A multilayer chip ceramic capacitor

Abstract

The application provides a multilayer chip ceramic capacitor, which comprises a ceramic body, cover sheets and outer electrode layers, the ceramic body comprises a plurality of dielectric layers and a plurality of inner electrode layers which are alternately laminated, the cover sheets are located on the upper and lower surfaces of the ceramic body, the cover sheets comprise inner cover sheets and outer cover sheets, one surface of the inner cover sheet is attached to the ceramic body, and the other surface is attached to one surface of the outer cover sheet; the materials of the inner cover sheets, the outer cover sheets and the dielectric layers are the same, and are all BaTiO3-based materials. The application can reduce the stress of the R angle of the chip ceramic capacitor after burning, reduce the proportion of the octagonal crack, and increase the bending strength of the chip ceramic capacitor by more than 17%, and the bending NG rate is reduced to 0%. The application is simple to implement and low in production cost.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramic materials and components technology, and particularly relates to a multilayer chip ceramic capacitor. Background Technology

[0002] Multilayer ceramic chip capacitors (MLCCs) are a new type of electronic component, mainly used in automobiles, aerospace, mobile phones, computers, and other fields. With the continuous development of technology, the number of MLCCs used in an electronic product is increasing. MLCCs are mainly used through surface mounting. If the MLCC's tensile strength against the PCB is poor, it will cause the electronic product to short-circuit and burn out during use. Therefore, MLCC products are required to have good bending strength to meet the mounting requirements.

[0003] The actual fracture strength of ceramic materials is much lower than the theoretical fracture strength. This is because MLCCs have pores, cracks, and glassy phases at grain boundaries during the manufacturing process, and sometimes various defects exist within the grains. These microstructural factors lead to low strength in ceramics. High-capacitance products have relatively high strength due to the high number of electrode layers, but low-capacitance products have fewer electrode layers, resulting in lower strength. They are prone to breakage during transportation and surface mounting, causing capacitor failure. MLCC products consist of a dielectric layer, inner electrode layer, cover plate, and outer electrode forming a whole. Generally, the sintering activity of the cover plate and dielectric layer is similar, regardless of whether they are made of the same or different materials. In addition, due to the adhesive removal characteristics of MLCC products, the porosity of the cover plate is significantly higher than that of the dielectric layer. Without the reinforcement of electrode layers, microcracks often appear at the four corners of the product. During the mounting process, these cracks propagate under tensile stress and eventually break.

[0004] Currently, several studies have been conducted to address the issue of low strength in low-capacity MLCC products: 1) One MLCC product is designed with a sandwich structure, where the cover sheet consists of a standard cover sheet, a buffer layer, and a reinforcing layer. The reinforcing layer has a higher strength than the buffer layer, which in turn has a higher strength than the standard layer, thus improving the product's strength. However, due to the different materials used in the cover sheet and its relatively complex structure, product cracking often occurs in actual production due to misaligned cover sheets. Furthermore, the different materials used in the reinforcing layer, buffer layer, standard layer, and dielectric layer make the cover sheet prone to cracking during sintering. 2) Reducing the particle size of the raw material powder reduces crystal defects, thereby improving its strength. However, this presents a series of problems, including difficulties in raw material dispersion, reduced product capacity, and increased costs. 3) Improving product strength through a suspension design increases the cost of MLCCs due to the addition of an extra electrode layer, and the incompleteness of the nickel electrode leads to difficulties in adhesive removal. 4) Doping alters the grain boundary characteristics, preventing stress concentration and improving strength. However, doping generally leads to the deterioration of other properties. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a multilayer chip ceramic capacitor with good bending strength and is not prone to cracking.

[0006] A second aspect of the present invention provides a method for preparing the multilayer chip ceramic capacitor described in the first aspect.

[0007] A third aspect of the present invention provides for the application of the multilayer ceramic chip capacitor described in the first aspect in electronic products.

[0008] According to the present invention, a multilayer chip ceramic capacitor includes a ceramic body, a cover plate, and an external electrode layer. The ceramic body comprises multiple dielectric layers and multiple internal electrode layers stacked alternately. The cover plate is located on the upper and lower surfaces of the ceramic body. The cover plate includes an inner cover plate and an outer cover plate. One side of the inner cover plate is attached to the ceramic body, and the other side is attached to one side of the outer cover plate. The materials constituting the inner cover plate, the outer cover plate, and the dielectric layer are the same, and all are BaTiO3-based ceramic materials.

