Solid electrolytic capacitor

Abstract

This solid electrolytic capacitor is provided with: a capacitor element which comprises a positive electrode part and a negative electrode part; a positive electrode lead frame which is connected to the positive electrode part; a negative electrode lead frame which is connected to the negative electrode part; and an insulating sealing material which covers the capacitor element, while partially covering the positive electrode lead frame and the negative electrode lead frame. With respect to this solid electrolytic capacitor, the capacitor element comprises a solid electrolyte; and if 5 g of the sealing material is immersed in 50 cc of water or an aqueous methanol solution that has a pH of 7.0 within a pressure-resistant container, and is subsequently heated at 121°C for 24 hours, the pH value of the water or aqueous methanol solution after the heating is 6.0 to 8.1. Consequently, the present invention is able to provide a solid electrolytic capacitor which is not susceptible to a decrease in the capacitance even if a voltage is applied thereto in a high-temperature high-humidity environment.

Description

solid electrolytic capacitor

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

[0002] Patent Document 1 proposes "a method for manufacturing a capacitor, comprising the steps of: providing an anode having a dielectric thereon; providing a first layer of a conductive polymer on the dielectric to form a capacitor precursor; providing one or more further layers of a conductive polymer from a dispersion on the first layer; and treating the capacitor precursor at a temperature of 50° C. or higher and 200° C. or lower and a relative humidity of 25 to 100%."

[0003] Patent Document 2 describes that aluminum hydroxide, magnesium hydroxide, zinc borate, etc. can be used as an inorganic filler having a flame retardant effect in an epoxy resin molding material for sealing electronic components.

[0004] Special Publication No. 2016-522573 Publication JP-A No. 10-259292

[0005] There is a growing demand for solid electrolytic capacitors that can be used in harsh environments such as high temperatures and humidity. However, the solid electrolytes used in solid electrolytic capacitors contain acidic components. These acidic components can be liberated when voltage is applied to solid electrolytic capacitors under high temperatures and humidity, corroding the cathode. As a result, the conductivity of the cathode decreases, resulting in a loss of capacitance.

[0006] One aspect of the present disclosure relates to a solid electrolytic capacitor comprising: a capacitor element including an anode portion and a cathode portion; an anode lead frame connected to the anode portion; a cathode lead frame connected to the cathode portion; and an insulating sealing material covering the capacitor element and partially covering each of the anode lead frame and the cathode lead frame, wherein the capacitor element comprises a solid electrolyte, and 5 g of the sealing material is immersed in 50 cc (50 mL) of water or an aqueous methanol solution having a pH value of 7.0 in a pressure-resistant container and heated at 121°C for 24 hours, after which the pH value of the water or aqueous methanol solution is 6.0 or more and 8.1 or less.

[0007] Another aspect of the present disclosure relates to a solid electrolytic capacitor including: a capacitor element including an anode portion and a cathode portion; an anode lead frame connected to the anode portion; a cathode lead frame connected to the cathode portion; and an insulating sealing material covering the capacitor element and partially covering each of the anode lead frame and the cathode lead frame, wherein the capacitor element includes a solid electrolyte; and the sealing material is immersed in water or an aqueous methanol solution having a pH value of 7.0 in a pressure-resistant container and heated until components eluted from the sealing material are saturated, after which the pH value of the water or aqueous methanol solution exceeds 7.

[0008] According to the present disclosure, it is possible to provide a solid electrolytic capacitor whose capacitance is less likely to decrease even when a voltage is applied in a high-temperature, high-humidity environment.

[0009] 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 application, will be better understood from the following detailed description taken in conjunction with the drawings.

[0010] 1 is a cross-sectional view schematically illustrating an example of a capacitor element of an electrolytic capacitor according to an embodiment of the present disclosure;

[0011] The following describes examples of embodiments of the solid electrolytic capacitor according to the present disclosure, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be used as examples. However, other numerical values ​​and materials may be used 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 interpreted as "numerical value A or greater 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 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.

[0012] 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.

[0013] The term "solid electrolytic capacitor" may be read as "electrolytic capacitor", and the term "capacitor" may be read as "capacitor".

[0014] The solid electrolytic capacitor according to the present disclosure includes a capacitor element having an anode portion and a cathode portion. The solid electrolytic capacitor may include only one capacitor element, or may include multiple laminated capacitor elements. The capacitor element may be formed from a valve metal foil or may be composed of a sintered body of valve metal powder. The capacitor element includes a solid electrolyte. The solid electrolyte includes, for example, a conductive polymer, and the conductive polymer includes a dopant.

[0015] An anode lead frame is electrically connected to the anode portion. A cathode lead frame is electrically connected to the cathode portion. A separate conductive member may be interposed between the anode lead frame and the anode portion. For example, when the anode portion includes a sintered body, a rod-shaped wire is embedded in the sintered body, and a portion of the wire protrudes from the sintered body. In this case, the anode lead frame is connected to the portion where the wire protrudes. The lead frame may be made of, for example, a bent metal plate or metal sheet.

