solid electrolytic capacitor

Abstract

A solid electrolytic capacitor (1) according to the present disclosure comprises: a capacitor element (2); a lead terminal (4) and a lead terminal (5), which are electrically connected to the capacitor element (2); and an outer case (3) which seals a part of the lead terminal (4), a part of the lead terminal (5) and the capacitor element (2). The outer case (3) comprises a resin part that contains a resin. In the resin part, if a glass transition temperature Tg of the resin is the temperature at which the loss elastic modulus stops increasing and takes a downward turn as determined by nanoscale dynamic viscoelasticity measurement that utilizes a nanoindentation method, the glass transition temperature Tg is 140°C or less; and within the temperature range from the glass transition temperature Tg to 260°C, the hardness of the resin part as determined by the nanoindentation method is 0.08 GPa or less.

Description

[Technical Field]

[0001] The present disclosure relates to solid electrolytic capacitors. [Background technology]

[0002] Solid electrolytic capacitors are used in a variety of electronic devices due to their low equivalent series resistance (ESR) and excellent frequency characteristics. A solid electrolytic capacitor includes a capacitor element, lead terminals electrically connected to the capacitor element, and an outer casing that seals a portion of the lead terminals and the capacitor element. By using a solid conductive polymer as the electrolyte in the capacitor element, solid electrolytic capacitors exhibit low ESR and excellent frequency characteristics.

[0003] Solid electrolytic capacitors are typically soldered to a substrate through a reflow process that exposes them to high temperatures. During this process, thermal stress can cause cracks to form in the exterior housing, weakening the sealing ability of the housing. When the sealing ability is weakened, moisture and oxygen penetrate the solid electrolytic capacitor, causing the conductive polymer in the solid electrolyte layer to oxidize and deteriorate. This results in a decrease in the conductivity of the solid electrolyte layer, leading to a decrease in the capacitance of the solid electrolytic capacitor and an increase in the ESR. Therefore, various solid electrolytic capacitors have been proposed with the aim of improving the sealing ability of the exterior housing.

[0004] For example, Patent Document 1 discloses a solid electrolytic capacitor comprising: a capacitor element including a sintered porous anode body, a dielectric disposed on the anode body, and a solid electrolyte disposed on the dielectric; an anode lead extending from a surface of the capacitor element; an anode termination electrically connected to the anode lead, and a cathode termination electrically connected to the solid electrolyte; and a casing material encapsulating the capacitor element and the anode lead, the casing material being formed from a curable resinous matrix having a thermal expansion coefficient of about 42 ppm / °C or less at a temperature higher than the glass transition temperature of the resinous matrix; the capacitor exhibits an initial equivalent series resistance of about 200 milliohms or less, measured at an operating frequency of 100 kHz and a temperature of 23°C, and wherein the ratio of the equivalent series resistance of the capacitor after exposure to a temperature of 125°C for 560 hours to the initial equivalent series resistance of the capacitor is about 2.0 or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2021-528851 Summary of the Invention [Problem to be solved by the invention]

[0006] At high temperatures, thermal expansion and contraction occur inside solid electrolytic capacitors, including the exterior housing, capacitor element, and lead terminals. Because the exterior housing encapsulates the capacitor element and also encapsulates part of the lead terminals, stress is also applied to the exterior housing from the capacitor element and lead terminals. This makes it easier for cracks to form inside the exterior housing. At the same time, cracks and peeling are also more likely to occur at the interfaces between the exterior housing and the capacitor element, and between the exterior housing and the lead terminals.

[0007] To prevent cracks and delamination caused by these internal stresses and improve the sealing performance of the exterior body, conventional techniques exist for reducing the thermal expansion and contraction of the exterior body. However, depending on the correlation between the thermal expansion coefficient of the exterior body and the thermal expansion coefficients of the capacitor element and lead terminals that are the adherends, the internal stress may be increased, making conventional techniques insufficient as technical solutions. Therefore, specifying the material properties of the exterior body that solely contribute to internal stress, i.e., the elastic modulus and hardness of the exterior body, is important for preventing cracks and delamination that occur at the interfaces between the exterior body and the capacitor element or lead terminals, and improving sealing performance.

[0008] In light of these circumstances, an object of the present disclosure is to provide a solid electrolytic capacitor having excellent heat resistance and having a high sealing property of its exterior even at high temperatures. [Means for solving the problem]

[0009] The present disclosure relates to a solid electrolytic capacitor including a capacitor element, lead terminals electrically connected to the capacitor element, and an exterior housing sealing a portion of the lead terminal and the capacitor element, wherein the exterior housing includes a resin portion containing a resin, and when the glass transition temperature Tg of the resin is defined as the temperature at which the loss modulus of the resin portion measured by nanoscale dynamic viscoelasticity measurement using nanoindentation starts to decrease, the glass transition temperature Tg is 140°C or lower, and the hardness of the resin portion measured by nanoindentation in the temperature range from the glass transition temperature Tg to 260°C is 0.08 GPa or lower.

[0010] As long as combinations are possible, the features of two or more claims arbitrarily selected from the claims set forth in the appended claims may be combined. Furthermore, as long as combinations are possible, the configurations described in the embodiments may be combined arbitrarily. [Effects of the Invention]

[0011] According to the present disclosure, a solid electrolytic capacitor with excellent heat resistance can be obtained. 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. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a longitudinal sectional view schematically illustrating a solid electrolytic capacitor according to an embodiment of the present disclosure. [Figure 2] 1 is a graph showing the relationship between the temperature and loss modulus of a resin contained in an exterior body of a solid electrolytic capacitor. [Figure 3] 1 is a graph showing the relationship between the temperature and hardness of a resin portion included in an exterior body of a solid electrolytic capacitor. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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 other materials may be applied as long as the invention of the present disclosure can be implemented. In this specification, the expression "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 of numerical values ​​related to 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 greater than the upper limit.

