Solid electrolytic capacitor and method for manufacturing same

Abstract

A solid electrolytic capacitor disclosed herein includes: a capacitor element including an anode part and a cathode part; an anode lead terminal electrically connected to the anode part; a cathode lead terminal electrically connected to the cathode part; and an exterior body covering the capacitor element. Each of the anode lead terminal and the cathode lead terminal includes an embedded part embedded in the exterior body and an exposed part exposed from the exterior body. A surface layer containing tin is formed on the surface of the anode lead terminal and the surface of the cathode lead terminal. The average thickness of the surface layer in the embedded part is 0.1-2.0 μm inclusive. The average thickness of the surface layer in the exposed part is at least 4 μm.

Description

Solid electrolytic capacitor and method for manufacturing the same

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

[0002] Solid electrolytic capacitors are mounted in various electronic devices. A solid electrolytic capacitor generally includes an anode lead terminal and a cathode lead terminal that are electrically connected to a capacitor element, and an exterior body that covers the capacitor element.

[0003] Claim 1 of Patent Document 1 (International Publication No. 2007-052652) discloses "a capacitor having an anode portion and a cathode portion provided with an insulating layer therebetween, the anode portion of the capacitor being joined to a first metal member, the cathode portion being joined to a second metal member, and the whole being resin-sealed so that a part of each metal member is exposed. In the capacitor, the first and / or second metal member has a region including a low-melting-point metal plating layer and a region not including a low-melting-point metal plating layer according to a predetermined pattern."

[0004] Claim 1 of Patent Document 2 (Japanese Unexamined Patent Application Publication No. 05-021290) discloses "a solid electrolytic capacitor in which an anodic oxide film formed on a valve metal plate or foil is used as a dielectric, a dielectric polymer layer and a dielectric layer are sequentially formed on a predetermined portion of the dielectric to form a capacitor element, a lead frame serving as a lead terminal is connected to the valve metal portion and the conductor layer portion of the capacitor element, and a part of the capacitor element and the lead frame is externally packaged with a molding resin. In the solid electrolytic capacitor, a solder alloy layer or a tin metal layer having a copper metal layer as a base is formed on the surface of the lead frame other than the portion in contact with the molding resin of the lead frame, only a copper metal layer is formed on the portion of the lead frame in contact with the molding resin, and the surface of the copper metal layer is roughened."

[0005] International Publication No. 2007-052652, Japanese Unexamined Patent Application Publication No. 05-021290

[0006] When mounting solid electrolytic capacitors on a circuit board or other surface, it is necessary to solder the lead terminals. Therefore, the lead terminals must be capable of good mounting. Furthermore, the lead terminals must have high adhesion to the casing. This is because poor adhesion between the lead terminals and the casing can easily reduce the lifespan of the solid electrolytic capacitor. One of the objectives of this disclosure is to provide a solid electrolytic capacitor with high mountability and reliability.

[0007] One aspect of the present disclosure relates to a solid electrolytic capacitor comprising: a capacitor element including an anode portion and a cathode portion; an anode lead terminal electrically connected to the anode portion; a cathode lead terminal electrically connected to the cathode portion; and an outer casing covering the capacitor element, wherein the anode lead terminal and the cathode lead terminal each include a buried portion embedded in the outer casing and an exposed portion exposed from the outer casing, and a surface layer containing tin is formed on the surface of the anode lead terminal and the surface of the cathode lead terminal, the average thickness of the surface layer in the buried portion is 0.1 μm or more and 2.0 μm or less, and the average thickness of the surface layer in the exposed portion is 4 μm or more.

[0008] Another aspect of the present disclosure relates to a method for manufacturing a solid electrolytic capacitor including a capacitor element, comprising the steps of: (i) forming a surface layer containing tin on the surfaces of an anode lead terminal and a cathode lead terminal; (ii) removing a portion of the surface layer; (iii) electrically connecting the anode lead terminal to the anode portion of the capacitor element and electrically connecting the cathode lead terminal to the cathode portion of the capacitor element; and (iv) covering a portion of the anode lead terminal, a portion of the cathode lead terminal, and the capacitor element with an outer casing, wherein the anode lead terminal and the cathode lead terminal after step (iv) each include an embedded portion embedded in the outer casing and an exposed portion exposed from the outer casing, wherein in step (i), the surface layer is formed such that the average thickness of the surface layer is 4 μm or more, and in step (ii), a portion of the surface layer is removed such that the average thickness of the surface layer in the portion that becomes the embedded portion is 0.1 μm or more and 2.0 μm or less.

