High voltage ceramic capacitor with pressure-resistant enhanced concave structure

Abstract

This invention discloses a high-voltage ceramic capacitor with a reinforced concave structure, aiming to solve the problem of insufficient edge breakdown withstand voltage in traditional ceramic capacitors due to edge effects. The capacitor includes a ceramic core composed of a ceramic dielectric. Its innovation lies in the fact that the upper and lower electrode surfaces of the ceramic core are not planar, but rather form a concave structure that curves inward from the center, causing the ceramic body thickness to gradually increase from the center to the edge. This structure significantly improves the edge breakdown withstand capability through the synergistic effect of electric field homogenization and improved molding density. This invention significantly improves the power frequency withstand voltage of the capacitor to over 3.5kV per millimeter, while also exhibiting excellent comprehensive electrical performance such as low loss, high insulation, and high partial discharge initiation voltage. Furthermore, the manufacturing process is simple, does not increase volume, and has strong industrial applicability.

Description

Technical Field

[0001] This invention relates to the field of high-voltage ceramic capacitor technology, and more particularly to a high-voltage ceramic capacitor with a voltage-strengthened concave structure. Specifically, it relates to a high-voltage ceramic capacitor that achieves synergistic effects of active electric field control and densification by reconstructing the three-dimensional macroscopic geometry of the ceramic core electrode surface. This invention also relates to a method for preparing this high-voltage ceramic capacitor. Background Technology

[0002] High-voltage ceramic capacitors are core components in power systems, pulse power systems, high-voltage power supplies, and power electronic equipment. Their performance directly determines the voltage level, operational reliability, and power density of related equipment and systems. In cutting-edge and high-reliability applications such as high-voltage direct current transmission, smart grids, electrified railways, new energy vehicles, and medical X-ray equipment, increasingly stringent requirements are placed on capacitors' withstand voltage, partial discharge characteristics, dielectric loss, and capacitance stability.

[0003] High-voltage ceramic capacitors typically employ a disc or cylindrical structure, with an internal dielectric material of high dielectric constant ceramic and metal electrodes covering the top and bottom surfaces. Ideally, the electric field inside such a parallel-plate capacitor is uniform. However, any parallel-plate capacitor of finite size inevitably suffers from an "edge effect," where electric field lines bend and concentrate at the electrode edges, resulting in a local electric field strength in that region that is much higher than the internal average electric field strength. This effect constitutes a physical bottleneck limiting the overall voltage withstand capability of the capacitor.

[0004] Currently, the development of high-voltage ceramic capacitor technology is uneven globally. Leading foreign companies, leveraging their high-purity raw materials, ultra-clean powder processing environments, precise molding and sintering processes, and advanced formulation systems, have achieved a high withstand voltage of approximately 3kV per millimeter of dielectric material with a dielectric constant exceeding 3500, operating at power frequency AC voltage. In contrast, the domestic industry lags significantly behind, with withstand voltages generally hovering around 2kV-2.5kV per millimeter under the same conditions. In-depth analysis reveals that the root cause of this gap lies in several long-standing systemic problems that are difficult to fundamentally reverse in the short term: First, the purity and microstructure consistency of the core electronic ceramic powder are insufficient, with trace impurities and lattice defects constituting potential breakdown weaknesses. Second, the environmental control and particle size management during powder processing are relatively lax, resulting in uneven micropores, abnormally large grains, or second-phase segregation in the final ceramic body. These microstructural defects can become electric field concentration points and sources of breakdown paths under strong electric fields. Third, the molding process, especially the dry pressing process, inherently suffers from uneven mechanical densification when molding large-diameter, high-thickness circular or cylindrical capacitor blanks. These three problems are coupled, causing significant technical bottlenecks for domestic high-voltage ceramic capacitors in pushing towards higher voltage levels and smaller packaging.

[0005] The third problem, the uneven densification in dry pressing, is directly related to the edge effect but has long been overlooked. In the unidirectional or bidirectional pressing process of traditional planar molds, the friction between the powder and the mold sidewall causes pressure to attenuate as it travels away from the press head, especially at the edges near the mold sidewalls, where the compaction work is minimal, easily forming loose zones. This inherent deficiency introduced by the process makes the already disadvantaged edge regions in terms of electric field distribution even weaker in terms of intrinsic material breakdown strength, creating a fatal overlap between the "most concentrated electric field" and the "weakest point in the material." This dual effect is the fundamental reason why capacitors almost invariably break down at the edges in practical applications.

[0006] More specifically, in practical applications, the failure mode of most disc or cylindrical high-voltage ceramic capacitors manifests as edge breakdown, rather than occurring in the central region where the electric field distribution should be most uniform. The physical root of this phenomenon lies in the well-known "edge effect." In an ideal parallel-plate capacitor, the internal electric field lines are uniform, parallel straight lines perpendicular to the electrode plane. However, in practical capacitors of finite size, the electric field lines at the edges bend, bulge outwards, and are highly concentrated near the electrode edges. This severe distortion of the electric field distribution results in the local electric field strength at the capacitor's edge region being much higher than the average internal electric field strength, forming an extremely weak link in electromechanical strength. When the applied voltage increases, this edge region will first reach or even exceed the intrinsic breakdown field strength of the ceramic dielectric, thus inducing breakdown and causing the entire capacitor to fail. The edge effect greatly limits the improvement of the overall withstand voltage level of the capacitor, making the potential for improving withstand voltage through simply optimizing the material itself constrained by this "weak point" of edge breakdown.

[0007] To address the edge breakdown problem, several solutions have been developed in existing technologies. One typical and mainstream method is the "electrode edge semiconductor glaze method." This method involves coating silver electrodes onto the upper and lower surfaces of the capacitor ceramic substrate, and then coating an additional layer of semiconductor-grade glaze onto the edge region of the electrodes. High-temperature sintering then allows the semiconductor glaze to bond well with the ceramic substrate and electrodes. The working principle is that the high resistivity of the semiconductor glaze creates a voltage transition region with gradually varying resistivity extending outward from the electrode edge. This region disperses the high electric field concentrated at the electrode edge, so that the voltage drop is no longer steeply concentrated at the electrode edge, but rather distributed over a wider annular area, thereby alleviating electric field concentration to some extent and improving the edge withstand voltage level.

[0008] However, this semiconductor glaze method introduces new and insurmountable problems in process implementation and product performance. First, the process is complex and difficult to control. Process parameters such as the semiconductor glaze formulation, coating width and thickness, and sintering temperature profile are extremely sensitive to the final result. Any deviation can lead to poor voltage equalization or weak bonding with the silvered electrode and ceramic body. The process window is narrow, making it difficult to guarantee the yield. Second, and more critically, it introduces resistive heating. The semiconductor glaze itself has non-zero resistivity. Under an alternating current field, especially at high frequencies or in the presence of harmonics, this resistance forms a through-current leakage path and generates Joule heating. This localized heating not only directly reduces the capacitor's power factor and energy efficiency, but more seriously, the continuous local temperature rise accelerates the aging of the ceramic dielectric in that area, significantly increases the risk of thermal breakdown, and may cause thermal damage to the surrounding encapsulation material, greatly limiting the reliability of the capacitor in high ambient temperatures and high ripple current scenarios. Third, to address the issues of heat generation and withstand voltage, a more common and direct approach is to simply increase the physical size of the capacitor, particularly the diameter of the ceramic body and the creepage distance. Increasing the size lengthens the creepage path at the edges and, to some extent, dilutes the impact of edge effects. However, this approach contradicts the growing trend of miniaturization, lightweight design, and high power density in electronic devices. It not only increases material costs and occupies more system space, but the larger ceramic body volume also presents a greater challenge to the uniformity of the sintering process.

[0009] Furthermore, existing technologies also include simple chamfering or rounding of the ceramic body edges. However, this approach merely removes the sharp corners of the edges, slightly reducing the electric field singularity at those points. While it decreases the creepage distance at the edges, the dielectric thickness at the chamfered areas remains unchanged, and may even be reduced, failing to fundamentally alter the physical pattern of highly concentrated electric fields at the edges due to uniform electrode spacing. This is a reactive measure that only addresses the symptoms, with very limited effectiveness; for example, it can only increase the withstand voltage by 5%-10%, failing to achieve a significant performance leap.

[0010] Therefore, how to significantly improve the overall withstand voltage level and operational reliability of high-voltage ceramic capacitors without significantly increasing or only slightly increasing the external volume of the capacitor, using a simpler process that does not introduce new thermal instabilities and can systematically solve the edge effect problem, has become a key common problem restricting the technological leap and industrial upgrading of high-voltage ceramic capacitors in China.

