Electrolytic capacitor

Abstract

An electrolytic capacitor according to the present invention includes an anode section, a dielectric layer covering at least a portion of the anode section, and a solid electrolyte layer covering at least a portion of the dielectric layer. The anode section includes an anode body and an anode wire protruding from a first surface of the anode body. The anode body is a sintered body of particles containing a valve metal. The anode wire contains a valve metal. The dielectric layer is divided into a first portion covering the surface of the anode body and a second portion covering the portion of the anode wire protruding from the first surface. On the surface of the second portion, the total number of defects is five or less when observing three arbitrary regions each with a field of view of 12,100 μm2 centered at a position 250 μm from the first surface.

Description

electrolytic capacitor

[0001] The present disclosure relates to electrolytic capacitors.

[0002] Patent Document 1 proposes "a method for producing a porous niobium material having a porous oxide coating on the surface of a niobium substrate, the method comprising anodizing the surface of the substrate with an electrolyte containing hydrofluoric acid." Patent Document 1 also proposes "a porous niobium material having a porous layer with a pore size of 10 to 20 nm on a barrier layer, the porous layer being free of pores or petal-shaped defects with a pore size of 0.2 to 1 μm or larger than this range."

[0003] Japanese Patent Application Laid-Open No. 2006-83425

[0004] One aspect of the present disclosure relates to an electrolytic capacitor. The electrolytic capacitor includes an anode section, a dielectric layer covering at least a portion of the anode section, and a solid electrolyte layer covering at least a portion of the dielectric layer. The anode section includes an anode body and an anode wire protruding from a first surface of the anode body. The anode body is a sintered body of particles containing a valve action metal, the anode wire contains a valve action metal, and the dielectric layer is divided into a first portion covering the surface of the anode body and a second portion covering the portion of the anode wire protruding from the first surface. On the surface of the second portion, three arbitrary regions are each divided into 12100 μm from a position 250 μm from the first surface. ２ When observed in a field of view, the total number of defects is 5 or less.

[0005] The leakage current in the electrolytic capacitor can be reduced.

[0006] 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure; 2 is a scanning electron microscope (SEM) image showing the surface of a dielectric layer formed on the surface of an anode wire of Example 1; 3 is an SEM image showing the surface of a dielectric layer formed on the surface of an anode wire of Comparative Example 1; 4 is a schematic diagram showing an example of how to set an observation area for defects in a second portion of the dielectric layer;

[0007] In electrolytic capacitors, metal foil containing a valve metal, porous bodies containing a valve metal (such as a sintered body of particles containing a valve metal), and the like are used as anode bodies. In Patent Document 1, a porous niobium material is used for the anode body. An anode wire for drawing electricity protrudes from the porous body, such as a sintered body. A dielectric layer is formed on the surface of the anode body by anodization, and a dielectric layer is also formed on part of the anode wire. In this case, defects in the dielectric layer of the anode wire are more likely to occur than in the anode body. Furthermore, when defects in the dielectric layer of the anode wire are significant, defects in the dielectric layer of the anode body are also likely to become significant. Leakage current is likely to occur in the defective areas.

[0008] When a sintered body of particles containing a valve metal is used as the anode body of an electrolytic capacitor, an anode wire is used for current collection. Hereinafter, the sintered body of particles containing a valve metal may be simply referred to as a sintered body or a porous sintered body.

[0009] The anode wire contains a valve metal and is rod-shaped (e.g., cylindrical). One end of the anode wire typically protrudes from the first surface of the porous sintered body, while the other end is embedded in the porous sintered body. Current collection occurs through the protruding portion of the anode wire. When anodizing an anode body, the portion of the anode wire facing the anode body may also be anodized, forming a dielectric layer on the surface. Anodizing is typically performed under conditions optimal for forming a dielectric layer on the anode body. Therefore, defects are more likely to occur in the dielectric layer on the anode wire than in the dielectric layer on the anode body. Furthermore, when defects become significant in the dielectric layer on the anode wire, defects often also occur in the dielectric layer on the anode body. Significant defects in the dielectric layer are likely to generate a large leakage current. Large leakage currents impair the reliability of electrolytic capacitors, making it difficult to achieve high capacitance and long life. Defects in the dielectric layer can reduce long-term reliability.

