Anode foil for solid electrolytic capacitors, solid electrolytic capacitor, and method for manufacturing anode foil for solid electrolytic capacitors

Abstract

Disclosed is an anode foil 10 for solid electrolytic capacitors, the anode foil 10 comprising at least one porous layer 20, wherein: the porous layer 20 comprises a first porous structure 21 and a second porous structure 22; pores 23 that constitute the first porous structure 21 are opened to the outer surface of the porous layer 20; and some of pores 24 that constitute the second porous structure 22 are opened to the inner surfaces of the pores 23 that constitute the first porous structure 21.

Description

Anode foil for solid electrolytic capacitor, solid electrolytic capacitor, and method for manufacturing anode foil for solid electrolytic capacitor

[0001] The present invention relates to an anode foil for a solid electrolytic capacitor, a solid electrolytic capacitor, and a method for manufacturing an anode foil for a solid electrolytic capacitor.

[0002] Patent Document 1 describes a method for producing an electrode material for an aluminum electrolytic capacitor, which includes: (1) a first step of forming a film made of a paste composition containing at least one powder of aluminum and an aluminum alloy, a binder resin, and a solvent on at least one surface of a substrate; (2) a second step of sintering the film; and (3) a third step of etching the sintered film.

[0003] JP 2014-138159 A

[0004] Increasing the capacity of solid electrolytic capacitors requires increasing the specific surface area by increasing the porosity and ensuring that the pores are filled with conductive polymer without any gaps. Conventional anode foils are formed by electrolytically etching rolled aluminum foil starting from the surface layer. Increasing the specific surface area requires deep etching in the thickness direction, which makes it difficult to fill the porous layer with conductive polymer.

[0005] Furthermore, Patent Document 1 describes etching a sintered film. Generally, etching utilizes impurities and crystal defects to control the pore structure. However, if heat treatment for sintering is performed before etching as described in Patent Document 1, recrystallization occurs, causing repair of crystal defects and uneven distribution of impurities, making it impossible to control the pore structure during etching, resulting in a problem of reduced capacity. Furthermore, etching such a sintered body results in an isotropic porous structure.

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide an anode foil for a solid electrolytic capacitor, a solid electrolytic capacitor, and a method for manufacturing an anode foil for a solid electrolytic capacitor, which can easily fill with a conductive polymer while suppressing a decrease in the capacitance of the solid electrolytic capacitor.

[0007] In a first aspect, the present invention provides an anode foil for a solid electrolytic capacitor, comprising at least one porous layer, the porous layer including a first porous structure and a second porous structure, pores forming the first porous structure opening at an outer surface of the porous layer, and some of the pores forming the second porous structure opening at inner surfaces of the pores forming the first porous structure.

[0008] A second aspect of the present invention is a solid electrolytic capacitor including the anode foil for a solid electrolytic capacitor according to the first aspect.

[0009] In a third aspect, the present invention provides a method for manufacturing an anode foil for a solid electrolytic capacitor having a porous layer on a surface thereof, the method comprising the steps of: scraping the surface of a substrate to form a first porous structure; and forming a second porous structure on an inner surface of the first porous structure.

[0010] In a fourth aspect, the present invention provides a method for manufacturing an anode foil for a solid electrolytic capacitor having a porous layer on a surface thereof, the method comprising the steps of growing a first porous structure on a surface of a substrate from the surface side, and forming a second porous structure on an inner surface of the first porous structure.

[0011] According to the present invention, it is possible to provide an anode foil for a solid electrolytic capacitor, a solid electrolytic capacitor, and a method for manufacturing an anode foil for a solid electrolytic capacitor, which can easily fill a conductive polymer while suppressing a decrease in the capacitance of the solid electrolytic capacitor.

[0012] FIG. 1 is a cross-sectional view schematically illustrating an anode foil for a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing an enlarged view of a first porous structure (the area surrounded by a dashed line) of the anode foil for a solid electrolytic capacitor shown in FIG. 1. FIG. 3 is a cross-sectional view schematically illustrating an example of how the first porous structure is formed in the method for manufacturing an anode foil for a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 4 is a cross-sectional view schematically illustrating another example of how the first porous structure is formed in the method for manufacturing an anode foil for a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 5 is a cross-sectional view schematically illustrating a configuration of a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 6 is a cross-sectional view showing an enlarged view of portion II in FIG. 5. FIG. 7 is a cross-sectional view of the solid electrolytic capacitor shown in FIG. 5, viewed from the direction of the arrows III-III.

[0013] The following describes the anode foil for a solid electrolytic capacitor, the solid electrolytic capacitor, and the method for manufacturing the anode foil for a solid electrolytic capacitor of the present invention. However, the present invention is not limited to the following configurations, and can be modified as appropriate within the scope of the present invention. Note that a combination of two or more of the individual desirable configurations described below also constitutes the present invention.