[0014] The solid electrolytic capacitor according to this embodiment includes a capacitor element, lead terminals electrically connected to the capacitor element, and an exterior housing that seals a portion of the lead terminals and the capacitor element. The exterior housing includes a resin portion containing a resin. Hereinafter, the resin may be referred to as "resin (R)." The glass transition temperature (Tg) of the resin (R) is defined as the temperature at which the loss modulus of the resin portion, measured by nanoscale dynamic viscoelasticity measurement using nanoindentation, changes from increasing to decreasing. The glass transition temperature (Tg) is 140°C or lower. Furthermore, the hardness of the resin portion measured by nanoindentation in the temperature range from the glass transition temperature (Tg) to 260°C (in other words, the hardness measured by nanoindentation) is 0.08 GPa or lower. In another embodiment, the hardness of the resin portion measured by nanoindentation in the temperature range from 140°C to 260°C may be 0.08 GPa or lower.

[0015] As described above, in order to improve the heat resistance of solid electrolytic capacitors, it is important to prevent cracks and peeling that occur at the interfaces between the exterior body and the capacitor element and lead terminals. As a result of investigations, the inventors of the present application have newly discovered that by controlling the glass transition temperature Tg of the resin (R) contained in the exterior body and the hardness of the resin portion containing the resin (R), the stress applied to the exterior body from the capacitor element and lead terminals can be alleviated.

[0016] When a resin having a glass transition temperature Tg is heated, it changes from a glassy state to a rubbery state at the glass transition temperature Tg. The resin (R) contained in the outer casing of the solid electrolytic capacitor according to this embodiment has a glass transition temperature Tg of 140°C or less, and becomes rubbery in the temperature range from the glass transition temperature Tg to 260°C or less. Furthermore, within this temperature range, the resin portion containing the resin (R) has a low hardness of 0.08 GPa or less as measured by nanoindentation.

[0017] Solid electrolytic capacitors are generally exposed to high temperatures (for example, temperatures in the range of 180°C to 260°C) during processes such as reflow soldering. Solid electrolytic capacitors are also sometimes used at high temperatures. When exposed to high temperatures, each component of the solid electrolytic capacitor thermally expands. However, because the thermal expansion coefficients of the components differ, thermal stress occurs inside the solid electrolytic capacitor. As a result, when conventional solid electrolytic capacitors are exposed to high temperatures, cracks and peeling easily occur at the interface between the exterior body and the capacitor element, and at the interface between the exterior body and the lead terminals.

[0018] When the solid electrolytic capacitor according to this embodiment is exposed to temperatures equal to or higher than the glass transition temperature Tg, the resin (R) contained in the outer casing becomes rubbery, and the hardness of the resin portion containing the resin (R) is sufficiently low, at 0.08 GPa or less. Therefore, the outer casing can distribute and mitigate the stress applied to the outer casing from the capacitor element and lead terminals throughout the entire casing. As a result, cracks inside the outer casing can be suppressed, and cracks and delamination at the interfaces between the outer casing, the capacitor element, and the lead terminals can also be suppressed. As described above, the solid electrolytic capacitor according to this embodiment has excellent sealing properties and heat resistance even at high temperatures.

[0019] (Resin part) The resin portion includes a resin (R). The resin portion may be composed of only the resin (R), or may include components other than the resin (R). Examples of components other than the resin (R) include a curing aid (curing accelerator), a stress reducing agent (flexible agent), a mold release agent, a coupling agent, a colorant, an ion scavenger, etc. The proportion of the resin (R) in the resin portion may be in the range of 70 to 100 mass%, 80 to 100 mass%, or 90 to 100 mass%.

[0020] (Resin(R)) The resin (R) contained in the resin portion may be composed of only one type of resin, or may contain multiple types of resins. When the resin (R) contains multiple types of resins, it is sufficient that 50 mass % or more of the resins constituting the resin (R) satisfy the above condition (glass transition temperature Tg). Preferably, all of the resins contained in the resin (R) satisfy the above condition (glass transition temperature Tg).

[0021] The glass transition temperature Tg of the resin (R) can be determined by nanoscale dynamic viscoelasticity measurement (nanoDMA) using the nanoindentation method. For example, it can be determined by cutting out a portion of the outer casing and performing the measurement on the resin portion of the cross section. An example of the measurement method will be described in detail in the Examples. When the resin portion contains a filler, the measurement is performed by contacting a triangular pyramidal indenter with a portion where the filler is not present. When the loss modulus of the resin (R) is measured at each temperature while increasing the temperature, a behavior in which the loss modulus increases and then decreases is observed. The temperature at which the loss modulus changes from increasing to decreasing is defined as the glass transition temperature Tg. In other words, when the loss modulus of the resin portion is measured while increasing the temperature by nanoscale dynamic viscoelasticity measurement using the nanoindentation method, the temperature at which the loss modulus changes from increasing to decreasing is defined as the glass transition temperature Tg of the resin (R). The loss modulus can be determined, for example, by performing dynamic viscoelasticity measurement on any five points of the resin portion and calculating the average of the measured values.

[0022] The glass transition temperature Tg of the resin (R) may be equal to or lower than 125° C. When the glass transition temperature Tg of the resin (R) is equal to or lower than 125° C., the exterior body can relax stress over a wide temperature range and maintain high sealing properties.

