Electrolytic capacitor and method for manufacturing the same

Abstract

To provide an electrolytic capacitor capable of reducing defects in the dielectric layer on the surface of the anode body, and a manufacturing method thereof.SOLUTION: The electrolytic capacitor has a capacitor element that includes a porous anode body 1, a dielectric layer formed on the surface of the anode body 1, and a solid electrolyte layer covering at least part of the dielectric layer. The anode body 1 has multiple main surfaces 101A, 101B, 101C, ..., multiple side portions (connection surfaces 102A, 102B, 102C, ...) that connect the multiple main surfaces, and corner portions (second connecting surface 103A and the like) that include the apex part where multiple main faces intersect each other. The surface layer of at least a portion of the corner portion is denser than the surface layer of the adjacent main surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor and a method for manufacturing the same.

Background Art

[0002] Electrolytic capacitors are mounted in various electronic devices because they have a small equivalent series resistance (ESR) and excellent frequency characteristics. An electrolytic capacitor usually includes a capacitor element having an anode portion and a cathode portion. The anode portion includes a porous anode body, and a dielectric layer is formed on the surface of the anode body. The dielectric layer is in contact with an electrolyte. There is an electrolytic capacitor using a solid electrolyte such as a conductive polymer as the electrolyte (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Improve the reliability of an electrolytic capacitor using a solid electrolyte.

Means for Solving the Problems

[0005] One aspect of the present disclosure includes a capacitor element including a porous anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer. The anode body has a plurality of main surfaces and corner portions. The corner portions include a plurality of side portions and vertex portions connecting the plurality of main surfaces to each other. At least a part of the surface layer X of the corner portion is denser than the surface layer Y of the main surface adjacent to the surface layer X. The present disclosure relates to an electrolytic capacitor.

[0006] Another aspect of the present disclosure relates to a method for manufacturing a solid electrolytic capacitor including a capacitor element including a porous anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer, the method including: preparing the anode body; covering at least a part of the anode body with the dielectric layer; and covering at least a part of the dielectric layer with the solid electrolyte layer, wherein the anode body has a plurality of main surfaces and a corner portion including a plurality of side portions and vertex portions connecting the plurality of main surfaces, and the step of preparing the anode body includes irradiating at least a part of the corner portion with laser light.

[0007] Still another aspect of the present disclosure relates to a method for manufacturing a solid electrolytic capacitor including a capacitor element including a porous anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer, the method including: preparing the anode body; covering at least a part of the anode body with the dielectric layer; and covering at least a part of the dielectric layer with the solid electrolyte layer, wherein the anode body has a plurality of main surfaces and a corner portion including side portions and vertex portions connecting the plurality of main surfaces, and the step of preparing the anode body includes colliding media particles with at least a part of the corner portion.

[0008] Still another aspect of the present disclosure relates to a method for manufacturing a solid electrolytic capacitor including a capacitor element including a porous anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer, the method including: preparing the anode body; covering at least a part of the anode body with the dielectric layer; and covering at least a part of the dielectric layer with the solid electrolyte layer, wherein the anode body has a plurality of main surfaces and a corner portion including side portions and vertex portions connecting the plurality of main surfaces, and the step of preparing the anode body includes vibrating the anode body together with a vibrating member. [[Effect of the Invention]]

[0009] The reliability of the electrolytic capacitor is improved. The novel features of the present invention are described in the appended claims. However, the present invention relates to both the configuration and the content, and will be better understood from the following detailed description in conjunction with the drawings, together with other objects and features of the present invention.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0011] [Electrolytic Capacitor] The electrolytic capacitor according to an embodiment of the present invention includes a capacitor element including a porous anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer. The anode body has a plurality of main surfaces and corner portions. The corner portions include, for example, a plurality of side portions connecting the plurality of main surfaces to each other, and one or a plurality of vertex portions connecting the plurality of main surfaces to each other. At least a part of the corner portion has a curved surface or is chamfered.

[0012] In the anode body, by having a curved surface or being chamfered at least in part of the side portion and / or the vertex portion, damage to the dielectric layer at the corner portion is suppressed, and an electrolytic capacitor with a small leakage current can be realized. Therefore, the reliability of the electrolytic capacitor can be enhanced.

[0013] The edge portion refers to the edge where two main surfaces of the anode body intersect and the region in the vicinity thereof. The vertex portion refers to the vertex where three main surfaces of the anode body intersect and the region in the vicinity thereof. Here, the edge portion and the vertex portion are collectively referred to as the "corner portion". That at least a part of the corner portion has a curved surface or is chamfered means, for example, that at least one edge portion and / or at least one vertex portion has a curved surface or is chamfered. Also included is the case where a part of one edge portion has a curved surface or is chamfered.

