A high-capacitance multi-layer ceramic capacitor for X6S characteristics and its preparation method

Abstract

The present invention relates to the technical field of ceramic capacitors, and particularly relates to a high-capacitance multilayer ceramic capacitor for X6S characteristics and a preparation method thereof. The capacitor is formed by the overlapping of dielectric ceramic layers and internal electrodes, and external electrodes are provided at both ends to be connected to the internal electrodes. The dielectric ceramic layer is formed by the aforementioned dielectric ceramic material. The preparation method prepares a multilayer ceramic capacitor by using barium titanate particles with a specific average particle size, a dopant with a specific composition, and specific preparation conditions. Compared with the prior art, the dielectric material and the corresponding capacitor have both the temperature stability of X6S characteristics and high capacitance, and still have high IR characteristics and low dielectric loss factor (tanδ) even in a high-temperature environment.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic capacitors, and particularly to a high-capacitance multilayer ceramic chip capacitor with X6S characteristics and a preparation method thereof. Background Art

[0002] Multilayer ceramic chip capacitors (MLCCs) are chip capacitors suitable for surface mount technology (SMT) and are essential components in almost all electronic devices. In particular, the demand for MLCCs in mobile communication products, computers, digital cameras, and new-generation digital household appliances is increasing day by day. Moreover, with the trend of electronic devices towards being lighter, thinner, shorter, and smaller, and the increasing popularity of surface mount technology, the development of MLCCs has greater potential and is continuously expanding towards miniaturization, high capacitance, and high stability.

[0003] As the application scenarios of MLCCs continue to increase, the performance requirements for MLCCs are becoming more and more diverse. The Electronic Industries Association (EIA) of the United States has formulated the X6S specification for high-temperature capacitors, requiring that the capacitors have a high dielectric constant and good temperature stability in the temperature range of -55°C to 105°C (the capacitance change range is less than ±22% compared to that at 25°C). Barium titanate (BaTiO3) has a high dielectric constant and is currently the main material for preparing high-capacitance multilayer ceramic capacitors. However, the dielectric properties of pure BaTiO3 change greatly at different temperatures. The dielectric constant changes relatively smoothly with temperature at room temperature (25°C), but the dielectric constant changes significantly with temperature in the high-temperature region and reaches a peak at the Curie point (125°C). To improve the capacitance temperature stability, modified additives need to be introduced. Existing dielectric ceramic materials are mainly composed of barium titanate and doped with oxides such as zirconium, barium, manganese, and silicon. However, when an electric field is applied at high temperatures, the insulation resistance (IR) of the irreversible multilayer ceramic capacitor is significantly deteriorated. That is to say, the existing dielectric ceramic materials have the defects of short IR life and low reliability. Type I ceramics (CaZrO3, SrCaTiZrO3, Ca(TiZr)O3) can improve the high-temperature IR deterioration and reliability problems, but the dielectric constant of type I ceramics is low (less than 100), so they cannot be used to prepare high-capacitance capacitors. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a high-capacitance multilayer ceramic chip capacitor with X6S characteristics and a preparation method thereof to improve the high-temperature IR deterioration and reliability problems. The present invention combines the temperature stability of X6S characteristics and high capacitance, and even in a high-temperature environment, it still has high IR characteristics and a low dielectric loss factor (tanδ).

[0005] For the above purposes, the present invention provides a preparation method for a high-capacitance multi-layer ceramic capacitor with X6S characteristics, including the following steps:

[0006] S1. Mix and grind barium titanate, a dopant, a dispersant, and a solvent to obtain a powder mixture slurry;

[0007] S2. Add a binder and a plasticizer to the mixture slurry and mix to form a ceramic slurry;

[0008] S3. Coat and shape the obtained ceramic slurry to obtain a ceramic film;

[0009] S4. Print internal electrodes on the ceramic film;

[0010] S5. Stack the ceramic films printed with internal electrode patterns to obtain a green body block;

[0011] S6. Press the green body block to be tight by isostatic pressing;

[0012] S7. Cut the tightly pressed green body block to obtain a capacitor green body;

