A twice-casting preparation method for improving reliability of MLCC product

Abstract

The application relates to the technical field of electronic component manufacturing, in particular to a preparation method for improving the quality of a dielectric layer and the reliability of an MLCC product by adopting a twice-casting process and a product prepared by the method; the twice-casting process is used to construct a ceramic dielectric film with a composite structure of a dense layer and a transition layer, micro defects in the dielectric layer are reduced, the interlayer bonding strength and the electric field uniformity are improved, so that the breakdown voltage, the insulation resistance and the long-term reliability of the MLCC product are significantly improved. The twice-casting process is equivalent to twice film forming of the ceramic slurry, the tiny bubbles in the slurry are released in the first casting and drying process, the second casting is formed on a more dense substrate, and the defects such as pores and pinholes in the film are effectively reduced. Test results show that the number of defects in the unit area of the ceramic film prepared by the method is reduced by more than 60% compared with that of the traditional single casting, and the fatal defect pinhole can reach 0 defects.

Description

Technical Field

[0001] This invention relates to the field of electronic component manufacturing technology, and in particular to a preparation method for improving the quality of the dielectric layer and enhancing the reliability of MLCC products using a two-stage casting process, and the resulting product. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are essential components in the electronics industry, characterized by small size, high capacitance, and high precision. They are widely used in automotive, aerospace, communications, consumer electronics, industrial, healthcare, and military applications. The manufacturing process of MLCCs generally includes processes such as material preparation, casting, printing internal electrodes, stacking, lamination followed by cutting, debinding and sintering, end sealing, and electroplating.

[0003] Casting is a core process in MLCC manufacturing, aiming to create ceramic dielectric films of required thickness from ceramic slurry through a casting process. To obtain green films with uniform thickness, smooth surfaces, and no internal defects, the ceramic powder must be highly dispersed in the slurry mixed with an organic solvent. The quality of the ceramic cast films obtained in the casting process is crucial to subsequent processes and product yield.

[0004] However, existing MLCC casting processes still have the following technical problems in actual production: (i) Microscopic defects exist within the dielectric layer, affecting product reliability. The root cause of MLCC failure is the presence of various microscopic defects, such as cracks, voids, and delamination, both externally and internally. These defects directly affect the electrical performance and reliability of MLCC products. Among these, delamination is a significant intrinsic defect—MLCCs are sintered by stacking and co-firing multiple layers of materials at temperatures exceeding 1000℃. Weak interlayer bonding, volatilization of internal contaminants during sintering, and improper sintering process control can all lead to delamination. Furthermore, voids within the ceramic dielectric are also a common failure mechanism. The formation of voids easily leads to leakage current, which in turn causes localized heating within the device, creating a vicious cycle.

[0005] (ii) The quality of dielectric films produced by single casting is unstable. Current technologies typically employ a single-pass casting method to prepare ceramic dielectric films, where a ceramic slurry is coated onto a carrier film and dried in a casting apparatus in a single operation. However, due to factors such as slurry dispersion uniformity and slurry supply stability, films produced by single-pass casting generally suffer from defects such as poor thickness uniformity and the presence of micropores. These defects are particularly pronounced as MLCCs (Multi-Layer Ceramic Capacitors) become increasingly thinner, requiring film thicknesses as low as 2 μm or even less.

[0006] (iii) The large difference in thickness of a single dielectric layer leads to uneven electric field distribution. For medium- and high-voltage MLCC products, the ceramic film tape is relatively thick, and the slurry used has a high viscosity. The thickness variation of the ceramic film tape obtained by casting is correspondingly large, resulting in problems such as poor electric field uniformity in the manufactured MLCC products. Under an applied electric field, the electric field distribution inside the MLCC is uneven, and it is easy to be broken down in areas where the single dielectric layer is thin or the internal electrodes are thin.

