Solid electrolytic capacitor

Abstract

A solid electrolytic capacitor according to the present invention comprises a positive electrode body, a dielectric layer that is formed on the surface of the positive electrode body, a solid electrolyte layer that includes a conductive polymer and covers at least a portion of the dielectric layer, and a negative electrode layer that covers at least a portion of the solid electrolyte layer. A layer that includes a boro-di-organic acid compound is provided between the dielectric layer and the negative electrode layer.

Description

solid electrolytic capacitor

[0001] The present invention relates to a solid electrolytic capacitor.

[0002] Electrolytic capacitors are used in a variety of electronic devices due to their low equivalent series resistance (ESR) and excellent frequency characteristics. Electrolytic capacitors typically include a capacitor element with an anode and a cathode. The anode 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 the electrolyte. Some solid electrolytic capacitors use a solid electrolyte, such as a conductive polymer, as the electrolyte.

[0003] Patent Document 1 proposes the use of a conductive polymer containing polythiophene as a solid electrolyte for an electrolytic capacitor.

[0004] The method for manufacturing an electrolytic capacitor includes the following steps: a first step of preparing an anode member having a dielectric layer; a second step of impregnating the anode member with a monomer, an oxidizer, a silane compound, and a solvent; and a third step of forming a solid electrolyte layer on the surface of the dielectric layer, the solid electrolyte layer including a conductive polymer containing a polymer of the monomer and a silicon-containing component derived from the silane compound. The method proposes the use of 3,4-ethylenedioxythiophene (alkyl EDOT) having an alkyl group in a side chain as the monomer. The method also proposes impregnating the capacitor element after the solid electrolyte layer has been formed with an electrolyte solution containing an organic salt dissolved in a nonaqueous solvent to improve the repair function of the dielectric layer.

[0005] Japanese Patent Publication No. 2004-96098

[0006] Electrolytic capacitors using the above-mentioned conductive polymers are prone to deterioration of the conductive polymers when exposed to high-temperature atmospheres for long periods of time. In this regard, there is a demand for electrolytic capacitors that exhibit little change in characteristics even in high-temperature environments and have high reliability.

[0007] In view of the above, one aspect of the present disclosure relates to a solid electrolytic capacitor including an anode body, a dielectric layer formed on a surface of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer and including a conductive polymer, and a cathode layer covering at least a portion of the solid electrolyte layer, the solid electrolyte layer having a layer including a borodiorgano acid compound between the dielectric layer and the cathode layer.

[0008] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0009] It is possible to realize a solid electrolytic capacitor that has high reliability even in high-temperature environments.

[0010] 1 is a cross-sectional view schematically illustrating an example of a capacitor element of a solid electrolytic capacitor according to an embodiment of the present disclosure. 2 is a cross-sectional view schematically illustrating a solid electrolytic capacitor according to an embodiment of the present disclosure. 3 is a cross-sectional view schematically illustrating an enlarged view of the vicinity of a surface of an anode body of the capacitor element shown in FIG.

[0011] A solid electrolytic capacitor according to an embodiment of the present disclosure includes an anode body, a dielectric layer formed on the surface of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode layer covering at least a portion of the solid electrolyte layer, and a layer containing a borodiorgano acid compound (hereinafter, sometimes referred to as a "BOD layer") between the dielectric layer and the cathode layer.

[0012] The BOD layer significantly suppresses the degradation of the conductive polymer even when exposed to high-temperature environments for long periods of time, resulting in an electrolytic capacitor with high reliability even at high temperatures. While the reason for this is unclear, one possible explanation is that the high acidity of the borodiorganic acid compound suppresses dedoping of the conductive polymer, allowing the conductive polymer to maintain its high conductivity for a long period of time. Furthermore, when the solid electrolyte layer is formed from multiple conductive polymer layers, the adhesion between the conductive polymer layers is improved, reducing defects due to peeling of the conductive polymer layers.

[0013] The BOD layer may be disposed on the surface of the dielectric layer or may be disposed within the solid electrolyte layer containing the conductive polymer. In order to efficiently obtain the above-described effects of the BOD layer, it is preferable that the BOD layer be the layer in the solid electrolyte layer that is in contact with the dielectric layer and closest to the dielectric layer, or at least be disposed biased toward the dielectric layer.

[0014] The BOD layer is formed, for example, by immersing the anode body in a solution in which a borodiorganic acid compound is dissolved in a solvent (e.g., water), or by applying a solution in which a borodiorganic acid compound is dissolved to the surface of the dielectric layer or the solid electrolyte layer, followed by drying.

