Method for preparing high-activity, high-dispersion and low-resistance silver powder and silver paste through amino acid modification

Abstract

The invention relates to a method for preparing high-activity, high-dispersion and low-resistance silver powder and silver paste through amino acid modification. The method comprises the following steps that A, silver oxalate is synthesized; b, silver particles are prepared, wherein silver oxalate, amino acid, amine and a solvent are subjected to thermal decomposition to obtain the silver particles; c, silver powder is prepared, specifically, silver particles are cleaned and freeze-dried to form silver blocks, and the silver blocks are ground into the silver powder; and D, silver paste preparation: taking 85-95% by mass of silver powder, adding a silane coupling agent, butyl carbamate and terpilenol, grinding, and filtering to obtain the high-activity and low-resistance nano silver paste.

Description

Technical Field

[0001] This invention relates to the field of silver powder preparation technology, and in particular to a method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification. Background Technology

[0002] Highly active and highly dispersed low-resistance silver powder is the core foundation for achieving breakthroughs in high-power chip applications such as silver-copper interconnects in chip packaging. Currently, it is difficult for commercially available silver powder in my country to simultaneously possess all three characteristics: high activity, high dispersion, and low resistance. Chinese companies generally use KM120 from Japan's Tokusen Kogyo Co., Ltd., which has similar characteristics, but its performance cannot fully meet the requirements. Its conductivity still needs improvement, and its particle size distribution is limited, only meeting the requirements of 0.15–0.3 μm. Summary of the Invention

[0003] In view of the above situation, it is necessary to propose a method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification of silver powder with different submicron particle size distribution range.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification, comprising the following steps: A. Synthetic silver oxalate; B. Preparation of silver particles: Silver particles are obtained by thermal decomposition of silver oxalate with amino acids, amines and solvents; C. Preparation of silver powder: Clean the silver particles, freeze-dry them to form silver blocks, and grind them into silver powder; D. Preparation of silver paste: Take 85%-95% silver powder by mass, add silane coupling agent, butylcarboxylate, and terpineol, grind and filter to obtain highly active and low-resistivity nano-silver paste.

[0005] Furthermore, step A includes: forming silver oxalate using silver nitrate and oxalate dihydrate.

[0006] Further, step A includes: dissolving oxalic acid dihydrate in water for 30 minutes, then adding silver nitrate dissolved in water dropwise for 30 minutes to form a white precipitate, stirring for 30 minutes and then stopping, and obtaining white solid silver oxalate by centrifugation.

[0007] Further, step A includes: taking 63g of oxalic acid dihydrate and pouring it into a 5L brown three-necked flask, adding 1.5L of deionized water, and stirring for 15 minutes to form a clear solution; dissolving 61.2g of silver nitrate in 1.5L of deionized water to form a transparent solution, and then adding it dropwise to the brown three-necked flask using a constant pressure funnel over a period of 30 minutes; during the dropwise addition, a white precipitate will gradually form in the flask; after the dropwise addition is complete, react at 300-800 rpm for another 30 minutes; pouring the white solid and solution into a centrifuge bottle and centrifuging to obtain a white solid, then washing it twice with ethanol and once with acetone before use.

[0008] Further, step B includes: mixing silver oxalate with amino acids, amines and solvents evenly, stirring to form a homogeneous mixture, maintaining a constant temperature of 110℃-120℃, heating for a period of time and then cooling to obtain a silver dispersion, and centrifuging the silver dispersion to obtain silver particles.

[0009] Furthermore, the solvent in step B is one or more selected from ethanol, ethylene glycol, n-butanol, isopropanol, pentanol, toluene, xylene, and diethylene glycol butyl ether.

[0010] Furthermore, the amino acid in step B includes one or more of alanine, arginine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine, and histidine.

[0011] Furthermore, the amine in step B includes diamines and straight-chain amines with a chain length of 3-18 carbons.

[0012] Furthermore, in step D, the mass percentage of the silane coupling agent is less than 0.5%, the mass percentage of the butylcarboxylate is 1%-5%, and the mass percentage of the terpineol is 1%-5%.

[0013] Further, step D includes: taking 93% silver powder by mass, adding 0.1% silane coupling agent, adding 3% butylcarboxylate, adding 3% terpineol, grinding with a three-roll mill and filtering with a 400-mesh filter to obtain a highly active and low-resistance nano-silver paste.

