Preparation method of sintered nano-silver powder with narrow particle size distribution, silver powder and application

Abstract

This invention discloses a method for preparing narrow-particle-size sintered silver nanoparticles, the silver powder itself, and its applications, relating to the field of metal material preparation technology. The preparation method includes the following steps: S1: preparing a reaction solution; S2: preparing a seed solution; S3: preparing a silver nanoparticle suspension; S4: preparing silver nanoparticles. By introducing a chitosan derivative as a nucleating agent at the seed synthesis end, the steric hindrance effect of the chitosan derivative and the electrostatic stabilizing effect of trisodium citrate are utilized, along with the ultrasonic cavitation effect to generate extremely strong micro-convection, allowing the reactants to be instantly and uniformly mixed at the microscale, thereby obtaining a seed product with good dispersibility. This achieves improved dispersibility, precise particle size control, and increased tap density of the silver nanoparticles, ultimately improving the sintering performance of silver solder paste.

Description

Technical Field

[0001] This invention relates to the field of metal material preparation technology, and in particular to a method for preparing narrow-particle-size sintered nano-silver powder, the silver powder, and its applications. Background Technology

[0002] Currently, silver solder paste is widely used in precision electronic manufacturing fields such as semiconductor chip packaging, LED packaging, and power device soldering. With the rapid development of electronic devices towards miniaturization, high density, and high performance, higher requirements are placed on silver solder paste: it needs to have lower sintering temperatures, higher sintering reliability, and lower sintering porosity. Silver powder, as a key functional phase, typically accounts for 60%-90% of the total solder paste mass, and its performance directly determines the solder paste's printability, sintering reliability, and the thermal conductivity and mechanical properties of the final silver joint. Therefore, the nano-silver powder used in silver solder paste should have narrow particle size distribution, high dispersibility, and high tap density.

[0003] Currently, the main method for preparing sintered silver nanopowder on the market is chemical reduction. However, existing traditional chemical reduction technologies suffer from problems such as excessively wide particle size distribution and large fluctuation range, which can lead to local concentration differences in silver solder paste during coating, affecting the mechanical properties and thermal conductivity of the sintered joint. At present, it is difficult for sintered silver nanopowder to simultaneously achieve small particle size, high dispersion performance, and high tap density. A single product can only achieve some parameters. For example, although CN119964872A solves the problem of weak bonding between solder ribbon and gate line, its silver nanopowder has a D10-D90 particle size distribution span of 300nm, which cannot meet the requirements of high-precision semiconductor device packaging for multi-parameter synergistic optimization of silver nanopowder.

[0004] To address the aforementioned issues, the industry urgently needs a preparation method that can simultaneously achieve high dispersibility, narrow particle size distribution, low surface coating agent, and high tap density of sintered nano-silver powder, in order to meet the stringent performance requirements of silver solder paste for semiconductor power device packaging. Summary of the Invention

[0005] This invention aims to provide a method for preparing narrow-particle-size sintered silver nanoparticles, the silver powder itself, and its applications. By introducing chitosan derivatives as nucleating agents at the seed crystal synthesis end, the steric hindrance effect of the chitosan derivatives and the electrostatic stabilizing effect of trisodium citrate are utilized. Combined with the ultrasonic cavitation effect to generate extremely strong micro-convection, the reactants are instantly and uniformly mixed at the microscale, thereby obtaining a seed crystal product with good dispersibility. This achieves improved dispersibility, precise particle size control, and increased tap density of the silver nanoparticles, thus improving the sintering performance of silver solder paste.

