Nano silver powder for ceramic filter, preparation method of nano silver powder and conductive silver paste

Abstract

The invention relates to the technical field of conductive silver paste, in particular to nano silver powder for a ceramic filter, a preparation method of the nano silver powder and conductive silver paste, and the preparation method at least comprises the following steps: silver salt, a reducing agent and a dispersing agent are subjected to an aqueous phase reduction reaction under the condition that the pH value is 9-10, and then a coating agent is added to prepare the nano silver powder. The ceramic filter conductive silver paste is prepared from the nano silver powder prepared by a specific method, the high-adhesion glass powder and the organic carrier matched with the spraying silver paste, and the ceramic filter conductive silver paste has relatively high flowability and can meet the process requirements of the spraying silver paste; and a uniform and compact silver film layer can be formed in a high-temperature sintering process, so that the technical requirement of a high Q value is met.

Description

Technical Field

[0001] This invention relates to the field of conductive silver paste technology, specifically to a nano silver powder for ceramic filters, its preparation method, and conductive silver paste. Background Technology

[0002] With the rapid popularization and large-scale application of emerging technologies such as 5G communication and the Internet of Things, the 5G ceramic substrate industry is entering a period of rapid development, with market demand showing a sustained and robust growth trend. As a core functional component of this industry, the production process of 5G ceramic substrate filters has become increasingly mature and has achieved mass production, widely used in various communication terminal equipment. Electrode paste, as a key raw material for ceramic substrate filters, directly affects the overall quality of the filter due to its performance compatibility.

[0003] Currently, the metallization processes for ceramic substrates mainly include electroplating, dip coating, and spraying. Among these, spraying has become the mainstream application process due to its advantages in film uniformity, production efficiency, and cost. The core application process of spray-applied silver paste is as follows: silver paste is uniformly coated onto the surface of the ceramic filter substrate using a professional spray gun. After drying pretreatment, a dense and continuous conductive silver film layer is formed on the ceramic surface through a high-temperature sintering process to achieve the conductivity and signal transmission functions of the electrodes. In the high-frequency operating scenarios of 5G communication, the key technical indicators for evaluating the performance of this type of silver paste mainly include two core dimensions: first, the quality factor (Q value), which directly determines the energy loss level of the silver paste in a high-frequency environment; and second, adhesion (i.e., the tensile strength between the silver film and the ceramic substrate), which affects the structural stability and service life of the filter.

[0004] Chinese invention patent CN112117026B discloses a silver paste for impregnation coating ceramic filters and its preparation method. The silver paste raw materials are silver powder: 70-83%, glass powder: 1-3%, and the balance being an organic carrier; the organic carrier includes organic resin, solvent, and dispersant. However, the combination of silver powder and glass powder in this technology results in a Q value of around 1900-2000, which cannot meet the requirements of current 5G ceramic filters for high Q-value conductive silver paste. Summary of the Invention

[0005] To address the problems in the prior art, the first aspect of the present invention provides a method for preparing nano-silver powder for ceramic filters, characterized by comprising at least the following steps: Nano-silver powder is prepared by carrying out an aqueous phase reduction reaction of silver salt, reducing agent, and dispersant at a pH of 9-10, followed by the addition of a coating agent.

[0006] In some embodiments, the silver salt, reducing agent, and dispersant are first prepared as silver salt solution, reducing agent solution, and dispersant solution, respectively, before being subjected to an aqueous phase reduction reaction.

[0007] In some embodiments, the silver salt solution, reducing agent solution, and dispersant solution are respectively an aqueous solution of silver salt, an aqueous solution of reducing agent, and an aqueous solution of dispersant.

[0008] In some embodiments, the silver salt includes one or more of silver nitrate, silver acetate, and silver carbonate.

[0009] In some embodiments, the concentration of the silver salt solution is 0.2-0.6 mol / L. Examples include 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, and 0.6 mol / L, or any value within the range of 0.2-0.6 mol / L.

[0010] In some embodiments, the reducing agent includes one or more of glycerol, ethylene glycol, ethanolamine, sodium borohydride, ascorbic acid, and glucose.

[0011] In some embodiments, the mass ratio of the silver salt to the reducing agent is 1:(1.2-1.5). For example, 1:1.2, 1:1.3, 1:1.4, 1:1.5, or any value within the range of 1:(1.2-1.5).

[0012] In some embodiments, the dispersant includes one or more of polyvinylpyrrolidone, gelatin, polyvinyl alcohol, and gum arabic.

