Electrolytic capacitor

Abstract

An electrolytic capacitor according to the present invention comprises: a capacitor element including an anode part and a cathode part; a cathode foil electrically connected to the cathode part; and an exterior body sealing the capacitor element. A laminate obtained by laminating the capacitor element and an electroconductive foil is configured such that the cathode part of the capacitor element is electrically connected to the cathode foil. The exterior body includes an epoxy resin, and the thickness of the exterior body positioned above or below the laminate as viewed from the lamination direction of the laminate is 24.9% or more of the thickness of the laminate in the lamination direction.

Description

electrolytic capacitor

[0001] The present invention relates to an electrolytic capacitor.

[0002] An electrolytic capacitor includes a capacitor element having an anode portion and a cathode portion, an exterior body that seals the capacitor element, and external electrodes that are electrically connected to the anode portion and the cathode portion of the capacitor element, respectively.

[0003] As a configuration of a solid electrolytic capacitor, Patent Document 1 proposes "a solid electrolytic capacitor comprising a capacitor element having a capacitance forming portion, an exterior resin covering the capacitance forming portion, an anode terminal and a cathode terminal at least a portion of which are arranged outside the exterior resin, and a lead, wherein the capacitor element includes an anode, a dielectric layer and a solid electrolyte layer laminated in this order on a portion of the anode, the lead being electrically connected to the solid electrolyte layer, and at least one of the members selected from the anode and the lead having an uneven surface at at least one connection portion selected from the connection portion between the anode and the anode terminal and the connection portion between the lead and the cathode terminal."

[0004] In the solid electrolytic capacitor described in Patent Document 1, the lead is exposed to the outside of the exterior resin, and a part of the exposed lead is electrically connected to the cathode terminal. According to Patent Document 1, the surface of the lead is processed at the connection portion with the cathode terminal to increase the surface area, thereby obtaining a solid electrolytic capacitor with a low equivalent series resistance (ESR).

[0005] Japanese Patent Application Laid-Open No. 2003-086459

[0006] In Patent Document 1, although it is possible to reduce the initial ESR of a solid electrolytic capacitor, it does not take into consideration the possibility that the ESR may increase from the initial ESR due to high-temperature treatment such as reflow.

[0007] The increase in ESR after reflow can occur when the sealing with the exterior resin is insufficient, allowing air or moisture to penetrate through unfilled areas of the exterior resin. Furthermore, the exterior resin swells and deforms due to stress caused by gas generation at high temperatures, which can cause cracks and degrade the capacitor's characteristics, including ESR. Furthermore, the swelling of the exterior resin can also cause the metal foil (lead) and capacitor element to separate, increasing contact resistance and resulting in an increase in ESR.

[0008] In order to prevent the swelling of the exterior resin, it is possible to use a resin material that is difficult to deform as the exterior resin, but such resin materials often have poor sealing properties or poor fluidity during molding, which makes it easy for unfilled portions of the exterior resin to occur during the sealing process.

[0009] On the other hand, by increasing the thickness of the exterior resin within the capacitor, it is possible to suppress deformation of the exterior resin at high temperatures, but this makes it difficult to obtain a high-capacity solid electrolytic capacitor.

[0010] One aspect of the present disclosure relates to an electrolytic capacitor including: a capacitor element having an anode portion and a cathode portion; a cathode foil electrically connected to the cathode portion; and an exterior body sealing the capacitor element, wherein the capacitor element and the conductive foil are laminated together such that the cathode portion of the capacitor element is electrically connected to the cathode foil, the exterior body containing an epoxy resin, and the thickness of the exterior body located above or below the laminate as viewed in the stacking direction of the laminate is 24.9% or more of the thickness of the laminate in the stacking direction.

[0011] Another aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element having foil-shaped anode and cathode portions, and an exterior body that seals the capacitor element, wherein an end face of the anode portion is exposed from the exterior body and the exposed portion is electrically connected to an external electrode, the exterior body contains an epoxy resin, and the thickness of the exterior body located above or below the capacitor element when viewed in a direction perpendicular to a main surface of the anode portion is 24.9% or more of the total thickness of the capacitor element in the perpendicular direction.

[0012] According to the present disclosure, an electrolytic capacitor having a low ESR even after undergoing a reflow process can be obtained.

[0013] 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.

[0014] 1 is a cross-sectional view schematically showing an electrolytic capacitor according to an embodiment of the present disclosure; FIG. 2 is a cross-sectional view schematically showing the structure of an example of a capacitor element; FIG. 3 is a cross-sectional view schematically showing an electrolytic capacitor according to another embodiment of the present disclosure; FIG. 4 is a cross-sectional view schematically showing an electrolytic capacitor according to yet another embodiment of the present disclosure; FIG. 5 is a cross-sectional view schematically showing an electrolytic capacitor according to yet another embodiment of the present disclosure;

[0015] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more materials may be used in combination.

[0016] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0017] "Electrolytic capacitor" may be read as "solid electrolytic capacitor", and "capacitor" may be read as "capacitor".

[0018] [Electrolytic Capacitor] An electrolytic capacitor according to one embodiment of the present invention includes a capacitor element. The form of the capacitor element is not particularly limited. The capacitor element includes an anode portion and a cathode portion. The capacitor element includes, for example, an anode body, a dielectric layer, and a cathode layer. The anode portion includes at least a portion of the anode body. The cathode portion includes the cathode layer.

[0019] The capacitor element is sealed in an exterior housing. The exterior housing is made of a sealing material. The sealing material may be a cured product of a thermosetting resin composition containing an epoxy resin or the like. In this case, the exterior housing contains an epoxy resin. Preferably, the exterior housing contains an epoxy resin and a filler.

[0020] In one embodiment, the electrolytic capacitor includes a cathode foil electrically connected to the cathode portion. A laminate is formed by stacking capacitor elements and cathode foils so that the cathode portions of the capacitor elements are electrically connected to the cathode foil. Within the laminate, for example, the cathode foil has a protruding end portion that protrudes in one direction parallel to the stacking direction relative to the cathode portion. The cathode foil may be a metal foil. The laminate is sealed with an exterior case, but a portion of the cathode foil (including at least the end face of the protruding end portion) is exposed from the exterior case. Electrical connection can be made between the cathode portions of the capacitor elements and an external electrode (external cathode electrode) via the exposed portion.

[0021] However, high-temperature processing such as reflow may cause the exterior body to swell and deform. This deformation may cause the cathode foil to peel off from the capacitor element, weakening the electrical connection between the capacitor element and the cathode foil. As a result, the ESR may increase after the reflow process.

[0022] In this electrolytic capacitor, the thickness T1 of the exterior body located above or below the laminate in the stacking direction is 24.9% or more of the thickness T2 of the laminate in the stacking direction (T1 / T2 > 0.249). When the thickness T1 is 24.9% or more of the thickness T2, peeling of the cathode foil due to swelling of the exterior body is significantly suppressed compared to when the thickness T1 is less than 24.9% of the thickness T2. This significantly suppresses the increase in ESR at high temperatures, allowing a low ESR to be maintained even after the reflow process. It is preferable that the thickness T1 be 25% or more of the thickness T2 (T1 / T2 > 0.25).

[0023] The thickness T1 of the exterior body located above the laminate may satisfy the above relationship with the thickness T2 of the laminate, and the thickness T1 of the exterior body located below the laminate may satisfy the above relationship with the thickness T2 of the laminate. Preferably, when the thicknesses of the exterior bodies located above and below the laminate are each designated as T1, the above relationship is satisfied. The upper limit of the thickness T1 of the exterior body is not particularly limited, but may be 200% or less, 100% or less, or 50% or less of the thickness T2 of the laminate in order to obtain a high capacity.

[0024] Furthermore, by using epoxy resin as the resin that constitutes the exterior body, cracks are less likely to occur even at high temperatures, and the intrusion of air, moisture, etc. can be suppressed, thereby preventing deterioration of the capacitor's characteristics.

[0025] Preferably, the outer casing contains a filler having an average particle size of 12 μm to 32 μm. The proportion of the filler in the outer casing is 73% by mass or more and 84% by mass or less. In this case, the fluidity of the outer casing resin during molding is good, preventing the occurrence of unfilled gaps between the outer casing and the laminate, thereby improving sealing performance. As a result, deterioration of capacitor characteristics due to the intrusion of air, moisture, etc. can be further suppressed. Note that the average particle size here refers to the particle size (median diameter D50) at which the cumulative volume, calculated from the smallest particle size in the volume-based particle size distribution, is 50% of the total. In the particle size distribution of the filler, the particle size D10, at which the cumulative volume, calculated from the smallest particle size in the volume-based particle size distribution, is 10% of the total, may be, for example, 1 μm or more. In the particle size distribution of the filler, the particle size D90, at which the cumulative volume, calculated from the smallest particle size in the volume-based particle size distribution, is 90% of the total, may be, for example, 35 μm or less.

