Electrolytic capacitor

Abstract

This electrolytic capacitor comprises: a porous anode body; an anode wire having an embedded part embedded in the anode body and a projection part projecting to the outside of the anode body; a dielectric layer formed on the surfaces of the anode body and the projection part; and a solid electrolyte layer covering at least a portion of the dielectric layer. The solid electrolyte layer has a first solid electrolyte part that covers the surface of the anode body with the dielectric layer therebetween, and a second solid electrolyte part that covers the root of the projection part with the dielectric layer therebetween. The length of the second solid electrolyte part along the projection part is 220 μm or less, and the thickness of the second solid electrolyte part in the radial direction of the anode wire is 15 μm or less.

Description

electrolytic capacitor

[0001] The present disclosure relates to electrolytic capacitors.

[0002] Patent Document 1 proposes a method for manufacturing a capacitor element, comprising the steps of: forming a dielectric coating on a surface of an anode body and on a lower surface of a protruding portion of an anode lead member embedded in the anode body; forming a precoat layer on the dielectric coating; partially removing the dielectric coating and the precoat layer to expose a circular portion of the lower surface; immersing the anode body in a solution in which a monomer is dissolved so that the portion of the lower surface is located on the liquid surface of the solution, and forming a conductive polymer layer on the precoat layer by electropolymerization; and removing burrs of the conductive polymer formed on the portion of the lower surface.

[0003] Patent Document 2 proposes "a solid electrolytic capacitor comprising: an anode body; an anode lead member protruding from one end surface of the anode body; a capacitor element having a dielectric coating integrally formed on a surface of the anode body and on a surface of the anode lead member near the anode body; a solid electrolyte layer formed on the dielectric coating; and a cathode extraction layer formed on the solid electrolyte on the anode body; an anode terminal connected to the anode lead member; a cathode terminal connected to the cathode extraction layer; and an insulating exterior member covering the outer periphery of the capacitor element, wherein the dielectric coating formed on the anode lead member and an end face of the solid electrolyte layer are formed on the same plane, and at least the anode lead member, the end face of the dielectric coating, the end face of the solid electrolyte layer, and the surface of the solid electrolyte layer on the anode lead member are covered with an insulating layer made of an insulating material."

[0004] JP 2005-045235 A JP 2011-071556 A

[0005] One aspect of the present disclosure relates to an electrolytic capacitor. The electrolytic capacitor includes a porous anode body, an anode wire having an embedded portion embedded in the anode body and a protruding portion protruding outside the anode body, a dielectric layer formed on the surfaces of the anode body and the protruding portion, and a solid electrolyte layer covering at least a portion of the dielectric layer. The solid electrolyte layer includes a first solid electrolyte portion covering the surface of the anode body via the dielectric layer, and a second solid electrolyte portion covering a base portion of the protruding portion via the dielectric layer. The length of the second solid electrolyte portion along the protruding portion is 220 μm or less, and the thickness of the second solid electrolyte portion in the radial direction of the anode wire is 15 μm or less.

[0006] According to the present disclosure, leakage current of an electrolytic capacitor at the base of a protruding portion of an anode wire protruding from an anode body can be suppressed.

[0007] 1 is a schematic cross-sectional view of a capacitor element of an electrolytic capacitor according to an embodiment of the present disclosure; FIG. 2 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure; FIG. 3 is a diagram showing the relationship between the thickness (T) of a second solid electrolyte portion and the leakage current (LC); and FIG. 4 is a diagram showing the relationship between the length (L) of a second solid electrolyte portion and the leakage current (LC).

[0008] As shown in Patent Document 2, a dielectric film and a solid electrolyte layer are formed on an anode lead member (anode wire) protruding from one end surface of an anode body. A portion of the solid electrolyte layer covering the anode wire is removed. This prevents a short circuit between the solid electrolyte layer and the anode terminal.

[0009] However, it was discovered that the part of the solid electrolyte layer remaining at the base of the anode wire was affecting the leakage current of the electrolytic capacitor. Specifically, it was discovered that defects that could exist in the dielectric covering the base of the anode wire were causing a short circuit between the anode wire and the solid electrolyte layer, resulting in leakage current.

[0010] Hereinafter, embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that components other than those characteristic of the present disclosure may be components of known capacitors. In this specification, when a "range from numerical value A to numerical value B" is mentioned, the range includes numerical value A and numerical value B. When multiple materials are exemplified, one may be selected from the materials and used alone, or two or more may be used in combination.