[0010] (Technology 1) An electrolytic capacitor according to one aspect of the present disclosure includes an anode portion, a dielectric layer covering at least a portion of the anode portion, and a solid electrolyte layer covering at least a portion of the dielectric layer. The anode portion includes an anode body and an anode wire protruding from a first surface of the anode body. The anode body is a sintered body of particles containing a valve action metal. The anode wire contains a valve action metal. The dielectric layer is divided into a first portion covering the surface of the anode body and a second portion covering the portion of the anode wire protruding from the first surface. On the surface of the second portion, three arbitrary regions are each divided into 12100 μm from a position 250 μm from the first surface. ２ When observed in a field of view, the total number of defects is 5 or less.

[0011] In the present disclosure, the second portion of the dielectric layer formed on the anode body side (more specifically, the first surface side) of the anode wire has fewer defects. This fewer defects allows for a reduction in leakage current in the anode wire compared to conventional methods. Furthermore, when the second portion of the dielectric layer has fewer defects, the first portion of the dielectric layer also often has fewer defects. This reduces leakage current in the electrolytic capacitor. Suppressing the occurrence of large leakage currents improves the reliability of the electrolytic capacitor, resulting in a longer lifespan and long-term reliability, while also enabling a larger capacitance.

[0012] Here, the defect refers to a crack formed in the second portion of the dielectric layer, having a maximum diameter of 6.3 μm or more and a maximum diameter in a direction perpendicular to the maximum diameter of 5.8 μm or more. The defect often has a petal-like shape, but is not limited to this shape. The dielectric layer is required to have an amorphous structure from the viewpoint of improving insulation properties. However, the area where the defect is formed usually has crystallinity. The defect may also be referred to as a crystalline defect. Because the area where the defect is formed has crystallinity, its appearance differs from that of the amorphous structure area. Therefore, by performing processing such as binarization on an image in which the defect is observed, the defect can be distinguished from the area other than the defect.

[0013] The number of defects in the anode wire can be observed using, for example, an SEM, without any particular limitation. For example, on the surface of the second portion, a 12100 μm (approximately 100 μm) SEM is used so that the position 250 μm from the first surface of the anode body is the center of the field of view. ２ An SEM image of a field of view of 1200 μm is taken. Such SEM images are taken at three arbitrary locations. If the anode wire is cylindrical, the second portion is divided into three equal parts at angles of 120° around the central axis of the cylinder. Three SEM images of 1200 μm and 12100 μm are taken, each of which is centered at each of the three intersections of this dividing line and a line 250 μm away from the first surface. ２ Three fields of view are determined, and an SEM image is taken that includes these areas. The number of defects included in the above fields of view in this SEM image is counted and totaled. The shape of the observation area may be rectangular, circular, or any other shape.

[0014] Fig. 4 shows an example of how to set an observation area for defects in the second portion of the dielectric layer. Fig. 4 is a diagram for explaining how to set the observation area, and the present disclosure is not limited to the case shown in Fig. 4. The following description is not limited to the description of Fig. 4 alone, but broadly corresponds to the description of the electrolytic capacitor of the present disclosure.

[0015] 4 shows an anode part 111 having a dielectric layer 114 on part of its surface. The anode part 111 includes a rectangular parallelepiped anode body 113 and a cylindrical anode wire 112, one end of which protrudes from a first surface S1 of the anode body 113. The other end of the anode wire 112 is embedded in the anode body 113. The dielectric layer 114 is divided into a first portion 114a formed on the surface of the anode body 113 and a second portion 114b formed on the surface of the anode wire 112, where the first portion 114a protrudes from the anode body 113. The number of defects in the second portion 114b is counted from SEM images taken of observation regions (observation fields) R at three arbitrary locations, each centered at a position 250 μm from the first surface S1 of the anode wire 112 (a position 250 μm high from the first surface S1). In Fig. 4, the cylindrical anode wire 112 is divided into three equal parts around the central axis thereof, and three observation regions (observation fields) R are determined with the intersections of these division lines and a line 250 µm high from the first surface S1 as centers. ２However, the shape of this area is not limited to a rectangle.

