Ceramic dielectric material for high-frequency MLCC and preparation method thereof

Abstract

The invention provides a ceramic dielectric material for a high-frequency MLCC (multilayer ceramic capacitor) and a preparation method of the ceramic dielectric material. The ceramic dielectric material comprises the following raw materials: a main component, a grain homogenizing and refining agent and a sintering aid, the main component comprises (100-x) CaCO3-xSrCO3-(100-y) ZrO2-yTiO2, x and y are mole percent, x is more than or equal to 10 and less than or equal to 90, and y is more than or equal to 1 and less than or equal to 10; the grain homogenizing and refining agent comprises at least one of SiO2, Al2O3 and MgO; the sintering aid is prepared from at least one of H3BO3, Li2CO3 and K2CO3. The ceramic dielectric material disclosed by the invention accords with C0G characteristics, the breakdown strength is greater than or equal to 140V / mu m, the insulation resistivity rho is greater than 1013 omega.cm, the ceramic dielectric material has low dielectric loss, low temperature rise and excellent capacity stability, the breakdown strength and the insulation resistivity of a ceramic body can be effectively improved, and the ceramic dielectric material can be well applied to a high-voltage-resistant resonant circuit. The ceramic dielectric material can be matched with a base metal Cu inner electrode, a base metal Ni inner electrode, a precious metal Ag inner electrode and a precious metal Ag-Pd inner electrode, and low cost and high performance of an MLCC device are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and particularly relates to a ceramic dielectric material for high-frequency MLCC and a preparation method thereof. Background Art

[0002] In recent years, with the intelligence, popularization and portability of electronic devices, electronic components have been continuously developing towards the direction of miniaturization, high frequency and low cost. As a main member of electronic components, capacitors are widely used in energy storage and information transmission. Among them, multilayer ceramic capacitors (MLCCs) are widely used in various devices due to their small size, large capacitance, good frequency characteristics and high reliability.

[0003] With the expansion of the global MLCC market, the industrial automation field needs to apply MLCCs to the AC / DC converters and DC / DC converter circuits of power supplies and inverters. For example, AC line filters and coupling capacitors combining primary and secondary both require an AC rated voltage of 250V or above. To reduce heat loss, in high-frequency switching applications of MLCCs, low-loss capacitors are generally required. Temperature-compensated MLCCs made of class I dielectric materials are often used. Such capacitors have extremely low dielectric loss, high insulation resistance, high breakdown voltage, excellent temperature characteristics and capacitance stability. In the temperature range of -55°C to +125°C, the capacitance change rate is less than ±30 ppm / °C, which very well meets the requirements of high breakdown voltage and resonant circuits for capacitors. At the same time, such capacitors have low power loss, can reduce the heat generated by the capacitors, and extend the service life of the capacitors.

[0004] Class I ceramic powders can be divided into three categories according to the dielectric constant: (1) low dielectric constant type, such as MgTiO3, Al2O3-TiO2 systems, etc.; (2) medium dielectric constant type, such as (Sr, Ca)(Zr, Ti)O3, (Zr, Sn)TiO4 systems, etc.; (3) high dielectric constant type, such as BaO-Ln2O3-TiO2 systems, etc.

[0005] However, the existing high-frequency dielectric materials mainly have two problems: (1) The inherent sintering temperature of the dielectric material is too high to meet the requirements of low-temperature sintering; (2) The anti-reduction performance of the dielectric material is poor, and its dielectric properties cannot be guaranteed when sintered in a neutral / reducing atmosphere. Summary of the Invention

[0006] The purpose of the present invention is to provide an MLCC ceramic dielectric material, a preparation method thereof and an application.

[0007] In the first aspect of the present invention, there is provided an MLCC ceramic dielectric material, comprising the following raw materials: a main component, a grain size uniform refining agent, and a sintering aid; the main component comprises (100 - x)CaCO3 - xSrCO3 - (100 - y)ZrO2 - yTiO2, where x and y are molar percentages, 10 ≤ x ≤ 90, 1 ≤ y ≤ 10; the grain size uniform refining agent comprises at least one of SiO2, Al2O3, and MgO; the sintering aid comprises at least one of H3BO3, Li2CO3, and K2CO3.