[0015] A solid electrolyte layer containing a conductive polymer can be formed, for example, by immersing an anode body having a dielectric layer formed thereon in a polymerization solution containing a monomer of the conductive polymer and polymerizing the monomer on the surface of the dielectric layer. The monomer polymerization method may be chemical polymerization or electrolytic polymerization. The monomer includes an oligomer. In this case, the solid electrolyte layer can be formed of multiple conductive polymer layers by immersing the anode body in the polymerization solution multiple times. In this case, coating or immersion in a solution of a borodiorganic acid compound is performed between two consecutive steps among the steps of forming multiple conductive polymer layers. The step of coating or immersion in a solution of a borodiorganic acid compound is preferably performed before the intermediate step among the steps of forming multiple conductive polymer layers.

[0016] A solid electrolyte layer containing a conductive polymer may be formed by immersing an anode element having a dielectric layer formed thereon in a dispersion liquid in which a conductive polymer is dissolved or dispersed in a dispersion medium. In this case, the solid electrolyte layer may be formed of a plurality of conductive polymer layers by immersing the anode element in the dispersion liquid multiple times. In this case, the application or immersion of the solution of the borodi-organic acid compound is performed between two successive steps among the steps of forming a plurality of conductive polymer layers. The step of applying or immersing the solution of the borodi-organic acid compound is preferably performed before the intermediate step among the steps of forming a plurality of conductive polymer layers. In this case, the BOD layer may be biased toward the dielectric layer within the solid electrolyte layer.

[0017] Assume that the solid electrolyte layer formation step is divided into N conductive polymer layer formation steps. Assume that the step of applying or immersing in a solution of a borodi-organic acid compound is performed after the mth conductive polymer layer formation step and before the (m+1)th conductive polymer layer formation step. m is preferably [(N-1) / 2] or less. Here, [X] represents the largest integer not exceeding X. m is more preferably 3 or less, and m=1 is even more preferable. m=0 may be used. When m=0, application or immersion in a solution of a borodi-organic acid compound is performed before the conductive polymer layer formation step, and a BOD layer is formed on the surface of the dielectric layer.

[0018] The content of the borodiorganic acid compound in the BOD layer is preferably 0.5 mass % or more and 10 mass % or less relative to the total mass of the conductive polymer contained in the solid electrolyte layer. In this case, higher reliability can be achieved at high temperatures. The mass of the borodiorganic acid compound is calculated from the molecular weight of the anion of the borodiorganic acid compound.

[0019] The presence of the borodiorganic acid compound in the conductive polymer layer and the content thereof can be determined by, for example, gas chromatography (GC).

[0020] The borodiorganic acid compound is a compound capable of generating a borodiorganic complex anion in which two bidentate ligands derived from an acid having a carboxyl group and / or an oxy group are coordinated around a boron atom. Examples of the borodiorganic coordination compound include borodisalicylic acid, borodisalic acid, and borodiglycolic acid. At least one borodiorganic acid compound selected from the group consisting of borodiorganic acid compounds may be used.

[0021] The borodisalicylic acid compound may be either an acid-type compound or a salt-type compound (borodisalicylic acid salt) as long as it has a structure capable of generating a borodisalicylic acid complex anion. For example, a salt of borodisalicylic acid, which is a borodisalicylic acid complex salt, may be a salt of borodisalicylic acid and an organic base. The salt of borodisalicylic acid is preferably a salt of borodisalicylic acid and an amine compound. The amine compound may be any of primary amines, secondary amines, and tertiary amines. Examples of the amine compound include aliphatic amines and cyclic amines.

[0022] The anode body may be a sintered body of a valve metal. The valve metal is preferably tantalum (Ta) because of its excellent corrosion resistance and high corrosion resistance against borodiorgano compounds.

[0023] Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These may be used alone or in combination. The conductive polymer may also be a copolymer of two or more monomers. In terms of excellent conductivity, polythiophene, polyaniline, and polypyrrole may be used, with polythiophene being more preferred.

[0024] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. refer to polymers having a basic skeleton of polypyrrole, polythiophene, polyfuran, polyaniline, etc. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc. may also include their respective derivatives.

