Conductive silver paste material for ink-jet printing, preparation method of conductive silver paste material and passive element

Abstract

The invention discloses a conductive silver paste material for ink-jet printing, a preparation method of the conductive silver paste material and a passive element. The conductive silver paste material is prepared from the following components in percentage by mass: 31%-48% of a conductive phase, 0.5%-2% of a dispersing agent, 0.5%-2% of an adhesive, 0.5%-2% of an adhesion promoter and the balance of a solvent, in the conductive phase, the mass of the first silver powder accounts for 25%-35% of the total mass of the conductive silver paste material, the mass of the second silver powder accounts for 5%-10% of the total mass of the conductive silver paste material, and the balance is the third silver powder; and the adhesion promoter is bismuth neodecanoate. The conductive silver paste material provided by the invention is low in viscosity, can be co-fired with low-temperature co-fired ceramic, and provides an innovative solution for manufacturing of next-generation high-frequency communication devices.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing materials technology, specifically relating to a conductive silver paste material for inkjet printing, its preparation method, and passive components. Background Technology

[0002] With the rapid development of 5G / 6G communication, millimeter-wave radar and high-density integrated circuits, LTCC (Low Temperature Co-fired Ceramic) technology has become a core platform technology for manufacturing key components such as multilayer radio frequency (RF) modules, filters and antennas due to its excellent high-frequency dielectric properties, high integration and high reliability.

[0003] Traditional LTCC conductor circuit manufacturing mainly relies on screen printing technology. However, when faced with increasingly refined and high-density wiring requirements, the limitations of screen printing are becoming more and more apparent: 1) resolution bottleneck, making it difficult to stably achieve fine lines below 50µm; 2) complex process variables, with printing quality affected by multiple factors such as screen tension, squeegee pressure, and ink rheology, making consistency control difficult; 3) high mask cost, and unsuitable for rapid prototype iteration and the manufacturing of complex three-dimensional structures.

[0004] Inkjet printing technology, as an additive manufacturing method, is considered an ideal solution for next-generation LTCC fine-line fabrication due to its advantages such as high resolution, maskless operation, digital drive, and high material utilization. However, developing inkjet conductive silver paste suitable for LTCC co-firing processes faces a series of severe technical challenges, which are often contradictory: 1. The contradiction between rheological properties and sintering performance: Industrial piezoelectric inkjet printheads require inks with extremely low viscosity (typically 10~20 cP) and precise surface tension (30~50 mN / m) to ensure reliable droplet ejection and avoid nozzle clogging. However, to match the shrinkage of the LTCC substrate during the 850℃ sintering process, the silver paste needs to contain larger-particle-size silver powder to delay sintering. In high-solids-content systems, how to stably disperse these large particles while maintaining low viscosity is a key challenge.

[0005] 2. The contradiction between adhesion and printability: Traditional thick-film inks rely on the addition of micron-sized glass powder as a binder, which is melted at high temperatures to achieve a strong bond between the conductor and the ceramic substrate. However, these solid glass particles cannot be used in inkjet inks because they would immediately clog the tiny nozzles. Therefore, it is necessary to develop a particle-free, innovative adhesion mechanism.

[0006] 3. The contradiction between viscosity and sintering temperature: Traditional silver paste suitable for LTCC co-firing (sintering temperature around 850℃) cannot be used for inkjet printing due to its excessively high viscosity (180,000 cp~2,000,000 cp). However, traditional silver ink suitable for inkjet printing has a low viscosity (10 cp~20 cp), but its sintering temperature is too low (≤300℃), making it unsuitable for co-firing with low-temperature co-fired ceramics.

[0007] 4. Silver ion migration problem: Under the influence of high temperature and electric field, silver ions can easily migrate into the glass phase of LTCC, changing the dielectric properties of the substrate, affecting the integrity of high-frequency signals, and potentially causing long-term reliability problems.

[0008] Therefore, there is an urgent need to develop a new conductive silver paste system that not only meets the stringent rheological requirements of inkjet printing, but also solves a series of key technical problems at the formulation level, such as thermomechanical compatibility with LTCC during co-firing, no particle adhesion, and the correlation between viscosity and sintering temperature.

[0009] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0010] To address the aforementioned problems in the prior art, this invention provides a conductive silver paste material for inkjet printing, its preparation method, and a passive component. The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, the present invention provides a conductive silver paste material for inkjet printing, which, by mass fraction, consists of 31% to 48% conductive phase, 0.5% to 2% dispersant, 0.5% to 2% binder, 0.5% to 2% adhesion promoter, and the balance being solvent. The conductive phase is composed of a first silver powder, a second silver powder, and a third silver powder; the first silver powder accounts for 25% to 35% of the total mass of the conductive silver paste material, the second silver powder accounts for 5% to 10% of the total mass of the conductive silver paste material, and the remainder is the third silver powder. The first silver powder is spherical silver powder with an average particle size of 0.8 μm, the second silver powder is spherical silver powder with an average particle size of 200 nm, and the third silver powder is spherical silver powder with an average particle size of 50 nm. The adhesion promoter is bismuth neodecanoate.

[0011] In one embodiment of the present invention, the solvent is a mixed solution of ethylene glycol and terpineol; wherein the mass ratio of ethylene glycol to terpineol is 1:(0.5~2).