[0011] An electrolytic capacitor according to one embodiment of the present disclosure (hereinafter also referred to as "capacitor (C)") includes a porous anode body, an anode wire having an embedded portion embedded in the anode body and a protruding portion protruding outside the anode body, a dielectric layer formed on the surfaces of the anode body and the protruding portion, and a solid electrolyte layer covering at least a portion of the dielectric layer. An electrolytic capacitor including a solid electrolyte layer may also be referred to as a "solid electrolytic capacitor."

[0012] Hereinafter, the smallest unit of an electrolytic capacitor, including an anode body, an anode wire, a dielectric layer, and a solid electrolyte layer, may be referred to as a "capacitor element." The term "capacitor (C)" is a concept that encompasses both electrolytic capacitors and capacitor elements. Note that "capacitor" may be read as "capacitor."

[0013] An electrolytic capacitor (or capacitor element) is divided into an anode portion and a cathode portion. The anode body and anode wire constitute the anode portion. The solid electrolyte layer constitutes the cathode portion. The anode portion and the cathode portion are insulated by a dielectric layer. The cathode portion includes at least the solid electrolyte layer and may also include a cathode extraction layer.

[0014] The dielectric layer is formed, for example, by subjecting the anode body to a chemical conversion treatment to grow an oxide film on the surface of the anode body. In the chemical conversion treatment, the anode body may be immersed in a chemical conversion solution to anodize the surface of the anode body. The oxide film may also be formed using a gas phase method such as atomic layer deposition (ALD). The surface of the anode body may also be oxidized by heating the anode body in an oxygen-containing atmosphere.

[0015] The solid electrolyte layer includes a first solid electrolyte portion and a second solid electrolyte portion, and the second solid electrolyte portion may be formed integrally with the first solid electrolyte portion.

[0016] The cathode extraction layer is formed to cover at least a portion of the first solid electrolyte portion. The cathode extraction layer is a conductive layer. The cathode extraction layer includes, for example, a carbon layer formed on the first solid electrolyte portion 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.

[0017] The first solid electrolyte portion covers the surface of the anode body via a dielectric layer. That is, the first solid electrolyte portion covers the surface of the dielectric layer that covers the metal portion that constitutes the anode body. The metal portion that constitutes the anode body may be a porous sintered body. The porous sintered body is a porous body formed by molding and sintering metal particles. The first solid electrolyte portion covers the surface of the dielectric layer that covers the inner walls of the pores of the porous body.

[0018] The porous sintered body may be a sintered body of metal particles containing a valve metal. Examples of the valve metal include, but are not limited to, Ta, Nb, Al, Ti, etc. Among them, the porous sintered body is preferably a sintered body of metal particles containing a valve metal including Ta. That is, the anode body may be a porous sintered body containing tantalum. For example, when a sintered body of tantalum particles is anodized, the dielectric layer is formed of Ta. ２ O ５ Includes.

[0019] The second solid electrolyte portion covers the base of the protruding portion of the anode wire via the dielectric layer. The base of the protruding portion is a part of the protruding portion whose base end is the outer surface of the anode body (more precisely, the outer surface of the dielectric layer covering the metal portion that constitutes the outer surface of the anode body). The length of the protruding portion is not particularly limited, but is, for example, in the range of 0.5 mm to 3 mm, and may be in the range of 1 mm to 2 mm. The second solid electrolyte portion may be formed integrally with the first solid electrolyte portion, and the first solid electrolyte portion and the second solid electrolyte portion may be continuous.

[0020] The length of the second solid electrolyte portion along the protrusion and the thickness of the second solid electrolyte portion in the radial direction of the anode wire have a significant effect on the occurrence of leakage current in the electrolytic capacitor. This finding is a new finding, and it was the starting point for completing the present invention.

[0021] Specifically, the length along the protruding portion of the second solid electrolyte portion needs to be 220 μm or less. The length along the protruding portion of the second solid electrolyte portion (hereinafter referred to as "length (L)") can be said to be the length of the base portion of the protruding portion of the anode wire where the second solid electrolyte portion is attached. The length (L) is the length from the outer surface of the anode body (more precisely, the outer surface of the dielectric layer covering the metal portion that constitutes the outer surface of the anode body) to its base end.

[0022] The thickness of the second solid electrolyte part in the radial direction of the anode wire must be 15 μm or less. The thickness of the second solid electrolyte part in the radial direction of the anode wire (hereinafter referred to as "thickness (T)") is the average thickness of the second solid electrolyte part attached to the base of the protruding part of the anode wire.

