Conductive slurry and preparation method and application method thereof

Abstract

The invention discloses a conductive paste and a preparation method and an application method thereof, according to the invention, electrosilvering coated nickel aluminum powder is added, so that the comprehensive cost of the conductive paste is reduced; during silver electroplating, a dispersing agent with cationic groups is used, so that the stability of a silver complexing solution is facilitated, and a compact silver deposition layer is formed; after the modified silver-coated nickel aluminum powder prepared from the glass sol is compounded with the fine silver powder, the agglomeration of a conductive phase is reduced, the conductive phase is easier to disperse during grinding, and the used glass powder component can be fused with a ceramic base material and is firmly attached to the surface of the base material; and the sintered conductive paste has the advantages of good conductivity, high adhesive force and the like.

Description

Technical Field

[0001] This invention relates to the field of conductive paste preparation, specifically to a conductive paste and its preparation and application methods. Background Technology

[0002] With the development of 5G technology and the photovoltaic field in China, the demand for silver paste is constantly increasing, and the market for silver paste and its upstream silver powder is gradually expanding, forming a certain degree of industrialization. Currently, the market share of domestically produced silver paste is continuously increasing, but compared with imported products, there is still a certain gap in high-quality silver paste. MLCC devices, 5G ceramic filters, LTCC devices, and other electronic components are important components of 5G communication. 5G communication requires higher bandwidth and higher power, placing higher demands on device size, weight, heat dissipation, and other performance aspects, thus requiring higher standards for conductive silver paste. Conductive silver paste is a filled conductive paste with silver powder as the conductive filler. It is a key material for ceramic devices because silver has advantages such as strong current carrying capacity, a thermal expansion coefficient close to that of ceramic blanks, good thermal stability, flexible and controllable construction processes, and the ability to directly weld signal structures onto silver layers, making it the best choice for electrode materials in ceramic devices. Forming a dense, highly adhesive, highly conductive, and solderable silver conductive layer on the surface of ceramic devices is particularly crucial for the conductive silver paste itself. The material properties and compatibility of the conductive silver paste, as well as functional additives, have a significant impact on device performance. Currently used electronic pastes primarily use silver powder as the conductive phase, consuming large amounts of the precious metal silver. Furthermore, silver migration can occur during the use of the conductive film, causing short circuits and equipment malfunctions. Core-shell copper / silver composite powders, as a novel conductive composite powder, combine the advantages of both materials while mitigating their disadvantages. They are an ideal alternative to silver powder in electronic pastes, conductive inks, and catalysts. However, when used in applications requiring high-temperature sintering, inert gas protection is necessary to reduce copper oxidation, making the application conditions quite demanding. Therefore, researching and preparing other base metal / silver composite conductive phase powder materials with core-shell structures is of great practical value and significance for developing high-value-added, high-quality conductive pastes, saving precious metals, and reducing costs. Summary of the Invention

[0003] In order to solve one of the above problems, this application provides a conductive paste and its preparation and application methods to solve the problems of high cost of conductive silver paste and poor conductivity or harsh addition requirements of other alternative conductive silver pastes in the prior art.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows: A conductive paste, by weight, comprises the following raw materials: 50-70 parts of modified silver-coated nickel-aluminum powder, 10-20 parts of fine silver powder, 10-30 parts of organic carrier, and 1-5 parts of other additives.

[0005] Furthermore, the fine silver powder is submicron-sized silver powder with a particle size of 0.3μm~1μm; The other additives are at least one of silver acetate and silver propionate.

[0006] Further, the organic carrier comprises terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, hydroxypropyl methylcellulose, lecithin and dimethyl phthalate in a mass ratio of (1~3):(25~27):(25~30):(10~12):(1~4):(1~3). The organic carrier is prepared by adding terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, hydroxypropyl methylcellulose, lecithin and dimethyl phthalate into a reaction vessel, heating the reaction vessel to 60~70℃, stirring at 200~500r / min for 0.5~1h, removing and sealing it and letting it stand at room temperature for more than 5h to obtain the organic carrier.