[0012] In one embodiment of the present invention, the adhesive is polyvinylpyrrolidone; the dispersant is BYKJET-9151.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned conductive silver paste material for inkjet printing, comprising the following steps: S1, adding bismuth neodecanoate to a first solvent and stirring until completely dissolved; then adding a dispersant until completely dissolved, and then adding a binder in batches and stirring until completely dissolved to obtain a mixed solvent; S2. Obtain a mixed powder of first silver powder, second silver powder and third silver powder, add it to the mixed solvent and stir evenly to obtain a premix; S3. Add a second solvent to the premix, adjust the viscosity of the premix to 10~20 cP, and then ball mill to obtain a pre-mixed slurry; wherein the second solvent is the same as the first solvent; S4. Let the pre-made slurry stand for 18-24 hours to mature, and filter the matured pre-made slurry using a polytetrafluoroethylene needle filter to obtain conductive silver paste material for inkjet printing.

[0014] In one embodiment of the present invention, step S2, the method for preparing the first silver powder includes the following steps: Step 1: Add bovine serum albumin aqueous solution to the first reaction vessel. The temperature of the first reaction vessel is 15~25℃. Step 2: Add the silver nitrate aqueous solution in batches to the first reaction vessel in Step 1 while stirring to obtain the first mixed solution; wherein the mass of bovine serum albumin is 10-15% of the mass of silver nitrate. Step 3: Add ammonia water dropwise to the first combined solution until the pH value is 9.5; add L-ascorbic acid and stir for 10-15 minutes, then sonicate for 7-10 minutes, and collect the first crude silver powder product by centrifugation at a relative centrifugal force of (2800-3200) × g, where g is the gravitational acceleration at the Earth's surface; wherein, the molar ratio of L-ascorbic acid to silver nitrate is (1.2-1.6):1; Step 4: After repeatedly ultrasonically cleaning and centrifuging the first silver powder crude product with deionized water, ultrasonically cleaning and centrifuging with ethanol at least once, and drying it to obtain the first silver powder; the relative centrifugal force of the centrifugation is (2800~3200)×g, where g is the gravitational acceleration at the Earth's surface.

[0015] In one embodiment of the present invention, step S2, the method for preparing the second silver powder includes the following steps: Step 10: Add the mixed solution of silver nitrate and polyvinylpyrrolidone to the second reaction vessel. The temperature of the second reaction vessel is 35~45℃. The mass ratio of polyvinylpyrrolidone to silver nitrate is (0.5~0.8):1. Step 20: Add NaOH solution or HNO3 solution dropwise to the mixed solution until the pH value is 7.0; add L-ascorbic acid and stir for 30-60 minutes; collect the second crude silver powder product by centrifugation at a relative centrifugal force of (7500-8500) × g, where g is the gravitational acceleration at the Earth's surface; wherein, the molar ratio of L-ascorbic acid to silver nitrate is (1.0-1.5):1; Step 30: After repeatedly vortexing and centrifuging the crude second silver powder product with deionized water, vortexing and centrifuging with ethanol at least once more, and drying it to obtain the second silver powder; wherein, the relative centrifugal force of the centrifugation is (7500~8500)×g, where g is the gravitational acceleration at the Earth's surface.

[0016] In one embodiment of the present invention, step S2, the method for preparing the third silver powder includes the following steps: Step 100: Add deionized water to a three-necked flask reactor, heat the deionized water to boiling at an oil bath temperature of 150~180℃, add silver nitrate solution and stir evenly to obtain a second mixed solution. Step 200: Add sodium citrate solution dropwise to the second mixed solution at a rate of 15-20 mL / min. After the sodium citrate solution is added, react for 45-70 min and cool to obtain the mixed solution to be washed. The molar ratio of sodium citrate to silver nitrate is (0.5-0.8):1. Step 300, the cleaning process includes: adding sodium citrate solution to the mixed solution to be cleaned, stirring evenly and letting it stand, centrifuging at 3800~4200 speed for 3~5 minutes, discarding the supernatant, adding deionized water to disperse and obtain the mixed solution to be cleaned; Repeat the washing process at least three times to obtain a third silver powder suspension, which is then centrifuged and dried to obtain the third silver powder.

[0017] In one embodiment of the present invention, in step S3, the ball milling is performed using a ball mill. The ball mill includes: S31. Set the rotation speed of the ball mill to 120~180 rpm and perform ball milling according to the ball milling process; The ball milling process includes a first stage, a second stage, and a third stage; In the first stage, the ball milling gap is 20 μm and the ball milling time is 20~40 min; in the second stage, the ball milling gap is 10 μm and the ball milling time is 20~40 min; in the third stage, the ball milling gap is 5 μm and the ball milling time is 20~40 min. S32. Repeat the ball milling process 2 to 4 times to complete the ball milling.

[0018] In one embodiment of the present invention, both the first solvent and the second solvent are mixed solutions of ethylene glycol and terpineol; wherein the mass ratio of ethylene glycol to terpineol is 1:(0.5~2). The adhesive is polyvinylpyrrolidone, and the dispersant is BYKJET-9151.

[0019] Thirdly, the present invention provides a passive component, including a ceramic substrate and a metal conductor disposed on the ceramic substrate, wherein at least a portion of the metal conductor is prepared using the conductive silver paste material for inkjet printing described above.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The conductive silver paste material for inkjet printing provided by this invention uses spherical silver powder with a three-peaked particle size distribution as the conductive phase. Specifically, the submicron-sized first silver powder (average particle size 0.8µm) serves as a structural framework and sintering delayer, delaying sintering to match LTCC (Low Temperature Co-fired Ceramic). The submicron-sized second silver powder (average particle size 0.2µm) acts as a highly efficient filler, increasing the density of the printed silver paste. The nano-sized third silver powder spheres (average particle size 50nm) serve as a high-temperature solder and sintering aid, promoting low-temperature neck formation and eventual densification. This mixture of the three silver powders improves the matching of the prepared conductive silver paste material with the co-firing temperature of the low-temperature co-fired ceramic, without affecting the performance of the conductive silver paste material after sintering or its adhesion to the ceramic matrix.