[0023] The thickness (T) is determined by measuring and averaging the following: a thickness T1 of the second solid electrolyte portion near the boundary between the first solid electrolyte portion and the second solid electrolyte portion; a thickness T2 of the second solid electrolyte portion at the middle of the length L (a position L / 2 away from the outer surface of the anode body); and a thickness T3 of the second solid electrolyte portion slightly closer to the base end than the position of the second solid electrolyte portion farthest from the outer surface of the anode body (for example, a position 0.9 L away from the outer surface of the anode body) (T=(T1+T2+T3) / 3).

[0024] As described above, by setting the length (L) to 220 μm or less, the probability of a short circuit between the second solid electrolyte portion and the anode wire is extremely low, even if a defect exists in the dielectric layer covering the protruding portion of the anode wire. Furthermore, by setting the length (L) to 220 μm or less and the thickness (T) to 15 μm or less, the volume of the second solid electrolyte portion attached to the base of the protruding portion is limited to a very small volume. Therefore, even if a short circuit occurs, the second solid electrolyte portion is easily insulated, so only a negligible leakage current flows.

[0025] The tip of the protruding portion of the anode wire is connected to an anode lead terminal. That is, the solid electrolytic capacitor may include an anode lead terminal electrically connected to the protruding portion of the anode wire, a cathode lead terminal electrically connected to a solid electrolyte layer (usually a cathode portion including a solid electrolyte layer), and an exterior body that covers the capacitor element (i.e., the anode body, anode wire, dielectric layer, and solid electrolyte layer (or cathode portion including a solid electrolyte layer)) with a portion of the anode lead terminal and a portion of the cathode lead terminal exposed. The cathode lead terminal is bonded to the cathode extraction layer, for example, via a conductive adhesive.

[0026] A distance must be provided between the second solid electrolyte portion and the anode lead terminal. Meanwhile, in the process of forming the first solid electrolyte portion and the second solid electrolyte portion, the solid electrolyte adheres not only to the base of the protruding portion of the anode wire but also to a wider area. The solid electrolyte adhering to the anode wire other than the base is removed by irradiating the area other than the base of the protruding portion with a laser. The type of laser is not particularly limited, but a YAG laser, a fiber laser, or the like can be used, for example. The laser output may be set appropriately, and may be, for example, 60 W to 80 W (preferably 70 W).

[0027] When the solid electrolyte adhering to the anode wire other than the base is removed by a laser, the length (L) is determined by the laser irradiated to the portion other than the base of the protrusion. The heat of the laser is conducted to the second solid electrolyte portion, insulating at least a portion of the second solid electrolyte portion. Even if the insulated second solid electrolyte portion comes into contact with the anode wire, no leakage current is generated.

[0028] When the length (L) is 220 μm or less and the thickness (T) is 15 μm or less, the volume of the second solid electrolyte portion attached to the base of the protrusion is very small, so that the insulation of the second solid electrolyte portion by the heat of the laser proceeds quickly.

[0029] The length (L) may be 220 μm or less, but if the length (L) is too short, current may concentrate in the first solid electrolyte portion near the base of the protruding portion of the anode wire, potentially accelerating deterioration of the first solid electrolyte portion. From the viewpoint of protecting the first solid electrolyte portion, the length (L) of the first solid electrolyte portion is preferably 10 μm or more, more preferably 30 μm or more, and even more preferably 50 μm or more. Similarly, the thickness (T) is preferably 1 μm or more, and even more preferably 5 μm or more.

[0030] The process for forming the first solid electrolyte portion and the second solid electrolyte portion is not particularly limited, and may be, for example, a process for forming a conductive polymer by electrolytic polymerization. Specifically, an anode body having a dielectric layer on its surface is precoated, and then immersed in a polymerization solution containing a precursor (such as a raw material monomer) of a conductive polymer (conjugated polymer). The anode wire is connected to the first electrode, and a voltage is applied between the first electrode and a second electrode placed in a container containing the polymerization solution, thereby electrolytically polymerizing the precursor. In this case, the solid electrolyte layer contains a conductive polymer.

[0031] In the precoat treatment, at least a portion of the surface of the dielectric layer is covered with a conductive material to form a precoat layer, which facilitates the progress of electrolytic polymerization.

[0032] The polymerization liquid contains raw material monomers for a conductive polymer (conjugated polymer), may contain a dopant, and may further contain a nitro group-containing compound. The nitro group-containing compound improves the orientation of the conductive polymer, improves the conductivity and heat resistance of the solid electrolyte layer, and contributes to a reduction in the equivalent series resistance (ESR) of the electrolytic capacitor. The nitro group-containing compound also contributes to the insulation repair properties of the second solid electrolyte portion.

