Electrolytic capacitor and method for manufacturing the same

Abstract

[Solution] An electrolytic capacitor 20 which is provided with a capacitor element 10 that comprises a porous positive electrode body 1, the surface of which is provided with a dielectric layer 3, and a solid electrolyte layer 4 which covers at least a part of the dielectric layer 3. The positive electrode body 1 has a plurality of main surfaces; and at least a part of the surface layer of each main surface of the positive electrode body is denser than the inner part of the positive electrode body.

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 Electrolytic capacitor according to includes a capacitor element including a porous anode body including an anode substrate and a dielectric layer formed on the surface of the anode substrate, and a solid electrolyte layer covering at least a part of the dielectric layer. is. The anode body has a plurality of main surfaces, and A plurality of at least a part of the First of at least one main surface front layer surface of the anode body is part denser than the inside of the anode body. is.

[0006] Another aspect of the present disclosure provides a capacitor element including a porous anode body including an anode substrate and a dielectric layer formed on a surface of the anode substrate, and a solid electrolyte layer covering at least a part of the dielectric layer. electric A method for manufacturing an electrolytic capacitor is. The method of the present disclosure The method includes preparing an anode base material including a binder body of metal powder, sintering the anode base material, obtaining the anode body including the anode substrate and the dielectric layer by subjecting the sintered anode base material to a forming treatment, and covering at least a part of the dielectric layer with the solid electrolyte layer. is. The method of the present disclosure The anode base material has a plurality of main surfaces, and at least one of the plurality of main surfaces of the anode base material main surface further includes a densification step of increasing the density of at least a part of the region. is.

Advantages of the Invention

[0007] By the electrolytic capacitor or the manufacturing method of the electrolytic capacitor of the present disclosure, Reliability of the electrolytic capacitor to Improvement can be made .

Brief Description of the Drawings

[0008]

FIG. 1

FIG. 2

FIG. 3A

FIG. 3B

FIG. 4A

FIG. 4B

Embodiments for Carrying Out the Invention

[0009] [Electrolytic capacitor] The electrolytic capacitor according to an embodiment of the present invention includes a porous anode body including an anode substrate and a dielectric layer formed on the surface of the anode substrate, and a solid electrolyte layer covering at least a part of the dielectric layer. The anode body has a plurality of main surfaces, and at least a part of the surface layer X of the main surface of the anode body is denser than the inside Y of the anode body.

[0010] The anode body usually has a rectangular parallelepiped shape. In this case, the plurality of main surfaces refer to each surface of the rectangular parallelepiped. The surface layer of the anode body refers to a region with a depth of 3 μm or less from the surface of the anode body. The inside of the anode body refers to a region with a depth of 20 μm or more from the surface of each main surface of the anode body.

[0011] When the anode body has a plurality of main surfaces, an edge portion connecting two of the plurality of main surfaces and / or a vertex portion connecting three or more of the plurality of main surfaces may be formed. The edge portion refers to an edge where two main surfaces of the anode body intersect and a region in the vicinity thereof. The vertex portion refers to a vertex where three main surfaces of the anode body intersect and a region in the vicinity thereof. Here, the edge portion and the vertex portion are collectively referred to as the "corner portion".

[0012] The dielectric layer is usually formed by subjecting an anode base material to a formation treatment to oxidize the surface of the anode base material. Therefore, the properties of the dielectric layer formed by formation are affected by the surface state of the anode base material before the formation treatment.

[0013] The anode substrate before formation treatment can be manufactured, for example, by putting metal powder into a mold, compacting it, and sintering it. In this case, fine particles of the metal are exposed on the main surface of the anode substrate, and when viewed microscopically, it is not flat, has a large surface roughness, and is likely to have an uneven shape. In particular, in the side portions connecting the two main surfaces of the anode substrate and the vertex portions connecting three or more main surfaces, the surface of the anode substrate is not flat when viewed microscopically, has a large surface roughness, and is likely to have an uneven shape. When a dielectric layer is grown by formation treatment in this state, defects are likely to occur in the dielectric layer in 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.

[0014] Further, the anode body after formation treatment having an outer shape reflecting the outer shape of the anode substrate before formation treatment is porous and thus brittle and easily broken. In particular, the corner portions of the anode body have lower mechanical strength than the portions other than the corner portions, 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.