[0011] Furthermore, the core of this challenge lies in how to simultaneously and synergistically address the coexisting and mutually reinforcing defects of "electric field concentration" and "material porosity" in the peripheral regions. The ideal solution should not merely be electrical compensation or material reinforcement, but rather a systematic innovation that integrates electrical performance optimization with mechanical strengthening, permeating the entire process of device structure and manufacturing. Summary of the Invention

[0012] The purpose of this invention is to address the aforementioned problems in the prior art, particularly edge breakdown of ceramic capacitors due to edge effects, and the complex processes and heat generation issues in existing solutions, by providing a high-voltage ceramic capacitor with a voltage-strengthened concave structure.

[0013] Another deeper objective of this invention is to provide a high-voltage ceramic capacitor whose structural design can achieve "active guidance" and "homogenization" of the edge electric field, while "in situ" strengthening of the material density in the edge region during the manufacturing process, thereby resolving the inherent contradiction that the "most concentrated point of electric field" coincides with the "weakest point of material".

[0014] Another objective of this invention is to provide a method for preparing the above-mentioned high-voltage ceramic capacitor, which systematically improves the overall electrical performance of the capacitor by optimizing key process steps.

[0015] The above-mentioned objective of this invention is achieved through the following technical solutions:

[0016] On one hand, the present invention provides a high-voltage ceramic capacitor with a voltage-strengthened concave structure, comprising a ceramic core made of dielectric ceramic material, the ceramic core having opposing upper and lower electrode surfaces. The geometry of the ceramic core is innovatively designed such that at least the central region of the upper electrode surface and / or the lower electrode surface forms a concave structure recessed into the interior of the ceramic core relative to their respective peripheral edge regions. From the center to the edge, the effective thickness of the ceramic body gradually increases continuously or in a stepped manner.

[0017] The design logic of this concave structure lies in fundamentally reconstructing the spatial relationship between electrodes, transforming the traditional equidistant planar electrodes into a three-dimensional gradient electrode system with the spacing gradually increasing from the center to the edge, thereby actively regulating the potential distribution and electric field intensity.

[0018] In a preferred embodiment of the present invention, the concave structure is specifically manifested as follows: the central region of the upper and lower electrode surfaces of the ceramic core is a planar or nearly planar base surface, which occupies 50% to 80% of the total electrode surface area; starting from the perimeter of this base surface, the thickness of the ceramic body smoothly increases towards the edge, forming a surrounding, gradually rising annular ridge, the highest point of which is located at the outer circumferential edge of the ceramic core. This shape resembles a shallow dish or chamfered concave surface with a flat center and warped edges.

[0019] This shallow, dish-shaped concave structure, with a flat center and raised edges, offers unique advantages. The flat central region ensures the capacitance of the main capacitor body, allowing the invention to significantly improve voltage withstand without sacrificing effective capacitance. The gradually rising annular ridges at the edges are specifically designed to address voltage withstand, achieving decoupling and separate optimization of capacitance and voltage withstand—the central region primarily contributes capacitance, while the edge regions mainly bear the voltage withstand.

[0020] In this invention, this unique shape is not a simple chamfer or arc, but a three-dimensional geometric structure with specific functionality. Its design parameters are directly related to the optimization of electric field distribution and the effect of mechanical enhancement. Preferably, the thickness of the ceramic core at the edge is 10% to 30% greater than the thickness of the central region; more preferably, this increase is 10% to 25%, with 16% being the most preferred ratio. If the thickness is increased too little, it will not be sufficient to guide the electric field lines and enhance the mechanical strength of the edge; if it is increased too much, it will significantly increase the volume of the ceramic body, violating the original intention of compactness, and may introduce new stress concentration points due to abrupt shape changes.

[0021] Extensive electric field simulations and experimental verifications have shown that a thickness increase of 10% to 30% achieves the optimal performance-volume balance. When the thickness increase is below 10%, the electric field conduction and mechanical reinforcement effects are limited, and the voltage withstand capability improvement is not significant. When the thickness increase is above 30%, excessive thickness at the edges may lead to inconsistent shrinkage between the center and edges during sintering, introducing new stresses, and potentially worsening parasitic parameters such as the equivalent series resistance (ESR) and equivalent series inductance (ESL) of the capacitor. A thickness increase of 10% to 25%, especially 16%, achieves the optimal balance between these two extremes, resulting in a synergistic improvement in voltage withstand capability, reliability, and electrical performance.

[0022] On the other hand, as the core of this invention, the concave structure is formed as follows: the upper and lower electrode surfaces of the ceramic core have a uniformly smooth concave surface that curves inward into the ceramic core. This concave surface rises from the lowest point in the central region, through an arc transition surface with a specific radius of curvature, to the highest point at the edge. This smooth concave structure avoids any sharp corners or edges, thus optimizing both the electric field distribution and the mechanical stress distribution.

[0023] Smooth, rounded transition surfaces are crucial for preventing secondary electric field and mechanical stress concentrations. If a stepped or broken-line transition with sharp angles is used, points with extremely small radii of curvature will form at each corner, which can become new points of electric field and mechanical stress concentration, potentially inducing new failure modes under high pressure or temperature cycling. Therefore, achieving a gradual thickness change through continuous, smooth surfaces with specific radii of curvature is one of the key technical features for achieving a "dual-optimal" distribution of electric and stress fields.

[0024] In another alternative embodiment, the concave structure can also consist of a central planar region, a circular or annular ridge surrounding the central planar region, and a sloped or curved surface sloping outward and downward from the ridge to the edge; this is the so-called "angular concave" structure. Whether smooth or angular, the core idea is to create a three-dimensional recess on the electrode surface.

[0025] Furthermore, the upper and lower electrode surfaces of the ceramic core are respectively covered with metal electrode layers, which completely cover the electrode surfaces with concave structures and extend to the side or near the edge of the ceramic core, while leaving necessary creepage safety distances. The periphery of the ceramic core and part of the electrodes is completely covered by an epoxy resin encapsulation layer to provide electrical insulation and mechanical protection from the environment.

[0026] The voltage withstand enhancement mechanism of the above-mentioned high voltage ceramic capacitor with concave structure can be creatively explained from two dimensions: electric field homogenization and mechanical strengthening. These two dimensions do not work independently, but produce a significant synergistic effect, that is, the final voltage withstand enhancement is "1+1>2", which far exceeds the linear superposition of their individual effects.

[0027] From the perspective of electric field homogenization: In traditional planar electrode capacitors, the electric field lines at the edges are highly concentrated due to their extremely small radius of curvature. This invention designs the electrode surfaces as concave, effectively "raising" or "thickening" the edge region of the parallel-plate capacitor. This reconstruction of the three-dimensional geometry alters and effectively guides the equipotential surface of the potential distribution between the electrodes. In the concave structure, the distance between the upper and lower electrodes is greater closer to the edge. According to the inverse relationship between capacitance and distance, the capacitance per unit area in the edge region naturally decreases. When the same voltage is applied, the stored charge density decreases. According to Gauss's law, the density of electric field lines leaving the electrodes decreases accordingly, thereby increasing the radius of curvature of the curved electric field lines at the edges, and making the electric field distribution more gradual and uniform.

[0028] This process can be more precisely described from the perspective of "field": the potential equipotential surfaces undergo a favorable distortion between the electrodes of the concave structure. In a parallel-plate capacitor, the equipotential surfaces are a series of parallel planes. However, in the concave structure of this invention, the equipotential surfaces gradually bend and "expand" from a flat shape at the center towards the edges, eventually forming a sparser distribution in the edge region. This "expanded" distribution of equipotential surfaces implies a significant reduction in the potential gradient (i.e., electric field strength). This invention actively "shapes" the morphology of the potential equipotential surfaces through changes in macroscopic geometry, "guiding" and "diluting" the sharp edge electric field into a wider and thicker annular region. This is fundamentally different from the passive strategies of semiconductor glaze methods that "dissipate" the electric field or chamfering methods that "cut off" high-field regions. This is equivalent to using a continuous, gradual structure to "guidance" and "dilute" the sharp, concentrated edge electric field into a wider and thicker annular region, significantly reducing the maximum electric field strength at the edges, thereby directly improving the edge's breakdown resistance. At the same time, this three-dimensional structure also physically increases the surface creepage distance between the upper and lower electrodes, enhancing the withstand voltage capability from another dimension.

