Preparation method of microsized spherical gold powder with controllable particle size range

Abstract

The application provides a preparation method of micron-sized spherical gold powder with controllable particle size range, which comprises the following steps: adding concentrated ammonia water and concentrated hydrochloric acid into tetrachloroauric acid solution in sequence to adjust pH, then adding a protective agent, long-chain alkyl sodium sulfate, and using diethanolamine or triethanolamine as a reducing agent, and precisely controlling the growth of micron-sized spherical gold powder particles by adjusting the amount of the protective agent and the adding amount of the concentrated ammonia water and the concentrated hydrochloric acid. The particle size of the gold powder prepared by the method is controllable in the range of 0.5-3.0 mu m, the particle size distribution range of any specific size gold powder in the particle size range is relatively narrow (within 0.15 mu m), and the sphericity and dispersibility are high. The method has the advantages of simple and safe overall steps, short reaction time, easy large-scale production, precise control of the size of the spherical gold powder, simple regulation mode, important application value and potential in the printing type gold conductor paste.

Description

Technical Field

[0001] This invention relates to the field of micron materials technology, and in particular to a method for preparing micron-sized spherical gold powder with controllable particle size range. Background Technology

[0002] Au possesses high ductility, high chemical inertness, and oxidation resistance. As a conductor, it exhibits almost no tendency for electron migration even under complex and harsh operating conditions. As a raw material, gold powder used in electronic pastes offers advantages such as high resolution, strong adhesion to substrates and dielectrics, low surface porosity, and high gold wire bonding. Therefore, it is widely used in large-scale integrated circuits, semiconductor packaging, and multilayer wiring circuits, playing a crucial role, especially in high-reliability military electronic technologies. To meet the performance requirements of high-performance military electronic equipment, the morphology and size of gold powder often have strict applicable ranges, generally requiring spherical particles with a particle size range of 1–3 μm. As the functional phase in gold conductor pastes, gold powder typically accounts for over 80% of the paste's solid content. The uniformity, dispersibility, particle size distribution, morphology, and size of its particles have a significant impact on the paste's electrical conductivity, sintering shrinkage, weldability, and thermal conductivity. If the particle size distribution is too wide or the gold powder particle size is too large, mesh clogging is likely to occur during gold paste printing, and the printed conductive lines are prone to breakage, resulting in a decline in screen printing quality and a tendency to cause incomplete sintering, which seriously affects film formation. If the gold powder particle size is too small, it will also affect the sintering compatibility, affecting the interfacial bonding strength between the substrate and the conductor after sintering, and even the lead wire welding strength.

[0003] Currently, some domestic patent documents have disclosed spherical gold powder particles, such as:

[0004] CN109622985A discloses a method for preparing highly dispersible submicron gold powder. The average particle size distribution of the prepared gold powder is 0.3 to 1.2 μm. The distribution range is wide and the size provided is small, which cannot meet the size requirements of gold powder for conductor paste.

[0005] CN106825606A discloses a method for preparing monodisperse gold nanoparticles of various sizes and their applications. The maximum size of the prepared gold nanoparticles is 90-120 nm. The nanoscale gold powder particles are too small to be used in gold conductor pastes.

[0006] CN111299607A discloses a method for preparing 5N-level micron-sized conductive gold spheres, which can prepare spherical gold powder particles with a size of 1 to 100 μm. Although the range is relatively wide, the content of spherical particles is only 48% in the distribution range of 0.5 to 1.5 μm, which is not suitable for preparing gold conductor paste.

[0007] In summary, the gold powder produced by methods disclosed in existing patent literature is insufficient to meet the practical requirements of gold conductor pastes. Therefore, how to easily and rapidly prepare micron-sized spherical gold powder and precisely control the particle size distribution of these spherical gold particles is one of the key technologies that urgently needs to be overcome in the preparation of gold conductor pastes in China. Against this background, this invention discloses a method for preparing micron-sized spherical gold powder with a precisely controllable particle size range for conductor pastes. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing micron-sized spherical gold powder with controllable particle size. This method allows for precise control of the size and distribution of the spherical gold powder within the range of 0.5–3.0 μm, and the control method is simple. In this invention, the inventors use long-chain alkyl sulfates (sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate) as a protective agent and diethanolamine or triethanolamine as a reducing agent. Micron-sized spherical gold powder is prepared in a single step at a relatively low temperature (30–50 °C) and a short reaction time (30–60 min). The gold powder prepared by this method can be widely used in conductor pastes, semiconductor packaging, multilayer wiring circuits, and high-reliability military electronic materials.