[0014] (Anode Foil for Solid Electrolytic Capacitor) First, an anode foil for a solid electrolytic capacitor according to an embodiment of the present invention will be described.

[0015] Fig. 1 is a cross-sectional view schematically showing an anode foil for a solid electrolytic capacitor according to an embodiment of the present invention. Fig. 2 is an enlarged cross-sectional view of a first porous structure (area surrounded by a dashed line) of the anode foil for a solid electrolytic capacitor shown in Fig. 1. Note that the second porous structure is not shown in Fig. 1.

[0016] The anode foil 10 for a solid electrolytic capacitor shown in FIG. 1 is an electrode foil for an anode of a solid electrolytic capacitor made of a valve metal, and includes a metal core (metal core portion) 12 and a pair of porous layers 20.

[0017] Examples of the valve metal include simple metals such as aluminum, tantalum, niobium, titanium, zirconium, magnesium, and silicon, as well as alloys containing these metals. Among these, aluminum and aluminum alloys are preferred.

[0018] The thickness of the anode foil 10 is preferably 5 μm or more and 200 μm or less, more preferably 15 μm or more and 180 μm or less, and even more preferably 70 μm or more and 150 μm or less. If the thickness of the anode foil 10 is less than 5 μm, the risk of foil breakage increases. If the thickness of the anode foil 10 exceeds 200 μm, the inner radius of curvature becomes smaller when the foil is bent, increasing the risk of structural damage, which may result in deterioration of electrical characteristics such as inductance L and capacitance C.

[0019] The core metal 12 is a foil-like portion located at the center of the anode foil 10 in the thickness direction.

[0020] The thickness of the core metal 12 is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 80 μm or less, and even more preferably 15 μm or more and 40 μm or less.

[0021] The porous layer 20 is provided on each of the two main surfaces of the core 12, but may be provided on only one of the main surfaces of the core 12.

[0022] The anode foil 10 may not substantially have a metal core 12. That is, the entire anode foil 10 may be composed of the porous layer 20. Because the metal core 12 is not porous, the presence of the metal core reduces the specific surface area of ​​the anode foil 10. Therefore, the metal core 12 is not particularly necessary as long as sufficient strength is ensured. Such an anode foil 10 can be formed, for example, by forming a porous layer from each of the main surfaces of a base material made of a valve metal to the center of the base material.

[0023] The thickness of the porous layer 20 per layer on one side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and even more preferably 20 μm to 70 μm.

[0024] The porous layer 20 has a first porous structure 21. The pores 23 forming the first porous structure 21 are open on the outer surface (the outermost surface located on the surface layer side) of the porous layer 20.

[0025] The first porous structure 21 is formed from the surface toward the inside of the anode foil 10, or from the inside toward the surface of the anode foil 10. Here, the surface of the anode foil 10 refers to the outermost surface located on the surface layer side of the anode foil 10, and the inside of the anode foil 10 refers to the center (deep part) in the thickness direction of the anode foil 10.

[0026] The first porous structure 21 has pores 23 formed therein that are larger (coarser) than those in the second porous structure described below.

[0027] 1 and 2, the first porous structure 21 has a sponge-like structure with a series of cubic pits. However, the first porous structure 21 is not limited to a sponge-like structure as long as it can ensure the specific surface area of ​​the first porous structure 21 and allow the conductive polymer and etching solution to penetrate. For example, the first porous structure 21 may have a particle structure in which powder is layered (deposited), a tunnel structure in which tunnel-shaped voids are provided, or an uneven structure in which unevenness is provided on the surface. Here, a pit means a single cavity (cluster) of a single shape.

[0028] Furthermore, when the first porous structure 21 is sponge-like, the shape of the pits is not particularly limited to a cubic shape and may be, for example, a spherical pit. Such spherical pits can be obtained, for example, by forming cubic pits by electrolytic etching and then chemically dissolving the surfaces of the pits. Note that cubic pits can be formed by electrolytic etching using an alternating current, as described below.

[0029] As shown in Fig. 2 , a second porous structure 22 is formed on the inner surface of the first porous structure 21. Here, the inner surface of the first porous structure 21 refers to the surface excluding the outermost surface located on the surface layer side of the anode foil 10. However, as shown in Fig. 2 , the second porous structure 22 is usually formed on the outermost surface (outer surface) of the first porous structure 21 in addition to the inner surface of the first porous structure 21.

[0030] That is, some of the pores 24 forming the second porous structure 22 are open to the inner surfaces of the pores 23 forming the first porous structure 21. Furthermore, the second porous structure 22 has pores 24 that are smaller (finer) than those of the first porous structure 21. The pores 24 of the second porous structure 22 are formed by a process different from that of the pores 23 of the first porous structure 21. First, the pores 23 of the first porous structure 21 are formed, and then the pores 24 of the second porous structure 22 are formed on the surface of the first porous structure 21.

