject the sodium acetic acid dispersion obtained in step (1) and the mixture containing lactic acid dispersion into the heated copper amine complex solution at a rate of 10 mL / min. React at 85 °C for 20 min, centrifuge and wash 3 times, and dry under vacuum to obtain copper nanoparticle powder.

[0127] In this example, the mass ratio of copper hydroxide to lactic acid in step (2) is 1:2, and the mass ratio of copper hydroxide to glucose is 1:2.

[0128] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0129] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for preparing copper nanoparticles, characterized in that, Includes the following steps: Preparation of copper-based complexing agent solution; Preparation of surface modifier dispersion; The reducing agent, the copper source complexing agent solution, and the surface modifier dispersion are thoroughly mixed to undergo a redox reaction. After the reaction is complete, a copper nanoparticle mixed solution is obtained, and then the copper nanoparticles are obtained by centrifugal solid-liquid separation. The steps for preparing the copper source complexing agent solution specifically include the following steps: mixing the dispersion of the copper source and the complexing agent to generate the copper source complexing agent solution; The molar ratio of the copper source to the complexing agent is 1:0.001 to 1:1000; The copper source is any one of copper oxide, cuprous oxide, copper chloride, copper nitrate, copper sulfate, copper formate, copper acetate, copper carbonate, and copper hydroxide. The complexing agent is any one of ethylenediamine, dipropylamine, and n-hexylamine; In the step of preparing the surface modifier dispersion, the surface modifier is either lactic acid or formic acid; The process of thoroughly mixing the reducing agent, the copper source complexing agent solution, and the surface modifier dispersion to undergo a redox reaction, obtaining a copper nanoparticle mixed solution after the reaction is complete, and then separating the copper nanoparticles by centrifugation to obtain the copper nanoparticles specifically includes the following steps: The weak reducing agent, the copper source complexing agent solution, and the surface modifier dispersion are thoroughly mixed. The mixed solution is heated to 60°C to 120°C for reaction. Then, a strong reducing agent is added to promote the reduction of the copper complex. After the reaction is completed, the reaction solution is cooled to room temperature. An alcohol solvent was added to the cooled reaction solution, and the mixture was then centrifuged, washed, separated, and dried sequentially to obtain the copper nanoparticles. The mass ratio of copper source to weak reducing agent is 1:0.001 to 1:1000; The molar ratio of copper source to strong reducing agent is 2:1, 1:1, or 1:2; The strong reducing agent is either ascorbic acid or glucose; The weak reducing agent is prepared by the following method: Collect and obtain plant biomass raw materials; the plant biomass raw materials are selected from one or more of the roots, stems, branches, leaves, flowers, fruits and seeds of evergreen trees, and the evergreen trees are at least one of lychee and longan; The plant biomass raw material is baked at 40℃~90℃ to obtain dried plant biomass. The dried plant biomass is soaked in an alcohol solution to obtain a plant biomass extract, wherein the weak reducing agent includes any one or a combination of at least two of the plant biomass extracts.

2. The method for preparing copper nanoparticles as described in claim 1, characterized in that, The alcohol solvent is an organic molecule containing at least one hydroxyl group, and the alcohol solvent is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, middle butanol, tert-butanol, n-pentanol, n-hexanol, n-octanol, and terpineol.

3. A copper nanoparticle, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 2.

4. An application of the copper nanoparticles as described in claim 3 in printed electronics or power chip packaging.

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