[0016] The solid electrolytic capacitor includes an insulating sealing material that covers the capacitor element and partially covers the anode lead frame and the cathode lead frame, respectively, with the portions of the anode lead frame and the cathode lead frame not covered by the sealing material functioning as the anode external terminal and the cathode external terminal.

[0017] The encapsulant is not particularly limited, but is generally a cured product of a thermosetting resin composition. Hereinafter, thermosetting resin compositions may be collectively referred to as encapsulants, regardless of whether they are cured or uncured. The resin composition may contain, for example, a base resin, a curing agent that reacts with the base resin, and a filler, and may also contain various additives. Examples of additives include, but are not limited to, curing accelerators, ion scavengers, coupling agents, pigments, and carbon black.

[0018] A cured product (sealant) of a thermosetting resin composition typically exhibits acidity, with a pH value of at least less than 6 and often around 4. If a sealant is immersed in water or aqueous methanol solution with a pH value of 7.0 in a pressure-resistant container and heated until the components eluted from the sealant are saturated, and the resulting water or aqueous methanol solution has an alkaline pH of more than 8.1, the sealant's physical properties will be impaired. Such a relatively alkaline sealant is prone to gelation in the uncured state, but the curing reaction does not proceed sufficiently even when heated for a long period of time. For example, if 5 g of sealant is immersed in 50 cc of water or aqueous methanol solution with a pH value of 7.0 in a pressure-resistant container and heated at 121°C for 24 hours in the pressure-resistant container, the water or aqueous methanol solution can be saturated with the components eluted from the sealant.

[0019] On the other hand, it is possible to increase the pH of the cured product to near neutral. The sealant used in the solid electrolytic capacitor according to the present disclosure is immersed in water or an aqueous methanol solution in a pressure vessel and heated until the components eluted from the sealant are saturated. The pH of the water (hereinafter also referred to as the "pH of the eluate") is controlled to be 6.0 or more and 8.1 or less (i.e., neutral or near neutral).

[0020] By controlling the pH value of the eluate to 6.0 or more and 8.1 or less, even if an acid component (e.g., a dopant) in the solid electrolyte is liberated, the acid component is neutralized, and a decrease in conductivity and a decrease in capacitance due to corrosion of the cathode portion can be suppressed. The pH value of the eluate is preferably 6.5 or more and may exceed 7. For example, the pH value of the eluate may be slightly alkaline, 7.1 or more. In this case, the acid component is quickly neutralized, thereby significantly suppressing corrosion of the cathode portion.

[0021] The method for controlling the pH value of the eluate to 6.0 or more and 8.1 or less is not particularly limited. For example, a filler that exhibits alkaline properties in water may be used. Examples of such fillers include inorganic powders such as metal hydroxides.

[0022] As the metal hydroxide, it is desirable to use, for example, at least one of magnesium hydroxide and aluminum hydroxide. These are inexpensive, do not make the eluate pH excessively alkaline, and are easy to control the eluate pH to 6.0 to 8.1, or 6.5 to 8.1, or 7.1 to 8.0. It is believed that metal hydroxides have a high effect of generating hydroxide ions to capture acid components when the acid components in the solid electrolyte are liberated.

[0023] The sealant desirably contains an inorganic powder other than a metal hydroxide as a filler. If the filler is mostly a metal hydroxide, the sealant may become too alkaline. On the other hand, if a metal hydroxide and an inorganic powder other than a metal hydroxide are used as fillers in combination, the pH value of the sealant can be easily controlled to the above-mentioned slightly alkaline state.

[0024] As the inorganic powder other than metal hydroxide, for example, a metal oxide can be used. As the metal oxide, it is preferable to use at least one selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, titanium oxide, and zirconium oxide. Among them, silicon oxide (silica) is preferable, and spherical fused silica is particularly preferable.

[0025] In order to easily control the pH value of the eluate of the sealant, it is desirable that the content of inorganic powder other than metal hydroxide contained in the sealant be greater than the content of metal hydroxide. For example, it is desirable that 50 mass% or more of the filler be inorganic powder other than metal hydroxide. 90 mass% or more of the inorganic powder other than metal hydroxide may be metal oxide. It is also desirable that 5 mass% to 30 mass% of the filler be metal hydroxide.

[0026] From the viewpoint of increasing strength, the content of the filler in the encapsulant is, for example, 70% by mass or more, or may be 75% by mass or more, or may be 80% by mass or more. In consideration of the viscosity of the encapsulant before curing, the content of the filler in the encapsulant may be, for example, 90% by mass or less.

[0027] As another method for controlling the pH value of the sealant eluate to 6.0 or more and 8.1 or less, for example, an ion trapping agent that exhibits alkaline properties in water may be used. For example, by using a larger amount of an ion trapping agent that exhibits alkaline properties in water than is generally used, the pH value of the sealant eluate may be controlled to 6.0 or more and 8.1 or less. In addition, the alkaline ion trapping agent may be used alone, or a metal hydroxide and such an ion trapping agent may be used in combination.

