A method for regulating sintering shrinkage of MLCC electrode nickel paste matched with BaTiO3 ceramic medium

Abstract

The present application relates to the technical field of capacitor manufacturing, and discloses a kind of MLCC electrode nickel paste sintering shrinkage and BaTiO3 ceramic medium matching regulation and control method, comprising the following steps: S1: the conductive ceramic shrinkage inhibitor powder, dispersing agent and organic carrier are ball milled to obtain pre-dispersion, the conductive ceramic is selected from at least one of titanium nitride, titanium carbide, calcium copper titanate, lanthanum titanate or lanthanum strontium manganese oxide;S2: nickel powder is heat treated in H2 / N2 mixed atmosphere to obtain surface-activated nickel powder;S3: pre-dispersion, surface-activated nickel powder, dispersing agent, organic carrier and additives are mixed to form paste;S4: grinding dispersion to fineness≤5 μm.The present application replaces insulating oxide with conductive ceramic, combines nickel powder activation and contains heat preservation platform's step temperature rise, constructs conductive rigid skeleton, realizes shrinkage matching, gives consideration to electrode conductivity and interface bonding force, solves the problem that shrinkage matching and conductive performance are difficult to give consideration to.

Description

Technical Field

[0001] This invention relates to the field of multilayer ceramic capacitor (MLCC) manufacturing technology, and in particular to a method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with BaTiO3 ceramic dielectric. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are the most widely used passive components in electronic devices. The mainstream material for their internal electrodes is nickel paste. During the co-firing process of MLCCs, the matching of the nickel electrode and the BaTiO3 ceramic dielectric layer in terms of sintering shrinkage behavior is the key to determining the product yield and reliability. The difference in shrinkage behavior between the two will generate huge thermal stress at the interface. This can cause the electrode to separate from the dielectric layer and microcracks, or even cause the electrode to break and the dielectric layer to crack, directly leading to capacitor failure. As MLCCs develop towards ultra-thin dielectric layers, the requirements for electrode shrinkage matching accuracy are further increasing, and existing technologies are no longer able to meet the needs of high-end products.

[0003] In the prior art, to achieve shrinkage matching, high-melting-point inert materials (such as oxides like MgO, Al2O3, and ZrO2) are usually added to the nickel paste as shrinkage inhibitors. These materials, due to their non-shrinkage properties, form a physical barrier to inhibit the densification shrinkage of the nickel powder. For example, Chinese Patent CN102222564B discloses an MLCC capacitor based on balancing the shrinkage rates of the inner electrode paste and the ceramic film, which regulates shrinkage behavior by adding a shrinkage inhibitor to the nickel paste. Chinese Patent CN105977022A also discloses a nanoscale nickel metal electrode paste for multilayer ceramic capacitors, in which MgCO3 nanopowder is added as a shrinkage inhibitor.

[0004] However, the above-mentioned technical solution of adding insulating oxide resistance agents has certain drawbacks: these insulating oxides remain inside the electrode as insulating phases, which hinders the conductive path, causing the sheet resistance of the electrode to increase sharply, the equivalent series resistance (ESR) to increase, and the heat generation to be severe, which limits the application of MLCC in high frequency and high current fields. Especially in ultra-thin dielectric layer (<1μm) and high capacity MLCC, the electrode layer thickness is only a few hundred nanometers. The introduction of insulating oxide particles will seriously damage the continuity of the electrode, resulting in a significant reduction in the effective conductive cross-sectional area, and the resistivity can even increase to 2 to 3 times that of pure nickel electrodes.

[0005] Therefore, how to effectively control the sintering shrinkage rate of nickel paste to match the BaTiO3 ceramic medium while avoiding the deterioration of electrode conductivity is a technical problem that urgently needs to be solved in this field, and it is also one of the key bottlenecks restricting the development of high-end MLCCs. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that although the existing technology can achieve sintering shrinkage matching between nickel electrode and BaTiO3 ceramic medium by adding insulating oxide shrinkage inhibitor to nickel paste, this scheme will cause the insulating phase to remain inside the electrode, which will cause the sheet resistance of the electrode to increase sharply and cannot take into account both shrinkage matching and conductivity. Therefore, we propose a method for controlling the sintering shrinkage of nickel paste and matching of BaTiO3 ceramic medium in MLCC electrode.

[0007] To achieve the above objectives, this application adopts the following technical solution: a method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic medium, characterized by comprising the following steps:

[0008] S1: The conductive ceramic shrinkage inhibitor powder, dispersant and organic carrier are mixed and then ball-milled to obtain a conductive ceramic pre-dispersion. The conductive ceramic shrinkage inhibitor is selected from at least one of titanium nitride, titanium carbide, calcium copper titanate, lanthanum titanate or lanthanum strontium manganese oxide.

[0009] S2: Heat-treat nickel powder in a mixed atmosphere of H2 and N2 to obtain surface-activated nickel powder;

[0010] S3: Mix the conductive ceramic pre-dispersion obtained in step S1, the surface-activated nickel powder obtained in step S2, the dispersant, the organic carrier and the additives to form a paste;

[0011] S4: Grind and disperse the paste obtained in step S3, controlling the fineness to ≤5μm;

[0012] S5: The nickel paste obtained in step S4 is coated onto the BaTiO3 ceramic green body, and co-fired in a stepwise heating process under a protective atmosphere. The heating process is as follows: first, the temperature is raised to 400℃ through a low-temperature debinding stage, then the temperature is slowly raised to 500℃ at a rate of 1-2℃ / min and held for 30-60 minutes, then the temperature is slowly raised to 650℃ at a rate of 1-2℃ / min, and finally the temperature is rapidly raised to the sintering peak temperature and held, and then cooled naturally.

[0013] The heating rate from 650℃ to the peak sintering temperature is 5-8℃ / min, the peak sintering temperature is 880-920℃, and the peak holding time is 15-30 minutes.

[0014] Preferably, the amount of conductive ceramic damping agent added in step S1 is 3% to 20% of the mass of nickel powder.

[0015] Preferably, the amount of conductive ceramic damping agent added in step S1 is 5% to 12% of the mass of nickel powder.

[0016] Preferably, the heat treatment temperature in step S2 is 350–500°C, the holding time is 30–120 minutes, and the H2 volume fraction is 3%–8%.

[0017] Preferably, the low-temperature debinding stage in step S5 includes: heating from room temperature to 200°C at a heating rate of 3-5°C / min; and heating from 200°C to 400°C at a heating rate of 2-4°C / min.

[0018] Preferably, the 500°C heat preservation time in step S5 is 45 to 60 minutes.

[0019] Preferably, the heating rate from 650°C to the sintering peak temperature in step S5 is 6–8°C / min.

[0020] A nickel paste for MLCC electrodes, employing a method for controlling the sintering shrinkage of the MLCC electrode nickel paste to match the BaTiO3 ceramic medium.