[0025] The polythiophene may be poly(3,4-ethylenedioxythiophene) (PEDOT). Poly(3,4-ethylenedioxythiophene) contains 3,4-ethylenedioxythiophene (EDOT) as a monomer unit. In terms of improving the withstand voltage, the polythiophene may have EDOT having an alkyl group on the side chain (hereinafter also referred to as "alkyl EDOT") as a monomer unit. The alkyl EDOT has, for example, a structure represented by the following chemical formula: The number of carbon atoms in the alkyl group R as the side chain may be from 2 to 4. 90% by mass or more of all monomer units constituting the polythiophene may be at least one of EDOT and alkyl EDOT.

[0026] Various dopants may be added to the polymerization liquid for forming the conductive polymer, or the solution or dispersion of the conductive polymer in order to improve the conductivity of the conductive polymer. The dopant is not particularly limited, but examples thereof include naphthalenesulfonic acid, p-toluenesulfonic acid, and polystyrenesulfonic acid.

[0027] When the conductive polymer is dispersed in the dispersion medium in the form of particles, the average particle size D50 of the particles is, for example, 0.01 μm or more and 0.5 μm or less. If the average particle size D50 of the particles is in this range, the particles can easily penetrate into the interior of the anode body 1.

[0028] As described above, the solid electrolyte layer may be composed of a layer (conductive polymer layer) containing a plurality of conductive polymers. When the solid electrolyte layer is composed of a plurality of conductive polymer layers, the conductive polymers used in each layer may have different compositions, thicknesses, or formation methods (polymerization methods). For example, in the first conductive polymer layer formation step, a first conductive polymer layer may be formed on the surface of the dielectric layer by polymerizing a raw material monomer on the dielectric layer. In the second or subsequent conductive polymer layer formation steps, a second conductive polymer layer may be formed by applying a dispersion liquid containing a conductive polymer.

[0029] The electrolytic capacitor according to this embodiment will be described below with reference to the accompanying drawings. However, the present invention is not limited thereto. Fig. 1 is a cross-sectional view schematically showing an example of a capacitor element of the electrolytic capacitor according to this embodiment. Fig. 2 is a cross-sectional view of the electrolytic capacitor according to this embodiment.

[0030] Electrolytic capacitor 20 includes capacitor element 10 having anode portion 6 and cathode portion 7, exterior body 11 sealing capacitor element 10, anode lead terminal 13 electrically connected to anode portion 6 and partially exposed from exterior body 11, and cathode lead terminal 14 electrically connected to cathode portion 7 and partially exposed from exterior body 11. Anode portion 6 includes anode body 1 and anode wire 2. Dielectric layer 3 is formed on the surface of the anode body. Cathode portion 7 includes solid electrolyte layer 4 covering at least a portion of dielectric layer 3, and cathode layer 5 covering at least a portion of the surface of solid electrolyte layer 4.

[0031] <Capacitor Element> Hereinafter, the capacitor element 10 will be described in detail, taking as an example a case where the capacitor element 10 includes a solid electrolyte layer as the electrolyte.

[0032] The anode part 6 includes an anode body 1 and an anode wire 2 extending from one surface of the anode body 1 and electrically connecting to an anode lead terminal 13. The anode body 1 is, for example, a rectangular porous sintered body obtained by sintering metal particles. Valve metal particles such as titanium (Ti), tantalum (Ta), and niobium (Nb) are used as the metal particles. One or more types of metal particles are used in the anode body 1. The metal particles may be an alloy of two or more metals. For example, an alloy containing a valve metal and silicon, vanadium, boron, or the like may be used. Alternatively, a compound containing a valve metal and a typical element such as nitrogen may be used. The valve metal alloy contains a valve metal as the main component, for example, at least 50 atomic % of the valve metal.

[0033] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited and includes, for example, copper, aluminum, aluminum alloys, and the like, in addition to the valve metals described above. The anode body 1 and the anode wire 2 may be made of the same material or different materials. The anode wire 2 has a first portion 2a that is embedded inside the anode body 1 from one surface of the anode body 1, and a second portion 2b that extends from the above surface of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited and includes, for example, a circle, a track shape (a shape consisting of parallel straight lines and two curves connecting the ends of these straight lines), an ellipse, a rectangle, a polygon, and the like.

[0034] The anode part 6 is produced, for example, by press-molding the first portion 2a into a rectangular parallelepiped shape while the first portion 2a is embedded in a powder of particles of the first metal, followed by sintering. This causes the second portion 2b of the anode wire 2 to extend from one surface of the anode body 1 in an upright manner. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, thereby electrically connecting the anode wire 2 and the anode lead terminal 13. The welding method is not particularly limited, and examples include resistance welding and laser welding.