[0028] The encapsulant or thermosetting resin composition can be molded into a predetermined shape and cured using a molding technique such as injection molding, insert molding, compression molding, etc. For example, the encapsulant or thermosetting resin composition is filled into a predetermined mold and heated so as to cover the outer surfaces of the capacitor element and a portion of each lead frame.

[0029] Examples of the base resin include epoxy resin, phenol resin, urea resin, polyimide resin, polyamideimide resin, polyurethane resin, diallyl phthalate resin, and unsaturated polyester resin. One type of base resin may be used alone, or multiple types may be used in combination. Among these, epoxy resin is preferred.

[0030] The epoxy resin is not particularly limited, and examples thereof include biphenyl-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol AD-type epoxy resins, naphthalene-type epoxy resins, glycidylamine-type epoxy resins, phenol novolac-type epoxy resins, alicyclic epoxy resins, dicyclopentadiene-type epoxy resins, polyether-type epoxy resins, and silicone-modified epoxy resins. These may be used alone or in combination of two or more.

[0031] The curing agent is not particularly limited, but phenolic resins, acid anhydrides, aliphatic or aromatic amines, imidazole, imidazole derivatives, etc. are preferably used.

[0032] An example of the curing accelerator is dicyandiamide.

[0033] The pH value of the sealing material can be measured by the following method.

[0034] First, the encapsulant (cured product) is separated from the solid electrolytic capacitor. The encapsulant is immersed in an appropriate amount of water (preferably ion-exchanged water or pure water) with a pH value of 7.0 and placed in a pressure-resistant container. The encapsulant is then heated until the components eluted from the encapsulant are saturated. For example, the encapsulant may be immersed in water in a pressure-resistant container and heated sufficiently under the conditions described below. The pH of the water in the pressure-resistant container (i.e., the pH value of the eluate) is then measured using a commercially available pH meter. If the pH value exceeds 7.0, the encapsulant itself is considered to be alkaline.

[0035] The water contained in the pressure vessel may contain methanol to promote the elution of components in the sealant. That is, the pH value of the eluate may be the pH value of the aqueous methanol solution. The methanol concentration is not particularly limited, but an aqueous solution containing methanol at a content of, for example, 5 to 10% by mass (preferably 8% by mass) may be used. The methanol in such an aqueous methanol solution does not affect the pH of the water. If the pH value of the water constituting the aqueous methanol solution is 7.0, the pH value of the aqueous methanol solution will also be 7.0.

[0036] To saturate the water or aqueous methanol solution in the pressure vessel with components eluted from the sealant, for example, 5 g of sealant is weighed out, placed in the pressure vessel together with 50 cc of water or aqueous methanol solution with a pH value of 7.0, and heated at 121°C for 24 hours. The pH of the water or aqueous methanol solution in the pressure vessel is then measured using a commercially available pH meter. If the resulting pH value is 6.0 or higher and 8.1 or lower, the sealant is considered to be neutral or near neutral. Furthermore, if the resulting pH value exceeds 7.0, the sealant is considered to be neutral to slightly alkaline.

[0037] The rate of capacitance change in a high-temperature, high-humidity environment has traditionally been measured in an environment of 85°C and 85% relative humidity. When a voltage is continuously applied to a solid electrolytic capacitor in an environment of 85°C and 85% relative humidity, for example, for 132 hours, the capacitance does not change significantly even if the pH value of the eluate from the sealing material is acidic and less than 6.0.

[0038] However, in recent years, tests have been conducted to simulate the use of solid electrolytic capacitors in harsher environments, such as high temperatures and high humidity. For example, tests are conducted in which a voltage is continuously applied to a solid electrolytic capacitor at temperatures as high as 110°C and a relative humidity of 85%. In such cases, the capacitance of the solid electrolytic capacitor varies significantly depending on the pH value of the eluate from the encapsulant.

[0039] When the pH value of the eluate from the encapsulant is less than 6, the capacitance decreases significantly when a voltage is applied to the solid electrolytic capacitor for 132 hours in an environment of 110°C and 85% relative humidity. On the other hand, when the pH value of the eluate from the encapsulant is 6.0 or higher, the capacitance decreases only slightly when a voltage is applied to the solid electrolytic capacitor for 132 hours in an environment of 110°C and 85% relative humidity, and the difference between the two is significant.

[0040] In addition, when a voltage is applied for 132 hours to a solid electrolytic capacitor in which the pH value of the eluate from the sealing material is less than 6.0 in an environment of 110°C / relative humidity 85%, the decrease in capacitance is approximately the same as when a voltage is applied for 1,000 hours to the same solid electrolytic capacitor in an environment of 85°C / relative humidity 85%.

[0041] As described above, the decrease in capacitance under high-temperature, high-humidity environments is a new problem that has become apparent in the process of developing solid electrolytic capacitors that are required to be used under conditions that are significantly more severe than those of the past. On the other hand, by making the pH value of the eluate of the encapsulant slightly alkaline, such as 6.0 or more, further 6.5 or more, or even more than 7.0, it is possible to obtain solid electrolytic capacitors that can adequately withstand use under such severe conditions.

