Solid electrolytic capacitor and method for producing solid electrolytic capacitor

Abstract

This solid electrolytic capacitor comprises: a plurality of flat-film capacitor elements; a plurality of flat-film cathode electrode foils; and an insulating resin. Each of the capacitor elements has a structure in which a dielectric layer and a solid electrolyte layer are sequentially formed on the surface of a flat-film anode electrode foil. The insulating resin seals a sheet laminate formed by alternately laminating the plurality of flat-film capacitor elements and the cathode electrode foils. The solid electrolyte layer and each of the cathode electrode foils are directly bonded to each other. The bonding surface where the cathode electrode foil is bonded to the solid electrolyte layer is roughened. The ratio of the opening width in a plan view of openings formed in the bonding surface as a result of the roughening with respect to the opening depth which is orthogonal to the bonding surface in the openings is 1 or more.

Description

Solid electrolytic capacitor and method for manufacturing the solid electrolytic capacitor

[0001] The present invention relates to a solid electrolytic capacitor that prevents moisture and impurities from entering the interior thereof.

[0002] Patent Document 1 describes a method for manufacturing a solid electrolytic capacitor and a solid electrolytic capacitor. The solid electrolytic capacitor described in Patent Document 1 includes a plurality of flat-film capacitor elements and a plurality of metal foils (cathodes). The flat-film capacitor elements include a foil-shaped valve metal substrate, a porous portion of the valve metal substrate and a dielectric layer formed on the surface thereof, and a solid electrolyte layer formed on the surface of the dielectric layer.

[0003] The flat film capacitor elements and the metal foils are alternately stacked to form an element stack, which is then sealed with an insulating resin.

[0004] Patent Document 2 describes a method for manufacturing a solid electrolytic capacitor and a solid electrolytic capacitor. The solid electrolytic capacitor described in Patent Document 2 includes an anode as a valve metal porous body, a dielectric oxide film formed on the entire surface of the valve metal porous body, a cathode made of a conductive polymer layer formed on the dielectric oxide film, an anode current collector electrically connected to the metal portion inside the dielectric oxide film formed on the surface, and a cathode current collector electrically connected to the cathode conductive polymer layer.

[0005] At least the surface of the cathode current collector in a solid electrolytic capacitor is roughened. Carbon particles are embedded in the surface, and the surface is roughened by the unevenness of the carbon particles. This physically and directly bonds the cathode conductive polymer layer and the cathode current collector. In other words, increasing the bonding area reduces resistance.

[0006] JP2019-79866A JP11-219861A

[0007] In the case of a laminated structure such as a typical solid electrolytic capacitor, moisture easily penetrates the interface of the laminated structure. Specifically, in a composite structure with an interface, the liquid or gas permeability can be determined not only by the permeability of the constituent components themselves, but also by the permeability of the interface. In particular, at a physical / mechanical bonded interface, there is nothing to obstruct permeation, so permeation at that location becomes the dominant factor determining the overall permeation amount. When the ease of permeation is constant, the time it takes to permeate the amount of permeation (or the overall speed slows down) depends on the distance to the destination, so extending the path is effective. Various studies have been conducted to solve these problems.

[0008] For example, in a solid electrolytic capacitor such as that disclosed in Patent Document 1, there is a risk that water vapor in the air may penetrate into the interior through the interfaces of the laminated structure, causing deterioration of the internal elements and degrading the characteristics of the solid electrolytic capacitor.

[0009] In addition, in the solid electrolytic capacitor exemplified in Patent Document 2, the cathode current collector, which forms the interface in the laminated structure, is roughened. However, the size, shape, etc. of the roughened surface are not specified. That is, depending on the roughening conditions, as in Patent Document 1, moisture and impurities such as water vapor in the plating solution and air may penetrate into the interior through the interface of the laminated structure. This moisture and impurities may deteriorate the internal elements, degrading the characteristics of the solid electrolytic capacitor. Furthermore, the long-term reliability of the solid electrolytic capacitor may be reduced.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a solid electrolytic capacitor that is highly reliable over a long period of time and that prevents moisture and impurities from entering the interior.