[0026] In terms of improving fluidity during molding, it is preferable that fillers having particle sizes in the range of 12 μm to 32 μm account for 30% to 90% of the total by volume, or may account for 30% to 70% of the total by volume. The filler proportion is determined by integrating the particle size distribution of the filler on a volume basis over the particle size range of 12 μm to 32 μm.

[0027] The average particle diameter D50 (and particle diameters D10 and D90) can be determined by observing the cross section of the outer package with a scanning electron microscope (SEM) and analyzing the cross section image. The outline of each filler particle in the cross section image is identified, and the area Sf occupied by each filler particle in the cross section is determined. From the area Sf, the diameter Df of the equivalent sphere (Df = 8√(Sf / π)) is calculated as the average cross section area of ​​the sphere. ３ ) is obtained, and the distribution of diameters Df is determined. Assuming that each filler is spherical with a diameter Df, the volume-based particle size distribution of the filler is obtained, and D50, D10, and D90 are derived. It is preferable to select at least 100 fillers and determine the particle size distribution.

[0028] Epoxy resins have excellent electrical insulation, water resistance, and chemical resistance, and the glass transition temperature (Tg) and hardness of the resin are easily controlled. Epoxy resins are generally obtained by crosslinking a curing agent with a base resin, which is a monomer or polymer (prepolymer) having an epoxy group. While the base resin is not particularly limited, polyaromatic epoxy resins are preferred. Prepolymers such as bisphenol epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, cresol novolac epoxy resins, and dicyclopentadiene epoxy resins may also be used. Polyaromatic epoxy resins are epoxy resins with multiple aromatic rings in the main skeleton. Among these, biphenyl epoxy resins and naphthalene epoxy resins have low viscosity at high temperatures and high fluidity during molding.

[0029] The curing agent is not particularly limited and may be appropriately selected depending on the type of base resin. Examples of the curing agent include polyfunctional or polyaromatic novolac curing agents such as phenol novolac, acid anhydride curing agents such as tetrahydrophthalic anhydride and hexahydrophthalic anhydride, and amine curing agents such as ethylenediamine and aromatic amine.

[0030] Among these, the epoxy resin preferably contains a biphenyl aralkyl resin, which is easy to mold and provides sufficient strength. More preferably, the epoxy resin may be a polyaromatic biphenyl aralkyl resin.

[0031] The linear expansion coefficient of the exterior body is α1=13×10 －６ / ℃ or more, 21 × 10 －６ / °C or less, and the linear expansion coefficient α2 is 52 × 10 －６ / ℃ or more, 74 x 10 －６ / °C or less. Here, the linear expansion coefficient α1 is the linear expansion coefficient of the exterior body at a temperature lower than the glass transition temperature Tg of the resin (epoxy resin) contained in the exterior body. The linear expansion coefficient α2 is the linear expansion coefficient of the exterior body at a temperature higher than the glass transition temperature Tg of the resin (epoxy resin) contained in the exterior body. The linear expansion coefficients α1 and α2 are determined by measurements in accordance with JIS K 7197.

[0032] The glass transition temperature Tg of the epoxy resin is, for example, 110°C or higher, and may be higher. The Tg may be, for example, 130°C or lower. The glass transition temperature Tg depends on the crosslink density and structure of the epoxy resin. Therefore, the glass transition temperature Tg can be controlled, for example, by the types of base resin and curing agent, the compounding ratio of the base resin and the curing agent, the molecular weight of the base resin, etc.

[0033] The moisture absorption rate of the epoxy resin may be 0.23% or more and 0.34% or less. The moisture absorption rate is determined by placing the resin in an environment of 85°C and a relative humidity of 85% for 72 hours, and measuring the mass M of the resin after 72 hours. １ and the mass of the resin before the test M ０ From the formula ((M １ -M ０ ) / M ０ ) × 100 (%). The resin used for measurement is in the form of a hardened sheet.

[0034] The epoxy resin may preferably have a flexural modulus of 0.19 GPa or more and 0.25 GPa or less at 260° C. The flexural modulus is measured in accordance with JIS K 7171.

[0035] The outer casing may contain other resins in addition to the epoxy resin. Examples of the other resins include phenolic resins, urea resins, polyimide resins, polyamideimide resins, polyurethane resins, diallyl phthalate resins, and unsaturated polyester resins. When the outer casing contains other resins in addition to the epoxy resin, the ratio of the epoxy resin to the total of the epoxy resin and the other resins may be 75% or more, 90% or more, or 95% or more by mass.

[0036] The filler is not particularly limited, and known fillers can be used. For example, insulating fillers such as insulating particles and insulating fibers can be used. Examples of insulating materials constituting the insulating filler include insulating compounds such as silica, alumina, aluminum nitride, and boron nitride, glass, and mineral materials (talc, mica, clay, etc.). The filler contained in the outer casing may be one type or two or more types.

[0037] A high filler content in the exterior body increases the strength of the exterior body and reduces the shrinkage rate during molding. It also reduces moisture absorption and flame retardancy. On the other hand, a low filler content increases the adhesion of the exterior body to the capacitor element, but reduces the rigidity of the exterior body, making it more susceptible to thermal deformation. Furthermore, a low filler content improves fluidity during molding, making it less likely for resin to be unfilled. For example, in the case of a laminate having multiple capacitor elements, resin is more likely to fill the gaps between the capacitor elements. To achieve a good balance of these properties, the filler content in the exterior body is preferably in the range of 70% to 90% by mass. The filler content may be 73% by mass or more and 84% by mass or less.

[0038] When the filler content in the exterior body is the same, a smaller filler particle size allows the resin present between the fillers to act as a buffer, making it easier to relieve stress. As a result, the overall exterior body can relieve more stress. Furthermore, a smaller filler particle size makes it easier for the resin to fill the gaps in the laminate. In this regard, the maximum particle size of the filler may be 50 μm or less (e.g., 35 μm or less). By setting the maximum particle size to 35 μm or less, stress is more easily relieved, as described above. Here, the maximum particle size refers to the particle size of the largest filler particle contained in the exterior body. The maximum particle size can be determined by photographing the cross-section of the exterior body, randomly selecting 100 particles, and measuring the cross-sectional area of ​​the particles. The maximum particle size is the diameter of the largest equivalent circle among the equivalent circles having the same area as the cross-sectional area of ​​each particle.

[0039] In an electrolytic capacitor, a portion of the cathode foil may be exposed from the exterior housing, and the exposed portion may be electrically connected to an external electrode (external cathode electrode). This configuration can reduce the ESR of the electrolytic capacitor. For example, a portion of the cathode foil may have a protruding tip that protrudes in one direction parallel to the stacking direction relative to the capacitor element, and at least a portion of the protruding tip, including its end face, may be electrically connected to the external electrode. In this case, high-temperature processing such as reflow may cause the exterior housing to swell and deform, which may lead to the separation of the cathode foil from the exterior housing, creating a gap between the exterior housing and the cathode foil. The infiltration of air, moisture, etc. through the gap may increase the ESR. Furthermore, the expansion of the exterior housing may weaken the electrical connection between the end face of the cathode foil and the external electrode, resulting in an increase in ESR. However, as described above, by setting the thickness T1 of the exterior housing to be 24.9% or more of the thickness T2 of the laminate, the expansion of the exterior housing is suppressed, significantly suppressing the increase in ESR at high temperatures and maintaining a low ESR even after the reflow process.

[0040] Similarly, a portion of the anode portion of the capacitor element may be exposed from the exterior housing, and the exposed portion may be electrically connected to an external electrode (external anode electrode). The anode portion of the capacitor element has a protruding tip that protrudes in one direction parallel to the stacking direction, and at least a portion of the anode portion, including the end face of the protruding tip, may be electrically connected to the external electrode. The protruding tip of the anode portion may protrude in a direction different from the protruding direction of the protruding tip of the cathode foil. In this case, as the exterior housing expands during a high-temperature treatment process such as reflow, the adhesion between the protruding tip of the anode portion and the exterior housing may peel off, creating a gap between the exterior housing and the anode portion. The ESR may increase due to the intrusion of air, moisture, etc. through the gap. Furthermore, as the exterior housing expands, the electrical connection between the end face of the protruding tip of the anode portion and the external electrode may be weakened, resulting in an increase in ESR. However, as described above, by making the thickness T1 of the outer casing 24.9% or more of the thickness T2 of the laminate, the swelling of the outer casing is suppressed, thereby significantly suppressing the increase in ESR at high temperatures and maintaining a low ESR even after the reflow process.