[0009] To achieve the above objectives, the present invention provides a method for preparing micron-sized spherical gold powder with controllable particle size range, employing the following technical solution:

[0010] The present invention provides a method for preparing micron-sized spherical gold powder with controllable particle size range, comprising the following steps:

[0011] (1) Dissolve chloroauric acid in deionized water to prepare solution a, and set aside;

[0012] (2) Dissolve the protective agent in deionized water to prepare solution b, and set aside;

[0013] (3) Dissolve the reducing agent in deionized water to prepare solution c, and set aside;

[0014] (4) Add concentrated ammonia to solution a under stirring to form an orange-yellow suspension, and then add concentrated hydrochloric acid to adjust the pH of the solution.

[0015] (5) Mix the solution obtained in step (4) and solution b thoroughly under stirring conditions to obtain mixed solution d;

[0016] (6) Add solution c to solution d at a certain dropping rate and stir the reaction at a certain temperature for a period of time to obtain gold powder stock solution;

[0017] (7) The gold powder stock solution obtained in step (6) is centrifuged, washed and separated with anhydrous ethanol, and the obtained precipitate is dried in a vacuum drying oven at 80°C for 120 min to obtain the micron-sized spherical gold powder.

[0018] The mass concentration of chloroauric acid in solution a is 50-100 g / L.

[0019] The protective agent in solution b is one of sodium tetradecyl sulfate (STS), sodium hexadecyl sulfate (SHS), and sodium octadecyl sulfate (ODS), with a mass concentration of 10.5–121 g / L. Preferably, the protective agent in solution b is sodium octadecyl sulfate, with a mass concentration of 103.2–109.6 g / L.

[0020] The reducing agent in solution c is diethanolamine or triethanolamine, and the mass concentration of the reducing agent is 8-36.3 g / L.

[0021] In step (4), add 40-50 mL of concentrated ammonia (25-28%) and 5-10 mL of concentrated hydrochloric acid (36-38%). The pH value is 2.0-3.5. The stirring speed is 250 rpm and the stirring time is 2 min.

[0022] The stirring speed in solution d is 250 rpm, and the stirring time is 3 min.

[0023] The temperature in step (6) is 30–50°C, the reducing agent is added at a rate of 16.7–33.3 ml / min, and the reaction time is 30–60 min. This invention also provides gold powder prepared by the above method, with spherical particles having a particle size range of 0.5–3.0 μm.

[0024] The technical principles of this invention are explained as follows:

[0025] First, chloroauric acid is added to concentrated ammonia to adjust the pH to alkaline, producing a pale yellow suspension. The chloroauric acid solution is converted into lignin, and the reaction equation is as follows:

[0026] HAuCl4+NH3H2O→Au2O·3NH3↓+HCl

[0027] Then, a small amount of concentrated hydrochloric acid was added to adjust the pH to acidic. Under stirring, a protective agent (sodium long-chain alkyl sulfate) was added and mixed thoroughly. Then, a reducing agent was added and the reaction was stirred. The reaction equation is as follows:

[0028] Au₂O·3NH₃ + reducing agent → Au↓ + oxidation product + HCl + NH₃·H₂O

[0029] The particle size of gold powder is directly related to crystal growth, which is generally divided into a nucleation stage and a growth stage. These two stages are in competition; when the nucleation rate is greater than the growth rate, the crystal particle size is smaller, and vice versa. The crystal growth stage is a thermodynamic and kinetic equilibrium process, which is influenced by multiple factors, such as temperature, pH, and the amount of protective agent. Among these, the reducing power of the reducing agent and the selection and addition amount of the protective agent have the most significant impact on gold powder preparation. In this invention, on the one hand, concentrated ammonia is first added to form lignin, and then the amount of concentrated hydrochloric acid added is adjusted to further regulate the reducing power of the reducing agent (diethanolamine or triethanolamine, whose reducing power is more moderate than that of traditional strong or weak reducing agents), thereby controlling the size of the gold powder. The higher the pH of the reaction solution, the lower the potential of the reducing agent and the stronger its reducing power, thus accelerating the nucleation rate of gold particles and tending to generate more small spherical particles. Conversely, the lower the pH, the more acidic the environment, which is conducive to crystal growth. The growth rate exceeds the nucleation rate, resulting in relatively large spherical gold powder particles. On the other hand, long-chain alkyl sulfate, as an anionic surfactant, has excellent dispersing properties. During the reaction, long-chain alkyl sulfate dissolves in water to form negatively charged anionic groups. Its hydrophilic ends readily electrostatically adsorb gold cations and the surface of gold particles, and the entire group remains negatively charged. The encapsulated gold particles repel each other due to their identical charges, effectively preventing them from approaching each other completely. This protects the gold nanoparticles generated in the early stages of the reaction, improves their monodispersity, and effectively prevents aggregation. Simultaneously, adjusting the amount of protective agent also affects the deposition rate of gold atoms, ultimately achieving precise control over the growth rate and size of the gold powder.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) Unlike ordinary spherical gold powder, the size of the gold powder prepared by this method can be precisely controlled between 0.5 and 3.0 μm, making it suitable as the main raw material for electronic pastes, especially high-reliability military electronic materials;

[0032] (2) By using anionic protective agent sodium long-chain alkyl sulfate and controlling its dosage and the amount of concentrated hydrochloric acid added, the present invention can achieve precise control over the morphology and size of spherical gold powder, and the particle size distribution range of any specific size gold powder is narrow (within ±0.15μm) and has high sphericity and dispersibility.

[0033] (3) The overall production process of this invention has low cost, easy-to-control conditions, safety and environmental protection, and is easy to industrialize. Attached Figure Description

[0034] Figure 1This is a process flow diagram of the present invention;

[0035] Figure 2 The image shows a scanning electron microscope (SEM) image of the micron-sized spherical gold powder prepared in Example 1 of this invention. The scale bar in the image is 20 μm.

[0036] Figure 3 The image shows a scanning electron microscope (SEM) image of the micron-sized spherical gold powder prepared in Example 2 of this invention. The scale bar in the image is 20 μm.

[0037] Figure 4 The image shows a scanning electron microscope (SEM) image of the micron-sized spherical gold powder prepared in Comparative Example 1 of this invention. The scale bar in the image is 20 μm.

[0038] Figure 5 The image shows a scanning electron microscope (SEM) image of the micron-sized spherical gold powder prepared in Comparative Example 2 of this invention. The scale bar in the image is 5 μm.

[0039] Figure 6 This is a scanning electron microscope (SEM) image of the micron-sized spherical gold powder prepared in Comparative Example 3 of this invention. The scale bar in the image is 5 μm.

[0040] Figure 7 The image shows a scanning electron microscope (SEM) image of the micron-sized spherical gold powder prepared in Comparative Example 4 of this invention. The scale bar in the image is 10 μm. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0042] like Figure 1 As shown, the present invention provides a method for preparing micron-sized spherical gold powder with controllable particle size range, comprising the following steps:

[0043] (1) Dissolve chloroauric acid in deionized water to prepare solution a, and set aside;

[0044] (2) Dissolve the protective agent in deionized water to prepare solution b, and set aside;

[0045] (3) Dissolve the reducing agent in deionized water to prepare solution c, and set aside;

[0046] (4) Add concentrated ammonia to solution a under stirring to form an orange-yellow suspension, and then add concentrated hydrochloric acid to adjust the pH of the solution.

[0047] (5) Mix the solution obtained in step (4) and solution b thoroughly under stirring conditions to obtain mixed solution d;

[0048] (6) Add solution c to solution d at a certain dropping rate and stir the reaction at a certain temperature for a period of time to obtain gold powder stock solution;

[0049] (7) The gold powder stock solution obtained in step (6) is centrifuged, washed and separated with anhydrous ethanol, and the obtained precipitate is dried in a vacuum drying oven at 80°C for 120 min to obtain the micron-sized spherical gold powder.