[0031] In Fig. 2, the second porous structure 22 has a sponge-like structure in which cubic pits are connected in a disordered manner, but any structure can be used as long as the specific surface area of ​​the second porous structure 22 can be ensured. For example, in the case of a sponge-like structure, the pits may have a shape other than a cube, such as a spherical or irregular shape. Furthermore, in the case of a structure other than a sponge-like structure, the pits may be tunnel-like spaces whose cross section is circular, polygonal, or irregular, or complex tunnel-like spaces formed by connecting these spaces in a branching manner. In other words, the second porous structure is not particularly limited to the sponge-like structure shown in Fig. 2.

[0032] Furthermore, when the second porous structure 22 is sponge-like, the shape of the pits is not particularly limited to a cubic shape, and may be, for example, a spherical pit.

[0033] When both the first porous structure 21 and the second porous structure 22 are sponge-like, the pit structure constituting the first porous structure 21 may be the same as or different from the pit structure constituting the second porous structure 22. Examples of the pit structure include the shape and dimensions (e.g., diameter) of the pits, and the state in which a plurality of pits are connected together.

[0034] As described above, the pores 23 forming the first porous structure 21 are open on the outer surface of the porous layer 20, and therefore can be formed without heat treatment such as sintering. In other words, the first porous structure 21 can be formed in a state where impurities and crystal defects that can be used to control the pore structure by etching are controlled. Therefore, when the second porous structure 22 is formed on the inner surface of the first porous structure 21, the etching structure can be controlled, resulting in a high specific surface area and little capacity loss.

[0035] Furthermore, by providing the first porous structure 21, the first porous structure 21 can be etched from other than the surface side to form the second porous structure 22, thereby enabling the etching depth for forming the second porous structure 22 to be shallower. This facilitates filling (impregnation) of the conductive polymer deep into the porous layer 20. Even if the second porous structure 22 is etched shallowly, the total pore volume of the pores 23 of the first porous structure 21 and the pores 24 of the second porous structure 22 can be ensured, preventing a decrease in the specific surface area. Furthermore, by providing the first porous structure 21, the conductive polymer can be filled into the porous layer 20 from other than the surface side, further facilitating filling (impregnation) of the conductive polymer.

[0036] In a cross section of the porous layer 20 taken along a direction perpendicular to the surface of the anode foil 10, the ratio of the area of ​​voids formed by interconnected pits in the second porous structure 22 to the area of ​​voids in the entire porous layer 20 is preferably less than 50%, more preferably 30% or less, and even more preferably 10% or less. If this ratio is 50% or more, it may be difficult to obtain the desired capacitance. This ratio is calculated by binarizing an image obtained by observing the cross section using a scanning electron microscope (SEM) or the like and analyzing the binarized image. The lower limit of this ratio is not particularly limited and may be, for example, 0%. In this way, voids formed by interconnected pits in the second porous structure 22 may not be present in the cross section.

[0037] Furthermore, here, the term "voids formed by interconnected pits in the second porous structure 22" refers to a state in which a plurality of fine pits that were initially formed individually by etching are enlarged due to excessive etching in areas where etching is locally concentrated, and the enlarged pits then interconnect with adjacent pits, forming large voids. However, the voids formed by interconnected pits in the second porous structure 22 are smaller (finer) voids than the voids in the first porous structure 21.

[0038] The pore size distribution of the anode foil 10 preferably has a first peak caused by the pores 23 of the first porous structure 21 and a second peak caused by the pores 24 of the second porous structure 22 .

[0039] The pore size distribution of the anode foil 10 can be measured by a common method for measuring pore size distribution, such as mercury porosimetry or gas adsorption.

[0040] In the pore size distribution, the first peak preferably exists in a pore diameter range of 1 μm or more and less than 10 μm, and the second peak preferably exists in a pore diameter range of 0.1 μm or more and less than 1 μm. In the pore size distribution, the first peak more preferably exists in a pore diameter range of 1 μm or more and 5 μm or less, and even more preferably exists in a pore diameter range of 1 μm or more and 3 μm or less. In the pore size distribution, the second peak more preferably exists in a pore diameter range of 0.1 μm or more and 0.5 μm or less, and even more preferably exists in a pore diameter range of 0.1 μm or more and 0.3 μm or less.

[0041] In the pore size distribution, the pore sizes of the second porous structure 22 are preferably distributed in the range of 0.01 μm to 1 μm inclusive. Here, the pore sizes of the second porous structure 22 being distributed in the range of A μm to B μm inclusive (A and B are any real numbers satisfying A<B) means that the pore size distribution of the second porous structure 22 falls within the range of A to B μm (or may be a part thereof).