[0029] From a mechanical strengthening perspective: During dry pressing, the powder is subjected to unidirectional or bidirectional pressure within the mold. The upper and lower concave mold of this invention, with its cavity geometry, generates an increased lateral force pointing towards the center in the edge region during pressure transmission. This force can more effectively compact the powder in the edge region of the ceramic body.

[0030] This mechanical process can be further explained through the following analysis: During the pressing process, the densification of the powder originates from two key mechanisms: particle rearrangement and plastic / brittle deformation. In traditional planar molds, the pressure transmitted to the edge powder is mainly axial force, with a small radial component, insufficient to overcome the strong friction between the powder particles and the mold wall. This results in insufficient particle rearrangement in the edge region, leaving a large number of voids. However, in the concave-convex mold configuration of this invention, when the convex surface of the upper die presses into the powder, the normal pressure N applied by its inclined surface to the contacting powder can be decomposed into a large vertical axial component Fz and a significant radial lateral component Fr. The direction of this lateral component Fr points towards the mold wall, forcefully pushing the powder against the mold sidewall. This behavior not only effectively compacts the edge powder, but more importantly, it provides a mechanism for "active densification" of the edge region, fundamentally overcoming the problem of uneven densification caused by friction. Furthermore, the particle shear strain induced by this lateral force helps break the arching effect between particles, promotes the discharge of pores and the rotation and sliding rearrangement of particles, thereby obtaining higher green density and a more uniform microstructure. As described in the background art, the edges of traditional planar green bodies are the areas with the worst densification, often exhibiting defects such as porosity and delamination, which are weaknesses both electrically and mechanically. The concave forming method of this invention, utilizing mechanical principles and optimizing the geometry of the mold cavity, substantially enhances the forming pressure in the edge region, greatly improving the sintering density and microstructure of the edges. It strengthens the weakest link from the material's origin, resulting in a dual improvement in electrical properties and mechanical strength. This improvement in edge porosity is difficult to achieve simply by extending ball milling time or other process methods.

[0031] The above-mentioned electric field homogenization (electric function) and mechanical enhancement (manufacturing process function) produce a deep synergistic effect, the core logic of which is:

[0032] (1) The simultaneous effect of “guiding” and “reinforcing”: The concave structure of the present invention makes the area (edge) where the electric field is “guided” and reduced, which is precisely the area that is “reinforcing” and strengthened during the molding process. This fundamentally solves the physical contradiction of the fatal overlap between the “strongest point of electric field” and the “weakest point of material” in traditional capacitors, and achieves the best matching between field and material.

[0033] (2) The mutual feedback amplification of "geometric effect" and "intrinsic effect": Improved edge compactness means that the ceramic grain boundaries in this region are cleaner and there are fewer microscopic defects such as pores, which directly increases the intrinsic breakdown field strength (Eb) of the ceramic material. On the other hand, electric field homogenization reduces the actual electric field strength (E_applied) that the region is subjected to. The condition for breakdown is that E_applied ≥ Eb. The synergistic effect of this invention achieves the simultaneous reduction of E_applied and increase of Eb, "pushing" the two values ​​that were originally close together away, thereby creating a safety margin far exceeding expectations and bringing about a leapfrog improvement in the withstand voltage level.

[0034] (3) Increased Defect Tolerance: Even if minute residual pores or weak grain boundaries exist in the edge region due to process fluctuations, the probability of partial discharge or breakdown induced by micro-defects of the same level is greatly reduced because the alumina material in this region has been uniquely densified and the electric field strength in this region has been reduced. This means that the technical solution of the present invention has a higher process window and fault tolerance, and the consistency and long-term reliability of the finished product are structurally guaranteed. This improvement in tolerance capability cannot be achieved by simply optimizing the material formulation or by simple electric field mitigation methods, and is an unexpected technical effect.

[0035] Regarding the preparation method, the present invention provides the following technical solution:

[0036] A method for fabricating a high-voltage ceramic capacitor with a voltage-strengthened concave structure includes the following steps:

[0037] Ingredient preparation steps: Weigh and mix the raw materials according to the predetermined stoichiometric ratio. The raw materials include strontium titanate, lead titanate, bismuth titanate, and additives containing magnesium and rare earth elements.

[0038] One ball milling step: Mix the raw materials weighed in the batching step with deionized water and ball milling media, and perform wet ball milling to mix evenly and pulverize to the predetermined particle size.

[0039] Pre-sintering step: The powder after ball milling and drying is pre-sintered at a temperature of 900℃~1150℃ to synthesize the main crystalline phase.

[0040] Secondary ball milling step: The pre-fired sintered material is mixed again with deionized water and ball milling media, and wet ball milling is performed to further refine and homogenize the powder, resulting in a submicron slurry with uniform particle size.

[0041] Secondary ball milling is a crucial step in the preparation of high-performance ceramic media. The inventors discovered that by strictly controlling the ball milling parameters to achieve a median particle size (D50) of 0.1–0.2 μm within a critical range, while maintaining high sphericity and a narrow particle size distribution, it has a vital impact on subsequent forming (especially concave forming) and sintering. If the particles are too coarse, the surface activity is insufficient, the sintering driving force is weak, and densification is difficult to achieve at the moderate temperature of 1200–1300 °C. Furthermore, the voids between coarse particles are difficult to fill with subsequent limited-volume liquid phase and diffusion. If the particles are too fine, the specific surface energy is too high. Although the sintering driving force is enhanced, agglomerates are easily introduced during forming. These agglomerates will preferentially densify and abnormally grow grains during sintering, forming defects such as "internal porosity" or "second-phase encapsulation," which become weak penetration paths. Ultrafine powders with a particle size below 0.1 μm also significantly reduce the forming density and strength of the green body, posing a challenge to the cavity filling performance of the mold. Only by precisely controlling the particle size of the powder to the submicron level of 0.1 to 0.2 μm and combining it with a narrow distribution can we ensure good flowability to fill the complex cavity of the concave mold during dry pressing, and at the same time obtain a fine-grained, uniform, and highly dense microstructure during sintering, laying a solid foundation for high pressure resistance.

[0042] Granulation step: Add binder and dispersant to the slurry after secondary ball milling, mix evenly, and then granulate by spray granulation to obtain spherical granules with good flowability.

[0043] Molding steps: The spherical granules obtained by granulation are filled into a mold cavity with a concave structure that complements the ceramic core, and dry-pressed under a pressure of 5MPa to 20MPa to obtain a green body with a concave structure.

[0044] The precision and surface finish of the mold are crucial to the quality of the green body. For molds used to form the concave structure, the surface roughness Ra of the convex arc surface must be controlled below 0.4 μm, and they should be made of high-hardness, high-wear-resistant cemented carbide or mold steel. Simultaneously, the arrangement of the mold cavities should consider the pressure distribution during the pressing process. For large-sized products, isostatic pressing-assisted dry pressing can be used, or a specially designed runner can be used to ensure uniform pressure transmission.

[0045] Sintering step: The shaped green body is sintered at a temperature of 1200℃~1300℃ to obtain a dense ceramic body with a concave structure.

[0046] Silvering and firing steps: Silver paste is coated on the upper and lower concave electrode surfaces of the sintered ceramic body, and then fired at a temperature of 700℃~750℃ to form a metal electrode layer.

[0047] Encapsulation step: Epoxy resin is used to cast or coat the silvered capacitor core to form an epoxy encapsulation layer.

[0048] Post-curing and testing steps: The encapsulated capacitors undergo post-curing heat treatment and aging treatment, and electrical performance tests are performed.

[0049] In the above preparation method, several key process parameters are strictly limited to achieve optimal control of the microstructure and ultimately improve performance: The optimization of ball milling time (preferably 5-7 hours for the first ball milling and 3-5 hours for the second ball milling) aims to obtain powder with a particle size of approximately 0.15 μm and excellent sphericity, laying the foundation for obtaining a ceramic body with a uniform structure and few defects through sintering. Modified alicyclic epoxy resin is used as the encapsulation material instead of traditional bisphenol A epoxy resin because it has lower curing shrinkage and internal stress, as well as better voltage resistance, which can prevent the encapsulation layer from cracking and failing during thermal cycling, and form a more compatible and protective insulating whole with the ceramic body.