[0013] In some embodiments, the mass ratio of the silver salt to the dispersant is 1:(0.5-1). For example, 1:0.5, 1:0.7, 1:0.8, 1:1, or any value within the range of 1:(0.5-1).

[0014] In some implementations, an alkaline solution is used to adjust the pH of the system to 9-10.

[0015] Optionally, the alkaline solution includes an aqueous solution of one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and sodium bicarbonate.

[0016] In some embodiments, the concentration of the alkaline solution is 0.05-0.1 mol / L. For example, 0.05 mol / L, 0.07 mol / L, 0.09 mol / L, 0.1 mol / L, or any value within the range of 0.05-0.1 mol / L.

[0017] In some embodiments, the coating agent includes one or more of oleic acid, stearic acid, lauric acid, and hexadecanoic acid.

[0018] In some embodiments, the mass ratio of the silver salt to the coating agent is 1:(0.1-0.3). For example, 1:0.1, 1:0.2, 1:0.3, or any value within the range of 1:(0.1-0.3).

[0019] In some embodiments, the conditions for the aqueous phase reduction reaction are: reaction time 1-2 hours, rotation speed 500-800 r / min.

[0020] A second aspect of the present invention provides a nano-silver powder for ceramic filters, which is prepared by the above-described preparation method.

[0021] In some embodiments, the average particle size of the nano-silver powder used in the ceramic filter is 400-500 nm.

[0022] In some embodiments, the nano-silver powder used in the ceramic filter includes spherical silver powder and flake silver powder. The mass ratio of the spherical silver powder to the flake silver powder is (90-95):(5-10). For example, 95:5, 90:10, 92:8, or any value within the range of (90-95):(5-10).

[0023] This invention utilizes small-particle-size spherical silver powder with an average particle size of 400-500 nm to achieve a denser silver film layer and improve electrical conductivity after spraying. By combining highly active nano-silver powder with Mn-Cu and Zn-Bi glass powder systems, a denser silver film with higher adhesion can be formed during the sintering process of ceramic filter electrodes. Due to the high activity of the silver powder and the high adhesion properties provided by the Mn-Cu and Zn-Bi systems, the glass powder content can be reduced in practical applications, minimizing the impact of metal elements in the glass on the performance of the ceramic filter during sintering. This maximizes the Q value of the ceramic filter and reduces energy loss during filter use.

[0024] A third aspect of the present invention provides a conductive silver paste, the raw materials of which include the above-mentioned nano-silver powder for ceramic filters, or the nano-silver powder for ceramic filters prepared by the above-mentioned preparation method.

[0025] In some embodiments, the raw materials for preparing the conductive silver paste, by weight percentage, include: Ceramic filters use 71-80% nano-silver powder. Glass powder 0.1-0.5% Organic carriers replenish the surplus.

[0026] In some embodiments, the glass powder comprises Mn-Cu system glass powder and Zn-Bi system glass powder.

[0027] In some embodiments, the mass ratio of the Mn-Cu system glass powder to the Zn-Bi system glass powder is (0.15-0.17):(0.03-0.05).

[0028] In some embodiments, the Mn-Cu system glass powder is composed of a first element containing Cu and O, a second element containing Mn, Bi, and Si, and an alkali metal element.

[0029] In some embodiments, the molar percentages of each component in the Mn-Cu glass powder are as follows: CuO content is 20-35%. SiO2 content is 30-40%. The sum of K₂O and Na₂O is 10-15%. The sum of MnO, CaO, and MgO is 3-8%. B2O3, Al2O3, and Bi2O3 are used to make up the balance.

[0030] In some embodiments, the Zn-Bi system glass powder is composed of a first element containing Bi and O, a second element containing Zn and Si, and an alkali metal element.

[0031] In some embodiments, the molar percentages of each component in the Zn-Bi glass powder are as follows: Bi2O3 65-75% ZnO 18-27% The sum of B2O3 and SiO2 is 2-5%. The sum of K₂O, Na₂O, and Al₂O₃ is 1-3%. Modified additives are used to make up the remaining amount; The modified additives contain Fe, Li, Mg, Ti, and W.

[0032] The elements of the modified additive are obtained by decomposing metal oxides.

[0033] In some embodiments, the modified additives include Fe3O4, Li2O, MgO, TiO2, and WO3.

[0034] In some embodiments, the method for preparing the glass powder includes: mixing the raw materials for preparing the glass powder and then passing them through a 750°C process. The glass powder is obtained by melting at 1250℃, cooling, drying, and pulverizing.

[0035] In some embodiments, the organic carrier includes an organic solvent, an organic resin, and additives.