[0007] In addition, the present invention also provides a method for preparing a conductive paste, the method comprising the following steps: The modified silver-coated nickel-aluminum powder, fine silver powder, organic carrier and other additives are added to the reaction vessel and stirred and dispersed at room temperature for 0.5h~1h to obtain a pre-dispersed conductive slurry. The conductive slurry is added to a three-roll mill for grinding. The roller spacing is adjusted to ensure that the fineness of the slurry after grinding is below 8μm. The slurry is then filtered out, and the viscosity is adjusted to 30Pa.s~150Pa.s. After being thoroughly stirred, the conductive slurry is obtained. Furthermore, the modified silver-coated nickel-aluminum powder is prepared by the following steps: Step 1: Add nickel-coated aluminum powder to sodium hydroxide solution, ultrasonically clean, then wash with deionized water until the pH value is 6.5~7.0, filter, and vacuum dry; Step 2: Prepare a dispersant, which is composed of cationic cellulose and chitosan. Add the nickel-coated aluminum powder treated in Step 1 to the dispersant and stir ultrasonically to obtain a nickel-coated aluminum powder dispersion. Step 3: Add silver ammonia solution and glucose solution dropwise to the nickel-coated aluminum powder dispersion obtained in step S2. After completion, continue the reaction for 0.5~1h. Then raise the temperature of the plating solution to 50~60℃ and continue the reaction for 0.5h. Wash, filter, dry, and add to ethanol to obtain an ethanol suspension of silver-coated nickel-aluminum powder. Step 4: Weigh the reagents according to the glass mass ratio SiO2:B2O3:Bi2O3:TiO2 = 16:60:15:9. First, weigh tetraethyl orthosilicate and add an appropriate amount of ethanol and distilled water. Stir for 0.5 h to fully hydrolyze it. Then, add the dissolved boric acid, bismuth acetate and titanium acetate solutions in sequence and stir for 1 h to prepare a glass sol. Add the prepared glass sol to the ethanol suspension of silver-coated nickel-aluminum powder, stir to react, evaporate and concentrate, and finally vacuum dry to obtain modified silver-coated nickel-aluminum powder with glass powder coating on the surface.

[0008] Further, in step 1, the particle size of the nickel-coated aluminum powder is 1~5μm, and the nickel content accounts for 10%~50% of the mass of the nickel-coated aluminum powder; The concentration of the sodium hydroxide solution is 0.3~0.5 g / L; The ultrasonic cleaning time is 0.5~1h.

[0009] Further, in step S2, the concentration of the dispersant is 0.1~0.5 g / L; The ultrasonic stirring time is 0.5~1h; The concentration of the nickel-coated aluminum powder dispersion is 50~150g / L.

[0010] Further, in step S3, the concentration of the silver ammonia solution is 0.3~0.5 g / L; The concentration of the glucose solution is 0.6~1g / L; The dropping rate is 0.5~3 mL / min; The concentration of the ethanol suspension of the silver-coated nickel-aluminum powder is 30~100g / L.

[0011] Furthermore, in step S4, the solid content of the glass sol is 3~10 g / L; The stirring reaction is carried out at 70-75℃ for 2-3 hours. The evaporation and concentration process involves evaporating and concentrating at 90-95°C for 0.5-1 hour. The vacuum drying temperature is 75℃~85℃.

