Superfine roller printing nickel paste for extreme high capacitance MLCC and preparation method thereof

Abstract

This invention relates to the field of nickel electrode paste preparation technology, and discloses an ultrafine roller-printed nickel paste for ultra-high capacitance MLCCs and its preparation method. The nickel paste includes nickel powder, Ni3Sn-coated nickel powder, diffusion barrier phase, resin, solvent, dispersant, and rheology modifier. The Ni3Sn-coated nickel powder is obtained by chemical plating, where Sn is bonded to Ni in the form of an intermetallic compound. The diffusion barrier phase is selected from nano-ZrO2 or TiO2 particles. After pre-dispersing each solid component with a portion of the dispersant and solvent, the mixture is ground and dispersed using a gradient grinding process, then mixed with an organic carrier to form a paste. After vacuum degassing and filtration, the nickel paste is obtained. This invention uses Ni3Sn-coated nickel powder to replace elemental Sn powder, inhibiting the formation of a dense SnO2 passivation layer. Combined with the blocking effect of the diffusion barrier phase at the grain boundaries and the protection of the coating layer integrity by the gradient grinding process, this invention solves the problem of long-term reliability degradation of MLCCs caused by Sn storage.

Description

Technical Field

[0001] This invention relates to the field of nickel electrode paste preparation technology, and in particular to an ultrafine roller printing nickel paste for ultra-high capacitance MLCCs and its preparation method. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are constantly evolving towards higher capacitance. To achieve the ultimate high capacitance, not only is the thickness of the internal electrode reduced to the submicron level, but stringent requirements are also placed on the continuity and compactness of the electrode. However, pure nickel electrodes are prone to defects such as discontinuities and voids at the thin scale, which can lead to a decrease in capacitance and a reduction in reliability. To address this, the industry is now trying to add alloying elements to nickel paste to improve electrode continuity. Tin (Sn) has become an important research direction due to its moderate cost and suitable solid solubility with nickel.

[0003] Existing research generally believes that after adding Sn, a SnO2 enrichment layer will form at the electrode-dielectric interface during re-oxidation. This enrichment layer can build a Schottky barrier to suppress leakage current, which is sufficient to ensure the long-term reliability of MLCCs. However, Hong Luyun et al. pointed out in their paper "Effect of tin addition to nickel internal electrodes on the insulation resistance degradation of MLCCs" published in the Journal of Materials Science: Materials in Electronics that the actual situation is not so optimistic. During re-oxidation, a dense SnO2 passivation layer will quickly form on the Sn surface. This passivation layer will become a barrier to oxygen diffusion inward, preventing the Sn inside the electrode from being further oxidized. More problematic is that during the long-term service of MLCCs, these sealed Sn metals will continue to diffuse into the BaTiO3 dielectric layer and be converted into Sn. 2+ The form of Ti replaces 4+ This continuously generates oxygen vacancies, ultimately causing the insulation resistance to degrade rapidly over time. Summary of the Invention

[0004] The technical problem to be solved by this invention is the technical problem of incomplete oxidation of Sn in existing Ni-Sn alloy nickel paste, which leads to long-term sealing of metallic Sn and continuous diffusion into the dielectric layer. In order to improve the long-term reliability of MLCC, we propose an ultrafine roller printing nickel paste for ultra-high capacitance MLCC and its preparation method.

[0005] To achieve the above objectives, this application adopts the following technical solution: an ultrafine roller printing nickel paste, comprising the following components by weight: 100 parts nickel powder, 15-35 parts Ni3Sn coated nickel powder, 0.5-2.0 parts diffusion barrier phase, 6-12 parts resin, 50-80 parts solvent, 1.0-3.0 parts dispersant, and 0.3-1.2 parts rheology modifier, wherein the Ni3Sn coated nickel powder is a core-shell structure particle formed by coating the surface of nickel powder with a Ni3Sn layer, and the atomic ratio of Ni to Sn in the coating layer is 2.8:1-3.2:1, and the diffusion barrier phase is selected from at least one of nano ZrO2 particles and nano TiO2 particles.

[0006] Preferably, the resin is selected from at least one of ethyl cellulose and acrylic resin.

