WO2024143173A1 - Solid electrolytic capacitor - Google Patents

Abstract

This solid electrolytic capacitor comprises: at least one capacitor element including an anode portion and a cathode portion; a substrate supporting the capacitor element; a sealing body sealing the capacitor element; and a plurality of external electrodes respectively electrically connected to the anode portion and the cathode portion. The substrate includes at least one insulating layer and at least one metal layer.

Description

Solid Electrolytic Capacitors

This disclosure relates to solid electrolytic capacitors.

A solid electrolytic capacitor comprises a capacitor element containing a solid electrolyte, a sealant that seals the capacitor element, and a number of external electrodes that are electrically connected to the anode and cathode sides of the capacitor element. Some solid electrolytic capacitors have a capacitor element that is sealed while placed on a substrate.

Patent Document 1 proposes a solid electrolytic capacitor that includes a rectangular resin molded body that includes an element stack, an insulating substrate, and a sealing resin, a first external electrode, and a second external electrode, and that has a dummy layer that does not contribute to the capacitor capacitance on one of the main surfaces in the stacking direction of the element stack, and the insulating substrate is positioned adjacent to the dummy layer.

International Publication No. 2021/112239

The substrate for a solid electrolytic capacitor may be, for example, an insulating substrate, a metal substrate, or a laminated substrate (such as a printed circuit board) on which a wiring pattern is formed. The substrate is in the form of a plate including an insulating layer formed from an organic material such as insulating resin. For this reason, substrates with an insulating layer are easily permeable to water vapor. If the substrate has a high water vapor permeability, moisture will penetrate the inside, and when the solid electrolytic capacitor is exposed to high temperatures during reflow processing, etc., gas will be generated inside and the volume will expand. The stress caused by the expansion is applied to the components inside the capacitor, damaging the components and causing fluctuations in the equivalent series resistance (ESR).

One aspect of the present disclosure is a capacitor comprising at least one capacitor element including an anode portion and a cathode portion;
A substrate supporting the capacitor element;
a sealant that seals the capacitor element;
a plurality of external electrodes electrically connected to the anode portion and the cathode portion,
The substrate relates to a solid electrolytic capacitor including at least one insulating layer and at least one metal layer.

It is possible to reduce fluctuations in ESR when a solid electrolytic capacitor with a substrate having an insulating layer is exposed to high temperatures.

FIG. 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to an embodiment of the present disclosure. FIG. 4 is a schematic cross-sectional view of a solid electrolytic capacitor according to another embodiment of the present disclosure.

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.

In solid electrolytic capacitors that include a substrate with an insulating layer, moisture can easily penetrate the inside if the substrate has a high water vapor permeability. When the solid electrolytic capacitor is exposed to high temperatures during reflow processing, the moisture that penetrates the inside vaporizes and expands, and the expansion can easily cause stress to be applied to the internal components. When stress is applied to the capacitor elements, sealant, or leads, cracks or peeling can occur, increasing resistance and increasing the ESR of the solid electrolytic capacitor. In addition, because it is difficult to control the degree of stress caused by the expansion of the penetrated moisture and the parts to which the stress is applied, the variation in the ESR range between individual units can also easily become large.

(1) In view of the above, a solid electrolytic capacitor according to one aspect of the present disclosure includes at least one capacitor element including an anode portion and a cathode portion, a substrate supporting the capacitor element, a sealant sealing the capacitor element, and a plurality of external electrodes electrically connected to the anode portion and the cathode portion, respectively. The substrate includes at least one insulating layer and at least one metal layer. By including the metal layer in the substrate, the water vapor permeability of the substrate can be kept low, and the fluctuation (particularly increase) of the ESR of the solid electrolytic capacitor when exposed to high temperatures such as in a reflow process can be reduced. In addition, in the present disclosure, the intrusion of moisture through the substrate into the solid electrolytic capacitor itself can be reduced, thereby reducing the variation in the ESR fluctuation range between individual capacitors. In addition, by including the metal layer in the substrate, the effect of suppressing the intrusion of noise components into the solid electrolytic capacitor is expected.

(2) In the above (1), the substrate may have one insulating layer and one metal layer. The metal layer may be adhered to the inner main surface of the insulating layer. Such a substrate can be easily obtained from commercially available substrates that are easy to obtain, and is cost-effective. Furthermore, even with such a simple layer structure, it is possible to reduce the intrusion of moisture through the substrate into the solid electrolytic capacitor. The inner main surface of the insulating layer is the inner main surface of the insulating layer in the solid electrolytic capacitor (in other words, the main surface of the insulating layer on the capacitor element side).

(3) In the above (1), the substrate may have two insulating layers, and the metal layer may be interposed between the two insulating layers and adhered to each of the opposing main surfaces of the two insulating layers. Such a substrate can be easily obtained from readily available commercially available substrates, and is cost-effective. In addition, even with this layer structure, the water vapor permeability of the substrate can be kept low, and the fluctuation in ESR of the solid electrolytic capacitor when exposed to high temperatures can be reduced, and the variation in the ESR fluctuation range between individual capacitors can be reduced.

(4) In any one of (1) to (3) above, the metal layer may be at least one selected from the group consisting of copper foil and copper alloy foil. Such a substrate can be easily obtained from a commercially available substrate that is easily available, and is advantageous in terms of cost.

(5) In any one of (1) to (4) above, the metal layer may be in contact with one of the multiple external electrodes and may not be in contact with the others. This can prevent short circuits between external electrodes of different polarities through the metal layer.

(6) In any one of (1) to (4) above, the metal layer may not be in contact with any of the multiple external electrodes. This can prevent short circuits between external electrodes with different polarities through the metal layer.

(7) In any one of (1) to (6) above, the metal layer may cover 50% or more of the area of the bonded main surface of the insulating layer. By covering a large portion of the main surface of the insulating layer with the metal layer, the intrusion of moisture into the solid electrolytic capacitor can be further reduced.

(8) In any one of (1) to (7) above, the thickness of the metal layer may be 5 μm or more and 100 μm or less. This can further reduce the intrusion of moisture into the solid electrolytic capacitor. In addition, the thickness of the solid electrolytic capacitor can be made relatively small, which is advantageous from the standpoint of miniaturization and cost reduction.

(9) In any one of (1) to (8) above, the insulating layer may contain at least one selected from the group consisting of epoxy resin and polyimide resin, and glass fiber. In this case, even though the substrate is easily available and relatively inexpensive, it is possible to reduce the fluctuation in ESR of the solid electrolytic capacitor when exposed to high temperatures, and to suppress the variation in the fluctuation range between individual capacitors.

(10) In any one of (1) to (9) above, the insulating layer may further contain ceramic particles. In this case, the intrusion of moisture into the solid electrolytic capacitor can be further suppressed, and the fluctuation of the ESR of the solid electrolytic capacitor when exposed to high temperatures can be further reduced.

(11) In any one of (1) to (10) above, the thickness of the insulating layer may be 50 μm or more and 500 μm or less. In this case, the substrate has a strength suitable for holding the capacitor element. In addition, the thickness of the solid electrolytic capacitor can be made relatively small.