[0050] The technical solution and beneficial effects of the present invention will be further illustrated below with reference to specific embodiments.

[0051] Example 1

[0052] (1) Dissolve 50g of chloroauric acid in 1L of deionized water to prepare solution a, and set aside;

[0053] (2) Dissolve 44g of sodium tetradecyl sulfate, the protective agent, in 1L of deionized water to prepare solution b, and set aside.

[0054] (3) Dissolve 19.2g of diethanolamine in 1L of deionized water to prepare solution c, and set aside for later use;

[0055] (4) Add 50 ml of concentrated ammonia to solution a under stirring to form an orange-yellow suspension. Then add 8 mL of concentrated hydrochloric acid to adjust the pH of the solution to 2.5. The stirring speed is 250 rpm and the stirring time is 2 min.

[0056] (5) Mix the solution obtained in step (4) and solution b thoroughly under stirring conditions to obtain mixed solution d. The stirring speed is 250 rpm and the stirring time is 3 min.

[0057] (6) Add solution c to solution d dropwise at a rate of 33.3 ml / min, stir at 30°C for 30 min, and then stop the reaction to obtain the gold powder stock solution;

[0058] (7) The gold powder stock solution obtained in step (6) is centrifuged, washed, and separated with anhydrous ethanol. The precipitate is then dried in a vacuum drying oven at 80°C for 120 minutes to obtain the gold powder stock solution. Figure 2 The gold powder shown is micron-sized spherical, with the powder size concentrated between 1.3 and 1.5 μm.

[0059] Example 2

[0060] (1) Dissolve 100g of chloroauric acid in 1L of deionized water to prepare solution a, and set aside;

[0061] (2) Dissolve 87.7g of the protective agent sodium octadecyl sulfate in 1L of deionized water to prepare solution b, and set aside for later use;

[0062] (3) Dissolve 19.2g of triethanolamine in 1L of deionized water to prepare solution c, and set aside for later use;

[0063] (4) Add 51 ml of concentrated ammonia to solution a under stirring to form an orange-yellow suspension. Then add 7.75 ml of concentrated hydrochloric acid to adjust the pH of the solution to 3.5. The stirring speed is 250 rpm and the stirring time is 2 min.

[0064] (5) Mix the solution obtained in step (4) and solution b thoroughly under stirring conditions to obtain mixed solution d. The stirring speed is 250 rpm and the stirring time is 3 min.

[0065] (6) Add solution c to solution d dropwise at a rate of 33.3 ml / min, stir at 30°C for 30 min, and then stop the reaction to obtain the gold powder stock solution;

[0066] (7) The gold powder stock solution obtained in step (6) is centrifuged, washed, and separated with anhydrous ethanol. The precipitate is then dried in a vacuum drying oven at 80°C for 120 minutes to obtain the gold powder stock solution. Figure 3 The gold powder shown is micron-sized spherical, with the powder size concentrated between 1.0 and 1.3 μm.

[0067] Comparative Example 1

[0068] (1) Dissolve 50g of chloroauric acid in 1L of deionized water to prepare solution a, and set aside;

[0069] (2) Dissolve 44g of sodium tetradecyl sulfate, the protective agent, in 1L of deionized water to prepare solution b, and set aside.

[0070] (3) Dissolve 19.2g of diethanolamine in 1L of deionized water to prepare solution c, and set aside for later use;

[0071] (4) Add 50 ml of concentrated ammonia to solution a under stirring to form an orange-yellow suspension. Then add 8 mL of concentrated hydrochloric acid to adjust the pH of the solution to 2.5. The stirring speed is 250 rpm and the stirring time is 2 min.

[0072] (5) Mix the solution obtained in step (4) and solution b thoroughly under stirring conditions to obtain mixed solution d. The stirring speed is 250 rpm and the stirring time is 3 min.