[0006] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows: A method for preparing narrow-particle-size sintered silver nanoparticles includes the following steps: S1: Prepare the reaction solution, including a first silver nitrate solution, a second silver nitrate solution, a nucleating agent solution, a dispersant solution, a first reducing agent solution, and a second reducing agent solution; S2: Add nucleating agent solution and first reducing agent solution to the reaction vessel, and rapidly add first silver nitrate solution under the assistance of ultrasound and stirring to obtain seed solution; S3: The dispersant solution and the seed crystal solution are mixed to obtain the base liquid. The second silver nitrate solution and the second reducing agent solution are simultaneously and slowly introduced into the base liquid. The reaction is carried out under stirring. After the introduction is completed, a suspension of nano silver powder is obtained. S4: Add an ethanol solution of a coating agent to a suspension of nano-silver powder to coat and modify the nano-silver powder. Then add a flocculant and proceed with separation, drying and pulverization to obtain sintered nano-silver powder with a narrow particle size distribution. In step S1, the nucleating agent is a mixed solution of chitosan derivative and trisodium citrate; The chitosan derivative is one or more of chitosan quaternary ammonium salt, chitosan sulfate, carboxymethyl chitosan, and acylated chitosan; The concentration of the chitosan derivative is 1-3 g / L, and the concentration of trisodium citrate is 0.5-2 g / L.

[0007] The mass ratio of the chitosan derivative to silver nitrate in the first silver nitrate solution is 1:2-1:1; the mass ratio of trisodium citrate to silver nitrate in the first silver nitrate solution is 1:4-1:2.

[0008] In step S1, the concentration of the first silver nitrate solution is 0.05-0.5 mol / L, and the concentration of the second silver nitrate solution is 0.8-5 mol / L.

[0009] In step S1, the first reducing agent and the second reducing agent are each independently any one or a mixture of multiple of ascorbic acid, hydrazine hydrate, sodium borohydride and ethylene glycol.

[0010] In step S1, the molar ratio of the reducing agent in the first reducing agent solution to the silver nitrate in the first silver nitrate solution is 0.5:1-3:1; the molar ratio of the reducing agent in the second reducing agent solution to the silver nitrate in the second silver nitrate solution is 0.5:1-3:1. In step S1, the dispersant is any one or a mixture of gelatin, hydroxypropyl methylcellulose, carboxymethyl cellulose and gum arabic.

[0011] In step S1, the concentration of the dispersant solution is 1-3 g / L, and the mass ratio of the dispersant to the silver nitrate in the second silver nitrate solution is 0.01:1-0.05:1.

[0012] In step S2, the ultrasonic power of the ultrasonic-assisted reaction is 500-1200W; the reaction temperature is 20-60℃; the reaction time is 0.5-2 hours; and the stirring speed is 200-400rpm.

[0013] In step S3, the rate at which the second silver nitrate solution and the second reducing agent solution are introduced is 150-500 mL / min. In step S3, the reaction temperature is 30-60℃ and the stirring speed is 150-300 rpm.

[0014] In step S4, the coating agent is any one or a mixture of more than one of stearic acid, palmitic acid, erucic acid, palmitic acid and lauric acid.

[0015] In step S4, the mass ratio of the coating agent to the silver nitrate in the second silver nitrate solution is 1:300-1:100.

[0016] In step S4, the flocculant is any one or a mixture of sodium citrate, sodium hydroxide, calcium chloride, and polydimethylammonium chloride.

[0017] In step S4, the amount of flocculant used is 1-2g.

[0018] A narrow-particle-size sintered silver nanoparticle powder prepared by the above steps has a particle size distribution span of <150nm, an average particle size D50 ≤165nm, and a tap density ≥4.0g / cm³. 3 .

[0019] An application of narrow particle size distribution sintered silver nanopowder prepared by the above preparation method in silver solder paste: 85% by mass of silver nanopowder is mixed evenly with 10% terpineol and 5% ethylene glycol and degassed to obtain the corresponding silver solder paste product.