[0023] The glass transition temperature Tg depends on the type, structure, crosslink density, etc. of the resin. For example, the glass transition temperature Tg tends to decrease when the crosslink density of the resin is reduced.

[0024] The hardness of the resin portion containing the resin (R) is also measured using the nanoindentation method, similar to the glass transition point of the resin (R). For example, it can be determined by cutting out a portion of the outer casing and performing continuous stiffness measurements on the cross-section of the resin portion. An example of a detailed measurement method will be described in the Examples. When the resin portion contains a filler, the measurement is performed by contacting a triangular pyramidal indenter with a portion where the filler is not present. The hardness can be determined, for example, by measuring five arbitrary points on the resin portion and averaging the measured values. From the viewpoint of ensuring that the outer casing sufficiently relieves stress from the capacitor element and the lead terminals at high temperatures and maintains high sealing performance, the hardness of the resin portion in the temperature range from the glass transition point Tg to 260°C may be 0.05 GPa or less, or 0.03 GPa or less. In another embodiment, the hardness of the resin portion in the temperature range from 140°C to 260°C may be 0.05 GPa or less, or 0.03 GPa or less.

[0025] The hardness of the resin portion may be changed by changing the type, structure, crosslink density, etc. of the resin (R), similarly to the glass transition temperature Tg. For example, increasing the distance between crosslink points of the resin (R) contained in the resin portion tends to decrease the hardness.

[0026] The resin (R) is not particularly limited as long as it has the above properties, and may be, for example, a thermosetting resin or a thermoplastic resin.

[0027] Examples of thermosetting resins include epoxy resins, phenolic resins, urea resins, polyimide resins, polyamideimide resins, polyurethane resins, diallyl phthalate resins, unsaturated polyester resins, etc. As the resin (R), one of these resins may be used alone, or two or more may be used in combination.

[0028] Examples of thermoplastic resins that can be used include polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), etc. As the resin (R), one of these resins may be used alone, or two or more of them may be used in combination.

[0029] The resin (R) may contain an epoxy resin or may be an epoxy resin. Epoxy resins have excellent electrical insulation, water resistance, and chemical resistance, and the glass transition temperature (Tg) and hardness of the resin (R) are easily controlled. Epoxy resins are generally obtained by crosslinking a base material, which is a monomer or polymer (prepolymer) having an epoxy group, with a curing agent. Prepolymers such as polyaromatic epoxy resins, biphenyl epoxy resins, cresol novolac epoxy resins, and dicyclopentadiene epoxy resins may be used as the base material. Polyaromatic epoxy resins are epoxy resins with multiple polycyclic aromatic rings in their main skeleton. Polyaromatic epoxy resins have low viscosity at high temperatures. Therefore, for example, when a lead terminal is subjected to a blasting treatment, the adhesive strength between the outer casing containing the polyaromatic epoxy resin and the lead terminal is physically increased due to the anchor effect.

[0030] When resin (R) contains an epoxy resin, the glass transition temperature (Tg) of resin (R) depends on the crosslink density and structure of the epoxy resin. Therefore, the glass transition temperature (Tg) can be controlled by, for example, the type of base resin and curing agent, the blending ratio of the base resin and curing agent, and the molecular weight of the base resin. For example, when the concentration of functional groups (epoxy groups) in the base resin is low or when the epoxy equivalent weight of the base resin is low, the crosslink density of the epoxy resin decreases, and the glass transition temperature (Tg) tends to decrease. Furthermore, for base resins with the same skeletal structure, the fewer the number of nuclei, the fewer the number of functional groups, which reduces the crosslink density of the epoxy resin and tends to lower the glass transition temperature (Tg). Similarly, for base resins with similar epoxy equivalent weights, the fewer the number of nuclei, the fewer the number of functional groups, which reduces the crosslink density of the epoxy resin and tends to lower the glass transition temperature (Tg). On the other hand, when the skeletal structure of an epoxy resin is highly rigid or symmetrical, the glass transition temperature (Tg) tends to be higher. Similarly, when an epoxy resin contains bulky substituents, the glass transition temperature (Tg) also tends to be higher.

[0031] The curing agent is not particularly limited and is selected appropriately depending on the type of base resin. Examples of curing agents 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. In order to obtain the resin (R) by reacting the base resin and curing agent, a polymerization initiator, a catalyst, etc. may be used in addition to the base resin and curing agent. The polymerization initiator, catalyst, etc. may also be selected appropriately depending on the type of base resin. Examples of catalysts include phosphorus compounds such as triphenylphosphine and its modified products, amines, and imidazoles.

[0032] (filler) The outer casing may further include a filler dispersed in the resin portion. The outer casing may be composed of a resin portion and a filler dispersed in the resin portion. The filler is dispersed in the resin portion containing the resin (R). The filler is not particularly limited, and known fillers can be used. For example, insulating fillers such as insulating particles and insulating fibers are 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.

[0033] 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 and lead terminals. It also reduces the elasticity of the exterior body, which tends to result in a low measured hardness. Furthermore, a low filler content makes it easier for the resin portion to fill the gaps between the capacitor element and the lead terminals. Furthermore, when multiple capacitor elements are included, it also makes it easier for the resin portion 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 75% to 90% by mass. The filler content may also be 78% by mass or more and 86% by mass or less.