[0008] In some embodiments, 20 ≤ x ≤ 70, 3 ≤ y ≤ 8.

[0009] In some embodiments, 50 ≤ x ≤ 70, 7 ≤ y ≤ 8.

[0010] In some embodiments, the grain size uniform refining agent is a mixture of SiO2, Al2O3, and MgO, and the mass ratio of the three is SiO2:Al2O3:MgO = (1 - 10):(1 - 8):(1 - 5).

[0011] In some embodiments, the sintering aid is a mixture of H3BO3, Li2CO3, and K2CO3, and the mass ratio of the three is H3BO3:Li2CO3:K2CO3 = (1 - 10):(5 - 10):(5 - 10).

[0012] In some embodiments, the MLCC ceramic dielectric material comprises the following raw materials in parts by weight: 100 parts of the main component, 0.2 - 10 parts of the grain size uniform refining agent, and 0.05 - 10 parts of the sintering aid.

[0013] In some embodiments, 100 parts of the main component, 0.2 - 4 parts of the grain size uniform refining agent, and 0.1 - 10 parts of the sintering aid.

[0014] In some embodiments, the MLCC ceramic dielectric material further comprises an anti - reducing agent, and the anti - reducing agent comprises MnCO3.

[0015] In some embodiments, the weight part of the anti - reducing agent is 0 - 1 part.

[0016] In some embodiments, the weight part of the anti - reducing agent is 0.15 - 1 part.

[0017] In the second aspect of the present invention, there is provided a preparation method of an MLCC ceramic dielectric material, comprising: mixing the raw materials, followed by grinding, granulating, and sintering to obtain the MLCC ceramic dielectric material.

[0018] In the third aspect of the present invention, there is provided a preparation method of an MLCC ceramic dielectric material, comprising the following steps:

[0019] S1. Weigh the main component, the grain size uniform refiner and the sintering aid, grind, granulate and sinter them to obtain the calcined powder.

[0020] S2. Add an anti-reducing agent to the calcined powder, grind, granulate and dry it to obtain the MLCC ceramic dielectric material.

[0021] In some embodiments, in the step S1, the sintering process is as follows: with a heating rate of 4 - 6 °C / min, heat up to 630 - 780 °C, keep warm for 5 - 7 h, then with a heating rate of 8 - 12 °C / min, heat up to 875 - 1150 °C, keep warm for 0.5 - 1.5 h and then cool down to room temperature.

[0022] In some embodiments, the preparation method of the MLCC ceramic dielectric material provided by the present invention specifically includes the following steps:

[0023] (1) Weigh the main component, the grain size uniform refiner and the sintering aid in proportion, and then ball-mill and mix the materials for 4 - 6 h according to the ratio of material: water: φ5 zirconia balls: dispersant = 1:1:5:0.02 to obtain the raw material slurry.

[0024] (2) Pour the raw material slurry into a sand mill, sand mill for 5 - 20 cycles, discharge with pure water, and control the solid content of the slurry to be 20%.

[0025] (3) Use spray drying to prepare the raw material slurry with a solid content of 20% into spherical powder with the maximum sphere diameter not exceeding 5 μm.

[0026] (4) Place the spherical powder in an alumina crucible for calcination. The sintering process is as follows: heat up to 630 - 780 °C at a heating rate of 4 - 6 °C / min, keep warm for 5 - 7 h, then heat up to 875 - 1150 °C at a heating rate of 8 - 12 °C / min, keep warm for 0.5 - 1.5 h and then cool down to room temperature to obtain the calcined powder.

[0027] (5) Add the anti-reducing agent MnCO3 to the calcined powder, and then stir and mix evenly for 4 - 6 h according to the ratio of material: water: φ5 zirconia balls: dispersant = 1:1:5:0.02, and then carry out sand milling to obtain the porcelain powder slurry.

[0028] (6) Pour the obtained porcelain powder slurry into a sand mill, select 0.5 mm zirconia balls, control the sand milling linear speed at 8 m / s, sand mill until the slurry particle size D50 = 0.5 ± 0.05 μm, D90 = 1.0 ± 0.05, then discharge with pure water, and control the solid content of the slurry to be 20% to obtain the finished product formula powder slurry.