[0014] The beneficial effects of this invention are as follows: through the reaction of silver oxalate, amino acids, and amines, the amino acids and amines act as complexing agents, dispersants, and morphology modifiers to obtain submicron, highly dispersed silver particles; then, through washing and centrifugation, high-purity silver powder is obtained; and then, the high-purity silver powder is added with silane coupling agent, tetracarboxylate, and terpineol to form silver paste; the addition of terpineol can improve printability and dispensing properties, wet the substrate, and volatilize during drying / sintering without leaving carbon residue; the addition of tetracarboxylate can prevent the silver paste from drying too quickly and clogging the screen, improve leveling, film formation, and printing clarity, making the silver layer denser and the surface smoother; the silane coupling agent acts as an interface bridge, improving adhesion, resistance to boiling water, and resistance to thermal shock, improving the dispersibility of silver powder, reducing agglomeration, and lowering resistance. It can control the particle size distribution range to prepare silver powder of different submicron sizes, meeting the needs of mainstream submicron silver powder particle sizes. It covers three different requirements: 100nm, 100-300nm, and 300-800nm, providing comprehensive coverage of the submicron silver powder particle size range. Furthermore, it exhibits strong conductivity and low resistivity. Attached Figure Description

[0015] Figure 1 This is a SEM image of the silver paste obtained in Embodiment 1 of the present invention; Figure 2 This is a resistivity variation diagram of silver paste obtained in Embodiment 1 of the present invention. Figure 3 This is a SEM image of the silver paste obtained in Embodiment 2 of the present invention; Figure 4 This is a resistivity variation diagram of silver paste obtained in Embodiment 2 of the present invention. Figure 5 This is a SEM image of the silver paste obtained in Embodiment 3 of the present invention; Figure 6 This is a resistivity variation diagram of silver paste obtained in Embodiment 3 of the present invention. Figure 7 These are SEM images and resistivity variation graphs of the existing KM120 technology. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description, in conjunction with the accompanying drawings and embodiments, provides a method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste using amino acid modification. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of the invention.

[0017] Please refer to Figures 1-6 A method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification includes the following steps: A. Synthetic silver oxalate; B. Preparation of silver particles: Silver particles are obtained by thermal decomposition of silver oxalate with amino acids, amines and solvents; C. Preparation of silver powder: Clean the silver particles, freeze-dry them to form silver blocks, and grind them into silver powder; D. Preparation of silver paste: Take 85%-95% silver powder by mass, add silane coupling agent, butylcarboxylate, and terpineol, grind and filter to obtain highly active and low-resistivity nano-silver paste.

[0018] Submicron, highly dispersed silver particles are obtained through the reaction of silver oxalate, amino acids, and amines. The amino acids and amines act as complexing agents, dispersants, and morphology modifiers. High-purity silver powder is then obtained through washing and centrifugation. The high-purity silver powder is then combined with silane coupling agent, tetracarboxylate, and terpineol to form silver paste. The addition of terpineol improves printability and dispensing properties, wets the substrate, and volatilizes during drying / sintering without leaving carbon residue. The addition of tetracarboxylate prevents the silver paste from drying too quickly and clogging the screen, improves leveling, film formation, and printing clarity, and makes the silver layer denser and the surface smoother. The silane coupling agent acts as an interfacial bridge, improving adhesion, resistance to boiling water and thermal shock, improving the dispersibility of silver powder, reducing agglomeration, and lowering electrical resistance. It can control the particle size distribution range to prepare silver powder of different submicron sizes, meeting the needs of mainstream submicron silver powder particle sizes. It covers three different requirements: below 100nm, 100-300nm, and 300-800nm, providing comprehensive coverage of the submicron silver powder particle size range. Furthermore, it exhibits strong electrical conductivity and low resistivity during low-temperature sintering.

[0019] Further, step A includes: forming silver oxalate using silver nitrate and oxalate dihydrate. There are five common methods for synthesizing silver oxalate, and any one can be chosen as needed. These include: the classic precipitation method using silver nitrate and oxalate dihydrate; the silver nitrate and oxalate method, where ammonia / ethylenediamine first react with Ag⁺ to form a silver-ammonia complex ion, followed by slow precipitation with oxalate; the microemulsion method using silver nitrate, oxalic acid, and a surfactant; and the solid-phase method using silver nitrate and oxalic acid / oxalate.