(12) In any one of (1) to (11) above, the water vapor permeability of the substrate may be 10 g/ ^m2 ·day or less, which can further suppress the intrusion of moisture into the solid electrolytic capacitor and further reduce the fluctuation of the ESR of the solid electrolytic capacitor when exposed to high temperatures.

(13) In any one of (1) to (12) above, the content of the metal layer in the entire substrate may be 1% by mass or more and 55% by mass or less. In this case, the intrusion of moisture into the solid electrolytic capacitor can be further suppressed, and the fluctuation of the ESR of the solid electrolytic capacitor when exposed to high temperatures can be further reduced.

(14) In any one of (1) to (13) above, the solid electrolytic capacitor may include two or more stacked capacitor elements. In the present disclosure, the intrusion of moisture into the solid electrolytic capacitor is reduced, so that even when the solid electrolytic capacitor is exposed to high temperatures, stress is suppressed from being applied to the components. Therefore, even when the solid electrolytic capacitor includes two or more stacked capacitor elements, electrical connection between the capacitor elements and the external electrodes is easily ensured when exposed to high temperatures, and high capacity is easily maintained.

Below, the solid electrolytic capacitor of the present disclosure will be described in more detail, including the above (1) to (14). To the extent that there is no technical contradiction, at least one of the above (1) to (14) may be combined with at least one of the elements described below.

[Solid electrolytic capacitor]
The present disclosure relates to a solid electrolytic capacitor that includes at least one capacitor element, a substrate that supports the capacitor element, a seal that seals the capacitor element, and a plurality of external electrodes. The capacitor element includes an anode portion and a cathode portion. The plurality of external electrodes are electrically connected to the anode portion and the cathode portion, respectively.

(substrate)
In a solid electrolytic capacitor, the substrate includes at least one insulating layer and at least one metal layer.

A substrate including an insulating layer is also called an insulating substrate. In general, examples of insulating substrates include glass epoxy substrates, paper phenol substrates, glass polyimide substrates, and fluorine substrates. Insulating substrates include an insulating layer formed of an insulating resin, and therefore are easily permeable to moisture. If moisture penetrates into a solid electrolytic capacitor through the substrate, as described above, the stress caused by the evaporation and expansion of moisture when exposed to high temperatures will damage the capacitor elements, etc., and the resistance will increase, resulting in an increase in ESR. Glass epoxy substrates and glass polyimide substrates are easy to obtain, but are relatively permeable to moisture, and the increase in ESR when exposed to high temperatures is likely to be significant. In the present disclosure, even when a substrate including such an insulating layer is used, the substrate further includes a metal layer, which reduces the penetration of moisture through the substrate into the solid electrolytic capacitor, and the fluctuation in ESR when exposed to high temperatures can be suppressed.

The capacitor element may be attached to the substrate by an adhesive. The adhesive used for attachment may be a conductive adhesive or a non-conductive (e.g., insulating) adhesive. Examples of conductive adhesives include adhesives containing conductive carbon and adhesives containing metal particles such as silver particles. Examples of non-conductive adhesives include, but are not limited to, adhesives containing a curable resin.

The substrate may have one insulating layer and one metal layer. In this case, the metal layer usually covers the inner principal surface of the insulating layer. The inner principal surface is the inner principal surface of the insulating layer in a solid electrolytic capacitor (in other words, the principal surface of the insulating layer on the capacitor element side). In this embodiment, the cathode portion of the capacitor element and the metal layer are bonded via a conductive adhesive layer, and when the metal layer is in contact with the external electrode, the metal layer also bears the electrical connection between the cathode portion of the capacitor element and the external electrode, thereby improving the electrical connectivity between the external electrode and the capacitor element.

The substrate may have multiple insulating layers. The substrate may have one or multiple metal layers. For example, the substrate may have two insulating layers with a metal layer interposed between the two insulating layers. In this case, the metal layer covers each of the opposing main surfaces of the two insulating layers.

The insulating layer includes, for example, an insulating resin. The insulating layer may further include an additive (such as a filler).

Insulating resins include epoxy resins, polyimide resins, fluororesins, polyamide resins, polyamideimide resins, phenolic resins, aromatic polyester resins, silicone resins, and rubber-like polymers. These resins may be modified resins. The coating may contain one of these insulating resins, or may contain two or more in combination. The insulating resin may be a thermoplastic resin or a curable resin (such as a thermosetting resin or a photocurable resin). The insulating resin may contain additives such as a catalyst, a curing agent, a crosslinking agent, a polymerization initiator, and a curing accelerator in addition to a resin or a precursor of a resin (such as a curable compound (monomer, oligomer, etc.)). When a thermoplastic resin (or a composition thereof) is used to form an insulating layer, the formed insulating layer contains a thermoplastic resin (or a composition thereof). When a curable resin (or a composition thereof) is used to form an insulating layer, the formed insulating layer contains a cured product of the curable resin (or a composition thereof).

Examples of the filler include insulating particles and insulating fibers. Examples of the insulating material constituting the filler include insulating compounds such as silica and alumina (oxides (including ceramics)), glass, and mineral materials (talc, mica, clay, etc.). The coating may contain one type of filler or a combination of two or more types. Fibrous fillers may be contained in the form of, for example, a nonwoven fabric.

From the viewpoint of ensuring a certain degree of strength, it is preferable that the insulating layer contains at least a fibrous filler. The fibrous filler is preferably glass fiber. The glass fiber may be contained in the form of a nonwoven fabric (for example, as glass cloth, etc.).

The insulating layer may further include a particulate filler. Ceramic particles are preferable as the particulate filler. In this case, the intrusion of moisture through the substrate is further suppressed, and the fluctuation of ESR when exposed to high temperatures can be further reduced. In addition, the variation in the amount of ESR fluctuation between individual units can be reduced.

Substrates having an insulating layer containing epoxy resin, polyimide resin, etc. are relatively inexpensive and easy to obtain. The insulating layer may contain at least one selected from the group consisting of epoxy resin and polyimide resin, and glass fiber (e.g., glass cloth). The insulating layer may further contain ceramic particles.

The amount of fibrous filler (such as glass fiber) may be 50 parts by mass or more and 1000 parts by mass or less, 60 parts by mass or more and 700 parts by mass or less, or 100 parts by mass or more and 300 parts by mass or less, per 100 parts by mass of insulating resin (including the cured product). When the amount of fibrous filler is within such a range, it is easy to ensure high moldability and high strength of the board while keeping the penetration of moisture through the board low.

The amount of particulate filler (such as ceramic particles) may be 5 parts by mass or more and 300 parts by mass or less, 10 parts by mass or more and 250 parts by mass or less, or 50 parts by mass or more and 200 parts by mass or less, relative to 100 parts by mass of insulating resin (including the cured product). When the amount of fibrous filler is within such a range, it is possible to further reduce the intrusion of moisture through the substrate, and it is easy to ensure high strength of the substrate.