[0021] An application of a control method in the preparation of multilayer ceramic capacitors involves preparing nickel paste using the control method and then applying it onto a BaTiO3 ceramic green body via screen printing or casting to form an electrode pattern. After co-firing, the inner electrode is formed.

[0022] The technical effects and advantages of this invention are as follows: By using conductive ceramics instead of traditional insulating oxides as shrinkage inhibitors, and combining the synergistic effects of nickel powder surface activation treatment, conductive ceramic pre-dispersion process, and stepped heating curve with insulation platform, a conductive rigid skeleton-nickel powder composite electrode structure was successfully constructed. During co-firing, the conductive ceramic skeleton effectively inhibits excessive shrinkage of nickel powder, enabling precise matching of the sintering shrinkage behavior of the nickel electrode and the BaTiO3 ceramic medium. At the same time, the high conductivity of the conductive ceramic itself provides a bridge for electron transport, maintaining excellent conductivity of the electrode. Furthermore, the anchoring effect formed by the conductive ceramic particles at the interface significantly enhances the bonding strength between the electrode and the medium. Thus, this invention fundamentally solves the technical problem of severe degradation of electrode conductivity caused by adding insulating shrinkage inhibitors to achieve shrinkage matching in existing technologies, achieving synergistic optimization of shrinkage matching and conductivity. Attached Figure Description

[0023] 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:

[0024] Figure 1 This is a schematic diagram of the stepped heating curve in step five of the present invention;

[0025] Figure 2 This is a comparison chart of the sintering shrinkage rate of the nickel electrode and the shrinkage rate of the BaTiO3 dielectric, as well as the sheet resistance of the electrode, in the embodiments and comparative examples of the present invention.

[0026] Figure 3This is a SEM cross-sectional view of the electrode and dielectric interface after sintering in Embodiment 1 of the present invention;

[0027] Figure 4 This is a SEM cross-sectional view of the electrode and dielectric interface after sintering in Comparative Example 2 of the present invention. Detailed Implementation

[0028] 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.

[0029] Raw materials and reagents:

[0030] All raw materials used in this specific embodiment are commercially available or prepared according to conventional methods in the art, as detailed below:

[0031] The nickel powder used is spherical, with an average particle size D50 of 300nm, a specific surface area of ​​2.8m² / g, and a purity of ≥99.9%.

[0032] The conductive ceramic TiN has an average particle size D50 of 80 nm, a specific surface area of ​​9.2 m² / g, and a purity of ≥99.5%.

[0033] The conductive ceramic TiC has an average particle size D50 of 100 nm, a specific surface area of ​​7.0 m² / g, and a purity of ≥99.5%.

[0034] The conductive ceramic LaTiO3 was prepared according to the method described in Example 2 below, with an average particle size D50 of 120 nm and a specific surface area of ​​6.5 m² / g.

[0035] Conductive ceramic CaCu3Ti4O 12 The sample was prepared according to the method described in Example 3 below, with an average particle size D50 of 150 nm and a specific surface area of ​​5.8 m² / g.

[0036] Conductive ceramics La 0·7 Sr 0·3 MnO3 was prepared according to the method described in Example 4 below, with an average particle size D50 of 110 nm and a specific surface area of ​​7.2 m² / g.

[0037] Insulating oxide MgO with an average particle size D50 of 80 nm and a purity ≥99.0%.

[0038] The insulating oxide Al2O3 has an average particle size D50 of 100 nm and a purity of ≥99.5%.

[0039] Terpineol, electronic grade, purity ≥99.0%.

[0040] Ethyl cellulose, viscosity 100-200 mPa·s, ethoxy content 48%-49.5%.

[0041] The dispersant selected is a polyester-type polymeric dispersant, model DISPERBYK-2150, with a molecular weight of approximately 3000 and an acid value of <3mgKOH / g; or a polyether-type polymeric dispersant, model DISPERBYK-110, with a molecular weight of approximately 4000 and an acid value of <5mgKOH / g.

[0042] The additive used is a leveling agent, model BYK-358.

[0043] BaTiO3 ceramic powder with an average particle size D50 of 200 nm, tetragonal phase, and c / a > 1.009.

[0044] It should be noted that those skilled in the art can add a small amount of co-solvent such as diethylene glycol butyl ether acetate to the organic carrier to adjust the evaporation rate according to actual needs. The above-mentioned conventional adjustments do not depart from the protection scope of this invention.

[0045] Preparation Example 1: Preparation of Organic Carriers

[0046] Add 800g of terpineol and 200g of ethyl cellulose to a three-necked flask equipped with a stirrer.

[0047] Heat the three-necked flask in an 80°C water bath, turn on the stirrer, and stir continuously at 300 rpm for 2 hours until the ethyl cellulose is completely dissolved, forming a transparent and homogeneous solution.

[0048] Cool the solution to room temperature, filter it through a 200-mesh filter to remove undissolved particles, and obtain the organic carrier. Seal and store for later use.

[0049] Preparation Example 2: Preparation of LaTiO3 Conductive Ceramics

[0050] Take 51.8 g (0.15 mol) of lanthanum nitrate (La(NO3)3・6H2O) and 34.0 g (0.15 mol) of tetrabutyl titanate (Ti(OC4H9)4), and dissolve them in 200 mL of anhydrous ethanol to obtain lanthanum nitrate solution and tetrabutyl titanate solution, respectively.

[0051] Under stirring conditions, tetrabutyl titanate solution was slowly added dropwise to lanthanum nitrate solution. During the addition process, 10 mL of glacial acetic acid was added as a hydrolysis inhibitor. After the addition was completed, stirring was continued for 30 minutes.

[0052] The mixed solution was transferred to a water bath and heated and stirred at 60°C for 2 hours to form a sol.

[0053] The sol was transferred to an evaporating dish and dried in an 80°C drying oven for 24 hours to obtain a dry gel.

[0054] The dry gel was ground into a fine powder in an agate mortar and placed in a muffle furnace. The temperature was increased to 800°C at a rate of 5°C / min, held for 2 hours, and then naturally cooled to room temperature to obtain LaTiO3 powder.

[0055] The obtained powder was placed in a planetary ball mill and ball-milled at 300 r / min for 4 hours to obtain LaTiO3 powder with an average particle size D50=120 nm.

[0056] Preparation Example 3: CaCu3Ti4O 12 Preparation of conductive ceramics

[0057] Take 16.4g (0.1mol) calcium carbonate (CaCO3), 63.8g (0.3mol) copper oxide (CuO) and 63.8g (0.4mol) titanium dioxide (TiO2), add anhydrous ethanol as the dispersion medium, place in a planetary ball mill, and ball mill at 400r / min for 8 hours.

[0058] The ball-milled mixture was transferred to an evaporating dish and dried in an 80°C drying oven for 12 hours to remove ethanol.