[0014] Also, that at least a part of the corner portion has a "curved surface" is not limited to the case where the cross-sectional shape of the corner portion is a curve. For example, the cross-sectional shape of the corner portion may be a broken line having a plurality of obtuse angles. When the cross-sectional shape is a convex shape and, in the cross-sectional shape, a straight line corresponding to one main surface and a straight line corresponding to another adjacent main surface are connected via at least one straight line and / or curve, it can be said that the corner has a curved surface. In other words, that the corner portion has a "curved surface" also means that in the cross-sectional shape of the corner portion in a cross-section perpendicular to two adjacent main surfaces, there is no region that tapers to 90° or less.

[0015] The dielectric layer is usually formed by subjecting the anode body to a formation treatment to grow an oxide film on the surface of the anode body. Therefore, the properties of the dielectric layer formed by formation are affected by the surface state of the anode body before the formation treatment.

[0016] The anode body usually has a rectangular parallelepiped shape. In this case, in the vicinity of the edge connecting two orthogonal main surfaces of the rectangular parallelepiped and / or in the vicinity of the vertex (corner portion) where three mutually orthogonal main surfaces of the rectangular parallelepiped intersect, the surface of the anode body is not flat when viewed microscopically, has a large surface roughness, and is likely to have an uneven shape. When the dielectric layer is grown by a formation treatment in this state, defects are likely to occur in the dielectric layer at the uneven portions. When defects occur in the dielectric layer, a current flow path may be generated between the solid electrolyte and the valve action metal through the defective portions, and the leakage current may increase.

[0017] In addition, since the anode body is porous, it is brittle and easily broken. In particular, the corner portion of the anode body has lower mechanical strength compared to the portions other than the corner portion, and thermal stress is likely to concentrate. When the porous portion is damaged, the dielectric layer covering the porous portion may be damaged. Due to the damage of the dielectric layer, the leakage current may increase.

[0018] In the electrolytic capacitor of the present embodiment, by forming at least a part of the corner portion of the anode body into a curved surface, defects during the formation of the dielectric layer can be reduced. As a result, the leakage current can be reduced. In addition, the mechanical strength can be increased and the thermal stress is relaxed. Thereby, damage to the dielectric layer after formation can be suppressed. As a result, an increase in the leakage current is suppressed.

[0019] A solid electrolyte layer is formed so as to cover the dielectric layer. When the corner portion of the anode body does not have a curved surface, the thickness of the solid electrolyte layer at the corner portion is likely to be formed thinly. In particular, when the solid electrolyte layer contains a conductive polymer and the conductive polymer is formed by chemical polymerization, the thickness of the solid electrolyte layer at the corner portion is likely to become thin. However, by forming at least a part of the corner portion into a curved surface, thinning of the solid electrolyte layer at the corner portion can be suppressed, and the solid electrolyte layer can be formed with a uniform thickness. Thereby, the electrolytic capacitor becomes stronger against external stress, and an increase in the leakage current and the occurrence of short-circuit defects can be suppressed. In addition, the withstand voltage is improved.

[0020] The surface layer X of at least a part of the corner portion may be denser than the surface layer Y of the main surface adjacent to the surface layer X. The surface layer Y is the surface layer of the main surface adjacent to the corner portion, and usually, the porous anode body is exposed. By forming the surface layer X of the corner portion densely, the mechanical strength of the corner portion can be further increased. Therefore, the effect of suppressing an increase in the leakage current through the corner portion can be enhanced.

[0021] In addition, when at least a part of the surface layer X of the corner portion is formed densely, the dense surface layer X may not be a curved surface or may not be a chamfered surface. Even when the corner portion does not have a curved surface and is not chamfered, sufficient mechanical strength can be obtained by the dense formation of the surface layer X of the corner portion. Therefore, an increase in leakage current through the corner portion can be suppressed. However, it is preferable that at least a part of the portion including the surface layer X has a curved surface shape or a chamfered shape, as the leakage current can be further suppressed. In this case, the surface layer Y can be a region adjacent to the portion having the curved surface shape or the chamfered shape of the surface layer X.

[0022] That the surface layer X is denser than the surface layer Y means, for example, that the porosity P1 in the surface layer X is smaller than the porosity P2 in the surface layer Y. The surface layer X may have, for example, a portion where the porosity P1 is 10% or less. In contrast, the porosity P2 in the surface layer Y is usually 20% or more.