[0007] Preferably, the solvent is selected from at least one of terpineol, diethylene glycol butyl ether acetate, and tributyl citrate.

[0008] Preferably, the dispersant is selected from at least one of DISPERBYK-110, phosphate ester, polyethylene glycol, and polyvinylpyrrolidone.

[0009] Preferably, the rheology modifier is selected from at least one of hydrogenated castor oil and polyamide wax.

[0010] A method for preparing ultrafine roller printing nickel paste includes the following steps: S1: Mixing and stirring nickel powder, Ni3Sn-coated nickel powder, diffusion barrier phase, first dispersant, and first solvent to prepare a pre-dispersed slurry; S2: Transferring the pre-dispersed slurry to a sand mill and grinding and dispersing it using a gradient grinding process to control the slurry fineness to ≤5μm; S3: Adding resin to the remaining solvent, then adding the remaining dispersant, heating and stirring until completely dissolved to prepare an organic carrier; S4: Mixing the organic carrier with the ground powder slurry, adding a rheology modifier, and stirring at high speed until homogeneous; S5: Vacuum degassing and filtering the mixed slurry to obtain the finished nickel paste.

[0011] Preferably, in S1, the first part of the dispersant accounts for 50%-70% of the total dispersant, and the first part of the solvent accounts for 40%-60% of the total solvent.

[0012] Preferably, in S2, the gradient grinding process includes a first-stage grinding and a second-stage grinding. The first stage uses grinding media with a diameter of 0.5 mm for 1-1.5 hours, and the second stage uses grinding media with a diameter of 0.3 mm for 1-1.5 hours.

[0013] Preferably, the slurry temperature is controlled at 30-50℃ during the gradient grinding process.

[0014] A method for applying ultrafine roller-printed nickel paste in MLCCs includes: coating the nickel paste onto a ceramic green body using a roller printing process to form an inner electrode layer, followed by debinding, sintering, and re-oxidation treatment.

[0015] The technical effects and advantages of this invention are as follows:

[0016] In this invention, Ni3Sn-coated nickel powder is used as the conductive phase, allowing Sn and Ni to be chemically bonded, reducing the oxidation activity of Sn and preventing the formation of a dense SnO2 layer. This allows oxygen to fully penetrate during the re-oxidation process, achieving complete oxidation of Sn. Simultaneously, nano-ZrO2 or TiO2 is added as a diffusion barrier phase, which agglomerates at the grain boundaries of nickel particles during sintering, forming a physical barrier and blocking the diffusion path of residual Sn. Furthermore, a gradient grinding process is used in slurry preparation, first breaking up agglomerates with larger particle size grinding media, and then finely grinding with smaller particle size media. This protects the structural integrity of the Ni3Sn coating layer and synergistically inhibits the sealing and continuous diffusion of metallic Sn. As a result, after 1500 hours of high-temperature aging, the insulation resistance decrease rate of the MLCC is controlled within 15%, while the capacitance is increased by more than 25%, and the breakdown voltage is increased to over 130V, achieving a synergistic improvement in long-term reliability and electrical performance. Attached Figure Description

[0017] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0018] Figure 1 SEM image of the MLCC sample prepared in Example 1 of the present invention;

[0019] Figure 2 SEM image of the MLCC sample prepared in Comparative Example 1 of this invention;

[0020] Figure 3 This is a graph showing the change rate of insulation resistance over time according to the present invention.

[0021] Figure 4 This is a comparison chart of the electrical performance test results of the present invention. Detailed Implementation

[0022] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0023] This invention provides an ultrafine roller printing nickel paste, which, by weight, comprises the following components: 100 parts of auxiliary conductive phase, 15-35 parts of conductive phase, 0.5-2.0 parts of diffusion blocking phase, 6-12 parts of resin, 50-80 parts of solvent, 1.0-3.0 parts of dispersant, and 0.3-1.2 parts of rheology modifier.

[0024] In this invention, the conductive phase is Ni3Sn-coated nickel powder, which is a core-shell structure particle formed by coating a Ni3Sn layer on the surface of nickel powder, and is obtained by chemical plating. The nickel powder is spherical with an average particle size D50 of 80-150 nm, a purity ≥99.9%, and a specific surface area of ​​8-15 m². 2 / g, the tin source is stannous chloride dihydrate (SnCl2·2H2O), CAS number is 10025-69-1, purity ≥98.0%.

