Spherical nano silver powder for low-temperature silver paste and preparation method of spherical nano silver powder

Abstract

The invention relates to spherical nano silver powder for low-temperature silver paste, the silver powder is spherical, silver powder particles are nanoscale, and according to ISO13310-2009, the particle size D10 of the silver powder is 10-30 nm, the particle size D50 of the silver powder is 40-100 nm, and the particle size D90 of the silver powder is 120-300 nm. Meanwhile, the invention further discloses a preparation method of the silver powder. The preparation method is simple, the production cost is low, the obtained silver powder does not need subsequent tedious fine treatment processes such as surface modification and protection and smashing, the silver powder is suitable for large-scale industrial production, and the obtained silver powder has the advantages of being narrow in particle size distribution, controllable in particle size and good in dispersity.

Description

Technical Field

[0001] The present invention relates to the technical fields of the electronics industry and the manufacturing technology of metal powders for low-temperature conductive silver pastes, and particularly relates to a spherical nano silver powder for low-temperature silver pastes and a preparation method thereof. Background Art

[0002] With the rapid development of the 5G information era and the low-carbon transformation of energy, low-temperature curing conductive silver paste, as an essential key material in the electronic information industry and the solar cell industry, has been widely used in fields such as flexible circuits, membrane switches, radio frequency identification, and heterojunction solar cells. The low-temperature curing conductive silver paste can be applied to plastic plates or flexible substrates with a low glass transition temperature and low price, and has the characteristics of low curing temperature (curing temperature below 250°C), environmental friendliness, and low loss. At the same time, it has excellent electrical conductivity, flexural resistance, printability, adhesion, and other properties, so it has extremely broad market application prospects.

[0003] Silver powder is the most important component in conductive silver paste and determines the electrical conductivity of conductive silver paste. The expansion of the market demand for silver paste and the structural changes have led to the expansion of the market demand for silver powder and the structural changes in products. The market demand for high-quality silver powder for low-temperature silver paste has increased rapidly. The high-end silver powder industry is highly concentrated, and the domestic market mainly relies on imports. The Japanese DOWA company has an obvious monopoly due to the small particle size range, good surface organic coating, good dispersibility, and stable quality of its silver powder products, accounting for more than 50% of the global silver powder market share. Domestic silver powder suppliers, especially high-end silver powder suppliers for low-temperature silver paste, generally have problems such as large particle size, wide distribution, poor dispersibility and stability, low tap density, and insufficient production capacity, and cannot meet the performance requirements of low-temperature curing conductive silver paste for silver powder. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a spherical nano silver powder for low-temperature silver paste with good performance.

[0005] Another technical problem to be solved by the present invention is to provide a preparation method for the spherical nano silver powder for low-temperature silver paste.

[0006] To solve the above problems, a spherical nano silver powder for low-temperature silver paste according to the present invention is characterized in that: the morphology of the silver powder is spherical, the silver powder particles are nano-scale, and according to ISO13310-2009, the particle size of the silver powder is D10 = 10 - 30nm, D50 = 40 - 100nm, D90 = 120 - 300nm.

[0007] A preparation method of spherical nano silver powder for low-temperature silver paste as described above, characterized in that: this method refers to using tap water as a solvent, Vc (L(+)-ascorbic acid) as a reducing agent, and one of silver nitrate, silver oxide or silver chloride as a silver source, adding a surface modifier, a dispersant, a protective agent and a pH regulator, controlling the pH value range of the reaction system to be 5-7, and using a one-pot chemical reduction method at room temperature to prepare spherical nano silver powder for low-temperature silver paste.

[0008] The dosage of the silver source is 2-10 w t% of the mass of the solvent; the molar ratio of the reducing agent to the silver in the silver source is 1:1-1:1.5.

[0009] The surface modifier is one or more of sodium polyphosphate, sodium pyrophosphate, and sodium hexametaphosphate, and its dosage is 1-20% of the mass of the silver source.

[0010] The dispersant is one or more of polyethylene glycol 2000-6000, triethanolamine, and ethylene glycol monobutyl ether, and its dosage is 1-20% of the mass of the silver source.

[0011] The protective agent is one or more of oleic acid, melamine, benzotriazole, and water-soluble lanolin, and its dosage is 0.5-10% of the mass of the silver source.

