Preparation method of ceramic powder material for base metal inner electrode X8R type MLCC

Abstract

The invention discloses a preparation method of a ceramic powder material for a base metal inner electrode X8R type MLCC. The ceramic powder takes barium titanate or partial substitutes thereof as basic dielectric components, rare earth metal oxide, transition metal oxide and alkaline earth metal oxide are synergistically added as modifiers, and a silicate sintering aid is supplemented. The preparation method comprises the following steps: raw material pretreatment, proportioning and wet ball-milling mixing, granulation and molding, rubber discharging and sintering at 1150-1250 DEG C in a reducing atmosphere. The ceramic powder can be well matched and co-fired with nickel, copper and other base metal electrodes in an H-N-HO reducing atmosphere, the dielectric constant change rate of the obtained ceramic material within the temperature range of-55 DEG C to 150 DEG C is smaller than or equal to + / -15%, the X8R specification is met, meanwhile, the dielectric constant (1kHz, 25 DEG C) of the ceramic material is larger than or equal to 1800, and the dielectric loss is smaller than or equal to 2%. The problem of compatibility of reduction sintering suitability and wide-temperature stability of the base metal electrode MLCC is successfully solved.

Description

Technical Field

[0001] This invention relates to the field of dielectric ceramic materials for electronic components, and specifically to a method for preparing ceramic powder material for X8R type MLCCs with base metal internal electrodes. Background Technology

[0002] Multilayer ceramic chip capacitors (MLCCs) are core passive components in electronic circuits, and their performance is highly dependent on the synergistic matching between the dielectric ceramic powder and the electrode materials. Traditional MLCCs commonly use precious metals (such as Pd-Ag alloys) as internal electrode materials. However, the scarcity and price volatility of precious metal resources result in high manufacturing costs for MLCCs, making it difficult to meet the cost control requirements for large-scale applications in consumer electronics, automotive electronics, and other fields.

[0003] To reduce costs, the industry is gradually shifting towards using base metals (such as Ni and Cu) as internal electrodes. However, this shift presents two major challenges to dielectric ceramic powders: First, the compatibility with reducing sintering. Base metal (Ni and Cu) electrodes are easily oxidized in oxidizing atmospheres, therefore co-firing must be completed in a reducing atmosphere of H2-N2 mixture. Traditional barium titanate (BaTiO3)-based ceramic powders are prone to reduction reactions in reducing atmospheres, leading to deterioration of dielectric properties. Second, the requirement for wide-temperature characteristics in X8R. Pure barium titanate has a Curie temperature of approximately 125°C, and its dielectric constant decreases by more than 30% at -55°C and by more than 20% at 150°C, failing to meet the wide-temperature stability required by the X8R specification. Therefore, effective elemental doping and modification are necessary to broaden and adjust the temperature characteristics of the ceramic powder.

[0004] In the prior art, Chinese invention patent CN114180952A discloses a doped bismuth ferrite-barium titanate-based lead-free piezoelectric ceramic and its two-step sintering preparation method. Through specific chemical composition design and a two-step sintering process (first holding at 950–1050℃ for 1–2 minutes, then cooling to 900–1000℃ for 6–10 hours), it aims to avoid the temperature range for impurity phase formation, thereby obtaining a ceramic material with good crystallinity, uniform composition, fine grains, and excellent piezoelectric and dielectric properties. However, this technical solution mainly targets the performance optimization of piezoelectric ceramics. Its composition and sintering process objectives (such as high-temperature rapid sintering followed by long-term holding) differ significantly from those of dielectric ceramic powders suitable for base metal electrode MLCCs, which require one-time sintering in a reducing atmosphere to achieve specific temperature stability. Therefore, it cannot solve the specific technical problems faced by the aforementioned base metal electrode X8R type MLCCs.