[0034] For a given filler content in an outer casing, a smaller filler particle size allows the resin (R) present between the filler particles to act as a buffer, making it easier to relieve stress. As a result, the entire outer casing can more easily relieve stress. Furthermore, a smaller filler particle size makes it easier for the resin to fill the gaps between the capacitor elements and the lead terminals. Furthermore, when multiple capacitor elements are included, it also makes it easier to fill the gaps between the capacitor elements. Therefore, the maximum particle size of the filler may be 100 μm or less (e.g., 55 μm or less). Setting the maximum particle size to 55 μm or less makes it easier to relieve stress, as described above. Here, the maximum particle size refers to the particle size of the largest filler particle contained in the outer casing. The maximum particle size can be determined by photographing a cross-section of the outer casing, 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 circles having the same area as the cross-sectional area of ​​each particle.

[0035] The solid electrolytic capacitor according to this embodiment has high heat resistance and maintains the sealing properties of the exterior body even at high temperatures. This prevents moisture and oxygen from entering the solid electrolytic capacitor, making it less likely for the conductive polymer in the solid electrolyte contained in the capacitor element to deteriorate. Therefore, the capacitance and ESR of the solid electrolytic capacitor are maintained even when exposed to high temperatures.

[0036] The following formula: Capacitance change rate (%) = 100 × (C1 - C0) / C0 (where C0 is the initial capacitance and C1 is the capacitance after heating at 125°C for 7000 hours) The average value of the capacitance change rate expressed by the formula may be -5.0% or more. The average value may be -3.0% or more, or -1.0% or more. Here, the average value is the average value of the capacitance change rates of at least 60 (e.g., 100) solid electrolytic capacitors. The capacitance can be measured, for example, using an LCR meter. The capacitance change rate of one solid electrolytic capacitor is preferably -5.0% or more, and more preferably -3.0% or more.

[0037] The solid electrolytic capacitor according to this embodiment includes a capacitor element, lead terminals, and an exterior body, and may include other components as necessary. An example of the configuration of the solid electrolytic capacitor is described below. However, the configuration of the solid electrolytic capacitor is not limited to the following example. Known configurations may be applied to configurations other than those characteristic of the solid electrolytic capacitor according to this embodiment. The solid electrolytic capacitor may also include a case made of metal or the like in addition to the exterior body.

[0038] [Capacitor element] A solid electrolytic capacitor has one or more capacitor elements. The number of capacitor elements included in a solid electrolytic capacitor is determined depending on the application. When two or more capacitor elements are included, the capacitor elements are usually stacked. In this case, an anode lead terminal is connected to an anode stack where multiple anode parts are stacked, and a cathode lead terminal is connected to a cathode stack where multiple cathode parts are stacked.

[0039] (anode body) The anode body may contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials may be used alone or in combination of two or more. Examples of preferred valve metals include aluminum, tantalum, niobium, and titanium. The surface of the anode body may have a porous structure. For example, the porous structure can be obtained by roughening the surface of a substrate (such as a foil-shaped or plate-shaped substrate) containing a valve metal by etching or the like. The anode body may also be a compact of particles containing a valve metal, or a sintered body thereof. When the anode body is a sintered body, the anode portion may include an anode wire partially embedded in the sintered body. In this case, one end of the anode lead terminal is connected to the anode wire.

[0040] (dielectric layer) The dielectric layer is an insulating layer formed to cover at least a portion of the surface of the anode body. It is not particularly limited as long as it functions as a dielectric layer. For example, it can be formed by anodizing the valve metal on the surface of the anode body using a chemical conversion treatment or the like. In this case, the dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3.

[0041] (solid electrolyte layer) The solid electrolyte layer is formed so as to cover at least a portion of the dielectric layer. The solid electrolyte layer includes a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, and derivatives thereof. Examples of the derivatives include poly(3,4-ethylenedioxythiophene).

[0042] A dopant may be added to the conductive polymer. The dopant can be selected depending on the conductive polymer, and known dopants may be used. Examples of the dopant include naphthalenesulfonic acid, p-toluenesulfonic acid, polystyrenesulfonic acid, and salts thereof.

[0043] The solid electrolyte layer containing the conductive polymer may be formed by polymerizing a raw material monomer on the dielectric layer, or by depositing a liquid containing the conductive polymer on the dielectric layer and then drying the liquid.

[0044] (Cathode extraction layer) The cathode extraction layer may include a first layer covering at least a portion of the solid electrolyte layer, or may include the first layer and a second layer covering the first layer. Both the first layer and the second layer are conductive. The first layer is formed, for example, from a layer containing conductive particles or metal foil. Examples of conductive particles include conductive carbon and metal powder. The second layer is formed, for example, from a layer containing metal powder or metal foil. The layer containing metal powder is formed, for example, using a composition (metal paste) containing metal powder such as silver particles and a resin (binder resin).

[0045] (Adhesive layer) The adhesive layer connects the cathode lead terminal and the cathode part. The adhesive layer contains conductive particles. Examples of the conductive particles include metal particles (e.g., silver particles). The adhesive layer is formed using a metal paste containing the metal particles and a resin.

[0046] [Lead terminal] The lead terminals include an anode lead terminal and a cathode lead terminal. One end of the anode lead terminal and the cathode lead terminal is sealed together with the capacitor element by an exterior housing. One end of the anode lead terminal is electrically connected to the anode portion of the capacitor element, and the other end is exposed to the exterior of the exterior housing. One end of the cathode lead terminal is electrically connected to the cathode portion of the capacitor element, and the other end is exposed to the exterior of the exterior housing. The anode lead terminal and the cathode lead terminal exposed from the exterior housing are used for soldering to a substrate on which the solid electrolytic capacitor is to be mounted, for example.