[0016] (Technology 2) In the above (Technology 1), the total number of defects in each of the fields of view may be three or less. This small number of defects in the second portion can further reduce the leakage current of the electrolytic capacitor. When the number of defects in the second portion is this small, it is considered that the number of defects in the first portion is also small.

[0017] (Technology 3) In the above (Technology 1) or (Technology 2), on the surface of the second portion, six arbitrary regions are each 440 μm apart from the first surface, with the center being a position 250 μm apart from the first surface. ２ When observed in a field of view, the total number of defects may be one or less. In this way, the number of defects is small when observing many locations in a smaller field of view, which further reduces the leakage current. When the number of defects in the second portion is small, it is considered that the number of defects in the first portion is also small.

[0018] In the above (Technology 3), the number of defects in the anode wire can be observed in the same manner as in the above (Technology 1). More specifically, on the surface of the second portion, a 440 μm (250 μm) measurement is performed so that the position 250 μm from the first surface of the anode body is the center of the field of view. ２ An SEM image of a field of view of 440 μm is taken. Such SEM images are taken at six arbitrary locations. If the anode wire is cylindrical, the second portion is divided into six equal parts at angles of 60° around the central axis of the cylinder. Six intersections of the dividing lines and a line 250 μm away from the first surface are taken at 440 μm intervals. ２ Six fields of view are determined, and an SEM image is taken that includes these areas. The number of defects included in the above fields of view in this SEM image is counted and totaled.

[0019] (Technology 4) In any one of the above (Technology 1) to (Technology 3), the anode body and the anode wire may each contain tantalum as the valve metal, thereby obtaining an electrolytic capacitor with a higher capacitance.

[0020] (Technology 5) In any one of (Technology 1) to (Technology 4) above, the second portion may be formed on the surface of the anode wire at least in a region extending from the first surface to a position 500 μm from the first surface. When the second portion of the dielectric layer is formed over a relatively wide region of the surface of the anode wire, defects are more likely to form. Even in such cases, the present disclosure can reduce the number of defects, thereby further minimizing leakage current in the electrolytic capacitor.

[0021] When the anode part is placed with the first surface of the anode body parallel to the horizontal direction and the anode wire positioned vertically above the first surface, the anode wire protrudes vertically upward from the first surface. In this state, when the height of the first surface of the anode body is 0, a position 250 μm from the first surface on the surface of the second part refers to a position 250 μm high from the first surface. Similarly, a position 500 μm high from the first surface refers to a position 500 μm high from the first surface. Therefore, in the above (Technology 5), the region from the first surface to a position 500 μm high from the first surface refers to a region 500 μm high from the first surface. In the above (Technology 5), the second part is formed in at least a region on the surface of the anode wire that is 500 μm high from the first surface.

[0022] The electrolytic capacitor of the present disclosure will be described in more detail below, including the above (Technology 1) to (Technology 5), with reference to the drawings as necessary. At least one of the above (Technology 1) to (Technology 5) may be combined with at least one of the elements described below, provided that no technical contradiction exists. Components other than those characteristic of the present disclosure may be those of known electrolytic capacitors.

[0023] [Electrolytic Capacitor] The electrolytic capacitor of the present disclosure includes an anode portion, a dielectric layer covering at least a portion of the anode portion, and a solid electrolyte layer covering at least a portion of the dielectric layer. Such an electrolytic capacitor may be referred to as capacitor (A).

[0024] In this specification, the minimum unit of an electrolytic capacitor including an anode part, a dielectric layer, and a solid electrolyte layer is sometimes referred to as a “capacitor element.” Therefore, the term “capacitor (A)” is a concept that encompasses both electrolytic capacitors and capacitor elements.

[0025] In the capacitor (A), the anode portion includes an anode body and an anode wire protruding from a first surface of the anode body. The anode body is a sintered body of particles containing a valve metal. The anode wire contains a valve metal. The dielectric layer is divided into a first portion covering the surface of the anode body and a second portion covering the portion of the anode wire protruding from the first surface.