[0009] In some embodiments of the present invention, the BaTiO3-based ceramic material is a BaTiO3 ceramic material or an element-doped BaTiO3 ceramic material. The element-doped BaTiO3 ceramic material is a BaTiO3 ceramic material doped with one or two divalent elements, including but not limited to Ca and Sr; or it is a BaTiO3 ceramic material doped with one or two trivalent or tetravalent elements, including but not limited to Zr and Y.

[0010] In some embodiments of the present invention, the inner cover and the outer cover have different specific surface areas, with the specific surface area of ​​the inner cover being greater than that of the outer cover.

[0011] In this invention, during sintering, the inner cover sheet has a larger specific surface area than the outer cover sheet, resulting in a greater sintering driving force and a larger sintering shrinkage, which in turn generates tensile stress on the outer cover sheet. At the same time, the inner cover sheet has a larger specific surface area, smaller grains, and more grain boundaries, which leads to a narrower range of movement for grain boundaries and dislocations, thus making the strength of the inner cover sheet higher than that of the outer cover sheet.

[0012] In some embodiments of the present invention, the specific surface area of ​​the outer cover sheet is the same as that of the dielectric layer.

[0013] In some embodiments of the present invention, the specific surface area of ​​the inner cover is 3.1 m². 2 / g~4.1m 2 / g.

[0014] In some embodiments of the present invention, the specific surface area of ​​the outer cover is 2.7 m². 2 / g~3.2m 2 / g.

[0015] In some embodiments of the present invention, the thickness of the cover sheet is 150 μm to 300 μm.

[0016] In this invention, the total thickness of the cover sheet is limited. When its total thickness is less than the range of this invention, the reliability of the product will decrease. When its total thickness is greater than the range of this invention, due to the limitations of low-capacity product specifications, the dielectric layer must be thinned, resulting in a decrease in product reliability and bending strength.

[0017] In some embodiments of the present invention, the volume of the inner cover and the volume of the outer cover are different percentages of the total cover volume.

[0018] In some preferred embodiments of the present invention, taking a cover plate located on the upper surface of the ceramic body or a cover plate located on the lower surface of the ceramic body as an example, the difference in specific surface area between the inner cover plate and the outer cover plate is 0.6 m². 2 / g~1.2m 2 / g.

[0019] In this invention, let F1 be the tensile stress generated by the inner cover plate on the outer cover plate, and F2 be the compressive stress generated by the outer cover plate on the inner cover plate. Then, the residual compressive stress of the product is F3 = F1 - F2. During the mounting process of MLCC products, the residual compressive stress F3 must be overcome first, and then the strength of the inner cover plate must be overcome, thereby preventing the MLCC product from cracking and damaging the electrodes, and improving the bending strength of low-capacitance products. However, the difference in specific surface area between the outer and inner cover plates cannot be infinitely large. If the difference in specific surface area between the outer and inner cover plates is lower than the range of this invention, the residual pressure F3 will be too small, and the strength of the product will not be improved. If the difference in specific surface area is greater than the range of this invention, the compressive stress at the dielectric layer and the outer electrode will be too large. When the product is subjected to thermal shock, it is more likely to develop thermal shock cracks, especially the proportion of octagonal cracks after copper burning will increase significantly.

[0020] In some preferred embodiments of the present invention, the cover plate located on the upper surface of the ceramic body or the cover plate located on the lower surface of the ceramic body is taken as the object, and the volume of the inner cover plate accounts for 35% to 60% of the volume of the cover plate.

[0021] In some preferred embodiments of the present invention, the cover plate located on the upper surface of the ceramic body or the cover plate located on the lower surface of the ceramic body is taken as the object, and the volume of the outer cover plate accounts for 40% to 65% of the volume of the cover plate.

[0022] In this invention, the percentage of the outer and inner cover sheets in the total volume of the cover sheet also affects the magnitude of residual stress and product performance. Since the stress interaction between the outer and inner cover sheets is mutual, the larger the percentage of the inner cover sheet's volume in the total cover sheet volume, that is, the thicker the inner cover sheet, the greater the residual stress. However, the total thickness of the product cover sheet is controlled. The larger the percentage of the inner cover sheet's volume in the total cover sheet volume, the smaller the percentage of the outer cover sheet's volume in the total cover sheet volume will be. When the percentage of the inner cover sheet's volume exceeds the range of this invention, it will lead to an increase in stress between the outer and inner cover sheets, and the outer cover sheet cannot buffer this stress. After sintering, the outer cover sheet is prone to cracking. Conversely, when the percentage of the inner cover sheet's volume is below the range of this invention, the tensile stress of the inner cover sheet on the outer cover sheet is too small, which will cause the residual compressive stress of the product to almost disappear. Moreover, the inner cover sheet itself is designed to have higher strength than the outer cover sheet. When the percentage of the outer cover sheet's volume is too large, it will be accompanied by a decrease in the overall strength of the cover sheet, resulting in poor bending strength of the product.