[0023] The surface layer X and the surface layer Y may have a portion where the ratio P2 / P1 of the porosity P2 to the porosity P1 satisfies, for example, 5 or more. P2 / P1 may be 10 or more or 50 or more. Any portion of the surface layer X and any portion of the surface layer Y may satisfy P2 / P1 of 5 or more.

[0024] In addition, when at least a part of the corner portion has a curved surface, the curvature of the curved surface is, for example, 0.002 (1 / μm) to 0.05 (1 / μm), and more preferably 0.005 (1 / μm) to 0.02 (1 / μm).

[0025] Note that the curvature and the porosity are obtained by image analysis of a cross-sectional photograph of the anode body in a predetermined region. In the electron micrograph of the cross-section, the area of the void portion in an arbitrary region A in the surface layer X is obtained, and the ratio of the area of the void portion to the region A is defined as the porosity P1. Similarly, the area of the void portion in an arbitrary region B in the surface layer Y is obtained, and the ratio of the area of the void portion to the region B is defined as the porosity P2.

[0026] The corner portion having a curved surface may be formed by pressure-molding the anode body using a mold that forms the curved surface, or by removing a part of the corner portion of the anode body. However, by irradiating the corner portion with laser light, a curved surface can be formed and / or the surface layer of the corner portion can be formed densely. By irradiating with laser light, the surface layer X of the corner portion melts. The surface layer X after laser light irradiation is a molten layer formed by melting the porous portion of the anode body and can be formed denser than the porous surface layer Y. The porosity P1 of the surface layer X formed by laser light irradiation is extremely small and can be, for example, 1% or less.

[0027] Alternatively, the anode body may be placed on a vibrating member such as a sieve or media particles, and the vibrating member may be vibrated to form the corner portion into a curved surface. In this case, the corner portion of the anode body collides with the vibrating member due to vibration, and the corner portion is compressed by the collision, and the corner portion can be formed into a curved surface shape. Thereby, the surface layer X of the corner portion can be formed denser (higher density) than the surface layer Y of the main surface where the porosity is maintained.

[0028] Among the corner portions, the portion having a curved surface shape or a chamfered shape includes, for example, a portion having a curvature radius R of 20 μm to 500 μm, and more preferably includes a portion having a curvature radius R of 50 μm to 200 μm. Here, the curvature radius of the corner portion is calculated by photographing the anode body from the side of a certain main surface and performing image analysis on the contour shape in the vicinity of the obtained corner (vertex). In the contour line of the anode body, the distance from the boundary between the region where the curved surface is formed (chamfered portion) and the side portion where the curved surface is not formed (not chamfered) to the vertex position (the position of the intersection of the side portions) before the curved surface is formed (before chamfering) is obtained and regarded as the curvature radius R. It is also possible to obtain the curvature radius R for each side portion of the anode body and calculate the average value. For example, when the anode body is substantially rectangular parallelepiped, the curvature radius R is obtained at both ends of 12 side portions, and the average value of 24 curvature radii R is obtained. By using a vibrating member, an anode body having an average value of the curvature radius R within the above range can be easily obtained.

[0029] In the corner portion of the anode body, the portion having a curved surface shape or a chamfered shape may include portions having different curvature radii R. In that case, the variation in the curvature radius R of the plurality of corner portions in the anode body can be, for example, 350 μm or less, more preferably 150 μm or less. The variation in the curvature radius R is the difference between the maximum value and the minimum value of the curvature radius R of the corner portion calculated by the above method (when the anode body is substantially rectangular parallelepiped, the difference between the maximum value and the minimum value among the 24 calculated curvature radii).

[0030] FIG. 1 is a schematic perspective view showing an example of an anode body used in the electrolytic capacitor of the present embodiment. As shown in FIG. 1, the anode body 1 has a substantially rectangular parallelepiped shape, and six main surfaces 101A to 101F are exposed. Note that 101D to 101F are not shown because they are in positions hidden from the paper surface.

[0031] In the main surfaces 101A to 101F, in the vicinity of the side where two adjacent main surfaces intersect, a connection surface is formed by chamfering the corner of the side portion. In the example of FIG. 1, a connection surface 102C is interposed between the main surfaces 101A and 101B, a connection surface 102A is interposed between the main surfaces 101B and 101C, and a connection surface 102A is interposed between the main surfaces 101B and 101C. Also, in the vicinity of the vertex where three main surfaces intersect, a second connection surface is formed by chamfering the corner of the vertex portion. In the example of FIG. 1, the vertex portion where the main surfaces 101A to 101C intersect has a second connection surface 103A. The second connection surface 103A interconnects the connection surfaces 102A to 102C with each other. The connection surfaces 102A to 102C and the second connection surface 103A are processed into rounded curved surfaces. The connection surfaces 102A to 102C and the second connection surface 103A may be curved surfaces, or may be constituted by one or a plurality of planes (for example, the corner portions are chamfered).