[0042] The volume of the voids due to the first porous structure 21 is preferably 50% or less of the volume of the voids in the entire porous layer 20. The volume of the voids due to the first porous structure 21 can be measured accurately by measuring it before forming the second porous structure 22. Various known methods can be used, such as gas adsorption, mercury intrusion, measuring from a binarized image of a cross-sectional SEM image, processing a cross-section with a focused ion beam (FIB) device, taking an SEM image each time processing is performed, reconstructing the two-dimensional data into three-dimensional data, and calculating the volume. The volume of the voids in the entire porous layer 20 can also be measured using the above method. The volume of the voids due to the first porous structure 21 is preferably 10% or more, more preferably 30% or more, of the volume of the voids in the entire porous layer 20.

[0043] As shown in FIG. 1 , it is preferable that all of the pores 23 in the first porous structure 21 are open pores. That is, it is preferable that all of the pores 23 in the first porous structure 21 are open to the surface of the anode foil 10. Note that "all of the pores 23 in the first porous structure 21 are open pores" means that all of the pores 23 in the first porous structure 21 throughout the anode foil 10 are open pores. This is because the first porous structure 21 serves as a pathway that facilitates the formation of a solid electrolyte layer. A solid electrolyte layer is typically formed by impregnation and polymerization of a monomer solution or impregnation with a dispersion of polymer fine particles, and the first porous structure 21 serves as the main pathway for impregnation. Whether or not all of the pores 23 in the first porous structure 21 can be said to be open pores can be confirmed by comparing the volume measurement by mercury intrusion porosimetry with the above-mentioned FIB-SEM measurement results after the first porous structure 21 is formed to verify the percentage of open pores. That is, volume measurement by mercury porosimetry can determine the volume of pores that are open pores, while FIB-SEM can determine the volumes of both open pores and closed pores. The closer the two values ​​are, the higher the open pore ratio.

[0044] The pore diameter of the first porous structure 21 is preferably 0.1 μm or more and 10 μm or less, more preferably 0.1 μm or more and 5 μm or less, and even more preferably 0.1 μm or more and 3 μm or less. When the pore diameter of the first porous structure 21 is 0.1 μm or more, the impregnation of the conductive polymer can be improved. When the pore diameter of the first porous structure 21 is 10 μm or less, a decrease in the specific surface area can be more effectively suppressed. Furthermore, when the first porous structure 21 is formed by etching, a pore diameter of 0.1 μm or more sufficiently diffuses metal ions (e.g., aluminum ions) eluted during etching, preventing an increase in the liquid resistance. This results in a similar etching pattern between the surface and center of the anode foil 10, thereby more effectively suppressing a decrease in capacity. The pore diameter of the first porous structure 21 can be measured by the volume measurement method described above (excluding the gas adsorption method).

[0045] The pore diameter of the second porous structure 22 is preferably 0.01 μm or more and 1 μm or less. If the pore diameter of the second porous structure 22 is 0.01 μm or more, the pores 24 of the second porous structure 22 can be prevented from being filled with a dielectric film when the anode foil 10 is anodized to form a dielectric layer, and a decrease in capacity can be more effectively suppressed. If the pore diameter of the second porous structure 22 is 1 μm or less, a decrease in specific surface area can be effectively prevented, and a decrease in capacity can be more effectively suppressed. The pore diameter of the second porous structure 22 can be measured in the same manner as the pore diameter of the first porous structure 21.

[0046] The ratio of the pore size of the first porous structure 21 to the pore size of the second porous structure 22 is preferably 0.1 or more and 1000 or less. When this ratio is 0.1 or more and 1000 or less, it is possible to achieve a high level of both impregnation with the conductive polymer and ensuring a sufficient specific surface area.

[0047] The depth of the pores 24 of the second porous structure 22 is preferably 1 μm or more and 50 μm or less. When the depth of the pores 24 of the second porous structure 22 is 1 μm or more, the specific surface area can be further increased. When the depth of the pores 24 of the second porous structure 22 is 50 μm or less, when the second porous structure 22 is formed by etching, it is easy to control the structure in the etching depth direction, and the specific surface area can be sufficiently increased. Furthermore, since the conduction path can be prevented from becoming long, deterioration of the ESR (equivalent series resistance) characteristics due to increased resistance can be prevented. The depth of the pores 24 of the second porous structure 22 can be measured by the following method. That is, the depth of the pores 24 may be determined by measuring the depth of the second porous structure 22 from the wall surface of the second porous structure 22 using a cross-sectional microscope image or SEM image. The first porous structure 21 (pores 23) and the second porous structure 22 (pores 24) may be distinguished based on the difference in their pore diameters, or by providing a threshold value to a binarized image obtained by image analysis. Alternatively, the first porous structure 21 may be filled in advance with a dispersion of large particles (a polymer dispersion or any other particle dispersion), and then the first porous structure 21 (pores 23) and the second porous structure 22 (pores 24) may be distinguished from a cross-sectional microscope image or SEM image, and the depth of the second porous structure 22 from the wall surface of the second porous structure 22 may be measured to determine the depth of the pores 24.

[0048] (Method for Manufacturing Anode Foil for Solid Electrolytic Capacitor) Next, a method for manufacturing an anode foil for a solid electrolytic capacitor according to an embodiment of the present invention will be described.