[0023] In some more preferred embodiments of the present invention, the difference in specific surface area between the inner cover and the outer cover is 0.8 m². 2 / g~1.0m 2 / g.

[0024] In some more preferred embodiments of the present invention, the volume of the inner cover sheet accounts for 40% to 50% of the volume of the cover sheet.

[0025] In some more preferred embodiments of the present invention, the volume of the outer cover sheet accounts for 50% to 60% of the volume of the cover sheet.

[0026] According to a second aspect of the present invention, a method for manufacturing the multilayer chip ceramic capacitor described in the first aspect is provided, comprising the following steps:

[0027] S1: Using the same ceramic slurry as the dielectric layer, outer and inner cover sheets with different specific surface areas are obtained by adjusting the dispersion degree of the ceramic slurry;

[0028] S2: The inner cover sheet and outer cover sheet described in S1 are sequentially stacked on the upper and lower surfaces of the ceramic body, respectively, and then encapsulated, pressed, cut, de-adhesiveed, sintered, ball-milled, and nickel-plated at the ends to obtain the multilayer chip ceramic capacitor.

[0029] In some embodiments of the present invention, the ceramic slurry in S1 comprises BaTiO3-based ceramic powder.

[0030] In some embodiments of the present invention, the ceramic slurry formulation comprises, by weight, 53-63 parts of BaTiO3-based ceramic powder, 3.5-5 parts of binder, 0.3-0.6 parts of dispersant, 2-3.5 parts of plasticizer, and 30-40 parts of solvent; the BaTiO3-based ceramic powder is selected from BaTiO3 ceramic materials or element-doped BaTiO3 ceramic materials, including but not limited to barium strontium titanate and calcium barium titanate; the binder is polyvinyl butyral; the dispersant is selected from at least one of polyesteramide, polycarboxylic acid ammonium salt, and polymethacrylamide; the plasticizer is selected from at least one of dioctyl phthalate, dibutyl phthalate, and dibutyl sebate; and the solvent is a mixture of toluene and isopropanol in a volume ratio of toluene:isopropanol = 2:3.

[0031] In some embodiments of the present invention, the preparation process of the above-mentioned ceramic slurry is as follows:

[0032] (1) Dissolve the dispersant in the solvent according to the above proportions to form slurry A;

[0033] (2) Mix the BaTiO3-based ceramic powder with the slurry A, grind at a frequency of 35Hz to 40Hz, and grind for a cycle time of 55min to 115min to obtain slurry B;

[0034] (3) Mix the adhesive, plasticizer and slurry B, grind at a frequency of 45Hz to 50Hz, and grind for 115min to 120min to obtain slurry C, which is the final slurry.

[0035] In this invention, the process of casting outer and inner cover sheets with different specific surface areas by adjusting the dispersion degree of ceramic slurry as described in S1 specifically involves controlling the grinding frequency and grinding cycle time of the ceramic slurry to obtain slurries with different particle sizes and different dispersion degrees, thereby enabling the casting of outer and inner cover sheets with different specific surface areas.

[0036] In some embodiments of the present invention, the specific surface area of ​​the inner cover sheet in S1 is greater than that of the outer cover sheet, and the difference in specific surface area between the inner cover sheet and the outer cover sheet is 0.6 m². 2 / g~1.2m 2 / g.

[0037] In some embodiments of the present invention, the thickness of the inner cover and the outer cover on the upper or lower surface of the ceramic body is 150 μm to 300 μm.

[0038] In some preferred embodiments of the present invention, the cover plate located on the upper surface of the ceramic body or the cover plate located on the lower surface of the ceramic body is taken as the object, and the volume of the inner cover plate accounts for 35% to 60% of the volume of the cover plate.

[0039] In some preferred embodiments of the present invention, the encapsulation pressing in S2 is performed by hot isostatic pressing, with a pressure of 90-110 MPa, a temperature of 75°C-85°C, and a holding time of 8-12 minutes.

[0040] In some preferred embodiments of the present invention, the temperature for discharging adhesive in step S2 is 290°C to 310°C, and the time is 30h to 40h.

[0041] In some preferred embodiments of the present invention, the sintering temperature in S2 is 1300℃~1400℃ and the time is 1.5h~2.5h.

[0042] In some preferred embodiments of the present invention, the ball milling process described in S2 is followed by copper coating and copper sintering.