[0026] In the present disclosure, on the surface of the second portion, three arbitrary regions are respectively formed at a position 250 μm from the first surface (a position at a height of 250 μm from the first surface) and a distance of 12100 μm. ２ When observed in a field of view, the total number of defects is 5 or less. This total number of defects is the sum of the number of defects observed in three regions, and the lower the number, the better. The total number of defects may be 3 or less, or may be 1 or less. The total number of defects is 0 or more. The total number of defects may be 0. Thus, in the present disclosure, the number of defects is small in the second portion of the dielectric layer formed on the surface of the anode wire. Furthermore, the number of defects in the second portion tends to be larger than that in the first portion. Therefore, when the number of defects in the second portion is small, it is considered that the number of defects in the first portion will also be even smaller. As a result, a dielectric layer with excellent film quality is formed on the surfaces of the anode body and anode wire, and leakage current in the electrolytic capacitor can be reduced compared to conventional methods.

[0027] In the present disclosure, on the surface of the second portion, six arbitrary regions are each divided into 440 μm regions, centered at a position 250 μm from the first surface (a position 250 μm high from the first surface). ２When observed from a field of view, the number of defects is small. In this case, the total number of defects may be 5 or less, 3 or less, 2 or less, or 1 or less. In this case, the total number of defects is 0 or more. The total number of defects may be 0. In these cases, too, it is considered that the small number of defects in the second portion will further reduce the number of defects in the first portion. Therefore, the leakage current in the electrolytic capacitor can be further reduced compared to conventional cases. The total number of defects in these cases is the sum of the number of defects in the six regions.

[0028] A dielectric layer with few defects is formed, for example, by cleaning the anode part before forming the dielectric layer with a cleaning solution. The anode body of the anode part is a sintered body of particles containing a valve metal. The anode wire is a wire containing a valve metal. The anode part is formed by embedding a portion of the wire containing a valve metal in particles containing a valve metal, molding the particles to form a porous compact, and sintering the porous compact. The resulting anode part includes a porous sintered body and an anode wire having one end portion protruding from one surface (the first surface) of the porous sintered body. The other end portion of the anode wire is embedded in the porous sintered body.

[0029] Valve metal-containing wires, valve metal-containing particles, and compacts thereof typically contain impurities such as foreign metals and carbon residues. While it was previously thought that there was a correlation between the amount of such impurities and the number of defects in the dielectric layer, a correlation has actually been observed. In other words, by thoroughly cleaning the anode part obtained by sintering with a cleaning solution, it is possible to form a dielectric layer with fewer defects. The anode part after cleaning is typically dried. Drying is performed, for example, at a temperature of 60°C to 150°C for a period of 5 to 60 minutes.

[0030] The cleaning liquid may be an acidic solution, an organic solvent, or the like. A mixture of an acidic solution and an organic solvent may also be used. Examples of organic solvents include alcohols (such as ethanol), ketones (such as acetone and ethyl methyl ketone), nitriles (such as acetonitrile), esters (such as ethyl acetate), ethers (such as diethyl ether and tetrahydrofuran), amides (such as dimethylformamide and N-methylpyrrolidone), and sulfoxides (such as dimethyl sulfoxide). The cleaning liquid may contain one organic solvent or a combination of two or more organic solvents. Examples of acidic solutions include aqueous sulfuric acid solutions, aqueous hydrochloric acid solutions, aqueous nitric acid solutions, and aqueous phosphoric acid solutions. One acid may be used alone, or two or more acids may be used in combination. The concentration of the acid in the cleaning liquid may be 1% by mass or more and 30% by mass or less.

[0031] The components of the capacitor (A) will be described in more detail below. The capacitor (A) includes at least one capacitor element. The capacitor element includes an anode portion and a cathode portion. The cathode portion includes a solid electrolyte layer. The anode portion includes an anode body and an anode wire. A dielectric layer is formed on at least a portion of the surface of the anode portion.