[0011] The solid electrolytic capacitor of the present invention includes a plurality of flat-film capacitor elements, a plurality of flat-film cathode electrode foils, and an insulating resin. The capacitor elements have a structure in which a dielectric layer and a solid electrolyte layer are sequentially formed on the surface of a flat-film anode electrode foil. The insulating resin seals a sheet laminate formed by alternately stacking the plurality of flat-film capacitor elements and the cathode electrode foil. The solid electrolyte layer and the cathode electrode foil are directly bonded to each other. The bonding surface where the cathode electrode foil is bonded to the solid electrolyte layer is roughened. The ratio of the opening width, when viewed in plan, of the opening depth perpendicular to the bonding surface is 1 or greater.

[0012] As a result, the cathode electrode foil is roughened at the interface between the solid electrolyte layer of the capacitor element and the cathode electrode foil, thereby lengthening the path for moisture and other contaminants to penetrate. Furthermore, the ratio of the opening width to the opening depth formed by roughening the bonding surface is 1 or greater, thereby reliably extending the path. This means that moisture penetration into the solid electrolytic capacitor is suppressed. Similarly, the amount of impurities penetrating the solid electrolytic capacitor per unit time is reduced. Furthermore, the roughened cathode electrode foil improves the adhesion between the solid electrolyte layer and the cathode electrode foil, allowing the solid electrolytic capacitor to achieve low resistance. This means that the long-term reliability of the solid electrolytic capacitor is improved.

[0013] The method for manufacturing a solid electrolytic capacitor of the present invention includes a capacitor element forming step, a cathode electrode foil forming step, and a sealing step. In the capacitor element forming step, a plurality of flat film capacitor elements are formed by sequentially forming a dielectric layer and a solid electrolyte layer on the surface of a flat film anode electrode foil. In the cathode electrode foil forming step, a plurality of flat film cathode electrode foils are formed. In the sealing step, a sheet laminate formed by alternately stacking a plurality of flat film capacitor elements and cathode electrode foils is sealed with an insulating resin.

[0014] The solid electrolyte layer and the cathode electrode foil are directly bonded to each other. The bonding surface of the cathode electrode foil and the solid electrolyte layer is roughened. The ratio of the opening width in a plan view of the roughened bonding surface to the opening depth of the opening perpendicular to the bonding surface is 1 or more.

[0015] According to this manufacturing method, the cathode foil is roughened at the interface between the solid electrolyte layer and the cathode foil of the capacitor element, thereby lengthening the path for moisture and other contaminants to penetrate. Furthermore, the ratio of the opening width to the opening depth formed by roughening the bonding surface is 1 or greater, thereby reliably extending the path. This means that moisture penetration into the solid electrolytic capacitor is suppressed. Similarly, the amount of impurities penetrating the solid electrolytic capacitor per unit time is reduced. Furthermore, the roughened cathode foil improves adhesion between the solid electrolyte layer and the cathode foil, allowing the solid electrolytic capacitor to achieve low resistance. This means that the long-term reliability of the solid electrolytic capacitor is improved.

[0016] According to the present invention, it is possible to provide a solid electrolytic capacitor that is highly reliable for a long period of time by preventing the intrusion of moisture and impurities into the interior.

[0017] FIG. 1 is a side cross-sectional view showing the configuration of a solid electrolytic capacitor according to the first embodiment. FIGS. 2A and 2B are side cross-sectional views showing the configuration of a set of capacitor elements and cathode electrodes before singulation. FIG. 3 is a schematic side cross-sectional view of a solid electrolytic capacitor according to the first embodiment. FIG. 4 is a schematic enlarged view of the surface of a cathode electrode of a solid electrolytic capacitor according to the first embodiment. FIG. 5A is a schematic view showing a portion of the configuration of a cathode electrode according to the first embodiment, and FIG. 5B is a schematic view showing a portion of the configuration of a cathode electrode in a conventional configuration. FIG. 6 is a flowchart showing an example of a process for forming a capacitor element sheet. FIGS. 7A, 7B, 7C, and 7D are schematic views showing the process for forming capacitor elements of the solid electrolytic capacitor according to the first embodiment. FIG. 8 is an external view of a multi-layered state. FIG. 9 is an external view of a cathode electrode before singulation. Fig. 10(A) is an exploded perspective view showing a stacked state of capacitor element sheets and cathode electrode sheets in a multi-layered state, and Fig. 10(B) is an external perspective view showing a stacked state of capacitor element sheets and cathode electrode sheets in a multi-layered state. Fig. 11 is a diagram schematically showing the configuration of a cathode electrode according to a second embodiment. Fig. 12 is a diagram schematically showing a side cross-sectional view of a solid electrolytic capacitor according to the second embodiment.