[0050] The choice of encapsulation material is equally crucial for leveraging the advantages of the concave structure of this invention. Traditional bisphenol A epoxy resins exhibit approximately 2-5% volume shrinkage during curing. This shrinkage generates significant internal stress on the ceramic surface, especially at complex concave surfaces and rounded corner transitions, potentially leading to micro-cracks in the ceramic or cracking of the encapsulation layer itself, forming potential creepage paths. In contrast, the selected alicyclic epoxy resin has epoxy groups directly attached to the alicyclic rings, resulting in higher cross-linking and a more stable chemical structure. Its curing shrinkage rate can be reduced to below 1%, and the cured product exhibits superior resistance to tracking (higher CTI value) and UV aging. This choice effectively protects the capacitor core with its complex three-dimensional surface, ensuring its long-term operational reliability and allowing the performance improvements resulting from structural optimization to be realized stably and persistently.

[0051] In summary, compared with the prior art, the present invention has at least one of the following beneficial technical effects:

[0052] First, a novel approach was proposed and implemented to systematically solve the physical problem of insufficient withstand voltage caused by edge effects by altering the macroscopic three-dimensional geometry of the capacitor core, specifically by constructing a concave structure on the electrode surface. This is drastically different from the traditional approach of addressing the issue solely through material formulation or increasing dimensions, representing a groundbreaking technological path.

[0053] Secondly, this concave structure achieves a synergistic effect of electric field homogenization and mechanical enhancement. On the one hand, it "actively guides" the electric field at the edge by changing the electrode distance; on the other hand, it "passively strengthens" the material itself in the edge region by utilizing a unique mechanical transmission path during the forming stage. The two complement each other, and the resulting technical effect is unattainable by simply improving the electric field or material. Experimental results show that the technical solution of this invention significantly improves the withstand voltage per millimeter from 2kV to 3.5kV or even higher. This is not a simple additive improvement, but a qualitative leap.

[0054] It is particularly worth emphasizing that the high degree of unity between this "active electric field conduction" and "in-situ mechanical reinforcement" in terms of physical location and functional logic has constructed an ideal anti-breakdown system of "field-material matching", which has produced a significant synergistic effect, that is, the increase in withstand voltage is far greater than the simple sum of the effects of a single method.

[0055] Third, the present invention has a simple and reliable process, overcoming the problems of localized heating and complex processes caused by the traditional "semiconductor glaze method". The formation of the concave structure depends entirely on the modified dry pressing mold, which is easy to design and manufacture, fully compatible with existing capacitor production lines, without introducing additional and cumbersome process steps, and without adding any semiconductor materials. This eliminates the risk of resistive heating from the root, greatly expanding the application range and operational reliability of capacitors.

[0056] Fourth, through the systematic optimization of supporting processes, such as the precise control of ball milling to prepare uniform submicron powders and the use of high-performance alicyclic epoxy resin for encapsulation, not only is the uniformity and density of the ceramic body ensured at the microscopic level, but the overall insulation and encapsulation are also strengthened at the macroscopic level, forming a complete technical system from the inside out and from materials to structure, which comprehensively improves the overall performance of the product.

[0057] In summary, this invention provides a groundbreaking high-voltage ceramic capacitor and its fabrication method, successfully achieving a significant improvement in withstand voltage levels in a simple and reliable manner without substantially increasing volume. Furthermore, the breakthrough achieved by this invention is not merely an increase in withstand voltage; more importantly, it provides a completely new capacitor design paradigm. Through the functional design of a three-dimensional structure, it intrinsically unifies electrical performance optimization with enhanced manufacturing processes, achieving a leapfrog development in performance. This has milestone significance for promoting the development of high-voltage ceramic capacitor technology towards higher voltages, higher reliability, and smaller size. Attached Figure Description

[0058] Figure 1 This is a schematic diagram illustrating the phenomenon of electric field line bending and edge electric field concentration caused by edge effects in existing disc ceramic capacitors.

[0059] Figure 2 This is a half-sectional view of a molding die for a high-voltage ceramic capacitor with a concave structure, provided for an embodiment of the present invention.

[0060] Figure 3 This is a side view of a ceramic blank with a concave structure obtained after molding and sintering, as provided in an embodiment of the present invention.

[0061] Figure 4This is a schematic cross-sectional view of a high-voltage ceramic capacitor with a concave structure after epoxy encapsulation, provided as an embodiment of the present invention.

[0062] Reference numerals: 1. Upper die punch; 2. Cavity; 3. Lower die punch; 4. Ceramic core; 41. Central region; 42. Edge region; 43. Arc transition surface; 5. Upper metal electrode layer; 6. Lower metal electrode layer; 7. Epoxy resin encapsulation layer. Detailed Implementation

[0063] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0064] In the following detailed description, numerous specific details will be set forth to provide a thorough understanding of embodiments of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without some or all of these specific details. In other instances, well-known processes or materials have not been described in detail in order not to unnecessarily obscure the core of the invention.

[0065] It should be noted that, unless otherwise stated, the raw materials and chemical reagents used in the embodiments of the present invention are all commercially available analytical grade or chemically pure products. All equipment involved is conventional equipment in the art.

[0066] Figure 1 This invention is used to schematically illustrate the physical root of the technical problem it aims to solve. In a typical disc ceramic capacitor of the prior art, the upper and lower electrode surfaces are two parallel planes. When a voltage is applied, ideally, the electric field lines (represented by dashed lines) should be perpendicular to the plate surface and uniformly distributed. However, at the edges of an actual capacitor, the electric field lines (represented by solid lines) bend significantly outwards, with the bending becoming more pronounced closer to the edge and the density of the electric field lines increasing. This indicates that the local electric field strength E_edge in the edge region is much greater than the uniform electric field strength E_center in the center region. This severe distortion of the electric field distribution, known as the "edge effect," causes the actual breakdown of the capacitor to typically begin at the edge. This invention addresses this phenomenon by fundamentally altering the physical geometry of the ceramic core to reshape the electric field distribution, thereby overcoming this problem.

[0067] Structural Examples of High Voltage Ceramic Capacitors

[0068] To gain a more complete understanding of the present invention, it is necessary to conduct a more in-depth analysis of the structural details of the capacitor and the functional synergy between its various parts.

[0069] Please refer to the following: Figure 2 , Figure 3 and Figure 4 Together, they depict the key structure of a high-voltage ceramic capacitor and its molding die in a preferred embodiment of the present invention.

[0070] Figure 3 A side view of the core component of the high-voltage ceramic capacitor prepared according to the present invention is shown separately. The ceramic core 4 is a dense body formed by molding and high-temperature sintering of dielectric ceramic material with a specific formulation. Its macroscopic geometry reflects the core concept of the present invention: the ceramic core 4 has opposing upper and lower electrode surfaces, which are not planes in the traditional sense, but are constructed as a concave structure recessed into the ceramic core.

[0071] Specifically analyzing this concave structure, the ceramic core 4 includes a relatively thin and uniformly thick central region 41, and an outer edge region 42 surrounding the central region 41, with its thickness gradually increasing and finally reaching its maximum at the outer circumferential edge of the ceramic core 4. At its thickest point, i.e., the outermost edge of the ceramic core 4, the thickness of the edge region 42 is significantly greater than the thickness of the central region 41. As a preferred proportional relationship, the maximum thickness of the edge region 42 is 15% to 25% greater than the thickness of the central region 41, ideally about 20%. Taking a specific, non-limiting set of design dimensions as an example, for a capacitor with a rated withstand voltage of 75kV, the thickness of the central region 41 of the ceramic core 4 can be designed to be 21mm, while the thickness of the outermost edge of the ceramic core 4 is increased to 25mm. In this case, the overall height of the ceramic core from the center to the edge is not a plane, but rather presents a continuous, smooth, sloping configuration.

[0072] The importance of this configuration lies in its smooth, gradual division of the capacitor's core functional areas into an "energy storage region" and a "voltage-enhancing region." The thickness of the central region 41 is a key parameter determining the capacitance; maintaining its uniformity ensures the capacitor's fundamental performance. The increasing thickness of the edge region 42 constitutes the complete voltage-enhancing region, responsible for bearing and buffering the concentrated electric field stress at the edges. This division and transition of functional areas is achieved through a continuous, smooth geometric structure, avoiding any abrupt structural changes that could introduce new failure points.

[0073] This smooth increase in thickness is achieved through one or more circular arc transition surfaces 43 with specific radii of curvature. For example... Figure 3As clearly shown, starting from the plane or curved surface terminating in the central region 41, the ceramic surface smoothly arches upwards in an arc until it intersects with the cylindrical sidewall of the ceramic core 4. The ingenuity of this design lies in completely avoiding any sharp corners or edges, whether on the electrode surface or at the junction of the electrode surface and the sidewall. As another optional embodiment, but also within the scope of this invention, the transition shape can also be angular, consisting of a central plane, a cylindrical or conical bevel, and a clearly visible circular ridge connecting the two. However, the smoothly transitioning arcuate structure is currently considered the best embodiment due to its superior characteristics in terms of electric field and stress concentration.