[0043] In some preferred embodiments of the present invention, S2, after nickel plating of the end, further includes tin plating on the nickel metal.

[0044] According to a third aspect of the present invention, an application of the multilayer chip ceramic capacitor described in the first aspect is proposed in electronic products.

[0045] The beneficial effects of this invention are as follows:

[0046] The multilayer ceramic chip capacitor of the present invention has good bending strength, which is improved by more than 17% and the bending failure rate can be reduced to 0%; it does not affect the electrical performance, reliability and other performance of MLCC products; it can also reduce the stress of the R-angle after the MLCC product is burned and reduce the proportion of octagonal cracks; it is simple to implement and has low production cost. Attached Figure Description

[0047] Figure 1 This is a simplified illustration of the position of the cover plate of the multilayer ceramic chip capacitor of the present invention;

[0048] Figure 2 This is a flowchart illustrating the preparation of slurry in the embodiments and comparative examples of the present invention;

[0049] Figure 3 This is a micrograph of the multilayer chip ceramic capacitor, which is a comparative example of the present invention (Example 2). Detailed Implementation

[0050] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0051] The ceramic slurry described in this invention is commercially available or can be prepared in-house. The ceramic slurry formulations used in the following examples and comparative examples, by weight, include 53-63 parts barium titanate ceramic powder, 3.5-5 parts polyvinyl butyral, 0.3-0.6 parts polyesteramide, 2-3.5 parts dioctyl phthalate, and 30-40 parts a mixture of toluene and isopropanol in a volume ratio of 2:3. The specific preparation process is as follows: Figure 2 process.

[0052] Example 1

[0053] This embodiment describes the fabrication of a multilayer chip ceramic capacitor, the specific process of which is as follows:

[0054] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 40 Hz for a grinding cycle time of 65 min to obtain slurry B1; mix the adhesive and plasticizer with slurry B1, and grind at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C1, which is the specific gravity of the inner cover sheet used in this embodiment, which is 3.52 m. 2 / g of slurry 1;

[0055] The dispersant is dissolved in the solvent according to the above proportions to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 35 Hz for a grinding cycle time of 76 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C2, which is the specific gravity of 2.92m used in the outer cover sheet of this embodiment. 2 / g of slurry 2;

[0056] (2) The slurry 1 and slurry 2 obtained in step (1) are cast and cast respectively, with a thickness of 15 μm, to obtain film strip 1 and film strip 2 respectively.

[0057] (3) Screen printing is performed on the film strip 2 obtained in step (2). Conventional nickel electrode paste is used for printing electrodes to obtain a printed sheet with electrode patterns.

[0058] (4) The membrane strips obtained in steps (3) and (2) are stacked according to the formula D. x Cy (AB) z C y D x The stacked layers are stacked to obtain a stacked body, where A and B represent the printed sheets obtained in step (3), Z represents the number of electrode layers of the multilayer ceramic capacitor, which is determined by the capacitance, D represents the outer cover sheet, using film tape 2, x represents the number of layers of the outer cover sheet, which is determined by the volume fraction of the cover sheet occupied by the outer cover sheet, C represents the inner cover sheet, using film tape 1, and y represents the number of layers of the inner cover sheet, which is determined by the volume fraction of the cover sheet occupied by the inner cover sheet. In this embodiment, the volume of the inner cover sheet accounts for 45% of the cover sheet volume, and the volume of the outer cover sheet accounts for 55% of the cover sheet volume.

[0059] (5) The stacked body obtained in step (4) is encapsulated and pressed by hot isostatic pressing at a pressure of 100 MPa and a temperature of 80°C for 10 min. Then, it is cut into green blanks with a length of 2.17 mm to 2.22 mm, a width of 1.38 mm to 1.42 mm, and a height of 1.00 mm to 1.11 mm (cutting tolerance).

[0060] (6) The green body obtained in step (5) is subjected to debinding treatment at 300°C for 35 hours in an air atmosphere, and then fired at 1310°C for 2 hours in a mixed atmosphere of nitrogen, hydrogen and water vapor to obtain the sintered ceramic body.

[0061] (7) The sintered ceramic body obtained in step (6) is ball-milled using a high-speed ball mill to fully expose the internal electrodes of the ceramic body on both ends. Then, external electrodes Cu are coated on both ends of the sintered ceramic body, dried at 110℃ / 10min, and then copper is fired at 800℃ for 7min in a mixed atmosphere of air and nitrogen to form external electrodes.

[0062] (8) The surface of the external electrode obtained in step (7) is first plated with a layer of nickel metal substrate by electroplating deposition, and then a layer of tin metal is plated on the nickel metal to produce a multilayer chip ceramic capacitor.