[0047] The anode lead terminal and the cathode lead terminal can be any lead terminal commonly used in solid electrolytic capacitors without any particular restrictions. Examples of materials include metals such as copper or alloys thereof. The surfaces of the anode lead terminal and the cathode lead terminal may be subjected to a blasting treatment. The blasting treatment improves the adhesive strength between the lead terminal and the outer casing, making it less likely for cracks or peeling to occur at the interface.

[0048] [Exterior body] The exterior casing seals the capacitor element and a portion of the anode lead terminal and the cathode lead terminal. The exterior casing may be any of the above-described exterior casings.

[0049] The exterior body can be formed using molding techniques such as injection molding, insert molding, and compression molding. An uncured resin mixture is used for molding. For example, a resin mixture containing a main agent (monomer, prepolymer, etc.) that is the raw material for the resin (R), a curing agent, a filler, etc. is used. Molding is performed, for example, by using a predetermined mold to fill the resin mixture into predetermined locations so as to cover the capacitor element and one end of the lead terminal. The resin mixture hardens during molding, and an exterior body including a resin portion containing the resin (R) is formed.

[0050] The method for manufacturing the solid electrolytic capacitor according to this embodiment is not particularly limited, and known processes may be used. For example, the capacitor element is manufactured by a manufacturing method including the steps of forming a dielectric layer to cover at least a portion of an anode body, forming a solid electrolyte layer to cover at least a portion of the dielectric layer, and forming a cathode extraction layer on at least a portion of the solid electrolyte layer. The step of forming the cathode extraction layer includes, for example, the steps of forming a carbon layer and forming a silver paste layer on at least a portion of the carbon layer. Furthermore, the method may include the step of preparing an anode body prior to the step of forming the dielectric layer.

[0051] The solid electrolytic capacitor is manufactured by a manufacturing method including, for example, a step of electrically connecting lead terminals to a capacitor element and a step of covering the capacitor element and a part of the lead terminals with an exterior body (sealing step). The solid electrolytic capacitor may be a wound type, or may be either a chip type or a laminate type.

[0052] The configuration of an example of a solid electrolytic capacitor according to this embodiment will be described with reference to Fig. 1. The components described above can be applied to the components of the example described below. Furthermore, the components of the example described below can be modified based on the above description.

[0053] 1 is a cross-sectional view schematically illustrating the structure of an example solid electrolytic capacitor 1 according to this embodiment. The solid electrolytic capacitor 1 includes a capacitor element 2, lead terminals (anode lead terminal 4 and cathode lead terminal 5), and an exterior housing 3 that seals portions of the lead terminals and the capacitor element 2. A portion of the anode lead terminal 4 and a portion of the cathode lead terminal 5 are exposed from the exterior housing 3. The exterior housing 3 is the same as that described above.

[0054] Capacitor element 2 includes an anode body 6 constituting an anode portion, a dielectric layer 7 covering anode body 6, and a cathode portion 8 covering dielectric layer 7.

[0055] The anode body 6 includes a region facing the cathode portion 8 and a region not facing the cathode portion 8. Of the region of the anode body 6 not facing the cathode portion 8, an insulating separation layer 13 is formed in a strip-like shape on the surface of the anode body 6 in a portion adjacent to the cathode portion 8, thereby restricting contact between the cathode portion 8 and the anode body 6. Of the region of the anode body 6 not facing the cathode portion 8, another part is electrically connected to the anode lead terminal 4 by welding. The cathode lead terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0056] Cathode section 8 includes a solid electrolyte layer 9 covering dielectric layer 7, and a cathode extraction layer 10 covering solid electrolyte layer 9. Cathode extraction layer 10 has a carbon layer 11 and a silver paste layer 12.

[0057] (Addendum) Based on the above description, the following techniques are disclosed. (Technology 1) A solid electrolytic capacitor including a capacitor element, a lead terminal electrically connected to the capacitor element, and an exterior body sealing a portion of the lead terminal and the capacitor element, the exterior body includes a resin portion containing a resin, a glass transition point Tg of the resin, which is defined as a temperature at which a loss modulus measured by nanoscale dynamic viscoelasticity measurement using a nanoindentation method in the resin portion changes from increasing to decreasing, the glass transition point Tg is 140°C or lower; A solid electrolytic capacitor, wherein the hardness of the resin portion measured by nanoindentation in a temperature range of not less than the glass transition point Tg and not more than 260°C is not more than 0.08 GPa. (Technology 2) The solid electrolytic capacitor according to claim 1, wherein the glass transition temperature Tg of the resin is 125° C. or lower. (Technology 3) 3. The solid electrolytic capacitor according to claim 1, wherein the resin is an epoxy resin. (Technology 4) 4. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the exterior body further includes a filler dispersed in the resin portion. (Technology 5) 5. The solid electrolytic capacitor according to claim 4, wherein the content of the filler in the exterior body is in the range of 75% by mass to 90% by mass. (Technology 6) 6. The solid electrolytic capacitor according to claim 4, wherein the maximum particle size of the filler is 55 μm or less. (Technology 7) The following formula: Capacitance change rate (%) = 100 × (C1 - C0) / C0 (where C0 is the initial capacitance and C1 is the capacitance after heating at 125°C for 7000 hours) 7. The solid electrolytic capacitor according to any one of claims 1 to 6, wherein the average value of the capacitance change rate expressed by the following formula is −5.0% or more. [Example]

[0058] The present disclosure will be specifically described below based on examples, but the present disclosure is not limited to the following examples. In these examples, solid electrolytic capacitors with different exterior bodies were fabricated and evaluated for heat resistance.