[0033] The solid electrolyte layer may contain a nitro group-containing compound. The nitro group-containing compound may be contained in both the first solid electrolyte part and the second solid electrolyte part.

[0034] Examples of the nitro group-containing compound include p-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrophenol, m-nitrophenol, p-nitroresorcinol, p-nitrobenzyl alcohol, etc. Among these, p-nitrophenol (para-nitrophenol) is preferred.

[0035] The method for forming the solid electrolyte layer is not limited to electrolytic polymerization. For example, the solid electrolyte layer may be formed by polymerizing a precursor of a conjugated polymer on a dielectric layer in the presence of a dopant, if necessary. The solid electrolyte layer may be formed by applying a liquid composition containing a conjugated polymer (and a dopant, if necessary) to the dielectric layer and then drying the liquid composition.

[0036] When the anode body has a front surface from which the anode wire protrudes and a back surface opposite the front surface, the mass content of the nitro group-containing compound in the first solid electrolyte portion on the front surface side of the anode body is, for example, 3000 ppm or more, preferably 3200 ppm or more, and preferably 4000 ppm or less. In this case, the mass content of the nitro group-containing compound in the second solid electrolyte portion is highly likely to be, for example, 3000 ppm or more.

[0037] When the content of the nitro group-containing compound in the first solid electrolyte portion is high on the front side of the anode body from which the anode wire protrudes, the content of the nitro group-containing compound in the second solid electrolyte portion also becomes high, and the insulation repairability of the second solid electrolyte portion tends to be high. The higher the insulation repairability of the second solid electrolyte portion, the more difficult it is for current to flow, and the more suppressed the leakage current.

[0038] The mass content of the nitro group-containing compound on the front side of the first solid electrolyte part (the first solid electrolyte part that can be recovered from the front side of the anode body) is preferably greater than the mass content of the nitro group-containing compound on the back side of the first solid electrolyte part (the first solid electrolyte part that can be recovered from the back side of the anode body). In this case, the electrical insulation of the second solid electrolyte part is improved, and the electrical conductivity of the solid electrolyte layer as a whole is also improved.

[0039] The mass content of the nitro group-containing compound in the first solid electrolyte portion on the back side of the anode body is, for example, 2800 ppm or less, preferably 2600 ppm or less, and preferably 2000 ppm or more, which further increases the overall conductivity of the solid electrolyte layer and significantly reduces the ESR of the electrolytic capacitor.

[0040] The anode body having a shape with a front surface from which the anode wire protrudes (is embedded) and a back surface opposite the front surface may be, for example, a generally rectangular anode body. The anode body may have, for example, a shape with a front surface, a back surface, a bottom surface on the mounting surface side, and a top surface opposite the bottom surface. The anode body may have a generally rectangular parallelepiped or hexahedral shape.

[0041] The front side of the anode body includes the midpoint of a line segment L connecting the center of area of ​​the front side from which the anode wire protrudes and the center of area of ​​the back side opposite the front side, and is the front side portion when the anode body is divided into two parts by a plane perpendicular to the line segment L. The back side of the anode body is the portion other than the front side.

[0042] The content of the nitro group-containing compound in the first solid electrolyte portion on the front side of the anode body can be measured by peeling off the first solid electrolyte portion on the front side of the anode body and analyzing it by gas chromatography-mass spectrometry (GC-MS). The content of the nitro group-containing compound in the first solid electrolyte portion on the back side of the anode body can be measured by peeling off the first solid electrolyte portion on the front side of the anode body and analyzing it by the same method as above.

[0043] In the solid electrolyte layer, the conductive polymer is not particularly limited, but is preferably, for example, a π-conjugated polymer, such as a polymer having a basic skeleton of polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, or polythiophene vinylene.

[0044] In particular, the conductive polymer preferably contains at least polypyrrole as a π-conjugated polymer because it is suitable for electropolymerization. Polypyrrole includes polypyrrole and its derivatives, or polymers containing polypyrrole derivatives. The weight-average molecular weight of polypyrrole is not particularly limited, but is, for example, 1,000 to 1,000,000.

[0045] Such polymers include homopolymers, copolymers of two or more types of monomers, and derivatives thereof (such as polymers of substituted compounds having a substituent group). For example, polythiophenes include poly(3,4-ethylenedioxythiophene). Such conductive polymers have high conductivity and excellent ESR characteristics. One type of conductive polymer may be used alone, or two or more types may be used in combination.

[0046] The weight average molecular weight of the conductive polymer is not particularly limited, but is, for example, 1,000 to 1,000,000.