[0041] An electrolytic capacitor does not necessarily have to include a cathode foil electrically connected to the cathode of the capacitor element. Even in this case, a low ESR electrolytic capacitor can be realized by exposing a portion of the anode of the capacitor element from the exterior housing and electrically connecting the exposed portion to an external electrode (external anode). Furthermore, by satisfying the above-described relationship between the thickness T1 of the exterior housing and the total thickness T2 of the capacitor elements, swelling of the exterior housing is suppressed, thereby significantly suppressing an increase in ESR at high temperatures.

[0042] In one embodiment, the electrolytic capacitor includes a capacitor element having a foil-shaped anode portion and a foil-shaped cathode portion, and an exterior housing that encapsulates the capacitor element. The end face of the anode portion is exposed from the exterior housing, and the exposed portion is electrically connected to an external electrode (external anode electrode). The exterior housing contains the above-described epoxy resin. The thickness T1 of the exterior housing located above or below the capacitor element when viewed from a direction perpendicular to the main surface of the anode portion is 24.9% or more of the total thickness T2 of the capacitor element in the perpendicular direction. When the electrolytic capacitor includes a laminate in which multiple capacitor elements are stacked, the direction perpendicular to the main surface of the anode portion may be the stacking direction of the multiple capacitor elements. When the electrolytic capacitor includes a laminate in which multiple capacitor elements are stacked, the total thickness T2 refers to the thickness of the laminate in the perpendicular direction (i.e., the sum of the thicknesses of the multiple capacitor elements in the stacking direction).

[0043] The laminate may be configured to include a plurality of capacitor elements. In this case, the laminate may include a plurality of cathode foils. A cathode foil may be interposed between adjacent capacitor elements. The cathode foil may electrically connect the cathode portion of one adjacent capacitor element to the cathode portion of the other adjacent capacitor element. Anode portions of the plurality of capacitor elements may be exposed from the exterior. End faces of the plurality of anode portions may be exposed from the exterior case, and at least a portion of the end faces of the anode portions may be electrically connected to an external electrode (external anode electrode). Furthermore, a portion of the plurality of cathode foils may be exposed from the exterior. End faces of the plurality of cathode foils may be exposed from the exterior case, and at least a portion of the end faces of the cathode foils may be electrically connected to an external electrode (external cathode electrode).

[0044] In the laminate, the multiple capacitor elements may face the same direction or different directions. For example, the anode and cathode parts may be stacked so that they alternately face in opposite directions, or the anode and cathode parts may be stacked so that they face in opposite directions in any order. The anode and cathode parts may be stacked so that they alternately cross at 90 degrees, or the anode and cathode parts may be stacked so that they cross at 90 degrees in any order.

[0045] Only the end face of the anode part may be exposed from the exterior housing and electrically connected to an external electrode. Only the end face of the cathode foil may be exposed from the exterior housing and electrically connected to an external electrode. However, in order to obtain a low ESR, it is preferable to expose both the end face of the anode part and the end face of the cathode foil from the exterior housing and electrically connect each to a corresponding external electrode.

[0046] The end face of the cathode foil may be exposed from a first main surface of the exterior package. In this case, the external electrode may be arranged to cover the first main surface. In this case, the end face of the anode portion may be exposed from a second main surface of the exterior package that is different from the first main surface (e.g., the opposite side to the first main surface).

[0047] When the laminate includes multiple cathode foils, some of the end faces of the multiple cathode foils may be exposed from the first main surface of the exterior body, and the end faces of the remaining cathode foils may be exposed from a second main surface different from the first main surface of the exterior body (e.g., the opposite side to the first main surface). In this case, two external electrodes (external cathode electrodes) are provided, one of which is disposed so as to cover the first main surface, and the other is disposed so as to cover the second main surface. In this case, the end face of the anode section may be exposed from a third main surface different from the first and second main surfaces of the exterior body. In this case, the external electrode (external anode electrode) may be disposed so as to cover the third main surface.

[0048] Similarly, when the laminate includes multiple capacitor elements, some of the end faces of the multiple anode portions may be exposed from the third main surface of the exterior body, and the other end faces of the multiple anode portions may be exposed from a fourth main surface different from the first to third main surfaces of the exterior body (for example, the opposite side to the third main surface). In this case, two external electrodes (external anode electrodes) are provided, one of which is arranged to cover the third main surface and the other of which is arranged to cover the fourth main surface.

[0049] The size of the electrolytic capacitor is not particularly limited, but the dimension of the electrolytic capacitor in the stacking direction of the laminate may be 100 μm or more and 10 mm or less, or 300 μm or more and 5 mm or less. In this case, sufficient rigidity is obtained, and the effect of suppressing an increase in ESR at high temperatures by setting the thickness T1 of the exterior body to 24.9% or more of T2 is high.

[0050] Next, an exemplary method for manufacturing an electrolytic capacitor will be described, but the method for manufacturing an electrolytic capacitor according to the present disclosure is not limited to the following.

[0051] A method for manufacturing an electrolytic capacitor includes, for example, the steps of preparing a capacitor element having an anode portion and a cathode portion, overlaying a cathode foil on the cathode portion of the capacitor element to obtain a laminate, sealing the capacitor element with an exterior body, exposing the end face of the cathode foil from the exterior body, and forming an external cathode electrode that is electrically connected to the cathode portion via the end face of the cathode foil.

[0052] The manufacturing method may further include the steps of exposing an end face of the anode unit from the exterior body and forming an external anode electrode electrically connected to the end face of the anode unit. Each step will be described in further detail below.

[0053] (Step of Preparing Capacitor Element) The step of preparing the capacitor element includes the step of preparing an anode body. The step of preparing the capacitor element may include the step of arranging a separation layer (insulating member) on a part of the anode body.

[0054] (Anode body) In the step of preparing an anode body, an anode body is prepared that includes a first portion (also referred to as an "anode lead portion") that includes a first end and a second portion (also referred to as a "cathode forming portion") that includes a second end. The anode portion includes the first portion of the anode body (anode lead portion). The first portion of the anode body may include an end portion to be removed later by cutting or the like. At least the second portion of the anode body has a porous portion. A dielectric layer will be formed later on the surface of at least the second portion.

[0055] The anode body includes a valve metal, an alloy containing a valve metal, a compound containing a valve metal (such as an intermetallic compound), etc. These materials can be used alone or in combination of two or more. Examples of the valve metal that can be used include aluminum, tantalum, niobium, and titanium. The anode body may be a foil (anode foil) of a valve metal, an alloy containing a valve metal, or a compound containing a valve metal, or may be a porous sintered body of a valve metal, an alloy containing a valve metal, or a compound containing a valve metal.

[0056] When a foil (anode foil) is used for the anode body, a porous portion is formed in the surface layer of at least the second portion of the anode foil. That is, the second portion has a metal core and a porous portion formed on the surface of the metal core. The porous portion may be formed by roughening the surface of at least the second portion of the anode foil by etching or the like. It is also possible to place a predetermined masking member on the surface of the first portion and then perform a roughening treatment such as etching. On the other hand, it is also possible to roughen the entire surface of the anode foil by etching or the like. In the former case, an anode foil is obtained that does not have a porous portion on the surface of the first portion but has a porous portion on the surface of the second portion. In the latter case, a porous portion is formed on the surface of the first portion as well as the surface of the second portion.

[0057] The etching treatment may be performed by a known method, such as electrolytic etching. The masking member is not particularly limited, but is preferably an insulating material such as a resin. The masking member may also be a conductor containing a conductive material.

[0058] When the entire surface of the anode foil is roughened, the porous portion also exists on the surface of the first portion. The porous portion of the first portion may be compressed in advance to crush the pores. This prevents air and moisture from entering the electrolytic capacitor through the porous portion from the end face of the anode exposed from the outer casing.

[0059] When a sintered body is used for the anode body, the sintered body is obtained by molding and sintering a powder containing a valve metal (e.g., a powder of a valve metal, or a powder of an alloy or compound containing a valve metal). For example, a porous anode body with a portion of the anode wire embedded therein can be formed by placing the valve metal powder and the embedded portion of the anode wire to be connected to the anode body in a mold so that the powder is embedded in the powder, press-molding, and sintering. Sintering is preferably performed under reduced pressure. The metal wire corresponds to the first portion, and the sintered body corresponds to the second portion.

[0060] (Separation Layer) When a foil (anode foil) is used for the anode body, an insulating separation layer may be provided to electrically separate the first portion from the second portion. In this step, an insulating member is placed on the first portion of the anode body via a dielectric layer. The insulating member is placed so as to separate the first portion from the cathode portion formed in a later step. The separation layer may be provided in proximity to the cathode portion so as to cover at least a portion of the surface of the first portion.