[0020] Further, step A includes: dissolving oxalic acid dihydrate in water for 30 minutes, then adding silver nitrate dissolved in water dropwise for 30 minutes, forming a white precipitate, stirring for 30 minutes and then stopping, and obtaining white solid silver oxalate by centrifugation.

[0021] Further, step A includes: 63g of oxalic acid dihydrate is poured into a 5L brown three-necked flask, 1.5L of deionized water is added, and the mixture is stirred for 15 minutes to form a clear solution; 61.2g of silver nitrate is dissolved in 1.5L of deionized water to form a transparent solution, which is then added dropwise to the brown three-necked flask using a constant pressure funnel over 30 minutes; a white precipitate will gradually form in the flask during the addition; after the addition is complete, the mixture is reacted at 300-800 rpm for another 30 minutes; the white solid and solution are then centrifuged in a centrifuge bottle to obtain a white solid, which is then washed twice with ethanol and once with acetone before use. This step yields approximately 66g of silver oxalate.

[0022] Further, step B includes: mixing silver oxalate with amino acids, amines, and a solvent until homogeneous, stirring to form a homogenate, maintaining a constant temperature of 110℃-120℃, heating for a period of time, and then cooling to obtain a silver dispersion. The silver dispersion is then centrifuged to obtain silver particles. Typically, ethanol is added during centrifugation to remove water, impurities, prevent agglomeration, and facilitate drying. High-purity silver particles with low residual salts can be obtained after centrifugation.

[0023] Furthermore, the solvent in step B is one or more of ethanol, ethylene glycol, n-butanol, isopropanol, pentanol, toluene, xylene, and diethylene glycol butyl ether. The solvent affects particle size, sphericity, and dispersibility. Stronger polarity results in more stable coordination, faster nucleation, slower growth, smaller particle size, and a more rounded appearance. Weaker polarity leads to easier dissociation of coordination, fewer nucleations, faster growth, larger particle size, and a tendency towards irregularity. Higher boiling point / viscosity results in slower particle migration, greater uniformity, and less agglomeration.

[0024] Furthermore, the amino acids in step B include one or more of the following: alanine, arginine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine, and histidine. These are the twelve non-essential amino acids.

[0025] Furthermore, the amines in step B include diamines and straight-chain amines with chain lengths of 3-18 carbons. Diamines include phenylenediamine, ethylenediamine, hexamethylenediamine, decanediamine, propylenediamine, butylenediamine, etc., such as dimethylphenylenediamine. Straight-chain amines with chain lengths of 3-18 carbons include propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecanylamine, and octadecylamine.

[0026] Furthermore, in step D, the mass percentage of the silane coupling agent is less than 0.5%, the mass percentage of the butylcarboxylate is 1%-5%, and the mass percentage of the terpineol is 1%-5%.

[0027] Further, step D includes: taking 93% silver powder by mass, adding 0.1% silane coupling agent, adding 3% butylcarboxylate, adding 3% terpineol, grinding with a three-roll mill and filtering with a 400-mesh filter to obtain highly active and low-resistance nano-silver paste.

[0028] Furthermore, performance testing is also included: silver paste is screen-printed onto PET film using a 240-mesh screen and baked at different temperatures to test line length, line width, film thickness, and corresponding resistivity.

[0029] Understandably, reaction temperature also affects particle size and morphology, generally categorized as room temperature (20-45℃) and high temperature (100-120℃). At room temperature, solvent polarity dominates particle size: the greater the polarity, the smaller the particles and the more spherical their shape. At high temperatures, solvent polarity and reducing power jointly control particle size: the greater the polarity, the smaller the particles; the lower the polarity, the larger the particles and the less spherical their shape.