[0035] A dielectric layer 3 is formed on the surface of the anode body 1. The dielectric layer 3 is made of, for example, a metal oxide. Methods for forming a layer containing a metal oxide on the surface of the anode body 1 include, for example, 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 oxygen-containing atmosphere. The dielectric layer 3 is not limited to the above-mentioned layer containing a metal oxide, and may be any layer that is insulating.

[0036] (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 portion of the dielectric layer 3. The solid electrolyte layer 4 has the above-described structure.

[0037] The cathode layer 5 has, for example, a carbon layer 5a formed 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. The configuration of the cathode layer 5 is not limited to this configuration. The configuration of the cathode layer 5 may be any configuration that has a current collecting function.

[0038] When the solid electrolyte layer 4 is composed of multiple conductive polymer layers, a basic compound may be interposed between the conductive polymer layers to improve adhesion between the conductive polymer layers. The cation contained in the basic compound suppresses the repulsion of the anionic dopant contained in the conductive polymer, thereby enhancing adhesion between the conductive polymer layers. Examples of the basic compound include inorganic bases such as ammonia and organic bases such as amine compounds. Among basic compounds, amine compounds are preferred from the viewpoint of their high effectiveness in suppressing a decrease in conductivity. The amine compound may be any of primary amines, secondary amines, and tertiary amines. Examples of the amine compound include aliphatic amines and cyclic amines. One type of basic compound may be used alone, or two or more types may be used in combination.

[0039] The borodiorganic acid compound may be a salt compound containing a borodiorganic complex anion and a cation of the basic compound, in which case the effects of the borodiorganic acid and the basic compound on enhancing adhesion between conductive polymer layers are synergistically enhanced, thereby enhancing the effect of inhibiting deterioration of the conductive polymer layers.

[0040] <Anode lead terminal> The anode lead terminal 13 is electrically connected to the anode body 1 via the second portion 2b of the anode wire 2. The material of the anode lead terminal 13 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The anode lead terminal 13 may be made of a metal such as copper, or a non-metal. The shape of the anode lead terminal 13 is not particularly limited as long as it is flat. 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, or may be 25 μm or more and 100 μm or less, from the viewpoint of reducing the height.

[0041] One end of the anode lead terminal 13 may be joined to the anode wire 2 with 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 extended 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) with carbon particles or metal particles.

[0042] <Cathode lead terminal> The cathode lead terminal 14 is electrically connected to the cathode part 7 at the joint portion 14a. The joint portion 14a is a portion of the cathode lead terminal 14 that overlaps with the cathode layer 5 when the cathode layer 5 and the cathode lead terminal 14 joined to the cathode layer 5 are viewed from the normal direction of the cathode layer 5.

[0043] 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 joining portion 14a and is disposed inside the exterior body 11. The other end of the cathode lead terminal 14 is led out to the outside. Therefore, a part of the cathode lead terminal 14, including the other end, is exposed from the exterior body 11.

[0044] The material of the cathode lead terminal 14 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The cathode lead terminal 14 may be made of a metal such as copper, or a non-metal. The shape of the cathode lead terminal 14 is also not particularly limited, and may be, for example, a long, flat plate. From the viewpoint of reducing the height, the thickness of the cathode lead terminal 14 may be 25 μm or more and 200 μm or less, or 25 μm or more and 100 μm or less.

[0045] <Exterior Body> The exterior body 11 is provided to electrically insulate the anode lead terminal 13 and the cathode lead terminal 14, and is made of an insulating material (exterior body material). The exterior body material includes, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, and unsaturated polyester.

[0046] FIG. 3 is an enlarged schematic cross-sectional view showing the vicinity of the surface of anode body 1 of capacitor element 10 shown in FIG.

[0047] A solid electrolyte layer 4 is disposed so as to cover the surface of the dielectric layer 3. The solid electrolyte layer 4 includes a conductive polymer and a layer containing a borodiorganic acid compound. The solid electrolyte layer 4 is covered with a cathode layer 5 (carbon layer 5a). Within the solid electrolyte layer 4, the borodiorganic acid compound 4X is distributed unevenly in a region closer to the dielectric layer 3 than the carbon layer 5a and at a depth within a certain range of distance from the dielectric layer 3.

[0048] <Method for Manufacturing Electrolytic Capacitor> An example of a method for manufacturing the electrolytic capacitor according to this embodiment will be described below.