[0059] The dried mixed powder was placed in a muffle furnace and heated to 1000°C at a heating rate of 5°C / min for 5 hours, then allowed to cool naturally.

[0060] The pre-calcined powder was placed back into the ball mill and ball-milled at 400 r / min for 4 hours, then dried and passed through a 200-mesh sieve.

[0061] The sieved powder was placed in a muffle furnace and heated to 1100℃ at a heating rate of 5℃ / min, sintered for 10 hours, and then naturally cooled to obtain CaCu3Ti4O. 12 Powder.

[0062] The obtained powder was ball-milled to an average particle size of D50 = 150 nm.

[0063] Preparation Example 4: La 0·7 Sr 0·3 Preparation of MnO3 conductive ceramics

[0064] Take 30.3 g (0.07 mol) lanthanum nitrate (La(NO3)3・6H2O), 4.2 g (0.03 mol) strontium nitrate (Sr(NO3)2) and 36.0 g (0.1 mol) manganese nitrate (Mn(NO3)2・4H2O), dissolve them in 500 mL of deionized water, and stir until completely dissolved to obtain a mixed salt solution.

[0065] Prepare a 2 mol / L sodium hydroxide solution and slowly add it dropwise to the mixed salt solution under stirring. Adjust the pH of the solution to 10 to form a precipitate.

[0066] Filter the precipitate, wash it three times with deionized water, then wash it once with anhydrous ethanol, and place the washed precipitate in an 80℃ drying oven to dry for 24 hours.

[0067] The dried material was ground into a fine powder in an agate mortar, placed in a muffle furnace, heated to 900°C at a heating rate of 5°C / min, held at that temperature for 5 hours, and then allowed to cool naturally to obtain La. 0·7 Sr 0·3 MnO3 powder.

[0068] The obtained powder was ball-milled to an average particle size of D50 = 110 nm.

[0069] This invention provides a method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic medium. The core of this method is to use a conductive ceramic shrinkage inhibitor to replace the traditional insulating oxide and to achieve precise control of shrinkage behavior through a stepped heating curve. The method includes five main steps: pre-dispersion treatment of the conductive ceramic shrinkage inhibitor, surface activation treatment of nickel powder, mixing and preparation of slurry, grinding, dispersion and fineness control, and sintering shrinkage control. The following provides a detailed description of each step and the embodiments.

[0070] Step 1: Pre-dispersion treatment of conductive ceramic shock absorber

[0071] The purpose of this step is to fully deagglomerate and uniformly disperse the nanoscale conductive ceramics in the organic carrier, ensuring that they form a continuous three-dimensional conductive network in the subsequent electrodes.

[0072] In specific operation, the conductive ceramic shrinkage inhibitor powder, dispersant and organic carrier are mixed in a mass ratio of (5-20):(0.5-2):(10-30), and pre-dispersed using a planetary ball mill. The grinding media is zirconia balls (0.5-3 mm in diameter), the ball-to-material ratio is (2-4):1, the rotation speed is 200-400 r / min, and the ball milling time is 3-6 hours.

[0073] After ball milling, samples were taken for testing until the average particle size D90 ≤ 0.5 μm, thus obtaining a conductive ceramic pre-dispersion. The conductive ceramic inhibitor was selected from titanium nitride (TiN), titanium carbide (TiC), and calcium copper titanate (CaCu3Ti4O). 12 ), lanthanum titanate (LaTiO3) or lanthanum strontium manganese oxide (La 0·7 Sr 0·3 The MnO3 is at least one of the following, with an average particle size D50 of 20-150 nm and a specific surface area of ​​5-15 m² / g.

[0074] It should be noted that nanoscale conductive ceramics have a large specific surface area (5-15 m² / g) and high surface energy, making them extremely prone to agglomeration. If directly mixed with nickel powder, the agglomerated conductive ceramic particles cannot form a uniform rigid framework and instead become stress concentration points or defect sources. Through the synergistic effect of high-energy ball milling and dispersants, the conductive ceramics are fully deagglomerated and stably dispersed in the organic carrier, ensuring uniform distribution in the electrode. If the ball milling time is insufficient (<3 hours), the conductive ceramic particles are not sufficiently dispersed and are prone to forming agglomerates in the electrode, resulting in an uneven rigid framework. If the ball milling time is too long (>6 hours), zirconia grinding ball impurities may be introduced, leading to an abnormal increase in the particle size of the conductive ceramics and destroying the dispersion stability. The dispersant selected is a weakly anchored polyester polymer to avoid strong adsorption interfering with particle rearrangement and interfacial bonding during the subsequent sintering process.

[0075] Step 2: Surface activation treatment of nickel powder

[0076] The purpose of this step is to remove the natural oxide layer on the surface of nickel powder, obtain a clean metal surface, and make the sintering densification behavior of nickel powder predictable and controllable.

[0077] In the specific operation, nickel powder is placed in a tube furnace, and a mixture of H2 / N2 gas (H2 volume fraction 3% to 8%) is introduced. The temperature is increased to 350 to 500°C at a rate of 3 to 6°C / min, held for 30 to 120 minutes, and then cooled naturally to obtain surface-activated nickel powder.

[0078] It should be noted that a NiO oxide layer (approximately 2-5 nm thick) naturally forms on the surface of nickel powder during storage and transportation. This oxide layer reduces the sintering activity of the nickel powder, leading to unstable shrinkage behavior. Furthermore, the thickness of the oxide layer varies depending on storage conditions, causing batch-to-batch fluctuations in shrinkage rate. Through heat treatment in a reducing atmosphere, NiO is reduced to metallic Ni, resulting in a clean metal surface. This makes the sintering densification behavior of the nickel powder predictable and controllable. If the treatment temperature is too low (<350℃), the oxide layer will not be completely removed. If the temperature is too high (>500℃), pre-sintering may occur between nickel powder particles, increasing the particle size, reducing the printability of the paste, and exacerbating shrinkage rate fluctuations. After this treatment, the batch-to-batch standard deviation of the sintering shrinkage rate of nickel powder can be reduced from ±0.8% to ±0.2%.

[0079] Step 3: Mixing and preparing the slurry

[0080] The purpose of this step is to thoroughly mix the conductive ceramic pre-dispersion, activated nickel powder, dispersant, organic carrier, and additives to form a uniform paste.

[0081] In specific operation, the conductive ceramic pre-dispersion obtained in step one, the surface-activated nickel powder obtained in step two, the dispersant, the organic carrier, and the additives are mixed in a mass ratio of (15-35):(60-80):(0.5-2):(10-25):(0-2). Pre-mixing is performed using a planetary mixer at a revolution speed of 20-30 r / min and a rotation speed of 400-600 r / min for 0.5-1.5 hours to form a uniform paste. The organic carrier is composed of a solvent and resin. The resin composition includes a solvent selected from one or more of terpineol, diethylene glycol butyl ether acetate, and dibutyl phthalate; a resin selected from one or more of ethyl cellulose, polyvinyl butyral, and acrylic resin; and a solvent-to-resin mass ratio of (70-85):(15-30). The dispersant is a polyester-type, polyether-type, or polyurethane-type polymeric dispersant with a molecular weight of 1500-8000 and an acid value <5 mgKOH / g. The additives are selected from at least one of leveling agents, defoamers, and coupling agents.