[0047] The solid electrolyte layer may include a self-doping conductive polymer or a non-self-doping conductive polymer. A solid electrolyte layer including a non-self-doping conductive polymer may include a dopant.

[0048] The dopant may be, for example, a low molecular weight compound (hereinafter also referred to as a "low molecular weight dopant") or a high molecular weight compound (hereinafter also referred to as a "high molecular weight dopant") having an acidic group (or an anionic group). One type of dopant may be used alone, or two or more types may be used in combination.

[0049] Low molecular weight dopants include sulfonic acid groups, carboxyl groups, and phosphoric acid groups (-O-P(=O)(-OH) ２ ), a phosphonic acid group (-P(=O)(-OH) ２ Examples of such compounds include low molecular weight compounds having an anionic group such as benzene, naphthalene, and anthracene. ６－１４ aromatic ring, etc.), or aromatic ring (C ６－１４A cyclic compound in which an anionic group is bonded to a condensed ring of an aliphatic ring (such as an aromatic ring) can be used.

[0050] The anionic group is preferably a sulfonic acid group, and may be a combination of a sulfonic acid group and an anionic group other than a sulfonic acid group.

[0051] The aromatic ring and / or aliphatic ring constituting the cyclic compound may have a substituent other than the anionic group (for example, an alkyl group such as a methyl group, an oxo group (═O), etc.).

[0052] Specific examples of low molecular weight dopants include alkylbenzenesulfonic acids such as benzenesulfonic acid and p-toluenesulfonic acid, naphthalenesulfonic acid, and anthraquinonesulfonic acid.

[0053] Examples of polymer dopants include sulfonic acid groups, phosphoric acid groups (-O-P(=O)(-OH) ２ ), a phosphonic acid group (-P(=O)(-OH) ２ Among the anionic groups, a sulfonic acid group is preferred.

[0054] Examples of polymeric dopants having a sulfonic acid group include homopolymers or copolymers of monomers having a sulfonic acid group (for example, vinyl monomers having a sulfonic acid group).

[0055] Examples of vinyl monomers having a sulfonic acid group include aliphatic vinyl monomers having a sulfonic acid group, such as vinyl sulfonic acid, allyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid, and aromatic vinyl monomers having a sulfonic acid group, such as styrene sulfonic acid. These vinyl monomers can be used alone or in combination of two or more. The copolymer may be a copolymer using two or more types of monomers having a sulfonic acid group, or may be a copolymer of a monomer having a sulfonic acid group and another monomer.

[0056] Specific examples of polymer dopants include polyester sulfonic acid and phenolsulfonic acid novolac resin.

[0057] In the low molecular weight dopants and high molecular weight dopants, the anionic group is not particularly limited as long as it can generate an anion in a dissociated state, and may be a salt or ester of the above-mentioned anionic group.

[0058] The weight average molecular weight of the polymer dopant is, for example, 1,000 to 1,000,000, and preferably 10,000 to 500,000.

[0059] The amount of the dopant contained in the solid electrolyte layer is preferably 10 to 1000 parts by mass, and more preferably 50 to 200 parts by mass, per 100 parts by mass of the conductive polymer.

[0060] The solid electrolyte layer may cover the dielectric layer in a layered manner, or may be a laminate of two or more layers of different solid electrolytes.

[0061] The exterior body is formed, for example, by injecting the exterior body's resin material (e.g., an uncured thermosetting resin composition) into a mold containing the capacitor element. Such a method may be transfer molding, compression molding, or the like. The exterior body is formed in a state in which a portion of the anode lead terminal and a portion of the cathode lead terminal are exposed. The ends of each lead terminal exposed from the exterior body are used for soldering to a substrate on which the electrolytic capacitor is to be mounted, for example.

[0062] Hereinafter, the configuration of an example of an electrolytic capacitor according to the present disclosure will be described in more detail with reference to the drawings.

[0063] Fig. 1 is a schematic cross-sectional view of a capacitor element 110 of an electrolytic capacitor 100 according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view schematically illustrating an example of the electrolytic capacitor 100.

[0064] The electrolytic capacitor 100 includes a capacitor element 110. The capacitor element 110 includes an anode portion 111, a dielectric layer 118 (not shown in FIG. 2 ), and a cathode portion 115. The electrolytic capacitor 100 includes the capacitor element 110, an anode lead terminal 120, a cathode lead terminal 130, a conductive layer 141, and an exterior body 101.