[0032] (Anode part) The anode body constituting the anode part is, for example, a sintered body of particles containing a valve metal. This sintered body is entirely porous. The porous anode body has a large surface area, which allows for high capacity.

[0033] The particles are particles of at least one type selected from the group consisting of valve metals, alloys containing valve metals, and metal compounds containing valve metals. Such particles may be used singly or in combination of two or more types. Examples of valve metals include aluminum, tantalum, niobium, and titanium. Among these, tantalum is preferred as the valve metal constituting the sintered body.

[0034] The anode body has a cathode forming portion. A cathode portion including a solid electrolyte layer is formed on the surface of the cathode forming portion of the anode body. The anode body has a shape of, for example, a rectangular parallelepiped.

[0035] The anode wire is a wire containing a valve metal. Examples of the valve metal include the valve metals exemplified for the anode body. The valve metal contained in the anode wire and the valve metal contained in the anode body may be different, but are usually the same. The anode wire may contain tantalum as the valve metal.

[0036] A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes outward from the end face (the first surface) of the anode body. For example, the anode wire may be embedded in the first surface of the rectangular parallelepiped anode body. The anode wire is used for electrical connection to an external electrode on the anode side. Specifically, the anode wire is connected to, for example, an anode lead terminal that is continuous with an external terminal.

[0037] The shape of the anode wire is not particularly limited, and may be cylindrical.

[0038] (Dielectric Layer) The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer may be formed by anodizing the valve metal on the surface of the anode part by chemical conversion treatment or the like. This results in an anode element consisting of the anode part and the dielectric layer. For example, if the anode body and the anode wire contain tantalum as the valve metal, the dielectric layer formed by anodization may be Ta. ２ O ５ Includes.

[0039] The dielectric layer covers at least a portion of the anode part. For convenience, in this specification, in the dielectric layer formed on the surface of the anode part, the portion covering the surface of the anode body is referred to as a first portion, and the portion covering the portion of the anode wire protruding from the first surface is referred to as a second portion.

[0040] A second portion may be formed on the surface of the anode wire at least in a region extending from the first surface to a position 500 μm away (a region extending from the first surface to a height of 500 μm from the first surface). In the axial direction of the anode wire, the length (or height) of the second portion from the first surface may be 400 μm to 1000 μm, 450 μm to 750 μm, or 500 μm to 700 μm. When the second portion of the dielectric layer is formed over a relatively wide region of the surface of the anode wire, defects are more likely to form. Even in such cases, the present disclosure can suppress the number of defects, thereby reducing leakage current in electrolytic capacitors compared to conventional methods.

[0041] (Capacitor Element) The capacitor element includes an anode portion, a dielectric layer, and a cathode portion covering at least a portion of the dielectric layer. The cathode portion includes at least a solid electrolyte layer and may include a cathode extraction layer. The cathode portion typically includes a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode extraction layer covering at least a portion of the solid electrolyte layer.

[0042] (Solid electrolyte layer) The solid electrolyte layer is formed on the cathode forming portion of the anode body via a dielectric layer. The solid electrolyte layer may cover the dielectric layer in a layered manner. The solid electrolyte layer may be a laminate of two or more layers of different solid electrolytes.

[0043] The solid electrolyte constituting the solid electrolyte layer is not particularly limited, and a solid electrolyte used in a known electrolytic capacitor may be used. The solid electrolyte is disposed so as to cover at least a portion of the dielectric layer. The solid electrolyte may be formed using, for example, at least one of a manganese compound and a conductive polymer. The conductive polymer may include, for example, a conjugated polymer and a dopant. The conductive polymer may include a self-doping conductive polymer.

[0044] Examples of conjugated polymers include polypyrrole, polythiophene, polyaniline, and derivatives thereof. These may be used alone or in combination. The conjugated polymer may also be a copolymer of two or more types of monomers. Note that a derivative of a conjugated polymer refers to a polymer having a conjugated polymer as its basic skeleton. An example of a polythiophene derivative is poly(3,4-ethylenedioxythiophene).