[0082] It should be noted that the purpose of adding the dispersant and organic carrier in stages is to optimize the wetting process. First, a portion of the organic carrier is mixed with the conductive ceramic pre-dispersion, and its low viscosity is used to fully wet the surface of the nickel powder. The remaining organic carrier is then added to adjust the overall rheology. The combined revolution and rotation of the planetary mixer generates strong shear and stretching effects, ensuring that each component is evenly distributed. The amount of conductive ceramic added is a key parameter for controlling the shrinkage rate. If the amount added is too low, the shrinkage inhibition effect is insufficient (the shrinkage rate is too high). If the amount added is too high, the shrinkage is excessively inhibited (the shrinkage rate is too low) and the sheet resistance increases. This invention determines through boundary experiments that the amount of conductive ceramic added is 3% to 20% of the mass of nickel powder, preferably 5% to 12%.

[0083] Step 4: Grinding, Dispersion, and Fineness Control

[0084] The purpose of this step is to fully open up the agglomerates in the paste through three-roll milling, control the fineness of the paste, and ensure the clarity and continuity of the electrode pattern during printing.

[0085] In specific operation, the paste obtained in step three is transferred to a three-roll mill for grinding and dispersion, and three grinding passes are performed in sequence: the first pass has a roller gap of 40-60μm and is ground once; the second pass has a roller gap of 20-40μm and is ground once; the third pass has a roller gap of 10-20μm and is ground twice. After each grinding pass, a sample is taken to test the fineness until the final fineness is ≤5μm.

[0086] It should be noted that the three-roll mill uses the high shear force generated by the rollers at different speeds to break up the agglomerates. The design of gradually decreasing roller spacing ensures that the large-particle nickel powder (300nm) is not excessively broken, while also fully dispersing any small agglomerates that may remain in the conductive ceramic pre-dispersion. The fineness is controlled to below 5μm, ensuring the clarity and continuity of the electrode pattern during subsequent printing.

[0087] Step 5: Sintering Shrinkage Control

[0088] The purpose of this step is to use a stepped heating curve to allow the rigid framework of the conductive ceramic to form a stable structure before the nickel powder begins to densify rapidly, thereby constraining the shrinkage behavior of the nickel powder and achieving matching with the BaTiO3 ceramic medium.

[0089] In practice, the nickel paste obtained in step four is applied to the BaTiO3 ceramic green body by screen printing or casting to form an electrode pattern. The green body is then placed in a sintering furnace and co-fired under a protective atmosphere (N2, oxygen content ≤10ppm). A stepped temperature rise curve is used for co-firing.

[0090] The first stage involves heating from room temperature to 200°C at a rate of 3–5°C / min. This stage primarily removes low-boiling-point solvents.

[0091] The second stage: heating from 200℃ to 400℃ at a rate of 2-4℃ / min. During this stage, the organic carrier begins to thermally decompose, and the heating rate needs to be controlled to avoid foaming.

[0092] The third stage: raise the temperature from 400℃ to 500℃ at a rate of 1-2℃ / min, and hold at 500℃ for 30-60 minutes.

[0093] Fourth stage: Increase the temperature from 500℃ to 650℃ at a rate of 1-2℃ / min.

[0094] Fifth stage: Increase the temperature from 650℃ to 880-920℃ at a rate of 5-8℃ / min, and hold for 15-30 minutes.

[0095] Finally, it cools naturally.

[0096] It should be noted that the sintering initiation temperature of conductive ceramics (such as TiN) is as high as 1200℃ or more, and they hardly shrink at the sintering temperature of MLCCs (≤950℃). Nickel powder, on the other hand, begins to densify rapidly in the 500–700℃ range. Therefore, the third-stage holding plateau and the fourth-stage slow heating together ensure that a stable three-dimensional network of conductive ceramic framework is formed before the nickel powder begins to densify rapidly. The design of the holding plateau (500℃ for 30–60 minutes) provides sufficient time for initial contact between conductive ceramic particles and framework formation. If the time is insufficient (<30 minutes), the skeleton will not be fully established, and the constraint effect will be weakened. If the holding time is too long (>60 minutes), the effect will not be significantly improved, and energy consumption may be increased. The slow heating in the fourth stage (1~2℃ / min) ensures that the skeleton continues to play a constraint role during the shrinkage of the nickel powder. If the heating rate is too fast (>2℃ / min), the nickel powder will densify rapidly, and the skeleton will not have enough time to fully constrain it, resulting in a high shrinkage rate. The heating rate in the fifth stage is adjusted to 5~8℃ / min, which can ensure rapid densification of the ceramic medium and avoid cracking of the green body due to excessive heating.

[0097] A schematic diagram of the above-mentioned step-like temperature rise curve is shown below. Figure 1 As shown.

[0098] from Figure 1 As can be seen, the heating curve of the present invention includes a clear holding plateau (holding at 500℃ for 45 minutes) and a slow heating section (heating rate of 1.5℃ / min in the range of 400 to 650℃), which ensures that the conductive ceramic skeleton has sufficient time to establish a stable structure before the nickel powder begins to rapidly densify, thereby effectively constraining the shrinkage behavior of the nickel powder.

[0099] The above method will be described in detail below through specific embodiments, wherein Embodiment 1 is a preferred embodiment.

[0100] Example 1: In this example, MLCC electrode nickel paste was prepared according to the control method provided by the present invention. The conductive ceramic damping agent was TiN, with an addition amount of 10 parts (approximately 14.3% of the nickel powder mass). The holding time was 45 minutes. The specific steps are as follows:

[0101] Step 1: Pre-dispersion treatment of conductive ceramic shock absorber

[0102] Weigh 10g of TiN powder, 1g of dispersant (DISPERBYK-2150), and 15g of the organic carrier prepared in Preparation Example 1. Add them to a planetary ball mill jar, add 78g of zirconia balls with a diameter of 2mm (ball-to-material ratio 3:1), set the ball mill speed to 300r / min, and the ball milling time to 4 hours. After the ball milling is completed, take a sample and test it with a laser particle size analyzer. The average particle size D90 of the obtained pre-dispersion is 0.42μm. Set aside for later use.

[0103] Step 2: Surface activation treatment of nickel powder

[0104] Weigh 100g of nickel powder and place it in a tube furnace. Introduce a mixture of H2 / N2 gas (H2 volume fraction 5%) at a flow rate of 200mL / min. Heat the mixture to 400℃ at a heating rate of 5℃ / min and hold for 60 minutes. Allow it to cool naturally to room temperature. Remove the activated nickel powder and seal it for later use.