[0065] The anode lead terminal 120 includes an anode terminal portion 121 and an anode connecting portion 122. The anode terminal portion 121 is exposed on the bottom surface 100b of the electrolytic capacitor 100. The anode connecting portion 122 is connected to the anode wire 112. The cathode lead terminal 130 includes a cathode terminal portion 131 and a cathode connecting portion 132. The cathode terminal portion 131 is exposed on the bottom surface 100b of the electrolytic capacitor 100. The cathode connecting portion 132 is electrically connected to the cathode extraction layer by a conductive layer 141.

[0066] The anode section 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. The surface of the anode body 113 is covered with a dielectric layer 118 (not shown in FIG. 2 ), and the surface of the protruding portion 112A of the anode wire 112 is covered with a dielectric layer 118A (not shown in FIG. 2 ). The protruding portion 112A of the anode wire 112 protrudes from a front surface 110f of the anode body 113 toward a front surface 100f of the electrolytic capacitor 100. The other portion of the anode wire 112 is an embedded portion 112B embedded in the anode body 113 and extends toward a back surface 110b of the anode body 113.

[0067] The cathode section 115 includes a solid electrolyte layer 114 disposed so as to cover at least a portion of the dielectric layer 118, a carbon layer 116 formed on the solid electrolyte layer 114, and a metal particle-containing layer 117 formed on the carbon layer 116. The metal particle-containing layer 117 is formed using, for example, silver paste. The carbon layer 116 and the metal particle-containing layer 117 function as cathode extraction layers.

[0068] The solid electrolyte layer 114 includes a first solid electrolyte portion 114A that covers the surface of the anode body 113 via the dielectric layer 118, and a second solid electrolyte portion 114B that covers the base portion 112C of the protruding portion 112A via the dielectric layer 118A. The second solid electrolyte portion 114B is formed integrally with the first solid electrolyte portion 114A. The length (L) of the second solid electrolyte portion 114B along the protruding portion is 220 μm or less, and the thickness (T) of the second solid electrolyte portion 114B in the radial direction of the anode wire 112 is 15 μm or less.

[0069] (Additional Note) The above description discloses the following techniques.

[0070] (Technology 1) An electrolytic capacitor comprising: a porous anode body; an anode wire having an embedded portion embedded in the anode body and a protruding portion protruding to the outside of the anode body; a dielectric layer formed on surfaces of the anode body and the protruding portion; and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the solid electrolyte layer has: a first solid electrolyte portion covering the surface of the anode body with the dielectric layer interposed therebetween; and a second solid electrolyte portion covering a base portion of the protruding portion with the dielectric layer interposed therebetween, wherein a length of the second solid electrolyte portion along the protruding portion is 220 μm or less, and a thickness of the second solid electrolyte portion in a radial direction of the anode wire is 15 μm or less.

[0071] (Technology 2) The electrolytic capacitor according to Technology 1, wherein the length of the second solid electrolyte portion along the protrusion is 10 μm or more.

[0072] (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein at least a part of the second solid electrolyte portion is insulated.

[0073] (Technology 4) The electrolytic capacitor according to any one of Technologies 1 to 3, wherein the first solid electrolyte portion contains a nitro group-containing compound, the anode body has a shape having a front side from which the anode wire protrudes and a back side opposite the front side, and the mass content of the nitro group-containing compound on the front side of the first solid electrolyte portion is 3000 ppm or more.

[0074] (Technology 5) The electrolytic capacitor according to Technology 4, wherein the mass content of the nitro group-containing compound on the front side of the first solid electrolyte portion is greater than the mass content of the nitro group-containing compound on the back side of the first solid electrolyte portion.

[0075] (Technology 6) The electrolytic capacitor according to Technology 4 or 5, wherein the mass content of the nitro group-containing compound on the back surface side of the first solid electrolyte portion is 2800 ppm or less.

[0076] (Technology 7) The solid electrolytic capacitor according to any one of Technologies 4 to 6, wherein the nitro group-containing compound is paranitrophenol.

[0077] (Technology 8) The electrolytic capacitor according to any one of Technologies 1 to 7, wherein the solid electrolyte layer contains a conductive polymer, and the conductive polymer contains polypyrrole.

[0078] (Technology 9) The electrolytic capacitor according to any one of Technologies 1 to 8, wherein the anode body is a porous sintered body containing tantalum.

[0079] (Technology 10) The solid electrolytic capacitor according to any one of Technologies 1 to 9, comprising: an anode lead terminal electrically connected to the protruding portion; a cathode lead terminal electrically connected to the solid electrolyte layer; and an exterior body covering the anode body, the anode wire, the dielectric layer, and the solid electrolyte layer, with a portion of the anode lead terminal and a portion of the cathode lead terminal exposed.