[0049] (1) Capacitor Element Preparation Step First, a capacitor element is prepared. The capacitor element preparation step includes, for example, the steps of preparing an anode body, covering at least a portion of the anode body with a dielectric layer, covering at least a portion of the dielectric layer with a solid electrolyte layer, and covering at least a portion of the solid electrolyte layer with a carbon layer. The capacitor element preparation step may further include the step of covering at least a portion of the carbon layer with a conductive resin layer.

[0050] (1a) Anode Body Preparation Step A porous sintered body can be used as the anode body 1. Valve metal particles and an anode wire 2 are placed in a mold so that the first portion 2a is embedded in the valve metal particles, and then press-molded and sintered to obtain an anode part 6 including the anode body 1, which is a porous body of valve metal. The first portion 2a of the anode wire is embedded inside the porous sintered body from one surface thereof. The pressure used in press-molding is not particularly limited. Sintering is preferably performed under reduced pressure. A binder such as polyacrylic carbonate may be mixed with the valve metal particles as needed.

[0051] Valve metal particles are usually pressure-molded using a mold having a rectangular parallelepiped internal space, and then sintered. In this case, the shape of the sintered anode body 1 is also rectangular parallelepiped and has multiple main surfaces.

[0052] (1b) Dielectric Layer Forming Step Next, the anode body 1 is subjected to a chemical conversion treatment to cover at least a portion of the anode body 1 with the dielectric layer 3. Specifically, the anode body 1 is immersed in a chemical conversion tank filled with an aqueous electrolytic solution (e.g., an aqueous phosphoric acid solution), the second portion 2b of the anode wire 2 is connected to the anode body in the chemical conversion tank, and anodization is performed to form the dielectric layer 3 made of an oxide film of a valve metal on the surface of the porous portion. The aqueous electrolytic solution is not limited to an aqueous phosphoric acid solution, and nitric acid, acetic acid, sulfuric acid, or the like can also be used.

[0053] (1c) Solid Electrolyte Layer Forming Step Subsequently, at least a portion of the dielectric layer 3 is covered with the solid electrolyte layer 4. This results in a capacitor element 10 including the anode body 1, the dielectric layer 3, and the solid electrolyte layer 4. The solid electrolyte layer 4 may include a plurality of conductive polymer layers.

[0054] The solid electrolyte layer forming step may be a step of forming a plurality of conductive polymer layers. The step of forming a plurality of conductive polymer layers includes a step of forming a first conductive polymer layer containing a first conductive polymer and a step of forming a second conductive polymer layer containing a second conductive polymer so as to cover the surface of the first conductive polymer layer. The step of forming the first conductive polymer layer may be a step of forming the mth conductive polymer layer. The step of forming the second conductive polymer layer may be a step of forming the (m+1)th conductive polymer layer. The steps of forming the first conductive polymer layer and the second conductive polymer layer may each be a step of impregnating the anode body with a solution containing a monomer or oligomer that serves as a raw material for the conductive polymer and polymerizing the monomer or oligomer on the surface of the dielectric layer or the conductive polymer layer (so-called "in situ polymerization"), or a step of impregnating the anode body with a dispersion containing a conductive polymer.

[0055] The conductive polymer may contain a dopant. The conductive polymer and the dopant may each be selected from the compositions described above. The dispersion may contain a binder and / or conductive inorganic particles (e.g., a conductive carbon material such as carbon black). The dispersion may contain known additives used in forming a solid electrolyte layer.

[0056] After the step of forming the first conductive polymer layer and before the step of forming the second conductive polymer layer, a step of immersing the anode body in a solution in which a borodiorganic acid compound is dissolved in a solvent or a step of applying the solution in which a borodiorganic acid compound is dissolved in a solvent is performed. The solvent is removed by drying, and a BOD layer is formed so as to cover the first conductive polymer layer.

[0057] When the total thickness of the solid electrolyte layer is T, the BOD layer is preferably disposed in a region whose distance from the dielectric layer is smaller than T / 2 and whose distance from the dielectric layer is within a certain range. In other words, the BOD layer is preferably disposed within the solid electrolyte layer, biased toward the dielectric layer relative to the outer surface of the solid electrolyte layer.

[0058] When the solid electrolyte layer formation step includes a step of forming N (N≧3) conductive polymer layers, the BOD layer is formed after the step of forming the mth conductive polymer layer (first conductive polymer layer) and before the step of forming the (m+1)th conductive polymer layer (second conductive polymer layer) (where 1≦m≦N). m is preferably [(N−1) / 2] or less. Here, [X] represents the largest integer not exceeding X. m is more preferably 3 or less, and m=1 is even more preferably. m=0 may also be used. That is, the BOD layer may be formed on the surface of the dielectric layer before the step of forming the conductive polymer layer.