[0012] The pH regulator is solid sodium hydroxide.

[0013] A preparation method of spherical nano silver powder for low-temperature silver paste as described above, comprising the following steps: ⑴ At room temperature, weigh according to the ratio; ⑵ Mix the reducing agent and the solvent evenly to obtain a reducing agent solution with a mass concentration of 5-15 w t%; then dissolve the surface modifier, the dispersant, and the protective agent in the remaining solvent to obtain a mixed solution A; ⑶ Add the silver source to the mixed solution A, stir at a rate of 100-500 revolutions per minute until the system becomes a milky white or dark brown suspension; under continuous stirring, quickly add the reducing agent solution to the suspension system, and then immediately add the pH regulator, and continue to stir for 0.5-2 hours; ⑷ Stop stirring, filter with a G6 sand core, wash with deionized water 3 times by filtration, and finally wash and filter once with anhydrous methanol or anhydrous ethanol, and dry overnight to obtain spherical nano silver powder for black low-temperature silver paste.

[0014] Step (3) is replaced by the following method: Add the silver source to the mixed solution A, stir evenly at a rate of 100 - 500 revolutions per minute, add a pH regulator until the system becomes a black-brown suspension; under continuous stirring, quickly add the reducing agent solution to the suspension system and continue stirring for 0.5 - 2 hours.

[0015] A method for preparing spherical nano silver powder for low-temperature silver paste as described above includes the following steps: S1 At room temperature, weigh according to the ratio. S2 Mix the reducing agent and the solvent evenly to obtain a reducing agent solution with a mass concentration of 5 - 15 w t%; then dissolve the surface modifier, dispersant, protective agent, and pH regulator in the remaining solvent to obtain a mixed solution B. S3 Add the silver source to the mixed solution B, stir evenly at a rate of 100 - 500 revolutions per minute to obtain a black-brown suspension; under continuous stirring, quickly add the reducing agent solution to the suspension system and continue stirring for 0.5 - 2 hours. S4 Stop stirring, filter with a G6 sand core, wash with deionized water 3 times by filtration, and finally wash and filter once with anhydrous methanol or anhydrous ethanol, and dry overnight to obtain spherical nano silver powder for black low-temperature silver paste.

[0016] The present invention has the following advantages compared with the prior art: 1. The reduction reaction of the present invention is carried out at room temperature (10 - 35 °C), without heating, and has low energy consumption.

[0017] 2. The reaction time and preparation cycle of the present invention are short, and the production efficiency is high.

[0018] 3. Silver nitrate, silver oxide, and silver chloride in the present invention can all be used as silver sources, and the raw material application range is wide.

[0019] 4. The raw materials of the present invention are simple, inexpensive, non-toxic, environmentally friendly, easy to obtain, and have low cost, and have good economic benefits.

[0020] 5. The operation of the present invention is simple, prepared by a one-pot method, without complex raw material addition steps and control units, and omits the subsequent surface modification, protection, pulverization and other cumbersome refinement processes of the conventional method for preparing silver powder, and is suitable for large-scale industrial production.

[0021] 6. The silver powder obtained by the present invention has a small particle size, a low melting point, adjustable particle size, a narrow particle size distribution, a moderate bulk density, good dispersibility and stability, and can be stored for a long time. Description of the Drawings

[0022] The following further details the specific embodiments of the present invention in conjunction with the drawings.

[0023] Figure 1 This is the particle size distribution diagram of the nano silver powder for low-temperature silver paste obtained in Example 1 of the present invention (wet measurement with a Malvern laser particle size analyzer).

[0024] Figure 2 This is the electron micrograph of the nano silver powder for low-temperature silver paste obtained in Example 1 of the present invention.

[0025] Figure 3 This is the XRD spectrum of the nano silver powder for low-temperature silver paste obtained in Example 1 of the present invention. Detailed implementation mode

[0026] A spherical nano silver powder for low-temperature silver paste, the morphology of the silver powder is spherical, the silver powder particles are nanoscale, and according to ISO13310-2009, the particle size of the silver powder is D10 = 10 - 30nm, D50 = 40 - 100nm, D90 = 120 - 300nm.

[0027] ISO13320-2009 in the present invention is the international standard "Particle Size Analysis - Laser Diffraction Method".