[0063] Example 2

[0064] This embodiment describes the fabrication of a multilayer chip ceramic capacitor, the specific process of which is as follows:

[0065] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 40 Hz for a grinding cycle time of 77 min to obtain slurry B1; mix the adhesive and plasticizer with slurry B1, and grind at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C1, which is the slurry with a specific gravity of 3.7 m used in the inner cover sheet of this embodiment. 2 / g of slurry 1;

[0066] The dispersant is dissolved in the solvent according to the above proportions to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 35 Hz for 88 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for 120 min to obtain slurry C2, which is the specific gravity of the outer cover sheet used in this embodiment, which is 2.94 m. 2 / g of slurry 2;

[0067] The subsequent processes (2) to (8) are the same as in Example 1 and will not be repeated here.

[0068] Example 3

[0069] This embodiment describes the fabrication of a multilayer chip ceramic capacitor, the specific process of which is as follows:

[0070] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 40 Hz for 85 min to obtain slurry B1; mix the binder and plasticizer with slurry B1, and grind at a frequency of 48 Hz for 120 min to obtain slurry C1, which is the specific gravity of the inner cover sheet used in this embodiment, which is 3.76 m. 2 / g of slurry 1;

[0071] The dispersant is dissolved in the solvent according to the above proportions to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 35 Hz for a grinding cycle time of 93 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C2, which is the specific gravity of 2.96m used in the outer cover sheet of this embodiment. 2 / g of slurry 2;

[0072] The subsequent processes (2) to (8) are the same as in Example 1 and will not be repeated here.

[0073] Example 4

[0074] This embodiment describes the fabrication of a multilayer chip ceramic capacitor, the specific process of which is as follows:

[0075] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 40 Hz for 100 min to obtain slurry B1; mix the adhesive and plasticizer with slurry B1, and grind at a frequency of 48 Hz for 120 min to obtain slurry C1, which is the specific gravity of the inner cover sheet used in this embodiment, which is 3.95m. 2 / g of slurry 1;

[0076] The dispersant is dissolved in the solvent according to the above proportions to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 37 Hz for a grinding cycle time of 75 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C2, which is the specific gravity of the outer cover sheet used in this embodiment, which is 3.03 m. 2 / g of slurry 2;

[0077] The subsequent processes (2) to (8) are the same as in Example 1 and will not be repeated here.

[0078] Example 5

[0079] This embodiment describes the fabrication of a multilayer chip ceramic capacitor, the specific process of which is as follows:

[0080] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 40 Hz for a grinding cycle time of 105 min to obtain slurry B1; mix the adhesive and plasticizer with slurry B1, and grind at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C1, which is the 4.05m specific gravity used in the inner cover sheet of this embodiment. 2 / g of slurry 1;

[0081] The dispersant is dissolved in the solvent according to the above proportions to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 37 Hz for a grinding cycle time of 86 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C2, which is the specific gravity of 3.05m used in the outer cover sheet of this embodiment. 2 / g of slurry 2;

[0082] The subsequent processes (2) to (8) are the same as in Example 1 and will not be repeated here.

[0083] Example 6

[0084] This embodiment describes the fabrication of a multilayer chip ceramic capacitor, the specific process of which is as follows:

[0085] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 40 Hz for a grinding cycle time of 115 min to obtain slurry B1; mix the adhesive and plasticizer with slurry B1, and grind at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C1, which is the slurry with a specific gravity of 4.10 m used in the inner cover sheet of this embodiment. 2 / g of slurry 1;

[0086] The dispersant is dissolved in the solvent according to the above proportions to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 35 Hz for a grinding cycle time of 68 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C2, which is the specific gravity of 2.90m used in the outer cover sheet of this embodiment. 2 / g of slurry 2;

[0087] The subsequent processes (2) to (8) are the same as in Example 1 and will not be repeated here.

[0088] Example 7

[0089] This embodiment prepares a multilayer chip ceramic capacitor. The specific process is roughly the same as in embodiment 4. In this embodiment, the specific surface area of ​​the inner and outer cover plates is the same as in embodiment 4, but the percentage of the cover plate volume is different; the volume fraction of the inner cover plate is 60%; and the volume fraction of the outer cover plate is 40%.

[0090] Example 8

[0091] This embodiment prepares a multilayer chip ceramic capacitor. The specific process is roughly the same as in embodiment 4. In this embodiment, the specific surface area of ​​the inner and outer cover plates is the same as in embodiment 4, but the percentage of the total cover plate volume is different; the volume fraction of the inner cover plate is 50%; and the volume fraction of the outer cover plate is 50%.