[0074] Figure 2 The semi-sectional view reveals the process of molding. Figure 3 The key component of the dry-pressing mold for the unique ceramic core 4 is shown. This mold mainly consists of an upper die punch 1, a lower die punch 3, and a concave mold cavity 2 that mates with both. The structure of this mold is complementary to and mirrors the concave structure of the ceramic core 4 to be formed. It can be seen that the forming end faces of the upper die punch 1 and the lower die punch 3 are not flat, but rather convex arc surfaces or stepped surfaces with a central bulge and concave edges. When the granulated ceramic powder is filled into the concave mold cavity 2, the powder is compressed as the upper die punch 1 and the lower die punch 3 move towards each other under the drive of the press. During this compression process, the convex surface of the mold shapes the electrode surface of the ceramic core 4 into a concave shape. Crucially, this curved surface design of the mold cavity cleverly alters the pressure transmission path within the powder. Figure 2 The pressure is not only vertically downward, but also generates a horizontal or lateral component force pointing outwards towards the mold sidewall due to the curved surface. This lateral component force applies additional extrusion pressure to the powder in the edge area, with an effect far exceeding that of traditional flat molds. Therefore, it can significantly improve the densification of the green body edge area, suppressing defects such as porosity and air trapping, thus perfectly achieving the "mechanical reinforcement" effect mentioned earlier. The molding pressure is generally controlled within the range of 5–20 MPa.

[0075] In this molding process, the direction of the lateral force generated by the convex arc surface is consistent with the tendency of the powder to flow towards the mold sidewall. This effectively promotes the "active" rather than "passive" densification of the edge powder. It is important to note that this mechanical enhancement effect is not achieved by increasing the overall molding pressure, but rather by "intelligently" guiding the pressure distribution through the geometry of the mold. Simply increasing the overall pressure to try to compact the edges often leads to overpressure in the central area, resulting in new defects such as delamination. The method of this invention achieves efficient compaction of the edge area without increasing or even using lower molding pressure (5-20 MPa), which is itself a significant technological advantage.

[0076] Figure 4 A cross-sectional schematic diagram of a complete high-voltage ceramic capacitor with a voltage-strengthened concave structure, fabricated according to the present invention, is shown. Metal electrode layers have been applied to the upper and lower surfaces of the concave ceramic core 4. The upper metal electrode layer 5 completely and conformally covers the upper electrode surface of the ceramic core 4 with its concave geometry, extending to a position near the edge of the ceramic core sidewall, but leaving a narrow insulating margin. Similarly, the lower metal electrode layer 6 also completely covers the lower electrode surface. The electrode material is typically a sintered silver electrode, with a thickness ranging from several micrometers to tens of micrometers.

[0077] "Conformal coating" of the metal electrode layer is a prerequisite for realizing the electrical function of this invention. If the silver paste coating is uneven, accumulating in the depressions of the concave surface or being too thin at the high points, it will change the designed electrode geometry, causing the actual electric field distribution to deviate from the expected one, and weakening the electric field homogenization effect of the concave structure. Therefore, high-precision and uniform silver electrode coating on the concave structure is an important process guarantee for realizing the effect of this invention.

[0078] Finally, the entire ceramic core 4 and the periphery of some electrodes are tightly encapsulated by a complete epoxy resin encapsulation layer 7. The material of this encapsulation layer 7 is preferably a modified alicyclic epoxy resin with low shrinkage and high voltage resistance. It not only provides electrical insulation between the capacitor and the external environment, preventing surface creep and arcing, but its good mechanical strength and compatibility with the ceramic body also serve to structurally reinforce and protect the concave capacitor core.

[0079] The combination of the epoxy resin encapsulation layer 7 and the concave ceramic core 4 produces another unexpected synergistic effect. Because the liquid resin perfectly fills all the depressions and curved surfaces of the concave structure before curing, the encapsulation layer formed after curing not only provides insulation macroscopically but also penetrates and anchors in the micropores of the ceramic body surface, forming a bubble-free, interface-free, tightly packed composite. Compared to encapsulation based on planar ceramic bodies, this significantly increases the bonding area and mechanical interlocking strength between the resin and the ceramic body, effectively resisting interface delamination that may be caused by thermal shock and mechanical vibration, and eliminating the risk of partial discharge developing from the interface. Therefore, the concave structure not only optimizes the internal electric field through geometric reconstruction but also unexpectedly improves the adhesion reliability and long-term insulation stability of the encapsulation layer by increasing the bonding area and enhancing mechanical interlocking, further perfecting the overall reliability chain of the capacitor.

[0080] Examples of methods for preparing high-voltage ceramic capacitors

[0081] The structural features of the core component of the capacitor of this invention have been described above. The complete fabrication method for achieving this structure and obtaining excellent performance will be elaborated below. This method is a systematic project involving the synergistic optimization of multiple key process nodes. The inventors recognized that the potential of an innovative concave structural design alone cannot be fully realized without a precision fabrication process that is compatible with its depth. Therefore, the method embodiments of this invention, particularly the powder processing, molding, and encapsulation processes, are specifically selected and optimized around the core objective of maximizing the synergistic effect of "electric field homogenization" and "mechanical strengthening."

[0082] Example 1

[0083] This embodiment provides a specific preparation process for a high-voltage ceramic capacitor with a voltage-strengthened concave structure. The formulation of its dielectric material and subsequent process parameters have been optimized based on previous orthogonal experiments.

[0084] Step 1: Ingredient Preparation. Accurately weigh the components according to the list in Example 1 of Table 1. Specifically, the total molar percentage of strontium titanate (SrTiO3), lead titanate (PbTiO3), and bismuth titanate (Bi2O3·nTiO2) is 100 mol%. In this example, SrTiO3 is 70 mol%, PbTiO3 is 22 mol%, and Bi2O3·nTiO2 is 8 mol%. Furthermore, based on the total mass of these three main ingredients, 1% magnesium carbonate (MgCO3) and 1% yttrium hydroxide (Y(OH)3) are added as modifying additives. After accurately weighing the raw materials in this proportion using a precision electronic balance, all of them are placed into a polyurethane or corundum ball mill jar.

[0085] This formulation system (SrTiO3-PbTiO3-Bi2O3·nTiO2) provides the foundation for high dielectric constant, low loss, and excellent voltage-capacitance stability. The added MgCO3 decomposes into MgO during sintering, which can act as an acceptor dopant, replacing B sites (such as Ti sites) in the perovskite structure, generating oxygen vacancies, and promoting sintering and uniform grain growth. The addition of rare earth element Y forms a high-resistivity layer at the grain boundaries, significantly improving the insulation resistance and breakdown field strength of the ceramic. By selecting specific rare earth elements and the amount of MgCO3 added in synergy with the concave structure, optimal matching of material properties and structural function is achieved.

[0086] Step 2: Primary ball milling. Deionized water is used as the milling medium, with a material:ball:water mass ratio of approximately 1:2:1. High-hardness, wear-resistant zirconia balls are used. The milling jar is placed on a ball mill and wet-milled at a certain speed for 6 hours to ensure thorough and uniform mixing of the components and refine the initial powder particle size to approximately 1 μm. After milling, the slurry is removed and placed in an oven at 120°C for thorough drying to obtain a uniformly mixed primary powder.

[0087] Step 3: Pre-firing. The dried primary powder is loaded into a mullite or alumina sagger and placed in a tunnel kiln or box furnace for pre-firing. The process parameters for pre-firing synthesis are set as follows: holding at 900℃ for 1 hour. The purpose of this step is to induce a solid-state reaction in some of the raw materials, forming the desired perovskite crystalline phase or intermediate phase, and to eliminate volatile components and structural water from the raw materials. Simultaneously, it aims to impart suitable activity to the powder, preparing it for subsequent fine grinding and final sintering and densification. After holding at this temperature, the powder is allowed to cool naturally to room temperature in the furnace, yielding a loose sintered mass.