[0021] 2. This invention uses bismuth neodecanoate as an adhesion promoter. As a precursor, bismuth neodecanoate can be completely dissolved in organic solvents, eliminating the risk of nozzle clogging caused by the binder phase. Furthermore, during the degreasing stage (heat treatment stage), bismuth neodecanoate thermally decomposes to directly generate nanoscale bismuth oxide particles in situ at the silver-ceramic interface. The formed bismuth oxide layer also inhibits the migration of silver ions into the LTCC dielectric layer at high temperatures, thereby improving the long-term reliability of the device.

[0022] 3. The preparation method of conductive silver paste material for inkjet printing provided by the present invention is simple, and the printed circuit prepared by the conductive silver paste material has high precision, indicating that the conductive silver paste material is uniformly dispensed during inkjet printing and there is no problem of nozzle clogging.

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 This is a flowchart of a method for preparing conductive silver paste material for inkjet printing provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the experimental board obtained by inkjet printing using the conductive silver paste material prepared in Example 1 of the present invention; Figure 3 This is a printed circuit diagram of the conductive silver paste material prepared in Example 1 of the present invention, which is prepared by inkjet printing.

[0025] Figure 4 yes Figure 3 SEM characterization of random areas of the printed circuit, and schematic diagram of line width and line spacing measurement; Figures 5 to 7 yes Figure 3 SEM characterization of random areas of the printed circuit and schematic diagram of accuracy measurement. Detailed Implementation

[0026] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following, in conjunction with the accompanying drawings and specific embodiments, provides a detailed description of a conductive silver paste material for inkjet printing, its preparation method, and passive components proposed according to the present invention.

[0027] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0028] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed.

[0029] This invention provides a conductive silver paste material for inkjet printing. By mass fraction, the conductive silver paste material comprises 31%–48% conductive phase, 0.5%–2% dispersant, 0.5%–2% binder, 0.5%–2% adhesion promoter bismuth neodecanoate, and the balance being solvent. The conductive phase consists of first silver powder, second silver powder, and third silver powder. The first silver powder accounts for 25%–35% of the total mass of the conductive silver paste material, the second silver powder accounts for 5%–10% of the total mass of the conductive silver paste material, and the balance is third silver powder. For example, when the mass fraction of the conductive phase is 45%, the first silver powder accounts for 30% of the total mass of the conductive silver paste material, the second silver powder accounts for 5% of the total mass of the conductive silver paste material, and the third silver powder accounts for 10% of the total mass of the conductive silver paste material.

[0030] The first silver powder is spherical silver powder with an average particle size of 0.8 μm, the second silver powder is spherical silver powder with an average particle size of 200 nm, and the third silver powder is spherical silver powder with an average particle size of 50 nm.

[0031] In this embodiment, the conductive phase uses spherical silver powder with a three-peaked particle size distribution. The submicron-sized first silver powder (average particle size 0.8µm) serves as a structural framework, acting as a sintering delayer to postpone sintering and match the LTCC. The submicron-sized second silver powder (average particle size 0.2µm) acts as a highly efficient filler to increase the density of the printed silver paste. The nano-sized third silver powder spheres (average particle size 50nm) serve as a high-temperature solder and sintering aid, promoting low-temperature neck formation and final densification. Simultaneously, in this embodiment, bismuth neodecanoate is used as the adhesion promoter. As a precursor, bismuth neodecanoate is completely soluble in organic solvents, eliminating the risk of nozzle clogging caused by the binder phase. Furthermore, during the debinding stage (heat treatment stage), bismuth neodecanoate thermally decomposes to directly generate nano-sized bismuth oxide particles in situ at the silver-ceramic interface. The resulting bismuth oxide layer also inhibits the migration of silver ions into the LTCC dielectric layer at high temperatures, thereby improving the long-term reliability of the device.

[0032] In one example, the mass fraction of the conductive phase in the conductive silver paste material is 40% to 48%.

[0033] In one embodiment of the present invention, the solvent is a mixed solution of ethylene glycol and terpineol; wherein the mass ratio of ethylene glycol to terpineol is 1:(0.5~2). Terpineol, as a solvent, can prevent the ink (conductive silver paste material) from drying at the nozzle during inkjet printing. Combined with ethylene glycol, it can synergistically control the rheological properties of the conductive silver paste material, preventing nozzle clogging and ejection during inkjet printing. For example, the mass ratio of ethylene glycol to terpineol is 1:0.5, 1:0.8, 1:1.1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, or 1:2.

[0034] Furthermore, the mass ratio of ethylene glycol to terpineol is 1:(1.2~2). Using terpineol as the main solvent can more effectively prevent the conductive silver paste material from drying too quickly at the tiny nozzles during use, thus preventing nozzle clogging.

[0035] In one example, the dispersant is BYKJET-9151. The dispersant can be combined with ethylene glycol to further improve control over the rheological properties of the conductive silver paste material.

[0036] In one example, the binder is polyvinylpyrrolidone (PVP). PVP acts as a temporary binder, temporarily binding together the loose silver powder particles after the conductive silver paste has dried, providing the necessary mechanical strength for the pattern printed before sintering, and allowing for clean burn-off with virtually no carbon residue affecting the final conductivity.

[0037] This invention also provides a method for preparing the conductive silver paste material for inkjet printing described above. The raw materials for the conductive silver paste material for inkjet printing are obtained according to the following mass fractions: 31%–48% conductive phase (first silver powder, second silver powder, and third silver powder), 0.5%–2% dispersant, 0.5%–2% binder, 0.5%–2% adhesion promoter (bismuth neodecanoate), and the balance being solvent (including first solvent and second solvent). Figure 1 As shown, the preparation method includes the following steps: S1. Add bismuth neodecanoate to the first solvent and stir until completely dissolved; then add the dispersant until completely dissolved, and then add the binder in batches, stirring until completely dissolved to obtain a mixed solvent.