[0020] The beneficial effects of this invention are: 1. In this invention, the steric hindrance effect generated by the cyclic long-chain structure of chitosan derivatives is utilized to coat the seed crystal surface and prevent inter-seed crystal aggregation. Simultaneously, the electrostatic interaction between the hydroxyl groups on the chitosan derivative surface and trisodium citrate further inhibits seed crystal agglomeration. Combined with ultrasonic assistance, the dispersion problem of seed crystals during the synthesis of sintered silver nanopowder is solved under the combined effect of multi-field coupling. Subsequently, combined with a simultaneous co-current synthesis method, silver nanopowder with a narrow particle size distribution and high tap density is obtained, with a particle size distribution span <150nm, an average particle size D50 ≤165nm, and a tap density ≥4.0g / cm³. 3 This nano-silver powder, used as a filler in silver solder paste, can avoid localized concentration differences during the coating process, which could affect the mechanical properties and thermal conductivity of the sintered joint.

[0021] 2. This invention introduces chitosan derivatives as specific nucleating agents during seed crystal synthesis, combined with ultrasonic assistance, to obtain a specially prepared highly dispersed seed crystal solution. Then, a second silver nitrate solution and a reducing agent solution are simultaneously injected into the mixed solution of seed crystals and dispersant, so that silver particles grow synchronously and uniformly, ensuring the stable acquisition of nano-silver powder with a narrow particle size distribution.

[0022] 3. The particle size range obtained in this invention is 100-250 nm, the particle size distribution span is <150 nm, and the tap density is ≥4.0 g / cm³. 3 With an average particle size D50 ≤ 165 nm, this method overcomes the problem of not being able to simultaneously achieve optimal size, tap density, and narrow particle size distribution in this type of silver nanopowder. Excellent seed dispersion results in sintered silver nanopowder with a particle size distribution of <150 nm. The simultaneous co-current growth method used in step S3 ensures uniform deposition of silver ions on the seed surface, resulting in better crystallinity and sphericity, leading to higher tap density.

[0023] 4. The nano-silver powder prepared in this invention has excellent sintering performance in silver solder paste applications. The average particle size of less than 165 nm can bring higher surface energy, thereby enabling lower temperature sintering (180-250℃); the higher tap density can achieve the preparation of silver solder paste with high solid content, thereby achieving high shear strength (>70MPa) after sintering; and the narrower particle size distribution can avoid local concentration differences during the silver solder paste coating process, which would affect the mechanical properties of the sintered joint. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the silver nanoparticles prepared in Example 1 of the present invention.

[0025] Figure 2 This is a scanning electron microscope image of the silver nanoparticles prepared in Example 2 of the present invention.

[0026] Figure 3 This is a scanning electron microscope image of the silver nanoparticles prepared in Comparative Example 1 of this invention.

[0027] Figure 4 This is a particle size distribution diagram of the nano-silver powder prepared in Example 1 of the present invention.

[0028] Figure 5 This is a particle size distribution diagram of the nano-silver powder prepared in Example 2 of the present invention.

[0029] Figure 6 This is a particle size distribution diagram of the nano-silver powder prepared in Comparative Example 1 of this invention.

[0030] Figure 7 This is a scanning electron microscope image of the silver solder paste after sintering of the nano-silver powder prepared in Example 1 of this invention.

[0031] Figure 8 This is a scanning electron microscope image of the push-pull force test after sintering of the silver solder paste containing the nano-silver powder prepared in Example 1 of this invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0033] Example 1 This embodiment provides a method for preparing narrow-particle-size sintered silver nanoparticles, comprising the following steps: S1: Prepare the reaction solution by dissolving 2.55g of silver nitrate in 150ml of deionized water to prepare the first silver nitrate solution; the nucleating agent solution is prepared by dissolving 2g of chitosan quaternary ammonium salt and 1g of trisodium citrate in 1L of deionized water; the first reducing agent solution is prepared by dissolving 3.25g of ascorbic acid in 300ml of deionized water; the second silver nitrate solution is prepared by dissolving 105g of silver nitrate in 620ml of deionized water; the dispersant solution is prepared by dissolving 2g of gelatin in 800ml of deionized water; the second reducing agent solution is prepared by dissolving 65.1g of ascorbic acid in 620ml of deionized water. S2: Add nucleating agent solution to ultrasonic reactor, set ultrasonic frequency to 800W, temperature to 40℃, stirring speed to 250rpm, add first reducing agent solution, stir for 5 minutes, quickly add first silver nitrate solution, ultrasonically stir for 30 minutes to obtain seed solution. S3: Maintain the temperature at 60℃ and the stirring speed at 300rpm. Add the prepared seed crystal solution to the dispersant solution and stir for 20 minutes. Then, add the second silver nitrate solution and the second reducing agent solution dropwise to the bottom liquid at a rate of 150mL / min. After the addition is complete, a nano silver powder suspension is obtained. S4: Add 0.5g of stearic acid to the suspension of nano silver powder to coat and modify the silver powder, then add 1.5g of sodium citrate flocculant. After flocculation, sedimentation and washing, the mixture is vacuum dried at 80℃ and pulverized to finally obtain nano silver powder.