[0059] (1) Fabrication of solid electrolytic capacitors A1, B1, and B2 Solid electrolytic capacitors A1, B1 and B2 were fabricated in the following manner.

[0060] (1-1) Fabrication of capacitor elements (1-a) Preparation of anode body An anode body was prepared by etching both sides of an aluminum foil (thickness: 100 μm).

[0061] (1-b) Formation of dielectric layer The anode body was immersed in a 0.3 mass % phosphoric acid solution (liquid temperature 70°C) and a DC voltage of 70 V was applied for 20 minutes to form a dielectric layer containing aluminum oxide (Al2O3) on the surface of the anode body.

[0062] (1-c) Formation of solid electrolyte layer In the anode body on which the dielectric layer was formed, insulating resist tape was attached between the region where the solid electrolyte layer was to be formed and the region where the solid electrolyte layer was not to be formed, thereby forming a separation portion. An aqueous solution containing pyrrole monomer and p-toluenesulfonic acid was prepared. The pyrrole monomer concentration in the aqueous solution was 0.5 mol / L, and the p-toluenesulfonic acid concentration was 0.3 mol / L. The anode body on which the dielectric layer was formed in (1-b) above and a counter electrode were immersed in the obtained aqueous solution. In this state, electrolytic polymerization was performed at 25°C with a polymerization voltage of 3 V (polymerization potential relative to a silver reference electrode) to form a solid electrolyte layer.

[0063] (1-d) Formation of cathode extraction layer The anode body obtained in (1-c) was immersed in a dispersion of graphite particles in water. The dispersion applied to the anode body was then dried to form a carbon layer on the surface of the solid electrolyte layer. Drying was performed at 150°C for 30 minutes.

[0064] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the carbon layer and heated at 150°C for 30 minutes to harden the binder resin, forming a silver paste layer. In this way, a cathode extraction layer composed of the carbon layer and the silver paste layer was formed, and a cathode part including a solid electrolyte layer and a cathode extraction layer was formed. A capacitor element was fabricated by steps (1-a) to (1-d).

[0065] (1-2) Assembly of solid electrolytic capacitors The cathode part of the capacitor element obtained in (1-d) was joined to one end of the cathode lead terminal with an adhesive layer made of a conductive adhesive. One end of the anode body protruding from the capacitor element was joined to one end of the anode lead terminal by laser welding.

[0066] Next, an exterior body was formed around the capacitor element and the lead terminals by molding using the following resin mixtures 1 to 3. At this time, the other end of the anode lead terminal and the other end of the cathode lead terminal were exposed from the exterior body. In this way, solid electrolytic capacitors A1, B1, and B2 were completed. As the exterior body materials, the following resin mixture 1 was used for solid electrolytic capacitor A1, the following resin mixture 2 was used for solid electrolytic capacitor B1, and the following resin mixture 3 was used for solid electrolytic capacitor B2. The resin part of the exterior body formed from resin mixture 1 contains a polyaromatic ring epoxy resin as the resin (R). The following resin mixtures have fillers dispersed therein.

[0067] Resin mixture 1: A resin mixture in which the glass transition temperature Tg measured by nano-DMA in the resin part formed upon hardening is around 125°C, and the hardness of the resin part is 0.08 or less in the temperature range above the glass transition temperature Tg. Resin mixture 2: A resin mixture in which the glass transition temperature Tg measured by nano-DMA in the resin part formed upon curing is around 145°C, and the hardness of the resin part is greater than 0.08 in the temperature range above the glass transition temperature Tg. Resin mixture 3: A resin mixture in which the glass transition temperature Tg measured by nano-DMA in the resin part formed upon curing is around 165°C, and the hardness of the resin part is greater than 0.08 in the temperature range above the glass transition temperature Tg.

[0068] (2) Evaluation The solid electrolytic capacitors A1, B1 and B2 fabricated in (1) were evaluated as follows.

[0069] (2-1) Evaluation of the exterior body (2-a) Glass transition temperature Tg of resin A portion of the outer casing of each of the solid electrolytic capacitors A1, B1, and B2 was cut out to serve as a sample. Nanoscale dynamic viscoelasticity measurements (nanoDMA) were performed using the nanoindentation method at five points on the cross section of each sample that did not contain filler, as described above. Specifically, a Triboindenter TI950 manufactured by Hysitron was used to measure the nanoscale dynamic viscoelasticity (particularly the loss modulus) at room temperature (25°C), 85°C, 105°C, 125°C, 145°C, 165°C, and 260°C. Measurements were performed by gradually increasing the temperature of the sample in a nitrogen atmosphere. Specifically, the sample was heated at a rate of 20°C / min, and after reaching the measurement temperature, it was held at that temperature for 20 minutes, after which measurements were performed at that temperature. The measurement frequency was 100 Hz. The nanoscale dynamic viscoelasticity measurements were performed as follows. A triangular diamond indenter (Berkovich indenter) was placed in contact with the filler-free portion of the sample cross section (the resin portion), and the indenter was subjected to minute vibrations. The response amplitude and phase difference to the vibration were obtained as a function of time, and the stiffness and sample damping were calculated. The loss modulus at each temperature was calculated using the calculated sample damping results. The loss modulus at each temperature was determined by averaging the measurements at five points. The results are shown in Figure 2.