[0013] S8. Debind the capacitor green body to remove organic substances;

[0014] S9. Sinter the debound capacitor green body into porcelain;

[0015] S10. Grind and chamfer the fired capacitor ceramic body to expose the internal electrodes and reduce the surface stress of the ceramic body;

[0016] S11. Copper-plate both ends of the chamfered capacitor ceramic body to connect the internal and external electrodes;

[0017] S12. Conduct firing at 700-800 °C under nitrogen protection;

[0018] S13. Deposit nickel and tin successively on the surface of the copper-plated end to obtain a high-capacitance multi-layer ceramic capacitor with X6S characteristics.

[0019] Based on 100 parts by mass of barium titanate, the dopant includes the following components in parts by mass: the addition amount of SiO2 is 1.0-2.0 parts by mass, the addition amount of MgCO3 is 0.5-0.7 parts by mass, the addition amount of Mn3O4 is 0.04-0.06 parts by mass, the addition amount of BaCO3 is 1.5-2.5 parts by mass, the addition amount of Nb2O5 is 0.2-0.5 parts by mass, the addition amount of V2O5 is 1.2-1.5 parts by mass, and the addition amount of rare earth oxide D2O3 is 0.8-1.2 parts by mass. If the dopant does not contain the foregoing composition, the dielectric ceramic material prepared cannot meet the X6S standard and has good high-temperature impedance characteristics and low dielectric loss factors.

[0020] In the rare earth oxide D2O3, D is any one or more of Y, Ho, Yb, Gd, and Dy.

[0021] The present invention uses the BaTiO3-Mn3O4-MgCO3-D2O3-BaCO3-Nb2O5-V2O5 system to prepare dielectric ceramic materials and their capacitors. A small amount of submicron or nanoscale compounds of silicon, magnesium, manganese, calcium, niobium, and vanadium, as well as two or more of yttrium, ytterbium, and holmium element oxides, are added to the barium titanate synthesized by the solid-phase method and mixed evenly by wet method. After being mixed evenly with a certain proportion of dispersant, plasticizer, and binder, a ceramic slurry is obtained. Through a series of processes, MLCC is prepared. During the calcination process of the dielectric ceramic, some additives will promote the formation of a shell-core structure of ceramic grains, inhibit the further growth of barium titanate grains, improve the temperature characteristics of the dielectric ceramic, and its temperature stability meets the X6S dielectric material standard formulated by the Electronic Industries Association of the United States. When barium titanate is sintered in a reducing atmosphere, it is easy to lose oxygen at high temperature and become a semiconductor. Compounds such as magnesium, calcium, and manganese play an acceptor role during the calcination process of the porcelain dielectric, and the oxygen vacancy concentration caused is greater than the oxygen vacancy concentration formed due to oxygen volatilization, so that barium titanate can also maintain a high electrical insulation resistivity when sintered in a reducing atmosphere. Therefore, the dielectric ceramic material of the present invention has both good high-temperature impedance characteristics and a low dielectric loss factor (tanδ). At the same time, reasonable sintering temperature and sintering atmosphere make the ceramic body have good densification, a suitable core-shell structure, and uniform particle size, so that the prepared multilayer ceramic capacitor has excellent dielectric properties and capacitance-temperature characteristics.

[0022] The barium titanate accounts for 92-95 wt% of the total amount of barium titanate and dopants, and the dosage of the dopant accounts for 15-8 wt% of the total amount of barium titanate and dopants.

[0023] The particle size of the BaTiO3 is 150-250 nm and is prepared by the solid-phase method.

[0024] The dispersant includes polyethylene oxide resins, and the addition amount of the dispersant is 0.5-2 parts by mass. The dispersant is used to disperse the components of the dielectric ceramic material. The dispersant of the present invention is not particularly limited, but for the purpose of achieving the aforementioned dispersion, the dispersant can be polyethylene oxide resins and other resins.

[0025] The solvent includes water, ethanol, and / or toluene, and the addition amount of the solvent is 60-80 parts by mass.