[0038] For example, the first solvent is a mixed solution of ethylene glycol and terpineol; the mass ratio of ethylene glycol to terpineol is 1:(0.5~2).

[0039] For example, the adhesive is polyvinylpyrrolidone and the dispersant is BYKJET-9151.

[0040] S2. Obtain a mixed powder of the first silver powder, the second silver powder and the third silver powder, add it to a mixed solvent and stir evenly to obtain a premix.

[0041] In some examples, the method for preparing the first silver powder includes the following steps: Step 1: Add bovine serum albumin aqueous solution to the first reaction vessel. The temperature of the first reaction vessel is 15~25℃. Step 2: Add the silver nitrate aqueous solution in batches to the first reaction vessel in Step 1 while stirring to obtain the first mixed solution; wherein the mass of bovine serum albumin is 10-15% of the mass of silver nitrate. Step 3: Add ammonia dropwise to the first mixed solution until the pH value is 9.5; add L-ascorbic acid and stir for 10-15 min, then sonicate for 7-10 min, and collect the first crude silver powder product by centrifugation at a relative centrifugal force of (2800-3200) × g, where g is the gravitational acceleration at the Earth's surface; wherein, the molar ratio of L-ascorbic acid to silver nitrate is (1.2-1.6):1; Step 4: After repeatedly ultrasonically cleaning and centrifuging the crude first silver powder product with deionized water, ultrasonically cleaning and centrifuging with ethanol at least once, and drying it, the first silver powder is obtained; the relative centrifugal force is (2800~3200)×g, where g is the gravitational acceleration at the Earth's surface.

[0042] In some examples, the preparation method of the second silver powder includes the following steps: Step 10: Add the mixed solution of silver nitrate and polyvinylpyrrolidone to the second reaction vessel. The temperature of the second reaction vessel is 35~45℃. The mass ratio of polyvinylpyrrolidone to silver nitrate is (0.5~0.8):1.

[0043] Step 20: Add NaOH solution or HNO3 solution dropwise to the mixed solution until the pH value is 7.0; add L-ascorbic acid and stir for 30-60 min; centrifuge and collect the second crude silver powder product at a relative centrifugal force of (7500-8500) × g, where g is the gravitational acceleration at the Earth's surface; wherein, the molar ratio of L-ascorbic acid to silver nitrate is (1.0-1.5):1; Step 30: After repeatedly vortexing and centrifuging the crude second silver powder product with deionized water, vortexing and centrifuging it at least once with ethanol, and then drying it to obtain the second silver powder; wherein, the relative centrifugal force of centrifugation is (7500~8500)×g, where g is the gravitational acceleration at the Earth's surface.

[0044] In some examples, the preparation method of the third silver powder includes the following steps: Step 100: Add deionized water to a three-necked flask reactor, heat the deionized water to boiling at an oil bath temperature of 150~180℃, add silver nitrate solution and stir evenly to obtain a second mixed solution. Step 200: Add sodium citrate solution dropwise to the second mixed solution at a rate of 15-20 mL / min. After the sodium citrate solution is added, react for 45-70 min and cool to obtain the mixed solution to be washed. The molar ratio of sodium citrate to silver nitrate is (0.5-0.8):1. Step 300, the cleaning process includes: adding sodium citrate solution to the mixed solution to be cleaned, stirring evenly and letting it stand, then centrifuging at 3800~4200 speed for 3~5 minutes, discarding the supernatant, adding deionized water to disperse, and obtaining the mixed solution to be cleaned as described above. The washing process was repeated at least three times to obtain a third silver powder suspension, which was then centrifuged and dried to obtain the third silver powder.

[0045] For example, the first silver powder is spherical silver powder with an average particle size of 0.8 μm, the second silver powder is spherical silver powder with an average particle size of 200 nm, and the third silver powder is spherical silver powder with an average particle size of 50 nm.

[0046] For example, after centrifuging the third silver powder suspension, it is dried in a drying oven at 60-80℃ for 6-8 hours or dried to constant weight to obtain the third silver powder.

[0047] S3. Add a second solvent to the premix, adjust the viscosity of the premix to 10-20 cP, and then ball mill to obtain a pre-mixed slurry; wherein the second solvent is a mixed solution of ethylene glycol and terpineol; wherein the mass ratio of ethylene glycol to terpineol is 1:(0.5-2). The second solvent is the same as the first solvent. For example, when the first solvent is a mixed solution of ethylene glycol and terpineol prepared in a mass ratio of 1:1.5, the second solvent is also a mixed solution of ethylene glycol and terpineol prepared in a mass ratio of 1:1.5.

[0048] In one example, ball milling is employed; ball milling includes the following processes: S31. Set the speed of the ball mill to 120~180 rpm and perform ball milling according to the ball milling process; The ball milling process includes three stages: the first stage, the second stage, and the third stage. In the first stage, the ball milling gap is 20 μm and the ball milling time is 20~40 min; in the second stage, the ball milling gap is 10 μm and the ball milling time is 20~40 min; in the third stage, the ball milling gap is 5 μm and the ball milling time is 20~40 min. S32. Repeat the ball milling process 2 to 4 times to complete the ball milling.

[0049] S4. Let the pre-made slurry stand for 18-24 hours to mature, and then filter the matured pre-made slurry using a polytetrafluoroethylene needle filter to obtain conductive silver paste material for inkjet printing.

[0050] For example, the pore size of a polytetrafluoroethylene needle filter is 1.0 μm.

[0051] This invention also provides a passive component, which is prepared using an LTCC co-firing process. The passive component includes a ceramic substrate and a metal conductor disposed on the ceramic substrate. At least a portion of the metal conductor is prepared using the conductive silver paste material described above for inkjet printing. The passive component can be a resistor, capacitor, inductor, etc.