[0030] In a room-temperature system, as solvents, n-butanol, ethanol, and toluene hardly reduce silver oxalate. Particle growth relies on complexation dissociation and amine coordination. The solvent mainly affects solubility, dispersibility, and nucleation rate. Strongly polar solvents mainly include ethanol, methanol, and water, which are mainly suitable for the preparation of silver paste with a particle size of 20-100 nm. Moderately polar solvents mainly include n-butanol, isopropanol, pentanol, and ethylene glycol, which are mainly suitable for the preparation of silver paste with a particle size of 100-300 nm. Weakly polar / non-polar solvents mainly include toluene, xylene, cyclohexane, and long-chain alkanes, which are mainly suitable for the preparation of silver paste with a particle size of 300-800 nm or even larger. In terms of morphology, highly polar and viscous solvents, due to their high viscosity and slow particle movement, result in uniform anisotropic crystal growth, leading to morphologies with high sphericity, smooth surfaces, and good dispersion, such as ethylene glycol and propylene glycol. Medium-polarity and medium-viscosity solvents produce near-spherical or quasi-spherical morphologies with good uniformity, making them ideal for printing silver paste—neither too round nor too irregular—and with high packing density, such as n-butanol and isopropanol. Weakly polar and low-viscosity solvents, due to their rapid growth and distinct crystal orientation, easily produce polyhedral morphologies, such as toluene and xylene. Pure water, on the other hand, has extreme polarity, making it prone to aggregation, uneven size, and adhesion.

[0031] In high-temperature systems, n-butanol acts as a mild reducing agent, significantly weakening the coordination of amines. Amino acids transform from "coordinating agents" into "slow-release agents," and the solvent simultaneously controls the reduction rate, growth rate, and the upper limit of the final particle size. Highly polar solvents, such as ethanol and ethylene glycol, result in rapid reduction, stable complexation, and numerous nucleation sites, making it difficult for particles to grow large. They are suitable for small particle sizes, producing ultrafine morphologies and good sphericity, but are prone to slight agglomeration. Moderately polar solvents, such as n-butanol, offer mild reduction, a moderate number of nucleation sites, and optimal spherical morphology with smooth surfaces and uniform distribution. Weakly polar solvents, such as toluene and xylene, exhibit extremely weak complexation, slow reduction, and very few nucleation sites. They are suitable for large particle sizes, but the resulting particles are large, prone to polyhedralization, and exhibit poor sphericity, easily leading to size inhomogeneity.

[0032] Understandably, different amino acids and amines react with silver nitrate, resulting in silver particles with varying morphologies and sizes due to differences in their complexing, dispersing, and morphology control abilities. The stronger the bond between the amine / amino acid and Ag⁺, the higher the decomposition temperature, the later the nucleation, the more complete the growth, and the larger the particle size. Longer side chains / carbon chains lead to greater steric hindrance, making particle migration / aggregation more difficult, resulting in more uniform particle size and controllable dimensions. Higher polarity results in more stable complexes, more uniform nucleation, smaller particle sizes, and better dispersion.

[0033] At room temperature, particle size increases with increasing steric hindrance of amino acids, while morphology regularity decreases with increasing molecular size. For ultrafine particle sizes (~100 nm), glycine, histidine, cysteine, and serine can be used; for small particle sizes (100-300 nm), proline, aspartic acid, asparagine, and glutamine can be used; and for large particle sizes (300-800 nm), glutamine, tyrosine, arginine, and histidine can be selected. For morphology, smaller side chains, simpler structures, better sphericity, and narrower distribution result in glycine and alanine > proline > aspartic acid / glutamic acid > tyrosine. Aromatic rings, long side chains, and multifunctional groups tend to be polyhedral, easily aggregate, and have a slightly wider distribution, such as tyrosine, arginine, and histidine.

[0034] At high temperatures, the regulatory mechanism shifts to a slow-release effect of silver ions. n-Butanol acts as a mild reducing agent, and glycine exhibits a complete reversal. For small-particle-size (~100 nm ultrafine silver powder), alanine, serine, and cysteine ​​can be used; for medium-particle-size (100-300 nm), proline, aspartic acid, asparagine, and glutamine can be used; and for large-particle-size (above 300 nm), glycine, glutamic acid, tyrosine, arginine, and histidine can be used. In terms of morphology, proline and aspartic acid compounds offer the best spherical shape, uniformity, and are most suitable for conductive silver powder; while small-particle-size powders have small size, high sphericity, and narrow distribution, and large-particle-size powders have large size and acceptable sphericity but tend to have a slightly narrower size distribution.