[0036] In some embodiments, the organic solvent accounts for 18-32 wt% of the weight of the conductive silver paste, the organic resin accounts for 2-2.5 wt% of the weight of the conductive silver paste, and the additive accounts for 0.4-0.9 wt% of the weight of the conductive silver paste.

[0037] In some embodiments, the organic solvent includes one or more of diethylene glycol methyl ether, diethylene glycol butyl ether acetate, propylene glycol methyl ether acetate, dodecyl alcohol ester, diethylene glycol monobutyl ether, dibutyl phthalate, and tributyl acetyl citrate.

[0038] Optionally, the organic solvent is diethylene glycol methyl ether, diethylene glycol butyl ether acetate, diethylene glycol monobutyl ether, and dodecyl alcohol ester.

[0039] In some embodiments, the organic resin includes one or more of ethyl cellulose, polyvinyl butyral resin, and cellulose acetate butyrate.

[0040] Optionally, the organic resin is ethyl cellulose and polyvinyl butyral.

[0041] In some embodiments, the additive includes at least one of a dispersant and a leveling agent.

[0042] Optionally, the additives include dispersants and leveling agents.

[0043] Optionally, the dispersant accounts for 0.3-0.5 wt% of the weight of the conductive silver paste, and the leveling agent accounts for 0.2-0.4 wt% of the weight of the conductive silver paste.

[0044] In some embodiments, the dispersant includes one or more of polyurethane, polyester, and polyacrylic acid dispersants.

[0045] In some embodiments, the leveling agent includes at least one of silicone-based and fluorocarbon-based leveling agents.

[0046] In some embodiments, the method for preparing the conductive silver paste includes at least the following steps: The conductive silver paste was prepared by weighing and mixing nano silver powder, glass powder and organic carrier with ceramic filter, grinding, adjusting viscosity and filtering.

[0047] Beneficial effects 1. This invention employs a simple liquid-phase reduction method to prepare highly dispersed and uniformly morphologically uniform nano-silver powder, avoiding the agglomeration of nano-silver powder due to excessively small particle size, which would negatively impact the coating effect. Simultaneously, the high activity of the nano-silver powder results in a denser silver film layer after sintering, leading to better electrical conductivity and performance.

[0048] 2. In the preparation of nano silver powder of the present invention, by using ascorbic acid reducing agent under weakly alkaline stirring conditions, the spherical morphology with a particle size between 200-500nm can be effectively controlled. Furthermore, by adding dispersants such as PVP, a high degree of dispersion between silver powder particles with a particle size of 200-500nm can be achieved.

[0049] 3. This invention provides a glass powder system that offers high Q-value and high adhesion for silver paste in ceramic filters. By combining the main glass powder of the Mn-Cu system with the auxiliary glass powder of the Zn-Bi system, the silver-melting ability of the glass powder is significantly enhanced, resulting in fewer defects and pores in the silver film layer and better density. Simultaneously, Cu-Bi oxide can form a Cu-Bi alloy under high temperatures, leading to even stronger adhesion. The glass system of this invention exhibits strong adhesion, allowing for the achievement of ideal adhesion and reliability with a relatively low glass content. The lower glass content also reduces the damage to ceramic filter devices caused by active metal elements at high temperatures, improving the Q-value and reducing energy loss.

[0050] 4. This invention provides an organic carrier system suitable for spraying silver paste onto ceramic filters. The combination of specific organic resins and solvents effectively encapsulates the silver powder, preventing agglomeration during spraying. Furthermore, the use of organic solvents such as diethylene glycol butyl ether acetate and dodecyl alcohol ester improves flowability and atomization, preventing spray gun clogging. The addition of polyurethane, polyester, and polyacrylic acid dispersants, as well as silicone and fluorocarbon leveling agents, to the organic carrier system successfully avoids orange peel and poor smoothness issues.

[0051] 5. This invention prepares a conductive silver paste for ceramic filters using the above-mentioned nano-silver powder, high-adhesion glass powder, and an organic carrier suitable for spraying silver paste. It has strong fluidity and can meet the process requirements of spraying silver paste. At the same time, through the combination of glass system and highly active nano-silver powder, it can form a uniform and dense silver film layer during high-temperature sintering, thereby achieving the technical requirement of high Q value.

[0052] 6. The preparation method of this invention has mild reaction conditions, simple process, low cost, and is relatively easy to realize industrial production. Attached Figure Description

[0053] Figure 1 This is the SEM image of the silver nanoparticles prepared in Example 1 of the present invention.