[0025] The Ni3Sn-coated nickel powder is prepared by chemical plating, specifically including the following steps:

[0026] C1: Place the nickel powder in a 6%-9% sodium hydroxide solution, adjust the pH to 10-11, activate it at 50℃ for 40-50 minutes, and wash it with deionized water until the pH of the washing solution is 7.

[0027] C2: Weigh 10-30 g / L of stannous chloride dihydrate, 15-25 g / L of sodium citrate, and 5-15 g / L of sodium hypophosphite, add them to deionized water to dissolve them, prepare a plating solution, and adjust the pH value to 8-10 with ammonia.

[0028] C3: Add the activated nickel powder to the plating solution at a solid-liquid ratio of 1:5-1:15 (g / mL), and stir at 200-400 r / min for 45-65 min at 60-80℃.

[0029] C4: After the reaction is complete, filter the solution, wash it with deionized water 3-5 times, and dry it under vacuum at 50-70℃ and -0.09MPa for 3-6 hours to obtain Ni3Sn coated nickel powder.

[0030] In the above preparation process, the thickness of the coating layer can be adjusted by the reaction time, and the atomic ratio of Ni to Sn in the coating layer needs to be controlled between 2.8:1 and 3.2:1.

[0031] In the Ni3Sn intermetallic compound, Sn and Ni are chemically bonded, and its oxidation activity is lower than that of elemental Sn. It is not easily oxidized to form SnO2 during the re-oxidation process. Even if the surface of the coating layer is slightly oxidized, due to the structural integrity of the Ni3Sn phase, it is difficult to form a continuous and dense SnO2 passivation layer. Therefore, Sn can be further oxidized during the re-oxidation process, or it can exist stably inside the electrode in the form of an intermetallic compound, thereby reducing the diffusion of metallic Sn into the dielectric layer.

[0032] The auxiliary conductive phase is spherical nickel powder with a particle size D50 in the range of 80-150nm. This nickel powder is of the same specification as the nickel powder used to prepare Ni3Sn coated nickel powder, but it is not coated. The two are measured separately in the formula.

[0033] The nickel powder in the auxiliary conductive phase constitutes the main conductive network of the electrode, ensuring the overall conductivity of the electrode. By adjusting the ratio of the auxiliary conductive phase to Ni3Sn coated nickel powder, the Sn content in the electrode can be controlled to avoid the diffusion risk caused by excessive Sn. At the same time, Ni3Sn coated nickel powder has good flow characteristics during sintering, which can fill the tiny pores in the electrode, thereby improving the density and continuity of the electrode.

[0034] The diffusion barrier phase is selected from at least one of nano ZrO2 particles and nano TiO2 particles, with an average particle size D50 in the range of 5-20 nm and a purity ≥99.5%.

[0035] After the diffusion barrier phase is uniformly dispersed in the slurry, it will agglomerate at the grain boundaries of nickel particles during sintering. When there are trace amounts of incompletely oxidized Sn in the electrode, these nanoparticles at the grain boundaries can block the diffusion path of Sn along the grain boundaries to the dielectric layer, thereby inhibiting the generation of oxygen vacancies by Sn entering the BaTiO3 dielectric layer. In addition, ZrO2, TiO2 and BaTiO3 dielectric layers are chemically compatible and will not introduce additional impurities or interface defects. Moreover, their coefficients of thermal expansion are matched with those of nickel and ceramic dielectrics, and will not affect the co-firing process of MLCC.

[0036] The resin is selected from at least one of ethyl cellulose and acrylic resin, with a weight-average molecular weight between 50,000 and 200,000, to ensure smooth transfer of the slurry during roller printing and prevent cracking of the green layer after drying.

[0037] The solvent is selected from at least one of terpineol, diethylene glycol butyl ether acetate, and tributyl citrate, and is used to dissolve the resin, adjust the viscosity of the slurry, and control the drying rate to avoid the film layer cracking due to excessive solvent evaporation during the drying process.