[0012] In addition, the present invention also provides a method for applying a conductive paste, the method being as follows: S1: Clean the squeegee, 250-400 mesh screen, and barium titanate or magnesium titanate ceramic substrate with alcohol. After the alcohol has evaporated, place the substrate on the worktable. Pour the evenly ground conductive paste onto the screen. With the squeegee at a 45° angle to the screen, slowly pull the squeegee from top to bottom to ensure that the silver paste can evenly cover the screen pattern. After screen printing, the sample needs to be left to stand and level for 5 minutes. Leveling will make the brush marks on the electrodes disappear and the electrode surface become smooth. Then, place it in a drying oven at 100-150℃ for 20 minutes to dry. During the drying process, the conductive paste will solidify. S2: Sinter the cured product under the following conditions: heat to 500-550℃ at a rate of 5-8℃ / min and hold for 5 minutes, then hold at a peak temperature of 800-950℃ for 10 minutes and cool with the furnace.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Compared with the prior art, the formulation system of this invention uses electroplated silver-coated nickel-aluminum powder, which helps to reduce the overall cost of conductive paste. The use of a dispersant with cationic groups during silver electroplating helps to stabilize the silver complex solution and facilitates the formation of a dense silver deposition layer. The modified silver-coated nickel-aluminum powder coated with glass powder prepared by glass sol and then compounded with fine silver powder helps to reduce the agglomeration of the conductive phase and makes it easier to disperse during grinding. The glass powder component used can be fused with the ceramic substrate and firmly adhered to the surface of the substrate, so that the sintered conductive paste has the advantages of good conductivity and high adhesion. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a SEM image of the silver layer surface after sintering in Example 2 of the present invention; Figure 2 This is a SEM image of the cross-section of the silver layer after sintering in Example 2 of the present invention; Figure 3 This is a SEM image of the silver layer surface after sintering in Comparative Example 1. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and do not limit the scope of protection of this application.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0017] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0018] Example 1: The conductive paste of this embodiment includes the following raw materials by weight: 60 parts modified silver-coated nickel-aluminum powder, 20 parts fine silver powder, 15 parts organic carrier and 3 parts silver acetate. The modified silver-coated nickel-aluminum powder is prepared by the following steps: Step 1: Add nickel-coated aluminum powder with a particle size of 5μm and a nickel content of 30% to a 0.5g / L sodium hydroxide solution, ultrasonically clean for 1h, then wash with deionized water until the pH value is 6.5~7.0, filter, and vacuum dry. Step 2: Prepare a 0.3 g / L dispersant, which consists of cationic cellulose and chitosan in a mass ratio of 1:1. Add the nickel-coated aluminum powder obtained in Step 1 to the dispersant and ultrasonically stir for 1 h to obtain a nickel-coated aluminum powder dispersion with a concentration of 100 g / L. Step 3: At room temperature, add 0.5 g / L silver ammonia solution and 1 g / L glucose solution dropwise to the nickel-coated aluminum powder dispersion at a dropping rate of 2 mL / min. After completion, continue the reaction at room temperature for 0.5 h, then raise the temperature of the plating solution to 55℃ and continue the reaction for 0.5 h. Finally, use deionized water to prepare an ethanol suspension of 50 g / L silver-coated nickel-aluminum powder. Step 4: Weigh the reagents according to the glass mass ratio SiO2:B2O3:Bi2O3:TiO2 = 16:60:15:9. First, weigh tetraethyl orthosilicate and add an appropriate amount of ethanol and distilled water. Stir for 0.5 h to fully hydrolyze it. Then, add the dissolved boric