[0073] (6) Add solution c to solution d dropwise at a rate of 33.3 ml / min, stir at 30°C for 30 min, and then stop the reaction to obtain the gold powder stock solution;

[0074] (7) The gold powder stock solution obtained in step (6) is centrifuged, washed, and separated with anhydrous ethanol. The precipitate is then dried in a vacuum drying oven at 80°C for 120 minutes to obtain the gold powder stock solution. Figure 4 The spherical gold powder shown is prepared using ascorbic acid as a reducing agent. The gold powder size is concentrated in two particle size ranges: 0.1–0.9 μm and 1.0–1.5 μm. The overall particle size distribution is relatively wide, which indicates that the reducing power of diethanolamine or triethanolamine in the reaction system of this invention is relatively moderate. Excessive or insufficient reducing power is not conducive to obtaining micron-sized spherical gold powder with a narrow particle size distribution.

[0075] Comparative Example 2

[0076] (1) Dissolve 50g of chloroauric acid in 1L of deionized water to prepare solution a, and set aside;

[0077] (2) Dissolve 44g of sodium tetradecyl sulfate, the protective agent, in 1L of deionized water to prepare solution b, and set aside.

[0078] (3) Dissolve 19.2g of diethanolamine in 1L of deionized water to prepare solution c, and set aside for later use;

[0079] (4) Add 50 ml of concentrated ammonia to solution a under stirring to form an orange-yellow suspension. Then add 8 mL of concentrated hydrochloric acid to adjust the pH of the solution to 2.5. The stirring speed is 250 rpm and the stirring time is 2 min.

[0080] (5) Mix the solution obtained in step (4) and solution b thoroughly under stirring conditions to obtain mixed solution d. The stirring speed is 250 rpm and the stirring time is 3 min.

[0081] (6) Add solution c to solution d quickly at once, stir and react at 30°C for 30 min, and stop the reaction to obtain the gold powder stock solution;

[0082] (7) The gold powder stock solution obtained in step (6) is centrifuged, washed, and separated with anhydrous ethanol. The precipitate is then dried in a vacuum drying oven at 80°C for 120 minutes to obtain the gold powder stock solution. Figure 5 The submicron-sized spherical gold powder shown has a concentrated size distribution between 0.1 and 0.9 μm, which is submicron-sized, and the particle size distribution is relatively wide. This indicates that the rapid addition of the reducing agent at one time is not conducive to obtaining micron-sized spherical gold powder with a narrow particle size distribution.

[0083] Comparative Example 3

[0084] (1) Dissolve 50g of chloroauric acid in 1L of deionized water to prepare solution a, and set aside;

[0085] (2) Dissolve 44g of nonionic protective agent polyvinylpyrrolidone in 1L of deionized water to prepare solution b, and set aside.

[0086] (3) Dissolve 19.2g of diethanolamine in 1L of deionized water to prepare solution c, and set aside for later use;

[0087] (4) Add 50 ml of concentrated ammonia to solution a under stirring to form an orange-yellow suspension. Then add 8 mL of concentrated hydrochloric acid to adjust the pH of the solution to 2.5. The stirring speed is 250 rpm and the stirring time is 2 min.

[0088] (5) Mix the solution obtained in step (4) and solution b thoroughly under stirring conditions to obtain mixed solution d. The stirring speed is 250 rpm and the stirring time is 3 min.

[0089] (6) Add solution c to solution d dropwise at a rate of 33.3 ml / min, stir at 30°C for 30 min, and then stop the reaction to obtain the gold powder stock solution;

[0090] (7) The gold powder stock solution obtained in step (6) is centrifuged, washed, and separated with anhydrous ethanol. The precipitate is then dried in a vacuum drying oven at 80°C for 120 minutes to obtain the gold powder stock solution. Figure 6 The micron-sized spherical gold powder shown has a concentrated distribution of gold powder size between 0.3 and 0.9 μm, but the overall particle size distribution is wider than that in Example 1, and the surface of the spherical gold powder is rough and irregular.

[0091] Comparative Example 4

[0092] (1) Dissolve 50g of chloroauric acid in 1L of deionized water to prepare solution a, and set aside;

[0093] (2) Dissolve 44g of cationic protective agent tetradecyltrimethylammonium bromide in 1L of deionized water to prepare solution b, and set aside.