[0045] The dopant can be selected depending on the conjugated polymer, and known dopants may be used. Examples of dopants include compounds capable of generating anions (e.g., aromatic sulfonic acids (e.g., naphthalenesulfonic acid, p-toluenesulfonic acid, etc.) or salts thereof), polyanions (e.g., polymer-type polyanions (e.g., polystyrenesulfonic acid)), etc. Examples of solid electrolytes include polypyrrole doped with aromatic sulfonic acids and poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid (PSS).

[0046] The solid electrolyte layer may be formed, for example, by polymerizing a precursor of a conjugated polymer (such as a raw material monomer) on a dielectric layer in the presence of a dopant as needed. The solid electrolyte layer may be formed by applying a liquid composition containing the conjugated polymer (and a dopant as needed) to the dielectric layer and then drying the applied composition.

[0047] (Cathode Extraction Layer) The cathode extraction layer is a conductive layer. The cathode extraction layer is disposed so as to cover at least a portion of the solid electrolyte layer. The configuration of the cathode extraction layer is not particularly limited, and a known cathode extraction layer may be employed. The cathode extraction layer may include, for example, a carbon layer formed on the solid electrolyte layer and a metal particle-containing layer formed on the carbon layer. The carbon layer may include a conductive carbon material such as graphite and a resin. The metal particle-containing layer may include metal particles (e.g., silver particles) and a resin. The metal particle-containing layer may be a silver particle-containing layer formed from a silver paste containing silver particles or silver alloy particles.

[0048] The cathode extraction layer may include a metal foil. The metal foil may be a valve metal (such as aluminum, tantalum, or niobium) or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0049] The cathode extraction layer may be electrically connected to one end of a cathode lead terminal that is continuous with the external terminal. The cathode lead terminal is bonded to the cathode extraction layer via a conductive adhesive applied to the cathode extraction layer. An anode wire protruding from the anode body may be electrically connected to one end of the anode lead terminal.

[0050] The other end of the anode lead terminal and the other end of the cathode lead terminal are each drawn out from the resin exterior body or the case. The other end of each terminal exposed from the resin exterior body or the case is used for soldering to a substrate on which the electrolytic capacitor is to be mounted. In addition to drawing out each lead terminal, at least one end face of the anode portion and the cathode portion may be exposed from the outer surface of the sealing body and electrically connected to an external electrode.

[0051] The capacitor element is sealed using a resin outer casing or case. For example, the capacitor element and the resin material of the outer casing (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed in the resin outer casing by transfer molding, compression molding, or the like. At this time, the other ends of the anode lead terminal and the cathode lead terminal connected to the anode wire drawn from the capacitor element are exposed from the mold.

[0052] FIG. 1 is a cross-sectional view schematically illustrating an example of an electrolytic capacitor according to the present disclosure. The electrolytic capacitor 100 shown in FIG. 1 includes a capacitor element 110, an anode lead terminal 120, a cathode lead terminal 130, an outer casing 101, and a conductive layer 141. The capacitor element 110 includes an anode portion 111, a dielectric layer 114, and a cathode portion 115. The anode portion 111 includes an anode body 113 and an anode wire 112. The anode body 113 is a sintered body of valve metal particles and has a rectangular parallelepiped shape. A portion of the anode wire 112 protrudes from a first surface of the anode body 113 toward a front surface 100f of the electrolytic capacitor 100. The other portion of the anode wire 112 is embedded in the anode body 113. A dielectric layer 114 is formed on the surface of the anode body 113 and on the portion of the anode wire 112 facing the anode body 113.

[0053] Cathode section 115 includes solid electrolyte layer 116 disposed so as to cover at least a portion of dielectric layer 114, and cathode extraction layer 117 formed on solid electrolyte layer 116. Cathode extraction layer 117 includes, for example, a carbon layer formed on solid electrolyte layer 116, and a metal particle-containing layer formed on the carbon layer. The metal particle-containing layer is formed using, for example, a metal paste (such as a silver paste).