[0061] The separation layer can be obtained, for example, by attaching a sheet-like insulating member (such as a resin tape) to the first portion. When an anode foil having a porous portion on its surface is used, the porous portion of the first portion may be compressed and flattened before the insulating member is attached to the first portion. The sheet-like insulating member preferably has an adhesive layer on the surface that is attached to the first portion.

[0062] The insulating member may be formed by applying or impregnating the first portion with a liquid resin. In the method using the liquid resin, the insulating member is formed so as to fill the irregularities on the surface of the porous portion of the first portion. The liquid resin easily penetrates into the recesses on the surface of the porous portion, and the insulating member can be easily formed in the recesses.

[0063] (Dielectric Layer) The dielectric layer is formed, for example, by anodizing the valve metal on at least the surface of the second portion of the anode body using a chemical conversion treatment or the like. The chemical conversion treatment can be performed, for example, by immersing the anode body in a chemical conversion solution to impregnate the surface of the anode body with the chemical conversion solution, and applying a voltage between the anode body as the anode and a cathode immersed in the chemical conversion solution. When the anode body has a porous portion on its surface, the dielectric layer is formed along the uneven surface of the porous portion. The dielectric layer contains an oxide of the valve metal. For example, when aluminum is used as the valve metal, the dielectric layer contains aluminum oxide. When tantalum is used as the valve metal, the dielectric layer contains tantalum oxide. The dielectric layer is formed along at least the surface of the second portion where the porous portion is formed (including the inner wall surfaces of the pores of the porous portion). Note that the method for forming the dielectric layer is not limited thereto, and any method may be used as long as an insulating layer that functions as a dielectric is formed on the surface of the second portion. The dielectric layer may also be formed on the surface of the first portion (e.g., on the porous portion on the surface of the first portion).

[0064] (Cathode Section) The cathode section includes a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode extraction layer covering at least a portion of the solid electrolyte layer.

[0065] (Solid Electrolyte Layer) The solid electrolyte layer includes, for example, a conductive polymer. Examples of the conductive polymer that can be used include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The solid electrolyte layer can be formed, for example, by chemically polymerizing and / or electrolytically polymerizing raw material monomers on the dielectric layer. Alternatively, the solid electrolyte layer can be formed by applying a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed to the dielectric layer. The solid electrolyte layer may also include a manganese compound.

[0066] (Cathode Extraction Layer) The cathode extraction layer includes, for example, a carbon layer and a conductive paste layer. The carbon layer may be conductive and may be made of a conductive carbon material such as graphite. The carbon layer may be formed, for example, by applying a carbon paste to at least a portion of the surface of the solid electrolyte layer. The conductive paste layer may be a hardened metal paste (metal paste layer) containing metal particles and a resin. The metal particles may be silver, copper, nickel, or other particles. Silver is particularly preferred. That is, the metal paste layer is preferably a silver paste layer. The resin preferably contains an epoxy resin. The metal paste may be a thermosetting resin composition containing metal particles and an epoxy resin. The metal paste layer is formed, for example, by applying a layer to the surface of the carbon layer. Note that the configuration of the cathode extraction layer is not limited thereto and may be any configuration that has a current collecting function. The conductive paste layer may be a hardened conductive carbon material paste containing carbon particles and a resin.

[0067] (Step of Obtaining a Laminate) Next, a cathode foil is placed on the cathode portion of the capacitor element to obtain a laminate. A plurality of capacitor elements and / or a plurality of cathode foils may be placed on top of each other to obtain a laminate. The cathode foil is electrically connected to the cathode extraction layer and to the external cathode electrode.

[0068] When a laminate having a plurality of capacitor elements is obtained, a cathode foil may be interposed between the cathode lead layers of one of the adjacent capacitor elements in the laminate, but this is not limited thereto, and the cathode lead layers of some capacitor elements may be directly connected to the cathode lead layers of the adjacent capacitor elements without a cathode foil therebetween.

[0069] (Cathode foil) The cathode foil is, for example, a metal foil, and may be a sintered foil, a vapor-deposited foil, or a coated foil. The cathode foil may be a sintered foil, a vapor-deposited foil, or a coated foil in which the surface of a metal foil (e.g., Al foil, Cu foil) is coated with a conductive film by vapor deposition or coating. The vapor-deposited foil may be an Al foil with Ni vapor-deposited on its surface. Examples of the conductive film include Ti, TiC, TiO, and C (carbon) films. The conductive film may be a carbon coating.

[0070] (Substrate) The electrolytic capacitor may include a substrate that supports one capacitor element or a laminate having multiple capacitor elements. The substrate may be, for example, an insulating substrate. If the external anode electrode and the external cathode electrode can be electrically separated, the substrate may be a metal substrate or a printed circuit board with a wiring pattern.

[0071] When the substrate is an insulating substrate, the capacitor element or the laminate having a plurality of capacitor elements may be mounted on the substrate using an adhesive (for example, an epoxy adhesive).

[0072] When the substrate is a metal substrate, a metal foil may be disposed between the cathode portion of one capacitor element and the substrate, or between the cathode portion of the capacitor element closest to the substrate in the element stack and the substrate. In this case, the metal foil may be bonded to the cathode portion and the substrate using a conductive adhesive. In this case, a conductive adhesive layer is formed not only between the metal foil and the cathode portion but also between the metal foil and the substrate. The conductive adhesive layer may include a first layer interposed between the cathode portion-side main surface of the metal foil and the cathode portion, a second layer interposed between the substrate-side main surface of the metal foil and the substrate, and a third layer filled in the through holes of the metal foil and integrally formed with the first and second layers. The presence of the third layer improves the adhesive strength between the cathode portion and the metal foil as well as the adhesive strength between the substrate and the metal foil.

[0073] Examples of insulating substrates include glass epoxy substrates, paper phenol substrates, glass polyimide substrates, and fluorine substrates. The thickness of the insulating substrate is, for example, 500 μm or less, or may be 250 μm or less, 200 μm or less, or 150 μm or less. The thickness of the insulating substrate may also be, for example, 50 μm or more.

[0074] The substrate may include a coating covering at least one of the main surfaces of the insulating substrate. The coating may include at least one of a cured product of a curable resin (e.g., an epoxy resin) and a thermoplastic resin (e.g., a fluororesin). The epoxy resin may be any of those exemplified above. Examples of fluororesins include polytetrafluoroethylene, perfluoroalkoxyalkane, perfluoroethylenepropene copolymer, perfluoroethylenepropene copolymer, polyvinylidene fluoride, and vinylidene fluoride copolymer.

[0075] (Step of Encapsulating the Capacitor Element in an Exterior Body) First, the capacitor element may be placed in a mold configured so that the end faces of the anode portion and the cathode portion are exposed and the remainder of the capacitor element is sealed, and then the capacitor element is sealed with a sealing material to form an exterior body. Second, the capacitor element may be placed in a mold configured so that the end faces of the anode portion and the cathode portion are not exposed and the entire capacitor element is sealed, and then the capacitor element is sealed with a sealing material to form an exterior body. In either case, it is efficient to form an assembly of multiple capacitor elements and then seal the assembly with a sealing material to form an exterior body. Such a process can be performed by transfer molding, compression molding, or the like. In the first method, the step of exposing the end faces of the anode portion and the cathode portion from the exterior body is also performed simultaneously.

[0076] The encapsulant preferably contains a thermosetting resin composition, and may contain a thermoplastic resin. In the transfer molding method or compression molding method, the uncured encapsulant is cured to form an exterior body. The thermosetting resin composition may contain a filler, a curing agent, a polymerization initiator, a catalyst, etc. in addition to a base resin such as an epoxy resin.

[0077] The capacitor element is sealed with a sealing material so that the thickness of the exterior body above or below the laminate as viewed in the lamination direction of the laminate is 24.9% or more of the thickness of the laminate in the lamination direction.

[0078] (Step of exposing the end face of the cathode foil or the anode part from the exterior package) When exposing the end face of the cathode foil from the exterior package, for example, a part of the exterior package may be removed. Specifically, after covering the capacitor element with the exterior package, the exterior package may be polished or a part of the exterior package may be cut off so that the end face of the cathode foil is exposed from the exterior package. A part of the cathode foil may be cut off together with a part of the exterior package.

[0079] When exposing the end face of the anode part from the exterior housing, the exterior housing may be partially removed to expose the end face of the anode part from the exterior housing. The method for exposing the end face of the anode part from the exterior housing can be the same as the method for exposing the end face of the cathode foil from the exterior housing. A part of the first portion may be cut off together with a part of the exterior housing. The surface of the exterior housing from which the end face of the first end of the anode part is exposed is preferably a surface different from the surface from which the end face of the cathode foil is exposed from the exterior housing.