[0028] D10, D50, and D90 in the present invention are parameters of the silver powder particle size, which refer to the cumulative percentage below this value accounting for 10%, 50%, and 90%. Among them, D50 is also called the median particle size, which refers to the particle size value corresponding to when the cumulative distribution percentage reaches 50%. It is a typical value representing the particle size. This value accurately divides the overall into two equal parts, that is, 50% of the particle diameters exceed this value, and 50% of the particle diameters are lower than this value. D50 is often used to represent the average particle size of the powder.

[0029] A preparation method of a spherical nano silver powder for low-temperature silver paste: using tap water as a solvent, Vc (L(+)-ascorbic acid) as a reducing agent, and one of silver nitrate, silver oxide, or silver chloride as a silver source, adding a surface modifier, a dispersant, a protective agent, and a pH regulator, controlling the pH value range of the reaction system to be 5 - 7, and using a one-pot chemical reduction method at room temperature (10 - 35°C) to obtain the spherical nano silver powder for low-temperature silver paste.

[0030] Among them: the dosage of the silver source is 2 - 10 w t%; the molar ratio of the reducing agent to the silver in the silver source is 1:1 - 1:1.5.

[0031] The surface modifier is one or more of sodium polyphosphate, sodium pyrophosphate, and sodium hexametaphosphate, and its dosage is 1 - 20% of the silver source mass.

[0032] The dispersant is one or more of polyethylene glycol 2000 - 6000, triethanolamine, and ethylene glycol monobutyl ether, and its dosage is 1 - 20% of the silver source mass.

[0033] The protective agent is one or more of oleic acid, melamine, benzotriazole, and water-soluble lanolin, and its dosage is 0.5-10% of the mass of the silver source.

[0034] The pH value regulator is solid sodium hydroxide.

[0035] In the present invention, the mass unit is g.

[0036] Vc (L(+)-ascorbic acid), silver nitrate, silver oxide, silver chloride, sodium polyphosphate, sodium pyrophosphate, sodium hexametaphosphate, polyethylene glycol 2000-6000, triethanolamine, ethylene glycol monobutyl ether, oleic acid, melamine, benzotriazole, water-soluble lanolin, and sodium hydroxide are all commercially available industrial-grade chemical raw materials.

[0037] There are 3 specific preparation methods as follows:

The first one

[0038]

The second one

[0039]

The third method

[0040] Example 1 A preparation method of spherical nano silver powder for low-temperature silver paste, comprising the following steps: ⑴ At room temperature, weigh the following raw materials: 624.25 g of tap water; 20 g of silver nitrate; 6.5 g of solid sodium hydroxide; 15.75 g of Vc.

[0041] Surface modifier: 3.0 g of sodium polyphosphate, 0.5 g of sodium pyrophosphate, 0.5 g of sodium hexametaphosphate.

[0042] Dispersant: 3.0 g of polyethylene glycol 6000, 0.5 g of triethanolamine, 0.5 g of ethylene glycol monobutyl ether.

[0043] Protective agent: 0.5 g of oleic acid, 0.5 g of melamine, 0.5 g of benzotriazole, 0.5 g of water-soluble lanolin.

[0044] ⑵ Mix 15.75 g of Vc with 299.25 g of tap water evenly to prepare a Vc tap water solution with a mass concentration of 5 w t%; then add the surface modifier, dispersant, and protective agent to a 1000 ml beaker containing 325 g of tap water, stir and dissolve to prepare a mixed solution A; ⑶ Add silver nitrate to the mixed solution A, stir at a rate of 100-500 revolutions per minute until the system becomes a milky white suspension; under continuous stirring, add 5wt The % Vc aqueous solution was rapidly added (within 5 seconds) to the suspension system, and then solid sodium hydroxide was immediately added, followed by continuous stirring for 1.0 hour; ⑷ Stop stirring, filter using a G6 sintered glass filter, wash the filter with deionized water 3 times, and finally wash the filter once with anhydrous methanol or anhydrous ethanol to obtain a good dispersion, and dry overnight to obtain 12.65 g of spherical nano-silver powder for low-temperature silver paste.