[0018] First Embodiment A solid electrolytic capacitor and a method for manufacturing the solid electrolytic capacitor according to a first embodiment of the present invention will be described with reference to the drawings.

[0019] (Explanation of Schematic Configuration of Solid Electrolytic Capacitor 1) First, the structure of a solid electrolytic capacitor according to an embodiment of the present invention and a method for manufacturing the solid electrolytic capacitor will be described. FIG. 1 is a side cross-sectional view showing the configuration of a solid electrolytic capacitor according to a first embodiment. FIGS. 2(A) and 2(B) are side cross-sectional views showing the configuration of a set of capacitor elements and a cathode electrode before singulation. FIG. 3 is a schematic side cross-sectional view of the solid electrolytic capacitor according to the first embodiment. FIG. 4 is a schematic overview showing an enlarged view of the surface of a cathode electrode of the solid electrolytic capacitor according to the first embodiment. FIG. 5(A) is a schematic view showing a portion of the configuration of the cathode electrode according to the first embodiment, and FIG. 5(B) is a schematic view showing a portion of the configuration of a cathode electrode in a conventional configuration.

[0020] As shown in Figures 1, 2(A), and 2(B), the solid electrolytic capacitor 1 includes a capacitor element laminate 100, an insulating resin 50, an external electrode 61, and an external electrode 62. The capacitor element laminate 100 includes a plurality of flat-film capacitor elements 10 and a plurality of flat-film cathode electrodes 20. The cathode electrodes 20 correspond to the "cathode electrode foil" of the present invention. The solid electrolytic capacitor 1 has a substantially rectangular parallelepiped shape. The cathode electrodes 20 have a first surface 201 and a second surface 202 facing the first surface 201.

[0021] 1, the number of flat film capacitor elements 10 is four, and the number of cathode electrodes (sheets) is five, but this is not limited to this. The side cross-sectional views in FIGS. 1, 2(A), and 2(B) are cross-sectional views taken along a plane perpendicular to the top surface 101 and bottom surface 102 of the capacitor element laminate 100 in FIG. 1. In these cross-sectional views, the axis parallel to the top surface 101 and bottom surface 102 is defined as the x-axis. The axis perpendicular to the top surface 101 and bottom surface 102, in other words, the axis perpendicular to the x-axis, is defined as the y-axis.

[0022] 2(B), capacitor element 10 includes flat film-like anode electrode 11, dielectric layer 12, and CP layer (solid electrolyte layer) 13. Anode electrode 11 corresponds to the "anode electrode foil" of the present invention.

[0023] Although detailed structural illustrations are omitted in Figures 2(A) and 2(B), the anode electrode 11 has numerous pores. In other words, the anode electrode 11 is porous (a porous body). The thickness ratio of the porous portion on one side of the anode electrode 11 to the core metal portion and the porous portion on the other side is approximately 1:1:1. A dielectric layer 12 covers the outer surface of the anode electrode 11. Because detailed structural illustrations of the anode electrode 11 are omitted in Figures 2(A) and 2(B), the dielectric layer 12 is schematically illustrated as covering the macroscopic surface of the anode electrode 11. In reality, the dielectric layer 12 covers not only the macroscopic surface of the anode electrode 11 but also the inner surfaces of the numerous pores in the anode electrode 11.

[0024] The CP layer 13 covers the surface of the dielectric layer 12. A frame-shaped CP dam 14 is formed on the outer periphery of the CP layer 13. The CP dam 14 has insulating properties. The CP dam 14 limits the area in which the CP layer 13 is formed.