[0049] The method for manufacturing an anode foil for a solid electrolytic capacitor according to this embodiment is a method for manufacturing an electrode foil for an anode of a solid electrolytic capacitor having a porous layer on the surface thereof, and is suitable for manufacturing the anode foil for a solid electrolytic capacitor according to the above-described embodiment.

[0050] In the manufacturing method according to this embodiment, first, a substrate is prepared.

[0051] The substrate is preferably a metal foil made of a valve metal, and examples of the valve metal include the materials described above. The metal foil is preferably a rolled metal foil.

[0052] FIG. 3 is a cross-sectional view schematically showing an example of how the first porous structure is formed in the method for producing an anode foil for a solid electrolytic capacitor according to an embodiment of the present invention.

[0053] 3, the surface of the substrate 30 is scraped to form the first porous structure 21. As a result, the first porous structure 21 is formed on at least one main surface (preferably both main surfaces) of the core metal 12. In this case, the thickness of the substrate 30 is preferably 15 μm or more and 500 μm or less, and more preferably 30 μm or more and 200 μm or less.

[0054] In this case, the method for forming the first porous structure 21 is not particularly limited, and examples include etching, texture transfer, and texture formation by blasting, etc. These methods allow the first porous structure 21 to be formed in a state where impurities and crystal defects are controlled without heat treatment. Furthermore, when heat treatment such as sintering is performed on rolled metal foil, the crystal strain generated during rolling is released and the tensile strength decreases. However, the above method allows the strength of the metal foil to be maintained, resulting in a higher capacity. Of these methods, texture transfer can easily form the first porous structure 21 without unevenly distributed impurities. Furthermore, texture formation by blasting, etc., allows crystal defects to be easily controlled.

[0055] In this specification, unless otherwise specified, etching refers to electrolytic etching. Examples of the electrolyte for etching include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0056] When forming the first porous structure 21 by etching, AC etching may be performed by alternately passing a positive current and a negative current through the substrate. Specifically, for example, a square-wave AC current is passed through the substrate. This allows the formation of a sponge-like first porous structure 21 composed of cubic pits. Note that in this AC etching, a sine-wave AC current may be passed through the substrate.

[0057] When the first porous structure 21 is formed by etching, direct current etching may be performed by intermittently passing only a positive current through the substrate, thereby forming the first porous structure 21 having a tunnel structure.

[0058] More specifically, the etching conditions for the first porous structure 21 may be, for example, the following conditions: a direct current is applied in an aqueous solution containing halogen (mainly chlorine) (for example, at 70° C. and a current density of 1000 mA / cm ２ (The etching time was 5 minutes.) The current waveform may be constant, but by varying the current value at regular intervals during application, the above-mentioned composite tunnel-like spatial structure can be obtained. Etching with a direct current results in a square-prism pit structure. After the pit formation, direct current electrolysis (for example, 90°C, current density 200 mA / cm) is performed using an acid (sulfuric acid, phosphoric acid, or nitric acid) that does not contain halogen (mainly chlorine). ２ Alternatively, an alternating current may be applied (for example, at 30°C and a current density of 200 mA / cm) in an aqueous solution containing halogen (mainly chlorine). ２ , frequency 50 Hz, etc.).

[0059] FIG. 4 is a cross-sectional view schematically showing another example of the mode of forming the first porous structure in the method for producing an anode foil for a solid electrolytic capacitor according to an embodiment of the present invention.

[0060] 4, the first porous structure 21 may be grown on the surface of the substrate 30 from its surface side. This also results in the first porous structure 21 being formed on at least one main surface (preferably both main surfaces) of the core metal 12. In this case, the thickness of the substrate 30 is preferably 5 μm or more and 100 μm or less, and more preferably 15 μm or more and 50 μm or less.

[0061] In this case, the method for forming the first porous structure 21 is not particularly limited, and examples include electrodeposition (e.g., aluminum), physical vapor deposition (PVD) such as vapor deposition and sputtering, chemical vapor deposition (CVD), and collision of metal powder (e.g., aluminum powder). These methods also allow the first porous structure 21 to be formed without heat treatment, while controlling impurities and crystal defects. Furthermore, the above methods allow the strength of the metal foil to be maintained, resulting in a higher capacity. Among these methods, electrodeposition allows the first porous structure 21 to be easily formed without unevenly distributed impurities.

[0062] Next, a second porous structure 22 is formed on the inner surface of the first porous structure 21 (see FIG. 2), thereby completing an anode foil for a solid electrolytic capacitor.

[0063] The method for forming the second porous structure 22 is not particularly limited, but etching is preferred.

[0064] When forming the second porous structure 22 by etching, AC etching may be performed by alternately passing a positive current and a negative current through the substrate. Specifically, for example, a square-wave AC current is passed through the substrate. This allows the formation of a sponge-like second porous structure 22 composed of cubic pits. Note that in this AC etching, a sine-wave AC current may be passed through the substrate.