acid, bismuth acetate and titanium acetate solutions in sequence and stir for 1 h to prepare a glass sol with a solid content of 5 g / L. Add the prepared glass sol to the ethanol suspension of silver-coated nickel-aluminum powder, stir and react at 75 ℃ for 2 h, evaporate and concentrate at 90 ℃ for 1 h, and finally vacuum dry at 80 ℃ to obtain modified silver-coated nickel-aluminum powder with glass powder coating on the surface. The fine silver powder is submicron-sized silver powder with a particle size of 1 μm. The organic carrier is prepared by adding terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, hydroxypropyl methylcellulose, lecithin and dimethyl phthalate in a mass ratio of 3:27:30:12:4:3 into a reaction vessel, heating the reaction vessel to 65°C, stirring at 300 r / min for 1 h, removing and sealing it and letting it stand at room temperature for 8 h; A method for preparing a conductive paste includes the following steps: adding the modified silver-coated nickel-aluminum powder, fine silver powder, organic carrier, and silver acetate into a reaction vessel, stirring and dispersing at room temperature for 1 hour to obtain a pre-dispersed conductive paste. The conductive slurry was then added to a three-roll mill for grinding. The roller spacing was adjusted to ensure that the fineness of the slurry after grinding was below 8μm. The slurry was then filtered out, and the viscosity was adjusted to 120Pa.s. After thorough mixing, the conductive slurry was obtained. Example 2: The conductive paste of this embodiment includes the following raw materials by weight: 70 parts modified silver-coated nickel-aluminum powder, 10 parts fine silver powder, 15 parts organic carrier and 5 parts silver propionate. The modified silver-coated nickel-aluminum powder is prepared by the following steps: Step 1: Add nickel-coated aluminum powder with a particle size of 5μm and a nickel content of 10% to a 0.3g / L sodium hydroxide solution, ultrasonically clean for 1 hour, then wash with deionized water until the pH value is 6.5~7.0, filter, and vacuum dry. Step 2: Prepare a 0.1 g / L dispersant, which consists of cationic cellulose and chitosan in a mass ratio of 1:1. Add the nickel-coated aluminum powder obtained in Step 1 to the dispersant and ultrasonically stir for 1 h to obtain a nickel-coated aluminum powder dispersion with a concentration of 50 g / L. Step 3: At room temperature, add 0.3 g / L silver ammonia solution and 0.6 g / L glucose solution dropwise to the nickel-coated aluminum powder dispersion at a dropping rate of 0.5 mL / min. After completion, continue the reaction at room temperature for 0.6 h, then raise the temperature of the plating solution to 60 °C and continue the reaction for 0.5 h. Finally, wash the prepared silver-coated nickel-aluminum powder twice with deionized water, filter, dry, and add it to ethanol to prepare an ethanol suspension of silver-coated nickel-aluminum powder with a concentration of 30 g / L. Step 4: Weigh the reagents according to the glass mass ratio SiO2:B2O3:Bi2O3:TiO2 = 16:60:15:9. First, weigh tetraethyl orthosilicate and add an appropriate amount of ethanol and distilled water. Stir for 0.5 h to fully hydrolyze it. Then, add the dissolved boric acid, bismuth acetate and titanium acetate solutions in sequence and stir for 1 h to prepare a glass sol with a solid content of 3 g / L. Add the prepared glass sol to the ethanol suspension of silver-coated nickel-aluminum powder, stir and react at 75℃ for 2 h, evaporate and concentrate at 90℃ for 1 h, and finally vacuum dry at 80℃ to obtain modified silver-coated nickel-aluminum powder with glass powder coating on the surface. The fine silver powder is submicron-sized silver powder with a particle size of 1 μm. The organic carrier is prepared by adding terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, hydroxypropyl methylcellulose, lecithin and dimethyl phthalate in a mass ratio of 3:27:30:12:4:3 into a reaction vessel, heating the reaction vessel to 70°C, stirring at 300 r / min for 1 h, removing and sealing it and letting it stand at room temperature for 8 h. A method for preparing a conductive paste includes