[0080] The anode body and the insulating member of the laminate may be partially removed together with the exterior housing to expose the end face of the first end and the end face of the insulating member from the exterior housing. In this case, the anode body and the insulating member each have a flush end face that is exposed from the exterior housing. This makes it possible to easily expose, from the exterior housing, the end face of the anode body and the end face of the insulating member that are flush with the surface of the exterior housing.

[0081] As described above, by cutting or the like, the end face of the anode body (first end) and the end face of the cathode foil on which no natural oxide film is formed can be easily exposed from the exterior body, and a highly reliable connection state with low resistance can be obtained between the anode body or the first portion and the external anode electrode.

[0082] When forming a laminate of multiple capacitor elements and sealing the assembly with a sealing material to form an exterior package, the assembly may be singulated by cutting the connecting portions connecting adjacent anode parts and adjacent cathode foil parts within the assembly. In this case, the end faces of the anode parts and the cathode foils are exposed at the cut surfaces. Such cut surfaces may be dry-etched using plasma or the like.

[0083] (Contact Layer) At least one of the end faces of the anode and cathode exposed from the outer casing may be connected to an external electrode via a contact layer. The contact layer may be formed, for example, of an electroless Ni-plated layer, or may be formed of an electroless Ni-plated layer covered with an electroless Ag-plated layer. When a contact layer is provided, the contact layer can more reliably connect the end face of the anode or cathode to the external electrode, which is advantageous in terms of improving the reliability of the solid electrolytic capacitor.

[0084] The contact layer may be selectively formed so as to cover only the end face of the anode or cathode exposed from the exterior body, without covering the surface of the exterior body as much as possible. Zincate treatment may be performed prior to the formation of the electroless Ni plating layer so that the electroless Ni plating layer is selectively formed on the end face of the anode or cathode.

[0085] (Step of Forming External Cathode Electrode or External Anode Electrode) The external electrode typically includes a first external electrode (external anode electrode) connected to the anode section and a second external electrode (external cathode electrode) connected to the cathode section. When the anode section includes an anode body having a dielectric layer, the anode body (second portion) may have a second end face exposed from the outer casing, and the second end face may be electrically connected to the second external electrode. Each external electrode may include a metal layer. The metal layer is, for example, a plating layer. The metal layer includes, for example, at least one selected from the group consisting of nickel (Ni), copper (Cu), zinc (Zn), tin (Sn), silver (Ag), and gold (Au). The metal layer may be formed using a film formation technique such as electrolytic plating, electroless plating, sputtering, vacuum deposition, chemical vapor deposition (CVD), cold spraying, or thermal spraying.

[0086] Each external electrode may have a laminated structure of, for example, a Ni layer and a Sn layer. Preferably, the outer surface of each external electrode is made of a metal that has excellent wettability with solder. Examples of such metals include Sn, Au, Ag, and Pd.

[0087] Each external electrode may have a laminated structure of, for example, a conductive paste layer and a plating layer. In view of excellent wettability with solder, a plating layer having the above-mentioned laminated structure of a Ni layer and a tin layer (such as a Ni / Sn plating layer) may be used as the plating layer.

[0088] To form a plating layer with sufficient thickness and to facilitate its formation on the exposed surface of the exterior body, a conductive layer may be formed before forming the plating layer, and then a plating layer may be formed on the conductive layer. The conductive layer may be a conductive paste layer. The conductive paste layer may be formed so as to cover at least one end face of the anode portion and the cathode portion of the capacitor element or multiple capacitor elements. In this case, the conductive paste layer may be formed so as to cover the end face via a contact layer. Furthermore, the conductive paste layer may be formed so as to cover not only the end face of the anode portion or the cathode portion, but also the surface (side surface, etc.) of the exterior body where the end face is exposed. In this way, the anode portion or the cathode portion of the capacitor element and the conductive paste layer are electrically connected.

[0089] The conductive paste layer can be formed by applying a conductive paste containing conductive particles and a resin material to the surface of the exterior body where the end face of the anode or cathode is exposed, and then drying the paste. Therefore, the conductive paste layer can also be referred to as a conductive resin layer containing conductive particles. The resin material is suitable for bonding to the exterior body and the contact layer, and can increase the bonding strength through chemical bonding (e.g., hydrogen bonding). Examples of conductive particles that can be used include metal particles such as silver or copper, and particles of a conductive inorganic material such as carbon.

[0090] The conductive paste layer may cover not only the surface (e.g., side surface) of the exterior body where the end face of the anode or cathode of the capacitor element is exposed, but also part of a surface (e.g., top surface or bottom surface) intersecting with this surface. Furthermore, when the surface of a substrate constitutes part of the outer surface of the capacitor element, the conductive paste layer may cover part of the surface of the substrate.

[0091] The external electrodes may be formed by a lead frame that covers at least a portion of the conductive layer, and a solder layer or another conductive layer may be formed between the conductive layer and the lead frame to form a strong electrical connection between the lead frame and the conductive layer.

[0092] Specific configurations of electrolytic capacitors according to embodiments of the present disclosure will be illustrated below with reference to the drawings, although the electrolytic capacitors according to the present disclosure are not limited to these.

[0093] Fig. 1 is a cross-sectional view schematically showing an electrolytic capacitor according to one embodiment. Fig. 2 is a cross-sectional view schematically showing the structure of an example of a capacitor element. Fig. 3 is a cross-sectional view schematically showing an electrolytic capacitor according to another embodiment of the present disclosure. Figs. 4, 5, and 6 are cross-sectional views schematically showing electrolytic capacitors according to still other embodiments of the present disclosure.

[0094] 1 , an electrolytic capacitor 100 includes a plurality of capacitor elements 10, an exterior body 14 that seals the capacitor elements 10, a plurality of cathode foils 20, a first external electrode (external anode electrode) 21, and a second external electrode (external cathode electrode) 22. The plurality of capacitor elements 10 and the cathode foils 20 are stacked to form a laminate.

[0095] Capacitor element 10 includes an anode body 3 and a cathode portion 6. Anode body 3 is an anode foil. Anode body 3 has a metal core portion 4 and a porous portion 5, and a dielectric layer (not shown) is formed on at least a portion of the surface of porous portion 5. Cathode portion 6 covers at least a portion of the dielectric layer. Cathode foil 20 is electrically connected to cathode portion 6 of the capacitor element.

[0096] In capacitor element 10, end face 1a of one end (first end) is not covered with a cathode portion 6 and anode body 3 is exposed, while end face 2a of the other end (second end) is covered with cathode portion 6. The portion of anode body 3 not covered with a cathode portion is first portion 1, and the portion of anode body 3 covered with a cathode portion is second portion 2. The end of first portion 1 is the first end, and the end of second portion 2 is the second end. A dielectric layer is formed on the surface of at least porous portion 5 formed in second portion 2. First portion 1 of anode body 3 is also called an anode lead portion. Second portion 2 of anode body 3 is also called a cathode forming portion.

[0097] More specifically, the second portion 2 has a metal core portion 4 and a porous portion 5 formed on the surface of the metal core portion 4 by roughening (etching, etc.). On the other hand, the first portion 1 may or may not have the porous portion 5 on its surface. The dielectric layer is formed along the surface of the porous portion 5. At least a portion of the dielectric layer covers the inner wall surfaces of the pores of the porous portion 5 and is formed along those inner wall surfaces.

[0098] The cathode part 6, which is a cathode layer, includes a solid electrolyte layer 7 that covers at least a portion of the dielectric layer, and cathode extraction layers 8 and 9 that cover at least a portion of the solid electrolyte layer 7. The surface of the dielectric layer has an uneven shape formed in accordance with the shape of the surface of the anode body 3. The solid electrolyte layer 7 can be formed to fill in the unevenness of the dielectric layer. The cathode extraction layer includes, for example, a carbon layer 8 that covers at least a portion of the solid electrolyte layer 7, and a conductive paste layer 9 that covers the carbon layer 8. The conductive paste layer 9 can be, for example, a silver paste layer containing silver particles as metal particles.

[0099] A cathode foil 20 is interposed between the cathode lead layers 8, 9 of the capacitor elements 10 adjacent to each other in the stacking direction of the element stack. The cathode foil 20 is shared by the capacitor elements 10 adjacent to each other in the stacking direction of the stack. A conductive adhesive layer may be interposed between the cathode foil 20 and the capacitor element 10. For example, a conductive adhesive is used for the adhesive layer. The adhesive layer contains, for example, silver. The adhesive layer may be a silver paste layer similar to the conductive paste layer 9.