[0034] like Figure 1 The image shown is a scanning electron microscope image of the silver nanoparticles prepared in this embodiment.

[0035] like Figure 4 The figure shown is a particle size distribution diagram of the silver nanoparticles prepared in this embodiment.

[0036] Example 2 This embodiment provides a method for preparing narrow-particle-size sintered silver nanoparticles, comprising the following steps: S1: Prepare the reaction solution by dissolving 0.85g of silver nitrate in 150ml of deionized water to prepare the first silver nitrate solution; the nucleating agent solution is prepared by dissolving 0.75g of chitosan sulfate and 0.25g of trisodium citrate in 0.5L of deionized water; the first reducing agent solution is prepared by dissolving 0.2g of 80% hydrazine hydrate in 300ml of deionized water; the second silver nitrate solution is prepared by dissolving 210g of silver nitrate in 620ml of deionized water; the dispersant solution is prepared by dissolving 2g of hydroxypropyl methylcellulose in 800ml of deionized water; the second reducing agent solution is prepared by dissolving 230g of 80% hydrazine hydrate in 620ml of deionized water. S2: Add nucleating agent solution to ultrasonic reactor, set ultrasonic frequency to 500W, temperature to 60℃, stirring speed to 200rpm, add first reducing agent solution, stir for 5 minutes, quickly add first silver nitrate solution, ultrasonically stir for 60 minutes to obtain seed solution. S3: Keep the temperature at 30℃ and the stirring speed at 150rpm. Add the prepared seed crystal solution to the dispersant solution and stir for 15 minutes. Then, add the second silver nitrate solution and the second reducing agent solution dropwise to the bottom liquid at a speed of 480mL / min. After the addition is complete, a nano silver powder suspension is obtained. S4: Add 0.7g of erucic acid to the suspension of nano-silver powder to coat and modify the silver powder, then add 1g of sodium hydroxide flocculant. After flocculation, sedimentation and washing, the mixture is vacuum dried at 80℃ and pulverized to finally obtain nano-silver powder.

[0037] like Figure 2 The image shown is a scanning electron microscope image of the silver nanoparticles prepared in this embodiment.

[0038] like Figure 5 The figure shown is a particle size distribution diagram of the silver nanoparticles prepared in this embodiment.