[0065] The etching conditions for the second porous structure 22 may be the same as those for general etching known for forming a sponge-like structure.

[0066] (Solid Electrolytic Capacitor) Next, a solid electrolytic capacitor according to an embodiment of the present invention will be described.

[0067] Fig. 5 is a cross-sectional view schematically showing the configuration of a solid electrolytic capacitor according to an embodiment of the present invention. Fig. 6 is an enlarged cross-sectional view of part II in Fig. 5. Fig. 7 is a cross-sectional view of the solid electrolytic capacitor of Fig. 5 as viewed from the direction of the arrow III-III. In Figs. 5 and 7, the length direction of the insulating resin body (described later) is indicated by L, the height direction of the insulating resin body by T, and the width direction of the insulating resin body by W. The height direction T is perpendicular to the length direction L, and the width direction W is perpendicular to both the length direction L and the height direction T. Note that the second porous structure is not shown in Fig. 6.

[0068] 5 to 7 has a substantially rectangular parallelepiped shape. In this embodiment, the solid electrolytic capacitor 100 has external dimensions of, for example, 7.3 mm in the length direction L, 4.3 mm in the width direction W, and 1.9 mm in the height direction T.

[0069] The solid electrolytic capacitor 100 includes three or more capacitor elements 180 , an insulating resin body 110 , a first terminal 120 , and a second terminal 130 .

[0070] Specifically, three or more capacitor elements 180 are provided inside insulating resin body 110. Insulating resin body 110 has a substantially rectangular parallelepiped outer shape. Insulating resin body 110 has first and second main surfaces 110a and 110b that face each other in height direction T, first and second side surfaces 110c and 110d that face each other in width direction W, and first and second end surfaces 110e and 110f that face each other in length direction L.

[0071] As described above, the insulating resin body 110 has a substantially rectangular parallelepiped outer shape, but the corners and ridges may be rounded. The corners are portions where three surfaces of the insulating resin body 110 intersect, and the ridges are portions where two surfaces of the insulating resin body 110 intersect. Concave and concave portions may be formed on at least one of the first main surface 110a, the second main surface 110b, the first side surface 110c, the second side surface 110d, the first end surface 110e, and the second end surface 110f.

[0072] The insulating resin body 110 is made of insulating resin such as epoxy resin in which glass or silicon oxide is dispersed and mixed as a filler.

[0073] Each of the three or more capacitor elements 180 includes an anode portion 140, a dielectric layer 150, and a cathode portion 160. The three or more capacitor elements 180 are stacked one on top of the other in the height direction T.

[0074] The anode part 140 is made of the above-mentioned anode foil 10 for a solid electrolytic capacitor.

[0075] The dielectric layer 150 is provided on the outer surface of the anode foil 10. In this embodiment, the dielectric layer 150 is made of aluminum oxide. Specifically, the dielectric layer 150 is made of aluminum oxide formed by anodizing the outer surfaces of the anode foil 10 (the pore surfaces of the first porous structure and the pore surfaces of the second porous structure).

[0076] The cathode section 160 has a solid electrolyte layer 161 and a current collector layer. The solid electrolyte layer 161 is provided on a part of the outer surface of the dielectric layer 150. The solid electrolyte layer 161 is not provided on the outer surface of the dielectric layer 150 provided on the outer surface closer to the second end face 110f of the anode foil 10, which is located opposite the cathode section 160. In this part of the dielectric layer 150, the outer surface of the part adjacent to the part where the solid electrolyte layer 161 is provided is covered with an insulating resin layer 151, which will be described later.

[0077] 6, the solid electrolyte layer 161 is provided so as to fill a plurality of recesses (pores of the first porous structure and pores of the second porous structure) in the anode foil 10. However, it is sufficient that the solid electrolyte layer 161 covers the above-mentioned part of the outer surface of the dielectric layer 150, and there may be recesses in the anode foil 10 that are not filled with the solid electrolyte layer 161. The solid electrolyte layer 161 is made of a polymer containing a conductive polymer such as poly(3,4-ethylenedioxythiophene).

[0078] The current collector layer is provided on the outer surface of the solid electrolyte layer 161. In this embodiment, the current collector layer is composed of a first current collector layer 162 provided on the outer surface of the solid electrolyte layer 161 and a second stack layer 163 provided on the outer surface of the first current collector layer 162. The first current collector layer 162 contains carbon. The second stack layer 163 contains silver.

[0079] As described above, in the portion of the dielectric layer 150 located on the opposite side from the cathode portion 160 side where the solid electrolyte layer 161 is not provided, the portion adjacent to the portion where the solid electrolyte layer 161 is provided has its outer surface covered with the insulating resin layer 151 having a composition different from that of the insulating resin body 110.