[0054] The anode lead terminal 120 includes an anode terminal portion 121 and a lead connection portion 122. The anode terminal portion 121 is exposed on the bottom surface 100b of the electrolytic capacitor 100. The lead connection portion 122 is connected to the anode wire 112. The cathode lead terminal 130 includes a cathode terminal portion 131 and a connection portion 132. The cathode terminal portion 131 is exposed on the bottom surface 100b of the electrolytic capacitor 100. The connection portion 132 is electrically connected to the cathode extraction layer 117 by a conductive layer 141.

[0055] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0056] Example 1 (1) Fabrication of Capacitor Element (i) Preparation of Anode Body Ta particles (Ta powder) were used as valve metal particles. The Ta powder was molded into a rectangular parallelepiped so that one end of an anode wire made of Ta was embedded in the Ta powder, and the molded body was then sintered in a vacuum. This resulted in an anode part including a sintered body (anode body) of a porous Ta particle molded body and an anode wire that was partially embedded in the sintered body (anode body) and the remainder protruding from a first surface of the anode body.

[0057] The anode part, which was composed of the sintered body (anode body) and the anode wire, was washed using isopropanol (IPA) as a cleaning liquid, and then dried at 150° C. for 30 minutes.

[0058] (ii) Formation of Dielectric Layer (Anode Element) 106 cleaned anode parts were lined up at regular intervals, and the anode wire was welded to a long, thin, plate-shaped first electrode. The anode body and a portion of the anode wire were immersed in an anodizing solution in a glass anodizing tank. With a Ta second electrode immersed in the anodizing solution, a DC voltage was applied between the first and second electrodes to oxidize the surface of the anode body and form a dielectric layer. A 0.06 mass % aqueous solution of nitric acid was used as the anodizing solution. The temperature of the anodizing solution was 60°C. A DC voltage of 15 V was applied for 10 hours. After anodization, the anode body was dried at 100°C for 10 minutes. In this way, a dielectric layer of tantalum oxide (TaO) was formed on the surface of the anode body and on the surface of a portion of the anode wire. ２ O ５ The immersion depth of the anode wire in the chemical conversion solution was adjusted so that a dielectric layer (second portion) having a length (height) of 500 μm from the first surface was formed on the surface of the anode wire.

[0059] (iii) Formation of a Solid Electrolyte Layer 3,4-ethylenedioxythiophene and polystyrene sulfonic acid were dissolved in ion-exchanged water to prepare a mixed solution. Iron (III) sulfate (oxidant) dissolved in ion-exchanged water was added to the mixed solution while stirring, and a polymerization reaction was carried out. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidant. A predetermined amount of water was removed from the resulting mixture, and isopropanol (IPA) was added to obtain a liquid dispersion containing polyethylenedioxythiophene doped with polystyrene sulfonic acid (PEDOT / PSS). The liquid dispersion was impregnated into the anode element on which the dielectric layer had been formed for 5 minutes, followed by drying at 150°C for 30 minutes, forming a solid electrolyte layer on the dielectric layer.

[0060] (iv) Formation of Carbon Layer A dispersion liquid (carbon paste) in which carbon particles were dispersed in water was applied to the solid electrolyte layer, and then heated at 200°C to form a carbon layer on the surface of the solid electrolyte layer.

[0061] (v) Formation of Metal Particle-Containing Layer A silver paste containing silver particles, a binder resin, and a solvent was applied to the surface of the carbon layer, and then heated at 200° C. to form a metal particle-containing layer, thereby obtaining a capacitor element.

[0062] (2) Fabrication of Electrolytic Capacitor A conductive adhesive was applied to the metal particle-containing layer of the capacitor element, and the cathode lead terminal and the metal particle-containing layer were bonded. The anode lead and the anode lead terminal were bonded by resistance welding. Next, the capacitor element with each bonded lead terminal was placed in a mold and sealed with an exterior material (thermosetting resin composition) by transfer molding. In this way, an electrolytic capacitor A1 with a rated voltage Rv of 35 V was fabricated.

[0063] Example 2 An electrolytic capacitor A2 was produced in the same manner as in Example 1, except that the anode part including the sintered body (anode body) and the anode wire was cleaned with a mixed solvent of isopropanol (IPA) and distilled water in a mass ratio of 60:40 (IPA:distilled water) as a cleaning liquid.