[0007] (iv) Insufficient bonding strength between single-cast film and internal electrode In the fabrication process of MLCCs, internal electrodes need to be printed on a cast film, and then multiple layers are stacked and hot-pressed. The surface density of the film produced by a single casting process is limited, and the bonding strength with the internal electrode paste is insufficient. During the lamination and subsequent sintering process, interface defects between the electrode and the dielectric layer are prone to occur, affecting the insulation resistance and withstand voltage performance of the product.

[0008] Therefore, developing a method for preparing MLCCs that can effectively improve the quality of the dielectric layer, reduce microscopic defects, and enhance product reliability has significant technological and industrial value. The microstructure of the cast film is strongly correlated with its permeability. Uneven slurry dispersion, the presence of air bubbles in the slurry, and improper drying processes can all lead to the formation of uneven pores or defects within the film, causing the permeability of that region to differ from that of the normal region. However, currently, there is no technical solution for monitoring permeability as a key quality indicator on MLCC casting production lines. Given the increasing number of layers and higher requirements for product reliability, this issue urgently needs to be addressed. Summary of the Invention

[0009] The purpose of this invention is to provide a two-stage casting method for improving the reliability of MLCC products. By constructing a ceramic dielectric film with a composite structure of a dense layer and a transition layer through a two-stage casting process, the micro-defects inside the dielectric layer are reduced, the interlayer bonding strength and electric field uniformity are improved, thereby significantly improving the breakdown voltage, insulation resistance and long-term reliability of MLCC products.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention provides a two-stage casting method for improving the reliability of MLCC products, comprising the following steps: Step S1: Prepare a pot of porcelain slurry with the same formula for use in the next casting process; Step S2: The first casting process involves coating the PET surface using casting equipment and then drying it at different wind speeds and temperatures using drying equipment to form the first ceramic film, which serves as the bottom layer. Step S3: Second casting molding. On the surface of the first ceramic film, ceramic slurry is coated onto it using casting equipment. The film is then dried a second time using drying equipment at different wind speeds and temperatures to form a composite ceramic film. The composite ceramic film includes a thick bottom layer and a thin top layer located on top of the thick bottom layer. Step S4: Internal Electrode Printing On the surface of the composite ceramic film obtained in step S3, an internal electrode pattern is formed by printing internal electrode paste. Step S5: Lamination and Pressing The composite ceramic films with internal electrodes printed in step S4 are stacked in a staggered manner to form a block; the block is subjected to isostatic pressing or hot pressing to make the film layers tightly bonded together. Step S6: Cutting and glue removal The pressed block is cut into individual chip blanks; the chip blanks are placed in a debinding furnace for debinding to remove organic binders; Step S7: Sintering The chip blank after debinding in step S6 is sintered at high temperature to obtain a ceramic sintered body. Step S8: End capping and electroplating The ceramic sintered body obtained in step S7 is coated with end electrode paste at both ends, and after end sintering treatment, it is electroplated to form external electrodes, thus obtaining the MLCC finished product.

[0011] Preferably, the viscosity of the ceramic slurry used in step S1 is less than 2500 mPa·s.

[0012] Preferably, the drying equipment for both steps S2 and S3 is a casting machine oven.

[0013] Preferably, the thickness of the thin upper layer obtained in step S3 is less than the thickness of the thick lower layer obtained in step S2.

[0014] Preferably, in step S4, an internal electrode paste is printed on the surface of the composite ceramic film obtained in step S3 using screen printing to form an internal electrode pattern.

[0015] Preferably, the thickness difference of the composite film of the ceramic sintered body obtained in step S7 is within ±0.5 μm.

[0016] As a preferred embodiment, the ceramic film of the ceramic sintered body obtained in step S7 has a defect number per unit area that is reduced by more than 60% compared with the traditional single casting process.

[0017] The core technical principle of this embodiment: A ceramic dielectric film with a composite structure is constructed by two casting processes.

[0018] The first layer of casting forms a bottom film with a certain thickness and density. This bottom film serves as the base layer and has good thickness uniformity and low internal defect density. The second layer of casting involves coating the surface of the bottom film with ceramic slurry and drying it to form a two-layer film.