[0088] Step 4: Secondary ball milling. The cooled sintered material blocks are crushed and put back into the ball mill jar. Deionized water is used as the medium, and a secondary ball milling is performed at a material:ball:water ratio of approximately 1:1:1.2. Smaller zirconia balls are still used as the grinding media. The purpose of this ball milling is to further grind the pre-sintered, partially phase-formed powder to the submicron level, narrowing its particle size distribution and sphericizing the particles. The secondary ball milling time is controlled at 3 hours. After ball milling, samples are taken from the slurry and analyzed using a laser particle size analyzer to ensure that the median particle size of the powder reaches approximately 0.15 μm, and electron microscopy shows good particle sphericity.

[0089] In this invention, controlling the powder particle size to approximately 0.15 μm (D50), ensuring spherical shape and narrow particle size distribution, is the key microscopic basis for achieving superior performance. These powder characteristics are inherently compatible with the unique concave structure of this invention: the high sphericity and narrow particle size distribution of the powder result in excellent flowability, allowing it to fill the various depths of the concave cavity in the mold without discrimination or obstruction, especially the most difficult-to-fill, deepest central thin region. This ensures uniform density throughout the green body, avoiding localized over- or under-firing defects caused by uneven filling, which is crucial for ceramic cores with non-uniform thickness and complex shapes. If the powder flowability is poor, the central region cannot be densely filled, directly leading to insufficient capacitance and decreased breakdown strength in that area, rendering the design advantages of the concave structure ineffective.

[0090] Step 5: Granulation and Molding. In the ultrafine slurry obtained in Step 4, approximately 5% (by weight) of an aqueous solution of CMC (sodium carboxymethyl cellulose) as a binder and a trace amount of dispersant (such as triethanolamine) are added, and the mixture is continuously stirred until homogeneous. This slurry, exhibiting good suspension and flowability, is then fed into a spray drying tower for granulation. The inlet temperature is controlled at approximately 250°C, and the outlet temperature at approximately 110°C. The resulting spherical agglomerates have a particle size concentrated between 80 and 150 μm and exhibit excellent flowability. The next crucial step is molding: the granulated powder is filled into a container with a... Figure 2 The molded part, designed to match the specifications, is capable of pressing a smooth concave structure onto both the upper and lower surfaces. Dry pressing is performed on a hydraulic press at a pressure of 12 MPa. After holding the pressure for a certain time, the part is demolded to obtain a cylindrical green body with a clear concave structure and uniform density. The ceramic body is designed with a diameter of approximately 32 mm, a central area height of approximately 21 mm, and an edge area that is approximately 2 mm higher on one side (approximately 4 mm higher on both sides) due to the mold's concavity, resulting in a thickness increase of approximately 16%.

[0091] Step 6: Sintering. Carefully place the formed green blanks into a clean sagger. Spread a layer of calcined zirconium dioxide powder at the bottom of the sagger as an insulating layer to prevent sintering adhesion. Push the sagger into a high-temperature tunnel furnace or box-type resistance furnace for sintering. The sintering regime is as follows: heat to 1250℃ at a rate of 2-3℃ / min, hold at this maximum temperature for 4 hours, and then cool down at the same rate or allow it to cool naturally to room temperature in the furnace. After removal, a dense, porcelain-white capacitor core 4 with uniform dimensional shrinkage and perfectly preserved concave structure is obtained.

[0092] During sintering, the concave green body with gradually varying thickness exhibited surprisingly good sintering consistency. Although theoretically, differences in thickness might lead to uneven shrinkage, experiments revealed that the edge regions, due to their higher density during forming, had relatively lower sintering driving forces; while the thinner, less dense central regions had greater sintering driving forces. This inverse complementarity between the initial density gradient and the sintering driving force gradient enabled the entire ceramic body to shrink almost synchronously during sintering, without warping or cracking. This demonstrates that concave forming not only did not introduce sintering obstacles but also created an intrinsic, self-regulating stress balance mechanism, further illustrating a synergistic effect.

[0093] Step 7: Silvering and Firing. A uniform, controlled-thickness layer of low-temperature silver paste (e.g., silver oxide glass system) is applied to the upper and lower concave surfaces of the ceramic core 4 obtained in Step 6 using screen printing or manual coating. A safe distance of approximately 2 mm is maintained between the edge of the silver paste coating and the edge of the ceramic body sidewall. After coating, the core is dried at 150°C and then placed in a mesh belt furnace for silvering at a peak temperature of 750°C for approximately 20 minutes, ensuring a strong mechanical-electrical interface and good ohmic contact between the silver layer and the ceramic body. After cooling, copper lead terminals are soldered along the center line of the silver layer.

[0094] Step 8: Encapsulation. This invention employs an improved epoxy resin encapsulation process. Instead of commonly used bisphenol A type epoxy resin (such as E-51), an alicyclic epoxy resin is used as the base resin, combined with a liquid acid anhydride (such as methylhexahydrophthalic anhydride) as a curing agent, and appropriate amounts of toughening agent and silica powder filler are added. The capacitor core is preheated to approximately 80°C, placed in a pre-vacuumed casting mold, and the prepared epoxy resin mixture is injected, followed by degassing under vacuum. Subsequently, curing is performed in an oven according to a stepped temperature increase program: 100°C for 2 hours, and 120°C for 4 hours, to ensure complete cross-linking and curing of the epoxy resin.

[0095] Step 9: Post-curing, aging, and testing. The encapsulated capacitor was heated in an oven at 100°C for 10 hours for post-curing to completely release internal stress. Subsequently, electrical aging was performed, and all electrical properties of the capacitor, including appearance, capacitance, dielectric loss, insulation resistance, power frequency withstand voltage, partial discharge, and temperature characteristics, were tested according to routine and type testing standards in the field. The test results were recorded in the final comprehensive performance table. The capacitor prepared in this embodiment achieved an average withstand voltage of 3.5kV per millimeter of thickness in the power frequency withstand voltage test, a significant improvement over traditional planar structures.

[0096] Example 2

[0097] The preparation steps and process parameters of this embodiment are the same as those of Example 1, except that the material formulation ratios are as follows (molar percentage, the total of the three main materials is 100 mol%): SrTiO3 is 68 mol%, PbTiO3 is 20 mol%, and Bi2O3·nTiO2 is 12 mol%. Meanwhile, the types and amounts of modifying additives are as follows: based on the total mass of the main materials, the amount of MgCO3 added is 1.9 wt%, and the amount of cerium hydroxide (Ce(OH)3) added is 0.1 wt%. A capacitor with the concave structure of this invention is obtained using this formulation and the above process, and its performance is also tested.

[0098] Example 3

[0099] The preparation steps and process parameters of this embodiment are the same as those of Example 1, the only difference being the material formulation ratio: SrTiO3 is 75 mol%, PbTiO3 is 14 mol%, and Bi2O3·nTiO2 is 11 mol%. The modifying additives are: based on the total mass of the main materials, the amount of MgCO3 added is 3.5 wt%, and the amount of lanthanum hydroxide (La(OH)3) added is 1.5 wt%.

[0100] Example 4

[0101] The preparation steps and process parameters in this embodiment are the same as in Example 1, except that: SrTiO3 is 73 mol%, PbTiO3 is 17 mol%, and Bi2O3·nTiO2 is 10 mol%. The modifying additive adopts a composite rare earth formula: based on the total mass of the main materials, the amount of MgCO3 added is 4.0 wt%, and cerium hydroxide (Ce(OH)3) and lanthanum hydroxide (La(OH)3) are each added at 0.5 wt%.

[0102] Example 5

[0103] The preparation steps and process parameters of this embodiment are the same as those of Example 1, except that: SrTiO3 is 75 mol%, PbTiO3 is 10 mol%, and Bi2O3·nTiO2 is 15 mol%. The modifying additives are: based on the total mass of the main materials, the amount of MgCO3 added is 2.8 wt%, and the amount of dysprosium hydroxide (Dy(OH)3) added is 1.2 wt%.

[0104] Example 6

[0105] The preparation steps and process parameters of this embodiment are the same as those of Example 1, except that: SrTiO3 is 80 mol%, PbTiO3 is 10 mol%, and Bi2O3·nTiO2 is 10 mol%. The modifying additives are: based on the total mass of the main materials, the amount of MgCO3 added is 1.4 wt%, and the amount of neodymium hydroxide (Nb(OH)3) added is 0.6 wt%.

[0106] Test and performance results analysis

[0107] To comprehensively and multidimensionally verify the substantial progress and synergistic effect of this invention compared to the prior art, not only were comprehensive electrical performance tests conducted, but a comparative ratio was also added to isolate the influence of key factors, and a reliability comparison analysis was performed.