[0039] Example 3 This embodiment provides a method for preparing narrow-particle-size sintered silver nanoparticles, comprising the following steps: S1: Prepare the reaction solution by dissolving 8.5g of silver nitrate in 150ml of deionized water to prepare the first silver nitrate solution; the nucleating agent solution is prepared by dissolving 6g of acylated chitosan and 4g of trisodium citrate in 2L of deionized water; the first reducing agent solution is prepared by dissolving 5.6g of sodium borohydride in 300ml of deionized water; the second silver nitrate solution is prepared by dissolving 525g of silver nitrate in 620ml of deionized water; the dispersant solution is prepared by dissolving 2g of hydroxypropyl methylcellulose in 800ml of deionized water; the second reducing agent solution is prepared by dissolving 116g of sodium borohydride in 620ml of deionized water. S2: Add nucleating agent solution to ultrasonic reactor, set ultrasonic frequency to 1200W, temperature to 20℃, stirring speed to 400rpm, add first reducing agent solution, stir for 10 minutes, then quickly add first silver nitrate solution, ultrasonically stir for 120 minutes to obtain seed solution. S3: Maintain the temperature at 60℃ and the stirring speed at 300rpm. Add the prepared seed crystal solution to the dispersant solution and stir for 15 minutes. Then, add the second silver nitrate solution and the second reducing agent solution dropwise to the bottom liquid at a rate of 150mL / min. After the addition is complete, a nano silver powder suspension is obtained. S4: Add 5.25g palmitic acid to the suspension of nano silver powder to coat and modify the silver powder, then add 2g of polydimethylammonium chloride flocculant. After flocculation, sedimentation and washing, the mixture is vacuum dried at 80℃ and pulverized to finally obtain nano silver powder.

[0040] Example 4 Compared with Example 1, the difference in this embodiment is that the reaction temperature in step S3 is adjusted to 30°C, the stirring rate is adjusted to 150 rpm, and the synchronous dropping speed of the second silver nitrate solution and the second reducing agent solution is adjusted to 500 mL / min. The other conditions are the same as in Example 1.

[0041] Example 5 The difference between this embodiment and Embodiment 1 is that, in this embodiment, the coating modifier in step S4 is replaced with an equal mass of lauric acid, and the flocculant is replaced with an equal mass of calcium chloride, while the other conditions are the same as in Embodiment 1.

[0042] Comparative Example 1 In this comparative example, no nucleating agent is added in step S2, and the other conditions are the same as in Example 1. like Figure 3 The image shown is a scanning electron microscope image of the silver nanoparticles prepared in this comparative example.

[0043] like Figure 6 The figure shown is a particle size distribution diagram of the silver nanoparticles prepared in this comparative example.

[0044] Comparative Example 2 In this comparative example, ultrasound assistance is not used in step S2, and the other conditions are the same as in Example 1.

[0045] Comparative Example 3 In this comparative example, the nucleating agent was replaced with an equal mass of conventional nucleating agent gelatin, and the other conditions were the same as in Example 1.

[0046] Comparative Example 4 In this comparative example, the nucleating agent was replaced with an equal mass of polyvinylpyrrolidone (PVPK30), and the other conditions were the same as in Example 1.

[0047] Experimental Example In this experimental example, the nano-silver powders prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to the following performance tests, and the test results are shown in Table 1.

[0048] In this experimental example, the test items include: 1. Particle size distribution: The particle size distribution was measured using a laser particle size analyzer according to standard GB / T19077-2016, and the D10, D50, and D90 values ​​were recorded.

[0049] 2. Tap density: Measured using a tap density meter in accordance with standard GB / T5162-2021.

[0050] 3. Specific surface area: measured according to standard GB / T19587-2017, using the nitrogen adsorption BET method.

[0051] Table 1 Performance parameters of the silver nanopowders prepared in Examples 1-5 and Comparative Examples 1-4

[0052] The silver nanoparticles prepared in all examples exhibited excellent narrow particle size distribution characteristics. Their D50 (median particle size) was concentrated in the range of 160-175 nm, and their D90 was all less than 260 nm, indicating that the vast majority of particles were very small and concentrated. The small particle size distribution range directly proves that the method of this invention can efficiently and controllably prepare silver nanoparticles with uniform particle size. Meanwhile, the tap density (4.0-4.5 g / cm³) and specific surface area (3.0-3.6 m² / g) data of each example were all within a good and mutually matching range, indicating that the obtained silver powder possesses both good filling properties and sintering activity.

[0053] The performance of Example 2 is very close to that of Example 1. The difference may stem from changes in the nucleating agent and reducing agent system. The data show that, within the framework of this invention, specific types of chitosan derivative nucleating agents, combined with different reducing agents, can also achieve narrow particle size distributions, demonstrating the method's material adaptability.