[0042] <Electrolytic Capacitor> An example of a solid electrolytic capacitor according to the present disclosure and a method for manufacturing the same will be described below with reference to the accompanying drawings. However, the present disclosure is not limited thereto. FIG. 1 is a cross-sectional view schematically illustrating an example of a capacitor element of a solid electrolytic capacitor according to the present disclosure. FIG. 2 is a cross-sectional view schematically illustrating an example of a solid electrolytic capacitor according to the present disclosure.

[0043] Solid electrolytic capacitor 20 includes capacitor element 10 having anode portion 6 and cathode portion 7, exterior body (sealant) 11 that seals capacitor element 10, anode lead frame 13 electrically connected to anode portion 6 and partially exposed from exterior body 11, and cathode lead frame 14 electrically connected to cathode portion 7 and partially exposed from exterior body 11. Anode portion 6 includes anode body 1 and anode wire 2. Dielectric layer 3 is formed on the surface of the anode body. Cathode portion 7 includes solid electrolyte layer 4 covering at least a portion of dielectric layer 3, and cathode layer 5 covering at least a portion of the surface of solid electrolyte layer 4.

[0044] <Capacitor Element> Hereinafter, the capacitor element 10 will be described in detail, taking as an example a case where the capacitor element 10 includes a solid electrolyte layer as the electrolyte.

[0045] The anode portion 6 has an anode body 1 and an anode wire 2 extending from one surface of the anode body 1 and electrically connecting to an anode lead frame 13 .

[0046] The anode body 1 is, for example, a rectangular parallelepiped porous sintered body obtained by sintering metal particles. Valve metal particles such as titanium (Ti), tantalum (Ta), and niobium (Nb) are used as the metal particles. One or more types of metal particles are used in the anode body 1. The metal particles may be an alloy containing two or more types of metals. For example, an alloy containing a valve metal and silicon, vanadium, boron, or the like may be used. A compound containing a valve metal and a typical element such as nitrogen may also be used. The valve metal alloy contains the valve metal as the main component, for example, at least 50 atomic % of the valve metal.

[0047] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited and includes, for example, copper, aluminum, aluminum alloys, and the like, in addition to the valve metals described above. The anode body 1 and the anode wire 2 may be made of the same material or different materials. The anode wire 2 has a first portion 2a that is embedded inside the anode body 1 from one surface of the anode body 1, and a second portion 2b that extends from the above surface of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited and includes, for example, a circle, a track shape (a shape consisting of parallel straight lines and two curves connecting the ends of these straight lines), an ellipse, a rectangle, a polygon, and the like.

[0048] The anode part 6 is fabricated, for example, by press-molding the first portion 2a into a rectangular parallelepiped shape while the first portion 2a is embedded in a powder of particles of the first metal, followed by sintering. This results in the second portion 2b of the anode wire 2 extending from one surface of the anode body 1 in an upright manner. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, thereby electrically connecting the anode wire 2 and the anode lead terminal 13. The welding method is not particularly limited, and examples include resistance welding and laser welding.

[0049] A dielectric layer 3 is formed on the surface of the anode body 1. The dielectric layer 3 is made of, for example, a metal oxide. Methods for forming a layer containing a metal oxide on the surface of the anode body 1 include, for example, a method of immersing the anode body 1 in a chemical conversion solution to anodize the surface of the anode body 1, and a method of heating the anode body 1 in an oxygen-containing atmosphere. The dielectric layer 3 is not limited to the above-mentioned layer containing a metal oxide, and may be any layer that is insulating.

[0050] The anode body 1 is not limited to a porous sintered body, but may be a metal foil made of a valve metal such as an aluminum foil.

[0051] (Cathode Section) The cathode section 7 has a solid electrolyte layer 4 and a cathode layer 5 covering the solid electrolyte layer 4. The solid electrolyte layer 4 is formed so as to cover at least a portion of the dielectric layer 3.

[0052] For example, a manganese compound or a conductive polymer is used for the solid electrolyte layer 4. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These may be used alone or in combination. The conductive polymer may also be a copolymer of two or more monomers. In terms of excellent conductivity, polythiophene, polyaniline, and polypyrrole may be used. In particular, in terms of excellent water repellency, polypyrrole may be used.

[0053] The solid electrolyte layer 4 containing a conductive polymer may be composed of two or more solid electrolyte layers. For example, the solid electrolyte layer 4 includes a first conductive polymer layer covering the dielectric layer 3 and a second conductive polymer layer covering the first conductive polymer layer. When the solid electrolyte layer 4 is composed of two or more layers, the conductive polymers used in each layer may have different compositions or formation methods (polymerization methods). For example, the first conductive polymer layer may be formed by polymerizing a raw material monomer on the dielectric layer 3. Alternatively, the second conductive polymer layer may be formed by applying a liquid containing the conductive polymer to the dielectric layer 3.