[0092] Example 9

[0093] This embodiment prepares a multilayer chip ceramic capacitor. The specific process is roughly the same as in embodiment 4. In this embodiment, the specific surface area of ​​the inner and outer cover plates is the same as in embodiment 4, but the percentage of the total cover plate volume is different; the volume fraction of the inner cover plate is 45%; and the volume fraction of the outer cover plate is 55%.

[0094] Example 10

[0095] This embodiment prepares a multilayer chip ceramic capacitor. The specific process is roughly the same as in embodiment 4. In this embodiment, the specific surface area of ​​the inner and outer cover plates is the same as in embodiment 4, but the percentage of the total cover plate volume is different; the volume fraction of the inner cover plate is 40%; and the volume fraction of the outer cover plate is 60%.

[0096] Example 11

[0097] This embodiment prepares a multilayer chip ceramic capacitor. The specific process is roughly the same as in embodiment 4. In this embodiment, the specific surface area of ​​the inner and outer cover plates is the same as in embodiment 4, but the percentage of the total cover plate volume is different; the volume fraction of the inner cover plate is 35%; and the volume fraction of the outer cover plate is 65%.

[0098] Comparative Example 1

[0099] This comparative example prepared a multilayer chip ceramic capacitor. The main difference from Example 1 is that the difference in specific surface area of ​​the outer cover plates does not fall within the range of the technical solution of this invention; the difference in specific surface area is too small. The specific process is as follows:

[0100] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 40 Hz for a grinding cycle time of 58 min to obtain slurry B1; mix the adhesive and plasticizer with slurry B1, and grind at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C1, which is the slurry with a specific gravity of 3.25 m used in the inner cover sheet of this embodiment. 2 / g of slurry 1;

[0101] The dispersant is dissolved in the solvent according to the above proportions to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 35 Hz for 82 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for 120 min to obtain slurry C2, which is the specific gravity of the outer cover sheet used in this embodiment, which is 2.93 m. 2 / g of slurry 2;

[0102] The subsequent processes (2) to (8) are the same as in Example 1 and will not be repeated here.

[0103] Comparative Example 2

[0104] This comparative example prepared a multilayer chip ceramic capacitor. The main difference from Example 1 is that the difference in specific surface area of ​​the outer cover plates does not fall within the range of the technical solution of this invention; the difference in specific surface area is too large. The specific process is as follows:

[0105] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 40 Hz for a grinding cycle time of 115 min to obtain slurry B1; mix the adhesive and plasticizer with slurry B1, and grind at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C1, which is the 4.1 m specific gravity used in the inner cover sheet of this embodiment. 2 / g of slurry 1;

[0106] The dispersant is dissolved in the solvent according to the above proportions to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 35 Hz for a grinding cycle time of 55 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C2, which is the specific gravity of 2.70m used in the outer cover sheet of this embodiment. 2 / g of slurry 2;

[0107] The subsequent processes (2) to (8) are the same as in Example 1 and will not be repeated here.

[0108] Comparative Example 3

[0109] This comparative example prepared a multilayer chip ceramic capacitor. The main difference from Example 1 is that the specific surface area of ​​the inner and outer cover plates is the same. The specific process is as follows:

[0110] (1) Dissolve the dispersant in the solvent according to the above ratio to form slurry A1; mix the barium titanate ceramic powder with slurry A1, and grind at a frequency of 37 Hz for a grinding cycle time of 105 min to obtain slurry B1; mix the adhesive and plasticizer with slurry B1, and grind at a frequency of 48 Hz for a grinding cycle time of 120 min to obtain slurry C1, which is the slurry with a specific gravity of 3.15 m used in the inner cover sheet of this embodiment. 2 / g of slurry 1;

[0111] The dispersant is dissolved in the solvent according to the above ratio to form slurry A2; the barium titanate ceramic powder is mixed with slurry A2 and ground at a frequency of 37 Hz for 105 min to obtain slurry B2; the binder and plasticizer are mixed with slurry B2 and ground at a frequency of 48 Hz for 120 min to obtain slurry C2, which is the slurry with a specific gravity of 3.15 m used in the outer cover sheet of this embodiment. 2 / g of slurry 2;

[0112] The subsequent processes (2) to (8) are the same as in Example 1 and will not be repeated here.

[0113] Comparative Example 4

[0114] This comparative example prepares a multilayer chip ceramic capacitor. The main difference from Examples 4 and 7-11 is that the percentage of the inner and outer cover plates in the total cover plate volume does not fall within the scope of the technical solution of this invention; in this comparative example, the volume fraction of the inner cover plate is 80% and the volume fraction of the outer cover plate is 20%. The remaining specific processes are as described in Example 4.