[0019] During the drying process, the two layers of film exhibit good interlayer intersolubility and bonding, ultimately forming a composite film with high density and strong interfacial bonding. The second ceramic slurry fills the defects and voids in the bottom layer of the first film, resulting in a higher density of the top layer film. This allows for a tighter bond when in contact with the inner electrode slurry, reducing interfacial defects between the electrode and the dielectric layer.

[0020] Furthermore, the two casting processes are equivalent to a secondary dispersion and leveling of the ceramic slurry, effectively eliminating microscopic defects such as pores and pinholes caused by uneven slurry dispersion and supply fluctuations during a single casting process. Since the quality of the cast film directly determines the four major electrical performance parameters of MLCCs—capacity, loss, insulation resistance, and withstand voltage—improvements in the dielectric layer quality directly translate into enhanced product reliability.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are as follows: 1. Significantly reduces microscopic defects within the dielectric layer. The two-stage casting process is equivalent to a two-stage film formation of the ceramic slurry. Microscopic air bubbles in the slurry are released during the first casting and drying process, and the second casting forms the film on a denser substrate, effectively reducing defects such as pores and pinholes within the film. Test results show that the ceramic film prepared using this method has more than 60% fewer defects per unit area compared to traditional single-stage casting, and the fatal defect of pinholes can be eliminated to zero.

[0022] 2. Improve the uniformity of dielectric layer thickness In the two-stage casting process, the film thickness is thinner in each stage, resulting in better slurry flow and higher precision in doctor blade control, thus significantly improving the uniformity of film thickness. The thickness difference of the composite film can be controlled within ±0.5μm, effectively avoiding local electric field concentration caused by uneven thickness and improving the breakdown voltage of MLCCs.

[0023] 3. Enhance the bonding strength between the dielectric layer and the internal electrode. The second ceramic layer has a higher density and better surface smoothness, significantly enhancing its wettability and adhesion to the internal electrode paste. This improved interfacial bonding strength effectively reduces delamination and cracking, thereby improving the insulation resistance and withstand voltage performance of the MLCC.

[0024] 4. Improve the overall reliability of the product By reducing internal defects, improving interlayer bonding strength, and enhancing electric field uniformity, the MLCC products prepared by this invention significantly outperform products manufactured using traditional methods in high-temperature and high-humidity aging tests, withstand voltage tests, and accelerated life tests. This demonstrates significant advantages in high-reliability applications such as automotive electronics and aerospace.

[0025] 5. It has good process compatibility and is easy to promote industrialization. This invention only improves the existing casting process without adding complex equipment and process steps. It has good compatibility with existing MLCC production lines, low modification cost, and is easy to achieve industrial mass production. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings. Figure 1 This is a schematic diagram of the two-stage casting method for improving the reliability of MLCC products according to the present invention; Figure 2 A schematic diagram showing the microscopic comparison between one-time and two-time casting processes; Figure 3 A comparison table of 1000-meter defect rates was collected for single-cast and double-cast appearance machines. Detailed Implementation

[0027] Example 1 This embodiment prepares an MLCC product with X7R characteristics, a rated voltage of 100V, and a capacitance of 1μF. The total thickness of the dielectric layer is designed to be 4.5μm.

[0028] Step S1: Weigh 100 parts of barium titanate-based ceramic powder, 8 parts of polyvinyl butyral binder, 3 parts of dibutyl phthalate plasticizer, and 1 part of dispersant. Adjust the solid content to 50% with toluene / ethanol mixed solvent, place in a ball mill and grind at different speeds for 24 hours to obtain a uniformly dispersed ceramic slurry with a viscosity of 180 mPa·s (25℃).