[0070] When the temperature was increased from 25°C to 260°C, the loss modulus increased and then decreased. The point at which the loss modulus changed from increasing to decreasing was determined as the glass transition temperature (Tg). The glass transition temperatures (Tg) of the resins contained in the outer casings of solid electrolytic capacitors A1, B1, and B2 were 125°C, approximately 145°C (temperatures in the range of 145°C to 165°C), and 165°C, respectively.

[0071] (2-b) Hardness of the resin part Samples were prepared by cutting out portions of the outer casings of solid electrolytic capacitors A1, B1, and B2. The hardness of five points on the resin portion of each sample's cross section was measured at room temperature (25°C), 85°C, 105°C, 125°C, 145°C, 165°C, and 260°C using a continuous stiffness measurement method utilizing nanoindentation. Measurements were performed using the aforementioned measuring device and heating method. Hardness measurements were performed as follows. A diamond triangular pyramidal indenter (Berkovich indenter) was used to perform indentation load and unload tests on the filler-free portion of the sample's cross section (the resin portion), continuously measuring the load and indentation depth. These tests yielded a curve relating load to indentation depth. The hardness was calculated using the projected area of ​​the indentation remaining after elastic deformation had recovered and the load. The hardness at each temperature was determined by averaging the measurements at the five points. The results are shown in Figure 3.

[0072] The hardness of the resin portion of solid electrolytic capacitor A1 was 0.08 GPa or less in the temperature range from the glass transition point Tg of the resin (125°C) to 260°C. On the other hand, the hardness of the resin portion of solid electrolytic capacitors B1 and B2 was greater than 0.08 GPa in the temperature range from the glass transition point Tg of the resin (resin of solid electrolytic capacitor B1: approximately 145°C, resin of solid electrolytic capacitor B2: 165°C) to 260°C.

[0073] From the above (2-a) and (2-b), it was confirmed that the solid electrolytic capacitor A1 was the solid electrolytic capacitor according to this embodiment. The solid electrolytic capacitors B1 and B2 were solid electrolytic capacitors of comparative examples.

[0074] (2-2) Evaluation of solid electrolytic capacitors (2-c) Capacitance change rate The capacitance changes of the solid electrolytic capacitors A1, B1, and B2 at 125° C. were measured using the following procedure: 100 solid electrolytic capacitors A1, 60 solid electrolytic capacitors B1, and 60 solid electrolytic capacitors B2 were prepared.

[0075] The capacitance (μF) of each solid electrolytic capacitor at a frequency of 120 Hz was measured using a four-terminal LCR meter at 20°C, and this was defined as the initial capacitance C0 (μF). Each solid electrolytic capacitor was then heated under the same temperature conditions as the reflow process in accordance with IPC / JEDEC J-STD-020D (maximum temperature 260°C, heating at 255°C or higher for 30 seconds). Next, a high-temperature storage test was conducted in which the solid electrolytic capacitors were left in a 125°C environment for 7000 hours. The capacitance C1 (μF) of the solid electrolytic capacitors immediately after the heat treatment equivalent to the reflow process (immediately after reflow) and after the specified time had elapsed in the high-temperature storage test was measured in the same manner as C0. The measured capacitance was used to calculate the rate of change of capacitance using the following formula: Capacitance change rate (%) = 100 × (C1 - C0) / C0

[0076] The capacitance change rates of 100 solid electrolytic capacitors A1 were arithmetically averaged to determine the average value. Similarly, the average capacitance change rates of 60 solid electrolytic capacitors B1 and 60 solid electrolytic capacitors B2 were calculated. The evaluation results are shown in Table 1. As the degradation of the solid electrolytic capacitor increases, the capacitance change rate becomes negative. A capacitance change rate close to 0 (or a large positive value) indicates little degradation of the solid electrolytic capacitor.

[0077] [Table 1]

[0078] As shown in Table 1, the average capacitance change rate of solid electrolytic capacitor A1 after the high-temperature storage test was -5% or more (i.e., -5.0≦100×(C1−C0) / C0). Note that if only the high-temperature storage test were performed without a heat treatment equivalent to a reflow process, the solid electrolytic capacitor would deteriorate less (i.e., the capacitance change rate would shift more toward the positive side). On the other hand, the average capacitance change rates of solid electrolytic capacitors B1 and B2 after the high-temperature storage test were lower than -5%. This means that, unlike solid electrolytic capacitors B1 and B2, solid electrolytic capacitor A1 exhibits less capacitance loss even when exposed to high temperatures for long periods of time.

[0079] (2-d) ESR change rate The change in ESR (equivalent series resistance) at 125° C. of the solid electrolytic capacitors A1, B1 and B2 was measured by the following procedure.

[0080] Using a four-terminal LCR meter at 20°C, the ESR (mΩ) of each solid electrolytic capacitor at a frequency of 120 kHz was measured and defined as the initial ESR (E0) (mΩ). Each solid electrolytic capacitor was then heated under the same temperature conditions as the reflow process in accordance with IPC / JEDEC J-STD-020D (maximum temperature 260°C, heated for 30 seconds at 255°C or higher). After a specified time had elapsed, the ESR (E1) (mΩ) was measured in the same manner as E0. The measured capacitance was used to calculate the ESR change rate using the following formula: ESR change rate (%) = 100 × (E1 - E0) / E0

[0081] Furthermore, the ESR change rates of 100 solid electrolytic capacitors A1 were arithmetically averaged to obtain an average value. Similarly, the average ESR change rates of 60 solid electrolytic capacitors B1 and 60 solid electrolytic capacitors B2 were calculated. The results are shown in Table 2. The greater the degradation of the solid electrolytic capacitor, the greater the ESR change rate. The smaller the ESR change rate, the less degradation of the solid electrolytic capacitor.