[0105] Step 3: Mixing and preparing the slurry

[0106] Weigh out 25g of the above TiN predispersant (containing about 10g of TiN), 70g of activated nickel powder, 1.5g of dispersant (DISPERBYK-2150), 18g of the organic carrier prepared in Preparation Example 1, and 0.5g of additive (BYK-358) according to the mass ratio. Add them sequentially to the hopper of a planetary mixer. Set the revolution speed to 25r / min and the rotation speed to 500r / min. Stir for 1 hour to form a uniform paste.

[0107] Step 4: Grinding, Dispersion, and Fineness Control

[0108] The above paste was transferred to a three-roll mill and milled in three passes: the first pass had a roller gap of 50 μm and was milled once; the second pass had a roller gap of 30 μm and was milled once; and the third pass had a roller gap of 15 μm and was milled twice. After the third pass, a sample was taken and measured with a scraper fineness gauge. The fineness was 4.5 μm, which meets the requirement of ≤5 μm.

[0109] Step 5: Sintering Shrinkage Control

[0110] The aforementioned nickel paste was applied to the BaTiO3 ceramic green body via screen printing (400 mesh, 30N tension) to form an electrode pattern. The coated green body was then placed in a sintering furnace and co-fired under a N2 protective atmosphere, with the oxygen content controlled at ≤8ppm. A stepped temperature rise curve was used for co-firing.

[0111] First stage: Increase the temperature from room temperature to 200℃ at a rate of 4℃ / min.

[0112] Second stage: Increase the temperature from 200℃ to 400℃ at a rate of 3℃ / min.

[0113] The third stage: the temperature is increased from 400℃ to 500℃ at a rate of 1.5℃ / min, and then held at 500℃ for 45 minutes.

[0114] Fourth stage: Increase the temperature from 500℃ to 650℃ at a rate of 1.5℃ / min.

[0115] Fifth stage: Increase the temperature from 650℃ to 900℃ at a rate of 8℃ / min (those skilled in the art can adjust the rate within the range of 5 to 8℃ / min according to the equipment conditions), and hold at 900℃ for 20 minutes.

[0116] Finally, it cools naturally in the furnace, completing the co-firing process.

[0117] Example 2: The difference between this example and Example 1 is that the conductive ceramic damping agent in step one is replaced by an equal amount of TiC instead of TiN, while the rest of the steps are the same as in Example 1.

[0118] Example 3: The difference between this example and Example 1 is that the conductive ceramic damping agent in step one is replaced by an equal amount of LaTiO3 (prepared in Example 2), while the other steps are the same as in Example 1.

[0119] Example 4: The difference between this example and Example 1 is that the conductive ceramic damping agent in step one is replaced by an equal amount of conductive ceramic CaCu3Ti4O. 12 (Prepared in Example 3), the remaining steps are the same as in Example 1.

[0120] Example 5: The difference between this example and Example 1 is that the conductive ceramic damping agent in step one is replaced by an equal amount of La instead of TiN. 0·7 Sr 0·3 MnO3, the remaining steps are the same as in Example 1.

[0121] Example 6: The difference between this example and Example 1 is that the amount of TiN pre-dispersion added in step one is adjusted to 18g, the amount of activated nickel powder in step three is adjusted to 77g, and the amount of organic carrier is adjusted to 20g. The remaining steps are the same as in Example 1.

[0122] Example 7: The difference between this example and Example 1 is that the amount of TiN pre-dispersion added in step one is adjusted to 35g, the amount of activated nickel powder in step three is adjusted to 63g, and the amount of organic carrier is adjusted to 16g. The remaining steps are the same as in Example 1.

[0123] Example 8: The difference between this example and Example 1 is that in step five, the holding time at 500°C is adjusted to 30 minutes, while the other steps are the same as in Example 1.

[0124] Example 9: The difference between this example and Example 1 is that the holding time at 500°C in step five is adjusted to 60 minutes, while the other steps are the same as in Example 1.

[0125] Comparative Example 1: The difference between this comparative example and Example 1 is that step one is omitted, no shrinkage inhibitor is added, and step three is prepared directly using 70g of activated nickel powder obtained in step two, 1.5g of dispersant (DISPERBYK-2150), 25g of organic carrier obtained in Preparation Example 1, and 0.5g of additive (BYK-358). The remaining steps are the same as in Example 1.

[0126] Comparative Example 2: The difference between this comparative example and Example 1 is that TiN in step one is replaced with an equal amount of MgO, while the remaining steps are the same as in Example 1.

[0127] Comparative Example 3: The difference between this comparative example and Example 1 is that TiN in step one is replaced with an equal amount of Al2O3, and the remaining steps are the same as in Example 1.

[0128] Comparative Example 4: The difference between this comparative example and Example 1 is that the amount of TiN pre-dispersion added in step one is adjusted to 10g, the amount of activated nickel powder in step three is adjusted to 76g, and the amount of organic carrier is adjusted to 23g. The remaining steps are the same as in Example 1.

[0129] Comparative Example 5: The difference between this comparative example and Example 1 is that the amount of TiN pre-dispersion added in step one is adjusted to 45g, the amount of activated nickel powder in step three is adjusted to 60g, and the amount of organic carrier is adjusted to 10g. The remaining steps are the same as in Example 1.

[0130] Comparative Example 6: The difference between this comparative example and Example 1 is that in the sintering curve of step five, the temperature rise from 400℃ to 650℃ is carried out at a continuous slow rate (1.5℃ / min), without the 500℃ holding plateau. The specific temperature rise curve is as follows: from room temperature, the temperature rises to 200℃ at 4℃ / min, then to 400℃ at 3℃ / min, then to 650℃ at 1.5℃ / min, and finally to 900℃ at 8℃ / min and holds for 20 minutes. The remaining steps are the same as in Example 1.

[0131] Comparative Example 7: The difference between this comparative example and Example 1 is that step two is omitted, and untreated commercially available nickel powder is used directly. The remaining steps are the same as in Example 1. This comparative example is used to verify the effect of nickel powder surface activation treatment on shrinkage behavior stability.

[0132] To verify the technical effectiveness of the present invention, performance tests were conducted on the nickel pastes prepared in the examples and comparative examples. The test scheme is as follows:

[0133] Experimental Example 1: Sintering Shrinkage Matching Test

[0134] To verify the effect of the method of the present invention on the control of the sintering shrinkage rate of nickel electrodes, the shrinkage rate of the nickel paste prepared in each embodiment and comparative example was tested.