[0029] (7) Spray granulate the finished product formula powder slurry with a solid content of 20% obtained in step (6) using a spray drying tower into a powder in the form of solid spheres with a maximum sphere diameter not exceeding 5 μm to obtain the MLCC ceramic powder. Alternatively, place the finished product formula powder slurry with a solid content of 20% obtained in step (6) in an oven at 120 - 140 °C to dry it, then powder it with a powder grinder and pass it through a 100 - mesh sieve to obtain the MLCC ceramic powder.

[0030] In the fourth aspect of the present invention, there is provided an application of an MLCC ceramic dielectric material in a chip ceramic capacitor.

[0031] In the fifth aspect of the present invention, there is provided a chip multi - layer ceramic capacitor, which includes a dielectric layer, a plurality of inner electrodes alternately laminated with the dielectric layer, and end electrodes connected to the inner electrodes, and the dielectric layer includes the above - mentioned MLCC ceramic dielectric material.

[0032] In some embodiments, the material of the inner electrodes of the chip multi - layer ceramic capacitor is Cu, Ni, Pd or Ag - Pd.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The ceramic dielectric material of the present invention conforms to the C0G characteristic, the insulation resistivity ρ > 10 13 Ω·cm, has low dielectric loss, low temperature rise and excellent capacitance stability, can effectively improve the breakdown strength and insulation resistivity of the porcelain body, the breakdown strength ≥ 140 V / μm, and can be well applied to high - voltage - resistant and resonant circuits.

[0035] (2) By adjusting the ratio and content of the sintering aid and the grain - size uniform refinement agent, the present invention can serially adjust the sintering temperature of the porcelain powder to 950 - 1280 °C, can match the base - metal Cu inner electrode, Ni inner electrode and the noble - metal Ag, Ag - Pd inner electrodes, and realize the low - cost and high - performance of the MLCC device. Description of the Drawings

[0036] Figure 1 It is the cross - sectional morphology of the porcelain body after sintering of the wafer in Example 1.

[0037] Figure 2 It is the cross - sectional morphology of the porcelain body after sintering of the wafer in Example 8.

[0038] Figure 3 It is the cross - sectional morphology of the porcelain body after sintering of the wafer in Example 10.

[0039] Figure 4 It is the physical cross - sectional view of the MLCC device prepared from the ceramic powder in Example 1. Detailed Embodiments

[0040] The content of the present invention will be further described in detail through specific embodiments below. The specific embodiments do not represent limitations on the protection scope of the present invention. Some non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the protection scope of the present invention. The raw materials, reagents or devices used in the embodiments can all be obtained from conventional commercial channels or can be obtained by existing technical methods. Unless otherwise specified, the test or measurement methods are all conventional methods in the art.

[0041] The raw materials used in the embodiments of the present invention include nano-powders of CaCO3, SrCO3, ZrO2, TiO2, SiO2, Al2O3, MgO, MnCO3 and powders of H3BO3, Li2CO3, K2CO3. Among them, the purity of CaCO3 and SrCO3 powders is >99.9% and the particle size D50≤800nm; the purity of ZrO2 and TiO2 powders is >99.9% and the particle size D50≤300nm; the SiO2 powder is a spherical amorphous powder with a particle size D50≤200nm; the purity of Al2O3 powder is >99.9% and the particle size D50≤500nm; the purity of MgO powder is >99.9%, the particle size D50≤800nm and the water content <1%; the purity of MnCO3 powder is >99.9% and the particle size D50≤500nm; the purity of H3BO3, Li2CO3, and K2CO3 powders is >99.9%.

[0042] Preparation of MLCC ceramic dielectric materials

[0043] The raw materials and their addition amounts in the MLCC ceramic dielectric materials of Examples 1-15 and Comparative Examples 1-7 are shown in Table 1. Among them, the weight parts of the main components (100-x)CaCO3-xSrCO3-(100-y)ZrO2-yTiO2 in Examples 1-15 and Comparative Examples 1-7 are all 100 parts.