[0080] 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.

[0081] (1) Fabrication of Capacitor Element (i) Preparation of Anode Body Ta particles (Ta powder) were used as valve metal particles. Ta powder was molded into a rectangular parallelepiped so that one end of the Ta anode wire was embedded in the Ta powder. The molded body was then sintered in a vacuum. This resulted in an anode assembly including a porous sintered anode body of Ta particles and an anode wire with an embedded portion embedded in the anode body and a protruding portion protruding from the front of the anode body. The anode assembly consisting of the anode body and anode wire was washed with isopropanol (IPA) as a cleaning solution and then dried at 150°C for 30 minutes.

[0082] (ii) Formation of a dielectric layer Forty-six cleaned anode parts were lined up at regular intervals, and the anode wires were welded to a thin, plate-like first electrode. The anode body and a portion of the anode wire were immersed in a chemical conversion solution in a glass chemical conversion tank, and a Ta second electrode was immersed in the chemical conversion 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.

[0083] The anodizing solution used was an aqueous solution containing phosphoric acid. The temperature of the anodizing solution was 60°C. A DC voltage of 7.3 V was applied for 7 hours. After the anodizing, the anode body and the anode wire were dried at 100°C for 10 minutes. In this way, a dielectric layer of tantalum oxide (Ta ２ O ５ ) to form a uniform dielectric layer (thickness: about 30 nm).

[0084] (iii) Formation of Solid Electrolyte Layer (Precoat Treatment) An aqueous solution of pyrrole monomer (first treatment liquid) was prepared. The concentration of the monomer in the first treatment liquid was 4 mass%. After an oxidizing agent was applied to the surface of the dielectric layer, the anode element on which the dielectric layer was formed was immersed in the first treatment liquid. The anode element was then dried to form a precoat layer.

[0085] (Step of Forming Solid Electrolyte Layers (First and Second Solid Electrolyte Portions)) An aqueous dispersion (second treatment liquid) containing pyrrole, a dopant (sulfonate having a naphthalene skeleton), and paranitrophenol was prepared.

[0086] The anode element on which the precoat layer was formed was immersed in the second treatment liquid, and electrolytic polymerization of pyrrole was carried out using the precoat layer as a base electrode, to form a solid electrolyte layer containing polypyrrole.

[0087] The concentration of pyrrole in the second treatment liquid was appropriately selected, for example, from the range of 1 to 6 mass %, the concentration of the dopant in the second treatment liquid was appropriately selected, for example, from the range of 3 to 12 mass %, and the concentration of paranitrophenol in the second treatment liquid was appropriately selected, for example, from the range of 0.1 to 1 mass %.

[0088] In this way, a solid electrolyte layer was formed having a first solid electrolyte portion and a second solid electrolyte portion before laser forming with various thicknesses (T). Note that by controlling the convection state of the second treatment liquid in the treatment tank, it is possible to locally control the content of paranitrophenol in the first solid electrolyte portion.

[0089] Next, a 70 W laser was applied to the solid electrolyte adhering to the anode wire except for the base portion, and a portion of the solid electrolyte adhering to the protruding portion was removed to form second solid electrolyte portions having various lengths (L). Note that at least a portion of the second solid electrolyte portion was insulated by the heat of the laser irradiation.

[0090] (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.

[0091] (v) Formation of Silver 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 silver particle-containing layer, thereby obtaining a capacitor element.

[0092] (2) Fabrication of an Electrolytic Capacitor A conductive adhesive was applied to the silver particle-containing layer of the capacitor element, and the cathode lead terminal and the metal particle-containing layer were bonded. The protruding portion of the anode wire was bonded to the anode lead terminal by resistance welding. Next, the capacitor element with each bonded lead terminal was placed in a mold and sealed with an exterior body by transfer molding. In this way, an electrolytic capacitor with a rated voltage Rv of 2.5 V was fabricated.

[0093] The electrolytic capacitors having the second solid electrolyte portions with various lengths (L) and thicknesses (T) were dried at 170° C. for 3 hours and then cooled to room temperature in a drying chamber. The electrolytic capacitors in this state were used to perform the following evaluations.

[0094] (Leakage Current (LC)) The electrolytic capacitor was charged by applying a rated voltage Rv in an environment of 20° C. The current flowing through the electrolytic capacitor in a charged state was measured and evaluated as the leakage current.

[0095] (ESR) The ESR (mΩ) of each electrolytic capacitor was measured at a frequency of 100 kHz in an environment of 20° C. using an LCR meter for four-terminal measurement.