[0082] [Table 2]

[0083] As shown in Table 2, the ESR change rate of solid electrolytic capacitor A1 was significantly lower than the ESR change rates of solid electrolytic capacitors B1 and B2.

[0084] (2-e) Airtightness The airtightness of solid electrolytic capacitors A1, B1, and B2 was evaluated using the following procedure. Each solid electrolytic capacitor was subjected to heat treatment under the same temperature conditions as the reflow process in accordance with IPC / JEDEC J-STD-020D (maximum temperature 260°C, heating above 255°C for 30 seconds). A temperature shock treatment was then performed. Specifically, each solid electrolytic capacitor was placed in a -55°C environment and then in a 125°C environment, repeating this cycle 100 times. Gross leak tests were performed initially (before heat treatment), after heat treatment, and after temperature shock treatment. Specifically, each solid electrolytic capacitor was placed in a small capsule, and the minute pressure drop caused by the internal pressure of the small capsule leaking into the exterior was measured. Capacitors whose pressure change was greater than a predetermined value were determined to have poor airtightness, and the airtightness failure rate (%) was calculated.

[0085] The above test was carried out on 100 solid electrolytic capacitors A1, B1 and B2, and the airtightness defect rate was calculated using the following formula. Airtightness defect rate (%) = 100 x (number of solid electrolytic capacitors judged to be airtight defective) / (number of solid electrolytic capacitors used in the test)

[0086] The airtightness defect rates for solid electrolytic capacitors A1, B1, and B2 were calculated initially, after heat treatment, and after temperature shock treatment. The results are shown in Table 3. In Table 3, the total airtightness defect rate refers to the percentage of the total number of solid electrolytic capacitors that were determined to have airtightness defects initially, after heat treatment, and after temperature shock treatment out of the total number of solid electrolytic capacitors tested initially (100 for each of solid electrolytic capacitors A1, B1, and B2).

[0087] [Table 3]

[0088] As shown in Table 3, solid electrolytic capacitor A1 had high airtightness, and maintained its airtightness even after heat treatment and thermal shock treatment. On the other hand, solid electrolytic capacitors B1 and B2 showed a decrease in airtightness. In particular, solid electrolytic capacitor B2 was found to have defective airtightness even at the early stage.

[0089] As described above, the solid electrolytic capacitor A1 is the solid electrolytic capacitor according to this embodiment. It has been confirmed that the decrease in capacitance and the increase in ESR of the solid electrolytic capacitor A1 are suppressed even when exposed to high temperatures.

[0090] The resin contained in the exterior body of solid electrolytic capacitor A1 became rubbery at 125°C during the high-temperature storage test, and the hardness of the resin portion containing this resin was low, at 0.08 GPa or less. This is thought to have enabled the entire exterior body to absorb the stress applied to the exterior body from the capacitor element and lead terminals, suppressing the occurrence of cracks and peeling and improving airtightness. As a result, it is believed that the exterior body was able to maintain high sealing properties even at high temperatures.

[0091] On the other hand, in the exterior packaging of solid electrolytic capacitors B1 and B2, the stress applied to the packaging was not sufficiently alleviated, and cracks and peeling occurred inside the packaging and at the interfaces between the packaging and the capacitor element and lead terminals, which is thought to have reduced airtightness.The reduced sealing performance of the packaging is thought to have reduced the conductivity of the solid electrolyte layer in the capacitor element, causing a decrease in capacitance and an increase in ESR of the solid electrolytic capacitor. [Industrial Applicability]

[0092] The solid electrolytic capacitor of the present disclosure has a high sealing property of the exterior body even at high temperatures, and can suppress a decrease in capacitance and an increase in ESR, making it suitable for a variety of applications requiring high reliability. 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. [Explanation of symbols]

[0093] 1 electrolytic capacitor 2 Capacitor elements 3. Exterior body 4 Anode lead terminal 5 Cathode lead terminal 6 Anode body 7 Dielectric Layer 8 Cathode 9 Solid electrolyte layer 10 Cathode extraction layer 11 Carbon layer 12 Silver paste layer 13 Separation layer 14 Adhesive layer

Claims

1. A solid electrolytic capacitor including a capacitor element, a lead terminal electrically connected to the capacitor element, and an exterior body sealing a portion of the lead terminal and the capacitor element, the exterior body includes a resin portion made of an epoxy resin and a filler dispersed in the resin portion, a glass transition point Tg of the epoxy resin is 140° C. or lower, when the temperature at which the loss modulus of the resin portion measured by nanoscale dynamic viscoelasticity measurement using a nanoindentation method changes from increasing to decreasing; In the solid electrolytic capacitor, the hardness of the resin portion measured by a nanoindentation method in a temperature range of not less than the glass transition point Tg and not more than 260°C is not more than 0.08 GPa.

2. 2. The solid electrolytic capacitor according to claim 1, wherein the glass transition temperature Tg of the epoxy resin is 125° C. or lower.

3. 2. The solid electrolytic capacitor according to claim 1, wherein the content of the filler in the exterior body is in the range of 75% by mass to 90% by mass.

4. 2. The solid electrolytic capacitor according to claim 1, wherein the maximum particle size of the filler is 55 μm or less.

5. The following formula: Capacitance change rate (%) = 100 × (C1 - C0) / C0 (where C0 is the initial capacitance and C1 is the capacitance after heating at 125°C for 7000 hours) 5. The solid electrolytic capacitor according to claim 1, wherein the average value of the capacitance change rate expressed by the formula (1) is −5.0% or more.

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