[0015] In the electrolytic capacitor of the present embodiment, by densely forming the surface layer of the main surface of the anode substrate before formation treatment, it is possible to reduce the defects during formation of the dielectric layer that occur when forming the dielectric layer by formation treatment. As a result, the leakage current can be reduced. In addition, the mechanical strength of the dielectric layer can be increased. Thereby, damage to the dielectric layer after formation can be suppressed. As a result, an increase in the leakage current is suppressed.

[0016] Regarding the density of the surface layer of the main surface of the anode body, it is preferable that the porosity P1 in the surface layer X of the main surface of the anode body is 0.02 times or more and 0.7 times or less of the porosity P2 in the interior Y of the anode body. When the porosity P1 is 0.7 times or less of the porosity P2, the surface layer X is sufficiently dense with respect to the interior Y, damage to the dielectric layer after formation is suppressed, and an increase in leakage current is suppressed. The porosity P1 is more preferably 0.5 times or less of the porosity P2, and may further preferably be 0.3 times or less. On the other hand, when the porosity P1 is 0.02 times or more of the porosity P2, it is easy to form a solid electrolyte layer covering the dielectric layer in the pores of the anode body. The porosity P1 is more preferably 0.05 times or more of the porosity P2, and may further preferably be 0.1 times or more.

[0017] The electrolytic capacitor may contain a trace amount of aluminum resulting from the manufacturing process in the vicinity of the surface layer of the dielectric layer or the anode body. Note that "trace amount" means that the content of aluminum in the dielectric layer is 0.001 wt% or more and 10 wt% or less in a region within a depth of 1 μm from the surface of the anode body. The content of aluminum in the dielectric layer may be 0.01 wt% or more and 10 wt% or less.

[0018] At least a part of the corner portion of the anode body may have a curved surface shape or a chamfered shape. By having a curved surface or being chamfered at least in part of the corner 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 improved. In addition to the surface layer of the main surface of the anode body, it is preferable that the corner portion is also densified.

[0019] That at least a part of the corner portion has a curved surface shape does not limit 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 portion has a curved surface shape or a chamfered shape. In other words, that the corner portion has a curved surface shape or a chamfered shape 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 sharpened to 90° or less.

[0020] 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 leakage current and the occurrence of short-circuit defects can be suppressed. Also, the withstand voltage is improved.

[0021] The surface layer Z of the corner portion adjacent to the surface layer X may be denser than the surface layer X and the interior Y. The surface layer Z is formed densely, whereby the mechanical strength of the corner portion can be further enhanced. Therefore, the effect of suppressing an increase in leakage current through the corner portion can be enhanced.

[0022] Even when the corner portion does not have a curved surface and is not chamfered, sufficient mechanical strength can be obtained by the surface layer Z being formed densely. 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 Z has a curved surface shape or a chamfered shape, as the leakage current can be further suppressed.

[0023] That the surface layer Z is denser than the surface layer X and the interior Y means that the porosity P3 in the surface layer Z is smaller than the porosity P1 in the surface layer X and the porosity P2 in the interior Y. The surface layer Z may have a portion where the ratio P3 / P1 of the porosity P3 to the porosity P1 satisfies less than 1. P3 / P1 may be 0.8 or less, or may be 0.5 or less. In any portion of the surface layer Z, P3 / P1 may satisfy less than 1.

[0024] Also, 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, may be 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. The cross-section is photographed with a scanning electron microscope (SEM), and in a field of view of, for example, 5 μm × 10 μm, image processing such as binarization of the photographed image is performed to distinguish the pore portion from the other portions. The porosity can be obtained as the area ratio of the pore portion to the total area of the pore portion and the other portions. It is desirable to measure the photographed image at 10 arbitrary locations and obtain the porosity as the average value of the area ratios of the pore portions obtained at the 10 locations. The porosity P1 (porosity P3) is obtained from the area ratio of the pore portion in the region A within the surface layer X (surface layer Z). Similarly, the porosity P2 is obtained from the area ratio of the pore portion in the region B within the interior Y. The curvature of the corner portion is also calculated by photographing the anode body from the side of a certain main surface and performing image analysis on the contour shape near the obtained corner (vertex).