[0009] According to this disclosure, a solid electrolytic capacitor with high implementability and reliability can be obtained. Novel features of the present invention are described in the appended claims, but the present invention, in conjunction with other objects and features of the present invention, will be better understood by the following detailed description with reference to the drawings, both in terms of structure and content.

[0010] This is a schematic cross-sectional view showing the configuration of an example of a solid electrolytic capacitor according to this disclosure. This is a schematic unfolded view showing an example of the lead terminals of the solid electrolytic capacitor shown in Figure 1. This is a schematic cross-sectional view showing the configuration of another example of a solid electrolytic capacitor according to this disclosure. This is a schematic cross-sectional view showing the configuration of yet another example of a solid electrolytic capacitor according to this disclosure.

[0011] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In addition, components other than those characteristic of this disclosure may be replaced with components of known solid electrolytic capacitors. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits are given as examples for numerical values ​​of specific physical properties or conditions, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0012] (Solid Electrolytic Capacitor) Hereinafter, the solid electrolytic capacitor according to this embodiment may be referred to as "solid electrolytic capacitor (C)". The solid electrolytic capacitor (C) includes a capacitor element including an anode portion and a cathode portion, an anode lead terminal electrically connected to the anode portion, a cathode lead terminal electrically connected to the cathode portion, and an outer casing covering the capacitor element. The anode lead terminal and the cathode lead terminal each include an embedded portion embedded in the outer casing and an exposed portion exposed from the outer casing. A surface layer containing tin is formed on the surface of the anode lead terminal and the surface of the cathode lead terminal. The average thickness of the surface layer in the embedded portion is 0.1 μm or more and 2.0 μm or less, and the average thickness of the surface layer in the exposed portion is 4 μm or more.

[0013] The anode lead terminal and cathode lead terminal are each divided into an embedded portion, which is embedded in the casing of the solid electrolytic capacitor (C), and an exposed portion, which is exposed from the casing. Note that a surface layer does not need to be formed on the side surfaces (non-main surfaces) of the exposed portion and the side surfaces (non-main surfaces) of the embedded portion.

[0014] A surface layer containing tin is formed on the exposed surface. Generally, solid electrolytic capacitors are mounted to circuit boards by soldering, with tin as the main component. When the surface layer of the lead terminals contains tin, the tin in the surface layer and the tin in the solder melt well during mounting. Therefore, the lead terminals can be firmly bonded to the circuit board. If the average thickness of the surface layer on the exposed portion is 4 μm or more, a sufficient amount of tin melts from the surface layer during mounting, resulting in a strong bond between the lead terminals and the circuit board.

[0015] The average thickness of the surface layer in the exposed portion is 4 μm or more (for example, 4.0 μm or more), and may be 5 μm or more, 7.5 μm or more, 10 μm or more, 11 μm or more, or 14 μm or more. The average thickness of the surface layer in the exposed portion may be 20 μm or less, 19 μm or less, 18 μm or less, or 17 μm or less. The thickness of 90% to 100% (area ratio) of the surface layer in the exposed portion may be 4 μm or more. The surface layer may be formed in an area of ​​90% to 100% (area ratio) of the surface of the exposed portion.

[0016] By forming a tin-containing surface layer on the surface of the embedded portion of a solid electrolytic capacitor (C), it is possible to strengthen the electrical connection between the anode (and / or cathode) portion and the embedded portion. On the other hand, forming a tin-containing surface layer may reduce the airtightness of the solid electrolytic capacitor (C). As a result of investigations, the inventors of the present invention have found that the reduction in the airtightness of the solid electrolytic capacitor (C) can be suppressed by making the thickness of the surface layer of the embedded portion 2.0 μm or less. This disclosure is based on these new findings.

[0017] By making the thickness of the surface layer (a tin-containing surface layer) formed on the embedded portion 0.1 μm or more, the anode portion (and / or cathode portion) and the embedded portion can be firmly connected. Furthermore, due to temperature increases during reflow soldering, etc., the metal constituting the embedded portion (e.g., copper) and the metal of the surface layer (tin, etc.) alloy together. Since the surface layer made of alloy has high adhesion to the outer casing (outer resin), the adhesion between the lead terminals and the outer casing is improved by the alloying of the surface layer. On the other hand, if the thickness of the surface layer is greater than 2.0 μm, the surface layer deforms significantly due to temperature increases during reflow soldering, etc., making it easier for gaps to form between the embedded portion (lead terminals) and the outer casing. By making the thickness of the surface layer 2.0 μm or less, the decrease in the airtightness of the solid electrolytic capacitor (C) can be suppressed.