[0029] Step S2: First Casting. The above slurry is placed in the casting machine bottle, and the slurry is coated onto a silicone-treated PET carrier film using a fully automatic casting machine. The wet film thickness is set to the target drying thickness of 3μm. The carrier film is conveyed into the casting machine oven, using an eight-stage temperature-wind speed combination: Stage 1: 30℃ / wind speed 400rpm; Stage 2: 40℃ / wind speed 500rpm; Stage 3: 50℃ / wind speed 600rpm; Stage 4: 60℃ / wind speed 700rpm; Stage 5: 70℃ / wind speed 800rpm; Stage 6: 80℃ / wind speed 900rpm; Stage 7: 85℃ / wind speed 1300rpm; Stage 8: 90℃ / wind speed 1500rpm. After drying, a first ceramic film with a thickness of 3μm is obtained and peeled off, serving as the thick bottom layer. Microscopic observation shows that the film surface is smooth and free of obvious pinholes.

[0030] Step S3: Second Casting. The first ceramic film obtained in Step S2 is placed back on the casting machine's film station, and the same ceramic slurry is coated again on its surface. The doctor blade gap is adjusted to achieve a target wet film thickness of 3 μm. The drying conditions are adjusted as follows: Section 1: 20℃ / 300 rpm; Section 2: 30℃ / 400 rpm; Section 3: 40℃ / 450 rpm; Section 4: 50℃ / 500 rpm; Section 5: 60℃ / 600 rpm; Section 6: 65℃ / 800 rpm; Section 7: 75℃ / 1000 rpm; Section 8: 90℃ / 1200 rpm. After drying, a thin upper layer tightly bonded to the bottom layer is formed, resulting in a composite ceramic film with a total thickness of 4.5 μm, of which the thick bottom layer is 3 μm and the thin upper layer is 1.5 μm. Multi-point thickness measurements show a thickness range of ±0.1 μm.

[0031] Step S4: Internal electrode printing. Using screen printing, nickel internal electrode paste is printed on the thin upper surface of the composite film. The electrode pattern is a rectangular block with margins. After drying, the internal electrode pattern layer is obtained.

[0032] Step S5: Lamination and Pressing. The composite films printed with internal electrodes are stacked in a staggered manner according to the design displacement, for a total of 200 layers, to obtain a green block. The block is then vacuum-sealed and subjected to warm water isostatic pressing at 25000 psi and 90°C for 5 minutes to ensure tight bonding between the layers.

[0033] Step S6: Cutting and Debonding. Cut the pressed block into individual chip blanks with dimensions of 1.0mm × 0.5mm. Place the chip blanks in a nitrogen atmosphere debonding oven, heat to 350℃ at 0.5℃ / min and hold for 2 hours, then heat to 600℃ at 1℃ / min and hold for 1 hour to completely remove the organic binder.

[0034] Step S7: Sintering. The debonded chip preform was heated to 1250℃ at a rate of 3℃ / min and held for 2 hours in a reducing atmosphere (N2 / H2 mixture), then cooled in the furnace to obtain a sintered ceramic body. The sintered body was cross-sectioned and inspected; the dielectric layer thickness range was ±0.09μm. The area per unit area (1mm²) was statistically analyzed using an optical microscope. 2 The average number of micro-defects in the film is 1, while the number of defects in a 4.5μm film prepared by a single casting with the same formula is 4, a reduction of 75%.

[0035] Step S8: End sealing and electroplating. Copper end electrode paste is applied to both ends of the ceramic sintered body. After an 800℃ end sealing process, nickel and tin layers are electroplated sequentially to form external electrodes, resulting in the MLCC finished product.

[0036] Comparative example (traditional single-pass tape) Using the exact same slurry formulation and final film thickness requirements as in Example 1, a 4.5 μm thick ceramic film was directly formed in a single casting process. The drying conditions were: first stage 40℃ / 500 rpm, second stage 50℃ / 600 rpm, third stage 60℃ / 700 rpm, fourth stage 70℃ / 800 rpm, fifth stage 80℃ / 900 rpm, sixth stage 85℃ / 1000 rpm, seventh stage 90℃ / 1300 rpm, and eighth stage 95℃ / 1500 rpm. All other printing, lamination, pressing, debinding, sintering, and end-capping electroplating processes were identical.