[0026] In S1, the grinding is carried out using a ball mill, the grinding balls are 0.2-0.4 mm zirconia balls, the grinding speed is 40-80 rpm, and the grinding and mixing time is 4-6 hours.

[0027] The binder includes polyvinyl butyral resin, and the addition amount of the binder is 20 to 30 parts by mass; the plasticizer includes dioctyl adipate, and the addition amount of the plasticizer is 0.5 to 2 parts by mass. The binder of the present invention is not particularly limited, but for the purpose of achieving the aforementioned bonding, the binder can be polyvinyl butyral resin (PVB) and other resins. The plasticizer of the present invention is not particularly limited, but for the purpose of improving the plasticity of the ceramic slurry.

[0028] The third step, fourth step, fifth step, sixth step, seventh step, and eighth step of the present invention are general processes in the industry, and those skilled in the art can understand the practices of each step without the need for detailed description of the present invention.

[0029] In S9, the sintering temperature is 1265 to 1275 °C, the sintering atmosphere is 1.8 to 2.2% H2-N2 by volume fraction, and the sintering time is 1.7 to 2.3 hours. Preferably, the sintering temperature is 1270 °C, the sintering atmosphere is 2% H2-N2, and the sintering time is 2 hours. It should be noted that if the sintering conditions are not within this range, it is impossible to make the capacitor ceramic body have good densification, a suitable core-shell structure, and uniform particle size, so that the prepared multilayer ceramic capacitor cannot have excellent dielectric properties and capacitance-temperature characteristics.

[0030] The tenth step, eleventh step, twelfth step, and thirteenth step of the present invention are general processes in the industry, and those skilled in the art can understand the practices of each step without the need for detailed description of the present invention. Among them, sintering is carried out at 700 to 800 °C under nitrogen protection, aiming to burn out the organic components in the copper terminal, improve the densification of the copper terminal, and make the copper terminal tightly connected to the ceramic body.

[0031] The present invention also provides a high-capacitance multilayer chip ceramic capacitor for X6S characteristics, which is prepared by the preparation method described in the claims. It includes a dielectric ceramic layer, an inner electrode layer, and an outer electrode. Among them, the dielectric ceramic layer and the inner electrode layer overlap each other, and the inner electrode is electrically connected to the outer electrodes at both ends. The outer electrode is a multilayer structure, which is copper, nickel, and tin from the inside to the outside in sequence. The capacitance of the present invention is in the specification of the imperial number 0805, and the actual size is 2.00 mm × 1.25 mm.

[0032] In the present invention, MgCO3:Mg 2+ Acceptor substitution is carried out to improve the anti-reduction performance of the material. Mg 2+ Can inhibit grain growth, promote the formation of the "core-shell" structure, and effectively improve the dielectric temperature stability of barium titanate-based ceramics in an ultra-wide temperature range. In addition, Mg 2+ The addition of will shift the Tc peak to the left.

[0033] D2O3 (D contains Y, Ho, Yb, Gd, Dy): D 3+As a typical amphoteric rare-earth ion, it can be doped with donors and acceptors simultaneously, resulting in defect association, reducing the high-temperature dielectric loss factor (tanδ), and improving the lifespan and reliability of the anti-reduction ceramic material.

[0034] In Mn3O4, Mn exhibits +2 and +3 valence states. During the re-oxidation stage, the low-valence manganese ions will be oxidized, reducing the concentration of oxygen vacancies used to compensate for acceptor defects and alleviating the problem of high-temperature semi-conduction.

[0035] In Nb2O5, Nb is doped as a donor element to replace the B-site Ti ions in BaTiO3. The addition of Nb causes the phase transition peak (Core peak) in the high-temperature region of the dielectric material to be depressed and broadened, while the phase transition peak (Shell peak) in the low-temperature region shifts towards lower temperatures.