[0044] Table 1 Raw materials and their addition amounts in the MLCC ceramic dielectric materials of Examples 1-15 and Comparative Examples 1-7

[0045]

[0046]

[0047]

[0048] The preparation methods of the MLCC ceramic dielectric materials of Examples 1-15 and Comparative Examples 1, 4-7 include the following steps:

[0049] (1) Based on 100 parts of the main components of (100 - x)CaCO3 - xSrCO3 - (100 - y)ZrO2 - yTiO2, add 0.2 - 10 parts of the grain uniformly refining agent and 0.05 - 10 parts of the sintering aid, and weigh CaCO3, SrCO3, ZrO2, TiO2, SiO2, Al2O3, MgO, H3BO3, Li2CO3, and K2CO3 according to Table 1. Among them, x and y are molar percentages. The base material of the high-frequency porcelain powder is CaCO3, SrCO3, ZrO2, and TiO2. The grain uniformly refining agent is a mixture of SiO2, Al2O3, and MgO, and the mass ratio of the three is SiO2:Al2O3:MgO = a:b:c. The sintering aid is a mixture of H3BO3, Li2CO3, and K2CO3, and the mass ratio of the three is H3BO3:Li2CO3:K2CO3 = d:e:f.

[0050] (2) Put the raw material powders of the high-frequency porcelain powder base material, the grain uniformly refining agent, and the sintering aid weighed in step (1) into a horizontal ball mill tank, and weigh the raw materials, deionized water, φ5 zirconium balls, and dispersant according to the ratio of material:water:φ5 zirconium balls:dispersant = 1:1:5:0.02. After ball milling and mixing for 5 h, separate the slurry and the zirconium balls using a sieve.

[0051] (3) Pour the raw material slurry obtained in step (2) into a sand mill and sand mill for 5 cycles. After ensuring that the raw materials are fully mixed, discharge with pure water and control the solid content of the slurry to be 20%.

[0052] (4) Dry the raw material slurry with a solid content of 20% obtained in step (3) into spheres using a spray drying tower, control the spray drying process, and obtain dry powder as solid spheres with the maximum sphere diameter not exceeding 5 μm.

[0053] (5) Place the dry spherical powder obtained in step (4) in an alumina crucible for calcination. During the process of loading the powder into the crucible, there is no need to press or tamp, ensuring that the powder in the crucible is loose and does not exceed 2 / 3 of the crucible volume. Calcinate using a box-type sintering furnace. The sintering process is: heat up at a heating rate of 5 °C / min to 630 °C - 780 °C and hold for 6 h, then heat up at a heating rate of 10 °C / min to 875 - 1150 °C, hold for 1 h, and then cool down to room temperature with the furnace to obtain the calcined powder of the calcium zirconate base material.

[0054] (6) Add the anti-reducing agent MnCO3 (the addition amount is shown in Table 1) to the calcined powder of the calcium zirconate base material obtained in step (5). Weigh the base material, auxiliary materials, deionized water, φ5 zirconium balls, and dispersant according to the ratio of material:water:φ5 zirconium balls:dispersant = 1:1:5:0.02, place them in a horizontal ball mill tank, ball mill and mix for 5 h, and then separate the slurry and the zirconium balls using a sieve to obtain the porcelain powder slurry.

[0055] (7) Pour the porcelain powder slurry obtained in step (6) into a sand mill for sanding. The sand mill uses 0.5 mm zirconium balls, and the sanding linear velocity is controlled at 8 m / s. After sanding until the particle size of the slurry is D50 = 0.5 ± 0.05 μm and D90 = 1.0 ± 0.05, discharge with pure water and control the solid content of the slurry to be 20% to obtain the finished product formula powder slurry.

[0056] (8) Spray granulate the finished product formula powder slurry with a solid content of 20% obtained in step (7) using a spray drying tower into a powder in the form of solid spheres with a maximum sphere diameter not exceeding 5 μm, that is, obtain the MLCC ceramic powder.