[0035] Amines, acting as ligands, form silver-amine complexes with silver oxalate. The carbon chain length, number of amine groups, and steric hindrance determine the complex strength, decomposition temperature, and particle growth rate, directly controlling the particle size.

[0036] At room temperature, coordination dominates; shorter chains result in stronger coordination and smaller particles, while longer chains result in weaker coordination and larger particles. Diamines and short-chain amines have small, spherical particles with narrow distribution, but excessive amounts can easily lead to slight agglomeration. Medium- and long-chain amines (such as dodecylamine) have spherical shapes and good dispersibility, making them ideal for silver paste. Oleylamines and long-chain amines have large particles with acceptable spherical shapes, but they are prone to polyhedral formation and have a slightly wider distribution. For straight-chain amines with chain lengths of 3-18 carbons, the particle size increases with the increase of carbon atoms. That is, longer carbon chains result in greater steric hindrance, better particle dispersion, and slightly larger particle sizes, while shorter carbon chains result in more compact coordination, denser nucleation, and smaller particle sizes. Specifically, propylamine forms the smallest particle size, while octadecylamine forms the largest. In the case of the same amino acid, the particle size formed is as follows: diamine 20-80nm < short chain monoamine (C3~C6) 50-120nm < medium and long chain amine (C10~C14) 100-300nm < long chain amine (C16~C18 + oleylamine) 300-800nm.

[0037] At high temperatures, the coordination ability of amines decreases significantly. Short-chain amines can no longer effectively lock in small particles, while long-chain amines mainly play a role in steric hindrance dispersion and morphology control. Diamines still maintain a strong nucleation ability. Diamines remain the smallest, ultrafine but prone to agglomeration, with relatively irregular morphology, suitable for 50-120 nm. Short-chain amines (C3-C8) have weakened coordination, resulting in larger particle sizes than at room temperature. The particles are finer and have better sphericity, but excessive amounts are prone to aggregation. They have the highest sphericity and the most uniform distribution, performing best at high temperatures, suitable for 80-180 nm. Medium- and long-chain amines (C10-C14) have a balance between nucleation and growth, suitable for 100-300 nm. Oleylamines and long-chain saturated amines have weak coordination and high steric hindrance, allowing for sufficient particle growth. The particles are large, smooth, and do not agglomerate, but they tend to have a slightly wider particle size distribution, suitable for 300-800 nm. At this point, mixed amines (short + medium + long) are most likely to produce uniform particles of 100–300 nm.

[0038] Therefore, at room temperature, to obtain 100nm silver particles / powder / paste, glycine, alanine, serine + butylamine, hexylamine, diamine + n-butanol, and ethanol can be used; to obtain 100-300nm silver particles / powder / paste, proline, aspartic acid, glutamine + hexylamine + dodecylamine + n-butanol can be used; and to obtain 300-800nm ​​silver particles / powder / paste, glutamic acid, tyrosine, arginine + dodecylamine, oleylamine as the main component + n-butanol + toluene / xylene can be used.

[0039] Recommended amino acids, amines, and solvents at room temperature are listed in the table below: Table 1: Compatibility of Amino Acids, Amines, and Solvents at Room Temperature At high temperatures, 100nm can be treated with alanine / serine / cysteine ​​+ butylamine, diamine + n-butanol; 100-300nm can be treated with proline + hexylamine, dodecylamine, oleylamine + n-butanol; and 300-800nm ​​can be treated with glycine + hexylamine, a small amount of oleylamine + n-butanol.

[0040] Recommended amino acids, amines, and solvents for high temperatures are shown in the table below: Table 2: High-Temperature Compatibility Table of Amino Acids, Amines, and Solvents , Example 1 Example 1 is the preparation of 100nm silver paste.

[0041] A. Synthetic silver oxalate 63g of oxalic acid dihydrate was poured into a 5L brown three-necked flask, and 1.5L of deionized water was added. After stirring for 15 minutes, a clear solution was formed. 61.2g of silver nitrate was dissolved in 1.5L of deionized water to form a transparent solution, which was then added dropwise to the brown three-necked flask using a constant pressure funnel over 30 minutes. A white precipitate gradually formed in the flask during the addition. After the addition was complete, the mixture was reacted at 300-800 rpm for another 30 minutes. The white solid and solution were then centrifuged to obtain a white solid. The solid was washed twice with ethanol and once with acetone before use. The yield was approximately 66g.