[0045] From Figures 1 - 3 It can be clearly seen that the spherical nano-silver powder for low-temperature silver paste prepared in Example 1 has a narrow particle size distribution. The electron micrograph shows that the particle size is consistent with the measurement result of the laser particle size analyzer. The silver powder particles are spherical. The XRD pattern indicates that the obtained silver powder has only diffraction peaks of different crystal planes of metallic silver, and no silver oxide or other silver species are detected, indicating that the silver salt is completely reduced to metallic silver powder by the one-pot liquid-phase chemical reduction preparation method.

[0046] Example 2 A preparation method of spherical nano-silver powder for low-temperature silver paste, comprising the following steps: S1 At room temperature, weigh the following raw materials: 202.1 g of tap water; 20 g of silver oxide; 6.2 g of solid sodium hydroxide; 18.9 g of Vc.

[0047] Surface modifier: 1.0 g of sodium polyphosphate, 0.5 g of sodium hexametaphosphate.

[0048] Dispersant: 3.0 g of polyethylene glycol 6000, 0.5 g of ethylene glycol monobutyl ether.

[0049] Protective agent: 0.5 g of melamine, 0.5 g of benzotriazole, 0.5 g of water-soluble lanolin.

[0050] S2 Mix 18.9 g of Vc with 107.1 g of tap water evenly to prepare a Vc aqueous solution with a mass concentration of 15 w t%; then add the surface modifier, dispersant, protective agent, and sodium hydroxide to a 500 ml beaker containing 95 g of tap water, stir and dissolve to prepare a mixed solution B; S3 Add silver oxide to the mixed solution B and stir evenly at a rate of 100 - 500 revolutions per minute to prepare a black-brown suspension; under continuous stirring, rapidly add (within 10 seconds) the 15 wt % Vc aqueous solution to the suspension system, and continue stirring for 2.0 hours; S4 Stop stirring, filter using a G6 sintered glass filter, wash the filter with deionized water 3 times, and finally wash the filter once with anhydrous methanol or anhydrous ethanol to obtain a good dispersion, and dry overnight to obtain 18.53 g of spherical nano-silver powder for low-temperature silver paste.

[0051] Example 3 A preparation method of spherical nano silver powder for low-temperature silver paste, comprising the following steps: ① At room temperature, weigh the following raw materials: 1000 g of tap water; 20 g of silver nitrate; 6.5 g of solid sodium hydroxide; 13 g of Vc.

[0052] Surface modifier: 0.2 g of sodium hexametaphosphate.

[0053] Dispersant: 4.0 g of polyethylene glycol 6000.

[0054] Protective agent: 1.0 g of benzotriazole, 0.5 g of water-soluble lanolin.

[0055] ② Mix 13 g of Vc with 117 g of tap water evenly to obtain a Vc tap water solution with a mass concentration of 10 wt %; then add the surface modifier, dispersant, and protective agent into a 1000 ml beaker containing 883 g of tap water, stir and dissolve to obtain a mixed solution A; ③ Add silver nitrate to the mixed solution A and stir evenly at a rate of 100 - 500 revolutions per minute. The system is a milky white suspension; add solid sodium hydroxide to the above milky white suspension, and the system becomes a black-brown suspension; under continuous stirring, quickly add (within 10 seconds) the 10 wt % Vc tap water solution to the suspension system and continue stirring for 1.0 hour; ④ Stop stirring, filter with a G6 sand core, wash with deionized water for 3 times, and finally wash and filter once with anhydrous methanol or anhydrous ethanol, and dry overnight to obtain 12.66 g of spherical nano silver powder for low-temperature silver paste.

[0056] Example 4 ⑴ At room temperature, weigh the following raw materials: 420 g of tap water; 20 g of silver chloride; 6.3 g of solid sodium hydroxide; 15 g of Vc.

[0057] Surface modifier: 1.0 g of sodium polyphosphate.

[0058] Dispersant: 1.0 g of ethylene glycol monobutyl ether.

[0059] Protective agent: 1.5 g of water-soluble lanolin.

[0060] ⑵ Mix 15 g of Vc with 135 g of tap water evenly to obtain a Vc tap water solution with a mass concentration of 10 w t%; then add the surface modifier, dispersant, and protective agent into a 500 ml beaker containing 285 g of tap water, stir and dissolve to obtain a mixed solution A; ⑶ Add silver chloride to the mixed solution A and stir at a rate of 300 revolutions per minute until the system becomes a milky white suspension; under continuous stirring, quickly add (within 5 seconds) a 10 wt % Vc aqueous solution in tap water to the suspension system, then immediately add solid sodium hydroxide to adjust the pH value to 7.0, and continue stirring for 2.0 hours; ⑷ Stop stirring, filter using a G6 sintered glass filter, wash the filter with deionized water 3 times, and finally wash the filter with anhydrous methanol or anhydrous ethanol once for good dispersion, and dry overnight to obtain 15.03 g of spherical nano-silver powder for low-temperature silver paste.