[0100] It can also be said that the portion of the anode body 3 on which the solid electrolyte layer 7 is formed via the dielectric layer is the second portion 2, and the portion of the anode body 3 on which the solid electrolyte layer 7 is not formed is the first portion 1.

[0101] Of the region of the anode body 3 that does not face the cathode layer, at least a portion adjacent to the cathode layer may have an insulating separation layer (or insulating member) 12 formed to cover the surface of the anode body 3. This prevents contact between the cathode part 6 and the exposed portion (first portion 1) of the anode body 3. The separation layer 12 is, for example, an insulating resin layer.

[0102] The structure sealed with the exterior body 14 has a substantially rectangular parallelepiped outer shape, and the electrolytic capacitor 100 also has a substantially rectangular parallelepiped outer shape. The exterior body 14 has a first main surface 14a, a second main surface 14b opposite the first main surface 14a, and a top surface 14c that is connected to the first main surface 14a and the second main surface 14b and intersects with the stacking direction of the stack. In the element stack, the first end 1a of the capacitor element 10 is exposed at the first main surface 14a.

[0103] Each of the end faces 1 a of the multiple first end portions (first portions) exposed from the exterior body 14 is electrically connected to a first external electrode 21 extending along the first main surface 14 a. In this case, the proportion of the first portion in the anode body can be reduced, thereby increasing the capacity. Also, the contribution of the first portion to the ESR and ESL is reduced.

[0104] Furthermore, end faces 20a of cathode foil 20 are exposed at second main surface 14b from package 14. Each end face of cathode foil 20 exposed from package 14 is electrically connected to a second external electrode 22 extending along second main surface 14b.

[0105] The first external electrode 21 includes, for example, a silver paste layer 21A and a Ni / Sn plating layer 21B. The silver paste layer 21A covers the end face of the first end portion 1a and the first main surface 14a (first surface) of the exterior body 14. The Ni / Sn plating layer 21B covers the silver paste layer 21A. The second external electrode 22 includes a silver paste layer 22A and a Ni / Sn plating layer 22B. The silver paste layer 22A covers the end face of the cathode foil 20 and the second main surface 14b (second surface) of the exterior body 14. The Ni / Sn plating layer 22B covers the silver paste layer 22A.

[0106] In Fig. 1 , the end face of first end portion 1a is flush with first main surface 14a. Also, in Fig. 1 , end face 20a of cathode foil 20 is flush with second main surface 14b. However, the end faces of first end portion 1a and end face 20a of cathode foil 20 do not necessarily have to be flush with the main surface of exterior body 14, and the end face of first end portion 1a may protrude or be recessed relative to first main surface 14a. Similarly, end face 20a of cathode foil 20 may protrude or be recessed relative to second main surface 14b.

[0107] In the electrolytic capacitor shown in Fig. 1 , the thickness T1 of the exterior body located above the laminate in the stacking direction is 24.9% or more of the thickness T2 of the laminate in the stacking direction (T1 / T2 ≥ 0.249). This prevents the cathode foil 20 from being separated from the cathode lead layer 9 due to swelling and deformation of the exterior body, even when the electrolytic capacitor is exposed to high temperatures during reflow or the like. This prevents an increase in ESR and maintains a low ESR. In the example of Fig. 1 , thickness T1 refers to the minimum distance from the laminate to the top surface 14c of the exterior body 14.

[0108] The laminate is supported by a substrate 17. The substrate may be, for example, an insulating substrate. It may be a metal substrate or a printed circuit board with a wiring pattern, as long as it can electrically isolate the first external electrode 21 and the second external electrode 22. A cathode foil may be disposed between the cathode lead layer located on the bottom surface of the element laminate and the substrate 17. The substrate 17 may be, for example, a laminate substrate with conductive wiring patterns formed on its front and back surfaces, and the wiring patterns on the front surface and the back surface may be electrically connected via through holes. The wiring pattern on the front surface may be electrically connected to the cathode portion 6 of the capacitor element laminated in the bottom layer, and the wiring pattern on the back surface may be electrically connected to a third external electrode (not shown). In this case, the third external electrode is electrically connected to the cathode portion 6 of each capacitor element in the element laminate via the substrate 17. Depending on the wiring pattern on the back surface, the third external electrode (cathode) may be arbitrarily disposed in the central region of the bottom surface of the electrolytic capacitor. For example, by arranging the third external electrode close to the first external electrode, ESL can be reduced.

[0109] The substrate 17 is a metal plate, and may have a lead frame structure in which a metal plate is processed into a predetermined shape and bent. A part of the metal plate is exposed from the exterior body, and the exposed part is electrically connected to an external terminal.

[0110] Second Embodiment Fig. 3 is a cross-sectional view schematically illustrating the structure of an electrolytic capacitor according to another embodiment of the present disclosure. The electrolytic capacitor 101 illustrated in Fig. 3 includes a plurality of capacitor elements 10a, 10b, an exterior body 14 that encapsulates the capacitor elements 10a, 10b, a first external electrode (external anode electrode) 21, and a second external electrode (external cathode electrode) 22. The plurality of capacitor elements 10a, 10b are stacked to form an element stack. The two first external electrodes 21 are spaced apart from each other, with one first external electrode 21 covering the first main surface 14a of the exterior body 14 and the other first external electrode 21 covering the second main surface 14b of the exterior body 14.

[0111] The plurality of capacitor elements 10a, b include a first capacitor element 10a having a first direction, which is the direction from the first portion 1 toward the second portion 2 of the anode body 3, and a second capacitor element 10b having a second direction, which is opposite to the first direction, which is the direction from the first portion 1 toward the second portion 2 of the anode body 3. An end face 1a of a first end of the first capacitor element 10a is exposed from the exterior body 14 at a first main surface 14a and is electrically connected to one of the first external electrodes 21. An end face 1a of a first end of the second capacitor element 10b is exposed from the exterior body 14 at a second main surface 14b and is electrically connected to the other of the first external electrodes 21. Meanwhile, although not shown, an end face of the cathode foil 20 is exposed from the exterior body 14 at a third main surface intersecting the first main surface 14a and the second main surface 14b and / or a fourth main surface opposite the third main surface and is electrically connected to a second external electrode 22.

[0112] In the electrolytic capacitor 101, the direction of current flow within the first capacitor element 10a is different from that within the second capacitor element 10b. As a result, the direction of the magnetic field generated by the current is different, and the magnetic flux generated within the element stack is reduced. This makes it possible to reduce the ESL.

[0113] 3, the first capacitor elements 10a and the second capacitor elements 10b are alternately stacked within the element stack. However, the first capacitor elements 10a and the second capacitor elements 10b do not necessarily have to be alternately stacked, and the element stack may have a portion where the first capacitor elements 10a are adjacent to each other and stacked in the same direction, and / or a portion where the second capacitor elements 10b are adjacent to each other and stacked in the same direction. Stacking the first capacitor elements and the second capacitor elements alternately even in part is preferable because it effectively reduces the magnetic flux generated within the element stack and effectively reduces ESL.

[0114] 3 , thickness T1 of the exterior body located above the laminate when viewed from the stacking direction (a direction perpendicular to the main surface of anode body 3, which is foil) is 24.9% or more of thickness T2 of the laminate in the stacking direction (T1 / T2≧0.249). As a result, even when the electrolytic capacitor is exposed to high temperatures due to reflow or the like, peeling of the adhesion between cathode foil 20 and cathode extraction layer 9 caused by swelling and deformation of the exterior body is suppressed, an increase in ESR is suppressed, and a low ESR can be maintained.

[0115] Third Embodiment Fig. 4 is a cross-sectional view schematically illustrating the structure of an electrolytic capacitor according to yet another embodiment of the present disclosure. A capacitor element 10 includes an anode body 3, which is a sintered body of metal particles, and a metal wire 1, a portion of which is embedded in the anode body 3. The metal wire 1 corresponds to the first portion, and the sintered body corresponds to the second portion. Thus, the end face of the anode body is the end face 1a of the tip of the metal wire 1. A dielectric layer 5 is formed on at least a portion of the surface of the anode body 3. A cathode body 6 covers at least a portion of the dielectric layer 5. The cathode body 6 includes a solid electrolyte layer 7 and a cathode extraction layer.

[0116] The anode body 3 can be obtained by molding and sintering a powder containing a valve metal. For example, the valve metal powder and the embedded portion of the metal wire 1 to be connected to the anode body 3 are placed in a mold so as to be embedded in the powder, and the powder is then molded by pressure and sintered to form a porous anode body 3 in which a portion of the metal wire 1 is embedded. Sintering is preferably performed under reduced pressure. The sintered body is subjected to a chemical conversion treatment to form a dielectric layer 5 on the surface of the sintered body.