[0026] The densification of the surface layer of the anode body can be carried out, for example, as described below. Before sintering or before forming the dielectric layer after sintering, the anode substrate is placed in a container together with a vibrating member such as media particles, and the container is vibrated. By vibrating, the main surface of the anode substrate collides with the vibrating member, and due to the collision, the surface layer portion of the main surface is formed more densely than the interior by compression. Here, the molding in which the powder of the valve action metal particles is pressure-molded into a rectangular parallelepiped shape in a state of being embedded in a pressure molding machine using a mold to obtain the anode substrate before forming the dielectric layer is called primary molding, and the molding of the above densification is called secondary molding.

[0027] At this time, the vibrating member collides not only with the main surface of the anode substrate but also with the corner portions. Since the corner portions have low mechanical strength, they are easily compressed by the collision. Therefore, when the corner portions are compressed by the collision, the corner portions can be formed into a curved surface shape. The density in the surface layer Z of the corner portions becomes higher (the porosity is lower) than that of the surface layer X and the interior Y of the main surface.

[0028] On the other hand, when the vibrating member is not provided and the anode substrates are directly collided with each other, only the corner portions of the anode substrates collide with the main surface of another anode substrate. As a result, cracks may occur due to the impact. Also, it takes a long time to densify the main surface, and as a result, the variation in the degree of densification becomes large, and the variation in the characteristics of the electrolytic capacitor becomes large. Also, cracks in the anode substrate are likely to occur. In contrast, by causing the vibrating member to collide with the anode substrate, cracks in the anode substrate can be suppressed, and the main surface of the anode substrate can be uniformly densified in a short time.

[0029] FIG. 1 is a schematic perspective view showing an example of the anode body (or anode substrate) 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.

[0030] In the main surfaces 101A to 101F, a connecting surface may be formed by chamfering the corners of the edge portions in the vicinity of the edges where two adjacent main surfaces intersect. In the example of FIG. 1, a connecting surface 102C is interposed between the main surfaces 101A and 101B, a connecting surface 102A is interposed between the main surfaces 101B and 101C, and the main surface 101 A and 101C, a connecting surface 102 B is interposed. Also, in the vicinity of the vertex where three main surfaces intersect, a second connecting surface is formed by chamfering the corners of the vertex portion. In the example of FIG. 1, at the vertex portion where the main surfaces 101A to 101C intersect, it has a second connecting surface 103A. The second connecting surface 103A mutually connects the connecting surfaces 102A to 102C. The connecting surfaces 102A to 102C and the second connecting surface 103A are processed into rounded curved surfaces. The connecting surfaces 102A to 102C and the second connecting surface 103A may be curved surfaces, or may be constituted by one or a plurality of planes (for example, the corner portions are chamfered).

[0031] Note that although FIG. 1 shows an example of the shape of the anode body, the anode substrate before the formation treatment also has a substantially rectangular parallelepiped shape in the same manner, six main surfaces 101A to 101F are exposed, the corners of the edge portions and vertex portions connecting the main surfaces are chamfered, and it is processed into a rounded surface.

[0032] At least a part of the surface layer of the main surfaces 101A to 101F is formed denser than the inside. Thereby, the surfaces of the main surfaces 101A to 101F have less irregularities, and the mechanical strength of the anode substrate and the anode body is enhanced. As a result, a dielectric layer with fewer defects is formed on the surface of the anode body 1. Consequently, the leakage current can be reduced. Also, the damage to the dielectric layer is suppressed, the increase in the leakage current due to the damage to the dielectric layer is suppressed, and the leakage current can be kept small.

[0033] In addition, since the anode substrate has an outer shape in which the corner portions are chamfered or subjected to curved surface processing, a dielectric layer with few defects can be formed even at the corner portions, and the effect of reducing leakage current can be enhanced. Further, the mechanical strength of the corner portions of the brittle and easily breakable anode body is increased, and the concentration of thermal stress is alleviated, so that the effect of suppressing an increase in leakage current due to damage to the dielectric layer is enhanced, and the leakage current can be maintained even smaller.

[0034] The surface layers of the connection surfaces 102A to 102C and / or the second connection surface 103A may be formed denser than the surface layers of the main surfaces 101A to 101F which are porous. That is, the porosity P3 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 inside the anode body 1 and also smaller than the porosity P1 in the surface layer of the main surfaces 101A to 101F.

[0035] 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.