[0064] Example 3 An electrolytic capacitor A3 was produced in the same manner as in Example 1, except that the anode part including the sintered body (anode body) and the anode wire was cleaned using a solution prepared by mixing isopropanol (IPA) and an aqueous sulfuric acid solution (sulfuric acid concentration: 1% by mass) in a mass ratio of 60:40 (IPA:distilled water) as a cleaning solution.

[0065] Comparative Example 1 An electrolytic capacitor B1 was produced in the same manner as in Example 1, except that the anode part composed of the sintered body (anode body) and the anode wire was washed using distilled water as a cleaning solution.

[0066] Comparative Example 2 An electrolytic capacitor B2 was produced in the same manner as in Example 1, except that the anode portion was not washed.

[0067] <Evaluation> The electrolytic capacitors obtained in the examples and comparative examples were dried at 170° C. for 3 hours and then cooled in a drying chamber to 20° C.±5° C. The electrolytic capacitors in this state were used to carry out the following evaluations.

[0068] A 1 kΩ resistor was connected in series to the electrolytic capacitor, and a voltage of 30 V to 60 V was applied from a DC power supply. The leakage current (LC) was measured 40 seconds after the start of voltage application, and the average value of 20 capacitors was calculated. The LC of each electrolytic capacitor is expressed as a relative value, with the value for electrolytic capacitor B1 being set at 100.

[0069] In addition, the total number of defects in a specific observation area of ​​the second portion was calculated using the anode part with the dielectric layer formed thereon, according to the procedure described above. ２ ) are shown in Figures 2 and 3, respectively.

[0070] The results of the examples and comparative examples are shown in Table 1.

[0071]

[0072] As shown in Table 1, the number of defects and LC were significantly reduced in electrolytic capacitors A1 to A3 compared to those in B1 and B2. As shown in Figure 3, many relatively large petal-shaped cracks were observed in the second portion of the dielectric layer used in Comparative Example 1 (B1). In contrast, the large cracks seen in B1 were hardly observed in the second portion of the dielectric layer used in Example 1 (A1).

[0073] The electrolytic capacitor of the present disclosure has low leakage current and high reliability. Therefore, the electrolytic capacitor is suitable for use in connection with electronic circuits, and can suppress malfunctions of the electronic circuits in such applications. However, the applications of the electrolytic capacitor are not limited to these.

[0074] 100: Electrolytic capacitor 100b: Bottom surface of electrolytic capacitor 101: Exterior body 110: Capacitor element 111: Anode portion 112: Anode wire 113: Anode body 114: Dielectric layer 114a: First portion 114b: Second portion R: Defect measurement area 115: Cathode portion 116: Solid electrolyte layer 117: Cathode extraction layer 120: Anode lead terminal 121: Anode terminal portion 122: Lead connection portion 130: Cathode lead terminal 131: Cathode terminal portion 132: Connection portion 141: Conductive layer

Claims

1. An anode comprising an anode part, a dielectric layer covering at least a portion of the anode part, and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the anode part comprises an anode body and an anode wire protruding from a first surface of the anode body, wherein the anode body is a sintered body of particles containing a valve action metal, and the anode wire contains a valve action metal, and the dielectric layer is divided into a first portion covering the surface of the anode body and a second portion covering the portion of the anode wire protruding from the first surface, and on the surface of the second portion, three arbitrary regions are each divided into 12100 μm from a position 250 μm from the first surface. ２ An electrolytic capacitor having a total of five or less defects when observed in a field of view.

2. The electrolytic capacitor according to claim 1, wherein the total number of defects in each of said fields is three or less.

3. On the surface of the second portion, six arbitrary regions are each 440 μm apart, centered at a position 250 μm from the first surface. ２ 3. The electrolytic capacitor according to claim 1, wherein the total number of defects is one or less when observed in a field of view.

4. The electrolytic capacitor according to claim 1 or 2, wherein the anode body and the anode wire each contain tantalum as the valve metal.

5. The electrolytic capacitor according to claim 1 or 2, wherein the second portion is formed on the surface of the anode wire at least in a region extending from the first surface to a position 500 μm away.

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