[0135] The nickel paste prepared in each embodiment and comparative example (after completing steps one to four) was used to prepare an electrode film with a thickness of approximately 50 μm on a PET film using a casting method. The film was dried at 80°C for 30 minutes to remove the solvent, and then cut into strips of 10 mm × 30 mm. Five parallel samples were prepared for each group, and the initial length of the strips was measured using vernier calipers. (Accuracy 0.01mm), sintering was performed according to the sintering curve in step five of each example (Examples 8 and 9 and Comparative Examples 6 and 7 used their specific curves). After sintering, the samples were allowed to cool naturally, and the final length of the specimens was measured. According to the formula Calculate the linear shrinkage rate, take the arithmetic mean of 5 parallel samples as the shrinkage rate of the sample, and calculate the standard deviation.

[0136] Meanwhile, BaTiO3 ceramic powder and organic carrier were mixed at a solid content of 60% to prepare a casting slurry, which was then cast into a dielectric film with a thickness of about 30 μm. After drying, the film was cut into strips of 10 mm × 30 mm and sintered according to the standard sintering curve (the same as step five in Example 1). The shrinkage rate was measured to be 16.5%, which was used as the benchmark value for dielectric shrinkage rate. The shrinkage rate of each sample and the difference between the shrinkage rate and the dielectric shrinkage rate are shown in Table 1.

[0137] Table 1. Test results of the sintering shrinkage rate of nickel electrodes and the compatibility of BaTiO3 ceramic dielectric in each embodiment and comparative example: Example 1 16.6 0.12 +0.1 Example 2 16.8 0.14 +0.3 Example 3 16.9 0.15 +0.4 Example 4 17.1 0.16 +0.6 Example 5 17.0 0.14 +0.5 Example 6 18.0 0.18 +1.5 Example 7 15.1 0.16 -1.4 Example 8 16.8 0.13 +0.3 Example 9 16.5 0.11 0.0 Comparative Example 1 21.3 0.25 +4.8 Comparative Example 2 17.0 0.14 +0.5 Comparative Example 3 17.3 0.16 +0.8 Comparative Example 4 19.7 0.21 +3.2 Comparative Example 5 13.5 0.17 -3.0 Comparative Example 6 17.8 0.18 +1.3 Comparative Example 7 18.6 0.22 +2.1

[0138] To visually demonstrate the differences in shrinkage matching effects among the samples, the above test results are presented in line form in Figure 2. Figure 2 The left vertical axis represents the shrinkage rate difference (%), and the horizontal axis represents the sample number. Examples 1 to 9 are denoted as E1 to E9, and Comparative Examples 1 to 7 are denoted as D1 to D7.

[0139] As can be seen from the data in Table 1, the shrinkage rate differences of Examples 1 to 5 are all between +0.1% and +0.6%, achieving precise matching with the BaTiO3 ceramic medium. Among them, Example 1 (TiN, 10 parts) has the best matching effect, with a difference of only +0.1%. The shrinkage rate of Example 6 (7.2 parts) is relatively high (18.0%), which may be because the amount of conductive ceramic added is insufficient, the rigid skeleton is not dense enough, and the constraint on the shrinkage of nickel powder is weak. The shrinkage rate of Example 7 (14 parts) is relatively low (15.1%), which may be because the amount of conductive ceramic added is too large, the skeleton is too dense, and the shrinkage of nickel powder is excessively suppressed. The above results indicate that the amount of conductive ceramic added needs to be controlled within an appropriate range. When the amount added is less than 3% of the mass of nickel powder, the shrinkage inhibition effect is insufficient (19.7% shrinkage rate of Comparative Example 4), and when the amount added is more than 20%, the shrinkage is excessively suppressed (13.5% shrinkage rate of Comparative Example 5).

[0140] Comparing Examples 8 and 9 with Example 1, it can be seen that the matching effect of 30 minutes (Example 8) is slightly different from that of 45 minutes (Example 1) and 60 minutes (Example 9), but both are within an acceptable range. This indicates that the heat preservation platform of the present invention has a wide process window, and heat preservation times of 30 to 60 minutes can achieve good shrinkage matching.

[0141] Comparative Example 1, without shrinkage inhibitor, had a shrinkage rate as high as 21.3%, with a difference of +4.8%, indicating poor matching. Comparative Examples 2 and 3 (insulating oxides) had shrinkage rates of 17.0% and 17.3%, respectively, showing good matching, indicating that insulating oxides can also achieve shrinkage matching.

[0142] Comparative Example 4 had insufficient addition, resulting in a shrinkage rate of 19.7%, while Comparative Example 5 had excessive addition, resulting in a shrinkage rate of 13.5%, both exceeding the matching range. This further verified the rationality of the conductive ceramic addition range. Comparative Example 6 lacked a 500℃ heat preservation platform, resulting in a shrinkage rate of 17.8%, higher than Example 1, indicating that the heat preservation platform is important for fully utilizing the constraint effect of the conductive ceramic skeleton. Comparative Example 7 had unactivated nickel powder, resulting in a shrinkage rate of 18.6%, higher than Example 1. This may be because the surface oxide layer reduced the sintering activity of the nickel powder, leading to unstable shrinkage behavior.

[0143] from Figure 2 It can be clearly seen that the shrinkage rate difference of Examples 1 to 5 is controlled within ±0.6%, while the matching effect of Examples 6 to 7 and Comparative Examples 1 to 7 is significantly worse, which is consistent with the data pattern in Table 1.

[0144] Experiment Example 2: Electrode Sheet Resistance Test

[0145] To verify the effect of the method of the present invention on the conductivity of nickel electrodes, sheet resistance tests were performed on the nickel pastes prepared in each embodiment and comparative example.

[0146] The nickel pastes prepared in each embodiment and comparative example were screen-printed onto an alumina substrate to form 10mm×10mm square electrode patterns (wet film thickness 20±2μm). After drying at 80℃ for 30 minutes and sintering according to their respective sintering curves, the sheet resistance of the electrodes was tested using a four-probe sheet resistance tester. Eight different positions were tested for each sample, the arithmetic mean was taken, and the standard deviation was calculated. The test results are shown in Table 2.

[0147] Table 2. Electrode sheet resistance test results for each embodiment and comparative example: Example 1 54 2.8 Example 2 58 3.2 Example 3 62 4.0 Example 4 65 4.3 Example 5 61 3.8 Example 6 46 2.5 Example 7 80 5.2 Example 8 56 3.0 Example 9 52 2.9 Comparative Example 1 88 6.0 Comparative Example 2 162 11.8 Comparative Example 3 170 12.5 Comparative Example 4 68 4.5 Comparative Example 5 112 8.6 Comparative Example 6 78 5.5 Comparative Example 7 95 7.1

[0148] To visually demonstrate the differences in sheet resistance among the samples, the above test results are overlaid on a line graph. Figure 2 middle, Figure 2 The right vertical axis represents the sheet resistance (mΩ / □), and the horizontal axis represents the sample number (E1~E9, D1~D7).