[0005] In summary, developing a dielectric ceramic powder for MLCCs that combines high dielectric constant, meets the wide temperature range of X8R, can be reductively sintered with base metal electrodes at lower temperatures, and is environmentally friendly and low-cost has become a key technical problem that the industry urgently needs to solve. Summary of the Invention

[0006] The purpose of this invention is to provide a dielectric ceramic powder for multilayer ceramic chip capacitors (MLCCs) that is compatible with base metal electrodes (nickel electrodes, copper electrodes) and meets the X8R temperature characteristic specifications (dielectric constant change rate ≤ ±15% within the temperature range of -55℃ to 150℃), as well as an industrial preparation method for the ceramic powder.

[0007] The technical solution of this invention: A method for preparing ceramic powder material for X8R type MLCCs with base metal internal electrodes, comprising the following steps: Step 1: Raw material preparation and pretreatment. Prepare the basic dielectric ceramic powder, modifier, and sintering aid, and then dry them. The basic dielectric ceramic powder is barium titanate or barium titanate partially substituted with divalent metal ions, with the general chemical formula Ba1₋. x A x TiO3, wherein A includes, but is not limited to, Sr and Ca, and the value of x is in the range of 0 ≤ x ≤ 0.05; the modifier comprises one or more of rare earth metal oxides, transition metal oxides and alkaline earth metal oxides; Step 2: Ingredient preparation and mixing. According to the final composition of the ceramic powder, weigh 90% to 97% of the basic dielectric ceramic powder, 0% to 14% of the modifier (preferably, the modifier is not 0% but specifically 3% to 10%), and sintering aid accounting for 0.05wt% to 3wt% of the total mass of the above-mentioned basic dielectric ceramic powder and modifier; mix the weighed raw materials with the dispersant and solvent, and perform wet ball milling to obtain a mixed slurry; Step 3: Granulation and molding. After drying and granulating the mixed slurry, it is pressed into a green body and then debinded. Step 4: Sintering: The blank after debinding is placed in a reducing atmosphere and sintered at a temperature of 1150℃~1250℃ to obtain porcelain powder material. The obtained ceramic powder material has a dielectric constant change rate of ≤±15% in the temperature range of -55℃ to 150℃, a dielectric constant of ≥1800 at 1kHz and 25℃, and a dielectric loss of ≤2%.

[0008] Furthermore, the rare earth metal oxides include, but are not limited to, at least one of Y2O3, Yb2O3, and Dy2O3; the transition metal oxides include, but are not limited to, one or more of Mn3O4, ZrO2, and NiO; and the alkaline earth metal oxides include, but are not limited to, one or more of MgO, BaO, and CaO.

[0009] Furthermore, based on the total molar amount of ceramic powder, the amount of rare earth metal oxide added is less than or equal to 5 mol%, the amount of transition metal oxide added is less than or equal to 4 mol%, and the amount of alkaline earth metal oxide added is less than or equal to 5 mol.

[0010] Furthermore, the sintering aid is a silicate, including but not limited to SiO3 and BaCaSiO3.

[0011] Furthermore, the dispersant in step 2 includes, but is not limited to, polyvinyl butyral, the solvent includes, but is not limited to, ethanol, and yttrium-stabilized zirconia balls are used as the ball milling medium in wet ball milling.

[0012] Further, the drying and granulation of the mixed slurry in step 3 specifically involves: spray drying the mixed slurry to obtain a dried powder. The dried powder is then added to a 7wt% PVA solution, sieved, and granulated.

[0013] Furthermore, the debinding process specifically involves using a tablet press to compress the granulated powder into a preform of the required size, and then placing it in a heating furnace for debinding.

[0014] Furthermore, in step 4, the reducing atmosphere is a mixture of H2, N2 and water vapor, wherein the volume fraction of H2 is 0.5% to 3%.

[0015] Furthermore, the average particle size D50 of the obtained ceramic powder material is 0.2–0.4 μm, and the loose packing density is 0.8–1.0 g / cm³; after sintering in a reducing atmosphere, the density of the ceramic body is ≥96%, and the grain size is 0.2–2 μm.