[0036] 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 thereto. FIG. 2 is a schematic cross-sectional view of the electrolytic capacitor according to the present embodiment.

[0037] 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 lead terminal 14 that is electrically connected to the cathode portion 7 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. The anode body 1 includes a dielectric layer 3 formed on its surface. 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.

[0038] <Capacitor element> Hereinafter, taking the case where the capacitor element 10 includes a solid electrolyte layer as the electrolyte as an example, it will be described in detail.

[0039] 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.

[0040] 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 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 metal and silicon, vanadium, boron, etc. can be used. Also, a compound containing a valve metal and a typical element such as nitrogen may be used. The alloy of the valve metal has the valve metal as the main component and contains, for example, 50 atomic% or more of the valve metal.

[0041] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited, and examples include, in addition to the above-mentioned valve metals, copper, aluminum, aluminum alloys, etc. The materials constituting the anode body 1 and the anode wire 2 may be the same or different. The anode wire 2 has a first portion 2a embedded from one surface of the anode body 1 into 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.

[0042] The anode part 6 is manufactured, for example, by pressure-molding a rectangular parallelepiped in a state where the first part 2a is embedded in the powder of the above metal particles and then sintering it. As a result, the second part 2b of the anode wire 2 is drawn out from one surface of the anode body 1 so as to stand upright. The second part 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 thereof include resistance welding and laser welding. Thereafter, a process of forming a curved surface on the corner portion of the rectangular parallelepiped may be performed.

[0043] 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. Examples of the method for forming a layer containing a metal oxide on the surface of the anode body 1 include a method of immersing the anode body 1 in a chemical conversion solution to anodize the surface of the anode body 1 and a method of heating the anode body 1 in an atmosphere containing oxygen. The dielectric layer 3 is not limited to the layer containing the above metal oxide, and may have insulation.

[0044] (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.

[0045] 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. Polythiophene, polyaniline, or polypyrrole may be used in terms of excellent conductivity. In particular, polypyrrole may be used in terms of excellent water repellency.

[0046] 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.

[0047] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. each mean a polymer having a basic skeleton such as polypyrrole, polythiophene, polyfuran, polyaniline, etc. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc. may each include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0048] Various dopants may be added to the polymerization solution, solution or dispersion of the conductive polymer for improving the conductivity of the conductive polymer. The dopant is not particularly limited, and examples thereof include naphthalenesulfonic acid, p-toluenesulfonic acid, polystyrenesulfonic acid, etc.

[0049] When the conductive polymer is dispersed in a dispersion medium in a particulate state, 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.

[0050] 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 (e.g., 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.

[0051] <Anode lead terminal> The anode lead terminal 13 is electrically connected to the anode body 1 via the second part 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.

[0052] 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.

[0053] <Cathode lead terminal> The cathode lead terminal 14 is electrically connected to the cathode part 7 at the joint part 14a. The joint part 14a is a part of the cathode lead terminal 14 that overlaps the cathode layer 5 when viewed from the normal direction of the cathode layer 5, where the cathode layer 5 and the cathode lead terminal 14 joined to the cathode layer 5 are concerned.

[0054] The cathode lead terminal 14 is joined to the cathode layer 5 via, for example, a conductive adhesive 8. One end of the cathode lead terminal 14 constitutes, for example, a part of the joint part 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.

[0055] 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.

[0056] <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. ≪Manufacturing method of electrolytic capacitor≫ An example of the manufacturing method of the electrolytic capacitor according to the present embodiment will be described below.

[0057] 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 including an anode substrate and a dielectric layer formed on the surface of the anode substrate, and a solid electrolyte layer covering at least a part of the dielectric layer, and includes a step of preparing an anode base material including a binder of metal powder, a step of sintering the anode base material, a step of obtaining an anode body including an anode substrate and a dielectric layer by subjecting the sintered anode base material to a forming treatment, and a step of covering at least a part of the dielectric layer with a solid electrolyte layer. The anode base material has a plurality of main surfaces. The manufacturing method further includes a densification step of increasing the density of at least a part of at least one of the plurality of main surfaces of the anode base material.

[0058] (1) Step of preparing anode base material First, prepare an anode substrate as a base material for manufacturing the anode body 1. As the anode substrate, a porous body can be used. In that case, the valve action metal particles and the anode wire 2 are placed in a mold so that the first portion 2a is embedded in the valve action metal particles, and pressure molding is performed to obtain an anode substrate containing an aggregate of valve action metal particles. The pressure during pressure molding is not particularly limited. A binder such as polyacrylic carbonate may be mixed with the valve action metal particles as necessary.