the following steps: adding the modified silver-coated nickel-aluminum powder, fine silver powder, organic carrier, and silver propionate into a reaction vessel, stirring and dispersing at room temperature for 1 hour to obtain a pre-dispersed conductive paste. The conductive slurry was then added to a three-roll mill for grinding. The roller spacing was adjusted to ensure that the fineness of the slurry after grinding was below 8μm. The slurry was then filtered out, and the viscosity was adjusted to 120Pa.s. After thorough mixing, the conductive slurry was obtained. Example 3: The conductive paste of this embodiment includes the following raw materials by weight: 50 parts modified silver-coated nickel-aluminum powder, 18 parts fine silver powder, 30 parts organic carrier and 2 parts silver acetate. The modified silver-coated nickel-aluminum powder is prepared by the following steps: Step 1: Add nickel-coated aluminum powder with a particle size of 3μm and a nickel content of 50% to a 0.4g / L sodium hydroxide solution, ultrasonically clean for 1 hour, then wash with deionized water until the pH value is 6.5~7.0, filter, and vacuum dry. Step 2: Prepare a 0.5 g / L dispersant, which consists of cationic cellulose and chitosan in a mass ratio of 1:1. Add the nickel-coated aluminum powder obtained in Step 1 to the dispersant and ultrasonically stir for 1 h to obtain a nickel-coated aluminum powder dispersion with a concentration of 150 g / L. Step 3: At room temperature, add 0.5 g / L silver ammonia solution and 1 g / L glucose solution dropwise to the nickel-coated aluminum powder dispersion at a dropping rate of 3 mL / min. After completion, continue the reaction at room temperature for 0.5-1 h, then raise the temperature of the plating solution to 60℃ and continue the reaction for 0.5 h. Finally, wash the prepared silver-coated nickel-aluminum powder twice with deionized water, filter, dry, and add it to ethanol to prepare an ethanol suspension of silver-coated nickel-aluminum powder with a concentration of 100 g / L. Step 4: Weigh the reagents according to the glass mass ratio SiO2:B2O3:Bi2O3:TiO2 = 16:60:15:9. First, weigh tetraethyl orthosilicate and add an appropriate amount of ethanol and distilled water. Stir for 0.5 h to fully hydrolyze it. Then, add the dissolved boric acid, bismuth acetate and titanium acetate solutions in sequence and stir for 1 h to prepare a glass sol with a solid content of 10 g / L. Add the prepared glass sol to the ethanol suspension of silver-coated nickel-aluminum powder, stir and react at 75°C for 3 h, evaporate and concentrate at 90°C for 1 h, and finally vacuum dry at 80°C to obtain modified silver-coated nickel-aluminum powder with glass powder coating on the surface. The fine silver powder is submicron-sized silver powder with a particle size of 1 μm. The organic carrier is prepared by adding terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, hydroxypropyl methylcellulose, lecithin and dimethyl phthalate in a mass ratio of 3:27:30:12:4:3 into a reaction vessel, heating the reaction vessel to 70°C, stirring at 300 r / min for 1 h, removing and sealing it and letting it stand at room temperature for 8 h. A method for preparing a conductive slurry includes the following steps: adding the modified silver-coated nickel-aluminum powder, fine silver powder, organic carrier, and silver acetate into a reaction vessel, stirring and dispersing at room temperature for 1 hour to obtain a pre-dispersed conductive slurry; then adding the conductive slurry to a three-roll mill for grinding, adjusting the roller spacing to ensure that the fineness of the slurry after grinding is below 8 μm, filtering out the material, adjusting the viscosity to 120 Pa·s, and stirring thoroughly to obtain the conductive slurry. Comparative Example 1: Compared with Example 2, Comparative Example 1 does not use glass powder to coat silver-coated nickel-aluminum powder. Instead, 3 parts of glass powder are added to the conductive paste. The glass powder used is silicon aluminum bismuth glass powder with a melting point of 600~650℃ and a particle size of 5μm. Otherwise, it is the same as Example 3.