The thickness of each insulating layer may be 50 μm or more and 500 μm or less, or may be 50 μm or more and 300 μm or less. When the thickness of the insulating layer is in this range, the strength suitable for holding the capacitor element is obtained, and the thickness of the solid electrolytic capacitor can be reduced. In addition, in a typical insulating substrate, the water vapor permeability of the insulating substrate tends to decrease as the thickness increases, but in the present disclosure, the substrate includes a metal layer, so that the water vapor permeability of the substrate can be kept low even if the thickness of the insulating layer is relatively small. The thickness of each insulating layer may be, for example, 50 μm or more and 200 μm or less, or may be 50 μm or more and 150 μm or less.

The metal layer may be at least one selected from the group consisting of metal foil and metal alloy foil. The metal layer may be a single layer or a laminate of multiple layers. The type of metal constituting the metal layer is not particularly limited. Examples of metals include aluminum, iron, copper, and alloys of these metals. From the viewpoint of easy availability of the substrate and cost advantage, it is preferable that the metal layer is at least one selected from the group consisting of copper foil and copper alloy foil. In addition, when the cathode part and the metal layer of the capacitor element are bonded via a conductive adhesive layer and the metal layer is in contact with the external electrode, if the metal layer contains copper, the electrical connectivity between the cathode part and the external electrode is improved, and the electrical connectivity between the external electrode and the capacitor element can be further improved.

The thickness of the metal layer may be 5 μm or more and 100 μm or less, 5 μm or more and 70 μm or less, or 10 μm or more and 30 μm or less. When the thickness of the metal layer is in such a range, it is possible to further reduce the intrusion of moisture through the substrate, and it is advantageous from the viewpoint of miniaturization and cost reduction of the solid electrolytic capacitor.

In this specification, the thickness of the insulating layer and the metal layer is determined by measuring the thickness at five or more randomly selected locations on each of the insulating layer and the metal layer based on a cross-sectional image that includes at least the substrate, and averaging the measured thicknesses.

The content of the metal layer in the entire substrate may be 1% by mass or more and 55% by mass or less, 10% by mass or more and 50% by mass or less, 20% by mass or more and 50% by mass or less, or 35% by mass or more and 50% by mass or less. If the content of the metal layer is in such a range, it is possible to further reduce the intrusion of moisture through the substrate, and it is advantageous from the viewpoint of reducing the cost of the solid electrolytic capacitor.

The metal layer may be in contact with one of the multiple external electrodes, or may be in contact with none of the multiple external electrodes. The metal layer may be in contact with one of the multiple external electrodes, but not with the other. The multiple external electrodes are two or more external electrodes of different polarities. By having the metal layer in contact with an external electrode of one polarity and not with an external electrode of the opposite polarity, insulation between the anode side external electrode and the cathode side external electrode can be ensured. For example, when the metal layer is electrically connected to the cathode part of the capacitor element, the metal layer is in contact with the cathode side external electrode and not with the anode side external electrode. However, the metal layer does not necessarily need to be in contact with the external electrodes, and does not need to be in contact with external electrodes of both polarities.

The metal layer is arranged to cover the main surface of the insulating layer. The area of the main surface of the insulating layer covered by the metal layer may be 50 area% or more, 70 area% or more, 75 area% or more, or 80 area% or more, 85 area% or more. The area of the main surface of the insulating layer covered by the metal layer is the area ratio of the part covered by the metal layer when the area of the entire main surface with which the metal layer is in contact is 100 area%. Hereinafter, this area ratio may be referred to as the coverage rate or the coverage rate by the metal layer. When the coverage rate is large, there is a tendency for the intrusion of moisture through the substrate to be reduced. However, since the external electrode on the anode side and the external electrode on the cathode side are short-circuited, it is difficult to cover the entire main surface of the insulating layer with the metal layer. The coverage rate by the metal layer may be less than 100 area% and less than 95 area%. The coverage may be, for example, 50 area% or more and less than 100 area%, 70 area% or more and less than 100 area%, or 80 area% or more and less than 100 area%.

The substrate has a low water vapor permeability by having a metal layer. The water vapor permeability of the substrate may be 10 g/m ² ·day or less, 9.0 g/m ² ·day or less, or 8.5 g/m ² ·day or less. By having the water vapor permeability in such a range, the intrusion of moisture through the substrate can be significantly reduced, and the fluctuation of ESR when the solid electrolytic capacitor is exposed to high temperatures can be further reduced. The water vapor permeability of the substrate is the water vapor permeability of the entire substrate including the insulating layer and the metal layer. The lower limit of the water vapor permeability of the substrate is preferably as low as possible, but it is difficult to make it completely 0 g/m ² ·day, and may be, for example, 0.1 g/m ² ·day or more.

The water vapor permeability of the substrate can be measured in accordance with JIS Z 0208:1976 "Test method for moisture permeability of moisture-proof packaging materials (cup method)". The test is carried out under temperature and humidity conditions of 85°C and 85% relative humidity. The substrate before the formation of the solid electrolytic capacitor (substrate in a wide state) is used as the measurement sample.

The moisture absorption amount of the solid electrolytic capacitor may be 155 μg/ ^cm2 or less, or may be 154 μg/ ^cm2 or less per unit surface area of one solid electrolytic capacitor. The lower the moisture absorption amount, the more preferable it is, but it is difficult to achieve 0 μg/ ^cm2 , and the amount may be 5 μg/ ^cm2 or more.

The water vapor permeability of the substrate (and the moisture absorption amount of the solid electrolytic capacitor) can be adjusted, for example, by the coverage rate of the metal layer, the thickness of the metal layer, the mass ratio of the metal layer to the substrate, the components contained in the insulating layer and their contents, the thickness of the insulating layer, etc. In the present disclosure, even when the moisture vapor permeability of the insulating layer is high (for example, when it exceeds 10 g/ ^m2 ·day), the metal layer can reduce the water vapor permeability of the substrate and the moisture absorption amount of the solid electrolytic capacitor, so that the fluctuation of ESR when the solid electrolytic capacitor is exposed to high temperatures can be suppressed.

The substrate can be formed, for example, by laminating an insulating layer and a metal layer. There are no particular limitations on the lamination method. Various lamination processes, vapor deposition, etc. may be used for lamination.

(Capacitor element)
The capacitor element placed on the substrate includes an anode portion and a cathode portion. An insulating separation layer may be provided to electrically separate the anode portion and the cathode portion. The solid electrolytic capacitor includes at least one capacitor element, and may include two or more capacitor elements. The two or more capacitor elements may be, for example, stacked.

(Anode body)
The anode body includes, for example, a first portion including one end (sometimes referred to as a first end) and a second portion including the other end opposite to the one end (sometimes referred to as a second end). The cathode part is formed in the second portion of the anode body. The portion of the anode body where the cathode part is not formed (more specifically, at least a part of the first portion) constitutes the anode part.

The anode body may contain, for example, a valve metal, an alloy containing a valve metal, or a compound containing a valve metal (such as an intermetallic compound). These materials may be used alone or in combination of two or more. Examples of valve metals include aluminum, tantalum, niobium, and titanium. The anode body may be a foil (anode foil) of a valve metal, an alloy containing a valve metal, or a compound containing a valve metal, or may be a molded body (porous molded body) or a sintered body (porous sintered body) of particles of a valve metal, an alloy containing a valve metal, or a compound containing a valve metal.