[0038] The dispersant is selected from at least one of DISPERBYK-110, phosphate ester, polyethylene glycol, and polyvinylpyrrolidone. The ultrafine nickel powder and nanoparticles have a large specific surface area and are easy to agglomerate. The dispersant is adsorbed on the powder surface and separates the particles through steric hindrance, ensuring the dispersibility of the slurry.

[0039] The rheology modifier is selected from at least one of hydrogenated castor oil and polyamide wax. It is used to adjust the thixotropic properties of the paste. During printing, the shear rate is high, and the viscosity of the paste needs to be reduced to ensure smooth transfer. After transfer, the shear rate is low, and the viscosity needs to be restored to prevent sagging.

[0040] This invention also provides a method for preparing the above-mentioned ultrafine roller printing nickel paste, specifically including the following steps:

[0041] S1: Mix the auxiliary conductive phase, conductive phase, diffusion blocking phase with the first part of the dispersant and the first part of the solvent, and stir at 2000-3000 r / min for 30-60 min to prepare a pre-dispersed slurry;

[0042] S2: Transfer the pre-dispersed slurry to a sand mill and grind and disperse it using a gradient grinding process to obtain a powder slurry, controlling the slurry fineness to ≤5μm;

[0043] S3: Add the resin to the remaining solvent, then add the remaining dispersant, and stir at 60-80℃ until completely dissolved to prepare an organic carrier;

[0044] S4: Mix the organic carrier with the powder slurry, add the rheology modifier, and stir at 1500-2000 r / min for 1-2 hours until homogeneous;

[0045] S5: Degas the mixed slurry at -0.09MPa for 20-40 minutes, then filter it through a 5-10μm filter screen to obtain the finished nickel slurry.

[0046] It should be noted that in step S1, the first part of the dispersant accounts for 50%-70% of the total amount added, in order to prevent excessive dispersant from causing excessive foaming during the grinding process; the first part of the solvent accounts for 40%-60% of the total amount added, in order to prevent excessive viscosity from causing separation of the grinding media and the slurry.

[0047] The gradient grinding process described in step S2 specifically includes two stages: the first stage uses grinding media with a diameter of 0.5 mm to grind for 1-1.5 hours, using the impact force of the larger diameter grinding media to break up large agglomerates and achieve initial dispersion; the second stage uses grinding media with a diameter of 0.3 mm to grind for 1-1.5 hours, using the shear force of the smaller diameter grinding media to further refine the fineness of the slurry to below 5 μm, while allowing the dispersant to form a stable adsorption layer on the powder surface.

[0048] During the grinding process, the slurry temperature should always be controlled between 30-50℃. If the temperature is too low, the slurry viscosity will increase and the grinding efficiency will decrease. If the temperature is too high, the solvent will evaporate faster, the solid content of the slurry will increase, and it may cause the dispersant to decompose or the surface activity of the powder to increase, inducing secondary agglomeration.

[0049] The present invention also provides a method for applying the above-mentioned ultrafine roller-printed nickel paste in MLCC, comprising: coating the nickel paste onto a ceramic green body by roller printing process to form an inner electrode layer, and then performing debinding, sintering and re-oxidation treatment.

[0050] In the roller printing process, the roller printing speed is 10-30 m / min, the roller pressure is 0.2-0.5 MPa, and the drying temperature is 80-120℃.

[0051] The sintering is carried out in a reducing atmosphere, with the temperature controlled at 800-1000℃ and the holding time at 1-3h. The original atmosphere is preferably a mixture of nitrogen and hydrogen, wherein the hydrogen component is 1-5%.

[0052] The re-oxidation is carried out in a nitrogen atmosphere with an oxygen content of 10-100 ppm, a temperature of 800-1000℃, and a time of 1-4 hours. The purpose is to repair the oxygen vacancies generated in the dielectric layer during sintering. At the same time, in this invention, since the Ni3Sn coating structure does not easily form a SnO2 passivation layer, oxygen can fully penetrate into the electrode during the re-oxidation process, further oxidizing any trace amounts of Sn that may be present, thereby reducing the risk of Sn diffusing into the dielectric layer.