[0149] As can be seen from the data in Table 2, the sheet resistance of Examples 1 to 5 is between 54 and 65 mΩ / □, which is much lower than that of Comparative Examples 2 to 3 (162 to 170 mΩ / □). Under the premise of achieving the same shrinkage matching effect (difference ≤ 0.6%), the sheet resistance of the conductive ceramic solution of the present invention is only one-third of that of the insulating oxide solution. This shows that using conductive ceramic to replace insulating oxide has a conductivity advantage.

[0150] Example 6, with an addition of 7.2 parts, had a sheet resistance of only 46 mΩ / □, the lowest among all samples. This is because the addition amount was small, resulting in a low proportion of conductive ceramic in the electrode and a denser sintering of the nickel powder. However, combined with Experiment 1, its shrinkage matching (difference +1.5%) was slightly worse. Example 7 (with an addition of 14 parts) had a sheet resistance of 80 mΩ / □, higher than Example 1. This may be because although the excessive conductive ceramic enhanced the skeleton constraint, it also partially blocked the conductive path. The above data indicate that when the amount of conductive ceramic added is in the range of 5% to 12%, the best balance can be achieved between shrinkage matching and conductivity.

[0151] Examples 8 and 9 were kept at a temperature of 30 and 60 minutes, respectively, and the sheet resistances were 56 and 52 mΩ / □, respectively, both lower than that of Example 1 (54 mΩ / □). This indicates that extending the holding time is beneficial to improving the conductive framework and reducing the resistance.

[0152] Comparative Example 1, without shrinkage inhibitor, has a sheet resistance of 88 mΩ / □. Although it has good conductivity, its shrinkage matching is poor (difference +4.8%). Comparative Examples 2 and 3 (insulating oxide) have sheet resistances as high as 162 to 170 mΩ / □, which is about twice that of pure nickel electrodes. This illustrates the problem of increased resistance caused by insulating shrinkage inhibitors.

[0153] Comparative Examples 4 and 5 represent the boundary of the addition amount, with sheet resistances of 68 and 112 mΩ / □, respectively. Although these are better than the insulating oxide scheme, the matching is poor. Comparative Example 6 has a sheet resistance of 78 mΩ / □, which is higher than Example 1, indicating that the thermal insulation platform helps to form a more complete conductive network. Comparative Example 7 has unactivated nickel powder with a sheet resistance of 95 mΩ / □, which is higher than Example 1. This may be because the surface oxide layer affects the formation of sintering necks between nickel powders, increasing the contact resistance.

[0154] from Figure 2 It can be intuitively seen that the sheet resistance of Examples 1 to 5 is much lower than that of Comparative Examples 2 to 3, while Example 6 (E6) has the lowest sheet resistance (46mΩ / □) but the matching is slightly worse. Example 7 (E7) has an increased sheet resistance (80mΩ / □), which further verifies the rationality of the range of conductive ceramic addition.

[0155] Experiment Example 3: Interface Microstructure Analysis

[0156] To observe the microstructure of the electrode formed by the method of the present invention, the sintered samples of Example 1 and Comparative Example 2 were analyzed by scanning electron microscopy.

[0157] Nickel pastes from Example 1 and Comparative Example 2 were screen-printed onto BaTiO3 ceramic green bodies (10mm × 10mm, wet film thickness 20μm), and co-fired according to the standard process (step five of Example 1). After scratching along the center of the sample with a diamond pen, the sample was manually broken to obtain a fresh fracture surface. The sample was fixed on the sample stage with the fracture surface facing upwards and sputtered with gold using an ion sputtering instrument (sputtering current 10mA, time 60 seconds). The morphology of the fracture surface was observed using a field emission scanning electron microscope with an accelerating voltage of 10kV and a magnification of 10000x.

[0158] Figure 3 This is a SEM cross-sectional image of the electrode and dielectric interface after sintering in Example 1. Figure 3 As can be seen, the interface between the electrode layer and the ceramic layer is clear and continuous, without cracks or delamination. Bright white particles (TiN, average particle size 80nm) are uniformly distributed between the light gray nickel network in the electrode layer. The two are in close contact, forming a three-dimensional conductive network. The TiN particles at the interface are embedded in the ceramic layer, forming an anchor structure.

[0159] Figure 4 This is a SEM cross-sectional image of the electrode and dielectric interface after sintering in Comparative Example 2. Figure 4 It can be seen that the interface between the electrode and the ceramic layer is acceptable, but a large number of dark gray agglomerated particles (MgO) are distributed between the nickel network in the electrode layer. In some areas, MgO particles aggregate to form insulating areas, which obviously interrupt the conductive path. No obvious anchor point structure is seen at the interface.

[0160] The above SEM images illustrate the structural advantages of the present invention: the conductive ceramic TiN is uniformly distributed in the electrode, which not only provides support for the rigid skeleton, but also forms good conductive contact with the nickel particles. Although the insulating oxide MgO can also suppress shrinkage, its insulation properties cause the conductive path inside the electrode to be blocked, which is consistent with the sheet resistance test results. The anchoring effect of the electroceramic at the interface enhances the mechanical bond between the electrode and the ceramic layer.

[0161] Experiment Example 4: Performance Verification of MLCC Capacitors

[0162] To verify the application effect of the nickel paste prepared by the method of the present invention in actual MLCCs, the nickel pastes of Example 1, Comparative Example 2, and Comparative Example 4 were prepared into samples according to the standard process of 0402 specification (1.0mm×0.5mm) MLCCs.

[0163] The sample parameters are as follows: dielectric layer thickness 2μm, number of inner electrode layers 100, electrode thickness of each layer 0.8μm, chip size 1.0mm×0.5mm×0.5mm, and 300 samples are prepared for each group.

[0164] The capacitance (C) and loss (DF) were tested using an LCR tester under the conditions of 1V and 1kHz. The withstand voltage was tested using a withstand voltage tester with a boost rate of 100V / s and a leakage current limit of 10mA.

[0165] The sample was placed in a high-temperature aging chamber and aged for 1000 hours at 125℃ and twice the rated voltage (2Ur). The capacitance (C) and insulation resistance (IR) were measured before and after aging, and the capacitance change rate was calculated using the following formula:

[0166] ,in and The values ​​represent the capacitance measured before and after the accelerated aging test, respectively. The pass rate was calculated with IR≥100MΩ as the pass standard. The test results are shown in Table 3.

[0167] Table 3. Electrical properties and aging reliability test results of MLCC samples prepared with different nickel pastes: Example 1 1.01 1.9 645 -2.6 96.7 Comparative Example 2 0.94 3.3 615 -4.9 88.3 Comparative Example 4 0.97 2.3 600 -4.3 91.0

[0168] As can be seen from the data in Table 3, the MLCC capacitance of Example 1 (1.01 μF) is higher than that of Comparative Example 2 (0.94 μF) and Comparative Example 4 (0.97 μF). This is because Example 1 has a lower sheet resistance, a larger effective conductive cross-sectional area of ​​the electrode, and a more uniform current distribution.