[0054] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. refer to polymers having polypyrrole, polythiophene, polyfuran, polyaniline, etc. as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc. may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0055] Various dopants may be added to the polymerization liquid for forming the conductive polymer, or the solution or dispersion of the conductive polymer in order to improve the conductivity of the conductive polymer. The dopant is not particularly limited, but examples thereof include naphthalenesulfonic acid, p-toluenesulfonic acid, and polystyrenesulfonic acid.

[0056] When the conductive polymer is dispersed in the dispersion medium in the form of particles, the particles have an average particle size D50 of, for example, 0.01 μm or more and 0.5 μm or less. If the average particle size D50 of the particles is in this range, the particles can easily penetrate into the interior of the anode body 1.

[0057] Although not shown in FIGS. 1 and 2 , the anode body 1 is porous, and therefore the dielectric layer 3 is formed so as to cover the inner walls of the pores of the porous anode body 1, and the solid electrolyte layer 4 permeates deep into the porous anode body 1 (for example, to the region in the vicinity of the anode wire 2) so as to block the pores of the anode body 1.

[0058] The cathode layer 5 has, for example, a carbon layer 5a formed to cover the solid electrolyte layer 4 and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a contains a conductive carbon material such as graphite and a resin. The metal paste layer 5b contains, for example, metal particles (e.g., silver) and a resin. The configuration of the cathode layer 5 is not limited to this configuration. The configuration of the cathode layer 5 may be any configuration that has a current collecting function.

[0059] <Anode Lead Frame> The anode lead frame 13 is electrically connected to the anode body 1 via the second portion 2b of the anode wire 2. The material of the anode lead frame 13 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The anode lead frame 13 may be made of a metal such as copper, or a non-metal. The shape of the anode lead frame 13 is not particularly limited as long as it is flat. The thickness of the anode lead frame 13 (the distance between the main surfaces of the anode lead frame 13) may be 25 μm or more and 200 μm or less, or may be 25 μm or more and 100 μm or less, from the viewpoint of reducing the height.

[0060] One end of the anode lead frame 13 may be joined to the anode wire 2 with a conductive adhesive or solder, or may be joined to the anode wire 2 by resistance welding or laser welding. The other end of the anode lead frame 13 is led out of the exterior package 11 and is exposed from the exterior package 11. The conductive adhesive is, for example, a mixture of a thermosetting resin with carbon particles or metal particles.

[0061] <Cathode lead frame> The cathode lead frame 14 is electrically connected to the cathode part 7 at the joint portion 14 a. The joint portion 14 a is a portion of the cathode lead frame 14 that overlaps with the cathode layer 5 when the cathode layer 5 and the cathode lead frame 14 joined to the cathode layer 5 are viewed from the normal direction of the cathode layer 5.

[0062] Cathode lead frame 14 is joined to cathode layer 5 via, for example, conductive adhesive 8. One end of cathode lead frame 14 constitutes, for example, part of joint portion 14a and is disposed inside package 11. The other end of cathode lead frame 14 is extended to the outside. Therefore, a part of cathode lead frame 14, including the other end, is exposed from package 11.

[0063] The material of cathode lead frame 14 is not particularly limited as long as it is electrochemically and chemically stable and conductive. Cathode lead frame 14 may be made of a metal such as copper, or a non-metal. The shape of cathode lead frame 14 is also not particularly limited, and may be, for example, a long, flat plate. From the viewpoint of reducing the height, the thickness of cathode lead frame 14 may be 25 μm or more and 200 μm or less, or 25 μm or more and 100 μm or less.

[0064] <Exterior Body> The exterior body 11 is made of the sealing material described above and is provided to electrically insulate the anode lead frame 13 and the cathode lead frame 14 from each other.

[0065] <Method for Manufacturing Electrolytic Capacitor> An example of a method for manufacturing a solid electrolytic capacitor according to the present disclosure will be described below.

[0066] (1) Capacitor Element Preparation Step First, a capacitor element is prepared. The capacitor element preparation step includes, for example, the steps of preparing an anode body, covering at least a portion of the anode body with a dielectric layer, covering at least a portion of the dielectric layer with a solid electrolyte layer, and covering at least a portion of the solid electrolyte layer with a carbon layer. The capacitor element preparation step may further include the step of covering at least a portion of the carbon layer with a conductive resin layer (conductive paste layer).

[0067] (1a) Anode Body Preparation Step A porous sintered body can be used as the anode body 1. Valve metal particles and an anode wire 2 are placed in a mold so that the first portion 2a is embedded in the valve metal particles, and then press-molded and sintered to obtain an anode part 6 including the anode body 1, which is a porous body of valve metal. The first portion 2a of the anode wire is embedded inside the porous sintered body from one surface thereof. The pressure used in press-molding is not particularly limited. Sintering is preferably performed under reduced pressure. A binder such as polyacrylic carbonate may be mixed with the valve metal particles as needed.