[0053] The present invention will be described in detail below with reference to specific embodiments. It should be noted that these embodiments are only used to explain the present invention and do not constitute any limitation on the scope of protection of the present invention. Those skilled in the art can make adaptive adjustments to the embodiments based on their understanding of the technical solutions of the present invention, and these adjustments still fall within the scope of protection of the present invention.

[0054] Example 1: This example provides an ultrafine roller printing nickel paste, which, by weight, includes 100 parts nickel powder, 25 parts Ni3Sn coated nickel powder, 1.0 part nano ZrO2, 8 parts ethyl cellulose, 65 parts terpineol, 1.5 parts DISPERBYK-110 and 0.6 parts hydrogenated castor oil.

[0055] The preparation steps of the Ni3Sn-coated nickel powder are as follows:

[0056] C1: Place the nickel powder in an 8% sodium hydroxide solution, adjust the pH to 10, activate it at 50°C for 45 minutes, and wash it with deionized water until the pH of the washing solution is 7.

[0057] C2: Weigh 20g of stannous chloride dihydrate, 20g of sodium citrate, and 10g of sodium hypophosphite, add them to 1L of deionized water to dissolve them, prepare a plating solution, and adjust the pH value to 8 with ammonia.

[0058] C3: Add the activated nickel powder to the plating solution at a solid-liquid ratio of 1:7, and stir at 300 r / min for 50 min at 70℃.

[0059] C4: After the reaction is complete, filter the solution, wash it three times with deionized water, and dry it under vacuum at 5°C and -0.09 MPa for 4 hours to obtain Ni3Sn coated nickel powder. X-ray diffraction analysis showed that the atomic ratio of Ni to Sn was approximately 2.9:1.

[0060] This embodiment also provides a method for preparing the ultrafine roller printing nickel paste, specifically including the following steps:

[0061] S1: Mix 100 parts of nickel powder, 25 parts of Ni3Sn-coated nickel powder, 1.0 part of nano ZrO2, 0.9 parts of DISPERBYK-110, and 32.5 parts of terpineol, and stir at 2500 r / min for 45 min to prepare a pre-dispersed slurry;

[0062] S2: Transfer the pre-dispersed slurry to a sand mill. In the first stage, grind with 0.5 mm diameter zirconia beads for 1 hour. In the second stage, grind with 0.3 mm diameter zirconia beads for 1.5 hours. The slurry temperature is controlled at 40℃. After grinding, use a scraper fineness gauge to check that the slurry fineness is 3 μm.

[0063] S3: Add 8 parts of ethyl cellulose resin to the remaining 32.5 parts of terpineol solvent, then add 0.6 parts of DISPERBYK-110, heat and stir at 70°C until completely dissolved to prepare an organic carrier;

[0064] S4: Mix the organic carrier with the powder slurry, add 0.6 parts of hydrogenated castor oil, and stir at 1800 r / min for 1.5 h until uniform;

[0065] S5: Degas the mixed slurry at -0.09MPa for 30 minutes, and then filter it through an 8μm filter screen to obtain the finished nickel slurry.

[0066] Example 2: This example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that the paste composition is adjusted, including 100 parts nickel powder, 15 parts Ni3Sn coated nickel powder, 0.5 parts nano ZrO2, 6 parts ethyl cellulose, 50 parts terpineol, 1.0 part DISPERBYK-110 and 0.3 parts hydrogenated castor oil.

[0067] Example 3: This example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that the paste composition is adjusted, including 100 parts nickel powder, 35 parts Ni3Sn coated nickel powder, 2.0 parts nano TiO2, 12 parts ethyl cellulose, 80 parts terpineol, 3.0 parts DISPERBYK-110 and 1.2 parts polyamide wax.

[0068] Example 4: This example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that in the preparation of Ni3Sn coated nickel powder, the activated nickel powder is added to the plating solution at a solid-liquid ratio of 1:13.

[0069] Example 5: This example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that nano ZrO2 is replaced with nano TiO2 particles of equal mass.

[0070] Comparative Example 1: This comparative example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that the Ni3Sn coated nickel powder is replaced with an equal mass of elemental Sn powder.

[0071] Comparative Example 2: This comparative example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that no diffusion blocking phase is added.