[0054] The D50 and D90 values ​​of Example 3 are slightly higher than those of Example 1, while the specific surface area is slightly lower. This is mainly due to the increase in the total amount of reactants and the pumping rate, which leads to a slight increase in the final particle size, resulting from the scale-up effect. However, the particle size distribution remains very narrow, demonstrating that the method has good scalability.

[0055] In Example 4, D50 and D90 were increased compared to Example 1, while the specific surface area decreased. This is directly attributed to the lower reaction temperature and slower stirring speed in step S3. This may have reduced the reduction and deposition rate of silver atoms, altered the growth kinetics, resulting in a relatively longer particle growth time and a slightly larger size, but the narrow distribution characteristics of the core were still maintained.

[0056] The differences in particle size distribution and specific surface area in Example 5 were mainly caused by changes in the coating modifier and flocculant. Different surfactants and flocculation systems may affect the final powder dispersion and agglomeration, but have little effect on the seed crystal size, further proving that the preceding process steps are the core of controlling particle size distribution.

[0057] Compared to Example 1, Comparative Example 1 (without chitosan derivative nucleating agent) showed a significantly wider particle size distribution in its silver powder (D90 reaching 1210 nm), with a large number of micron-sized particles. This is because the lack of a specific chitosan derivative as a guide makes it difficult for the nucleation process of silver reduction to proceed uniformly and controllably, resulting in random nucleation and growth, and an intensified Ostwald ripening effect, thus generating particles with vastly different sizes. This defect directly leads to the deterioration of the rheological properties of the silver powder when preparing slurries, resulting in poor film density and numerous pores after sintering, severely degrading its reliability as a conductive or thermally conductive material.

[0058] Compared to Example 1, Comparative Example 2 (preparation of silver powder without ultrasonic assistance) showed a decrease in particle size distribution uniformity (increased distribution span). This is because, during the critical stage of seed formation, the lack of intense, instantaneous mixing provided by ultrasonic energy resulted in insufficient concentration of the nucleation explosion period and inadequate size uniformity of the initial seed crystals. This deficiency jeopardizes the batch consistency and stability of the final product, potentially leading to performance fluctuations in demanding high-precision electronic packaging applications.

[0059] Compared to Example 1, Comparative Example 3 (using gelatin instead of chitosan derivative nucleating agent) showed a severely degraded product performance, with D50 increasing to 813 nm, exceeding the nanoscale. This is because the traditional dispersant gelatin primarily serves a later-stage protective function; its molecular structure lacks the ability to actively and effectively guide and stabilize silver crystal nuclei in the early stages of the reaction, thus failing to achieve the controllable nucleation required by this invention. This results in a product that completely fails to meet the requirements of high-end electronic devices for the sintering activity and fine printability of nano-silver powder.

[0060] Compared to Example 1, Comparative Example 4 (using PVP instead of chitosan derivative nucleating agent) produced a product exhibiting micron-sized aggregates (D50 reaching 1475 nm) with a very low specific surface area. This is because PVP, as a common steric hindrance protectant, works by adsorbing onto the surface of already formed particles to prevent aggregation, but it cannot function as a "nucleating agent" for directional regulation during the nucleation stage. In this process, its nucleation failed, leading to the disordered deposition and growth of silver atoms into coarse aggregates, thus losing the basic properties and application value of nanomaterials.

[0061] Application examples In this application example, the nano-silver powder obtained in Examples 1-5 and Comparative Examples 1-4 was used to prepare silver solder paste. 85% by weight of the nano-silver powder was mixed evenly with 10% terpineol and 5% ethylene glycol, and then degassed to obtain the corresponding silver solder paste. The prepared silver solder paste was printed onto an AMB substrate, dried at 140°C for 20 minutes, and then SiC chips (5*5mm) were mounted using a pick-and-place machine. 2 The solder paste was sintered at 250℃, 15MPa pressure, and nitrogen protection for 5 minutes. Shear strength was tested using a push-pull force tester, the microstructure of the damaged interface was observed using a scanning electron microscope, and the resistivity of the sintered silver solder paste was measured using a four-probe resistivity meter according to standard GB / T1551-2021.