[0016] The beneficial effects of this invention are: 1. This invention fundamentally solves the compatibility problem of reducing sintering for base metal electrodes. Through specific combinations of modifiers and component design, the ceramic powder maintains the chemical stability of its structure during sintering in the reducing atmosphere, thereby ensuring that the sintered ceramic body has high insulation resistance and low dielectric loss, achieving process compatibility with base metal electrodes, and laying the material foundation for the widespread application of low-cost electrodes.

[0017] 2. This invention successfully achieves wide-temperature-range dielectric stability meeting the X8R standard. Through the synergistic doping of multiple modifiers, this invention precisely controls the temperature characteristics of the ceramic powder. Ultimately, the resulting ceramic powder exhibits a dielectric constant change rate effectively controlled within ≤±15% across the entire operating temperature range of -55℃ to 150℃, fully meeting the stringent X8R specifications and satisfying the temperature stability requirements of high-end applications such as automotive electronics and industrial control.

[0018] 3. By introducing an appropriate amount of sintering aid, the present invention optimizes the sintering temperature window of the ceramic powder to 1150℃~1250℃. This temperature range is highly matched with the sintering process of base metal electrodes, which promotes the full densification of the ceramic body and avoids the adverse effects of excessively high temperatures on the electrode.

[0019] 4. This invention provides an industrialization path that combines high performance and low cost. This invention unifies three key characteristics—high dielectric constant, wide temperature range of X8R, and compatibility with base metal reduction sintering—which were considered difficult to achieve simultaneously in the prior art, into a single material system and preparation method, obtaining a product that meets all the above requirements. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should not be construed that the scope of the subject matter of the present invention is limited to the following embodiments. All modifications, substitutions and alterations made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0021] The ceramic powder material for X8R type MLCCs with base metal internal electrodes of the present invention is composed of a basic dielectric ceramic component, a modifier component, and an optional sintering aid component, as detailed below: (1) Basic dielectric ceramic components: As the core carrier of the dielectric properties of ceramic powder, barium titanate-based compounds (such as BaTiO3, Ba1-xAxTiO3, where A is a divalent metal ion such as Sr, Ca, etc., and x=0~5%) are preferred, with a content of 90%~97%.

[0022] (2) Modifier components: used to adjust the temperature characteristics (to achieve X8R), dielectric constant and microstructure of ceramic powder, preferably one or more of rare earth metal oxides (such as Y2O3, Yb2O3, Dy2O3), transition metal oxides (such as Mn3O4, ZrO2, NiO), and alkaline earth metal oxides (such as MgO, BaO, CaO), and their specific types and amounts are shown in Table 1 below: Table 1

[0023] (3) Sintering aid components: used to reduce the sintering temperature of ceramic powder (to match the sintering temperature of base metal electrodes), preferably silicates (such as SiO3, BaCaSiO3), the specific types and amounts of which (account for 0.05wt%~3wt% of the total mass of ceramic powder).

[0024] The method for preparing the ceramic powder includes the following steps: Step 1: Raw material pretreatment. Select the raw materials for the basic dielectric ceramic components (such as BaTiO3, Ba1-xAxTiO3, where A is divalent metal ions such as Sr and Ca, and x=0~5%), the raw materials for the modifier components (such as Y2O3, Yb2O3, Dy2O3, Mn3O4, ZrO2, NiO, MgO, BaO, CaO, etc.), and the raw materials for the sintering aid components (such as SiO2, BaCaSiO3, etc.). Dry them separately (drying temperature: 120℃, drying time: 2h) and grind them to remove impurities and moisture. Step 2: Ingredient preparation and mixing. Weigh the pretreated raw materials according to the above proportions of ceramic powder composition, add dispersant (such as polyvinyl butyral) and solvent (such as ethanol), and place them in a ball mill for wet mixing (ball milling media: yttrium oxide-stabilized ZrO2 balls, ball milling time: 8h) to obtain a mixed slurry; Step 3: Drying and granulation. The mixed slurry is spray-dried to obtain a dried powder. The dried powder is then added to a 7wt% PVA solution and granulated by passing it through an 80-mesh sieve. Step 4: Molding and debinding. Use a tablet press to press the granulated powder into a preform of the required size and place it in a heating furnace for debinding (600℃, 2h). Step 5: Sintering. Place the debinding blank in an atmosphere sintering furnace, introduce H2, N2 and water vapor, and sinter at 1150℃~1250℃ for 2 hours. After cooling, take out the prepared X8R type ceramic.