[0036] In V2O5, V ions can effectively inhibit the diffusion of doped ions D and Mg into the BaTiO3 grains, changing the distribution of the doped ions in the grains, thereby forming a "core-shell" structure. Therefore, V can increase the intensity of the Curie peak and improve the capacitance temperature stability. The multivalent V ions mainly exist in the +3 and +4 states in a reducing atmosphere, which can enhance the anti-reduction property of the dielectric material, increase the insulation resistivity, and reduce the dielectric loss. Beneficial effects

[0037] The present invention uses a BaTiO3-Mn3O4-MgCO3-D2O3-BaCO3-Nb2O5-V2O5 system to prepare a ceramic dielectric material. A small amount of sub-micron or nano-scale compounds of silicon, magnesium, manganese, calcium, niobium, vanadium, and two or more rare-earth element oxides such as yttrium, ytterbium, and holmium are added to the barium titanate synthesized by the solid-phase method, and wet-mixed evenly and then processed through a series of processes to obtain the dielectric porcelain material for MLCC. During the calcination process of the dielectric ceramic, some additives will promote the formation of a shell-core structure in the ceramic grains, inhibit the further growth of the barium titanate grains, and improve the temperature characteristics of the dielectric ceramic. Its temperature stability meets the X6S dielectric material standard formulated by the Electronic Industries Association of the United States. When barium titanate is sintered in a reducing atmosphere, it is prone to losing oxygen at high temperatures and becoming a semiconductor. Compounds such as magnesium, calcium, manganese, niobium, and vanadium play an acceptor role during the calcination process of the porcelain dielectric. The concentration of oxygen vacancies caused is greater than the concentration of oxygen vacancies formed due to oxygen volatilization, enabling barium titanate to maintain a high electrical insulation resistivity even when sintered in a reducing atmosphere. Therefore, the dielectric ceramic material of the present invention has both good high-temperature impedance characteristics and a low dielectric loss factor (tanδ).

[0038] On the other hand, through reasonable sintering temperature, sintering atmosphere, and sintering time, the ceramic body has good densification, a suitable core-shell structure, and uniform particle size, thereby ensuring that the prepared multilayer ceramic capacitor has excellent dielectric properties and capacitance-temperature characteristics.

[0039] The prepared multilayer ceramic capacitor has both X6S characteristic temperature stability and high capacitance, and it still has high IR characteristics and low dielectric loss factor (tan δ) even in a high-temperature environment. Brief Description of the Drawings

[0040] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0041] Figure 1 It is a flowchart for preparing the MLCC of the present invention;

[0042] Figure 2 It is a schematic structural diagram of the MLCC. Detailed Embodiments

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further details the present invention in combination with specific embodiments.

[0044] It should be noted that unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those with ordinary skills in the field to which the present invention belongs. Example 1

[0045] Mix 100 parts by mass of barium titanate particles with an average particle size of 0.15 μm to 0.25 μm, a certain mass of dopants (the composition is shown in Table 1), 1 part by mass of polyethylene oxide, and 60 parts by mass of an ethanol / toluene mixed solvent, and use a ball mill to grind for 5 hours. The grinding balls are 0.3 mm zirconium balls, and the grinding speed is 50 rpm to obtain a powder mixture slurry. Then add 25 parts by mass of PVB binder and 1 part by mass of plasticizer DOA to the powder mixture slurry, and mix evenly to obtain a ceramic slurry. The obtained ceramic slurry is processed through the steps of coating and film-forming, inner electrode printing, stacking, hydrostatic pressure, cutting, debinding, etc. to obtain a capacitor green body. The capacitor green body is sintered in a 2% H2-N2 atmosphere at a sintering temperature of 1270 °C and a heating and cooling rate of 3 °C / min for 2 hours. Then, through processes such as chamfering, copper plating, baking at 700 - 800 °C under nitrogen protection, electroplating, etc., an MLCC ceramic capacitor is obtained for the subsequent evaluation test, and the evaluation results are listed in Table 1 below.

[0046] Examples 2 - 3 and Comparative Examples 1 - 4

[0047] Examples 2-3 and Comparative Examples 1-4 were all manufactured in a similar manner to Example 1. The difference is that in Examples 2-3 and Comparative Examples 1-4, the amount of dopant or the sintering conditions were changed. The specific conditions and evaluation results are shown in Table 1 below.