[0037] Performance Comparison The following tests were performed on the MLCC products prepared in Example 1 and the comparative example: Breakdown voltage: The average breakdown voltage of Example 1 was 5.8 times the rated voltage, and that of the comparative example was 4.6 times.

[0038] Insulation resistance: Example 1 shows an insulation resistance >10 ohms under rated voltage. 4 MΩ, comparative example approximately 8×10 3 MΩ.

[0039] High temperature and high humidity aging test (85℃ / 85%RH, rated voltage for 1000 hours): Example 1 capacity change rate <5%, comparative example capacity change rate about 12%, and 2% of the comparative example samples failed.

[0040] Acceleration life test: The mean failure time of Example 1 was about 40% longer than that of the comparative example, and there were no products with early failure, while 2.5% of the samples in the comparative example failed.

[0041] Microscopic defect number: density of voids and cracks per unit area in the dielectric layer after sintering, which was reduced by 76% in Example 1.

[0042] Therefore, the method of the present invention significantly improves the quality of the dielectric layer of MLCCs and enhances the reliability and electrical performance of the products.

[0043] refer to Figure 2 In the microscopic image, white represents the printed internal electrode, and black represents the ceramic layer. Because the ceramic layer has defects, the reliability will be poor.

[0044] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A two-stage casting method for improving the reliability of MLCC products, characterized in that, Includes the following steps: Step S1: Prepare a pot of porcelain slurry with the same formula for use in the next casting process; Step S2: The first casting process involves coating the PET surface using casting equipment and then drying it at different wind speeds and temperatures using drying equipment to form the first ceramic film, which serves as the bottom layer. Step S3: Second casting molding. On the surface of the first ceramic film, ceramic slurry is coated onto it using casting equipment. The film is then dried a second time using drying equipment at different wind speeds and temperatures to form a composite ceramic film. The composite ceramic film includes a thick bottom layer and a thin top layer located on top of the thick bottom layer. Step S4: Internal Electrode Printing On the surface of the composite ceramic film obtained in step S3, an internal electrode pattern is formed by printing internal electrode paste. Step S5: Lamination and Pressing The composite ceramic films with internal electrodes printed in step S4 are stacked in a staggered manner to form a block; the block is subjected to isostatic pressing or hot pressing to make the film layers tightly bonded together. Step S6: Cutting and Glue Removal The pressed block is cut into individual chip blanks; the chip blanks are placed in a debinding furnace for debinding to remove organic binders; Step S7: Sintering The chip blank after debinding in step S6 is sintered at high temperature to obtain a ceramic sintered body. Step S8: End capping and electroplating The ceramic sintered body obtained in step S7 is coated with end electrode paste at both ends, and after end sintering treatment, it is electroplated to form external electrodes, thus obtaining the MLCC finished product.

2. The two-stage casting method for improving the reliability of MLCC products according to claim 1, characterized in that: The viscosity of the ceramic slurry used in step S1 is less than 2500 mPa·s.

3. The two-stage casting method for improving the reliability of MLCC products according to claim 1, characterized in that: The drying equipment for both steps S2 and S3 is a casting machine oven.

4. The two-stage casting method for improving the reliability of MLCC products according to claim 1, characterized in that: The thickness of the thin upper layer obtained in step S3 is less than the thickness of the thick lower layer obtained in step S2.

5. The two-stage casting method for improving the reliability of MLCC products according to claim 1, characterized in that: In step S4, an internal electrode paste is printed on the surface of the composite ceramic film obtained in step S3 using screen printing to form an internal electrode pattern.

6. The two-stage casting method for improving the reliability of MLCC products according to claim 1, characterized in that: The thickness range of the composite film of the ceramic sintered body obtained in step S7 is within ±0.5μm.

7. The two-stage casting method for improving the reliability of MLCC products according to claim 6, characterized in that: The ceramic film of the ceramic sintered body obtained in step S7 has a defect number per unit area that is reduced by more than 60% compared with the traditional single casting process.

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