[0108] To verify the advancement and effectiveness of the technical solution of this invention, we conducted comprehensive electrical performance tests on the high-voltage ceramic capacitors with concave structures prepared in Examples 1 to 6 above. The test items and standard instruments used are as follows:

[0109] Capacitance and dielectric loss: Measured using a precision LCR meter at 5V and 1000Hz.

[0110] DC insulation resistance: Using an insulation resistance tester, apply a 1000V DC voltage and read the resistance value after 1 minute.

[0111] Power frequency AC withstand voltage: Using power frequency high voltage test equipment, the voltage is increased from zero to the specified test voltage at the specified rate and held for 1 minute.

[0112] Partial discharge quantity: Using a high-voltage partial discharge test system, the partial discharge initiation voltage and extinction voltage are measured under a specific AC voltage (e.g., 12kV), and the apparent discharge quantity under the specified voltage is recorded.

[0113] Voltage-capacitance characteristics: The rate of change of capacitance was measured using a high-voltage Schering bridge over an AC voltage range of 1000V to 15kV.

[0114] Temperature-capacity characteristics: The rate of change of capacitance is measured using an LCR meter with the capacitance at +25℃ as the reference, within a temperature range of -25℃ to +85℃.

[0115] The specific test data for each embodiment are summarized in Table 1 below.

[0116] Table 1 Comparison of Ceramic Capacitor Performance Tests for Each Embodiment

[0117] Example Capacitance (pF) <![CDATA[Dielectric loss (×10 -4 )]]> <![CDATA[Insulation Resistance (×10 12 Ω)]]> AC withstand voltage (kV, AC) Partial discharge initiation voltage 36kV·AC Voltage Capacity Characteristics Temperature capacity characteristics: -25℃ to +85℃ 1 1083 9 ＞10 ＞78 <1pc ＜10% ＜±22% 2 1095 8 ＞10 ＞75 <1pc ＜10% ＜±20% 3 1048 9 ＞10 ＞75 <1pc ＜10% ＜±20% 4 1077 8 ＞10 ＞80 <1pc ＜10% ＜±22% 5 1097 8 ＞10 ＞75 <1pc ＜10% ＜±21% 6 1060 8 ＞10 ＞77 <1pc ＜10% ＜±20%

[0118] As can be seen from the test results in Table 1, all six embodiments of high-voltage ceramic capacitors manufactured using the technical solution provided by this invention, namely the specific concave ceramic core structure and the optimized complete set of manufacturing processes, exhibit satisfactory and commercially competitive electrical performance indicators.

[0119] The specific analysis is as follows: First, regarding the most critical withstand voltage performance, all embodiments, with a ceramic body thickness of only 21mm in the central region, consistently achieved a power frequency withstand voltage exceeding 75kV, equivalent to a withstand voltage of over 30kV per millimeter of thickness. Furthermore, through preferred embodiments 1, 4, and 6, the withstand voltage per millimeter could stably reach or even exceed 3.5kV. This represents a qualitative leap, almost doubling, compared to the baseline level mentioned in the background of this invention, where "planar structure capacitors under the same process can only achieve 2kV per millimeter." This undoubtedly verifies that the concave and convex structures have a significant withstand voltage enhancement effect, breaking through the ceiling of traditional processes. Second, regarding other key electrical performance parameters, the dielectric loss of all embodiments remained at 8–9 × 10⁻⁶. -4 Extremely low levels, with insulation resistance all greater than 10 × 10⁻⁶. 13The capacitor exhibits excellent dielectric properties and extremely high insulation reliability. Furthermore, regarding application stability, under the preset 36kV AC high voltage, the partial discharge quantity in all embodiments is less than 1pC. This indicates that the electric field distribution inside and at the edges of the capacitor is extremely uniform, with almost no concentrated air gaps or high field strength points that could lead to partial discharge, fundamentally guaranteeing its long-term reliability and lifespan. Simultaneously, the voltage-capacitance change rate is less than 10%, and the temperature-capacitance change rate is less than 22%, both lower than the capacitance change rate (25%-28%) of similar dielectric ceramics. This demonstrates that the capacitor of this invention can maintain a stable capacitance over a wide voltage and temperature range, and can well adapt to complex and harsh operating conditions.

[0120] Comparative Example

[0121] To better highlight the non-obvious beneficial effects of the concave structure of this invention, the inventors also set up and implemented a representative comparative example. Using the exact same formulation, powder processing technology, sintering regime, and encapsulation process as Example 1, the only difference being the use of a traditional flat mold, a batch of conventional planar cylindrical ceramic capacitors with the exact same diameter and central region thickness as Example 1 were produced. The same AC withstand voltage test was performed on this batch of comparative products. Typical test results showed that 75% of the samples broke down when a voltage of 50kV was applied, and only a very small portion could withstand 55kV. Converted to withstand voltage per unit thickness, this is only about 2.0–2.2kV / mm. This comparative result clearly and powerfully demonstrates that the huge improvement in withstand voltage achieved in Example 1, from 2kV / mm to over 3.5kV / mm, is solely and decisively contributed by the original concave structure design of this invention. Such a significant difference in effect would not be expected by those skilled in the art from the simple logic of the prior art (e.g., chamfering or increasing dimensions).

[0122] To further reveal the unique contribution of the "mechanical strengthening" effect brought about by the concave structure, the inventors conducted a second set of comparative experiments. Using selective laser sintering (SLS) 3D printing technology, and directly using the same granulated powder as in Example 1, they printed concave ceramic core green bodies with uniform densification and shapes completely identical to those in Example 1. The 3D printing process completely eliminates the uneven densification effect caused by mold wall friction in traditional dry pressing; therefore, the edge areas of this green body did not achieve the additional densification effect seen in Example 1. This 3D-printed green body was then subjected to the same sintering, silvering, and encapsulation processes as in Example 1 to produce capacitors. Test results showed that the average power frequency withstand voltage of this batch of 3D-printed concave structure capacitors was approximately 60kV, equivalent to 2.4kV / mm.

[0123] This result is very enlightening:

[0124] (1) It confirms that the "electric field homogenization" effect of the concave structure does indeed exist independently. Compared with the 2.0kV / mm of the parallel plate capacitor, the 2.4kV / mm of the 3D printed group achieves a performance improvement of about 20%, which is a direct contribution of the "electric field homogenization" principle.

[0125] (2) It further demonstrates the significant contribution of "mechanical strengthening". In Embodiment 1 of the present invention, "electric field homogenization + mechanical strengthening" are achieved simultaneously through mold forming, with a withstand voltage of over 3.5 kV / mm. This is approximately 46% higher than that of the 3D printed assembly (2.4 kV / mm) which only has the effect of "electric field homogenization".

[0126] Therefore, the performance leap achieved in Embodiment 1 of this invention (2.0 → 3.5 kV / mm) can be deconstructed as follows: electric field homogenization contributed an improvement from 2.0 to 2.4 (+0.4), while mechanical strengthening contributed an improvement from 2.4 to 3.5 (+1.1). This is not a simple superposition of "1+1=2" (i.e., an improvement of 0.4+0.4=0.8), but rather produces a synergistic effect far exceeding the superposition (an improvement of 1.5). This fully demonstrates that the intrinsic breakdown strength of the edge-dense material strengthened "in situ" during dry pressing in this invention, and the electric field strength reduced by the "active" conduction of the concave structure, exhibit a multiplicative rather than additive synergistic amplification effect, producing unexpected technical results.

[0127] To further verify the superiority of the product of this invention, a reliability comparison test was conducted on the products of Example 1 and Comparative Example 1. An accelerated aging test was performed under humid heat conditions of 85°C / 85%RH, applying 70% of the rated voltage. After 1000 hours, the insulation resistance of the product of Example 1 remained at 5 × 10⁻⁶. 13 Above Ω, there were no failures. In contrast, approximately 30% of the comparative products with traditional planar structures experienced a significant drop in insulation resistance or breakdown. This demonstrates that the concave structure of this invention not only improves the initial withstand voltage level but also significantly delays the long-term electrochemical corrosion and aging process caused by the combined effects of high temperature, high humidity, and electric field, resulting in a structural improvement in long-term operational reliability.

[0128] Through the above structural description, detailed method description, embodiments, and comparative data, the key technical problems solved by the present invention and the unexpected technical effects achieved can be systematically summarized.

[0129] Technical Problem: As thoroughly analyzed in the background section, this invention aims to solve the problem of low edge breakdown voltage and poor reliability in ceramic capacitors caused by the coupling of electric field edge effects and inherent defects in the molding process, a problem that cannot be overcome by traditional methods or solely through material formulation. In particular, it aims to provide a solution that does not rely on introducing heating elements (such as semiconductor glaze), does not significantly increase the size and weight of the capacitor, and is simple and highly controllable in its process.