[0059] Prior to the step of forming the solid electrolyte layer, a step of immersing the anode body in a solution in which a borodiorganic acid compound is dissolved in a solvent or a step of applying a solution in which a borodiorganic acid compound is dissolved in a solvent to the anode body may be performed to form a BOD layer on the surface of the dielectric layer.

[0060] (1d) Step of Forming Carbon Layer and Conductive Resin Layer Next, a carbon paste and a metal paste are applied in this order to the surface of the solid electrolyte layer 4 to form a cathode layer 5 composed of a carbon layer 5a and a metal paste layer 5b. The configuration of the cathode layer 5 is not limited to this, and any configuration may be used as long as it has a current collecting function.

[0061] (2) Step of Electrically Connecting the Capacitor Element and the Lead Terminal Next, the anode lead terminal 13 and the cathode lead terminal 14 are prepared. The second portion 2b of the anode wire 2 embedded in the anode body 1 is joined to the anode lead terminal 13 by laser welding, resistance welding, or the like. After applying the conductive adhesive 8 to the cathode layer 5, the cathode lead terminal 14 is joined to the cathode portion 7 via the conductive adhesive 8.

[0062] Next, the capacitor element 10 and the materials for the exterior body 11 (e.g., uncured thermosetting resin and filler) are placed in a mold, and the capacitor element 10 is sealed by transfer molding, compression molding, or the like. At this time, a portion of the anode lead terminal 13 and the cathode lead terminal 14 are exposed from the mold. The molding conditions are not particularly limited, and the time and temperature conditions may be set appropriately taking into consideration the curing temperature of the thermosetting resin used, etc.

[0063] Finally, the exposed portions of the anode lead terminal 13 and the cathode lead terminal 14 are bent along the exterior package 11 to form bent portions, whereby a portion of the anode lead terminal 13 and the cathode lead terminal 14 is disposed on the mounting surface of the exterior package 11. By the above method, the electrolytic capacitor 20 is manufactured.

[0064] (Additional Notes) The above embodiments disclose the following technologies. (Technology 1) A solid electrolytic capacitor comprising: an anode body; a dielectric layer formed on the surface of the anode body; a solid electrolyte layer containing a conductive polymer and covering at least a portion of the dielectric layer; and a cathode layer covering at least a portion of the solid electrolyte layer, the solid electrolytic capacitor having a layer containing a borodiorganic acid compound between the dielectric layer and the cathode layer. (Technology 2) The solid electrolytic capacitor according to Technology 1, wherein the layer containing a borodiorganic acid compound is disposed on the surface of the dielectric layer. (Technology 3) The solid electrolytic capacitor according to Technology 1, wherein the layer containing a borodiorganic acid compound contains the conductive polymer and constitutes a part of the solid electrolyte layer. (Technology 4) The solid electrolytic capacitor according to Technology 3, wherein the layer containing a borodiorganic acid compound is disposed biased toward the dielectric layer within the solid electrolyte layer. (Technology 5) The solid electrolytic capacitor according to any one of Technology 1 to 4, wherein the anode body is a sintered body of a valve metal. (Technology 6) The solid electrolytic capacitor according to any one of Technologies 1 to 5, wherein the conductive polymer includes a polythiophene containing, as a monomer unit, 3,4-ethylenedioxythiophene (EDOT) or EDOT having an alkyl group on the side chain. (Technology 7) The solid electrolytic capacitor according to Technology 6, wherein the polythiophene contains, as a monomer unit, 3,4-ethylenedioxythiophene having an alkyl group on the side chain.

[0065] 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.

[0066] Example 1 An electrolytic capacitor was fabricated as follows. (Formation of anode body) Tantalum metal particles were used as the valve metal. Tantalum metal particles were molded into a rectangular parallelepiped so that one end of an anode wire made of tantalum metal was embedded in the tantalum metal particles, and the molded body was then sintered in a vacuum. This resulted in an anode part including an anode body (1.7 mm × 3.3 mm × 4.4 mm) made of a porous sintered body of tantalum and an anode wire with one end embedded in the anode body and the remaining portion embedded in one surface of the anode body.