[0052] In one embodiment of the present invention, the preparation of a passive component includes the following steps: Obtain conductive silver paste and ceramic material slurries; The precursor is obtained by 3D printing according to the structure of the target passive component using inkjet printing. The precursor is co-fired at 800-900℃ to obtain the target passive component.

[0053] This invention also provides an electronic device that includes the aforementioned passive components, such as filters, baluns, and LC resonant sensors.

[0054] The conductive silver paste material for inkjet printing and its preparation method provided by the present invention are further illustrated below with reference to specific embodiments.

[0055] Example 1 (1) Weigh the raw materials according to the mass fractions shown in Table 1. The preparation processes for the first silver powder, second silver powder, and third silver powder are as follows: a. Preparation of the first silver powder Accurately weigh 7.87 g of silver nitrate (AgNO3), dissolve it in deionized water, and bring the volume to 92.5 mL. Accurately weigh 0.94 g of bovine serum albumin (BSA) (12% of the mass of silver nitrate), and dissolve it in 50 mL of deionized water. Accurately weigh 12.24 g of L-ascorbic acid, dissolve it in deionized water, and bring the volume to 87 mL.

[0056] The temperature of the jacketed glass reactor was precisely controlled and stabilized at 20°C using a thermostatic circulator. The prepared stabilizer solution (BSA aqueous solution) was added to the reactor. The top-mounted mechanical stirrer was started, and the stirring speed was set to 300 rpm to ensure uniform mixing. Under continuous stirring, all the silver precursor solution (AgNO3 aqueous solution) was slowly added to the stabilizer solution in the reactor. After uniform mixing, ammonia water (25%~28%) was slowly added dropwise using a pH meter to precisely adjust the pH of the mixed solution to 9.5. This step is crucial for activating the template function of BSA and must be performed slowly to avoid excessively high local pH values.

[0057] After the reaction system temperature and pH value are stable at the set values ​​(20℃, pH 9.5), the reducing agent solution (L-ascorbic acid solution) is rapidly injected into the reactor using a peristaltic pump or syringe pump to initiate the reduction reaction.

[0058] Maintain a constant stirring rate and reaction temperature, allowing the reaction to continue for 10-15 minutes. During this period, the solution color will gradually change from colorless and transparent or pale yellow to grayish-brown or dark gray, indicating that silver particles have been formed.

[0059] Purification, Collection, and Drying: After the reaction, the resulting silver powder suspension was transferred to a large beaker and treated with an ultrasonic water bath for 7-10 minutes. This was to break up any loose agglomerates that might form during the reaction and improve the dispersibility of the product. The ultrasonically treated suspension was then aliquoted into centrifuge tubes and centrifuged at a relatively low speed (3000×g) for 15 minutes using a high-speed centrifuge. (g represents the acceleration due to gravity at the Earth's surface) This caused the submicron-sized silver powder to settle to the bottom of the tube and form a precipitate. The supernatant was carefully removed, and sufficient deionized water was added to the supernatant. The precipitate was then redispersed into a homogeneous suspension using a glass rod. The above two steps were repeated, washing 2-3 times in total, to thoroughly remove any residual ions and unreacted BSA.

[0060] After washing with water, replace deionized water with anhydrous ethanol and repeat the washing-centrifugation step 1-2 times. Ethanol washing helps remove residual moisture and organic impurities and prepares the material for the subsequent drying process.

[0061] After the final centrifugation, discard the ethanol supernatant and collect the gray silver powder precipitate at the bottom of the tube. Transfer the collected wet silver powder to a clean petri dish and place it in a vacuum drying oven. Vacuum dry at a relatively mild temperature (55-60℃) for 4-8 hours until constant weight is achieved. The final product is a loose, well-flowing first silver powder.

[0062] b. Preparation of the second silver powder Accurately weigh 7.87 g of silver nitrate (AgNO3) into a beaker. Based on the requirement of a PVP / AgNO3 mass ratio of 0.6, accurately weigh 4.72 g of polyvinylpyrrolidone (PVP). Dissolve both in 400 mL of deionized water, stirring continuously until completely dissolved to form a clear mixed solution. Based on the requirement of an ascorbic acid to silver nitrate molar ratio of approximately 1.2:1, accurately weigh 9.79 g of L-ascorbic acid and dissolve it in 50 mL of deionized water to prepare a reducing agent solution.

[0063] Transfer the entire prepared PVP / AgNO3 mixed solution to a jacketed glass reactor. Start mechanical stirring and heating, using a thermostatic circulator to precisely control and stabilize the solution temperature at 40°C. Once the solution reaches 40°C, monitor the pH value using a calibrated pH meter. Add pre-prepared dilute NaOH or dilute HNO3 solution dropwise to the reactor, precisely adjusting the pH value to 7.0. This process requires patient operation to ensure pH stability.

[0064] After confirming that the temperature (40℃) and pH (7.0) of the reaction system have stabilized, the reducing agent solution is quickly added to the reactor in one go to start the reduction reaction. The reaction is allowed to proceed for 30-60 minutes under constant stirring and temperature. During the reaction, the solution color will change from colorless to pale yellow, then brown, and finally become an opaque grayish-black dispersion.

[0065] To effectively settle 200nm particles, a higher centrifugal force or a longer centrifugation time is required. A high-speed centrifuge was used, centrifuged for 20 minutes at a relative centrifugal force of 8000 × g, where g is the gravitational acceleration at the Earth's surface.