[0032] In this way, since the anode body 1 has a shape in which the pointed portions are removed, a dielectric layer with few defects can be formed on the surface of the anode body 1. As a result, the leakage current can be reduced. Further, the mechanical strength of the anode body is increased, and the concentration of thermal stress is alleviated. As a result, damage to the dielectric layer is suppressed, an increase in the leakage current due to damage to the dielectric layer is suppressed, and the leakage current can be kept small.

[0033] The surface layers of the connection surfaces 102A to 102C and / or the second connection surface 103A may be formed more densely than the surface layers of the main surfaces 101A to 101F that are porous. That is, the porosity P1 in the surface layer of the connection surfaces 102A to 102C and / or the second connection surface 103A may be smaller than the porosity P2 in the surface layer of the main surfaces 101A to 101F. In this case, the mechanical strength at the corner portions of the anode body can be further increased.

[0034] The anode wire 2 extends from the main surface 101B of the anode body 1. The anode body 1 and the anode wire 2 constitute the anode portion 6.

[0035] Hereinafter, the configuration of the electrolytic capacitor according to the present embodiment will be described with appropriate reference to the drawings. However, the present invention is not limited to this. FIG. 2 is a schematic cross-sectional view of the electrolytic capacitor according to the present embodiment.

[0036] The electrolytic capacitor 20 includes a capacitor element 10 having an anode portion 6 and a cathode portion 7, an exterior body 11 that seals the capacitor element 10, an anode lead terminal 13 that is electrically connected to the anode portion 6 and a part of which is exposed from the exterior body 11, and a cathode portion 7 and a cathode lead terminal 14 that is electrically connected and a part of which is exposed from the exterior body 11. The anode portion 6 has an anode body 1 and an anode wire 2. A dielectric layer 3 is formed on the surface of the anode body. The cathode portion 7 has a solid electrolyte layer 4 that covers at least a part of the dielectric layer 3 and a cathode layer 5 that covers the surface of the solid electrolyte layer 4.

[0037] <Capacitor element> Hereinafter, the case where the capacitor element 10 includes a solid electrolyte layer as an electrolyte will be described in detail as an example.

[0038] The anode portion 6 has an anode body 1 and an anode wire 2 that extends from one surface of the anode body 1 and is electrically connected to the anode lead terminal 13. The anode body 1 is, for example, a rectangular parallelepiped porous sintered body obtained by sintering metal particles. As the metal particles, particles of valve action metals such as titanium (Ti), tantalum (Ta), and niobium (Nb) are used. One or more kinds of metal particles are used for the anode body 1. The metal particles may be an alloy composed of two or more metals. For example, an alloy containing a valve action metal and silicon, vanadium, boron, etc. can be used. Also, a compound containing a valve action metal and a typical element such as nitrogen may be used. The alloy of the valve action metal has the valve action metal as a main component, and contains, for example, 50 atomic% or more of the valve action metal.

[0039] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited, and examples include copper, aluminum, aluminum alloy, etc. in addition to the above valve action metals. The materials constituting the anode body 1 and the anode wire 2 may be of the same kind or different kinds. The anode wire 2 has a first portion 2a embedded from one surface of the anode body 1 into the inside of the anode body 1 and a second portion 2b extending from the one surface of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited, and examples include circular, track-shaped (a shape composed of two parallel straight lines and two curves connecting the ends of these straight lines), elliptical, rectangular, polygonal, etc.

[0040] The anode portion 6 is produced, for example, by pressure-molding in a rectangular parallelepiped shape with the first portion 2a embedded in the powder of the metal particles and then sintering. Thereby, the second portion 2b of the anode wire 2 is drawn out so as to stand on one surface of the anode body 1. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, and the anode wire 2 and the anode lead terminal 13 are electrically connected. The welding method is not particularly limited, and examples include resistance welding, laser welding, etc. Thereafter, a process of forming a curved surface at the corner portion of the rectangular parallelepiped may be performed.

[0041] A dielectric layer 3 is formed on the surface of the anode body 1. The dielectric layer 3 is composed of, for example, a metal oxide. As a method of forming a layer containing a metal oxide on the surface of the anode body 1, for example, a method of immersing the anode body 1 in a forming solution to anodize the surface of the anode body 1, or a method of heating the anode body 1 in an atmosphere containing oxygen can be mentioned. The dielectric layer 3 is not limited to the layer containing the above metal oxide, and it may have insulation.