[0054] Figure 2 This is a SEM image of the silver film layer after sintering the conductive silver paste of the ceramic filter prepared in Example 1 of the present invention.

[0055] Figure 3 The image shows the SEM image of the silver film layer after sintering the silver paste in the ceramic filter of Comparative Example 1. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Experimental methods not specifying specific conditions in the embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0057] Examples 1-10 and Comparative Examples 4-9 The first aspect provides a method for preparing nano-silver powder for ceramic filters, comprising the following steps: Weigh 50g of silver nitrate and dissolve it in 300mL of deionized water, stirring until homogeneous. Separately, weigh 25g of dispersant and dissolve it in 1000mL of deionized water, stirring until homogeneous to prepare a dispersant solution. Simultaneously, heat the dispersant solution to 160°C. Then, prepare an ascorbic acid reducing agent solution. Add the silver nitrate solution and reducing agent solution sequentially to the dispersant solution. Finally, add sodium hydroxide aqueous solution to adjust the pH to 9.5. Stir with a magnetic stirrer for 1.5 hours at 600 rpm. After the reaction is complete, add 5g of coating agent to coat the silver powder and terminate the reaction. Then, wash with deionized water, centrifuge, and dry to obtain the nano-silver powder for ceramic filters.

[0058] The coating agent is oleic acid; the dispersant is polyvinylpyrrolidone; and the reducing agent is ascorbic acid, with a dosage of 60g.

[0059] The second aspect provides a nano-silver powder for ceramic filters, wherein the nano-silver powder for ceramic filters includes spherical silver powder and flake silver powder in a mass ratio of 95:5.

[0060] The third aspect provides a conductive silver paste, and the raw materials for its preparation are shown in Tables 1-3: Molar percentage content of glass powder components in the Mn-Cu system: Table 1

[0061] Molar percentage content of glass powder components in Zn-Bi system: Table 2

[0062] Conductive silver paste weight composition table: Table 3

[0063] The method for preparing the glass powder includes: mixing the raw materials for preparing the glass powder, melting at 1000℃, cooling, drying, and pulverizing to obtain the glass powder.

[0064] The organic carrier is an organic solvent, an organic resin, a dispersant, and a leveling agent.

[0065] Table 3 shows the total organic carrier content as 19.8%, the organic solvents as follows: diethylene glycol methyl ether 3%, diethylene glycol butyl ether acetate 2%, diethylene glycol monobutyl ether 4%, and dodecyl alcohol ester 7.7%, the organic resins as follows: ethyl cellulose 1.2%, and polyvinyl butyral 1%. The dispersant used is BYK-2155 (0.5%), and the leveling agent used is BYK-110 (0.4%).

[0066] The total organic carrier content is 24.8%. The organic solvents used are diethylene glycol methyl ether (4%), diethylene glycol butyl ether acetate (2%), diethylene glycol monobutyl ether (4%), and dodecyl alcohol ester (11.7%). The organic resins used are ethyl cellulose (1.2%) and polyvinyl butyral (1%). The dispersant used is BYK-2155 (0.5%), and the leveling agent used is BYK-110 (0.4%).

[0067] The total organic carrier content is 34.8%. The organic solvents used are: diethylene glycol methyl ether (4%), diethylene glycol butyl ether acetate (5%), diethylene glycol monobutyl ether (4%), and dodecyl alcohol ester (18.4%). The organic resins used are: ethyl cellulose (1.2%) and polyvinyl butyral (1.3%). The dispersant used is BYK-2155 (0.5%), and the leveling agent used is BYK-110 (0.4%).

[0068] The method for preparing the conductive silver paste includes the following steps: The ceramic filter was prepared by weighing and mixing nano silver powder, glass powder and organic carrier evenly, grinding and adjusting the viscosity to 10-20 Pa·s using alcohol ester twelve, and filtering.

[0069] Figure 1 The image shows the SEM image of the silver nanoparticles prepared in Example 1.

[0070] Figure 2 The image shows the SEM image of the silver film layer after sintering the conductive silver paste of the ceramic filter prepared in Example 1.

[0071] Comparative Example 1 The specific implementation method in this example is the same as in Example 1, except that the ceramic filter uses nano silver powder with an average particle size of 1.05µm.

[0072] Comparative Example 2 The specific implementation method of this example is the same as that of Example 1, except that the glass powder is a Zn-Bi system glass powder.

[0073] Comparative Example 3 The specific implementation method in this example is the same as in Example 1, except that the glass powder is a Mn-Cu system glass powder.