[0061] Example 5 A method for preparing spherical nano-silver powder for low-temperature silver paste, comprising the following steps: At room temperature, weigh the following raw materials: 862.5 g of tap water; 20 g of silver nitrate; 6.3 g of solid sodium hydroxide; 12.5 g of Vc.

[0062] Surface modifier: 1.5 g of sodium pyrophosphate, 1.5 g of sodium hexametaphosphate.

[0063] Dispersant: 0.2 g of triethanolamine.

[0064] Protective agent: 0.05 g of oleic acid, 0.05 g of benzotriazole.

[0065] ⑵ Mix 12.5 g of Vc with 237.5 g of tap water evenly to prepare a Vc aqueous solution in tap water with a mass concentration of 5 w t%; then add the surface modifier, dispersant, and protective agent to a 1000 ml beaker containing 625 g of tap water, stir and dissolve to prepare a mixed solution A; ⑶ Add silver nitrate to the mixed solution A and stir at a rate of 300 revolutions per minute until the system becomes a milky white suspension; under continuous stirring, quickly add (within 5 seconds) a 5 wt % Vc aqueous solution in tap water to the suspension system, then immediately add solid sodium hydroxide, and continue stirring for 1.0 hour; ⑷ Stop stirring, filter using a G6 sintered glass filter, wash the filter with deionized water 3 times, and finally wash the filter with anhydrous methanol or anhydrous ethanol once for good dispersion, and dry overnight to obtain 12.66 g of spherical nano-silver powder for low-temperature silver paste.

[0066] Example 6 A method for preparing spherical nano-silver powder for low-temperature silver paste, comprising the following steps: ⑴ At room temperature, weigh the following raw materials: 337.5 g of tap water; 20 g of silver nitrate; 6.8 g of solid sodium hydroxide; 12.5 g of Vc.

[0067] Surface modifiers: 1.0 g of sodium pyrophosphate and 1.0 g of sodium hexametaphosphate.

[0068] Dispersant: 4.0 g of polyethylene glycol 2000.

[0069] Protectant: 0.5 g of water-soluble lanolin and 0.5 g of oleic acid.

[0070] ⑵ Mix 12.5 g of Vc evenly with 112.5 g of tap water to prepare a Vc tap water solution with a mass concentration of 10 w t%. Then add the surface modifier, dispersant, and protectant into a 500 ml beaker containing 225 g of tap water, stir and dissolve to prepare a mixed solution A; ⑶ Add silver nitrate into the mixed solution A, stir at a rate of 300 revolutions per minute until the system becomes a milky white suspension; under continuous stirring, quickly add (within 20 seconds) the 10 wt % Vc tap water solution into the suspension system, and then immediately add solid sodium hydroxide to adjust the pH value to 5.0, and continue stirring for 1.0 hour; ⑷ Stop stirring, filter with a G6 sintered filter, wash with deionized water 3 times, and finally wash and filter once with anhydrous methanol or anhydrous ethanol to obtain good dispersion, and dry overnight to obtain 12.61 g of spherical nano-silver powder for low-temperature silver paste.

[0071] The particle size parameters and apparent density of the spherical nano-silver powder for low-temperature silver paste prepared in Examples 1-6 of the present invention are shown in Table 1 as measured by a Malvern laser particle size analyzer.

[0072] Table 1: Particle size parameters and apparent density of spherical nano-silver powder for low-temperature silver paste It can be clearly seen from Table 1 that the particle size parameters of the spherical nano-silver powder for low-temperature silver paste prepared in Examples 1-6 are D10 = 10 - 30 nm, D50 = 40 - 100 nm, D90 = 120 - 300 nm. The particle size distribution of the silver powder is relatively narrow, with good apparent density. The raw materials for its preparation are widely available and easy to obtain. The one-pot liquid-phase chemical reduction method has a simple preparation process, good repeatability, and lower production cost.