When an anode foil is used as an anode body, a porous portion is usually formed on the surface of at least the second portion of the anode foil in order to increase the surface area. Such an anode foil has a core and a porous portion formed on the surface of the core. The porous portion is formed, for example, by forming irregularities on the surface of the anode foil. An anode foil having a porous portion may be formed, for example, by roughening the surface of at least the second portion of the anode foil by etching (electrolytic etching, etc.). It is also possible to perform a roughening process such as an etching process after placing a predetermined masking member on the surface of the first portion. On the other hand, it is also possible to roughen the entire surface of the anode foil by etching or the like. In the former case, an anode foil is obtained that does not have a porous portion on the surface of the first portion and has a porous portion on the surface of the second portion. In the latter case, a porous portion is formed on the surface of the first portion in addition to the surface of the second portion. As the etching process, a known method may be used, for example, electrolytic etching. The masking member is not particularly limited and may be a conductor containing a conductive material, but an insulator such as a resin is preferable. The masking material is removed before the solid electrolyte layer is formed.

When the entire surface of the anode foil is roughened, the surface of the first portion has a porous portion. In this case, in order to prevent air from entering the solid electrolytic capacitor through the contact portion between the porous portion and the sealing body, at least a portion of the porous portion formed in the first portion may be removed in advance or compressed to crush the pores of the porous portion. This makes it possible to prevent a decrease in the reliability of the solid electrolytic capacitor due to air entering the solid electrolytic capacitor.

When stacking multiple capacitor elements, the first ends of the anode bodies of the capacitor elements may be bundled together and connected to a lead, and electrically connected to an external electrode. However, instead of bundling, the end faces of the multiple first ends may each be exposed from the outer surface of the encapsulant and electrically connected to an external electrode.

The outer surface of the encapsulant is the surface that defines the outer shape of the encapsulant. For example, if the encapsulated product in which the capacitor element is encapsulated together with the substrate has a rectangular or cubic shape, one surface (e.g., the bottom surface) may correspond to the surface of the substrate, and the remaining five surfaces other than the substrate surface (e.g., the sides, top surface, etc.) may correspond to the outer surfaces of the encapsulant.

(Dielectric Layer)
The dielectric layer is formed, for example, by anodizing the valve metal on at least the surface of the second portion of the anode body by chemical conversion treatment or the like. The dielectric layer contains an oxide of the valve metal. For example, when aluminum is used as the valve metal, the dielectric layer contains aluminum oxide. The dielectric layer is formed along at least the surface of the second portion in which the porous portion is formed (including the inner wall surface of the hole of the porous portion). Note that the method of forming the dielectric layer is not limited to this, and it is sufficient if an insulating layer that functions as a dielectric can be formed on the surface of the second portion. The dielectric layer may also be formed on the surface of the first portion (for example, the porous portion on the surface of the first portion).

The chemical conversion treatment can be carried out, for example, by immersing the anode body in a chemical conversion solution, thereby impregnating the surface of the anode body with the chemical conversion solution, and applying a voltage between the anode body as the anode and a cathode immersed in the chemical conversion solution. If the surface of the anode body has a porous portion, the dielectric layer is formed to conform to the uneven shape of the surface of the porous portion.

(Cathode)
The cathode part is formed on the second part of the anode body having the dielectric layer, and may cover the surface of the separation layer facing the second part.

The cathode portion includes, for example, a solid electrolyte layer that covers at least a portion of the dielectric layer, and a cathode lead layer that covers at least a portion of the solid electrolyte layer. The cathode portion is formed by forming a solid electrolyte so as to cover at least a portion of the dielectric layer, and by forming a cathode lead layer so as to cover at least a portion of the solid electrolyte layer. A capacitor element is obtained by forming the cathode portion on a portion of an anode body having a dielectric layer.

(Solid electrolyte layer)
The solid electrolyte layer includes, for example, a conductive polymer (conjugated polymer, dopant, etc.). As the conjugated polymer, for example, a π-conjugated polymer (polypyrrole, polythiophene, polyaniline, and derivatives thereof, etc.) may be used. For example, polythiophene derivatives include poly(3,4-ethylenedioxythiophene) (PEDOT) and the like. As the dopant, polystyrene sulfonic acid (PSS) and the like may be used, and naphthalene sulfonic acid, toluene sulfonic acid, and the like may be used. The solid electrolyte layer can be formed, for example, by polymerizing a precursor of the conjugated polymer (monomer, oligomer, etc.) and a dopant (naphthalene sulfonic acid, toluene sulfonic acid, etc.) on a dielectric layer using at least one of chemical polymerization and electrolytic polymerization. Alternatively, a solution in which the conjugated polymer and the dopant are dissolved, or a dispersion in which the conjugated polymer and the dopant are dispersed, may be attached to the dielectric layer and dried to form the solid electrolyte layer. As the dispersion medium (solvent), for example, water, an organic solvent, or a mixture thereof may be used. The solid electrolyte layer may include a manganese compound.

(Cathode extraction layer)
The cathode extraction layer may include, for example, a conductive layer in contact with the solid electrolyte layer and covering at least a portion of the solid electrolyte layer. The cathode extraction layer includes at least a first layer covering at least a portion of the solid electrolyte layer. The cathode extraction layer may include the first layer covering at least a portion of the solid electrolyte layer and a second layer covering at least a portion of the first layer.

For example, the cathode lead layer may be formed of a metal foil as the first layer. For example, the metal foil may be an Al foil, a Cu foil, a metal foil formed of a valve metal (aluminum, tantalum, niobium, etc.), or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion film, or a coating of a metal (heterogeneous metal) or a nonmetal different from the metal constituting the metal foil may be provided. Examples of heterogeneous metals and nonmetals include metals such as titanium and nickel, and nonmetals such as carbon (conductive carbon, etc.). The metal foil may be a sintered foil, a vapor-deposited foil, or a coated foil in which the surface of the metal foil (for example, Al foil, Cu foil) is covered with a conductive film by vapor deposition or coating. The vapor-deposited foil may be an Al foil with Ni vapor-deposited on the surface. Examples of the conductive film include Ti, TiC, TiO, and C (carbon) films. The conductive film may be a carbon coating.

In the cathode extraction layer, the first layer may be a coating of the dissimilar metal or nonmetal (e.g., conductive carbon), and the second layer may be the metal foil.

The cathode extraction layer may include, for example, a layer containing conductive carbon (also referred to as a carbon layer) as a first layer, and a metal-containing layer (for example, a layer containing metal powder or a metal foil) as a second layer.

The conductive carbon contained in the carbon layer serving as the first layer can be, for example, graphite (artificial graphite, natural graphite, etc.).