[0066] The centrifugation and washing cycle was similar to that of the first silver powder. First, the powder was washed three times with deionized water to remove inorganic salt ions and residual reducing agent. Then, it was washed twice with anhydrous ethanol to remove moisture and residual PVP. After each wash, the precipitate was thoroughly redispersed using methods such as vortexing. The collected ethanol-coated wet powder was dried in a vacuum oven at 60°C until constant weight was achieved, yielding spherical second silver powder with an average particle size of 200 nm.

[0067] c. Preparation of the third silver powder Take silver nitrate (AgNO3, 0.81g) and prepare a silver nitrate aqueous solution with a concentration of 0.16mol / L using deionized water (30mL); the reducing agent is sodium citrate dihydrate (Na3C6H5O7·2H2O, 1.5g), which is dissolved in deionized water (150mL) and prepared into a sodium citrate solution with a concentration of 0.03mol / L by magnetic stirring.

[0068] Set up a three-necked flask reaction vessel and pre-fill it with 300 mL of deionized water. Set the oil bath to 160 °C and heat the deionized water to boiling. Add 30 mL of silver nitrate solution to the boiling deionized water and stir until homogeneous. Adjust the mechanical stirrer speed to 300 r / min and start adding the prepared sodium citrate solution dropwise (a total of 90 mL is added at a dropping rate of 18 mL / min). After titration is completed, let the reaction proceed for another 1 hour. After the reaction is completed, cool the reaction vessel to room temperature to obtain the mixed solution to be cleaned.

[0069] The cleaning process of the mixed solution to be cleaned includes: adding 5 mL of pre-prepared sodium citrate solution to the mixed solution to be cleaned and stirring evenly, allowing it to stand, centrifuging at 4000 rpm for 3 min to obtain a precipitate; adding 20 mL of deionized water to the precipitate to disperse it and obtain the mixed solution to be cleaned. The above cleaning process is repeated three times to obtain a third silver powder suspension, which is then centrifuged and dried to obtain the third silver powder.

[0070] (2) Mix terpineol and ethylene glycol, stir with a magnetic stirrer (100 rpm) until homogeneous, take a portion and add bismuth neodecanoate and continue stirring until completely dissolved to form a transparent solution; then add dispersant BYKJET-9151. After the dispersant is completely dissolved, slowly add polyvinylpyrrolidone in batches and continue stirring until all components are completely dissolved to obtain a mixed solvent.

[0071] (3) Mix the first silver powder, the second silver powder and the third silver powder in proportion to make them initially mixed; slowly add the initially mixed silver powder to the mixed solvent obtained in step 2 and stir evenly to obtain a premix.

[0072] (4) Add the remaining terpineol and ethylene glycol solvent to the premix for dilution, and adjust its viscosity to 10~20 cP; add the premix after viscosity adjustment to a ball mill, set the speed to 300 rpm, and ball mill according to the ball milling process; the ball milling process includes the first stage, the second stage and the third stage; in the first stage, the ball milling gap is 20 μm and the ball milling time is 30 min; in the second stage, the ball milling gap is 10 μm and the ball milling time is 30 min; in the third stage, the ball milling gap is 5 μm and the ball milling time is 30 min; repeat the above ball milling process 3 times to complete the ball milling and obtain the pre-made slurry.

[0073] (5) The pre-made slurry is allowed to stand and mature for 24 hours. The matured slurry is then filtered using a polytetrafluoroethylene (PTFE) needle filter with a pore size of 1.0 μm to obtain a conductive silver paste material for inkjet printing. The final conductive silver paste material can be stored in a sealed, light-proof brown HDPE bottle at a constant temperature of approximately 4°C for later use. The conductive silver paste material prepared in this embodiment is defined as conductive silver paste material 1.

[0074] Table 1. Mass fraction of each raw material in Example 1

[0075] Performance testing and analysis: 1. Using the LTCC co-firing process, the conductive silver paste material 1 prepared in Example 1 was fabricated into an experimental board with a ceramic substrate by inkjet printing. For example... Figure 2As shown, three experimental plates were prepared. Each plate includes a ceramic substrate and two circular conductive blocks embedded in the ceramic substrate. Figure 2 The conductive blocks are numbered 1 to 6 respectively.

[0076] According to GB / T 5210-2006 standard (experimental ambient temperature / humidity: 21.0℃ / 30%RH), the single-column single-sided tensile test method was used, and the tensile rate was ≤1MPa / s. The test results are shown in Table 2.

[0077] Table 2. Adhesion test results between conductive block and ceramic substrate

[0078] The adhesion test results in Table 2 show that the conductive silver paste formed excellent bonding strength after co-firing with the LTCC substrate. The average adhesion reached 3.70 MPa, demonstrating strong mechanical reliability, sufficient to withstand the thermal and mechanical stresses during subsequent packaging, assembly, and long-term service, effectively preventing delamination and peeling of the conductor layer.

[0079] 2. The conductive silver paste material 1 obtained in the example was used to fabricate a printed circuit by inkjet printing, such as... Figure 3 As shown. According to the standard GB / T 4677-2002 Printed Circuit Board Test Method, a random area was selected on the printed circuit, and SEM (Scanning Electron Microscopy) was used to measure the line width, line spacing, and accuracy of the printed circuit wires. See the results below. Figures 4-7 , and Table 3.

[0080] Table 3. Summary of measurement results for line width, line spacing, and accuracy

[0081] The conductive silver paste material prepared in Example 1, when used for inkjet printing, produced circuits with an average linewidth and line spacing of 50.1 μm, both within the preset linewidth (50 ± 5 μm) and preset line spacing (50 ± 5 μm) ranges. The average accuracy was 2.2 μm, within the preset accuracy requirement (< 5 μm). This indicates that the conductive silver paste material prepared by the method provided in this invention can be used for inkjet printing, and the obtained samples exhibit high accuracy.