[0059] The valve action metal particles are usually pressure molded and sintered (secondary molding) using a mold having an internal space in the shape of a rectangular parallelepiped. In this case, the anode substrate before sintering has a plurality of main surfaces corresponding to the rectangular parallelepiped. Also, the shape of the anode substrate 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 usually, the corner portions, which are the side portions and / or vertex portions connecting the plurality of main surfaces, have a sharp tip at the tip and do not have a curved surface.

[0060] Densification (high densification) of the main surface of the anode substrate can be performed on the anode substrate after pressure molding. In the densification process, for example, densification (high densification) of the main surface is performed by causing media particles to collide with the main surface of the anode substrate. Preferably, densification may be performed by vibrating the anode substrate together with the media particles. More specifically, the anode substrate is placed on a container or pedestal together with the media particles, and densification can be performed by vibrating the container or pedestal in the vertical direction and / or the horizontal direction. As the container or pedestal vibrates, the anode substrate and the media particles vibrate, promoting the collision between the anode substrate and the media particles. When the media particles collide with the main surface of the anode substrate, the surface layer of the main surface of the anode substrate is compressed and formed at a high density.

[0061] In addition to colliding with the main surface of the anode substrate, the media particles can also collide with the corner portions (side portions and vertex portions) connecting the main surfaces of the anode substrate. As a result, in addition to the main surface of the anode substrate, a curved surface is formed by compressing the corner portions, and at least a part of the corner portions can be formed at a higher density than the densified region of the main surface.

[0062] The pedestal (or the bottom of the container) may be a sieve. The coefficient of static friction is moderately small, which easily induces the movement of the media particles and the collision between the media particles and the anode substrate. Due to the collision with the media particles, most of the surface layer of the anode substrate is in a compressed state. When the pedestal is a sieve, the anode wire collides with the pedestal directly less frequently, so the risk of the anode wire bending can be reduced. The mesh opening of the sieve may be less than the minimum value of the outer dimensions of the anode substrate so that the anode substrate does not fall through the opening of the sieve. The mesh opening 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 opening is 1 mm or more, it is easy to reduce the variation in curvature at the corner portion to a certain value or less.

[0063] With the anode substrate placed on the media particles, an external force may be applied to the media particles to vibrate the anode body together with the media particles. More specifically, for example, the anode substrate may be mixed with the media particles, and the anode substrate 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. On the other hand, even if the anode substrate and the media particles are put into a rotary barrel, since it does not apply vibrations to the anode substrate and the media particles, it is difficult to obtain the effect of densifying the main surface of the anode substrate. Although the rotation of the anode substrate and the media particles can induce the collision between the media particles and the anode substrate, it takes a long time for densifying the main surface, and it is difficult to densify the main surface uniformly. In addition, since the anode substrate and the media particles are pushed upward as the barrel rotates, the impact when they fall is large, and cracks and chips are likely to occur in the anode substrate.

[0064] The density of the media particles may be 0.15 to 0.4 times the density (true density) of the anode substrate. 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 compression deformation of the anode substrate.

[0065] As the media particles, alumina particles, zirconia particles, etc. can be used. The particle size (average particle size) of the media particles may be 1 / 3 or less of the maximum dimension of the anode body, or may be 1 / 5 or less. In this case, the media particles are more likely to collide with the main surface than the corner portions of the anode substrate, and the main surface of the anode substrate is easily compressed uniformly by the collision. Note that the maximum dimension of the anode body refers to the maximum Feret diameter of the anode body excluding the anode wire, and when the anode body is a rectangular parallelepiped, it refers to the length of the longest side. The particle size (average particle size) of the media particles is, for example, 0.1 mm to 3 mm, and may be 0.5 mm to 2 mm.