[0018] The average thickness of the surface layer in the buried portion is 0.1 μm or more, and may be 0.2 μm or more, 0.3 μm or more, 0.4 μm or more, or 0.5 μm or more. The average thickness of the surface layer in the buried portion is 2.0 μm or less, and may be 1.8 μm or less, 1.6 μm or less, 1.4 μm or less, 1.2 μm or less, or 1.0 μm or less. The thickness of 90% to 100% (area ratio) of the surface layer in the buried portion may be 0.1 μm or more and 2.0 μm or less. The surface layer may be formed in an area of ​​90% to 100% (area ratio) of the surface of the buried portion.

[0019] The ratio B / A of the average thickness B of the surface layer of the buried portion to the average thickness A of the surface layer of the exposed portion may be 0.50 or less, 0.45 or less, 0.40 or less, or 0.35 or less. The ratio B / A may also be 0.005 or more, 0.010 or more, 0.025 or more, or 0.030 or more.

[0020] The average thickness of the exposed and buried portions can be measured, for example, by the following method: First, the product is cut at an arbitrary point to form a cross-section. Next, the tin-containing surface layer is identified using elemental analysis (elemental mapping) by energy-dispersive X-ray spectroscopy (EDX). Then, a cross-sectional image of the surface layer is obtained using a scanning electron microscope (SEM) or transmission electron microscope (TEM). Based on the obtained cross-sectional image, the thickness of the surface layer is measured. The average thickness of the surface layer is taken as the average of the thicknesses at 10 arbitrary points on the surface layer.

[0021] The tin content in the surface layer may be 50% by mass or more. The tin content in the surface layer may be 10% by mass or more, 25% by mass or more, 75% by mass or more, or 90% by mass or more. The tin content in the surface layer may be 90% by mass or less, 75% by mass or less, 25% by mass or less, or 10% by mass or less. The metal contained in the surface layer is preferably a metal with a low melting point. A metal with a low melting point is, for example, tin (melting point: 231.9°C). When mounted (e.g., during reflow), the tin melts from the surface layer of the lead terminal, strengthening the bond between the lead terminal and the circuit board in the exposed parts. The tin melted from the surface layer can strengthen the bond between the lead terminal and the anode (and / or cathode) in the embedded parts. For this reason, it is preferable that the surface layer contains tin, and the content is preferably 50% by mass or more. Examples of metals other than tin that are included in the surface layer include nickel, gold, silver, lead, zinc, and palladium.

[0022] The surface layer may be an alloy containing tin and copper. The surface layer may also contain other metals such as nickel, gold, silver, lead, zinc, and palladium, and may be formed from alloys of these metals. The alloy may be, for example, a copper-tin alloy, a copper-nickel alloy, a copper-silver alloy, a copper-gold alloy, a copper-zinc alloy, or a nickel-tin alloy. In particular, when the alloy contains tin and copper, the lead terminal can maintain high heat resistance even in high-temperature environments.

[0023] (Capacitor element) The capacitor element may include an anode portion, a dielectric layer, and a cathode portion. The dielectric layer is formed on the surface of the anode portion. There are no particular limitations on the capacitor element, and capacitor elements used in known solid electrolytic capacitors may be used.

[0024] (Anode section) The anode section may consist only of an anode body. Alternatively, the anode section may include an anode body and an anode wire. The anode body may be a porous sintered body or a metal foil with a porous surface. The dielectric layer is formed on the surface of the anode body. The cathode section may include an electrolyte layer (solid electrolyte layer) and a cathode layer. The electrolyte layer is disposed between the dielectric layer formed on the surface of the anode body and the cathode layer. These components are not particularly limited, and components used in known solid electrolytic capacitors may be applied. Examples of these components are described below.

[0025] (Anode) The anode may be formed by sintering material particles. Examples of material particles include valve metal particles, alloy particles containing valve metal, and compound particles containing valve metal. These particles may be used individually or in mixtures of two or more types. Alternatively, a metal foil with valve properties may be used as the anode. Examples of valve metals include titanium (Ti), tantalum (Ta), niobium (Nb), and aluminum (Al). A preferred example of a sintered anode is a sintered tantalum body. A preferred example of a metal foil anode is aluminum foil.