[0048] Table 1

[0049]

[0050] Referring to Table 1, compared with Comparative Examples 1-4, the capacitance temperature change rate of the dielectric ceramic materials in Examples 1-3 was not greater than ±22% from -55°C to 105°C, and the dielectric constant was greater than 3000, and the dielectric loss factor was less than 6.50%. It can be seen that containing a dopant with a specific composition and specific sintering conditions can reduce the capacitance temperature coefficient of the prepared dielectric ceramic material, and increase the dielectric constant and reduce the dielectric loss factor.

[0051] Those of ordinary skill in the art should understand that the discussion of any above example is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above examples or different examples can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, and they are not provided in detail for the sake of brevity. Any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a multilayer ceramic capacitor with X6S characteristics and high capacitance, characterized in that: The steps include: S1, mixing and grinding barium titanate, a dopant, a dispersant, and a solvent to obtain a powder mixture slurry; S2, adding a binder and a plasticizer to the mixture slurry to form a ceramic slurry; S3, applying the obtained ceramic slurry to form a ceramic film; S4, printing an inner electrode on the ceramic film; S5, stacking the ceramic films printed with the inner electrode patterns to obtain a green embryo block; S6, pressing the green embryo block to be compacted by isostatic hydropressure; S7, cutting the compacted green embryo block to obtain a capacitor green embryo; S8, removing the glue from the capacitor embryo to remove organic matter; S9, sintering the capacitor green body after debinding into porcelain; S10, rolling and chamfering the fired capacitor ceramic body to expose the inner electrode and reduce the surface stress of the ceramic body; S11, copper plating is performed on both ends of the chamfered capacitor ceramic body to connect the inner and outer electrodes; S12, sintering at 700~800℃ under nitrogen protection; S13, plating nickel and tin on the copper-plated end surface in sequence to obtain a high-capacitance multilayer chip ceramic capacitor with X6S characteristics; Based on 100 parts by mass of barium titanate, the dopant includes the following components in parts by mass: SiO2 added in an amount of 1.0-2.0 parts by mass, MgCO3 added in an amount of 0.5-0.7 parts by mass, Mn3O4 added in an amount of 0.04-0.06 parts by mass, BaCO3 added in an amount of 1.5-2.5 parts by mass, Nb2O5 added in an amount of 0.2-0.5 parts by mass, V2O5 added in an amount of 1.2-1.5 parts by mass, and rare earth oxide added in an amount of 0.8-1.2 parts by mass of D2O3; D in the rare earth oxide D2O3 is any one or more of Y, Ho, Yb, Gd, and Dy; the sintering temperature in the S9 is 1265-1275°C, the sintering atmosphere is 1.8-2.2% H2-N2 by volume, and the sintering time is 1.7-2.3 hours.

2. The method for preparing a multilayer ceramic capacitor with X6S characteristics and high capacitance according to claim 1, characterized in that: The dispersant includes polyethylene oxide resin, and the added amount of the dispersant is 0.5 to 2 parts by mass.

3. The method for preparing a multilayer ceramic capacitor with X6S characteristics and high capacitance according to claim 1, characterized in that: The solvent includes water, ethanol and / or toluene, and the added amount of the solvent is 60 to 80 parts by weight.

4. The method for preparing a multilayer ceramic capacitor with X6S characteristics and high capacitance according to claim 1, characterized in that: The grinding in S1 is performed using a ball mill, the grinding balls are 0.2-0.4 mm zirconium balls, the grinding speed is 40-80 rpm, and the grinding and mixing time is 4-6 hours.

5. The method for preparing a multilayer ceramic capacitor with X6S characteristics and high capacitance according to claim 1, characterized in that: The binder includes polyvinyl butyral resin, and the added amount of the binder is 20-30 parts by mass; the plasticizer includes dioctyl adipate, and the added amount of the plasticizer is 0.5-2 parts by mass.

6. A multilayer ceramic capacitor with X6S characteristics and high capacitance, characterized in that: The method is prepared by any one of claims 1 to 5.

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