[0068] Valve metal particles are usually pressure-molded using a mold having a rectangular parallelepiped internal space, and then sintered. In this case, the shape of the sintered anode body 1 is also rectangular parallelepiped and has multiple main surfaces.

[0069] (1b) Dielectric Layer Forming Step Next, the anode body 1 is subjected to a chemical conversion treatment to cover at least a portion of the anode body 1 with the dielectric layer 3. Specifically, the anode body 1 is immersed in a chemical conversion tank filled with an aqueous electrolytic solution (e.g., an aqueous phosphoric acid solution), the second portion 2b of the anode wire 2 is connected to the anode body in the chemical conversion tank, and anodization is performed to form the dielectric layer 3 made of an oxide film of a valve metal on the surface of the porous portion. The aqueous electrolytic solution is not limited to an aqueous phosphoric acid solution, and nitric acid, acetic acid, sulfuric acid, or the like can also be used.

[0070] (1c) Solid Electrolyte Layer Forming Step Subsequently, at least a portion of the dielectric layer 3 is covered with the solid electrolyte layer 4. This results in a capacitor element 10 including the anode body 1, the dielectric layer 3, and the solid electrolyte layer 4. The solid electrolyte layer 4 may include a plurality of conductive polymer layers.

[0071] As an example of forming a solid electrolyte layer 4 including a plurality of conductive polymer layers, the process of forming the solid electrolyte layer may include step (i) of impregnating the anode body with a first solution containing a first monomer that is a raw material for a first conductive polymer, and polymerizing the first monomer on the surface of the dielectric layer to form a first conductive polymer layer that covers the dielectric layer, and step (ii) of impregnating the anode body with a solution or dispersion containing a second conductive polymer to form a second conductive polymer layer that covers the first conductive polymer layer.

[0072] In step (i), a first conductive polymer layer is formed on the anode body 1 on which the dielectric layer 3 has been formed by impregnating a monomer or an oligomer and then polymerizing the monomer or oligomer by chemical polymerization or electrolytic polymerization. The first conductive polymer may contain a dopant. The conductive polymer and the dopant may be selected from those exemplified for the solid electrolyte layer 4.

[0073] In the step (i) of forming the first conductive polymer layer, raw material monomers of the first conductive polymer are oxidatively polymerized (so-called "in situ polymerization") above the dielectric layer 3 to form the first conductive polymer layer on the dielectric layer 3. For this reason, fine irregularities may occur on the surface of the first conductive polymer layer due to non-uniformity of the polymerization reaction or non-uniformity of the layer growth.

[0074] In step (ii), the anode body is impregnated with a solution or dispersion containing the second conductive polymer to cover the surface of the first conductive polymer layer with the second conductive polymer layer. The second conductive polymer layer is formed so as to fill the recesses in the surface of the first conductive polymer layer, thereby improving adhesion between the first conductive polymer layer and the second conductive polymer layer.

[0075] Prior to step (ii), the anode element on which the first conductive polymer layer has been formed may be washed to remove unnecessary components contained in the first conductive polymer layer, such as unreacted monomer, dopant, and oxidant.

[0076] Following step (ii), the anode element may be impregnated with a solution or dispersion containing a third conductive polymer to form a third conductive polymer layer covering the second conductive polymer layer.

[0077] The second conductive polymer may contain a dopant. The conductive polymer and the dopant may be selected from those exemplified for the solid electrolyte layer 4. A known binder may be used. The dispersion may contain a known additive used in forming the solid electrolyte layer.

[0078] After the conductive polymer layer is formed, a step of impregnating the solid electrolyte layer 4 with a salt compound is performed. When the salt compound is an ionic liquid, the impregnation of the salt compound can be performed by immersing the anode body 1 on which the conductive polymer layer is formed in the ionic liquid, which is the salt compound. The anode body 1 on which the conductive polymer layer is formed may also be immersed in a liquid mixture of the ionic liquid and another solvent. The solid electrolyte layer may also be impregnated with the salt compound in a reduced pressure atmosphere.

[0079] (1d) Cathode Layer Formation Step Subsequently, a carbon paste and a metal paste are applied in this order to the surface of the solid electrolyte layer 4 to form a cathode layer 5 composed of a carbon layer 5a and a conductive resin layer (metal paste layer) 5b. The configuration of the cathode layer 5 is not limited to this, and any configuration having a current collecting function may be used.

[0080] (2) Step of Electrically Connecting Capacitor Element and Lead Frame Next, an anode lead frame 13 and a cathode lead frame 14 are prepared. The second portion 2b of the anode wire 2 embedded in the anode body 1 is joined to the anode lead frame 13 by laser welding, resistance welding, or the like. After applying a conductive adhesive 8 to the cathode layer 5, the cathode lead frame 14 is joined to the cathode portion 7 via the conductive adhesive 8.