[0019] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that silver propionate (other additives) was not added; otherwise, they are the same as Example 2.

[0020] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the ratio of the conductive paste is different from that in Example 2, but the rest is the same as in Example 2.

[0021] The raw material ratio of the conductive paste in Comparative Example 3 is as follows: 68 parts of modified silver-coated nickel-aluminum powder, 30 parts of organic carrier, and 2 parts of silver propionate.

[0022] The conductive paste samples prepared in Examples 1-3 and the conductive paste samples prepared in Comparative Examples 1-3 were screen printed and sintered, and their resistance, adhesion and morphology were tested. The results are shown in Table 1 below.

[0023] The application methods for conductive pastes are as follows: Step 1: Clean the squeegee, 250-400 mesh screen, and barium titanate or magnesium titanate ceramic substrate with alcohol. After the alcohol has evaporated, place the substrate on the worktable. Pour the evenly ground conductive paste onto the screen. With the squeegee at a 45° angle to the screen, slowly pull the squeegee from top to bottom to ensure the silver paste evenly covers the screen pattern. After screen printing, allow the sample to stand and level for 5 minutes. Leveling will remove the brush marks on the electrodes and make the electrode surface smooth. Then, place the sample in a 150°C drying oven for 20 minutes to dry. During the drying process, the paste will solidify. Step 2: Place the dried and cured sample into a muffle furnace under an air atmosphere for sintering. Sintering conditions: heat up to 550℃ at 8℃ / min, hold for 5 min, and hold at the peak temperature of 950℃ for 10 min, then cool with the furnace.

[0024] Table 1: Performance Test Results

[0025] As shown in Table 1, the conductive paste prepared in this application has better conductivity and adhesion. During the preparation process, the use of a dispersant with cationic groups during silver electroplating helps stabilize the silver complex solution, which is beneficial for forming a dense silver deposition layer. The use of glass sol to prepare modified silver-coated nickel-aluminum powder coated with glass powder, combined with fine silver powder, helps reduce the agglomeration of the conductive phase and makes it easier to disperse during grinding. The glass powder component used can fuse firmly with the ceramic substrate and adhere to the substrate surface, resulting in a conductive paste with good conductivity and high adhesion after sintering. Furthermore, the use of electroplated silver-coated nickel-aluminum powder in the formulation system helps reduce the overall cost of the conductive paste.

[0026] In addition, the present invention also provides Figure 1 as well as Figure 3 ,in Figure 1 This is a SEM image of the silver layer surface after sintering of the conductive paste in Example 2 of the present invention. Figure 2 This is a SEM image of the cross-section of the silver layer after sintering the conductive paste in Example 2 of the present invention; from Figure 1 as well as Figure 2 As can be seen, the conductive paste prepared by this invention has excellent surface morphology after sintering. Figure 3 The image shows a SEM image of the silver layer after sintering the conductive paste prepared in Comparative Example 1. Figure 3 It can be clearly seen that after sintering, there are many small pores, with pores larger than 3μm, and the surface morphology is not as good as in Example 2.

[0027] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0028] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A conductive paste, characterized in that, According to the mass fraction, the conductive paste comprises the following raw materials: 50-70 parts of modified silver-coated nickel-aluminum powder, 10-20 parts of fine silver powder, 10-30 parts of organic carrier, and 1-5 parts of other additives.

2. The conductive paste according to claim 1, characterized in that, The fine silver powder is submicron-sized silver powder with a particle size of 0.3μm~1μm; The other additives are at least one of silver acetate and silver propionate.

3. The conductive paste according to claim 1, characterized in that, The organic carrier comprises terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, hydroxypropyl methylcellulose, lecithin and dimethyl phthalate in a mass ratio of (1~3):(25~27):(25~30):(10~12):(1~4):(1~3); The organic carrier is prepared by adding terpineol, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, hydroxypropyl methylcellulose, lecithin and dimethyl phthalate into a reaction vessel, heating the reaction vessel to 60~70℃, stirring at 200~500r / min for 0.5~1h, removing and sealing it and letting it stand at room temperature for more than 5h to obtain the organic carrier.

4. A method for preparing a conductive paste, characterized in that, The preparation method is used to prepare the conductive paste as described in any one of claims 1 to 3, and the preparation method includes the following steps: The modified silver-coated nickel-aluminum powder, fine silver powder, organic carrier and other additives are added to the reaction vessel and stirred and dispersed at room temperature for 0.5h~1h to obtain a pre-dispersed conductive slurry. The conductive slurry is added to a three-roll mill for grinding. The roller spacing is adjusted to ensure that the fineness of the slurry after grinding is below 8μm. The slurry is then filtered out, and the viscosity is adjusted to 30Pa.s~150Pa.s. After being thoroughly stirred, the conductive slurry is obtained.