[0067] (Formation of Dielectric Layer) Next, the anode body and a portion of the anode wire implanted from the anode body were immersed in an anodization bath filled with an aqueous phosphoric acid solution, which was an electrolytic solution, and the other end of the anode wire was connected to the anode body in the anodization bath. Then, anodization was performed to form a tantalum oxide (TaO) layer on the surface of the anode body (the surface of the porous sintered body including the inner wall surfaces of the pores) and on the surface of a portion of the anode wire. ２ O ５ ) to form a uniform dielectric layer.

[0068] Next, the anode body was immersed in an aqueous solution of ethylmethyldiamine borodisalicylate. Thereafter, the anode body was removed from the aqueous solution and dried in the air at 130°C for 10 minutes to form a BOD layer. The BOD layer was formed so that the mass of the portion of ethylmethyldiamine borodisalicylate corresponding to borodisalicylic acid was 5% of the total mass of the solid electrolyte layer (conductive polymer layer) to be subsequently formed.

[0069] (Formation of Solid Electrolyte Layer) Next, a polymerization solution was prepared by mixing 3,4-ethylenedioxythiophene, in which one hydrogen group in the ethylene group was substituted with an ethyl group, iron(III) p-toluenesulfonate, and 1-butanol as raw materials for the conductive polymer. After immersing the anode body in the polymerization solution, the anode body was removed from the polymerization solution and subjected to heat treatment in the air. In this case, iron(III) p-toluenesulfonate functions as an oxidizing agent. In this way, a conductive polymer layer containing poly(3,4-ethylenedioxythiophene) (PEDOT) was formed on the dielectric layer.

[0070] The above-described formation of the conductive polymer layer was repeated 10 times to form a solid electrolyte layer consisting of 10 conductive polymer layers.

[0071] (Fabrication of Electrolytic Capacitor) Copper lead frames (anode lead frame and cathode lead frame) plated with three layers of Ni / Pd / Au were prepared. After applying a conductive adhesive to the cathode layer, the cathode lead frame was bonded to the cathode layer via the conductive adhesive. The anode wire and the anode lead frame were bonded by resistance welding.

[0072] Next, the capacitor element with the joined lead terminals and the materials for the exterior body (uncured thermosetting resin and filler) were placed in a mold, and the capacitor element was sealed by transfer molding. After sealing, the exposed portions of the anode lead frame and cathode lead frame from the exterior body were folded along the surface of the exterior body, thereby obtaining a solid electrolytic capacitor A1 according to Example 1 having the configuration shown in FIG.

[0073] (Evaluation) The solid electrolytic capacitor was evaluated as follows.

[0074] 1. High-Temperature Load Test After manufacturing, the capacitance of each solid electrolytic capacitor was measured at a frequency of 120 Hz using an LCR meter in an environment of 20°C, and the average value of 20 pieces was taken as the initial capacitance value X. ０ (F) was calculated.

[0075] X ０ After the measurement, a high temperature load test was carried out. That is, a rated voltage (35 V) was applied to the solid electrolytic capacitor for 500 hours at a temperature of 125° C. After 500 hours, the average capacitance value X １ (F) was calculated in the same manner as for the initial capacitance value. ０ and X １ Using the above, the capacity change rate Δcap1 in the high temperature load test was calculated using the following formula: Δcap1 (%) = (X １ / X ０ −1) × 100

[0076] 2. Charge / discharge test X after manufacturing ０ After the measurement, the solid electrolytic capacitor was subjected to 100,000 cycles of charging by applying the rated voltage and discharging by applying 0 V in an environment of 20° C. The average capacitance value Y １ (F) was determined in the same manner as for the initial capacitance value. ０ and Y １ The capacity change rate Δcap2 in the charge / discharge test was calculated using the following formula: Δcap2 (%) = (Y １ / X ０ −1) × 100

[0077] Example 2 In Example 1, the formation of the BOD layer was changed to be performed after the formation of the first conductive polymer layer and before the formation of the second conductive polymer layer. Except for this, a solid electrolytic capacitor A2 according to Example 2 was produced in the same manner as in Example 1 and evaluated in the same manner.

[0078] Example 3 In Example 1, the formation of the BOD layer was changed to be performed after the fifth formation of the conductive polymer layer and before the sixth formation of the conductive polymer layer. Except for this, a solid electrolytic capacitor A3 according to Example 3 was produced in the same manner as in Example 1 and evaluated in the same manner.

[0079] Example 4 In Example 1, the formation of the BOD layer was changed to be performed after the tenth formation of the conductive polymer layer. Except for this, a solid electrolytic capacitor A4 according to Example 4 was produced in the same manner as in Example 1 and evaluated in the same manner.