[0080] 6 , the insulating resin layer 151 is provided so as to fill a plurality of recesses (pores of the first porous structure and the second porous structure) in the outer surface of the anode foil 10 in a portion adjacent to the portion where the solid electrolyte layer 161 is provided. The insulating resin layer 151 contains an insulating resin such as a polyimide resin or a polyamide-imide resin.

[0081] 5 and 7 , the current collector layers of capacitor elements 180 adjacent to each other in the stacking direction are electrically connected to each other by a connecting conductor layer 190. The width of the connecting conductor layer 190 in the width direction W is equal to the width of the anode foil 10 in the width direction W. The connecting conductor layer 190 contains silver.

[0082] The ends of the anode foils 10 of the capacitor elements 180 adjacent to each other in the stacking direction, which are closer to the second end faces 110f, are electrically connected to each other by resistance welding or the like.

[0083] The first terminal 120 is a lead frame. The first terminal 120 is electrically connected to the cathode portions 160 of the three or more capacitor elements 180 and is extended to the outside of the insulating resin body 110. A portion of the first terminal 120 located inside the insulating resin body 110 faces the current collector layers of two capacitor elements 180 adjacent to each other in the stacking direction and is connected to each of the current collector layers by a connecting conductor layer 190. A portion of the first terminal 120 located outside the insulating resin body 110 is bent along the first end surface 110e and the second main surface 110b of the insulating resin body 110.

[0084] The second terminal 130 is a lead frame. The second terminal 130 is electrically connected to the anode portion 140 of each of the three or more capacitor elements 180 and is extended to the outside of the insulating resin body 110. A portion of the second terminal 130 located inside the insulating resin body 110 is sandwiched between ends of the anode foils 10 of two capacitor elements 180 adjacent to each other in the stacking direction, the ends being closer to the second end faces 110f, and is connected to each of the anode foils 10 by resistance welding or the like. A portion of the second terminal 130 located outside the insulating resin body 110 is bent along the second end face 110f and the second main surface 110b of the insulating resin body 110.

[0085] In the above embodiment, a pair of lead frames drawn out from a pair of end faces are used as a pair of terminals (external electrodes) electrically connected to the anode and cathode portions of each capacitor element, respectively. However, in the solid electrolytic capacitor of the present invention, a pair of electrode layers formed on a pair of end faces, respectively, may also be used as a pair of terminals (external electrodes).

[0086] Although the above embodiment describes a chip-type solid electrolytic capacitor, the solid electrolytic capacitor of the present invention may be used by being embedded in a package substrate included in a semiconductor device, for example, such as a semiconductor composite device in which a voltage regulator (voltage control device) and a load are mounted on a package substrate.

[0087] The present specification discloses the following:

[0088] <1> An anode foil for a solid electrolytic capacitor, comprising: at least one porous layer; the porous layer includes a first porous structure and a second porous structure; pores forming the first porous structure are open on an outer surface of the porous layer; and some of the pores forming the second porous structure are open on inner surfaces of the pores forming the first porous structure.

[0089] <2> The anode foil for a solid electrolytic capacitor according to <1>, wherein in a cross section of the porous layer taken along a direction perpendicular to a surface of the anode foil for a solid electrolytic capacitor, a ratio of an area of ​​voids formed by interconnected pits of the second porous structure to an area of ​​voids in the entire porous layer is less than 50%.

[0090] <3> The anode foil for a solid electrolytic capacitor according to <1> or <2>, wherein a pore size distribution has a first peak caused by pores of the first porous structure and a second peak caused by pores of the second porous structure.

[0091] <4> The anode foil for a solid electrolytic capacitor according to <3>, wherein in the pore size distribution, the first peak exists in a pore size range of 1 μm or more and less than 10 μm, and the second peak exists in a pore size range of 0.1 μm or more and less than 1 μm.

[0092] <5> The anode foil for a solid electrolytic capacitor according to <3> or <4>, wherein the pore size distribution of the second porous structure is in the range of 0.01 μm or more and 1 μm or less.

[0093] <6> The anode foil for a solid electrolytic capacitor according to any one of <1> to <5>, wherein the volume of the voids due to the first porous structure is 50% or less of the volume of the voids in the entire porous layer.

[0094] <7> The anode foil for a solid electrolytic capacitor according to any one of <1> to <6>, wherein all of the pores of the first porous structure are open pores.

[0095] <8> The anode foil for a solid electrolytic capacitor according to any one of <1> to <7>, wherein the pore diameter of the first porous structure is 0.1 μm or more and 10 μm or less.

[0096] <9> The anode foil for a solid electrolytic capacitor according to any one of <1> to <8>, wherein the pore diameter of the second porous structure is 0.01 μm or more and 1 μm or less.

[0097] <10> The anode foil for a solid electrolytic capacitor according to any one of <1> to <9>, wherein a ratio of a pore size of the first porous structure to a pore size of the second porous structure is 0.1 or more and 1000 or less.