[0081] Next, capacitor element 10 and a sealing material (an uncured thermosetting resin composition) that forms exterior body 11 with an eluate pH value of 6.0 or more and 8.1 or less are placed in a mold, and capacitor element 10 is sealed by transfer molding, compression molding, or the like. At this time, a portion of anode lead frame 13 and cathode lead frame 14 are exposed from the mold. The molding conditions are not particularly limited, and time and temperature conditions may be set appropriately taking into consideration the curing temperature of the sealing material used, etc.

[0082] Finally, the exposed portions of anode lead frame 13 and cathode lead frame 14 are bent along package 11 to form bent portions, whereby a portion of anode lead frame 13 and a portion of cathode lead frame 14 are disposed on the mounting surface of package 11. By the above method, electrolytic capacitor 20 is manufactured.

[0083] [Examples] Hereinafter, embodiments of the present invention according to the present disclosure will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

[0084] Examples 1 to 7 Solid electrolytic capacitors were fabricated as follows. (Formation of anode body) Tantalum metal particles were used as the valve metal. Tantalum metal particles were formed into a rectangular parallelepiped so that one end of an anode wire made of tantalum metal was embedded in the tantalum metal particles, and the formed body was then sintered in a vacuum. This resulted in an anode part including an anode body made of a porous tantalum sintered body and an anode wire with one end embedded in the anode body and the remaining portion embedded in one surface of the anode body.

[0085] Next, the anode body and a part of the anode wire embedded in the anode body were immersed in an electrolytic bath filled with an aqueous phosphoric acid solution, and the other end of the anode wire was connected to the anode body in the electrolytic bath. Then, anodization was performed to deposit tantalum oxide (TaO) on the surface of the anode body (the surface of the porous sintered body including the inner wall surfaces of the pores) and on the surface of a part of the anode wire. ２ O ５ ) to form a uniform dielectric layer.

[0086] Next, 3,4-ethylenedioxythiophene, iron(III) p-toluenesulfonate, and 1-butanol, which are raw materials for the first conductive polymer, were mixed to prepare a dispersion (reaction solution) containing the first monomer. After immersing the anode body in the dispersion, the anode body was removed from the dispersion and subjected to heat treatment in the air. In this case, iron(III) p-toluenesulfonate functioned as an oxidizing agent. In this way, the first monomer was polymerized on the dielectric layer to form a solid electrolyte layer containing poly(3,4-ethylenedioxythiophene) (PEDOT) as the first conductive polymer layer.

[0087] Subsequently, the anode element on which the first conductive polymer layer was formed was washed, and then poly(3,4-ethylenedioxythiophene) as a second conductive polymer was mixed with p-toluenesulfonate to prepare a second dispersion. After immersing the anode element in the second dispersion, the anode element was removed from the second dispersion and impregnated with the second dispersion. Thereafter, a drying treatment was performed under atmospheric pressure to form a second conductive polymer layer.

[0088] Carbon paste and metal paste were applied in this order to a predetermined area on the surface of the second conductive polymer layer to form a cathode layer consisting of a carbon layer and a silver paste layer, thereby obtaining a capacitor element.

[0089] An anode lead frame and a cathode lead frame were placed on the capacitor element and sealed with sealing materials a1 to a7 to form an exterior body, and then the anode lead frame and cathode lead frame protruding from the exterior body were bent along the exterior body to obtain solid electrolytic capacitors E1 to E7.

[0090] The sealing materials a1 to a7 are thermosetting epoxy resin compositions containing an epoxy resin as a main resin. The filler contains silica (SiO ) so that the pH value of the eluate of the sealing material becomes the value shown in Table 1. ２ ) particles and magnesium hydroxide (Mg(OH) ２ ) particles were mixed and used.

[0091] Comparative Example 1 A solid electrolytic capacitor C1 was obtained in the same manner as in Example 1, except that a sealing material b1 containing only silica particles as a filler and not containing magnesium hydroxide particles was used.

[0092] Comparative Example 2 A solid electrolytic capacitor C2 was obtained in the same manner as in Example 1, except that the sealing material b2 was used. The content of silica particles in the filler was increased and the content of magnesium hydroxide particles was decreased compared to any of the sealing materials a1 to a7, so that the pH value of the eluate from the sealing material b2 was the value shown in Table 1.

[0093] The solid electrolytic capacitors of the examples and comparative examples thus fabricated were evaluated as follows.

[0094] [Evaluation] In an environment of 20°C, the initial capacitance C of the solid electrolytic capacitors of the examples and comparative examples was measured using an LCR meter for four-terminal measurement. ０ The initial capacitance (F) was measured under two conditions: when a voltage 0.8 times the rated voltage was applied, and when no voltage was applied. 60 solid electrolytic capacitors were fabricated for each example and comparative example. ０ (F) is the average value of 30 samples with and without voltage application.