[0117] The cathode extraction layer includes, for example, a carbon layer 8 that covers at least a portion of the solid electrolyte layer 7, and a conductive paste layer 9 that covers the carbon layer 8. The conductive paste layer 9 may be, for example, a silver paste layer that contains silver particles as metal particles. The carbon layer 8 is made of a composition that contains a conductive carbon material such as graphite.

[0118] Cathode foil 20 is connected to the cathode lead layer via conductive adhesive layer 30. The adhesive layer may be, for example, a conductive adhesive. The adhesive layer may contain, for example, silver. The adhesive layer may be a silver paste layer similar to conductive paste layer 9. Cathode foil 20 is stacked on capacitor element 10 so as to overlap with it, thereby forming a laminate.

[0119] The anode body 3 has a substantially rectangular parallelepiped outer shape, and the electrolytic capacitor 200 also has a substantially rectangular parallelepiped outer shape. The exterior housing 14 has a first main surface 14a and a second main surface 14b opposite the first main surface 14a. The end faces 1a of the protruding ends of the metal wires of the capacitor element 10 are exposed on the first main surface 14a. The end faces 1a exposed from the exterior housing 14 are electrically connected to the first external electrode 21 extending along the first main surface 14a. The end faces 20a of the cathode foil 20 are exposed from the exterior housing 14 on the second main surface 14b. The end faces 20a of the cathode foil 20 exposed from the exterior housing 14 are electrically connected to the second external electrode 22 extending along the second main surface 14b. This reduces the length of the metal wires in the anode portion, thereby increasing capacitance. Furthermore, the contribution of the metal wires to ESR and ESL is reduced.

[0120] An end face 1 a of the tip of the metal wire exposed from the outer casing 14 and an end face 20 a of the cathode foil 20 exposed from the outer casing 14 are respectively covered with a first external electrode 21 and a second external electrode 22. The first external electrode 21 and the second external electrode 22 have the same configuration as the first external electrode 21 and the second external electrode 22 of the electrolytic capacitor 100 shown in FIG.

[0121] 4 , thickness T1 of the exterior body located above the laminate as viewed in the lamination direction of capacitor element 10 and cathode foil 20 is 24.9% or more of thickness T2 of the laminate in the lamination direction (T1 / T2≧0.249). As a result, even when the electrolytic capacitor is exposed to high temperatures due to reflow or the like, peeling of the adhesion between cathode foil 20 and cathode lead layer 9 caused by swelling and deformation of the exterior body is suppressed, an increase in ESR is suppressed, and a low ESR can be maintained.

[0122] 5 is a cross-sectional view schematically illustrating the structure of an electrolytic capacitor according to yet another embodiment of the present disclosure. The electrolytic capacitor 201 according to this embodiment has a similar configuration to the electrolytic capacitor 200 according to the third embodiment, except for the configurations of the first external electrode 21 and the second external electrode 22.

[0123] The first external electrode 21 and the second external electrode 22 of the electrolytic capacitor 201 have silver paste layers (conductive layers) 21A and 22A that respectively cover the first main surface 14a and the second main surface 14b of the exterior body 14. The silver paste layer 21A covers the first main surface 14a of the exterior body 14 and also covers the end faces 1a of the protruding ends of the metal wires. The silver paste layer 22A covers the second main surface 14b of the exterior body 14 and also covers the end face 20a of the cathode foil 20. The first external electrode 21 and the second external electrode 22 each include a first lead frame 21B that covers at least a portion of the silver paste layer 21A and a second lead frame 22B that covers at least a portion of the silver paste layer 22A.

[0124] 5 , thickness T1 of the exterior body located above the laminate as viewed in the lamination direction of capacitor element 10 and cathode foil 20 is 24.9% or more of thickness T2 of the laminate in the lamination direction (T1 / T2≧0.249). As a result, even when the electrolytic capacitor is exposed to high temperatures due to reflow or the like, peeling of the adhesion between cathode foil 20 and cathode lead layer 9 caused by swelling and deformation of the exterior body is suppressed, an increase in ESR is suppressed, and a low ESR can be maintained.

[0125] Fifth Embodiment Fig. 6 is a cross-sectional view schematically illustrating the structure of an electrolytic capacitor according to yet another embodiment of the present disclosure. The electrolytic capacitor 102 according to this embodiment has a configuration similar to that of the electrolytic capacitor 100 according to the first embodiment, except that it does not include the cathode foil 20. A plurality of capacitor elements are stacked such that their cathode extraction layers (conductive paste layers 9) overlap one another to form a laminate. The stacking direction of the laminate is perpendicular to the main surface of the anode foil.

[0126] 6 , the thickness T1 of the exterior body located above the laminate as viewed in the stacking direction is 24.9% or more of the total thickness T2 of the laminate in the stacking direction (T1 / T2≧0.249). As a result, even when the electrolytic capacitor is exposed to high temperatures by reflow or the like, the bulging deformation of the exterior body reduces the adhesion between the first portion 1 of the anode body 3 and the exterior body 14, preventing air, moisture, and the like from entering through gaps between the first portion 1 and the exterior body 14. As a result, an increase in ESR is suppressed even after high-temperature treatment, and a low ESR can be maintained.

[0127] The capacitor element and the laminate can be electrically connected to the wiring pattern on the substrate 17 via the conductive adhesive layer 18. The conductive adhesive layer 18 may extend toward the second external electrode 22. An end face of the conductive adhesive layer 18 may be exposed from the exterior body at the second main surface 14b of the exterior body and electrically connected to the second external electrode 22.

[0128] <<Appendix>> The above embodiments disclose the following techniques. (Technology 1) An electrolytic capacitor comprising: a capacitor element having an anode portion and a cathode portion; a cathode foil electrically connected to the cathode portion; and an exterior body sealing the capacitor element, wherein the capacitor element and the cathode foil are stacked to form a laminate such that the cathode portion of the capacitor element is electrically connected to the cathode foil, the exterior body contains an epoxy resin, and the thickness of the exterior body located above or below the laminate in the stacking direction of the laminate is 24.9% or more of the thickness of the laminate in the stacking direction. (Technology 2) The electrolytic capacitor according to Technology 1, wherein a portion of the cathode foil is exposed from the exterior body, and the exposed portion is electrically connected to an external electrode. (Technology 3) An electrolytic capacitor comprising: a capacitor element having foil-shaped anode and cathode portions; and an exterior housing sealing the capacitor element, wherein an end face of the anode portion is exposed from the exterior housing and the exposed portion is electrically connected to an external electrode, the exterior housing contains an epoxy resin, and a thickness of the exterior housing located above or below the capacitor element as viewed in a direction perpendicular to a main surface of the anode portion is 24.9% or more of the total thickness of the capacitor element in the perpendicular direction. (Technology 4) The electrolytic capacitor according to any one of Technologies 1 to 3, wherein the exterior housing contains a filler having an average particle size of 12 μm to 32 μm, and the proportion of the filler in the exterior housing is 73% by mass or more and 84% by mass or less. (Technology 5) The electrolytic capacitor according to any one of Technologies 1 to 4, wherein the exterior housing contains a filler, and wherein the particle size distribution of the filler is such that the filler having a particle size in the range of 12 μm to 32 μm accounts for 30% to 90% of the total by volume. (Technology 6) The electrolytic capacitor according to any one of Technologies 1 to 5, wherein the epoxy resin contains a biphenyl aralkyl resin. (Technology 7) The linear expansion coefficient α1 of the outer casing is 13×10 －６ / ℃ or more, 21 × 10 －６ / °C or less, and the linear expansion coefficient α2 of the outer casing is 52 × 10 －６ / ℃ or more, 74 x 10 －６ / °C or less. (Technology 8) The electrolytic capacitor according to any one of Technologies 1 to 7, wherein the moisture absorption rate of the epoxy resin at 85°C and a relative humidity of 85% is 0.23% or more and 0.34% or less.

[0129] [Examples] The electrolytic capacitor according to the present disclosure will be specifically described below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0130] Example 1 (1) Fabrication of Electrolytic Capacitor To fabricate an electrolytic capacitor similar to the electrolytic capacitor 100 shown in FIG. 1 , multiple capacitor elements were prepared. An aluminum anode foil with a porous portion formed by etching was used as the anode body. Seven capacitor elements were stacked with a carbon-coated aluminum cathode foil interposed between them to obtain a laminate. The cathode foil was positioned so that a portion of the cathode foil protruded from the cathode layer toward the opposite side of the anode portion.