[0057] The difference between the preparation method of Comparative Example 2 and that of Example 1 is only that in step (1), BaCO3 is used to replace MgO. That is to say, the grain uniform refining agent of Comparative Example 2 is a mixture of SiO2, Al2O3, and BaCO3, and the mass ratio of the three is SiO2:Al2O3:BaCO3 = a:b:c = 8:5:3.

[0058] The difference between the preparation method of Comparative Example 3 and that of Example 1 is only that in step (1), Na2CO3 is used to replace K2CO3. That is to say, the sintering aid of Comparative Example 3 is a mixture of H3BO3, Li2CO3, and Na2CO3, and the mass ratio of the three is H3BO3:Li2CO3:Na2CO3 = d:e:f = 2:6:6.

[0059] Performance testing of MLCC ceramic dielectric materials

[0060] For the MLCC ceramic powders obtained in Examples 1 - 15 and Comparative Examples 1 - 7, granulate by adding a 4 wt% PVA aqueous solution according to the ratio of MLCC ceramic powder:PVA = 10 g:2.0 ml, and press into round sheet samples with a thickness of 1.3 - 1.5 mm under the condition of 1.8 - 2.2 MPa. The round sheet sintering process is: degreasing temperature 500 °C, degreasing time 2 h, sintering temperature between 980 - 1280 °C, and heat preservation time 4 h. The cross-sectional morphologies of the porcelain bodies after sintering of the round sheets in Examples 1, 8, and 10 are as Figures 1-3 shown.

[0061] The electrical properties after sintering of Examples 1 - 15 and Comparative Examples 1 - 7 at their respective optimal sintering temperatures are shown in Table 2.

[0062] Among them, Cp and tanδ at 1MHz were tested using an Agilent E4980A precision LCR meter, and εr was calculated from Cp; the insulation resistance was tested using a Hioki SM7110 insulation resistance tester from Japan and then converted into insulation resistivity through a formula; the porcelain body grain size was obtained by statistically averaging all grain sizes in the SEM cross-sectional image of the porcelain body at 15000 times magnification; the temperature coefficients of the wafer and MLCC device were tested using a dielectric temperature spectrometer. The breakdown strength (BDV) of the MLCC device was obtained by testing with a DC withstand voltage breakdown strength tester.

[0063] Table 2 Electrical properties of Examples 1-15 and Comparative Examples 1-7

[0064]

[0065]

[0066] It can be seen from Example 1 and Comparative Example 2 that when BaCO3 is used to replace MgO in the grain uniform refining agent, the dielectric loss of the prepared MLCC ceramic dielectric material increases, the resistivity decreases significantly, and it does not conform to the C0G characteristics.

[0067] It can be seen from Example 1 and Comparative Example 3 that when Na2CO3 is used to replace K2CO3 in the sintering aid, the dielectric loss of the prepared MLCC ceramic dielectric material increases significantly, and the resistivity decreases significantly.

[0068] It can be seen from Example 1 and Comparative Example 4 that when the mass ratio of the grain uniform refining agents SiO2, Al2O3, and MgO exceeds a certain range, the resistivity of the prepared MLCC ceramic dielectric material decreases significantly.

[0069] It can be seen from Example 1 and Comparative Example 5 that when the addition amount of the grain uniform refining agent is lower than a certain range, the dielectric loss of the prepared MLCC ceramic dielectric material increases, and the resistivity decreases significantly.

[0070] It can be seen from Example 1 and Comparative Example 6 that when the mass ratio of the sintering aids H3BO3, Li2CO3, and K2CO3 exceeds a certain range, the dielectric loss of the prepared MLCC ceramic dielectric material increases significantly, and the resistivity decreases significantly.

[0071] It can be seen from Example 1 and Comparative Example 7 that when the addition amount of the sintering aid exceeds a certain range, the dielectric loss of the prepared MLCC ceramic dielectric material increases significantly, and the resistivity decreases significantly.