[0026] (Dielectric layer) There are no particular limitations on the dielectric layer formed on the surface of the anode body, and it may be formed by known methods. For example, the dielectric layer may be formed by anodizing the surface of the anode body.

[0027] (Anode Wire) The anode wire can be made of a metal. Examples of materials for the anode wire include the valve metals mentioned above, copper, and aluminum alloys. Part of the anode wire is embedded in the anode body, and the remaining part protrudes from the end face of the anode body.

[0028] (Cathode section) The cathode section includes, for example, an electrolyte layer (solid electrolyte layer) and a cathode layer. The cathode layer is a conductive layer and is arranged to cover at least a portion of the electrolyte layer. The cathode layer may include a conductive cathode extraction layer. The cathode layer may include other conductive layers (e.g., a carbon layer) arranged between the electrolyte layer and the cathode extraction layer. The cathode extraction layer may be formed of a metal paste (e.g., silver paste) containing metal particles (e.g., silver particles) and resin, or it may be formed of a known silver paste. The carbon layer is a carbon-containing layer and may be formed of a conductive carbon material such as graphite and resin.

[0029] (Cathode Extraction Layer) The cathode extraction layer is arranged to cover at least a portion of the electrolyte layer. The cathode extraction layer may include, for example, a carbon layer and a metal paste layer (e.g., a silver paste layer) formed on the surface of the carbon layer. The carbon layer is composed of a composition containing a conductive carbon material such as graphite. The metal paste layer is composed of, for example, a composition containing silver particles and a binder resin. However, the configuration of the cathode extraction layer is not particularly limited and is acceptable as long as it has a current collection function.

[0030] (Electrolyte Layer) There are no particular limitations on the electrolyte layer (solid electrolyte layer), and an electrolyte layer used in known solid electrolytic capacitors may be applied. The electrolyte layer is arranged to cover at least a part of the dielectric layer. The electrolyte layer may be formed using a manganese compound or a conductive polymer. Examples of conductive polymers include polypyrrole, polythiophene, polyaniline, and derivatives thereof. These may be used individually or in combination. The conductive polymer may also be a copolymer of two or more monomers. A derivative of a conductive polymer means a polymer that has a conductive polymer as its basic skeleton. For example, an example of a derivative of polythiophene is poly(3,4-ethylenedioxythiophene).

[0031] The conductive polymer may have a dopant added to it. The dopant can be selected depending on the conductive polymer, and known dopants (e.g., polymer dopants) may be used. Examples of dopants include naphthalene sulfonic acid, p-toluenesulfonic acid, polystyrene sulfonic acid, and their salts. One example of an electrolyte layer is formed using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS).

[0032] The electrolyte layer containing the conductive polymer may be formed by polymerizing the monomer raw material on a dielectric layer. Alternatively, it may be formed by placing a liquid containing the conductive polymer (and optionally a dopant) on a dielectric layer and then drying it.

[0033] (Outer casing) The outer casing is positioned around the capacitor element so that the capacitor element is not exposed on the surface of the solid electrolytic capacitor (C). Furthermore, the outer casing is positioned to cover the embedded portions of the anode lead terminal and the cathode lead terminal. The outer casing usually includes resin (insulating resin) and insulating filler.

[0034] The exterior body may be formed from a resin composition comprising an insulating resin and an insulating filler (e.g., an inorganic filler). In addition to the insulating resin and insulating filler, the resin composition may also include a curing agent, a polymerization initiator, and / or a catalyst. Examples of insulating resins include insulating thermosetting resins and insulating thermoplastic resins. Specifically, examples of insulating resins include epoxy resins, phenolic resins, urea resins, polyimides, polyamide-imides, polyurethanes, diallyl phthalates, unsaturated polyesters, polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), and the like.

[0035] Examples of insulating fillers include insulating particles and insulating fibers. Examples of insulating materials that constitute insulating fillers include insulating compounds (oxides, etc.) such as silica and alumina, glass, and mineral materials (talc, mica, clay, etc.). The insulating filler contained in the outer casing may be one type or two or more types.

[0036] (Anode lead terminals and cathode lead terminals) The anode lead terminals and cathode lead terminals are metal terminals for connecting the capacitor element to the circuit board, respectively. The base material of each lead terminal may be a copper base material (copper, copper alloy, etc.). Rolled copper sheet can be used as the copper base material (lead terminals). The thickness of the base material is not particularly limited and may be in the range of 25 μm to 200 μm (for example, in the range of 25 μm to 100 μm).