The layer containing metal powder as the second layer can be formed, for example, by laminating a composition containing metal powder onto the surface of the first layer. An example of such a second layer is a metal paste layer formed using a composition containing metal powder and a resin (binder resin). An example of the metal paste layer is a silver paste layer containing silver particles and a resin. Although a thermoplastic resin can be used as the resin, it is preferable to use a thermosetting resin such as an imide resin or an epoxy resin.

Examples of the metal foil for the second layer include the metal foils exemplified for the first layer.

The metal foil may be attached to the solid electrolyte layer or the first layer (such as the carbon layer) via a conductive adhesive. Examples of the conductive adhesive include an adhesive containing conductive carbon and an adhesive containing metal particles such as silver particles.

If the cathode portion includes a metal foil, it is advantageous because the end face of the metal foil can be exposed from the outer surface of the sealing body and easily electrically connected to the external electrode. If the solid electrolytic capacitor includes multiple stacked capacitor elements, the metal foil may be provided on at least one of the multiple capacitor elements, or may be provided so that the metal foil is interposed between adjacent capacitor elements. For example, one metal foil may be shared between adjacent capacitor elements. For example, if the solid electrolytic capacitor includes multiple stacked capacitor elements, the metal foil may be sandwiched between adjacent capacitor elements.

(Separator)
When a metal foil is used for the cathode extraction layer, a separator may be disposed between the metal foil and the anode foil. The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

(Separation Layer)
The separation layer is formed before the cathode portion is formed. The separation layer may be provided in the vicinity of the cathode portion so as to cover at least a part of the surface of the first portion. From the viewpoint of suppressing the intrusion of air into the inside of the solid electrolytic capacitor, the separation layer may be in close contact with the first portion and the sealing body. The separation layer may be disposed on the first portion via a dielectric layer. Such a separation layer is provided after the dielectric layer is formed. This is not limited to this case, and may be provided before the dielectric layer is formed, as necessary.

The separation layer may contain, for example, a resin, and may be one of the examples of the sealing body described below. The dielectric layer formed in the porous portion of the first part may be compressed and densified to provide insulation.

The separation layer may be provided, for example, by attaching a sheet-like insulating member (such as a resin tape) to the first portion. When using an anode foil having a porous portion on its surface, at least a portion of the porous portion of the first portion may be removed or compressed to flatten it, and then the insulating member may be adhered to the first portion. It is preferable that the sheet-like insulating member has an adhesive layer on the surface that is attached to the first portion.

Also, a liquid resin may be applied to or impregnated into at least a part of the first part to form an insulating member that adheres to the first part. In the method using a liquid resin, the insulating member may be formed so as to fill in the unevenness of at least the surface layer of the porous part of the first part. In this case, the liquid resin easily penetrates into the recesses in the surface layer of the porous part, and the insulating member can be easily formed in the recesses as well. In this case, since the porous part of the surface layer of the anode body is protected by the insulating member, the collapse of the porous part of the anode body is suppressed when the end of the anode body is partially removed together with the sealing body to form the outer surface of the sealing body and the end face of the anode body is exposed from the outer surface of the sealing body. Since the surface layer of the porous part of the anode body and the insulating member are firmly adhered to each other, the insulating member is suppressed from peeling off from the surface of the porous part of the anode body when the end of the anode body is partially removed together with the sealing body.

As the liquid resin, for example, a curable resin composition exemplified for the sealing body described later may be used, or a solution in which the resin is dissolved in a solvent may be used. Also, a sheet-like insulating material may be used in addition to coating or impregnation with the liquid resin.

(others)
The capacitor element (or two or more stacked capacitor elements) may be placed on the substrate via an adhesive as described above. Of the multiple stacked capacitor elements, the cathode-forming portion of the capacitor element closest to the substrate may have a metal foil on the substrate side.

(Spacer)
The solid electrolytic capacitor may include a spacer as necessary. For example, the spacer is disposed at least one between the ends of adjacent anode parts and between the ends of adjacent cathode parts of the laminated capacitor elements. The spacer may be conductive (metallic, etc.) or insulating. When an insulating spacer is used, the spacer may be exposed from the outer surface of the sealing body together with the end surface of the anode part or the cathode part. The insulating spacer is formed of, for example, a thermoplastic resin or a curable resin. The material of the spacer may be a resin exemplified as the material of the sealing body.

(Sealing body)
The capacitor element (or a plurality of laminated capacitor elements) is sealed by being covered with a sealing body. The capacitor element may be sealed so that at least one end face of the anode part and the cathode part is exposed from the outer surface of the sealing body, or after sealing, the sealing body may be partially removed to form the outer surface and expose at least one end face of the anode part and the cathode part from the outer surface. The other end of the lead electrically connected to one of the anode part and the cathode part may be sealed with a sealing body so that it is in a state of being drawn out from the sealing body, and the other end of the lead may be connected to an external electrode. In addition, a plate-shaped external lead terminal bent into a predetermined shape may be attached to the surface of the cathode part exposed in the capacitor element (or the lowermost or uppermost layer of the laminated plurality of capacitor elements) via a conductive paste or the like, thereby electrically connecting the capacitor element and the lead terminal.

The encapsulant preferably contains, for example, a cured product of a curable resin composition, and may contain a thermoplastic resin or a composition containing the same.

The encapsulant may be formed, for example, by using a molding technique such as injection molding. The encapsulant may be formed, for example, by using a specified mold to fill a curable resin composition or a thermoplastic resin (composition) in a specified location so as to cover the capacitor element supported on the substrate.

The curable resin composition may contain, in addition to the curable resin, at least one selected from a filler, a curing agent, a polymerization initiator, a catalyst, etc. An example of the curable resin is a thermosetting resin. The curing agent, polymerization initiator, catalyst, etc. are appropriately selected depending on the type of curable resin.

Examples of the curable resin include epoxy resin, phenol resin, urea resin, polyimide, polyamideimide, polyurethane, diallyl phthalate, and unsaturated polyester. Examples of the thermoplastic resin include polyphenylene sulfide (PPS) and polybutylene terephthalate (PBT). A thermoplastic resin composition containing a thermoplastic resin and a filler may also be used.

From the viewpoint of increasing the strength of the sealing body, it is preferable that the sealing body contains a filler. The filler may be selected from the fillers described for the coating. The sealing body may contain one type of filler or a combination of two or more types.

(contact layer)
At least one of the end faces of the anode part and the cathode part exposed from the sealing body may be connected to an external electrode via a contact layer. The contact layer may be formed of, for example, an electroless Ni plating layer, or may be formed of an electroless Ni plating layer and an electroless Ag plating layer covering the electroless Ni plating layer. When the contact layer is provided, the contact layer can ensure the electrical connection between the end face of the anode part or the cathode part and the external electrode, which is advantageous in terms of improving the reliability of the solid electrolytic capacitor.

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

(External electrode)
The external electrodes usually include a first external electrode connected to the anode portion of the capacitor element and a second external electrode connected to the cathode portion. Each external electrode may include a metal layer. The metal layer is, for example, a plating layer. The metal layer includes, for example, at least one selected from the group consisting of nickel (Ni), copper (Cu), zinc (Zn), tin (Sn), silver (Ag), and gold (Au). The metal layer may be formed using a film formation technique such as electrolytic plating, electroless plating, sputtering, vacuum deposition, chemical vapor deposition (CVD), cold spray, or thermal spray.