[0025] The ceramic powder for X8R type MLCCs with base metal electrodes described in this invention achieves a dielectric constant change rate of ≤±15% within the range of -55℃ to 150℃ through the synergistic effect of the basic dielectric components and modifiers, fully meeting the X8R specification requirements. The dielectric constant (1kHz, 25℃) is ≥1800, and the dielectric loss (1kHz, 25℃) is ≤2%, enabling high capacity and low loss in MLCCs. By adjusting the sintering aids, the sintering temperature of the ceramic powder can be controlled between 1150℃ and 1250℃, matching the reducing sintering atmosphere and temperature of base metal electrodes (such as Ni electrodes).

[0026] Example 1: The present invention will be further illustrated by specific examples below, but the present invention is not limited to the following examples.

[0027] Porcelain powder composition: Basic dielectric composition: BaTiO3 (96.5 mol%); Modifier components: Y2O3 (1.0 mol %), Yb2O3 (0.3 mol %), Dy2O3 (0.5 mol %), Mn3O4 (0.2 mol %), MgO (1.5 mol %); Sintering aid composition: BaCaSiO3 (0.2wt%); After weighing the raw materials according to the above proportions, they were dried (drying temperature: 120℃, drying time: 2h) and ground to remove impurities and moisture. A dispersant (such as polyvinyl butyral) and a solvent (such as ethanol) were added, and the mixture was placed in a ball mill for wet mixing (milling media: yttrium oxide-stabilized ZrO2 balls, milling time: 8h) to obtain a mixed slurry. The mixed slurry was then spray-dried to obtain a dried powder. The dried powder was added to a 7wt% PVA solution and granulated through an 80-mesh sieve. The granulated powder was pressed into 1cm diameter discs using a tablet press and placed in a heating furnace for debinding (600℃, 2h). The debinded discs were then placed in an atmosphere sintering furnace, purged with H2, N2, and steam, and sintered at 1150℃~1250℃ for 2h. After cooling, the discs were removed, coated with silver electrodes on both sides, and then subjected to performance testing.

[0028] Performance testing includes: Dielectric properties: Tested using an Agilent E4980A LCR tester at a frequency of 1kHz and a voltage of 1V. Temperature characteristics: A Thermotron SE-1000 high and low temperature chamber was used to control the temperature range of -55℃ to 150℃, and the dielectric constant was recorded every 10℃. Density: Archimedes' displacement method was used, and the test medium was deionized water; Grain size: The average size of 50 grains was determined using a Zeiss Sigma 300 field emission scanning electron microscope (SEM). The performance test results are shown in Table 2: Table 2

[0029] This invention solves the problem of dielectric property degradation under reducing atmosphere, ensuring that the ceramic powder maintains stable dielectric properties after sintering in H2-N2 atmosphere; it achieves a dielectric constant change rate of ≤±15% in the temperature range of -55℃ to 150℃, while increasing the dielectric constant (1kHz, 25℃) to ≥1800; and it controls the ceramic powder sintering temperature at 1150~1250℃, which is perfectly matched with the reducing sintering process of Ni and Cu electrodes.

[0030] The prepared ceramic powder can be used in fields with stringent requirements for wide temperature stability and high reliability of MLCCs, such as automotive electronics (e.g., vehicle radar, engine control unit ECU), consumer electronics (e.g., smartphone power management modules, laptop motherboards), and industrial control (e.g., frequency converters, sensor signal processing units).