[0025] The CP layer 13 has a laminated structure of an inner layer CP (inner layer solid electrolyte layer) 131 and an outer layer CP (outer layer solid electrolyte layer) 132. The inner layer CP 131 is formed on the surface of the dielectric layer 12, and the outer layer CP 132 is formed on the surface of the inner layer CP 131.

[0026] The plurality of capacitor elements 10 and the plurality of cathode electrodes 20 are alternately stacked so that their respective flat film surfaces are parallel and overlap in plan view. In this case, the outer layer CP132 of the capacitor element and the cathode electrode 20 are directly connected. In the structure shown in FIGS. 2(A) and 2(B), the outer layer CP132 of the capacitor element 10 and the first surface 201 of the cathode electrode 20 are joined so as to abut against each other. This first surface 201 corresponds to the "joint surface" in the present invention. This physically joins and electrically connects the adjacent capacitor elements 10 and cathode electrodes 20. A more specific structure of the cathode electrode 20 will be described later.

[0027] In this stacked state, the first ends 10E1 (see FIG. 1) of the plurality of capacitor elements 10 are located at approximately the same position in side view. Similarly, the second ends 10E2 (see FIG. 1) of the plurality of capacitor elements 10 are located at approximately the same position in side view. Furthermore, the first ends 20E1 (see FIG. 1) of the plurality of cathode electrodes 20 are located at approximately the same position in side view. Similarly, the second ends 20E2 (see FIG. 1) of the plurality of cathode electrodes 20 are located at approximately the same position in side view.

[0028] The first ends 10E1 of the plurality of capacitor elements 10 and the second ends 20E2 of the plurality of cathode electrodes 20 are arranged on the first end side of the capacitor element stack 100. The first ends 10E1 of the plurality of capacitor elements 10 protrude outward beyond the second ends 20E2 of the plurality of cathode electrodes 20.

[0029] The second ends 10E2 of the plurality of capacitor elements 10 and the first ends 20E1 of the plurality of cathode electrodes 20 are arranged on the second end side of the capacitor element stack 100. The first ends 20E1 of the plurality of cathode electrodes 20 protrude outward beyond the second ends 10E2 of the plurality of capacitor elements 10.

[0030] With this structure, a capacitor element stack 100 having a top surface 101 and a bottom surface 102 at both ends in the stacking direction of the plurality of capacitor elements 10 and the plurality of cathode electrodes 20 is realized.

[0031] The capacitor element stack 100 is sealed with insulating resin 50. More specifically, the insulating resin 50 covers the capacitor element stack 100 except for first ends 10E1 of the plurality of capacitor elements 10 (first ends 10E1 of the anode electrodes 11) and first ends 20E1 of the plurality of cathode electrodes 20.

[0032] The external electrode 61 covers a first end (first end 10E1 of the anode electrode 11) of the insulating resin 50, which is the first end side of the capacitor element laminate 100. The external electrode 61 is connected to the first ends 10E1 of the anode electrodes 11 of the plurality of capacitor elements 10. The external electrode 62 covers a second end (first end 20E1 of the cathode electrode 20) of the insulating resin 50, which is the second end side of the capacitor element laminate 100. The external electrode 62 is connected to the first ends 20E1 of the plurality of cathode electrodes 20.

[0033] The solid electrolytic capacitor 1 is realized by the above configuration.

[0034] (Structure of Cathode Electrode 20) The specific structures of the first surface 201 and second surface 202 of the cathode electrode 20 will be described with reference to Figures 3, 4, 5(A), and 5(B). The following description will be given using an example in which the first surface 201 of the cathode electrode 20 and the outer layer CP 132 of the CP layer 13 abut against each other. However, the second surface 202 has a similar structure.

[0035] 3, the first surface 201 of the cathode electrode 20 has a plurality of projections and recesses formed by shapes whose heights vary in the y-axis direction depending on the position on the plane including the x-axis direction in the xy plane. In other words, the first surface 201 in plan view (viewed in a direction perpendicular to the xy plane) is roughened as shown in FIG.

[0036] Next, the structure of the first surface 201 will be described in more detail with reference to Figures 4 and 5(A). The first surface 201 has a plurality of openings 250. These openings 250 are formed by locally recessing the first surface 201, and are formed by roughening the first surface 201. In this case, the size of each opening 250 in the x-axis direction is defined as opening width w, and the size of each opening 250 in the y-axis direction is defined as opening depth dp.