[0042] B. Preparation of silver particles Add 40g of silver oxalate solid to a three-necked sintering vessel, along with 200g of n-butanol, 10g of n-butylamine, 17g of n-hexylamine, 10g of dodecylamine, 5g of oleylamine, 2g of oleic acid, and 11g of alanine. Mix thoroughly and stir for 15 minutes until a homogeneous medium is formed. Heat to 116℃, ensuring slight temperature fluctuations during heating are controlled within the range of 110℃-120℃, preferably 115℃-118℃. After reaching 116℃, maintain this temperature for 1 hour, then cool to obtain a silver dispersion. Mix the silver dispersion with ethanol at a 1:1 volume ratio, stir, and centrifuge to obtain silver particles.

[0043] C. Preparation of silver powder After washing twice with ethanol and once with acetone, the silver powder was dried using a freeze dryer and then ground through a 100-mesh sieve to obtain fine silver powder.

[0044] D. Preparation of silver paste Take 20g of silver powder, add 0.04g of silane coupling agent KH560, add 0.6g of butylcarboxylate, add 0.6g of terpineol, disperse with double star dispersant at 1000rpm for 60s, and then grind with a three-roll mill to obtain silver paste.

[0045] E. Performance Testing Silver paste was screen-printed onto PET film using a 240-mesh screen and baked at different temperatures. The line length, line width, film thickness, and corresponding resistivity were tested.

[0046] The higher proportions of n-butylamine and n-hexylamine compress the particle size, while dodecylamine and oleylamine, although they have the effect of increasing particle size, are limited by alanine and n-butanol due to their low proportions. These substances improve dispersion and promote better sphericity. A small amount of oleic acid only improves morphology, dispersion, and sphericity. Alanine can rapidly coordinate and dissolve silver oxalate, quickly releasing a large number of silver ions, resulting in a large number of nucleation sites and thus controlling the particle size to 100 nm.

[0047] Please refer to Figure 1 and Figure 2 The graph shows the 100nm particle size, sintering morphology, and silver paste resistivity obtained in Example 1. Figure 2 The double-line diagram represents two tests, both of which are test results of the silver paste obtained in Example 1.

[0048] Example 2 Example 2 is the preparation of 100-300nm silver paste.

[0049] A. Preparation of silver oxalate 63g of oxalic acid dihydrate was poured into a 5L brown three-necked flask, and 1.5L of deionized water was added. After stirring for 15 minutes, a clear solution was formed. 61.2g of silver nitrate was dissolved in 1.5L of deionized water to form a transparent solution, which was then added dropwise to the brown three-necked flask using a constant pressure funnel over 30 minutes. A white precipitate gradually formed in the flask during the addition. After the addition was complete, the mixture was reacted at 300-800 rpm for another 30 minutes. The white solid and solution were then centrifuged to obtain a white solid. The solid was washed twice with ethanol and once with acetone before use. The yield was approximately 66g.

[0050] B. Preparation of silver particles Add 40g of silver oxalate solid to a three-necked sintering vessel, then add 200g of n-butanol, 40g of n-hexylamine, 20g of dodecylamine, 10g of oleylamine, 2g of oleic acid, and 24g of L-proline. Mix thoroughly and stir for 15 minutes until a homogeneous medium is formed. Heat to 116℃, ensuring slight temperature fluctuations during heating are controlled within the range of 110℃-120℃, preferably 115℃-118℃. After reaching 116℃, maintain this temperature for 1 hour, then cool to obtain a silver dispersion. Mix the silver dispersion with ethanol at a 1:1 volume ratio, stir, and centrifuge to obtain silver particles.

[0051] C. Preparation of silver powder After washing twice with ethanol and once with acetone, the silver powder was dried using a freeze dryer and then ground through a 100-mesh sieve to obtain fine silver powder.

[0052] D. Preparation of silver paste Take 20g of silver powder, add 0.04g of silane coupling agent KH560, add 0.6g of butylcarboxylate, add 0.6g of terpineol, disperse with double star dispersant at 1000rpm for 60s, and then grind with a three-roll mill to obtain silver paste.