5. The preparation method according to claim 4, characterized in that, The modified silver-coated nickel-aluminum powder is prepared by the following steps: Step 1: Add nickel-coated aluminum powder to sodium hydroxide solution, ultrasonically clean, then wash with deionized water until the pH value is 6.5~7.0, filter, and vacuum dry; Step 2: Prepare a dispersant, which is composed of cationic cellulose and chitosan. Add the nickel-coated aluminum powder treated in Step 1 to the dispersant and stir ultrasonically to obtain a nickel-coated aluminum powder dispersion. Step 3: Add silver ammonia solution and glucose solution dropwise to the nickel-coated aluminum powder dispersion obtained in step S2. After completion, continue the reaction for 0.5~1h. Then raise the temperature of the plating solution to 50~60℃ and continue the reaction for 0.5h. Wash, filter, dry, and add to ethanol to obtain an ethanol suspension of silver-coated nickel-aluminum powder. Step 4: Weigh the reagents according to the glass mass ratio SiO2:B2O3:Bi2O3:TiO2 = 16:60:15:

9. First, weigh tetraethyl orthosilicate and add an appropriate amount of ethanol and distilled water. Stir for 0.5 h to fully hydrolyze it. Then, add the dissolved boric acid, bismuth acetate and titanium acetate solutions in sequence and stir for 1 h to prepare a glass sol. Add the prepared glass sol to the ethanol suspension of silver-coated nickel-aluminum powder, stir to react, evaporate and concentrate, and finally vacuum dry to obtain modified silver-coated nickel-aluminum powder with glass powder coating on the surface.

6. The preparation method according to claim 5, characterized in that, In step 1, the particle size of the nickel-coated aluminum powder is 1~5μm, and the nickel content accounts for 10%~50% of the mass of the nickel-coated aluminum powder; The concentration of the sodium hydroxide solution is 0.3~0.5 g / L; The ultrasonic cleaning time is 0.5~1h.

7. The preparation method according to claim 5, characterized in that, In step S2, the concentration of the dispersant is 0.1~0.5 g / L; The ultrasonic stirring time is 0.5~1h; The concentration of the nickel-coated aluminum powder dispersion is 50~150g / L.

8. The preparation method according to claim 5, characterized in that, In step S3, the concentration of the silver ammonia solution is 0.3~0.5 g / L; The concentration of the glucose solution is 0.6~1g / L; The dropping rate is 0.5~3 mL / min; The concentration of the ethanol suspension of the silver-coated nickel-aluminum powder is 30~100g / L.

9. The preparation method according to claim 5, characterized in that, In step S4, the solid content of the glass sol is 3~10 g / L; The stirring reaction is carried out at 70-75℃ for 2-3 hours. The evaporation and concentration process involves evaporating and concentrating at 90-95°C for 0.5-1 hour. The vacuum drying temperature is 75℃~85℃.

10. A method for applying a conductive paste, characterized in that, The conductive paste is the conductive paste according to any one of claims 1 to 3, and the application method is as follows: S1: Clean the squeegee, 250-400 mesh screen, and barium titanate or magnesium titanate ceramic substrate with alcohol. After the alcohol has evaporated, place the substrate on the worktable. Pour the evenly ground conductive paste onto the screen. With the squeegee at a 45° angle to the screen, slowly pull the squeegee from top to bottom to ensure that the silver paste can evenly cover the screen pattern. After screen printing, the sample needs to be left to stand and level for 5 minutes. Leveling will make the brush marks on the electrodes disappear and the electrode surface become smooth. Then, place it in a drying oven at 100-150℃ for 20 minutes to dry. During the drying process, the conductive paste will solidify. S2: Sinter the cured product under the following conditions: heat to 500-550℃ at a rate of 5-8℃ / min and hold for 5 minutes, then hold at a peak temperature of 800-950℃ for 10 minutes and cool with the furnace.

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