[0037] As described above, a surface layer containing tin is formed on the surface of each lead terminal. The anode lead terminal is electrically connected to the anode portion. The cathode lead terminal is electrically connected to the cathode portion. Each lead terminal includes an embedded portion embedded inside the casing and an exposed portion exposed from the casing. The embedded portion of each lead terminal may be connected to the anode portion and the cathode portion by welding or the like. The exposed portion of each lead terminal may be connected to the circuit board by soldering or the like.

[0038] (Method for Manufacturing Solid Electrolytic Capacitors (C)) An example of the method for manufacturing solid electrolytic capacitors (C) according to this disclosure is described below. This manufacturing method may be referred to as "Manufacturing Method (M)" below. According to Manufacturing Method (M), solid electrolytic capacitors (C) according to this disclosure can be manufactured. Matters described regarding solid electrolytic capacitors (C) can be applied to the manufacturing method (M) below, so redundant explanations may be omitted. Matters described regarding Manufacturing Method (M) may also be applied to solid electrolytic capacitors (C). Note that solid electrolytic capacitors (C) may be manufactured by a manufacturing method other than Manufacturing Method (M). Manufacturing Method (M) includes steps (i), (ii), (iii), and (iv). These steps are described below.

[0039] (Step (i)) Step (i) is a step of forming a surface layer containing tin on the surfaces of the anode lead terminal and the cathode lead terminal. In step (i), the surface layer is formed such that the average thickness of the surface layer is 4 μm or more.

[0040] However, forming the surface layer only on the exposed surface would complicate the manufacturing process; therefore, the surface layer is usually formed over the entire surface of the lead terminal. In other words, the surface layer, with an average thickness of 4 μm or more, is formed on both the exposed and embedded portions.

[0041] The method for forming the surface layer on the surface of the lead terminal is not particularly limited and may be formed by known methods. For example, a tin-containing solution may be sprayed onto the surface of the lead terminal, and the surface layer may be formed by drying or firing. Alternatively, it may be carried out by plating the lead terminal. Specifically, this may involve polishing the substrate surface of the lead terminal, then performing acid cleaning, and using electricity to adhere the surface layer to the lead terminal (electroplating method).

[0042] (Process (ii)) Process (ii) is a process of removing a portion of the surface layer. More specifically, it is a process of removing a portion of the surface layer so that the average thickness of the surface layer of the portion to be embedded is 0.1 μm or more and 2.0 μm or less. Here, in process (i), the surface layer formed over the entire surface of the lead terminal has an average thickness of 4 μm or more, and the surface layer of the portion to be embedded is removed so that the average thickness is 0.1 μm or more and 2.0 μm or less. This distinguishes the embedded portion from the exposed portion. At this time, a portion of the surface layer may be removed so that the ratio B / A of the average thickness B of the surface layer of the embedded portion to the average thickness A of the surface layer of the exposed portion is 0.025 or more and 0.50 or less.

[0043] By making the average thickness of the surface layer of the buried portion 0.1 μm or more, the bonding strength between the anode (and / or cathode) portion and the buried portion can be increased. Furthermore, by making the average thickness of the surface layer of the buried portion 2.0 μm or less, the decrease in the airtightness of the solid electrolytic capacitor (C) can be suppressed.

[0044] The method for removing a part of the surface layer is not particularly limited and may be formed by a known method. For example, there are methods such as removal by sublimation using a laser and mechanical shaving with a cutting tool or the like. It is preferable that step (ii) is performed so that the thickness of the surface layer of the embedded portion becomes substantially uniform. The thickness of 90% to 100% (area ratio) of the surface layer of the embedded portion may be in the range of 0.1 μm to 2.0 μm.

[0045] In step (ii), a part of the surface layer may be removed by irradiating the surface layer with laser light. As a specific example, using "MX-Z2050H-V1" manufactured by Omron Corporation, a part of the surface layer may be removed by irradiating and scanning the surface layer with a laser. The conditions for laser scanning may be a laser output of 20 W and a scanning speed of 1500 mm / s.

[0046] As long as a part of the surface layer can be removed, the laser light to be irradiated is not particularly limited. The wavelength of the laser light may be 1100 nm or less, 700 nm or less, or 600 nm or less. The wavelength of the laser light may be 300 nm or more or 350 nm or more.