[0073] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the content of the present invention.

Claims

1. A spherical nano silver powder for low-temperature silver paste, characterized in that: The silver powder has a spherical morphology, and the silver powder particles are nanoscale. According to ISO13310-2009, the particle size of the silver powder is D10 = 10~30nm, D50 = 40~100nm, and D90 = 120 - 300nm.

2. The preparation method of spherical nano silver powder for low-temperature silver paste according to claim 1, characterized in that: This method refers to using tap water as a solvent, Vc as a reducing agent, and one of silver nitrate, silver oxide or silver chloride as a silver source, adding a surface modifier, a dispersant, a protective agent and a pH regulator, controlling the pH value range of the reaction system to be 5~7, and using a one-pot chemical reduction method at room temperature to prepare spherical nano silver powder for low-temperature silver paste.

3. The preparation method of spherical nano silver powder for low-temperature silver paste according to claim 2, wherein: The dosage of the silver source is 2 to 10 w t% of the mass of the solvent; the molar ratio of the reducing agent to the silver in the silver source is 1:1 to 1:1.

5.

4. The preparation method of spherical nano silver powder for low-temperature silver paste according to claim 2, characterized in that: The surface modifier is one or more of sodium polyphosphate, sodium pyrophosphate, and sodium hexametaphosphate, and its dosage is 1~20% of the mass of the silver source.

5. The preparation method of spherical nano silver powder for low-temperature silver paste according to claim 2, characterized in that: The dispersant is one or more of polyethylene glycol 2000 - 6000, triethanolamine, and ethylene glycol monobutyl ether, and its dosage is 1~20% of the mass of the silver source.

6. The preparation method of spherical nano silver powder for low-temperature silver paste according to claim 2, characterized in that: The protective agent is one or more of oleic acid, melamine, benzotriazole, and water-soluble lanolin, and its dosage is 0.5~10% of the mass of the silver source.

7. The preparation method of spherical nano silver powder for low-temperature silver paste according to claim 2, characterized in that: The pH regulator is solid sodium hydroxide.

8. A method for preparing spherical nano silver powder for low-temperature silver paste according to claim 2, comprising the following steps: ⑴ At room temperature, weigh according to the ratio; ⑵ Mix the reducing agent and the solvent evenly to obtain a reducing agent solution with a mass concentration of 5 to 15 w t%; then dissolve the surface modifier, dispersant, and protective agent in the remaining solvent to obtain a mixed solution A; ⑶ Add the silver source to the mixed solution A, and stir at a rate of 100~500 revolutions per minute until the system becomes a milky white or black-brown suspension; Under continuous stirring, quickly add the reducing agent solution to the suspension system, and then immediately add the pH regulator, and continue to stir for 0.5~2 hours; ⑷ Stop stirring, filter with a G6 sand core, wash with deionized water by filtration 3 times, and finally wash with anhydrous methanol or anhydrous ethanol by filtration once, and dry overnight to obtain black spherical nano silver powder for low-temperature silver paste.

9. The preparation method of spherical nano silver powder for low-temperature silver paste according to claim 8, characterized in that: The step ⑶ is replaced by the following method: Add the silver source to the mixed solution A, stir evenly at a rate of 100~500 revolutions per minute, add the pH regulator until the system becomes a black-brown suspension; Under continuous stirring, quickly add the reducing agent solution to the suspension system, and continue to stir for 0.5~2 hours.

10. A method for preparing spherical nano silver powder for low-temperature silver paste according to claim 2, comprising the following steps: S1 At room temperature, weigh according to the ratio; S2 Mix the reducing agent and the solvent evenly to obtain a reducing agent solution with a mass concentration of 5-15 w t%; then dissolve the surface modifier, dispersant, protective agent, and pH regulator in the remaining solvent to obtain a mixed solution B; S3 Add the silver source to the mixed solution B, and stir evenly at a rate of 100~500 revolutions per minute to obtain a black-brown suspension; Under continuous stirring, quickly add the reducing agent solution to the suspension system, and continue to stir for 0.5~2 hours; S4 Stop stirring, filter with a G6 sand core, wash with deionized water by filtration 3 times, and finally wash with anhydrous methanol or anhydrous ethanol by filtration once, and dry overnight to obtain black spherical nano silver powder for low-temperature silver paste.

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