[0062] The prepared silver solder paste underwent the following performance tests, and the test results are shown in Table 2.

[0063] Table 2 Performance parameters of silver solder pastes prepared from nano-silver powder in Examples 1-5 and Comparative Examples 1-4

[0064] like Figure 7 The image shown is a scanning electron microscope (SEM) image of the silver solder paste obtained from the nano-silver powder prepared in Example 1 after sintering.

[0065] like Figure 8 The image shown is a scanning electron microscope (SEM) image of the push-pull force of the silver solder paste prepared in Example 1 after sintering.

[0066] Figure 7The solder paste prepared from the narrow-particle-size silver nanoparticles of this invention forms a highly dense, uniform, and extremely low-porosity sintered silver bonding layer under the sintering process. The silver particles are well-fused, and the sintered necks are large and continuous, directly corresponding to its excellent electrical conductivity and mechanical strength.

[0067] Figure 8 The fracture morphology after shear testing is shown. The fracture type is ductile fracture, and it mainly occurs within the sintered silver layer, rather than at the interface between the silver layer and the chip or substrate. This demonstrates that the sintered body formed by the silver powder of this invention has high inherent strength and forms a strong metallurgical bond with the substrate and chip, exhibiting excellent interface reliability.

[0068] Table 2 shows that the narrow-particle-size silver nanoparticles prepared in this invention are key to achieving high-performance silver sintering bonding. The silver solder pastes prepared in Examples 1-5 all exhibit excellent comprehensive performance, directly attributable to the inherent high uniformity and high sintering activity of their silver powders. Example 1 shows the best performance. The performance of Examples 2-5 shows slight differences: Example 2 is slightly lower due to changes in the nucleating agent and reducing agent system; Examples 3 and 4 are slightly affected by the slightly larger initial particle size of the silver powder, resulting in slightly lower sintering densification; Example 5 may have introduced interface defects due to changes in the coating and flocculation system. These differences further demonstrate that, under the premise of ensuring the core processes (specific nucleation, ultrasonic assistance, and simultaneous growth), the method of this invention has a certain process window and material adaptability, and can obtain sintered materials that meet the requirements of high-end applications.

[0069] In contrast, the silver powder in the comparative examples suffered from inherent defects that led to severe degradation or even failure of the solder paste performance. The silver powder in Comparative Examples 1 and 2 exhibited poor sintering density due to insufficient particle size distribution uniformity (caused by the absence of nucleating agent guidance and ultrasonic assistance, respectively), resulting in a significant decrease in shear strength and an increase in resistivity, directly impacting the reliability of the packaged devices. Comparative Examples 3 (using gelatin) and 4 (using PVP) showed the most complete failure: the former resulted in extremely low sintering activity of the micron-sized silver powder due to the complete inability of the nucleating agent to control nucleation, leading to extremely poor bonding strength and conductivity; the latter resulted in the formation of unsinterable agglomerates due to nucleation failure, and even failed to form an effective testable bonding layer. These comparative results strongly demonstrate from an application perspective that the specific chitosan derivative nucleating agent, ultrasonic-assisted seed preparation, and simultaneous drop-growth process employed in this invention are indispensable core technologies for obtaining nano-silver powder with highly reliable sintering performance.

[0070] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for preparing narrow-particle-size sintered silver nanoparticles, characterized in that: Includes the following steps: S1: Prepare the reaction solution, including a first silver nitrate solution, a second silver nitrate solution, a nucleating agent solution, a dispersant solution, a first reducing agent solution, and a second reducing agent solution; S2: Add nucleating agent solution and first reducing agent solution to the reaction vessel, and rapidly add first silver nitrate solution under the assistance of ultrasound and stirring to obtain seed solution; S3: The dispersant solution and the seed crystal solution are mixed to obtain the base liquid. The second silver nitrate solution and the second reducing agent solution are simultaneously and slowly introduced into the base liquid. The reaction is carried out under stirring. After the introduction is completed, a suspension of nano silver powder is obtained. S4: Add an ethanol solution of a coating agent to a suspension of nano-silver powder to coat and modify the nano-silver powder. Then add a flocculant and proceed with separation, drying, and pulverization to obtain sintered nano-silver powder with a narrow particle size distribution.

2. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S1, the nucleating agent is a mixed solution of chitosan derivative and trisodium citrate.

3. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 2, characterized in that: The chitosan derivative is one or more of chitosan quaternary ammonium salt, chitosan sulfate, carboxymethyl chitosan, and acylated chitosan.

4. The method for preparing narrow particle size distribution sintered nano-silver powder according to claim 2, characterized in that: The concentration of the chitosan derivative is 1 g / L-3 g / L, and the concentration of trisodium citrate is 0.5 g / L-2 g / L.

5. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 2, characterized in that: The mass ratio of the chitosan derivative to silver nitrate in the first silver nitrate solution is 1:2-1:1; the mass ratio of trisodium citrate to silver nitrate in the first silver nitrate solution is 1:4-1:

2.

6. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S1, the concentration of the first silver nitrate solution is 0.05 mol / L-0.5 mol / L, and the concentration of the second silver nitrate solution is 0.8 mol / L-5 mol / L.

7. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S1, the first reducing agent and the second reducing agent are each independently any one or a mixture of multiple of ascorbic acid, hydrazine hydrate, sodium borohydride and ethylene glycol.

8. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S1, the molar ratio of the reducing agent in the first reducing agent solution to the silver nitrate in the first silver nitrate solution is 0.5:1-3:1; the molar ratio of the reducing agent in the second reducing agent solution to the silver nitrate in the second silver nitrate solution is 0.5:1-3:

1.

9. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S1, the dispersant is any one or a mixture of gelatin, hydroxypropyl methylcellulose, carboxymethyl cellulose and gum arabic.

10. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 9, characterized in that: In step S1, the concentration of the dispersant solution is 1 g / L-3 g / L, and the mass ratio of the dispersant to the silver nitrate in the second silver nitrate solution is 0.01:1-0.05:

1.

11. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S2, the ultrasonic power of the ultrasonic-assisted reaction is 500W-1200W; the reaction temperature is 20℃-60℃; the reaction time is 0.5-2 hours; and the stirring speed is 200rpm-400rpm.

12. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S3, the rate at which the second silver nitrate solution and the second reducing agent solution are introduced is 150-500 mL / min.

13. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S3, the reaction temperature is 30℃-60℃ and the stirring speed is 150rpm-300rpm.

14. The method for preparing narrow particle size distribution sintered silver nanoparticles according to claim 1, characterized in that: In step S4, the coating agent is any one or a mixture of more than one of stearic acid, palmitic acid, erucic acid, palmitic acid and lauric acid.

15. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 14, characterized in that: In step S4, the mass ratio of the coating agent to the silver nitrate in the second silver nitrate solution is 1:300-1:

100.

16. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 1, characterized in that: In step S4, the flocculant is any one or a mixture of sodium citrate, sodium hydroxide, calcium chloride, and polydimethylammonium chloride.

17. The method for preparing narrow particle size distribution sintered silver nanopowder according to claim 16, characterized in that: In step S4, the amount of flocculant used is 1-2g.

18. A narrow-particle-size sintered silver nanoparticle powder prepared by the preparation method according to any one of claims 1-17, wherein the particle size distribution span is <150 nm, the average particle size D50 is ≤165 nm, and the tap density is ≥4.0 g / cm³. 3 .

19. An application of narrow particle size distribution sintered nano-silver powder prepared by any one of claims 1-17 in silver solder paste, wherein 85% by mass of nano-silver powder is mixed evenly with 10% terpineol and 5% ethylene glycol and degassed to obtain the corresponding silver solder paste product.

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