[0042] (Cathode part) The cathode part 7 has a solid electrolyte layer 4 and a cathode layer 5 covering the solid electrolyte layer 4. The solid electrolyte layer 4 is formed so as to cover at least a part of the dielectric layer 3.

[0043] For example, a manganese compound or a conductive polymer is used for the solid electrolyte layer 4. Examples of the conductive polymer include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These may be used alone or in combination of multiple types. Further, the conductive polymer may be a copolymer of two or more monomers. In terms of excellent conductivity, it may be polythiophene, polyaniline, or polypyrrole. In particular, in terms of excellent water repellency, it may be polypyrrole.

[0044] The solid electrolyte layer 4 containing the above conductive polymer is formed, for example, by polymerizing a raw material monomer on the dielectric layer 3. Alternatively, it is formed by applying a liquid containing the above conductive polymer to the dielectric layer 3. The solid electrolyte layer 4 is composed of one layer or two or more solid electrolyte layers. When the solid electrolyte layer 4 is composed of two or more layers, the composition and formation method (polymerization method) of the conductive polymer used in each layer may be different.

[0045] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. each mean a polymer having a basic skeleton such as polypyrrole, polythiophene, polyfuran, polyaniline, etc. Therefore, derivatives of polypyrrole, polythiophene, polyfuran, polyaniline, etc. may be included. For example, poly(3,4-ethylenedioxythiophene) etc. are included in polythiophene.

[0046] In the polymerization solution, solution or dispersion of the conductive polymer for forming the conductive polymer, various dopants may be added to improve the conductivity of the conductive polymer. The dopant is not particularly limited, and examples thereof include naphthalenesulfonic acid, p-toluenesulfonic acid, polystyrenesulfonic acid, etc.

[0047] When the conductive polymer is dispersed in the dispersion medium in the form of particles, the average particle diameter D50 of the particles is, for example, 0.01 μm or more and 0.5 μm or less. If the average particle diameter D50 of the particles is within this range, the particles are likely to penetrate into the anode body 1.

[0048] The cathode layer 5 has, for example, a carbon layer 5a formed so as to cover the solid electrolyte layer 4, and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a contains a conductive carbon material such as graphite and a resin. The metal paste layer 5b contains, for example, metal particles (for example, silver) and a resin. Note that the configuration of the cathode layer 5 is not limited to this configuration. The configuration of the cathode layer 5 may be any configuration having a current collecting function.

[0049] <Anode lead terminal> The anode lead terminal 13 is electrically connected to the anode body 1 via the second portion 2b of the anode wire 2. The material of the anode lead terminal 13 is not particularly limited as long as it is electrochemically and chemically stable and has conductivity. The anode lead terminal 13 may be, for example, a metal such as copper or a non-metal. Its shape is not particularly limited as long as it is a flat plate shape. The thickness of the anode lead terminal 13 (the distance between the main surfaces of the anode lead terminal 13) may be 25 μm or more and 200 μm or less, and may be 25 μm or more and 100 μm or less from the viewpoint of reducing the height.

[0050] One end of the anode lead terminal 13 may be joined to the anode wire 2 by a conductive adhesive or solder, or may be joined to the anode wire 2 by resistance welding or laser welding. The other end of the anode lead terminal 13 is led out to the outside of the exterior body 11 and is exposed from the exterior body 11. The conductive adhesive is, for example, a mixture of a thermosetting resin described later and carbon particles or metal particles.

[0051] <Cathode lead terminal> The cathode lead terminal 14 is electrically connected to the cathode portion 7 at the joint portion 14a. The joint portion 14a is a portion where the cathode layer 5 and the cathode lead terminal 14 joined to the cathode layer 5 overlap the cathode layer 5 when viewed from the normal direction of the cathode layer 5.

[0052] The cathode lead terminal 14 is joined to the cathode layer 5 via, for example, the conductive adhesive 8. One end of the cathode lead terminal 14 constitutes, for example, a part of the joint portion 14a and is disposed inside the exterior body 11. The other end of the cathode lead terminal 14 is led out to the outside. Therefore, a part including the other end of the cathode lead terminal 14 is exposed from the exterior body 11.

[0053] The material of the cathode lead terminal 14 is not particularly limited as long as it is electrochemically and chemically stable and has conductivity. The cathode lead terminal 14 may be, for example, a metal such as copper, or may be a non-metal. Its shape is also not particularly limited. For example, it may be long and flat. From the perspective of reducing the height, the thickness of the cathode lead terminal 14 may be 25 μm or more and 200 μm or less, or may be 25 μm or more and 100 μm or less.