[0037] The relationship between the opening width w and the opening depth dp is defined as follows: The value Ra obtained by dividing the opening depth dp by the opening width w is 1 or more and 5 or less. In this case, it is preferable that the opening width w is 10 μm or less. Therefore, for example, if the opening width w is 10 μm, it is preferable that the opening depth dp is 10 μm or more and 50 μm or less. Note that the multiple openings 250 do not need to have the same size in a planar view, but they may be the same.

[0038] A comparison is made between the first surface 201 having the opening 250 shown in Figure 5(A) and a surface without the opening 250 in a conventional configuration shown in Figure 5(B). The distance measured along the roughened surface of the first surface 201 from the first end 20E1 to the second end 20E2 in the present invention is defined as distance d1. Furthermore, the distance measured along the non-roughened surface from the first end 20E1 to the second end 20E2 in the conventional configuration is defined as distance d2. Since the first surface 201 in the present invention is roughened, d1 > d2.

[0039] By providing the cathode electrode 20 with a roughened surface, adhesion between the outer layer CP132 and the cathode electrode 20 is improved. This reduces the resistance of the solid electrolytic capacitor 1. Furthermore, by roughening the first surface 201 and the second surface 202 of the cathode electrode 20, the distance d1 from the first end 20E1 to the second end 20E2 of the cathode electrode 20 can be increased. As described above, in a composite structure having an interface, when the ease of permeation is constant, the amount of permeation increases over time (or the overall rate decreases) depending on the distance to the destination, so increasing the path is effective. Therefore, even if impurities such as moisture or gas penetrate through the interface, this distance d1 prevents the moisture or gas from completely penetrating into the capacitor element 10. This means that a solid electrolytic capacitor 1 with excellent long-term reliability can be provided.

[0040] (Method for Manufacturing Solid Electrolytic Capacitor 1) The solid electrolytic capacitor 1 having the above-described configuration is manufactured, for example, as follows. FIG. 6 is a flowchart showing an example of a general flow of a method for manufacturing a solid electrolytic capacitor according to this embodiment. FIGS. 7(A), 7(B), 7(C), and 7(D) are schematic diagrams showing the steps of forming capacitor elements of the solid electrolytic capacitor according to the first embodiment. FIG. 8 is an external view in a multi-layered state. FIG. 9 is an external view of the cathode electrodes before singulation. FIG. 10(A) is an exploded perspective view showing the stacked state of capacitor element sheets and cathode electrode sheets in a multi-layered state, and FIG. 10(B) is an external perspective view showing the stacked state of capacitor element sheets and cathode electrode sheets in a multi-layered state. Note that FIGS. 7(A), 7(B), 7(C), and 7(D) show portions of capacitor elements in a multi-layered state.

[0041] First, a capacitor element sheet is formed by the procedure of steps S11 to S13 in FIG.

[0042] More specifically, as shown in Fig. 7A, anode 11 is subjected to chemical conversion treatment to form dielectric layer 12 (Fig. 6: S11). At this time, numerous holes are formed in the surface of anode 11 by etching, and the vicinity of the surface of anode 11 is porous. Dielectric layer 12 covers the surface of anode 11, including the inner surfaces of the holes.

[0043] Next, a CP layer (solid electrolyte layer) 13 is formed on the surface of the dielectric layer 12 (S12 in FIG. 6). More specifically, as shown in FIG. 7B, a CP dam 14 having a frame-shaped opening is formed. Then, as shown in FIG. 7C, an inner layer CP 131 is first formed within the opening of the CP dam 14, and then an outer layer CP 132 is formed to cover the inner layer CP 131. This forms a CP layer 13 having a laminated structure of the inner layer CP 131 and the outer layer CP 132.