[0115] Comparative Example 5

[0116] This comparative example prepares a multilayer chip ceramic capacitor. The main difference from Examples 4 and 7-11 is that the percentage of the inner and outer cover plates in the total cover plate volume does not fall within the scope of the technical solution of this invention; in this comparative example, the volume fraction of the inner cover plate is 20% and the volume fraction of the outer cover plate is 80%. The remaining specific processes are the same as in Example 4.

[0117] The parameters of Examples 1-11 and Comparative Examples 1-5 are shown in Table 1 below:

[0118] Table 1

[0119]

[0120]

[0121] The differences in specific surface area between the inner and outer cover plates of Examples 1-6 and Comparative Examples 1-3 are shown in Table 2 below:

[0122] Table 2

[0123]

[0124]

[0125] Test case

[0126] I. Residual compressive stress:

[0127] The film strips prepared in step (2) of Examples 1-11 and Comparative Examples 1-5 were stacked to prepare combined cover plate samples with a length of 20 mm, a width of 20 mm, and a thickness of 300 μm. After debinding and sintering, the warpage (deformation L) of each combined cover plate sample after sintering was calculated by 3D microscope to evaluate the residual compressive stress.

[0128] II. Hardness of the cover plate:

[0129] Hardness is determined by the resistance to initial plastic deformation and the resistance to continued plastic deformation. The higher the material strength, the higher the resistance to plastic deformation, and the higher the hardness, which can be used to evaluate the strength of the cover plate. Since the hardness of the inner and outer cover plates is not affected by the thickness, for the convenience of testing, the film strips prepared in step (2) of Examples 1-11 and Comparative Examples 1-5 were stacked and cut into 20mm×20mm×20mm combined cover plate squares. After sintering, they were tested with a Vickers hardness tester with a load of 50g and a loading time of 10s.

[0130] The hardness value is calculated using the following formulas based on the average length D of the diagonals d1 and d2 of the indentation and the applied test force:

[0131] HV = 0.1891 × F / (D) 2

[0132] In the above formula, HV is the Vickers hardness value; F is the test force corresponding to the test sample, in Newtons (N), 1g = 0.0098N; D is the arithmetic mean of the diagonals d1 and d2 of the indentation of the sample, D = (d1 + d2) / 2, in millimeters (mm).

[0133] III. Methods for testing flexural strength:

[0134] The multilayer ceramic chip capacitors prepared in Examples 1-11 and Comparative Examples 1-5 were soldered onto a dedicated PCB board, and the appearance of each soldered PCB board was inspected.

[0135] Connect the leads at both ends of each PCB board to a capacitance meter; place them on the test fixture and measure the capacitance. Apply pressure with a test head at a rate of 1.0 mm / s and observe the change in capacitance value displayed on the capacitance meter. When the PCB board bends until the capacitor capacitance exceeds the capacitance change range (capacity fluctuation required ≤10%), record the distance (in mm) the test head descends. The bending resistance NG rate, i.e., for 100 products undergoing crystal bend resistance testing, determines the number of defective products and calculates: (Number of NG / Total number of tests) * 100%.

[0136] The following tests are conducted to verify multilayer ceramic chip capacitors with dimensions of 2.0mm × 1.25mm × 0.85mm:

[0137] Performance standards:

[0138] (1) Residual compressive stress: The warpage (deformation) range should be controlled between 1.2 mm and 1.9 mm, based on the evaluation of the warpage of the sintered product.

[0139] (2) Cover plate hardness: Due to its product characteristics, the cover plate strength will not exceed 600 kgf / mm². 2The minimum must not be lower than 450 kgf / mm 2 .

[0140] (3) Bending strength: The bending strength is required to be greater than 3mm.

[0141] The results of the above tests are shown in Tables 3 and 4 below:

[0142] Table 3 shows the performance indicators of Examples 1-6 and Comparative Examples 1-3.

[0143]

[0144] Results analysis:

[0145] As can be seen from Comparative Example 1, the difference in specific surface area between the inner and outer cover plates is less than 0.6 m². 2 At a specific surface area ratio of / g, the residual compressive stress is too small, resulting in low bending resistance and a high NG rate for bending resistance; as can be seen from Comparative Example 2, the specific surface area difference is greater than 1.2m². 2 At a value of / g, the residual stress is too high, and the product is prone to thermal shock cracking. See Figure 3 As shown by the middle arrow; during the bending test, the corners of the product are prone to 45° octagonal cracks due to excessive stress, leading to failure; in Comparative Example 3, the specific surface area of ​​the inner and outer cover plates is the same, with no difference. Compared with the embodiment, it can be found that the technical solution of the present invention can improve the bending strength by at least 17%, and the bending failure rate is 0%; moreover, it can be seen from Examples 1 to 6 that the strength of the inner cover plate is at least 10% higher than that of the outer cover plate, thereby achieving the purpose of preventing the MLCC product from cracking and damaging the electrode, and improving the bending strength of low-capacitance products.