[0054] <Outer package> The outer package 11 is provided to electrically insulate the anode lead terminal 13 and the cathode lead terminal 14, and is composed of an insulating material (outer package material). The outer package material includes, for example, a thermosetting resin. Examples of the thermosetting resin include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, unsaturated polyester, and the like.

[0055] ≪Manufacturing method of electrolytic capacitor≫ Hereinafter, an example of the manufacturing method of the electrolytic capacitor according to the present embodiment will be described. The manufacturing method of the electrolytic capacitor is a method for manufacturing a solid electrolytic capacitor including a capacitor element including a porous anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer, and includes a step of preparing the anode body, a step of covering at least a part of the anode body with the dielectric layer, and a step of covering at least a part of the dielectric layer with the solid electrolyte layer. The anode body has a plurality of main surfaces, and a corner portion including a plurality of side portions and vertex portions connecting the plurality of main surfaces. The step of preparing the anode body includes a step of forming a curved surface on at least a part of the corner portion or chamfering at least a part of the corner portion.

[0056] (1) Step of preparing the anode body As the anode body 1, a porous sintered body can be used. A valve action metal particle and an anode wire 2 are placed in a mold such that the first portion 2a is embedded in the valve action metal particle, and after pressure molding and sintering, an anode portion 6 including the anode body 1 which is a porous body of the valve action metal is obtained. The first portion 2a of the anode wire is embedded from one surface of the porous sintered body into the inside thereof. The pressure during pressure molding is not particularly limited. Sintering is preferably performed under reduced pressure. A binder such as polyacrylic carbonate may be mixed with the valve action metal particles as necessary.

[0057] The valve action metal particles are usually pressure molded and sintered using a mold having an internal space in the shape of a rectangular parallelepiped. In this case, the shape of the anode body 1 after sintering is also a rectangular parallelepiped and has a plurality of main surfaces. In this case, the plurality of main surfaces are directly connected to form sides and vertices, and the tip portions of the corner portions which are the side portions and / or vertex portions connecting the plurality of main surfaces are in a sharp state.

[0058] For the anode body in a state where the tip portion is sharp, a process of forming a curved surface on at least a part of the corner portion or a process of chamfering at least a part of the corner portion can be performed. Thereby, the corners at the tip portions can be removed and processed into, for example, a rounded shape. The process of forming a curved surface on the corner portion can be performed, for example, by removing a part of the corner portion to remove the tip portion.

[0059] In the processing step of forming a curved surface on at least a part of the corner portion or chamfering at least a part of the corner portion, at least a part of the corner portion may be formed with high density. For example, by irradiating the corner portion with laser light, a curved surface is formed on the corner portion and at least a part of the corner portion can be formed with high density. Alternatively, the anode body may be vibrated together with a vibrating member. Along with the vibration, particularly the corner portion of the anode body collides with the vibrating member, and the corner portion is compressed to form a curved surface and at least a part of the corner portion can be formed with high density.

[0060] By irradiating the corner portion with laser light, a curved surface may be formed on the corner portion. By irradiating the corner portion with laser light, the corner portion can be melted and the tip portion can change from a pointed shape to a shape having a curved surface. The molten layer formed after melting is denser than the porous portion of the anode body and has a very low porosity. Therefore, the mechanical strength of the corner portion can be significantly increased, and the effect of suppressing damage to the dielectric layer at the corner portion is great. The thickness of the molten layer may be, for example, 1 μm to 100 μm.

[0061] The laser used for laser irradiation is not limited, but for example, a YAG (Yttrium Aluminum Garnet) laser (wavelength 1064 nm) can be used.

[0062] From the viewpoint of facilitating the escape of air present in the pores of the anode body during the formation of the solid electrolyte layer, it is preferable that the laser light irradiation is performed on the corner portion and the main surface of the anode body adjacent to the corner portion is not substantially irradiated with laser light. Note that the above description means that the main surface is not irradiated with laser light in most regions, and does not exclude the case where a part of the main surface region (for example, the region on the main surface adjacent to the corner portion) is irradiated with laser light.

[0063] The laser light irradiation may be performed on the sintered anode body or on the pressure-molded valve-acting metal particles before sintering. However, considering the deformation accompanying the volume shrinkage after sintering, it is preferable to irradiate the sintered anode body with laser light.