[0047] The removal of a part of the surface layer may be performed by scanning the laser light. Alternatively, it may be performed by moving the laser processing machine and / or the lead terminal. Also, the laser light may be pulsed laser light or continuous wave laser light (CW laser light). There is no particular limitation on the number of times of laser light irradiation, and it may be irradiated a plurality of times at any location so that the average thickness of the surface layer of the embedded portion is in the range of 0.1 μm or more and 2.0 μm or less.

[0048] (Step (iii)) Step (iii) is a step of electrically connecting the anode lead terminal to the anode portion of the capacitor element and the cathode lead terminal to the cathode portion of the capacitor element. Here, the embedded portions of each lead terminal are electrically connected to the anode portion and the cathode portion of the capacitor element. There is no particular limitation on these connection methods, and known connection methods may be used. For example, the embedded portion of the anode lead terminal may be connected to the anode portion by welding (such as resistance welding or laser welding), may be connected to the anode portion using solder, or may be connected to the anode portion using a conductive adhesive. The same applies to the cathode lead terminal. The conductive adhesive is, for example, a mixture of a curable resin and conductive particles (such as metal particles like carbon particles and silver particles).

[0049] (Step (iv)) Step (iv) is a step of covering a part of the anode lead terminal, a part of the cathode lead terminal, and the capacitor element with an exterior body. The anode lead terminal and the cathode lead terminal after Step (iv) each include an embedded portion embedded in the exterior body and an exposed portion exposed from the exterior body. The method of covering a part of each lead terminal and the capacitor element with the exterior body is not particularly limited and can be performed by known methods. Specifically, it can be performed by covering the part that becomes the embedded portion of each lead terminal and the capacitor element with a resin composition that becomes the exterior body and then curing the resin composition. Here, the portion of each lead terminal that is not covered by the exterior body is the exposed portion. As the exterior body, an exterior body including a resin (insulating resin) and an insulating filler can be used. In the above manner, the solid electrolytic capacitor (C) can be manufactured.

[0050] (Embodiment 1) FIG. 1 is a cross-sectional view schematically showing the configuration of a solid electrolytic capacitor 100 according to the present disclosure. In FIGS. 1, 3, and 4, hatching is omitted. The solid electrolytic capacitor 100 includes a capacitor element 110 including an anode portion 111 and a cathode portion 112, an anode lead terminal 120, a cathode lead terminal 130, and an exterior body 140 covering the capacitor element 110. A dielectric layer (not shown) is formed on the surface of the anode portion 111 (the same applies in the following figures).

[0051] In the capacitor element 110, a cathode portion 112 is laminated on an anode portion 111. The anode portion 111 includes a metal foil (anode body) with a roughened surface. This metal foil includes a valve metal. The anode portion 111 is in the form of a sheet or a flat plate.

[0052] The anode lead terminal 120 and the cathode lead terminal 130 each have a main surface having an anode connection surface (embedded portion 121A) and a cathode connection surface, and a side surface intersecting the main surface. The anode lead terminal 120 includes an embedded portion 120A embedded in the casing 140 and an exposed portion 120B exposed from the casing 140. The cathode lead terminal 130 includes an embedded portion 130A embedded in the casing 140 and an exposed portion 130B exposed from the casing 140. Both the anode lead terminal 120 and the cathode lead terminal 130 are led out to the outside from the bottom surface of the solid electrolytic capacitor 100. The inner surface layers of the exposed portions 120B and 130B (the surface layers on the side in contact with the casing) are not embedded in the casing.

[0053] The anode connection surface (buried portion 121A) of the anode lead terminal 120 is electrically connected to the anode portion 111 by physical contact. Here, the anode portions 111 of multiple capacitor elements 110 are stacked and sandwiched in a part of the buried portion 120A of the anode lead terminal 120, and crimped to the anode connection surface (buried portion 121A). In addition, the cathode connection surface (buried portion 131A) of the buried portion 130A of the cathode lead terminal 130 is connected to the cathode portion 112, for example, via a conductive adhesive.

[0054] The exposed portion 120B of the anode lead terminal 120 and the exposed portion 130B of the cathode lead terminal 130 have a surface layer formed on them that contains tin and has an average thickness of 4 μm or more. The embedded portion 120A of the anode lead terminal 120 and the embedded portion 130A of the cathode lead terminal 130 have a surface layer formed on them that contains tin and has an average thickness of 0.1 μm or more and 2.0 μm or less.