[0066] When alumina particles are used as the media particles, if the anode substrate is made of a valve action metal other than aluminum (for example, tantalum), when the media particles collide with the anode substrate, a small amount of alumina derived from the media particles may adhere to the anode substrate. By subjecting the anode substrate with the adhered alumina to a forming treatment, the anode body may include a dielectric layer containing aluminum oxide. Aluminum oxide contained in the dielectric layer, if it is a small amount, has the effect of improving the insulation of the dielectric layer, improving the breakdown voltage, and reducing the leakage current. However, if the amount of aluminum oxide contained in the dielectric layer is excessive, a decrease in capacitance may occur due to the inclusion of a plurality of materials having different dielectric constants in the dielectric layer. The amount of alumina adhering to the anode substrate can be controlled to an appropriate amount by factors such as the vibration frequency, the particle size of the media particles, the mixing ratio of the anode substrate and the media particles charged into the container, and the time for the media particles to collide.

[0067] The media particles may have at least a part of their surfaces coated in advance with the same metal as the constituent metal of the metal powder of the anode substrate. Here, the constituent metal means the main component, not the impurities contained in the anode substrate. Thereby, when the media particles collide with the anode substrate, the adhesion of metals (or metal compounds) other than the valve-acting metal constituting the anode body to the anode substrate is suppressed. For example, when alumina particles are used as the media particles, the adhesion of alumina to the surface of the anode substrate is suppressed. The coating of the surface of the media particles can be performed by known methods. However, when the media particles (for example, alumina particles) collide with the anode substrate, while alumina derived from the media particles adheres to the anode substrate, the constituent metal of the anode substrate adheres to the surface of the media particles. As a result, the surface of the media particles can be coated with the same metal as the constituent metal of the anode substrate. Thus, media particles whose surfaces are coated with the same metal as the constituent metal of the anode substrate may be used.

[0068] In this way, in the method of vibrating the anode substrate together with the media particles and causing the anode substrate to collide with the media particles, it is possible to efficiently compress the surface layer of the main surface of the anode substrate and densify the main surface.

[0069] On the other hand, when the anode substrates are directly collided with each other without using the media particles, only the corner portions of the anode substrate collide with the main surface of another anode substrate. As a result, cracks are likely to occur due to the impact. In particular, since the weight of other anode substrates is applied to the anode substrate located at the bottom of the container, cracks or chips are likely to occur. Also, the anode wire provided on the anode substrate may collide with another anode substrate, and the anode wire may be bent. In addition, since it takes a long time to densify the main surface, the variation in density within the main surface also becomes large, and it is difficult to compress the main surface of the anode substrate with a uniform density. From the above, when the media particles are not used, the productivity of the anode body is likely to decrease.

[0070] However, by causing the media particles to collide with the anode substrate, it is easily possible to compress and densely form the surface layer of the main surface of the anode substrate through the media particles, and it is possible to densify the main surface of the anode body with a uniform density in a short time. Also, the occurrence of bending of the anode wire is suppressed.

[0071] (2) Sintering step Thereafter, the anode substrate is sintered. Sintering is preferably performed under reduced pressure. The first portion 2a of the anode wire is embedded from one surface of the porous sintered body into the inside thereof.

[0072] Densification may be performed on the porous sintered body after sintering. However, since the bond between metal particles is not strong and it is easily compressed, the densification step is preferably performed on the anodized substrate that has been pressure-molded before sintering. When densification is performed on the anode substrate which is a porous sintered body after sintering, the densification can be performed in the same manner as the densification of the anode substrate before sintering.

[0073] When obtaining the anode substrate by pressure-molding metal powder, regardless of whether it is before or after sintering, metal fine particles adhere to the main surface of the anode substrate, and microscopically, it is not flat and often has an uneven shape. However, the metal fine particles adhering to the main surface do not contribute to the capacitance because the dielectric layer is formed so as to cover the entire surface of the fine particles during the formation of the dielectric layer. In the densification step, by compressing the surface layer of the anode substrate together with the metal fine particles, the dielectric layer formed on the surface of the fine particles can also contribute to the capacitance, and the capacitance is improved.

[0074] (3) Step of obtaining the anode body (formation treatment step) Next, a chemical conversion treatment is performed on the sintered anode substrate to obtain a porous anode body 1 including an anode substrate and a dielectric layer formed on the surface of the anode substrate. Specifically, the anode substrate is immersed in a chemical conversion tank filled with an electrolytic aqueous solution (for example, a phosphoric acid aqueous solution), and the second portion 2b of the anode wire 2 is connected to the anode body in the chemical conversion tank, and anodic oxidation is performed to form a dielectric layer 3 made of an oxide film of a 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. The non-anodized core portion of the anode body 1 constitutes the anode substrate.