[0064] When vibrating the anode body together with the vibrating member, for example, the removal of the tip portion can be performed, for example, by placing the anode body on a pedestal (vibrating member) having unevenness on its surface such as a sieve or a file, and vibrating the pedestal in the vertical direction and / or the horizontal direction. Along with the vibration of the pedestal, the anode body rolls and moves while bouncing on the pedestal. Along with this, a part of the tip portion of the corner portion is scraped off, and a curved surface is formed at the corner portion. However, most of the tip portion can remain in the surface layer of the corner portion in a compressed state without being scraped off. As a result, the surface layer of the corner portion having a curved surface can be formed with high density. The pedestal is easy to remove because the residue with the tip portion scraped off falls downward, and also has an appropriately small coefficient of static friction, making it easy to roll and move the anode body. A sieve may be used. The mesh size of the sieve only needs to be less than the minimum value of the outer diameter of the anode body so that the anode body does not pass through the opening of the sieve and fall. The mesh size of the sieve may be 1 mm or more, or may be 2 mm or more and 3.4 mm or less. When the mesh size is 1 mm or more, it is easy to reduce the variation in the radius of curvature R at the corner portion to a certain value or less.

[0065] The anode body may be vibrated together with the media particles by applying an external force to the media particles with the anode body placed on the media particles. For example, the anode body may be mixed with the media particles, and the anode body and the media particles may be put into a shaker and the shaker may be operated. The shaker preferably can apply vibrations in the vertical direction in addition to the horizontal direction. As the media particles, alumina particles, zirconia particles, etc. can be used. The particle size (average particle size) of the media particles is, for example, 0.1 mm to 3 mm, or may be 0.5 mm to 2 mm.

[0066] The media particles put into the shaker together with the anode body vibrate due to the operation of the shaker and collide with the anode body. Since the corner portion of the anode body has low mechanical strength, it is easily deformed by the collision, and the porous portion of the corner portion is easily crushed and compressed. Therefore, the surface layer of the corner portion can be formed with high density.

[0067] The density of the media particles may be 0.15 to 0.4 times the density (true density) of the anode body. When the density of the media particles is within the above range, the energy due to the collision of the media particles can be efficiently utilized for the compressive deformation of the corner portions. Also, the ratio at which the corner portions are shaved off by the collision can be reduced.

[0068] In the method of vibrating the media particles in a state where the anode body and the media particles are mixed, compared with the method of vibrating the sieve on which the anode body is placed, a curved surface can be formed or chamfered at the corner portions in a shorter time. Therefore, the variation in the radius of curvature R at the corner portions is likely to be reduced.

[0069] When forming a curved surface or chamfering the corner portions using a vibrating member, it is preferable to perform the formation of the curved surface or chamfering of the corner portions on the porous body before sintering because the mechanical strength is increased by sintering and it becomes difficult to compress the corner portions.

[0070] By using a pre-chamfered mold to press-mold and sinter the valve-action metal particles, an anode body with a curved surface formed at the corner portions may be obtained.

[0071] (2) Dielectric layer formation step Next, the anode body 1 is subjected to formation treatment, and at least a part of the anode body 1 is covered with the dielectric layer 3. Specifically, the anode body 1 is immersed in a formation tank filled with an electrolytic aqueous solution (for example, a phosphoric acid aqueous solution), the second portion 2b of the anode wire 2 is connected to the anode body in the formation tank, and anodic oxidation is performed to form a dielectric layer 3 made of an oxide film of the valve-action metal on the surface of the porous portion. The electrolytic aqueous solution is not limited to a phosphoric acid aqueous solution, and nitric acid, acetic acid, sulfuric acid, etc. can be used.

[0072] (3) Solid electrolyte layer formation step Subsequently, at least a part of the dielectric layer 3 is covered with the solid electrolyte layer 4. Thereby, a capacitor element 10 including the anode body 1, the dielectric layer 3, and the solid electrolyte layer 4 is obtained. The solid electrolyte layer 4 containing a conductive polymer is formed, for example, by impregnating the anode body 1 on which the dielectric layer 3 is formed with a monomer or an oligomer and then polymerizing the monomer or the oligomer by chemical polymerization or electrolytic polymerization, or by impregnating the anode body 1 on which the dielectric layer 3 is formed with a solution or dispersion of a conductive polymer and drying it, so as to form at least a part of the dielectric layer 3.

[0073] The solid electrolyte layer 4 can be formed, for example, by impregnating the anode body 1 on which the dielectric layer 3 is formed with a dispersion containing a conductive polymer, a binder, and a dispersion medium, taking it out, and drying it. The dispersion may contain a binder and / or conductive inorganic particles (for example, a conductive carbon material such as carbon black). Further, the conductive polymer may contain a dopant. The conductive polymer and the dopant may be selected from those exemplified for the solid electrolyte layer 4, respectively. Known binders can be used. The dispersion may contain known additives used when forming the solid electrolyte layer.