[0044] Next, as shown in FIG. 7(D), anode through holes are formed in the anode electrode 11 (FIG. 6: S13). More specifically, a plurality of cylindrical anode through holes 19C and groove-shaped anode through holes 19L are formed in the anode electrode 11. At this time, the plurality of cylindrical anode through holes 19C and groove-shaped anode through holes 19L penetrate not only the anode electrode 11 but also the CP dam 14. The plurality of cylindrical anode through holes 19C and groove-shaped anode through holes 19L are alternately arranged along the direction in which the portions that will become the plurality of anode electrodes 11 are arranged. The plurality of cylindrical anode through holes 19C are formed at positions that will realize first ends 10E1 of the anode electrodes 11, and the groove-shaped anode through holes 19L are formed at positions that straddle the portions that will become adjacent anode electrodes 11 and at positions that will realize second ends 10E2 of adjacent anode electrodes 11.

[0045] This structure is implemented in a multi-state in which a plurality of capacitor elements 10 (a structure consisting of an anode electrode 11, a dielectric layer 12, a CP layer 13, and a CP dam 14) are arranged two-dimensionally, as shown in Figures 7(A), 7(B), 7(C), 7(D), and 8.

[0046] Next, a cathode electrode sheet is formed (S14). More specifically, the surface of the cathode electrode sheet (the surface corresponding to the first surface 201 and the second surface 202 in FIG. 2(B)) is roughened by electrolytic etching or chemical etching. By roughening the cathode electrode sheet, openings 250 are formed. At this time, a plurality of irregularities (opening depth dp) are formed by grinding the cathode electrode sheet in the depth direction using electrolytic etching or chemical etching. Note that the roughening method is not limited to etching, and a method of forming a plurality of irregularities (opening depth dp) by adding thickness to the cathode electrode sheet using wet plating or dry plating may also be used.

[0047] 9 , a plurality of cylindrical cathode through holes 29C and groove-shaped cathode through holes 29L are formed in the cathode electrode 20. The cylindrical cathode through holes 29C and the groove-shaped cathode through holes 29L are alternately arranged along the direction in which the portions that will become the cathode electrodes 20 are arranged. The cylindrical cathode through holes 29C are formed at positions that will realize first ends 20E1 of the cathode electrodes 20, and the groove-shaped cathode through holes 29L are formed at positions that straddle the portions that will become adjacent cathode electrodes 20 and at positions that will realize second ends 20E2 of adjacent cathode electrodes 20.

[0048] Next, as shown in Figures 10(A) and 10(B), the capacitor element sheet and the cathode electrode sheet are stacked and heated and pressed to form a sheet laminate (Figure 6: S15). At this time, the capacitor element sheet and the cathode electrode sheet are joined so that the outer layer CP132 and the cathode electrode sheet abut against each other. Note that the cathode electrode sheet is formed with an array of multiple cathode electrodes 20 that form different solid electrolytic capacitors 1. This forms a structure in which multiple capacitor element laminates 100 are arranged in a plane. In other words, the sheet laminate is a structure in which multiple capacitor element laminates 100 are arranged in a plane.

[0049] Next, the sheet stack is sealed with insulating resin 50 (FIG. 6: S16). As will be described in detail later, at this time, through holes that penetrate from the top surface to the bottom surface of the sheet stack are provided in the sheet stack, and resin sealing is performed by compression molding.

[0050] The process up to this sealing with insulating resin 50 is carried out in a multi-state (state in which a plurality of what will become solid electrolytic capacitors 1 are arranged) before the solid electrolytic capacitor 1 is divided into individual pieces.

[0051] Next, the sheet laminate sealed with insulating resin 50 is cut and singulated ( S17 in FIG. 6 ). Specifically, the sheet laminate is cut along predetermined cutting lines (see FIGS. 7A to 7D ) to singulate. This results in a plurality of solid electrolytic capacitors 1 (referred to as "elements of solid electrolytic capacitor 1") without external electrodes. The elements of solid electrolytic capacitor 1 are then secondary-sealed with insulating resin 50. More specifically, the side surfaces of the elements of solid electrolytic capacitor 1 (surfaces cut along predetermined cutting lines (top surface, bottom surface, and side surfaces other than the end surfaces where anode electrode 11 and cathode electrode 20 are exposed)) are covered with the secondary sealing of insulating resin 50. This allows the anode electrode 11 and cathode electrode 20 that are unnecessarily exposed during singulation to be covered with insulating resin 50.