[0075] Furthermore, in this chemical conversion treatment, it is preferable to include a first chemical conversion step and a second chemical conversion step. The first chemical conversion step uniformly forms a dielectric layer on the surface layer portion and inside of the porous anode substrate. The second chemical conversion step forms a dielectric layer thicker than the dielectric layer formed in the first chemical conversion step on the surface layer portion and in the vicinity of the surface layer of the porous anode body. The second chemical conversion step is preferably carried out after the first chemical conversion step. Note that a series of chemical conversion treatments including the first chemical conversion step and the second chemical conversion step is referred to as double chemical conversion.

[0076] In the first chemical conversion step, for example, the anode substrate is immersed in an electrolytic aqueous solution (for example, a phosphoric acid aqueous solution), and anodic oxidation is performed to form a dielectric layer 3 made of an oxide film of a valve action metal on the surface of the porous portion.

[0077] In the second chemical conversion step, for example, the anode substrate is immersed in an electrolytic aqueous solution (for example, sodium tetraborate), and anodic oxidation is performed to form a dielectric layer 3 made of an oxide film of a valve action metal on the surface of the porous portion. The applied voltage for anodic oxidation in the second chemical conversion step is preferably higher than the applied voltage for anodic oxidation in the first chemical conversion step. The time for anodic oxidation in the second chemical conversion step is preferably shorter than the time for anodic oxidation in the first chemical conversion step.

[0078] Further, in terms of reducing the leakage current of the electrolytic capacitor 20, suppressing the occurrence of short-circuit defects, and improving the withstand voltage characteristics, it is preferable that the thickness of the surface layer portion of the anode body 1 where the dielectric layer 3 is thickly formed by the second formation process and the region near the surface layer portion is thicker than the thickness of the region densified by the secondary forming.

[0079] By performing the first formation process and the second formation process, the density and mechanical strength of the surface layer portion of the anode body 1 and the region near the surface layer portion can be increased, making it stronger against external stress. As a result, an increase in the leakage current of the electrolytic capacitor 20 and the occurrence of short-circuit defects are suppressed, and the withstand voltage characteristics are improved.

[0080] The density and mechanical strength on the surface layer of the anode body 1 can be evaluated, for example, by comparing the Vickers hardness. Table 1 is a comparison of the Vickers hardness of the anode body 1 with and without Implementation secondary forming and double formation table . The Vickers hardness is the average value of the measurement results at eight arbitrary locations on the main surface of the anode body 1. As a result, the Vickers hardness became the largest in the anode body 1 subjected to secondary forming and double formation. That is, by Implement performing secondary forming and double formation, the electrolytic capacitor 20 becomes stronger against external stress, can suppress an increase in leakage current and the occurrence of short-circuit defects, and improves the withstand voltage. Implement

Table 1

[0081] (4) Solid electrolyte layer formation process Subsequently, at least a part of the dielectric layer 3 is covered with the solid electrolyte layer 4. Thereby, the capacitor element 10 is obtained.

[0082] ​The solid electrolyte layer 4 containing a conductive polymer is formed, for example, by impregnating a monomer or oligomer into the anode body 1 on which the dielectric layer 3 is formed and then polymerizing the monomer or 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.

[0083] The solid electrolyte layer 4 can be formed, for example, by impregnating the anode body 1 on which the dielectric layer 3 is formed into 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.

[0084] 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.

[0085] 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 part 7 via the conductive adhesive 8.

[0086] Subsequently, the materials of the capacitor element 10 and the exterior body 11 (for example, uncured thermosetting resin and filler) are placed in a mold, and the capacitor element 10 is encapsulated 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.

[0087] 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.

[0088] The electrolytic capacitor 20 is manufactured by the above method.

[0089] FIGS. 3A and 3B show electron micrographs of the surface of the main surface of the anode substrate in the manufacturing method of the present embodiment. The valve action metal (Ta) is present in the white portion, and the black portion is a void (pore). FIG. 3A is a photograph before the densification process, and FIG. 3B is a photograph after the densification process. Note that FIGS. 3A and 3B are electron micrographs at the same magnification. FIG. 3B shows the result when, in the densification process, the anode wire is embedded, and the pre-sintering anode substrate (0.8 mm × 3.7 mm × 5.2 mm) having a substantially rectangular parallelepiped outer shape is put into a shaker together with alumina particles having an average particle diameter of 1 mm and the shaker is operated. In all the anode substrates, cracks or chips were not observed, and bending of the anode wire was not observed either.