[0053] E. Performance Testing Silver paste was screen-printed onto PET film using a 240-mesh screen and baked at different temperatures. The line length, line width, film thickness, and corresponding resistivity were tested.

[0054] Hexylamine has the highest proportion, providing sufficient nucleation and preventing excessive particle size, resulting in an overall medium to small particle size. Dodecylamine and oleylamine are suppressed by L-proline and n-butanol, providing steric hindrance and allowing particles to grow to a certain size. A small amount of oleic acid is also used only for morphology modification. The amount of L-proline nucleation is moderate, resulting in particles that are neither too large nor too small. The obtained morphology is spherical / near-spherical, with good dispersibility, suitable for medium-temperature conductive silver paste, screen printing, fine lines, and general thick-film circuits.

[0055] Please refer to Figure 3 and Figure 4 The resistivity of the 100-300nm silver paste obtained by the above steps in Example 2 is comparable to that of KM120 with a similar particle size. Figure 7 (Lower temperature, better conductivity)

[0056] Example 3 Example 3 is the preparation of 300-800nm ​​silver paste.

[0057] A. Preparation of silver oxalate 63g of oxalic acid dihydrate was poured into a 5L brown three-necked flask, and 1.5L of deionized water was added. After stirring for 15 minutes, a clear solution was formed. 61.2g of silver nitrate was dissolved in 1.5L of deionized water to form a transparent solution, which was then added dropwise to the brown three-necked flask using a constant pressure funnel over 30 minutes. A white precipitate gradually formed in the flask during the addition. After the addition was complete, the mixture was reacted at 300-800 rpm for another 30 minutes. The white solid and solution were then centrifuged to obtain a white solid. The solid was washed twice with ethanol and once with acetone before use. The yield was approximately 66g.

[0058] B. Preparation of silver particles Add 40g of silver oxalate solid to a three-necked sintering vessel, along with 200g of n-butanol, 40g of n-hexylamine, 2g of oleylamine, and 15g of glycine. Mix thoroughly and stir for 15 minutes until a homogeneous medium is formed. Heat to 116℃, ensuring slight temperature fluctuations during heating are controlled within the range of 110℃-120℃, preferably 115℃-118℃. After reaching 116℃, maintain this temperature for 1 hour, then cool to obtain a silver dispersion. Mix the silver dispersion with ethanol at a 1:1 volume ratio, stir, and centrifuge to obtain silver particles.

[0059] C. Preparation of silver powder After washing twice with ethanol and once with acetone, the silver powder was dried using a freeze dryer and then ground through a 100-mesh sieve to obtain fine silver powder.

[0060] D. Preparation of silver paste Take 20g of silver powder, add 0.04g of silane coupling agent KH560, add 0.6g of butylcarboxylate, add 0.6g of terpineol, disperse with double star dispersant at 1000rpm for 60s, and then grind with a three-roll mill to obtain silver paste.

[0061] E. Performance Testing Silver paste was screen-printed onto PET film using a 240-mesh screen and baked at different temperatures. The line length, line width, film thickness, and corresponding resistivity were tested.

[0062] The combination of n-butanol solvent, glycine, and temperature-induced decomposition forms particles with a diameter of 300-800 nm. The role of glycine is not to create small particles but to slowly release Ag⁺. Due to the extremely small number of nuclei, the particles grow rapidly. In this formulation, n-butanol itself also slowly reduces silver, acting as both a solvent and a mild reducing agent. The reduction rate is mild and stable, allowing the particles to grow slowly and easily to a size of over 300 nm. Although n-hexylamine appears to be a short chain, excess combined with high temperature results in weak coordination, which strengthens the alkalinity of the system. Silver oxalate dissolves rapidly, but the amine coordination weakens at high temperatures, so it does not inhibit growth and instead produces large particles. Similarly, a small amount of oleylamine is used only for morphology control, preventing particle aggregation and maintaining a spherical shape.

[0063] Please refer to Figure 5 and Figure 6 The changes in the 300-800nm ​​silver paste particle size, sintering morphology, and resistivity obtained by following the steps described in Example 3 are shown.