[0080] Example 5 An anode body was immersed in an aqueous solution of borodisalicylic acid instead of ethylmethyldiamine borodisalicylate, and then dried in the air at 130°C for 10 minutes to form a BOD layer. The BOD layer was applied so that the mass of borodisalicylic acid was 5% of the total mass of the solid electrolyte layer (conductive polymer layer) excluding borodisalicylic acid. A solid electrolytic capacitor A5 according to Example 5 was fabricated in the same manner as in Example 2 and evaluated in the same manner.

[0081] Example 6 In forming the solid electrolyte layer, 3,4-ethylenedioxythiophene (EDOT), a raw material for conductive polymers, was used to form a conductive polymer layer containing poly(3,4-ethylenedioxythiophene). Except for this, a solid electrolytic capacitor A6 according to Example 6 was fabricated in the same manner as in Example 1 and evaluated in the same manner.

[0082] Example 7 In forming the solid electrolyte layer, 3,4-ethylenedioxythiophene (EDOT), a raw material for conductive polymers, was used to form a conductive polymer layer containing poly(3,4-ethylenedioxythiophene). Except for this, a solid electrolytic capacitor A7 according to Example 7 was fabricated in the same manner as in Example 2 and evaluated in the same manner.

[0083] Comparative Example 1 A solid electrolytic capacitor B1 according to Comparative Example 1 was produced in the same manner as in Example 1 except that a solid electrolyte layer was formed without forming a BOD layer, and was evaluated in the same manner.

[0084] Examples 8 to 15 In forming the BOD layer, the concentration of the aqueous solution used when immersing the anode body in the aqueous solution of ethylmethyldiamine borodisalicylate was changed. This changed the content of borodisalicylic acid in the BOD layer. The BOD layer was formed so that the mass of the portion of ethylmethyldiamine borodisalicylate corresponding to borodisalicylic acid was the mass % shown in Table 1 relative to the total mass of the solid electrolyte layer (conductive polymer layer) excluding ethylmethyldiamine borodisalicylate. Except for this, solid electrolytic capacitors A8 to A15 according to Examples 8 to 15 were fabricated in the same manner as in Example 2 and evaluated in the same manner.

[0085] The evaluation results are shown in Table 1. In Table 1, the initial capacitance value X ０ is the initial capacitance value X of the solid electrolytic capacitor B1 of Comparative Example 1 ０ The values ​​are expressed as relative values ​​with the value of 100. In Table 1, the location of the BOD layer means that the nth layer (n≧1) is formed on the surface of the nth conductive polymer layer, and the 0th layer means that it is formed on the surface of the dielectric layer. As shown in Table 1, the solid electrolytic capacitors A1 to A15, which have a BOD layer between the dielectric layer and the cathode layer, showed improved rates of capacitance change in high-temperature load tests and charge-discharge tests.

[0086]

[0087] The present invention can be used in electrolytic capacitors, and preferably in electrolytic capacitors that use a porous body as an anode body.

[0088] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0089] 20: Electrolytic capacitor 10: Capacitor element 1: Anode body 2: Anode wire 2a: First portion 2b: Second portion 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode layer 5a: Carbon layer 5b: Metal paste layer 6: Anode portion 7: Cathode portion 8: Conductive adhesive 11: Outer casing 13: Anode lead terminal 14: Cathode lead terminal 14a: Joint portion

Claims

1. A solid electrolytic capacitor comprising: an anode body; a dielectric layer formed on a surface of the anode body; a solid electrolyte layer covering at least a portion of the dielectric layer and including a conductive polymer; and a cathode layer covering at least a portion of the solid electrolyte layer, wherein a layer containing a borodiorgano acid compound is disposed between the dielectric layer and the cathode layer.

2. The solid electrolytic capacitor according to claim 1, wherein the layer containing the borodiorganic acid compound is disposed on the surface of the dielectric layer.

3. The solid electrolytic capacitor according to claim 1, wherein the layer containing the borodiorgano acid compound contains the conductive polymer and constitutes a part of the solid electrolyte layer.

4. The solid electrolytic capacitor according to claim 3, wherein the layer containing the borodiorganic acid compound is biased toward the dielectric layer within the solid electrolyte layer.

5. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the anode body is a sintered body of a valve metal.

6. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the conductive polymer includes polythiophene.

7. The solid electrolytic capacitor according to claim 6, wherein the polythiophene contains, as a monomer unit, 3,4-ethylenedioxythiophene having an alkyl group on the side chain.

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