[0072] Comparative Example 3: This comparative example provides an ultrafine roller printing nickel paste and its preparation method, which differs from Example 1 in that no conductive phase is added.

[0073] Comparative Example 4: This comparative example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that no conductive phase and diffusion blocking phase are added.

[0074] Comparative Example 5: This comparative example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that in the preparation process of the paste, only 0.3 mm diameter zirconia beads are used for grinding for 3 hours.

[0075] Comparative Example 6: This comparative example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that, in the preparation process of Ni3Sn coated nickel powder, the activated nickel powder is added to the plating solution at a solid-liquid ratio of 1:20.

[0076] Comparative Example 7: This comparative example provides an ultrafine roller printing nickel paste and its preparation method. The difference from Example 1 is that the amount of nano ZrO2 added is increased to 3.5 parts.

[0077] To verify the technical effect of the nickel paste prepared in the above embodiments and comparative examples of the present invention, the performance of the nickel paste and corresponding MLCC samples prepared in Examples 1-5 and Comparative Examples 1-7 were tested to evaluate the actual effect of the technical solution of the present invention in solving the long-term reliability problem caused by Sn sealing.

[0078] Experimental Example 1: This example aims to observe the microstructure of the electrode layer inside MLCC using scanning electron microscopy, compare the differences in electrode continuity between Example 1 and Comparative Example 1, and verify the improvement effect of the technical solution of the present invention on electrode density.

[0079] The nickel paste prepared in Example 1 was applied to a ceramic green body using a roller printing process to form an inner electrode layer. The roller printing speed was set to 20 m / min, the roller pressure to 0.3 MPa, and the drying temperature to 100 °C. Then, the sample was subjected to debinding, sintering, and re-oxidation treatment. The sintering temperature was 850 °C and the holding time was 2 h. The oxygen content in the re-oxidation treatment was 50 ppm, the temperature was 900 °C, and the time was 2.5 h, resulting in an MLCC sample.

[0080] The nickel paste prepared in Comparative Example 1 was used to prepare MLCC samples using the same roller printing process parameters and sintering and re-oxidation conditions as in Example 1 to ensure the comparability of experimental conditions.

[0081] The MLCC samples prepared above were cut along the direction perpendicular to the electrode layer. After grinding and polishing, the microstructure of the inner electrode layer was observed using backscattered electron imaging mode of a field emission scanning electron microscope. The focus was on observing the continuity of the electrode layer and the distribution of pores. The results are shown in [Figure number missing]. Figure 1 and Figure 2 As shown.

[0082] Depend on Figure 1 and Figure 2 It can be seen that the MLCC inner electrode layer prepared in Example 1 is continuous and dense, the nickel particles are well sintered, a tight conductive network is formed between the particles, the electrode layer thickness is uniform, no obvious pores or cracks are observed, and the porosity inside the electrode is extremely low.

[0083] The MLCC inner electrode layer prepared in Comparative Example 1 exhibits discontinuity, with multiple large pores visible in the electrode layer, electrode fracture in some areas, incomplete sintering of nickel particles, and obvious gaps between particles.

[0084] Experimental Example 2: This embodiment aims to simulate the insulation resistance degradation behavior of MLCC during long-term service through high-temperature accelerated aging test, and verify the effect of the technical solution of the present invention on improving the long-term reliability of MLCC.

[0085] This experiment uses the nickel paste prepared in Examples 1, 4, and 5, as well as Comparative Examples 1-7, as the experimental objects. All samples were prepared using the same method as in Example 1 for MLCCs. The specific roller printing process parameters and sintering and re-oxidation conditions were the same as in Example 1.

[0086] The MLCC samples prepared above were placed in a 125℃ high-temperature test chamber, and a rated voltage of 10V was applied for a test duration of 1500h. The insulation resistance (IR) was tested at 100h intervals during the test, and the insulation resistance change rate (%) was calculated using the following formula:

[0087] ;

[0088] Where IR0 is the initial insulation resistance, IR t The insulation resistance is measured after t hours. Ten samples were tested in each group, and the arithmetic mean was taken. The results are shown in Table 1 below. Figure 3 As shown.