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

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

(Conductive paste layer)
The conductive paste layer may be formed to cover at least one end face of the anode part and the cathode part of the capacitor element or a plurality of capacitor elements. In this case, the conductive paste layer may be formed to cover the end face via a contact layer. The conductive paste layer may be formed to cover not only the end face of the anode part or the cathode part, but also the surface (side surface, etc.) of the sealing body where the end face is exposed. In this way, the anode part or the cathode part of the capacitor element and the conductive paste layer are electrically connected.

The conductive paste layer can be formed by applying a conductive paste containing conductive particles and a resin material to the surface of the sealing body with the end face of the anode or cathode exposed, and then drying it. Therefore, the conductive paste layer can also be called a conductive resin layer containing conductive particles. The resin material is suitable for bonding with the sealing body and the contact layer, and can increase the bonding strength by chemical bonding (e.g., hydrogen bonding). As the conductive particles, for example, metal particles such as silver or copper, or particles of a conductive inorganic material such as carbon can be used.

The conductive paste layer may cover not only the surface (e.g., side) of the encapsulant where the end face of the anode or cathode of the capacitor element is exposed, but also part of the surface (e.g., top or bottom) that intersects with this surface. In addition, when the surface of the substrate constitutes part of the outer surface of the capacitor element, it may cover part of the surface of the substrate.

When a laminated substrate including an insulating substrate is used as the insulating substrate, an external electrode (such as a second external electrode electrically connected to the cathode portion) may be formed in advance on the side of the laminated substrate opposite to the side on which the element stack is placed. By placing the external electrode (such as the second external electrode) can be electrically connected to the anode portion or cathode portion (usually the cathode portion) of the capacitor element via the wiring pattern formed on the laminated substrate and the through hole connecting the wiring pattern on the front side and the wiring pattern on the back side. In this case, the second external electrode is electrically connected to the cathode portion of each capacitor element via the substrate. Depending on the wiring pattern on the back side, the second external electrode (cathode) can be arbitrarily placed in the central region of the bottom surface of the solid electrolytic capacitor. For example, the second external electrode may be placed close to the first external electrode.

FIG. 1 is a cross-sectional view showing a schematic structure of a solid electrolytic capacitor according to one embodiment of the present disclosure.

As shown in FIG. 1, the solid electrolytic capacitor 100 includes a plurality of stacked capacitor elements 10, a sealing body 14 that seals the capacitor elements 10, a first external electrode 21, and a second external electrode 22. In the illustrated example, the stacked capacitor elements 10 are supported by a substrate 17.

The substrate 17 includes an insulating layer 17a and a metal layer 17b covering one of the main surfaces of the insulating layer 17a. The metal layer 17b prevents moisture from penetrating into the solid electrolytic capacitor 100 through the substrate 17, reducing the amount of moisture absorbed by the solid electrolytic capacitor. Even if the solid electrolytic capacitor 100 is exposed to high temperatures such as during a reflow process, the expansion stress caused by the evaporation of moisture is reduced on the capacitor element 10, etc., reducing damage and keeping ESR fluctuations low. In the illustrated example, the metal layer 17b is formed on the main surface (inner main surface) of the insulating layer 17a on the side where the capacitor element 10 is placed.

Each capacitor element 10 includes an anode body 3 constituting an anode portion, and a cathode portion 6. The anode body 3 is, for example, an anode foil. The anode body 3 has a core portion 4 and a porous portion 5 formed on the surface of the core portion 4 (the surface layer of the anode body 3). A dielectric layer (not shown) is formed on at least a portion of the surface of the porous portion 5. The cathode portion 6 covers at least a portion of the dielectric layer. The cathode portion 6 includes a solid electrolyte layer 7 and a cathode lead layer.

At one end (first end) of the capacitor element 10, the anode body 3 is exposed without being covered by the cathode portion 6. The other end (second end) of the capacitor element 10 is covered by the cathode portion 6. The portion of the anode body 3 that is covered by the cathode portion 6 (particularly the solid electrolyte layer 7) is referred to as the second portion 2, and the other portion is referred to as the first portion 1. The first portion 1 is not covered by the cathode portion 6 of the anode body 3. The end of the first portion 1 is the first end, and the end of the second portion 2 is the second end.

In the illustrated example, the second portion 2 has a core portion 4 and a porous portion 5 formed on the surface of the core portion 4. The first portion 1 may or may not have a porous portion 5 on its surface. The dielectric layer is formed at least along the surface of the porous portion 5 formed in the second portion 2. At least a portion of the dielectric layer covers the inner wall surface of the hole in the porous portion 5 and is formed along that inner wall surface.

The cathode section 6 comprises a solid electrolyte layer 7 covering at least a portion of the dielectric layer, and a cathode lead layer covering at least a portion of the solid electrolyte layer 7. The surface of the dielectric layer is formed with an uneven shape corresponding to the shape of the surface of the anode body 3. The solid electrolyte layer 7 is formed, for example, so as to fill in the unevenness of the dielectric layer. The cathode lead layer may comprise, for example, a first layer 8 such as a carbon layer that covers at least a portion of the solid electrolyte layer 7, and a metal foil 20 as a second layer that covers at least a portion of the first layer 8.

The metal foil 20 is interposed between the second portions 2 of the capacitor elements 10 adjacent in the stacking direction. The metal foil 20 constitutes part of the cathode portion 6 of the capacitor element 10 and is shared between the capacitor elements 10 adjacent in the stacking direction. The metal foil 20 has a carbon layer 20b on its surface. An adhesive layer 9 having electrical conductivity may be interposed between the metal foil 20 (more specifically, the carbon layer 20b) and the capacitor element 10. For the adhesive layer 9, for example, a conductive adhesive is used. The adhesive layer 9 contains, for example, silver. An adhesive layer 23 may be interposed between the substrate 17 and the metal foil 20 (more specifically, the carbon layer 20b) facing the substrate 17. The adhesive layer 23 may be formed of a conductive adhesive or a non-conductive adhesive.

In the region of the anode body 3 that does not face the cathode portion 6, at least the portion adjacent to the cathode portion 6, an insulating separation layer (or insulating member) 12 may be formed so as to cover the surface of the anode body 3. This restricts contact between the cathode portion 6 and the exposed portion (first portion 1) of the anode body 3. The separation layer 12 is, for example, an insulating resin layer.

The sealing body 14 has a substantially rectangular parallelepiped outer shape, and the solid electrolytic capacitor 100 also has a substantially rectangular parallelepiped outer shape. In the illustrated example, the sealing body 14 has a first outer surface 14a and a second outer surface 14b opposite the first outer surface 14a. The end face 1a of the first end of the anode body 3, which is the anode portion of each capacitor element 10, is exposed at the first outer surface 14a. In addition, the end face 20a of the metal foil 20 constituting the cathode portion 6 is exposed from the sealing body at the second outer surface 14b.