[0130] Technical effects:

[0131] Firstly, it creatively provides and validates a capacitor withstand voltage enhancement paradigm based on an "electrode surface concave structure." Instead of simply chamfering or rounding the edges, it designs the entire electrode surface as a functional three-dimensional concave curved surface, realizing a transformation from "passively accepting" edge effects to "actively controlling" the electric field distribution.

[0132] Secondly, it achieves a synergistic effect of "killing two birds with one stone"—electric field homogenization and mechanical strengthening. Through precise mold design, a single molding process simultaneously optimizes the electrode surface geometry (electrical function) and achieves ultra-dense molding of the green body edge region (mechanical function). After sintering, the ceramic body exhibits not only a more gentle electric field distribution at the edge region, but also a more uniform and dense microstructure, reducing primary defects that could trigger breakdown. This electro-mechanical integrated design concept is highly original in the field of ceramic capacitors. Its core lies in the fact that this effect is not simply the coexistence of two independent advantages, but rather a synergistic effect of "1+1>2". Comparative data irrefutably demonstrates that the performance improvement of only the electric field homogenization function (3D printing group) is approximately 20%, while the solution of this invention, which simultaneously achieves both functions, improves performance by over 75%, far exceeding the sum of the two. The root of this synergistic effect is that it allows the weakened external electric field stress to act on the strengthened material body, achieving an optimal match between the field and the material.

[0133] Thirdly, it has achieved a remarkably significant improvement in withstand voltage performance. Test data conclusively demonstrates that, while maintaining the same center thickness and approximate volume, this invention can increase the power frequency withstand voltage of ceramic capacitors by more than 75%, from approximately 2kV / mm to over 3.5kV / mm, enabling domestic products to directly match or even surpass international advanced levels in withstand voltage.

[0134] Fourth, the overall electrical performance is excellent. Besides a significant improvement in the core withstand voltage, the capacitor prepared by this invention also exhibits high insulation, low loss, high partial discharge initiation voltage, and excellent voltage and temperature capacitance stability. The balance and optimization of various performance characteristics have reached a new level. In particular, the partial discharge initiation voltage is stable above 36kVAC and the discharge quantity is less than 1pC, indicating that the concave structure successfully eliminates the microscopic air gaps and high field strength points in the edge region, achieving a near-ideal "partial discharge-free" high-voltage operation state, which is extremely difficult to achieve in traditional planar capacitors.

[0135] Fifth, it possesses extremely strong industrial applicability. The solution of this invention can be implemented entirely on existing production lines, requiring only the replacement of a key mold and adaptation optimization of processes such as ball milling and encapsulation. The modification cost is extremely low, product consistency is excellent, yield is high, and it perfectly avoids the heat generation problem inherent in semiconductor glaze solutions. It has immediate industrial-scale promotion value and significant economic benefits. Furthermore, the reliability improvement brought about by this invention can significantly reduce maintenance costs and failure risks throughout the equipment's lifecycle, creating long-term value for users that exceeds the initial purchase cost. Therefore, the technical solution of this invention is not only a laboratory innovation but also a high-value innovation geared towards industrial applications.

[0136] Obviously, the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description, such as changing the curvature of the concave transition region, adjusting the edge thickening ratio to adapt to different voltage levels, using other types of microwave dielectric ceramic systems, replacing different rare earth elements, or adopting a single-sided concave structure. It is neither necessary nor possible to exhaustively list all possible implementations here. However, these obvious variations or modifications derived from the spirit of the present invention are still within the protection scope of the present invention.

[0137] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-voltage ceramic capacitor with a voltage-strengthened concave surface structure, characterized in that, The device includes a cylindrical ceramic core (4) made of dielectric ceramic material, the ceramic core (4) having an upper electrode surface and a lower electrode surface arranged opposite to each other; the upper electrode surface and / or the lower electrode surface are not planar, but form a concave structure that is recessed from the central region (41) of the electrode surface into the interior of the ceramic core (4), so that the thickness of the ceramic core (4) is minimal in the central region (41), and its thickness increases continuously or stepwise from the central region (41) to the outer edge region (42), reaching the maximum thickness at the outer circumferential edge of the ceramic core (4); the upper electrode surface and the lower electrode surface are respectively covered with a metal electrode layer that completely covers their respective concave structures; the periphery of the ceramic core (4) and part of the metal electrode layer is covered by an epoxy resin encapsulation layer (7).

2. A high-voltage ceramic capacitor with a voltage-strengthened concave surface structure according to claim 1, characterized in that, The maximum thickness of the edge region (42) of the ceramic core (4) is 10% to 30% greater than the minimum thickness of the central region (41).

3. A high-voltage ceramic capacitor with a voltage-strengthened concave surface structure according to claim 2, characterized in that, The maximum thickness of the edge region (42) is 10% to 25% greater than the minimum thickness of the central region (41).

4. A high-voltage ceramic capacitor with a voltage-strengthened concave surface structure according to claim 1, characterized in that, The concave structure is a smooth concave surface, and the surface from the central region (41) to the edge region (42) is one or more circular arc transition surfaces (43) with a specific radius of curvature.

5. A high-voltage ceramic capacitor with a voltage-strengthened concave structure according to any one of claims 1 to 4, characterized in that, The composition and content of the dielectric ceramic material constituting the ceramic core (4) include, in molar percentage, 68%–80% SrTiO3, 10%–22% PbTiO3, and 8%–15% Bi2O3·nTiO2; and, relative to the total mass of SrTiO3, PbTiO3 and Bi2O3·nTiO2, an additional 1%–5% MgCO3 and 0.1%–1.5% Re(OH)3 are added, wherein Re is at least one rare earth element selected from Y, Ce, La, Dy and Nd.

6. A method for preparing a high-voltage ceramic capacitor with a voltage-strengthened concave structure as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Ingredient preparation and primary ball milling: Weigh out the SrTiO3, PbTiO3, Bi2O3·nTiO2, MgCO3 and Re(OH)3 powders according to the predetermined amount, mix them, add deionized water and ball mill to obtain mixed powder; Pre-sintering: The dried mixed powder is pre-sintered at a temperature of 900℃~1150℃ to obtain pre-sintered composite material; Secondary ball milling: The pre-calcined synthetic material is added to deionized water again for ball milling to obtain an ultrafine slurry with a median particle size D50 in the range of 0.1 to 0.2 μm; Granulation and molding: After adding binder to ultrafine powder slurry, spray granulation is performed to obtain spherical agglomerates; then the spherical agglomerates are filled into the mold cavity with a concave structure that matches the target ceramic core (4), and dry pressing is performed under a pressure of 5 to 20 MPa to obtain a green body with a concave structure. Sintering: The green body is sintered at 1200℃~1300℃ for 180~300 minutes to obtain a densified ceramic core (4); Silvering and firing: Silver paste is coated on the upper and lower concave surfaces of the ceramic core (4) and fired at 700℃~750℃ to form a metal electrode layer; Encapsulation: The capacitor core with soldered leads is encapsulated by casting or coating with epoxy resin.

7. The method for preparing a high-voltage ceramic capacitor with a voltage-strengthened concave structure according to claim 6, characterized in that, The first ball milling time is 5 to 7 hours, and the second ball milling time is 3 to 5 hours. The powder particles obtained after the second ball milling have high sphericity and narrow particle size distribution.

8. The method for preparing a high-voltage ceramic capacitor with a voltage-strengthened concave structure according to claim 6, characterized in that, The mold used in the dry pressing step has a complementary convex arc surface that matches the smooth arc transition surface (43) of the concave structure, thereby generating a lateral component force during pressing to strengthen the densification of the green edge region (42).

9. The method for preparing a high-voltage ceramic capacitor with a voltage-strengthened concave structure according to claim 6, characterized in that, In the encapsulation step, the epoxy resin used is an alicyclic epoxy resin, and it is cured in conjunction with an acid anhydride curing agent.

10. A high-voltage ceramic capacitor prepared by the method for preparing a high-voltage ceramic capacitor with a voltage-strengthened concave structure according to any one of claims 6 to 9, characterized in that, In the power frequency AC withstand voltage test, when the withstand voltage of the ceramic body center region (41) thickness per millimeter is not less than 3.5kV and the partial discharge initiation voltage is not less than 36kV, the apparent partial discharge amount is less than 1pC.

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