[0031] The preparation method of ceramic powder material for X8R type MLCC with base metal internal electrode provided by the present invention has been described in detail above. Specific examples have been used to illustrate the structure and working principle of the present invention. The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing ceramic powder material for X8R type MLCCs with base metal internal electrodes, characterized in that: Includes the following steps, Step 1: Raw material preparation and pretreatment. Prepare the basic dielectric ceramic powder, modifier, and sintering aid, and then dry them. The basic dielectric ceramic powder is barium titanate or barium titanate partially substituted with divalent metal ions, with the general chemical formula Ba1₋. x A x TiO3, wherein A includes, but is not limited to, Sr and Ca, and the value of x is in the range of 0 ≤ x ≤ 0.05; the modifier comprises one or more of rare earth metal oxides, transition metal oxides and alkaline earth metal oxides; Step 2: Ingredient preparation and mixing. According to the final composition of the ceramic powder, weigh 90% to 97% of the basic dielectric ceramic powder, 0% to 14% of the modifier, and 0.05 wt% to 3 wt% of the sintering aids, based on the total mass of the above-mentioned basic dielectric ceramic powder and modifier. Mix the weighed raw materials with the dispersant and solvent, and perform wet ball milling to obtain a mixed slurry. Step 3: Granulation and molding. After drying and granulating the mixed slurry, it is pressed into a green body and then debinded. Step 4: Sintering: The blank after debinding is placed in a reducing atmosphere and sintered at a temperature of 1150℃~1250℃ to obtain porcelain powder material. The obtained ceramic powder material has a dielectric constant change rate of ≤±15% in the temperature range of -55℃ to 150℃, a dielectric constant of ≥1800 at 1kHz and 25℃, and a dielectric loss of ≤2%.

2. The method for preparing ceramic powder material for X8R type MLCC with base metal internal electrode according to claim 1, characterized in that: The rare earth metal oxides include, but are not limited to, at least one of Y2O3, Yb2O3, and Dy2O3; the transition metal oxides include, but are not limited to, one or more of Mn3O4, ZrO2, and NiO; and the alkaline earth metal oxides include, but are not limited to, one or more of MgO, BaO, and CaO.

3. The method for preparing the ceramic powder material for X8R type MLCC with base metal internal electrode according to claim 2, characterized in that: Based on the total molar amount of ceramic powder, the amount of rare earth metal oxide added is less than or equal to 5 mol%, the amount of transition metal oxide added is less than or equal to 4 mol%, and the amount of alkaline earth metal oxide added is less than or equal to 5 mol.

4. The method for preparing ceramic powder material for X8R type MLCC with base metal internal electrode according to claim 1, characterized in that: The sintering aid is a silicate, including but not limited to SiO3 and BaCaSiO3.

5. The method for preparing ceramic powder material for X8R type MLCC with base metal internal electrode according to claim 1, characterized in that: The dispersant in step 2 includes, but is not limited to, polyvinyl butyral, and the solvent includes, but is not limited to, ethanol. Yttrium-stabilized zirconia balls are used as the ball milling medium in wet ball milling.

6. The method for preparing ceramic powder material for X8R type MLCC with base metal internal electrode according to claim 1, characterized in that: The drying and granulation of the mixed slurry in step 3 specifically involves: spray drying the mixed slurry to obtain a dried powder; adding the dried powder to a 7wt% PVA solution; and granulating the powder after sieving.

7. The method for preparing ceramic powder material for X8R type MLCC with base metal internal electrode according to claim 1, characterized in that: The debinding process involves using a tablet press to compress the granulated powder into preforms of the required size, and then placing them in a heating furnace for debinding.

8. The method for preparing ceramic powder material for X8R type MLCC with base metal internal electrode according to claim 1, characterized in that: In step 4, the reducing atmosphere is a mixture of H2, N2 and water vapor, wherein the volume fraction of H2 is 0.5% to 3%.

9. The method for preparing ceramic powder material for X8R type MLCC with base metal internal electrode according to claim 1, characterized in that: The average particle size D50 of the obtained ceramic powder material is 0.2-0.4 μm, and the loose packing density is 0.8-1.0 g / cm³. After sintering in a reducing atmosphere, the density of the ceramic body is ≥96%, and the grain size is 0.2-2 μm.

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