Each of the end faces 20a of the metal foil 20 exposed from the sealing body 14 and the second outer surface 14b are covered with a second external electrode 22. A contact layer 15 is formed on the end face 20a of the metal foil 20 so as to cover the end face 20a. The second external electrode 22 is electrically connected to the end face 20a of the metal foil 20 constituting the cathode section 6 via the contact layer 15. In addition, the metal layer 17b of the substrate 17 is in contact with the second external electrode 22 and is not in contact with the first external electrode 21.

In the solid electrolytic capacitor 100, each of the end faces 1a exposed from the sealing body 14 at the first ends of the multiple anode bodies 3 and the first outer surface 14a are covered with a first external electrode 21. A contact layer 15 is formed on the end face 1a of the anode body 3 so as to cover the end face 1a. In the illustrated example, the end face of the separation layer 12 is also exposed from the first outer surface 14a of the sealing body 14, and this exposed end face is also covered with a first external electrode 21. The first external electrode 21 is electrically connected to the end face 1a of the anode body 3 via the contact layer 15.

The first external electrode 21 comprises, for example, a conductive paste layer 21A, such as a silver paste layer, and a Ni/Sn plating layer 21B covering the conductive paste layer 21A. Similarly, the second external electrode 22 comprises, for example, a conductive paste layer 22A, such as a silver paste layer, and a Ni/Sn plating layer 22B covering the conductive paste layer 22A.

The first external electrode 21 covers the entire first outer surface 14a of the sealing body 14, and also covers a third outer surface perpendicular to the first outer surface 14a and a portion of the first outer surface 14a side of the substrate 17. Similarly, the second external electrode 22 covers the entire second outer surface 14b, and also covers a third outer surface 14c perpendicular to the second outer surface 14b and a portion of the second outer surface 14b side of the substrate 17. This configuration can further improve adhesion between the first external electrode 21 and the first outer surface 14a, and between the second external electrode 22 and the second outer surface 14b. The first external electrode 21 and the second external electrode 22, which cover a portion of the substrate 17, are each exposed on the bottom surface of the solid electrolytic capacitor 100. These exposed portions constitute the anode terminal and the cathode terminal of the solid electrolytic capacitor 100, respectively.

FIG. 2 is a cross-sectional view showing a schematic structure of a solid electrolytic capacitor according to another embodiment of the present disclosure. The solid electrolytic capacitor in FIG. 2 differs from FIG. 1 only in the layer configuration of the substrate 17, and is otherwise the same as FIG. 1, so the explanation for FIG. 1 can be referred to. In FIG. 2, the substrate 17 has two insulating layers 17a and a metal layer 17b interposed between them. The metal layer 17b is in contact with the second external electrode 22, but not with the first external electrode 21.

[Example]
The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

<<Solid electrolytic capacitors E1 to E5 and C1>>
Solid electrolytic capacitors (solid electrolytic capacitors E1 to E6) including a plurality of (specifically, seven) capacitor elements 10 stacked as shown in Figure 1 or Figure 2 were fabricated and their characteristics were evaluated in the following manner. Solid electrolytic capacitor C1 was fabricated in the same manner as solid electrolytic capacitor E1, except that a substrate having only an insulating layer without copper foil as a metal layer was used.

(1) Preparation of Substrate 17 In E1, E2, E4, and E5, substrate 17 was used in which the inner principal surface of the insulating layer was covered with copper foil as a metal layer as shown in Fig. 1. For substrate 17, a commercially available copper foil-attached insulating substrate was used, and the copper foil was etched in the vicinity of the first external electrode 21 side, so that the coverage of the principal surface of insulating layer 17a by metal layer 17b (copper foil) was adjusted to the value shown in Table 1.

After adjusting the coverage rate in the same manner as in the case of E1, another insulating layer 17a was placed on the copper foil so as to cover it, and the copper foil and insulating layer 17a were welded together to form a substrate 17 having a structure in which the copper foil as the metal layer 17b is sandwiched between two insulating layers 17a as shown in Figure 2. Note that in this substrate 17, layers of the same composition were used for the two insulating layers 17a.

In E1 to E5, the average thickness of the insulating layer was approximately 100 μm per insulating layer, and the average thickness of the copper foil was 18 μm.

For C1, all of the copper foil from the substrate used in E1 was removed by etching to prepare a substrate with only the insulating layer (average thickness approximately 100 μm).

The content of each component in each board is shown in Table 1. However, the total content of the components does not exceed 100% by mass.

(2) Preparation of Anode Body 3 Both surfaces of an aluminum foil (thickness: 100 μm) serving as a substrate were roughened by etching to prepare an anode body 3 .

(3) Formation of Dielectric Layer The second portion of the anode body 3 was immersed in a chemical conversion solution, and a direct current voltage of 7 V was applied for 20 minutes to form a dielectric layer containing aluminum oxide.

(4) Formation of solid electrolyte layer 7 Separation layer 12 was formed on a first end of anode body 3. Solid electrolyte layer 7 containing a conductive polymer was formed so as to cover a second portion of anode body 3 on which separation layer 12 was formed.

(5) Formation of Cathode Extraction Layer and Lamination of Capacitor Element 10 Anode body 3 obtained in (4) above was immersed in a dispersion liquid in which graphite particles were dispersed in water, and then removed from the dispersion liquid and dried by heating, thereby forming a carbon layer as first layer 8 on at least the surface of solid electrolyte layer 7.

Seven elements with first layers 8 formed were laminated with metal foil 20 (aluminum foil with carbon layer 20b, thickness 20 μm) as the second layer interposed between the first layers 8 of adjacent elements so that the first portions overlapped. At this time, the metal foil 20 of the second layer was attached to the adjacent first layer 8 via an adhesive layer 9 using a conductive adhesive. In this way, a cathode lead layer including the first layer 8 and the metal foil 20 as the second layer was formed, and a capacitor element 10 including the cathode lead layer was completed. In each capacitor element 10, the cathode portion 6 includes a solid electrolyte layer 7 and a cathode lead layer.

(6) Sealing with sealing body 14 The seven stacked capacitor elements 10 obtained in (4) above were bonded to the substrate 17 (on the insulating substrate in C1, on the insulating layer 17a in E3, and on the metal layer 17b in the other cases) prepared in (1) above using an epoxy adhesive, and a sealing body 14 made of insulating resin was formed around the capacitor elements 10 by molding. The side surface of the sealing body 14 was cut by dicing to form a first outer surface 14a and a second outer surface 14b. At this time, the sealing body 14 was cut so that the end surface 1a of the anode body 3 of each capacitor element 10 and the insulating layer 17a of the substrate 17 were exposed from the first outer surface 14a, and the end surface 20a of the metal foil 20 and the metal layer 17b and insulating layer 17a of the substrate 17 were exposed from the second outer surface 14b. In this manner, a precursor was obtained in which end face 1a and insulating layer 17a of anode body 3 were exposed from first outer surface 14a, and end face 20a, insulating layer 17a, and metal layer 17b of metal foil 20 constituting cathode portion 6 were exposed from second outer surface 14b. First outer surface 14a and second outer surface 14b of sealing body 14, and the end face of separation layer 12 exposed from first outer surface 14a were subjected to a cleaning treatment and a hydrophilization treatment.