[0074] Performance testing The resistivity, Q value, and tensile strength test results of the conductive silver pastes prepared in each embodiment and comparative example are shown in Table 4. The resistivity test method was as follows: conductive silver paste was first sprayed onto the surface of a ceramic filter, then sintered to prepare a ceramic filter electrode sample. After cooling, the sheet resistance was measured using a four-probe sheet resistance meter. The sheet resistance value was divided by the silver film thickness to obtain the resistivity data. Similarly, samples were prepared first, and the Q value was measured using a vector network analyzer. For tensile strength, samples were prepared first, and traction pins were soldered onto the surface of the silver film layer, then the tensile strength was measured using a tensile testing machine.

[0075] Table 4

[0076] As can be seen from Table 4, the silver nanoparticles prepared by this invention are uniformly dispersed and have a highly uniform morphology, exhibiting a near-spherical structure, supplemented by a small amount of plate-like silver powder. Figure 2 and 3 The comparison shows that the silver film layer after sintering of the silver paste of the present invention has a dense and pore-free structure.

[0077] As shown in Table 4, the conductive silver paste prepared in this invention exhibits superior overall performance in terms of volume resistivity, Q value, and tensile strength compared to the comparative example. Its resistivity is as low as 1.72 µΩ·cm, indicating excellent conductivity and the ability to effectively reduce energy loss during current transmission. Simultaneously, the Q value reaches 2250, indicating that this conductive silver paste can significantly improve the quality factor of ceramic filters, thereby optimizing their filtering effect. Furthermore, the tensile strength reaches 32 N / cm. 2 This demonstrates that the conductive silver paste has good adhesion and mechanical strength to the ceramic filter substrate, which helps to improve the reliability and durability of the product.

[0078] In comparison, although Comparative Example 1 has a slightly higher tensile strength than Example 1, its resistivity and Q value are significantly inferior to Example 1. In particular, the significant reduction in Q value will directly affect the performance of the ceramic filter. Comparative Examples 2 and 3 all perform worse than this application in terms of volume resistivity, Q value, and tensile strength.

Claims

1. A method for preparing nano-silver powder for ceramic filters, characterized in that, At least the following steps are included: Nano-silver powder is prepared by carrying out an aqueous phase reduction reaction of silver salt, reducing agent, and dispersant at a pH of 9-10, followed by the addition of a coating agent.

2. The method for preparing nano-silver powder for ceramic filters according to claim 1, characterized in that, The coating agent includes one or more of oleic acid, stearic acid, lauric acid, and hexadecanoic acid; the mass ratio of the silver salt to the coating agent is 1:(0.1-0.3).

3. A nano-silver powder for ceramic filters, characterized in that, It is prepared according to the preparation method according to claim 1 or 2.

4. The nano-silver powder for ceramic filters according to claim 3, characterized in that, The average particle size of the nano-silver powder used in the ceramic filter is 400-500 nm.

5. A conductive silver paste, characterized in that, The raw materials include the nano-silver powder for ceramic filters as described in claim 3 or 4, or the nano-silver powder for ceramic filters prepared by the method of claim 1 or 2.

6. The conductive silver paste according to claim 5, characterized in that, The raw materials for preparation, by weight percentage, include: Ceramic filters use 71-80% nano-silver powder. Glass powder 0.1-0.5% Organic carriers replenish the surplus.

7. The conductive silver paste according to claim 6, characterized in that, The glass powder includes Mn-Cu system glass powder and Zn-Bi system glass powder.

8. The conductive silver paste according to claim 7, characterized in that, The Mn-Cu system glass powder is composed of a first element containing Cu and O, a second element containing Mn, Bi, and Si, and an alkali metal element; the Zn-Bi system glass powder is composed of a first element containing Bi and O, a second element containing Zn and Si, and an alkali metal element.

9. The conductive silver paste according to claim 8, characterized in that, The molar percentages of each component in the Mn-Cu glass powder system are as follows: CuO 20-35% SiO2 30-40% The sum of K₂O and Na₂O is 10-15%. The sum of MnO, CaO, and MgO is 3-8%. B2O3, Al2O3, and Bi2O3 are used to make up the balance.

10. The conductive silver paste according to claim 8, characterized in that, The molar percentages of each component in the Zn-Bi glass powder system are as follows: Bi2O3 65-75% ZnO 18-27% The sum of B2O3 and SiO2 is 2-5%. The sum of K₂O, Na₂O, and Al₂O₃ is 1-3%. Modified additives are used to make up the remaining amount; The modified additives contain Fe, Li, Mg, Ti, and W.

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