[0082] Example 2 The difference from Example 1 is that in step 1, the raw materials, by mass fraction, include 25% first silver powder, 5% second silver powder, 1% third silver powder, 1.5% polyvinylpyrrolidone (PVP K-15), 0.5% dispersant (BYKJET-9151), 1% bismuth neodecanoate, 44% terpineol, and 22% ethylene glycol. The remaining steps are the same as in Example 1. The conductive silver paste material for inkjet printing prepared in Example 2 is defined as conductive silver paste material 2.

[0083] Using the same method as in Example 1, the conductive silver paste material 2 was prepared into an experimental board with a ceramic substrate using the LTCC co-firing process. The adhesion between the conductive block and the ceramic substrate was tested and found to be comparable to the results in Example 1, with an average adhesion of 2.6 MPa.

[0084] Using the same method as in Example 1, the printed circuit was prepared using conductive silver paste material 2. The average linewidth of the printed circuit was measured to be 64.5 μm, the average line spacing to be 65.2 μm, and the average accuracy measurement to be 4.8 μm. In this example, the viscosity of the obtained conductive silver paste material 2 decreased and the adhesion was reduced, possibly due to the reduced silver powder content and increased organic solvent content. The accuracy and resolution of the printed circuit were also reduced; however, the performance of the conductive silver paste material 2 still met the application requirements.

[0085] Example 3 The difference from Example 1 is that in step 1, the raw materials, by mass fraction, include 27% first silver powder, 6% second silver powder, 2% third silver powder, 0.5% polyvinylpyrrolidone (PVP K-15), 1.5% dispersant (BYKJET-9151), 2% bismuth neodecanoate, 20% terpineol, and 31% ethylene glycol. The remaining steps are the same as in Example 1. The conductive silver paste material for inkjet printing prepared in Example 3 is defined as conductive silver paste material 3.

[0086] Using the same method as in Example 1, the conductive silver paste material 3 was prepared into an experimental board with a ceramic substrate using the LTCC co-firing process. The adhesion between the conductive block and the ceramic substrate was tested and found to be comparable to the results in Example 1, with an average adhesion of 3.6 MPa.

[0087] Using the same method as in Example 1, the printed circuit was prepared using conductive silver paste material 3. The average linewidth of the printed circuit was measured to be 57.8 μm, the average line spacing to be 58.5 μm, and the average accuracy measurement to be 3.7 μm. In this example, compared with Example 1, the green body formed after printing with conductive silver paste material 3 had insufficient strength, slightly reduced adhesion, and a lower resolution.

[0088] Example 4 The difference from Example 1 is that in step 1, the raw materials, by mass fraction, include 29% first silver powder, 8% second silver powder, 3% third silver powder, 1.5% polyvinylpyrrolidone (PVP K-15), 2% dispersant (BYKJET-9151), 0.5% bismuth neodecanoate, 28% terpineol, and 28% ethylene glycol. The remaining steps are the same as in Example 1. The conductive silver paste material for inkjet printing prepared in Example 4 is defined as conductive silver paste material 4.

[0089] Using the same method as in Example 1, the conductive silver paste material 4 was prepared into an experimental board with a ceramic substrate using the LTCC co-firing process. The adhesion between the conductive block and the ceramic substrate was tested and found to be comparable to the results in Example 1, with an average adhesion of 2.1 MPa.

[0090] Using the same method as in Example 1, the printed circuit was prepared using conductive silver paste material 4. The average line width of the printed circuit was measured to be 55.1 μm, the average line spacing was 54.7 μm, and the average accuracy measurement was 3.2 μm.

[0091] Example 5 The difference from Example 1 is that in step 1, the raw materials, by mass fraction, include 35% first silver powder, 10% second silver powder, 3% third silver powder, 1% polyvinylpyrrolidone (PVP K-15), 1% dispersant (BYKJET-9151), 1.5% bismuth neodecanoate, 28.5% terpineol, and 20% ethylene glycol. The remaining steps are the same as in Example 1. The conductive silver paste material for inkjet printing prepared in Example 5 is defined as conductive silver paste material 5.

[0092] Using the same method as in Example 1, the conductive silver paste material 5 was prepared into an experimental board with a ceramic substrate using the LTCC co-firing process. The adhesion between the conductive block and the ceramic substrate was tested and found to be comparable to the results in Example 1, with an average adhesion of 4.3 MPa.

[0093] Using the same method as in Example 1, the printed circuit was prepared using conductive silver paste material 5. The average line width of the printed circuit was measured to be 49.2 μm, the average line spacing was 49.5 μm, and the average accuracy measurement was 1.9 μm.

[0094] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A conductive silver paste material for inkjet printing, characterized by, According to the mass fraction, 31%-48% of the conductive phase, 0.5%-2% of the dispersant, 0.5%-2% of the adhesive, 0.5%-2% of the adhesion promoter, and the balance of the solvent are composed; The conductive phase is composed of first silver powder, second silver powder and third silver powder; the mass of the first silver powder accounts for 25%-35% of the total mass of the conductive silver paste material, the mass of the second silver powder accounts for 5%-10% of the total mass of the conductive silver paste material, and the balance is the third silver powder; The first silver powder is spherical silver powder with an average particle size of 0.8 μm, the second silver powder is spherical silver powder with an average particle size of 200 nm, and the third silver powder is spherical silver powder with an average particle size of 50 nm; The adhesion promoter is bismuth neodecanoate.

2. The electrically conductive silver paste material for inkjet printing according to claim 1, characterized in that, The solvent is a mixed solution of ethylene glycol and terpineol; wherein the mass ratio of ethylene glycol to terpineol is 1:(0.5-2).

3. The electrically conductive silver paste material for inkjet printing according to claim 1, characterized in that, The adhesive is polyvinylpyrrolidone; the dispersant is BYKJET-9151.