(7) Formation of Contact Layer 15 Using the precursor obtained in (6) above, an electroless Ni plating layer was formed so as to cover end face 1a of anode body 3 exposed from first outer surface 14a, and then an electroless Ag plating layer was formed on the electroless Ni plating layer. In this manner, contact layer 15 consisting of an electroless Ni plating layer and an electroless Ag plating layer was formed.

(8) Formation of the First External Electrode 21 and the Second External Electrode 22 The first external electrode 21 and the second external electrode 22 were formed so as to cover the contact layer 15 formed in (7) above and the first outer surface 14a and the second outer surface 14b, respectively.

More specifically, a conductive paste containing silver particles and resin was applied to the contact layer 15 and the outer surface of the sealing body, and heated and dried to form conductive paste layers 21A and 22A, respectively. Next, an electrolytic Ni plating layer and an electrolytic Sn plating layer were formed to cover the conductive paste layers 21A and 22A, respectively. In this manner, Ni/ Sn plating layers 21B and 22B, respectively, were formed. The surfaces of the plating layers were washed with water and dried to obtain solid electrolytic capacitors having a first external electrode 21 and a second external electrode 22. A total of 20 solid electrolytic capacitors were produced for each example using the same procedure.

(9) Evaluation The following evaluations were carried out using the obtained solid electrolytic capacitors or substrates 17.

(a) Measurement of ESR In an environment of 20° C., the initial ESR (mΩ) at a frequency of 100 kHz was measured for each of the 20 solid electrolytic capacitors using an LCR meter for four-terminal measurement.

Next, a moisture absorption reflow test was carried out according to the following procedure.
First, the solid electrolytic capacitor was left in a thermostatic chamber at 30°C and 60% RH for 192 hours. The solid electrolytic capacitor removed from the thermostatic chamber was cooled to 25°C. Next, the solid electrolytic capacitor was subjected to a reflow treatment in accordance with IPC/JEDEC J-STD-020D. Specifically, the solid electrolytic capacitor was preheated at a holding temperature of 150°C to 200°C and a holding time of 180 seconds or less. The solid electrolytic capacitor after preheating was heated at a temperature of 255°C or more (maximum temperature 260°C) for 30 seconds. At this time, the heating at the maximum temperature of 260°C was limited to 10 seconds or less. Next, the solid electrolytic capacitor was cooled to 25°C over 10 minutes, and this heating and cooling were repeated two more times (i.e., a total of three times). Then, the ESR of the solid electrolytic capacitor was measured at 20°C using the same procedure as above. The amount of change in ESR due to the moisture absorption reflow test was determined by subtracting the initial ESR from the ESR after the moisture absorption reflow test, and the average value (mΩ) of 20 pieces was calculated.

(b) Measurement of Water Vapor Permeability of Substrate The water vapor permeability (g/m ² ·day) of the substrate was measured by the procedure described above.

(c) Moisture Absorption Amount of Solid Electrolytic Capacitor The moisture absorption amount per unit surface area (μg/cm ² ) of the solid electrolytic capacitor was determined by the procedure described above, and the average value of 20 capacitors was calculated.

The evaluation results are shown in Table 1. In Table 1, E1 to E6 are examples, and C1 is a comparative example.

As shown in Table 1, when the substrate has a metal layer, the amount of moisture absorbed by the solid electrolytic capacitor is reduced compared to when the substrate does not have a metal layer, and the amount of ESR fluctuation due to reflow processing is reduced (comparison of C1 with E1 to E5). Comparing E1 with E2, it can be seen that the amount of ESR fluctuation tends to decrease as the coverage rate of the main surface of the insulating layer by the metal layer increases. Furthermore, when the insulating layer contains ceramic particles, the amount of moisture absorbed by the solid electrolytic capacitor is reduced, and the amount of ESR fluctuation is significantly reduced (comparison of E1 with E5).

Although the present invention has been described with respect to the presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various modifications and alterations will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be construed to embrace all such modifications and alterations without departing from the true spirit and scope of the invention.

The solid electrolytic capacitor according to the present disclosure can prevent moisture from penetrating into the interior through a substrate including an insulating layer, and can suppress fluctuations in ESR when exposed to high temperatures such as during reflow processing. Therefore, the solid electrolytic capacitor according to the present disclosure can be used in a variety of applications requiring high reliability, and is also useful in applications requiring high heat resistance and applications in high humidity environments. However, the applications of the solid electrolytic capacitor are not limited to these.

1 First part (anode lead part)
1a: end surface of first end portion; 2: second portion (cathode forming portion);
3 anode body 4 core portion 5 porous portion 6 cathode portion 7 solid electrolyte layer 8 first layer 9 second layer 10 capacitor element 12 separation layer (insulating member)
DESCRIPTION OF SYMBOLS 14 Sealing body 14a First outer surface of sealing body 14b Second outer surface of sealing body 15 Contact layer 17 Substrate 17a: Insulating layer 17b: Metal layer 20 Cathode foil 20a End surface of metal foil 20b Carbon layer 21 First external electrode 21A Silver paste layer 21B Ni/Sn plating layer 22 Second external electrode 22A Silver paste layer 22B Ni/Sn plating layer 23 Adhesive layers 100, 200 Solid electrolytic capacitor

Claims (14)

1. At least one capacitor element including an anode portion and a cathode portion;
   A substrate supporting the capacitor element;
   a sealant that seals the capacitor element;
   a plurality of external electrodes electrically connected to the anode portion and the cathode portion,
   The substrate includes at least one insulating layer and at least one metal layer.
2. The substrate has one of the insulating layers and one of the metal layers;
   2. The solid electrolytic capacitor according to claim 1, wherein the metal layer covers an inner main surface of the insulating layer.
3. The substrate has two insulating layers;
   2. The solid electrolytic capacitor according to claim 1, wherein the metal layer is interposed between the two insulating layers and covers each of the opposing main surfaces of the two insulating layers.
4. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the metal layer is at least one selected from the group consisting of copper foil and copper alloy foil.
5. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the metal layer is in contact with one of the plurality of external electrodes and is not in contact with the other.
6. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the metal layer is not in contact with any of the plurality of external electrodes.
7. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the metal layer covers 50% or more of the area of the main surface.
8. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the thickness of the metal layer is 5 μm or more and 100 μm or less.
9. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the insulating layer contains at least one selected from the group consisting of epoxy resin and polyimide resin, and glass fiber.
10. The solid electrolytic capacitor of claim 9, wherein the insulating layer further contains ceramic particles.
11. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the thickness of the insulating layer is 50 μm or more and 500 μm or less.
12. 4. The solid electrolytic capacitor according to claim 1, wherein the water vapor permeability of the substrate is 10 g/m ² ·day or less.
13. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the content of the metal layer in the entire substrate is 1% by mass or more and 55% by mass or less.
14. The solid electrolytic capacitor according to any one of claims 1 to 3, comprising two or more of the capacitor elements stacked together.

Images