[0072] Preparation of MLCC devices

[0073] The MLCC ceramic powders of Examples 1, 8, 10, and 15 were formulated into tape-casting slurries, and MLCC devices were prepared through processes such as tape-casting, printing, laminating, cutting, sintering, chamfering, sealing the ends, and electroplating. The cross-sectional view of the physical object of the MLCC device prepared from the MLCC ceramic powder of Example 1 is as shown in Figure 4 . The performance test data of the MLCC devices prepared from the ceramic powders of Examples 1, 8, 10, and 15 are shown in Table 3.

[0074] Table 3 Performance test data of the MLCC devices prepared from the ceramic powders of Examples 1, 8, 10, and 15

[0075]

[0076] In summary, the MLCC ceramic dielectric material described in the present invention not only conforms to the C0G characteristics, but also has low dielectric loss, low temperature rise, and excellent capacitance stability. It can effectively improve the breakdown strength and insulation resistivity of the ceramic body, and has good application prospects.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An MLCC ceramic dielectric material, characterized in that, It includes the following raw materials: main component, grain size uniform refiner and sintering aid; The main component includes (100 - x)CaCO3 - xSrCO3 - (100 - y)ZrO2 - yTiO2, where x and y are molar percentages, 10 ≤ x ≤ 90, 1 ≤ y ≤ 10; The grain size uniform refiner includes at least one of SiO2, Al2O3 and MgO; The sintering aid includes at least one of H3BO3, Li2CO3 and K2CO3.

2. The MLCC ceramic dielectric material according to claim 1, wherein The main component is (100 - x)CaCO3 - xSrCO3 - (100 - y)ZrO2 - yTiO2, where 20 ≤ x ≤ 70, 3 ≤ y ≤ 8; preferably, 50 ≤ x ≤ 70, 7 ≤ y ≤ 8.

3. The MLCC ceramic dielectric material according to claim 1, characterized in that The grain size uniform refiner is a mixture of SiO2, Al2O3 and MgO, and the mass ratio of the three is SiO2:Al2O3:MgO = (1 - 10):(1 - 8):(1 - 5).

4. The MLCC ceramic dielectric material according to claim 1, characterized in that, The sintering aid is a mixture of H3BO3, Li2CO3 and K2CO3, and the mass ratio of the three is H3BO3:Li2CO3:K2CO3 = (1 - 10):(5 - 10):(5 - 10).

5. The MLCC ceramic dielectric material according to claim 1, characterized in that, It includes the following raw materials in parts by weight: 100 parts of main component, 0.2 - 10 parts of grain size uniform refiner and 0.05 - 10 parts of sintering aid; preferably, 100 parts of main component, 0.2 - 4 parts of grain size uniform refiner and 0.1 - 10 parts of sintering aid.

6. The MLCC ceramic dielectric material according to claim 1, wherein It also includes an anti - reducing agent, and the anti - reducing agent includes MnCO3; preferably, the weight part of the anti - reducing agent is 0 - 1 part; preferably, the weight part of the anti - reducing agent is 0.15 - 1 part.

7. A preparation method of the MLCC ceramic dielectric material as described in any one of claims 1-6, characterized in that, It includes: Mix the raw materials, and obtain the MLCC ceramic dielectric material through grinding, granulation and sintering.

8. A preparation method of the MLCC ceramic dielectric material as described in claim 6, characterized in that, It includes the following steps: S1. Weigh the main component, grain size uniform refiner and sintering aid, and obtain the calcined powder through grinding, granulation and sintering; S2. Add the anti - reducing agent to the calcined powder, and obtain the MLCC ceramic dielectric material through grinding, granulation and drying; Preferably, in step S1, the sintering process is: use a heating rate of 4 - 6°C / min, heat up to 630 - 780°C, keep warm for 5 - 7 h, then use a heating rate of 8 - 12°C / min, heat up to 875 - 1150°C, keep warm for 0.5 - 1.5 h and then cool down to room temperature.

9. Application of an MLCC ceramic dielectric material as described in any one of claims 1 - 6 in a chip ceramic capacitor.

10. A chip multilayer ceramic capacitor, the capacitor comprising a dielectric layer, a plurality of internal electrodes alternately laminated with the dielectric layer, and end electrodes connected to the internal electrodes, characterized in that, The dielectric layer includes an MLCC ceramic dielectric material as described in any one of claims 1 - 6.

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