[0169] The loss in Example 1 (1.9%) was significantly lower than that in Comparative Example 2 (3.3%), which is consistent with the sheet resistance test results. The low-resistance electrode reduced the ESR, thereby reducing dielectric loss.

[0170] The withstand voltage (645V) of Example 1 is slightly higher than that of Comparative Example 2 (615V) and Comparative Example 4 (600V), indicating that the interface bonding of the present invention is better and reduces the electric field concentration points.

[0171] After accelerated aging, Example 1 had the smallest absolute value of capacity change rate (-2.6%), while Comparative Example 2 had the largest (-4.9%). This indicates that the electrode and dielectric interface of Example 1 was the most stable under thermal stress and the interface degradation caused by aging was the least.

[0172] Example 1 showed the highest insulation resistance pass rate (96.7%), while Comparative Example 2 showed the lowest (88.3%), indicating that the MLCCs prepared with nickel paste according to the present invention have better long-term reliability.

[0173] Experiment Example 5: Interfacial Bond Strength Test

[0174] To quantitatively evaluate the effect of the method of the present invention on the bonding strength of the electrode and dielectric interface, the same MLCC green blank as in Experimental Example 4 was prepared, but only a single layer of electrode was printed, with an electrode size of 5mm × 5mm.

[0175] After sintering, the shear strength of the electrode-ceramic interface was tested using a shear tester. The test conditions were a shear rate of 50 μm / s and a shear height of 5 μm. Ten points were tested for each sample, and the arithmetic mean was taken. The test results are shown in Table 4.

[0176] Table 4. Test results of the interfacial shear strength between different sample electrodes and BaTiO3 ceramic medium: Example 1 28.5 2.1 Comparative Example 1 23.4 2.5 Comparative Example 2 25.1 2.3 Comparative Example 4 24.6 2.4

[0177] As can be seen from the data in Table 4, Example 1 has the highest interfacial shear strength, which is 21.8% higher than Comparative Example 1 (without shrinkage agent). Although the shear strength of Comparative Example 2 (insulating oxide MgO) (25.1 MPa) is higher than that of Comparative Example 1, it is lower than that of Example 1. The shear strength of Comparative Example 4 (insufficient amount of conductive ceramic) (24.6 MPa) is also lower than that of Example 1.

[0178] The reason for this may be the anchoring effect formed by the conductive ceramic TiN particles at the electrode and dielectric interface (such as...). Figure 3 As shown in the figure, mechanical interlocking is created between the electrode and the ceramic layer, which enhances the interfacial bonding. However, the insulating oxide MgO has poor chemical compatibility with the ceramic, and a weak layer is easily formed at the interface, so the enhancement effect is limited.

[0179] In summary, the present invention provides a method for controlling the sintering shrinkage of nickel paste in MLCC electrodes and matching it with the BaTiO3 ceramic medium. Through the synergistic effect of conductive ceramic shrinkage inhibitor, nickel powder surface activation, pre-dispersion process, and a stepped heating curve with a heat preservation platform, it successfully solves the technical problem of difficulty in balancing matching and conductivity in the prior art.

[0180] Experimental results show that the present invention can precisely control the sintering shrinkage rate of nickel electrodes between 16.5% and 17.0%, with a matching difference of ≤ ±0.5% with BaTiO3 dielectric. At the same time, the electrode sheet resistance is as low as 52-65 mΩ / □, which is only one-third of that of the insulating oxide scheme. The interfacial shear strength is improved by 21.8%. The MLCC has a small capacitance change rate and a high insulation resistance qualification rate after aging, which has good industrial application value.

[0181] 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. A method for controlling the sintering shrinkage of nickel paste in MLCC electrodes and matching it with the BaTiO3 ceramic dielectric, characterized in that, Includes the following steps: S1: The conductive ceramic shrinkage inhibitor powder, dispersant and organic carrier are mixed and then ball-milled to obtain a conductive ceramic pre-dispersion. The conductive ceramic shrinkage inhibitor is selected from at least one of titanium nitride, titanium carbide, calcium copper titanate, lanthanum titanate or lanthanum strontium manganese oxide. S2: Heat-treat nickel powder in a mixed atmosphere of H2 and N2 to obtain surface-activated nickel powder; S3: Mix the conductive ceramic pre-dispersion obtained in step S1, the surface-activated nickel powder obtained in step S2, the dispersant, the organic carrier and the additives to form a paste; S4: Grind and disperse the paste obtained in step S3, controlling the fineness to ≤5μm; S5: The nickel paste obtained in step S4 is coated onto the BaTiO3 ceramic green body, and co-fired in a stepwise heating process under a protective atmosphere. The heating process is as follows: first, the temperature is raised to 400℃ through a low-temperature debinding stage, then the temperature is slowly raised to 500℃ at a rate of 1-2℃ / min and held for 30-60 minutes, then the temperature is slowly raised to 650℃ at a rate of 1-2℃ / min, and finally the temperature is rapidly raised to the sintering peak temperature and held, and then cooled naturally. The heating rate from 650℃ to the peak sintering temperature is 5-8℃ / min, the peak sintering temperature is 880-920℃, and the peak holding time is 15-30 minutes.

2. The method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic dielectric according to claim 1, characterized in that: The amount of conductive ceramic damping agent added in step S1 is 3% to 20% of the mass of nickel powder.

3. The method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic dielectric according to claim 2, characterized in that: The amount of conductive ceramic damping agent added in step S1 is 5% to 12% of the mass of nickel powder.

4. The method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic dielectric according to claim 1, characterized in that: The heat treatment in step S2 is performed at a temperature of 350–500°C for 30–120 minutes, with a volume fraction of H2 of 3%–8%.

5. The method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic dielectric according to claim 1, characterized in that: The low-temperature debinding stage in step S5 includes: heating from room temperature to 200°C at a rate of 3-5°C / min; and heating from 200°C to 400°C at a rate of 2-4°C / min.

6. The method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic dielectric according to claim 1, characterized in that: The heat preservation time at 500℃ in step S5 is 45 to 60 minutes.

7. The method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic dielectric according to claim 1, characterized in that: The heating rate from 650°C to the sintering peak temperature in step S5 is 6–8°C / min.

8. A nickel paste for MLCC electrodes, characterized in that: The method for controlling the sintering shrinkage of MLCC electrode nickel paste and matching it with the BaTiO3 ceramic medium, as described in any one of claims 1 to 7, is adopted.

9. The application of the control method as described in any one of claims 1 to 7 in the preparation of multilayer ceramic capacitors, characterized in that, The nickel paste prepared by the control method according to any one of claims 1 to 7 is applied to the BaTiO3 ceramic green body by screen printing or casting to form an electrode pattern, and then formed into an inner electrode after co-firing.

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