[0055] The cathode lead terminal 130 has an element mounting portion (buried portion 131A) positioned adjacent to a part of the capacitor element 110. At least a part of the element mounting portion (buried portion 131A) is the cathode connection surface. The element mounting portion (buried portion 131A) has a guide portion (buried portion 132A) that rises from the cathode connection surface and restricts the position of the capacitor element 110.

[0056] The guide portion (buried portion 132A) of the cathode lead terminal 130 is provided on each of the two sides of the buried portion 131A having a cathode connection surface. The guide portion (buried portion 132A) extends upward from the cathode connection surface.

[0057] Figure 2 is a schematic exploded view showing an example of the anode lead terminal 120 and the cathode lead terminal 130. The anode lead terminal 120 and the cathode lead terminal 130 can be used in the manufacture of the solid electrolytic capacitor according to this disclosure.

[0058] The anode lead terminal 120 includes a buried portion 120A and an exposed portion 120B. The cathode lead terminal 130 includes a buried portion 130A and an exposed portion 130B. A portion of the buried portion is hatched. Note that a portion of the part not hatched in Figure 2 is also embedded in the outer casing.

[0059] In the stage after step (i) and before step (ii), a surface layer containing tin and having an average thickness of 4 μm or more is formed on the entire surface of the anode lead terminal 120 and the cathode lead terminal 130. By removing at least a portion of the surface layer of the portions of each lead terminal that will become the embedded portions 120A and 130A, the average thickness of the surface layer in the embedded portions 120A and 130A becomes 0.1 μm or more and 2.0 μm or less.

[0060] The anode lead terminal 120 and the cathode lead terminal 130 are bent. The buried portion 120A and the buried portion 130A are embedded in the outer casing 140 in step (iv). The exposed portion 120B and the exposed portion 130B are exposed from the outer casing 140.

[0061] (Embodiment 2) Figure 3 is a schematic cross-sectional view showing the configuration of an example of another solid electrolytic capacitor 100A according to the present disclosure. The solid electrolytic capacitor 100A has a capacitor element 110 similar to the capacitor element 110 described in Embodiment 1. On the other hand, the structure of the anode lead terminal 120 and the cathode lead terminal 130 is different from the structure of the anode lead terminal 120 and the cathode lead terminal 130 described in Embodiment 1.

[0062] Parts of the anode lead terminal 120 and parts of the cathode lead terminal 130 are exposed to the outside from the side of the outer casing 140.

[0063] The inner surface layers of the exposed portions 120B and 130B (the surface layers on the side in contact with the exterior body) are not embedded in the exterior body.

[0064] (Embodiment 3) Figure 4 is a schematic cross-sectional view showing the configuration of yet another solid electrolytic capacitor 100B according to the present disclosure. The solid electrolytic capacitor 100B has a capacitor element 110 similar to the capacitor element 110 described in Embodiment 1. On the other hand, the structure of the anode lead terminal 120 and the cathode lead terminal 130 is different from the structure of the anode lead terminal 120 and the cathode lead terminal 130 described in Embodiment 1.

[0065] Both the anode lead terminal 120 and the cathode lead terminal 130 are led out to the outside from the side of the outer casing 140.

[0066] The inner surface layers of the exposed portions 120B and 130B (the surface layers on the side in contact with the exterior body) are not embedded in the exterior body.

[0067] The embedded portion 120A of the anode lead terminal 120 has a clamped portion (embedded portion 121A). The clamped portion (embedded portion 121A) of the anode lead terminal 120 is positioned between two adjacent anode portions (first anode portion and second anode portion) of the stacked plurality of anode portions 111. The embedded portion 130A of the cathode lead terminal 130 has a clamped portion (embedded portion 131A) positioned between the first element 110A and the second element 110B.

[0068] At least a portion of the clamped portion (embedded portion 121A) of the anode lead terminal 120 is the anode connection surface. The anode connection surface (embedded portion 121A) is connected to the anode portion 111, for example, by welding. At least a portion of the clamped portion (embedded portion 131A) of the cathode lead terminal 130 is the cathode connection surface. The cathode connection surface (embedded portion 131A) is connected to the cathode portion 112, for example, via a conductive adhesive.

[0069] The guide portions (buried portions 132A) of the cathode lead terminal 130 are provided in pairs on each of the two sides of the buried portion 131A having a cathode connection surface. Two of the guide portions (buried portions 132A) extend upward from the cathode connection surface, while the other two guide portions (buried portions 132A) extend downward from the cathode connection surface.