[0074] Subsequently, a cathode layer 5 composed of a carbon layer 5a and a metal paste layer 5b is formed by sequentially applying a carbon paste and a metal paste on the surface of the solid electrolyte layer 4. The configuration of the cathode layer 5 is not limited to this, and any configuration having a current collecting function may be used.

[0075] Next, an anode lead terminal 13 and a cathode lead terminal 14 are prepared. The second part 2b of the anode wire 2 implanted from the anode body 1 is joined to the anode lead terminal 13 by laser welding, resistance welding, or the like. Further, after applying a conductive adhesive 8 to the cathode layer 5, the cathode lead terminal 14 is joined to the cathode portion 7 via the conductive adhesive 8.

[0076] Subsequently, the materials of the capacitor element 10 and the exterior body 11 (for example, uncured thermosetting resin and filler) are accommodated in a mold, and the capacitor element 10 is sealed by a transfer molding method, a compression molding method, or the like. At this time, a part of the anode lead terminal 13 and the cathode lead terminal 14 is exposed from the mold. The molding conditions are not particularly limited, and the time and temperature conditions may be set as appropriate in consideration of the curing temperature of the thermosetting resin used.

[0077] Finally, the exposed portions of the anode lead terminal 13 and the cathode lead terminal 14 are bent along the exterior body 11 to form bent portions. As a result, a part of the anode lead terminal 13 and the cathode lead terminal 14 is disposed on the mounting surface of the exterior body 11. The electrolytic capacitor 20 is manufactured by the above method.

[0078] FIG. 3 shows an electron micrograph of a cross section of a corner portion of the anode body after laser light irradiation. In FIG. 3, the valve action metal (Ta) is present in the white portion, and the black portion is a void. It can be seen that the corner portion has a curved surface, and the surface layer X of the corner portion having the curved surface is formed densely. On the other hand, the inside of the surface layer X maintains a porous state.

Industrial Applicability

[0079] The present invention can be used for an electrolytic capacitor, and preferably, it can be used for an electrolytic capacitor using a porous body as an anode body. Although the present invention has been described with respect to the presently preferred embodiments, such disclosure should not be construed in a limiting sense. Various modifications and alterations will no doubt become apparent to those skilled in the art in the technical field to which this invention pertains upon reading the above disclosure. Accordingly, the appended claims are to be construed to include all modifications and alterations without departing from the true spirit and scope of this invention.

Explanation of Reference Numerals

[0080] 20: Electrolytic capacitor 10: Capacitor element 1: Anode body 2: Anode wire 2a: First part 2b: Second part 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode layer 5a: Carbon layer 5b: Metal paste layer 6: Anode part 7: Cathode part 8: Conductive adhesive 11: Outer package 13: Anode lead terminal 14: Cathode lead terminal 14a: Joint part 101A~101C: Main surfaces of the anode body 102A~102C: Connection surfaces 103A: Second connection surface

Claims

1. A porous anode body, a dielectric layer formed on the surface of the anode body, a solid electrolyte layer covering at least a part of the dielectric layer, A capacitor element comprising: The anode body has a plurality of main surfaces and corner portions, The corner portion includes a plurality of side portions and vertex portions connecting the plurality of main surfaces, At least a part of the surface layer X of the corner portion has a portion where the porosity P1 exceeds 1% and is 10% or less, The surface layer Y of the main surface adjacent to the surface layer X has a portion where the porosity P2 is 20% or more. An electrolytic capacitor.

2. The ratio P2 / P1 of the porosity P2 to the porosity P1 is 5 or more. The electrolytic capacitor according to Claim 1.

3. The portion including at least a part of the surface layer X of the corner portion has a curved surface shape or a chamfered shape. The electrolytic capacitor according to Claim 1 or 2.

4. Among the corner portions, the portion having the curved surface shape or the chamfered shape includes a portion having a curvature radius R of 20 μm to 500 μm. The electrolytic capacitor according to Claim 3.

5. Among the corner portions, the portion having the curved surface shape or the chamfered shape includes portions having different curvature radii R, and the difference between the maximum value and the minimum value of the different curvature radii is 350 μm or less. The electrolytic capacitor according to Claim 3 or 4.

6. The solid electrolyte layer contains a conductive polymer. The electrolytic capacitor according to any one of Claims 1 to 5.

7. The anode body is a sintered body of metal particles having a valve action. The electrolytic capacitor according to any one of Claims 1 to 6.

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