[0096] FIG. 3 shows the relationship between the thickness (T) of the second solid electrolyte portion and the leakage current (LC).

[0097] FIG. 4 shows the relationship between the length (L) of the second solid electrolyte portion and the leakage current (LC).

[0098] Each figure shows the standard pass line. When the thickness (T) of the second solid electrolyte portion is 15 μm or less and the length (L) is 220 μm or less, there is a significant tendency for leakage current to be suppressed.

[0099] Table 1 shows the relationship between the mass content (X) of paranitrophenol on the front side of the first solid electrolyte portion, the mass content (Y) of paranitrophenol on the back side, the length (L), the thickness (T), and the leakage current and ESR. Examples were randomly selected from electrolytic capacitors satisfying the conditions of thickness (T) ≦ 15 μm and length (L) ≦ 220 μm. Comparative examples were randomly selected from electrolytic capacitors not satisfying the conditions of thickness (T) ≦ 15 μm and length (L) ≦ 220 μm. The contents (X) and (Y) were measured by gas chromatography-mass spectrometry (GC-MS) after dividing the anode body with the solid electrolyte formed into the front side and the back side with nippers.

[0100]

[0101] From Table 1, it can be seen that the effect of suppressing leakage current is high by increasing the concentration of the nitro group-containing compound on the front side of the first solid electrolyte portion compared to that on the back side. On the other hand, even if the concentration of the nitro group-containing compound on the front side of the first solid electrolyte portion is high, no substantial increase in ESR is observed.

[0102] The electrolytic capacitor according to the present disclosure has low leakage current and high reliability. Such an electrolytic capacitor is suitable for use in connection with an electronic circuit, and can suppress malfunctions of the electronic circuit. However, the uses of the electrolytic capacitor are not limited to these.

[0103] 100: Electrolytic capacitor 110: Capacitor element 111: Anode portion 112: Anode wire 113: Anode body 114: Solid electrolyte layer 115: Cathode portion 116: Carbon layer 117: Metal particle-containing layer 118: Dielectric layer 120: Anode lead terminal 121: Anode terminal portion 122: Anode connection portion 130: Cathode lead terminal 131: Cathode terminal portion 132: Cathode connection portion 141: Conductive layer

Claims

1. An electrolytic capacitor comprising: a porous anode body; an anode wire having an embedded portion embedded in the anode body and a protruding portion protruding outside the anode body; a dielectric layer formed on the surfaces of the anode body and the protruding portion; and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the solid electrolyte layer has: a first solid electrolyte portion covering the surface of the anode body with the dielectric layer interposed therebetween; and a second solid electrolyte portion covering a base portion of the protruding portion with the dielectric layer interposed therebetween, wherein the length of the second solid electrolyte portion along the protruding portion is 220 μm or less, and the thickness of the second solid electrolyte portion in the radial direction of the anode wire is 15 μm or less.

2. The electrolytic capacitor according to claim 1, wherein the length of the second solid electrolyte portion along the protrusion is 10 μm or more.

3. The electrolytic capacitor according to claim 1, wherein at least a portion of said second solid electrolyte portion is insulated.

4. The electrolytic capacitor according to claim 1, wherein the first solid electrolyte portion contains a nitro group-containing compound, the anode body has a shape having a front side from which the anode wire protrudes and a back side opposite the front side, and the mass content of the nitro group-containing compound on the front side of the first solid electrolyte portion is 3000 ppm or more.

5. The electrolytic capacitor described in claim 4, wherein the mass content of the nitro group-containing compound on the front side of the first solid electrolyte portion is greater than the mass content of the nitro group-containing compound on the back side of the first solid electrolyte portion.

6. The electrolytic capacitor according to claim 4, wherein the mass content of the nitro group-containing compound on the back surface side of the first solid electrolyte portion is 2800 ppm or less.

7. The solid electrolytic capacitor according to claim 4, wherein the nitro group-containing compound is paranitrophenol.

8. The electrolytic capacitor according to claim 1, wherein the solid electrolyte layer includes a conductive polymer, and the conductive polymer includes polypyrrole.

9. The electrolytic capacitor according to claim 1, wherein the anode body is a porous sintered body containing tantalum.

10. The solid electrolytic capacitor according to claim 1, comprising: an anode lead terminal electrically connected to the protrusion; a cathode lead terminal electrically connected to the solid electrolyte layer; and an exterior body covering the anode body, the anode wire, the dielectric layer, and the solid electrolyte layer, with a portion of the anode lead terminal and a portion of the cathode lead terminal exposed.

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