[0146] Table 4 shows the performance indicators of Examples 7-11 and Comparative Examples 4-5.

[0147]

[0148]

[0149] Results analysis:

[0150] By comparing Comparative Examples 4 and 5 with Examples 7-11, it can be seen that the volume fraction of the inner and outer cover sheets in the total cover sheets is very important. An inappropriate volume fraction will lead to performance degradation. Comparative Example 4 shows that when the volume fraction of the inner cover sheet exceeds 60% (that is, the volume fraction of the outer cover sheet is less than 40%), the inner cover sheet shrinks more, while the outer cover sheet shrinks less and is thinner. Therefore, when the inner cover sheet shrinks, the outer cover sheet is too thin to keep up with the stress generated by the inner cover sheet, which will cause cracking. This results in cracking and a decrease in strength in some products during bending tests. Comparative Example 5 shows that when the volume fraction of the inner cover sheet is less than 35% (that is, the volume fraction of the outer cover sheet is greater than 65%), it will generate very little tensile stress on the outer cover sheet. The residual compressive stress of the product is too small, and the overall strength of the cover sheet decreases, resulting in a decrease in bending strength. Only when the volume fraction of the inner and outer cover sheets in the total cover sheets is within a reasonable range can the effect of improving the bending strength of the product be achieved.

[0151] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A multilayer chip ceramic capacitor, comprising a ceramic body, a cover plate, and an external electrode layer, wherein the ceramic body comprises multiple dielectric layers and multiple internal electrode layers alternately stacked, characterized in that, The cover plate is located on the upper and lower surfaces of the ceramic body. The cover plate includes an inner cover plate and an outer cover plate. One side of the inner cover plate is attached to the ceramic body, and the other side is attached to one side of the outer cover plate. The inner cover, the outer cover, and the dielectric layer are made of the same material, and all of them are BaTiO3-based ceramic materials; The multilayer ceramic chip capacitor is prepared by a method comprising the following steps: S1: Using the same ceramic slurry as the dielectric layer, outer and inner cover sheets with different specific surface areas are obtained by adjusting the dispersion degree of the ceramic slurry; S2: The inner cover sheet and outer cover sheet described in S1 are sequentially stacked on the upper and lower surfaces of the ceramic body, respectively, and then encapsulated, pressed, cut, de-adhesiveed, sintered, ball-milled, and nickel-plated at the ends to obtain the multilayer chip ceramic capacitor. The inner cover has a larger specific surface area than the outer cover, and the difference in specific surface area between the inner and outer cover is 0.6 m². 2 / g~1.2 m 2 / g.

2. The capacitor according to claim 1, characterized in that, The thickness of the cover plate is 150 μm to 300 μm.

3. The capacitor according to claim 2, characterized in that, The specific surface area of ​​the inner cover plate is 3.1 m². 2 / g~4.1m 2 / g.

4. The capacitor according to claim 3, characterized in that, The specific surface area of ​​the outer cover is 2.7 m². 2 / g~3.2m 2 / g.

5. The capacitor according to claim 4, characterized in that, The volume of the inner cover plate accounts for 35% to 60% of the total volume of the cover plate.

6. The capacitor according to claim 5, characterized in that, The difference in specific surface area between the inner cover plate and the outer cover plate is 0.8 m². 2 / g~1.0 m 2 / g.

7. A method for preparing a multilayer ceramic chip capacitor as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Using the same ceramic slurry as the dielectric layer, outer and inner cover sheets with different specific surface areas are obtained by adjusting the dispersion degree of the ceramic slurry; S2: The inner cover sheet and outer cover sheet described in S1 are sequentially stacked on the upper and lower surfaces of the ceramic body, respectively, and then encapsulated, pressed, cut, de-adhesiveed, sintered, ball-milled, and nickel-plated at the ends to obtain the multilayer chip ceramic capacitor. The specific surface area of ​​the inner cover plate S1 is greater than that of the outer cover plate, and the difference in specific surface area between the inner and outer cover plates is 0.6 m². 2 / g~1.2 m 2 / g.

8. The application of a multilayer ceramic chip capacitor as described in any one of claims 1 to 6 in electronic products.

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