[0070] (Note) The above description of embodiments discloses the following technologies. (Technology 1) A solid electrolytic capacitor comprising: a capacitor element including an anode portion and a cathode portion; an anode lead terminal electrically connected to the anode portion; a cathode lead terminal electrically connected to the cathode portion; and an outer casing covering the capacitor element, wherein the anode lead terminal and the cathode lead terminal each include an embedded portion embedded in the outer casing and an exposed portion exposed from the outer casing, and a surface layer containing tin is formed on the surface of the anode lead terminal and the surface of the cathode lead terminal, the average thickness of the surface layer in the embedded portion being 0.1 μm or more and 2.0 μm or less, and the average thickness of the surface layer in the exposed portion being 4 μm or more. (Technology 2) The solid electrolytic capacitor according to Technology 1, wherein the tin content in the surface layer is 50% by mass or more. (Technology 3) The solid electrolytic capacitor according to Technology 1 or 2, wherein the surface layer is made of an alloy containing tin and copper. (Technical 4) A method for manufacturing a solid electrolytic capacitor including a capacitor element, comprising the steps of: (i) forming a surface layer containing tin on the surfaces of an anode lead terminal and a cathode lead terminal; (ii) removing a part of the surface layer; (iii) electrically connecting the anode lead terminal to the anode portion of the capacitor element and electrically connecting the cathode lead terminal to the cathode portion of the capacitor element; and (iv) covering a part of the anode lead terminal, a part of the cathode lead terminal, and the capacitor element with an outer casing, wherein the anode lead terminal and the cathode lead terminal after step (iv) each include an embedded portion embedded in the outer casing and an exposed portion exposed from the outer casing, wherein in step (i) the surface layer is formed such that the average thickness of the surface layer is 4 μm or more, and in step (ii) a part of the surface layer is removed such that the average thickness of the surface layer in the portion that becomes the embedded portion is 0.1 μm or more and 2.0 μm or less. (Technical 5) The manufacturing method according to Technical 4, wherein in step (ii), a portion of the surface layer is removed by irradiating the surface layer with laser light.

[0071] This disclosure can be applied to solid electrolytic capacitors and methods for manufacturing the same. Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be constrained. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be construed as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0072] 100, 100A, 100B: Solid electrolytic capacitor 110: Capacitor element 111: Anode part 112: Cathode part 120: Anode lead terminal 120A, 121A, 130A, 131A, 132A: Buried part 120B, 130B: Exposed part 130: Cathode lead terminal 140: Outer casing

Claims

1. A solid electrolytic capacitor comprising: a capacitor element including an anode portion and a cathode portion; an anode lead terminal electrically connected to the anode portion; a cathode lead terminal electrically connected to the cathode portion; and an outer casing covering the capacitor element, wherein the anode lead terminal and the cathode lead terminal each include a buried portion embedded in the outer casing and an exposed portion exposed from the outer casing, and a surface layer containing tin is formed on the surface of the anode lead terminal and the surface of the cathode lead terminal, the average thickness of the surface layer in the buried portion being 0.1 μm or more and 2.0 μm or less, and the average thickness of the surface layer in the exposed portion being 4 μm or more.

2. The solid electrolytic capacitor according to claim 1, wherein the tin content in the surface layer is 50% by mass or more.

3. The solid electrolytic capacitor according to claim 1 or 2, wherein the surface layer is made of an alloy containing tin and copper.

4. A method for manufacturing a solid electrolytic capacitor including a capacitor element, comprising: (i) forming a surface layer containing tin on the surfaces of an anode lead terminal and a cathode lead terminal; (ii) removing a portion of the surface layer; (iii) electrically connecting the anode lead terminal to the anode portion of the capacitor element and electrically connecting the cathode lead terminal to the cathode portion of the capacitor element; and (iv) covering a portion of the anode lead terminal, a portion of the cathode lead terminal, and the capacitor element with an outer casing, wherein the anode lead terminal and the cathode lead terminal after going through step (iv) each include an embedded portion embedded in the outer casing and an exposed portion exposed from the outer casing, wherein in step (i) the surface layer is formed such that the average thickness of the surface layer is 4 μm or more, and in step (ii) a portion of the surface layer is removed such that the average thickness of the surface layer in the portion that becomes the embedded portion is 0.1 μm or more and 2.0 μm or less.

5. The manufacturing method according to claim 4, wherein in step (ii), a portion of the surface layer is removed by irradiating the surface layer with laser light.

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