[0090] FIGS. 4A and 4B show electron micrographs of the cross section of the anode substrate after the densification process. FIG. 4A is a cross-sectional photograph of the surface layer X of the main surface of the anode substrate, and FIG. 4B is a cross-sectional photograph of the inside Y of the anode substrate. Note that FIGS. 4A and 4B are electron micrographs at the same magnification. As shown in FIG. 4A, the surface layer X has fewer void portions and is denser than the inside Y. In FIG. 4A, the porosity P1 in the surface layer X was calculated to be 0.016, and in FIG. 4B, the porosity P2 in the inside Y was calculated to be 0.057.

[0091] In contrast, the pre-sintering anode substrate was placed into a stainless steel container with dimensions of φ55mm×55mm, and was subjected to a rotation process at 150 rpm for 5 minutes on a ball mill turntable. In this case, the surface layer X was not densified, cracks or chips were observed in 20% of the entire anode substrate, and significant bending of the anode wire was confirmed in 0.7% of the entire anode substrate. Note that when the rotation speed was less than 150 rpm, the anode substrate slid on the container wall surface, and a uniform process could not be achieved.

[0092] Also, the pre-sintering anode substrate and φ1mm alumina particles were placed into a stainless steel container with dimensions of φ55mm×55mm, and were subjected to a rotation process at 80 rpm for 5 minutes on a ball mill turntable. In this case, cracks or chips were observed in 5% of the entire anode substrate.

[0093] As described above, when the pre-sintering element was rotationally processed in the container, it is considered that a large local force was applied between the corner of the anode substrate and the container wall surface, etc., causing cracks or chips, or bending of the anode wire.

Industrial Applicability

[0094] The present invention can be used for electrolytic capacitors, and preferably can be used for electrolytic capacitors using a porous body as the anode body.

Explanation of Signs

[0095] 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: Exterior body 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 method for manufacturing an electrolytic capacitor comprising a capacitor element including a porous anode body including an anode substrate and a dielectric layer formed on the surface of the anode substrate, and a solid electrolyte layer covering at least a part of the dielectric layer, the method comprising: preparing an anode substrate including a binder of metal powder; sintering the anode substrate; performing a forming treatment on the sintered anode substrate to obtain the anode body including the anode substrate and the dielectric layer; covering at least a part of the dielectric layer with the solid electrolyte layer, wherein the anode substrate has a plurality of main surfaces, further comprising a densification step of increasing the density of at least a part of a region of at least one of the plurality of main surfaces of the anode substrate, in the densification step, colliding media particles with at least one of the plurality of main surfaces of the anode substrate, a method for manufacturing an electrolytic capacitor.

2. The method for manufacturing an electrolytic capacitor according to claim 1, wherein in the densification step, the anode substrate is vibrated together with the media particles.

3. The method for manufacturing an electrolytic capacitor according to claim 1 or 2, wherein an average particle diameter of the media particles is 1 / 3 or less of a maximum dimension of the anode body.

4. The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 3, wherein the media particles include alumina particles.

5. The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 4, wherein at least a part of a surface of the media particles is coated with the same metal as a constituent metal of the metal powder.

6. The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 5, wherein the densification step is performed on the anode substrate before sintering.

7. The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 5, wherein the densification step is performed on the anode substrate after sintering and before performing the forming treatment.

8. The anode substrate has a side portion connecting two of the plurality of main surfaces and a vertex portion connecting three or more of the plurality of main surfaces, the anode substrate further has a corner portion including the vertex portion and a plurality of side portions each of which is the side portion, in the densification step, the corner portion is formed to have a higher density than at least a part of a region of at least one of the plurality of main surfaces, a method for manufacturing an electrolytic capacitor according to any one of claims 1 to 7.

9. The formation treatment includes a first formation step and a second formation step, The method for manufacturing an electrolytic capacitor according to any one of claims 1 to 8, wherein the thickness of the dielectric layer formed in the second formation step is greater than the thickness of the dielectric layer formed in the first formation step.

Images