4. A method for preparing the conductive silver paste material for inkjet printing according to any one of claims 1 to 3, characterized in that, Comprising the following steps: S1, add bismuth neodecanoate to the first solvent and stir until completely dissolved; then add the dispersant until completely dissolved, then add the adhesive in batches, stir until completely dissolved, and obtain a mixed solvent; S2, obtain a mixed powder of first silver powder, second silver powder and third silver powder, add the mixed solvent and stir uniformly to obtain a premix; S3, add a second solvent to the premix to adjust the viscosity of the premix to 10-20 cP, then perform ball milling to obtain a pre-prepared paste; wherein the second solvent is the same as the first solvent; S4, let the pre-prepared paste stand for 18-24 h, filter the matured pre-prepared paste with a polytetrafluoroethylene needle filter to obtain a conductive silver paste material for inkjet printing.

5. The method for preparing conductive silver paste material for inkjet printing according to claim 4, characterized in that, In step S2, the preparation method of the first silver powder comprises the following steps: Step 1, add an aqueous bovine serum albumin solution to a first reaction kettle, and the temperature of the first reaction kettle is 15-25℃; Step 2, add an aqueous silver nitrate solution to the first reaction kettle in step 1 in batches under stirring to obtain a first mixed solution; wherein the mass of bovine serum albumin is 10-15% of the mass of silver nitrate; Step 3, add ammonia water dropwise to the first mixed solution until the pH value is 9.5; after adding L-ascorbic acid and stirring for 10-15 min, ultrasonic treatment for 7-10 min, and centrifugal collection of the first silver powder crude product under a relative centrifugal force of (2800-3200) ×g, g is the acceleration of gravity on the earth's surface; wherein the molar ratio of L-ascorbic acid to silver nitrate is (1.2-1.6):1; Step 4, repeatedly ultrasonic cleaning and centrifugation of the first silver powder crude product with deionized water, and at least once ultrasonic cleaning and centrifugation with ethanol, and drying to obtain the first silver powder; the relative centrifugal force of the centrifugation is (2800-3200) ×g, g is the acceleration of gravity on the earth's surface.

6. The method for preparing conductive silver paste material for inkjet printing according to claim 4, characterized in that, In step S2, the preparation method of the second silver powder comprises the following steps: Step 10, a mixed solution of silver nitrate and polyvinylpyrrolidone is added into a second reaction kettle, and the temperature of the second reaction kettle is 35-45℃; wherein the mass ratio of polyvinylpyrrolidone to silver nitrate is (0.5-0.8):1; Step 20, NaOH solution or HNO3 solution is added dropwise into the mixed solution until the pH value is 7.0; L-ascorbic acid is added and stirred for 30-60 min, and the second silver powder crude product is collected by centrifugation under a relative centrifugal force of (7500-8500)×g, g being the acceleration of gravity on the surface of the earth; wherein the molar ratio of L-ascorbic acid to silver nitrate is (1.0-1.5):1; Step 30, the second silver powder crude product is washed by vortex oscillation and centrifugation with deionized water for multiple times, and then washed by vortex oscillation and centrifugation with ethanol at least once, and the second silver powder is obtained after drying; wherein the relative centrifugal force of the centrifugation is (7500-8500)×g, g being the acceleration of gravity on the surface of the earth.

7. The method for preparing conductive silver paste material for inkjet printing according to claim 4, characterized in that, In step S2, the preparation method of the third silver powder comprises the following steps: Step 100, deionized water is added into a three-necked flask reactor, and after the deionized water is heated to boiling at an oil bath temperature of 150-180℃, silver nitrate solution is added and stirred uniformly to obtain a second mixed solution; Step 200, sodium citrate solution is added dropwise into the second mixed solution at a dropwise adding speed of 15-20 mL / min, and after the dropwise adding of the sodium citrate solution is completed, the reaction is carried out for 45-70 min, and the cooled product is obtained as a to-be-cleaned mixed solution; wherein the molar ratio of sodium citrate to silver nitrate is (0.5-0.8):1; Step 300, the cleaning process comprises: sodium citrate solution is added into the to-be-cleaned mixed solution, stirred uniformly and left to stand, and then centrifuged at a speed of 3800-4200 rpm for 3-5 min, and the supernatant is discarded, and deionized water is added to disperse to obtain the current to-be-cleaned mixed solution; The cleaning process is repeated at least three times to obtain a third silver powder suspension, and the third silver powder is obtained after centrifugation and drying.

8. The method for preparing electrically conductive silver paste material for inkjet printing according to any one of claims 4 to 7, characterized in that, In step S3, the ball milling is carried out by using a ball mill; The ball mill comprises: S31, the rotating speed of the ball mill is set to 120-180 rpm, and the ball milling is carried out according to a ball milling process; The ball milling process comprises a first stage, a second stage and a third stage; In the first stage, the ball milling gap is 20 μm, and the ball milling time is 20-40 min; in the second stage, the ball milling gap is 10 μm, and the ball milling time is 20-40 min; in the third stage, the ball milling gap is 5 μm, and the ball milling time is 20-40 min; S32, the ball milling process is repeated 2-4 times to complete the ball milling.

9. The method for preparing conductive silver paste material for inkjet printing according to claim 8, characterized in that, The first solvent and the second solvent are both mixed solutions of ethylene glycol and terpineol; wherein the mass ratio of ethylene glycol to terpineol is 1:(0.5-2); The binder is polyvinylpyrrolidone, and the dispersant is BYKJET-9151.

10. A passive element, characterized by, The ceramic substrate and the metal conductor arranged on the ceramic substrate, and at least part of the metal conductor is prepared by using the conductive silver paste material for inkjet printing according to any one of claims 1-3.

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