[0095] Next, 60 solid electrolytic capacitors were placed in an environment of 110°C / relative humidity 85%, and a voltage of 0.8 times the rated voltage was continuously applied to 30 solid electrolytic capacitors. No voltage was applied to the remaining 30 solid electrolytic capacitors. After 132 hours, the solid electrolytic capacitors were recovered, and the capacitance C of the 30 solid electrolytic capacitors to which a voltage was continuously applied was measured. １ The average value of (F) and the capacitance C of 30 solid electrolytic capacitors to which no voltage was applied ２ The average value of (F) was calculated. The initial capacitance C ０ Capacitance C １ and capacitance C ２ The rate of change was calculated, and the results are shown in Table 1.

[0096] Next, 60 solid electrolytic capacitors of each Example and Comparative Example that had been separately manufactured were placed in an environment of 85°C / relative humidity 85%, and a voltage of 0.8 times the rated voltage was continuously applied to 30 solid electrolytic capacitors. No voltage was applied to the remaining 30 solid electrolytic capacitors. After 1000 hours, the solid electrolytic capacitors were recovered, and the capacitance C of the 30 solid electrolytic capacitors to which a voltage had been continuously applied was measured. ３ The average value of (F) and the capacitance C of 30 solid electrolytic capacitors to which no voltage was applied ４ The average value of (F) was calculated. The initial capacitance C ０ Capacitance C ３ and capacitance C ４ The rate of change was calculated, and the results are shown in Table 1.

[0097]

[0098] As shown in Table 1, even in a test simulating the use of a solid electrolytic capacitor in a severe high-temperature, high-humidity environment (110°C / relative humidity 85%), when the pH value of the encapsulant eluate was 6.0 or higher and 8.1 or lower, the capacitance of the solid electrolytic capacitor did not fluctuate significantly even when voltage was continuously applied, and there was almost no decrease in capacitance.

[0099] On the other hand, when the pH value of the eluate of the sealing material is less than 6, a significant decrease in capacitance occurs after only 132 hours of voltage application in an environment of 110° C. / relative humidity 85%.

[0100] It can be seen that even when voltage is continuously applied to a solid electrolytic capacitor with a sealant pH value of less than 6.0 in an 85°C / 85% relative humidity environment, the capacitance decrease does not reach the same level as in the test in an 110°C / 85% relative humidity environment until 1000 hours have passed. After 132 hours, no significant change in capacitance was observed, and sufficient capacitance was maintained.

[0101] 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.

[0102] The present disclosure can be used in solid electrolytic capacitors used in high-temperature and high-humidity environments.

[0103] 20: Solid electrolytic capacitor 10: Capacitor element 1: Anode body 2: Anode wire 2a: First portion 2b: Second portion 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode layer 5a: Carbon layer 5b: Conductive resin layer 6: Anode portion 7: Cathode portion 8: Conductive adhesive 11: Exterior body (sealing material) 13: Anode lead frame 14: Cathode lead frame 14a: Joint portion

Claims

1. A capacitor element including an anode portion and a cathode portion; an anode lead frame connected to the anode portion; a cathode lead frame connected to the cathode portion; an insulating sealing material that covers the capacitor element and partially covers each of the anode lead frame and the cathode lead frame, the capacitor element comprises a solid electrolyte; A solid electrolytic capacitor in which 5 g of the sealing material is immersed in 50 cc of water or an aqueous methanol solution having a pH value of 7.0 in a pressure-resistant container and heated at 121° C. for 24 hours, after which the pH value of the water or the aqueous methanol solution is 6.0 or more and 8.1 or less.

2. 2. The solid electrolytic capacitor according to claim 1, wherein the pH value of the water or the aqueous methanol solution after heating at 121° C. for 24 hours is 6.5 or more.

3. A capacitor element including an anode portion and a cathode portion; an anode lead frame connected to the anode portion; a cathode lead frame connected to the cathode portion; an insulating sealing material that covers the capacitor element and partially covers each of the anode lead frame and the cathode lead frame, the capacitor element comprises a solid electrolyte; A solid electrolytic capacitor in which the sealant is immersed in water or an aqueous methanol solution having a pH value of 7.0 in a pressure-resistant container, and the water or the aqueous methanol solution is heated until components eluted from the sealant are saturated, and then the pH value of the water or the aqueous methanol solution exceeds 7.

4. the encapsulant includes a filler; The solid electrolytic capacitor according to claim 1 , wherein the filler comprises a metal hydroxide.

5. 5. The solid electrolytic capacitor according to claim 4, wherein the metal hydroxide comprises at least one of magnesium hydroxide and aluminum hydroxide.

6. 5. The solid electrolytic capacitor according to claim 4, wherein the filler further contains an inorganic powder other than a metal hydroxide.

7. The solid electrolytic capacitor according to claim 6 , wherein the inorganic powder other than a metal hydroxide contains a metal oxide.

8. 7. The solid electrolytic capacitor according to claim 6, wherein the content of the inorganic powder other than the metal hydroxide in the sealing material is greater than the content of the metal hydroxide.

9. 8. The solid electrolytic capacitor according to claim 7, wherein the metal oxide comprises at least one selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, titanium oxide, and zirconium oxide.

10. 5. The electrolytic capacitor according to claim 4, wherein the content of the filler in the sealing material is 80 mass % or more.