[0094] (3) Dissolve 19.2g of diethanolamine in 1L of deionized water to prepare solution c, and set aside for later use;

[0095] (4) Add 50 ml of concentrated ammonia to solution a under stirring to form an orange-yellow suspension. Then add 8 mL of concentrated hydrochloric acid to adjust the pH of the solution to 2.5. The stirring speed is 250 rpm and the stirring time is 2 min.

[0096] (5) Mix solution a and solution b obtained in step (4) thoroughly under stirring conditions to obtain mixed solution d. The stirring speed is 250 rpm and the stirring time is 3 min.

[0097] (6) Add solution c to solution d dropwise at a rate of 33.3 ml / min, stir at 30°C for 30 min, and then stop the reaction to obtain the gold powder stock solution;

[0098] (7) The gold powder stock solution obtained in step (6) is centrifuged, washed, and separated with anhydrous ethanol. The precipitate is then dried in a vacuum drying oven at 80°C for 120 minutes to obtain the gold powder stock solution. Figure 7 The image shows micron-sized gold powder. The gold powder mainly consists of irregular spherical particles and flake-like gold powder with a diameter of 1.0–3.0 μm. Analysis of the scanning electron microscopy results shows that cationic long-chain alkyl ammonium halide surfactants also disperse the gold powder and control its size to the micron level. However, the cationic protective agent primarily restricts the growth of gold crystals along their long axis, offering limited protection to other crystal planes. Therefore, the resulting particles all have irregular edges and corners, making it difficult to control the uniformity of their morphology and size.

[0099] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the technical solutions of the present invention. Any technical solution that can be implemented based on the above embodiments without creative effort should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing micron-sized spherical gold powder with controllable particle size range, characterized in that, Includes the following steps: (1) Dissolve chloroauric acid in deionized water to prepare solution a, and set aside; (2) Dissolve the protective agent in deionized water to prepare solution b, and set aside; (3) Dissolve the reducing agent in deionized water to prepare solution c, and set aside; (4) Add concentrated ammonia to solution a under stirring to form an orange-yellow suspension, and then add concentrated hydrochloric acid to adjust the pH of the solution; (5) Mix the solution obtained in step (4) and solution b thoroughly under stirring conditions to obtain mixed solution d; (6) Add solution c to solution d at a dropping rate of 16.7 to 33.3 ml / min and stir at 30 to 50 °C for 30 to 60 min to obtain gold powder stock solution; (7) The gold powder stock solution obtained in step (6) is centrifuged, washed and separated with anhydrous ethanol, and the obtained precipitate is dried in a vacuum drying oven at 80 °C for 120 min to obtain the micron-sized spherical gold powder. in: The protective agent in solution b is one of sodium tetradecyl sulfate, sodium hexadecyl sulfate, and sodium octadecyl sulfate, and the mass concentration of the protective agent is 10.5–121 g / L; The reducing agent in solution c is diethanolamine or triethanolamine, and the mass concentration of the reducing agent is 8–25.6 g / L.

2. The method for preparing micron-sized spherical gold powder with controllable particle size range according to claim 1, characterized in that, The mass concentration of chloroauric acid in solution a is 50–100 g / L.

3. The method for preparing micron-sized spherical gold powder with controllable particle size range according to claim 1, characterized in that, The concentration of the added concentrated ammonia is 25-28%, and the amount added is 40-50 mL; the concentration of the added concentrated hydrochloric acid is 36-38%, and the amount added is 5-10 mL.

4. The method for preparing micron-sized spherical gold powder with controllable particle size range according to claim 1, characterized in that, In step (4), the solution pH is 2.0 to 3.5, the stirring speed is 250 rpm, and the stirring time is 2 min.

5. The method for preparing micron-sized spherical gold powder with controllable particle size range according to claim 1, characterized in that, In step (6), the stirring speed is 250 rpm and the stirring time is 3 min.

6. A micron-sized spherical gold powder product prepared by a method for preparing micron-sized spherical gold powder with controllable particle size range according to any one of claims 1-5, characterized in that: The particle size ranges from 0.5 to 3.0 μm.

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