[0131] The substrate with the laminate placed on it was placed in a predetermined position in a mold, and an epoxy resin composition was poured into the mold. The resin was then cured, and the entire laminate was sealed with an outer casing by compression molding. The epoxy resin composition contained a filler and an epoxy resin, and the filler content was 73 mass% of the total solid content. The epoxy resin used was a polyaromatic biphenyl aralkyl epoxy resin (G720TD Ver.GR, manufactured by Sumitomo Bakelite Co., Ltd.). The linear expansion coefficient α1 of the outer casing measured by the above-mentioned method was 21 × 10 －６ / °C, and the linear expansion coefficient α2 is 74×10 －６ / °C, and the moisture absorption rate of the epoxy resin was 0.34%.

[0132] The thickness T2 of the laminate in the stacking direction was 1.482 mm. The outer casing had a thickness T1 of 0.369 mm above the laminate. The ratio of thickness T1 to thickness T2 was 24.9% (T1 / T2 = 0.249).

[0133] Next, a portion of the first end of the first portion of the anode body and the exterior body were simultaneously removed by cutting to expose the end face of the anode part. Similarly, the protruding portion of the cathode foil and the exterior body were simultaneously removed by cutting to expose the end face of the cathode foil.

[0134] Next, the end faces of the anodes, the exposed surface of the exterior where the anodes are exposed, and the end faces of the cathode foil, the exposed surface of the exterior where the cathode foil is exposed, were covered with silver paste and dried to form a conductive layer (silver paste layer) with a thickness of 20 μm. Further, a Ni plating layer (5 μm thick) and a Sn plating layer (5 μm thick) were sequentially formed on the surface of the conductive layer by barrel plating to form a first external electrode and a second external electrode, thereby obtaining electrolytic capacitor A1.

[0135] (2) Evaluation The electrolytic capacitors after manufacture were subjected to the following evaluations.

[0136] The electrolytic capacitor was connected to an impedance measuring device and an AC voltage was applied to measure the initial ESR at 100 kHz and the initial capacitance C at 100 kHz. ０ was measured.

[0137] The electrolytic capacitor was placed in an environment of 155°C for 24 hours, then placed in an environment of 85°C and 85% relative humidity for 12 hours, and then heated to a maximum temperature of 260°C for a maximum of 30 seconds to simulate reflow.

[0138] After the heat treatment, the electrolytic capacitor was again connected to the impedance measuring device, and the ESR and capacitance were measured in the same manner. ０ , ESR after heat treatment is R １ Then, ΔESR=R １ -R ０ The initial capacitance was evaluated as the ESR increase rate. ０ , the capacitance after heat treatment is C １ Then, ΔCap = C ０ -C １ was evaluated as the amount of decrease in capacity.

[0139] Furthermore, the electrolytic capacitors after the heat treatment were checked for swelling of the exterior body. The height Z in the stacking direction at the location where the displacement in the stacking direction was the largest on the surface of the exterior body located above the stack (upper surface 14c in FIG. 1) was measured. １ The height Z of the upper surface 14c before the heat treatment ０ Difference from ΔZ = Z １ -Z ０ When ΔZ is positive, it means that the exterior body is deformed so as to swell in a convex shape when viewed from the stacking direction.

[0140] Examples 2 and 3 Two electrolytic capacitors having the same structure as in Example 1 were fabricated and evaluated in the same manner.

[0141] Examples 4 to 7, Comparative Examples 1 and 2 In Example 1, the ratio T1 / T2 of the thickness T1 of the exterior body to the thickness T2 of the laminate in the lamination direction was changed. Otherwise, electrolytic capacitors were produced in the same manner as in Example 1 and evaluated in the same manner.

[0142] In Examples 2 and 3, similar to Example 1, the thickness T2 of the laminate in the stacking direction was 1.482 mm, and the thickness T1 of the exterior body above the laminate was 0.369 mm. The ratio of thickness T1 to T2 was 24.9% (T1 / T2 = 0.249). In Example 4, the thickness T2 of the laminate in the stacking direction was 1.482 mm, and the thickness T1 of the exterior body above the laminate was changed to 0.370 mm. The ratio of thickness T1 to T2 was 24.97% (T1 / T2 = 0.2497). In Example 5, the thickness T2 of the laminate in the stacking direction was 1.482 mm, and the thickness T1 of the exterior body above the laminate was changed to 0.371 mm. The ratio of thickness T1 to T2 was 25.04% (T1 / T2 = 0.2504). In Examples 6 and 7, the thickness T2 of the laminate in the stacking direction was set to 1.482 mm, and the thickness T1 of the outer casing above the laminate was changed to 0.372 mm. The ratio of thickness T1 to thickness T2 was 25.1% (T1 / T2 = 0.251).

[0143] The evaluation results are shown in Table 1. In Table 1, electrolytic capacitors A1 to A7 correspond to Examples 1 to 7, and electrolytic capacitors B1 and B2 correspond to Comparative Examples 1 and 2, respectively. Table 2 shows that electrolytic capacitors A1 to A7 with a thickness ratio T1 / T2 of 0.249 (24.9%) or more have small ΔZ and suppressed swelling of the exterior body. Furthermore, it can be seen that when the thickness ratio T1 / T2 is 0.249 (24.9%) or more, ΔESR is significantly reduced compared to electrolytic capacitors B1 and B2 with a thickness ratio T1 / T2 of less than 0.249 (24.9%), and the increase in ESR after high-temperature treatment is dramatically suppressed.

[0144]

[0145] The electrolytic capacitor according to the present invention can maintain a low ESR even in a high-temperature environment, and therefore can be used in a variety of applications.

[0146] 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.

[0147] LIST OF SYMBOLS 1 First portion (anode lead portion), metal wire 1a End surface of first end portion 2 Second portion (cathode forming portion) 2a End surface of second end portion 3 Anode body 4 Metal core portion 5 Porous portion 6 Cathode portion 7 Solid electrolyte layer 8 Carbon layer 9 Silver paste layer 10 Capacitor element 10a First capacitor element 10b Second capacitor element 12 Separation layer (insulating member) 14 Outer casing 14a First main surface of outer casing 14b Second main surface of outer casing 14c Upper surface of outer casing 17 Substrate 18 Resin adhesive layer 20 Cathode foil 20a End surface of cathode foil 21 First external electrode (external anode electrode) 21A Silver paste layer 21B Ni / Sn plating layer, first lead frame 22 Second external electrode (external cathode electrode) 22A Silver paste layer 22B Ni / Sn plating layer, second lead frame 100 to 102, 200, 201 electrolytic capacitor

Claims

1. An electrolytic capacitor comprising: a capacitor element having an anode portion and a cathode portion; a cathode foil electrically connected to the cathode portion; and an exterior body sealing the capacitor element, wherein the capacitor element and the cathode foil are laminated together so that the cathode portion of the capacitor element is electrically connected to the cathode foil, the exterior body containing an epoxy resin, and the thickness of the exterior body located above or below the laminate when viewed from the stacking direction of the laminate is 24.9% or more of the thickness of the laminate in the stacking direction.

2. The electrolytic capacitor according to claim 1, wherein a portion of said cathode foil is exposed from said exterior body, and the exposed portion is electrically connected to an external electrode.

3. An electrolytic capacitor comprising: a capacitor element having foil-shaped anode and cathode portions; and an exterior body sealing the capacitor element, wherein an end face of the anode portion is exposed from the exterior body and the exposed portion is electrically connected to an external electrode, the exterior body contains an epoxy resin, and the thickness of the exterior body located above or below the capacitor element when viewed in a direction perpendicular to a main surface of the anode portion is 24.9% or more of the total thickness of the capacitor element in the perpendicular direction.

4. An electrolytic capacitor as described in any one of claims 1 to 3, wherein the outer casing contains a filler having an average particle size of 12 μm to 32 μm, and the proportion of the filler in the outer casing is 73 mass % or more and 84 mass % or less.

5. The electrolytic capacitor according to any one of claims 1 to 3, wherein the exterior body contains a filler, and in the particle size distribution of the filler, the filler having a particle size in the range of 12 μm to 32 μm accounts for 30% to 90% of the total filler by volume.

6. The electrolytic capacitor according to any one of claims 1 to 3, wherein the epoxy resin includes a biphenyl aralkyl type epoxy resin.

7. The linear expansion coefficient α1 of the exterior body is 13×10 －６ / ℃ or more, 21 x 10 －６ / °C or less, and the linear expansion coefficient α2 of the outer casing is 52×10 －６ / ℃ or more, 74 x 10 －６ The electrolytic capacitor according to any one of claims 1 to 3, wherein the temperature is 0.1 to 1.5°C.

8. The electrolytic capacitor according to any one of claims 1 to 3, wherein the moisture absorption rate of the epoxy resin at 85°C and a relative humidity of 85% is 0.23% or more and 0.34% or less.

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