[0089] Table 1. High-temperature aging insulation resistance test results:

[0090] ;

[0091] According to Table 1 and Figure 3 The data shows that the insulation resistance of Example 1 decreased by 12.3% after 1500h aging, while that of Examples 4 and 5 was -14.8% and -14.0% respectively. In contrast, the decrease rate of Comparative Example 1 was as high as -43.8%, and the decrease rates of Comparative Examples 2-7 were between -29.5% and -39.0%.

[0092] Comparative Example 1 uses elemental Sn powder for direct mixing. The insulation resistance decreases rapidly and continuously. During the re-oxidation process, a SnO2 passivation layer is quickly formed on the Sn surface, preventing oxygen from diffusing inward, resulting in the internal Sn being sealed in a metallic state. During use, these metallic Sn continuously diffuse into the dielectric layer, generating oxygen vacancies and forming leakage current channels.

[0093] In Comparative Example 2, even though the Ni3Sn coating structure prevents the formation of the SnO2 passivation layer, local defects or trace amounts of incompletely oxidized Sn in the coating layer can still diffuse along the grain boundaries; in Comparative Example 5, the thermal effect and shear force generated by long-term grinding with a single small-particle abrasive medium can damage the Ni3Sn coating layer, leading to partial Sn exposure; in Comparative Example 6, an excessively high solid-liquid ratio leads to Sn in the plating solution... 2+ Insufficient concentration and uneven coating result in incomplete coating of some nickel powder surfaces, creating weak points.

[0094] Experimental Example 3: This embodiment aims to verify whether the technical solution of the present invention has a negative impact on the basic electrical performance of MLCC while solving the Sn sealing problem by testing the capacitance, loss tangent, breakdown voltage and electrode sheet resistance of the MLCC sample.

[0095] This experiment uses MLCC samples prepared in Examples 1, 4, and 5, as well as Comparative Examples 1-7, as experimental subjects. The preparation methods for each sample are the same as in Example 1.

[0096] The capacitance (C) and loss tangent (tanδ) were tested using an LCR meter. The test conditions were set to a frequency of 1kHz and a test voltage of 1V. The MLCC sample was placed in the test fixture, ensuring good contact between the electrodes and the fixture. The test environment temperature was 25±2℃ and the relative humidity was ≤50%. Ten parallel samples were set up for each group, and each sample was measured three times. The arithmetic mean was taken as the final test result of the sample.

[0097] The breakdown voltage (BDV) test is performed using a DC withstand voltage tester. The MLCC sample is placed in the test fixture, and the voltage is continuously increased at a rate of 100V / s from 0V as the starting voltage until the sample breaks down. The voltage value at the moment of breakdown is recorded. Ten parallel samples are set up for each group, and the arithmetic mean is taken as the breakdown voltage value of the sample.

[0098] Electrode sheet resistance was tested using a four-probe tester with a probe spacing of 1 mm and probe pressure controlled at 200 g ± 10 g. The MLCC sample was placed on the test stage, the dielectric layer was peeled off to expose the inner electrode layer surface, and the four probes were pressed vertically onto the electrode layer surface. Five different locations were selected for testing each sample, and the arithmetic mean was taken as the electrode sheet resistance value of that sample. The test results are shown in Table 2 below. Figure 4 As shown.

[0099] Table 2 Electrical performance test results:

[0100] ;

[0101] From Table 2 and Figure 4 It can be seen that the capacitance value of Example 1 is improved compared with pure nickel paste. The Ni3Sn phase in the Ni3Sn coated nickel powder has good fluidity during sintering and can fill the electrode pores to form a continuous and dense electrode layer. In Comparative Example 1, the elemental Sn is unevenly distributed and the SnO2 passivation layer affects the densification of the electrode, resulting in poor continuity and a lower capacitance value. The capacitance values ​​of Examples 4 and 5 are slightly lower but still better than those of Comparative Example 1, indicating that the fluctuation of coating process parameters does not have a decisive impact on the capacitance value.