[0098] <11> The anode foil for a solid electrolytic capacitor according to any one of <1> to <10>, wherein the pores of the second porous structure have a depth of 1 μm or more and 50 μm or less.

[0099] <12> The anode foil for a solid electrolytic capacitor according to any one of <1> to <11>, having a thickness of 5 μm or more and 200 μm or less.

[0100] <13> The anode foil for a solid electrolytic capacitor according to any one of <1> to <12>, which is substantially free of a metal core.

[0101] <14> A solid electrolytic capacitor comprising the anode foil for a solid electrolytic capacitor according to any one of <1> to <13>.

[0102] <15> A method for manufacturing an anode foil for a solid electrolytic capacitor having a porous layer on a surface thereof, the method comprising: scraping a surface of a substrate to form a first porous structure; and forming a second porous structure on an inner surface of the first porous structure.

[0103] <16> A method for manufacturing an anode foil for a solid electrolytic capacitor having a porous layer on a surface thereof, the method comprising: growing a first porous structure on a surface of a substrate from the surface side; and forming a second porous structure on an inner surface of the first porous structure.

[0104] REFERENCE SIGNS LIST 10 Anode foil for solid electrolytic capacitor 12 Metal core 20 Porous layer 21 First porous structure 23 Pores of first porous structure 22 Second porous structure 24 Pores of second porous structure 30 Substrate 100 Solid electrolytic capacitor 110 Insulating resin body 110a First main surface 110b Second main surface 110c First side surface 110d Second side surface 110e First end surface 110f Second end surface 120 First terminal 130 Second terminal 140 Anode portion 150 Dielectric layer 151 Insulating resin layer 160 Cathode portion 161 Solid electrolyte layer 162 First current collector layer 163 Second integrated layer 180 Capacitor element 190 Connecting conductor layer

Claims

1. at least one porous layer; the porous layer includes a first porous structure and a second porous structure; the pores forming the first porous structure are open at an outer surface of the porous layer; anode foil for a solid electrolytic capacitor, wherein some of the pores forming the second porous structure are open to the inner surfaces of the pores forming the first porous structure;

2. 2. The anode foil for a solid electrolytic capacitor according to claim 1, wherein in a cross section of the porous layer taken along a direction perpendicular to a surface of the anode foil for a solid electrolytic capacitor, a ratio of an area of ​​voids formed by interconnected pits of the second porous structure to an area of ​​voids in the entire porous layer is less than 50%.

3. 3. The anode foil for a solid electrolytic capacitor according to claim 1, wherein a pore size distribution thereof has a first peak caused by the pores of the first porous structure and a second peak caused by the pores of the second porous structure.

4. 4. The anode foil for a solid electrolytic capacitor according to claim 3, wherein in the pore size distribution, the first peak exists in a pore size range of 1 μm or more and less than 10 μm, and the second peak exists in a pore size range of 0.1 μm or more and less than 1 μm.

5. 4. The anode foil for a solid electrolytic capacitor according to claim 3, wherein the pore diameters of the second porous structure are distributed in the range of 0.01 μm or more and 1 μm or less in the pore diameter distribution.

6. 3. The anode foil for a solid electrolytic capacitor according to claim 1, wherein a volume of the voids due to said first porous structure is 50% or less of a volume of the voids in said entire porous layer.

7. 3. The anode foil for a solid electrolytic capacitor according to claim 1, wherein all of the pores in the first porous structure are open pores.

8. 3. The anode foil for a solid electrolytic capacitor according to claim 1, wherein the pore diameter of the first porous structure is 0.1 μm or more and 10 μm or less.

9. 3. The anode foil for a solid electrolytic capacitor according to claim 1, wherein the pore diameter of the second porous structure is 0.01 μm or more and 1 μm or less.

10. 3. The anode foil for a solid electrolytic capacitor according to claim 1, wherein a ratio of a pore size of the first porous structure to a pore size of the second porous structure is 0.1 or more and 1000 or less.

11. 3. The anode foil for a solid electrolytic capacitor according to claim 1, wherein the depth of the pores of the second porous structure is 1 μm or more and 50 μm or less.

12. 3. The anode foil for a solid electrolytic capacitor according to claim 1, having a thickness of 5 μm or more and 200 μm or less.

13. 3. The anode foil for a solid electrolytic capacitor according to claim 1, which is substantially free of a metal core.

14. A solid electrolytic capacitor comprising the anode foil for a solid electrolytic capacitor according to claim 1 or 2.

15. A method for producing an anode foil for a solid electrolytic capacitor having a porous layer on a surface thereof, comprising: scraping the surface of the substrate to form a first porous structure; and forming a second porous structure on the inner surface of the first porous structure.

16. A method for producing an anode foil for a solid electrolytic capacitor having a porous layer on a surface thereof, comprising: growing a first porous structure on a surface of a substrate from the surface side; and forming a second porous structure on the inner surface of the first porous structure.