[0064] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0065] Furthermore, if the embodiments of the present invention involve descriptions such as "first" or "second," such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0066] In summary, this invention provides a method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste through amino acid modification. The method involves the reaction of silver oxalate, amino acids, and amines, where the amino acids and amines act as complexing agents, dispersants, and morphology modifiers to obtain submicron, highly dispersed silver particles. High-purity silver powder is then obtained through washing and centrifugation. This high-purity silver powder is then combined with a silane coupling agent, tetracarboxylate, and terpineol to form a silver paste. The addition of terpineol improves printability and dispensing properties, wets the substrate, and volatilizes during drying / sintering, leaving no carbon residue. The addition of tetracarboxylate prevents the silver paste from drying too quickly and clogging the screen, improves leveling, film formation, and printing clarity, resulting in a denser silver layer and a smoother surface. The silane coupling agent acts as an interfacial bridge, improving adhesion, resistance to boiling water and thermal shock, improving silver powder dispersibility, reducing agglomeration, and lowering resistance. It can control the particle size distribution range to prepare silver powder of different submicron sizes, meeting the needs of mainstream submicron silver powder particle sizes. It covers three different requirements: 100nm, 100-300nm, and 300-800nm, providing comprehensive coverage of the submicron silver powder particle size range. Furthermore, it exhibits strong conductivity and low resistivity.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification, characterized in that, Includes the following steps: Synthetic silver oxalate; Preparation of silver particles: Silver particles are obtained by thermal decomposition of silver oxalate with amino acids, amines and solvents; Preparation of silver powder: clean silver particles, freeze-dry to form silver blocks, and grind them into silver powder; Preparation of silver paste: Take 85%-95% silver powder by mass, add silane coupling agent, tetracarboxylate, and terpineol, grind and filter to obtain highly active and low-resistivity nano-silver paste.

2. The method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to claim 1, characterized in that, Step A includes: forming silver oxalate using silver nitrate and oxalate dihydrate.

3. The method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to claim 1, characterized in that, Step A includes: dissolving oxalic acid dihydrate in water for 30 minutes, then adding silver nitrate dissolved in water dropwise for 30 minutes to form a white precipitate. Stirring is then stopped after 30 minutes, and the white solid silver oxalate is obtained by centrifugation.

4. A method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to any one of claims 1-3, characterized in that, Step A includes: taking 63g of oxalic acid dihydrate and pouring it into a 5L brown three-necked flask, adding 1.5L of deionized water, and stirring for 15 minutes to form a clear solution; dissolving 61.2g of silver nitrate in 1.5L of deionized water to form a transparent solution, and then adding it dropwise to the brown three-necked flask using a constant pressure funnel over a period of 30 minutes; during the dropwise addition, a white precipitate will gradually form in the flask; after the dropwise addition is complete, react at 300-800 rpm for another 30 minutes; pouring the white solid and solution into a centrifuge bottle and centrifuging to obtain a white solid, then washing it twice with ethanol and once with acetone before use.

5. The method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to claim 1, characterized in that, Step B includes: mixing silver oxalate with amino acids, amines and solvents until homogeneous, stirring to form a homogeneous mixture, maintaining a constant temperature of 110℃-120℃, heating for a period of time and then cooling to obtain a silver dispersion, and centrifuging the silver dispersion to obtain silver particles.

6. The method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to claim 1, characterized in that, The solvent in step B is one or more of ethanol, ethylene glycol, n-butanol, isopropanol, pentanol, toluene, xylene, and diethylene glycol butyl ether.

7. The method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to claim 1, characterized in that, The amino acids in step B include one or more of alanine, arginine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine, and histidine.

8. The method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to claim 1, characterized in that, The amines in step B include diamines and straight-chain amines with a chain length of 3-18 carbons.

9. The method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to claim 1, characterized in that, In step D, the mass percentage of the silane coupling agent is less than 0.5%, the mass percentage of the butylcarboxylate is 1%-5%, and the mass percentage of the terpineol is 1%-5%.

10. The method for preparing highly active, highly dispersed, and low-resistivity silver powder and silver paste by amino acid modification according to claim 1, characterized in that, Step D includes: taking 93% silver powder by mass, adding 0.1% silane coupling agent, adding 3% butylcarboxylate, adding 3% terpineol, grinding with a three-roll mill and filtering with a 400-mesh filter to obtain a highly active and low-resistance nano-silver paste.

Images