[0102] The tanδ of Example 1 was 2.4%, the lowest among all samples, indicating that its electrode layer had the best density and the fewest interface defects. Its breakdown voltage was higher than that of Comparative Example 1 and Comparative Example 4. In Comparative Example 1, the continuous diffusion of metallic Sn into the dielectric layer generated oxygen vacancies, which reduced the insulation strength. In Example 1, the Ni3Sn coating structure allowed Sn to be fully oxidized, and the diffusion barrier phase blocked the diffusion of residual Sn. The oxygen vacancy concentration in the dielectric layer was low, and the breakdown voltage of Comparative Example 7 dropped to 95V, which verified that an excessive amount of diffusion barrier phase would introduce interface defects.

[0103] The sheet resistance of the electrode in Example 1 is lower than that in Comparative Example 5, indicating that the gradient grinding process helps to reduce resistance by protecting the integrity of the coating layer and making the Ni3Sn phase more uniformly distributed. The sheet resistance of Comparative Example 7 is the highest, indicating that excessive diffusion barrier phase will have a negative impact on conductivity.

[0104] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. An ultra-fine roll printed nickel paste for extreme high capacitance MLCC, characterized in that, The product comprises, by weight, the following components: 100 parts nickel powder, 15-35 parts Ni3Sn-coated nickel powder, 0.5-2.0 parts diffusion barrier phase, 6-12 parts resin, 50-80 parts solvent, 1.0-3.0 parts dispersant, and 0.3-1.2 parts rheology modifier. The Ni3Sn-coated nickel powder is a core-shell structured particle formed by coating a Ni3Sn layer onto the surface of nickel powder. The atomic ratio of Ni to Sn in the coating layer is 2.8:1-3.2:

1. The diffusion barrier phase is selected from at least one of nano-ZrO2 particles and nano-TiO2 particles.

2. The ultra-fine roll-on nickel paste as claimed in claim 1, wherein: The resin is selected from at least one of ethyl cellulose and acrylic resin.

3. The ultra-fine roll-on nickel paste as claimed in claim 1, wherein: The solvent is selected from at least one of terpineol, diethylene glycol butyl ether acetate, and tributyl citrate.

4. The ultra-fine roll-on nickel paste of claim 1, wherein: The dispersant is selected from at least one of DISPERBYK-110, phosphate ester, polyethylene glycol, and polyvinylpyrrolidone.

5. The ultra-fine roll-on nickel paste of claim 1, wherein: The rheology modifier is selected from at least one of hydrogenated castor oil and polyamide wax.

6. A method for preparing ultrafine roller printing nickel paste as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Nickel powder, Ni3Sn-coated nickel powder, diffusion barrier phase, first part of dispersant, and first part of solvent are mixed and stirred to prepare a pre-dispersed slurry; S2: Transfer the pre-dispersed slurry to a sand mill and grind and disperse it using a gradient grinding process to control the slurry fineness to ≤5μm; S3: Add the resin to the second part of the solvent, then add the second part of the dispersant, heat and stir until completely dissolved to form an organic carrier. The second part of the solvent is the remaining part after removing the first part of the solvent from the total amount of solvent, and the second part of the dispersant is the remaining part after removing the first part of the dispersant from the total amount of dispersant. S4: Mix the organic carrier with the ground powder slurry, add the rheology modifier, and stir at high speed until uniform; S5: After vacuum degassing the mixed slurry, filter it to obtain the finished nickel slurry.

7. The method of preparing ultrafine roll-on nickel paste as claimed in claim 6 wherein: In S1, the first part of the dispersant accounts for 50%-70% of the total dispersant, and the first part of the solvent accounts for 40%-60% of the total solvent.

8. The method of preparing ultrafine roll-on nickel paste as claimed in claim 6 wherein: In S2, the gradient grinding process includes a first-stage grinding and a second-stage grinding. The first stage uses a grinding media with a diameter of 0.5 mm for 1-1.5 hours, and the second stage uses a grinding media with a diameter of 0.3 mm for 1-1.5 hours.

9. The method of preparing ultrafine roll-on nickel paste as claimed in claim 8 wherein: The slurry temperature is controlled at 30-50℃ during the gradient grinding process.

10. A method of using the ultra-fine roll printed nickel paste as claimed in any one of claims 1 to 5 in MLCC, characterized in that, include: The nickel paste is applied to the ceramic green body using a roller printing process to form an inner electrode layer, followed by debinding, sintering, and re-oxidation treatment.

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