[0052] Next, external electrodes 61 and 62 are formed on the end surfaces of the element body of solid electrolytic capacitor 1 (FIG. 6: S18).

[0053] The sealing process with insulating resin in step S16 has the following characteristics: When viewed in the stacking direction, the plurality of cylindrical anode through holes 19C in the capacitor element sheet overlap with the groove-shaped cathode through holes 29L in the cathode electrode sheet (see FIGS. 7(D), 9, 10(A), and 10(B)). When viewed in the stacking direction, the groove-shaped anode through holes 19L in the capacitor element sheet overlap with the plurality of cylindrical cathode through holes 29C in the cathode electrode sheet (see FIGS. 7(D), 9, 10(A), and 10(B)). When viewed in the stacking direction, the groove-shaped anode through holes 19L in the capacitor element sheet overlap with the groove-shaped cathode through holes 29L in the cathode electrode sheet (see FIGS. 7(D), 9, 10(A), and 10(B)).

[0054] With this configuration, through holes including multiple layers of anode through holes 19C and multiple layers of cathode through holes 29L, and multiple layers of anode through holes 19L and multiple layers of cathode through holes 29C are formed. These through holes penetrate the upper and lower surfaces of the sheet laminate.

[0055] The number of these through holes formed corresponds to the number of capacitor elements arranged in the sheet laminate, and therefore the sheet laminate is provided with a plurality of through holes that penetrate from the top surface to the bottom surface of the sheet laminate.

[0056] In the above configuration, the CP dam 14 is formed in step S12, and then the anode through-hole is formed in the anode electrode 11 in step S13. However, the CP dam 14 may be formed after the anode through-hole is formed in the anode electrode 11 so as not to block the anode through-hole.

[0057] As described above, the method of roughening the cathode electrode sheet by electrolytic etching or chemical etching has been described. This method reduces the aspect ratio of the irregularities, making it easy to roughen the cathode electrode. By using such an easy formation method, the path extension effect can be achieved, thereby improving long-term reliability. Furthermore, since the thickness of the cathode electrode sheet can be reduced, a thin-layer laminate can be formed. This allows for the realization of a solid electrolytic capacitor 1 with high capacitance and suppressed increases in ESR. In other words, a solid electrolytic capacitor 1 with an excellent balance between initial characteristics (high capacitance, low ESR) and improved long-term reliability can be realized.

[0058] [Second Embodiment] A solid electrolytic capacitor and a method for manufacturing a solid electrolytic capacitor according to a second embodiment of the present invention will be described with reference to the drawings. Fig. 11 is a diagram schematically showing the relationship between the opening width and depth of the solid electrolytic capacitor according to the second embodiment. Fig. 12 is a diagram schematically showing a part of the configuration of the cathode electrode according to the second embodiment.

[0059] The solid electrolytic capacitor 1A according to the second embodiment differs in the structure of the opening 250A formed by roughening the cathode electrode 20A and in the method for roughening the cathode electrode 20A. The other configuration of the solid electrolytic capacitor 1A is the same as that of the solid electrolytic capacitor 1, and a description of the same parts will be omitted.

[0060] 11 , the first surface 201A of the cathode electrode 20 has a plurality of projections and recesses in the xy plane. More specifically, the first surface 201A in plan view (viewed in a direction perpendicular to the xy plane) is roughened. Note that, although the following example will describe the first surface 201A, the second surface 202A opposite to the first surface 201A has a similar configuration.

[0061] Next, the structure of the first surface 201A will be described in more detail using Figure 12. The first surface 201A has a plurality of openings 250A. The size of the openings 250A in the x-axis direction is defined as opening width w1, and the size of the openings 250A in the y-axis direction is defined as opening depth dp1. The relationship between the opening width w1 and the opening depth dp1 is defined as follows: The value Ra1 obtained by dividing the opening depth dp1 by the opening width w1 is greater than 5. In this case, it is preferable that the opening width w is 10 μm or less. Therefore, for example, if the opening width w is 10 μm, it is preferable that the opening depth dp is greater than 50 μm.

[0062] A comparison is made between the first surface 201A having the opening 250A shown in FIG. 12 and the surface without the opening 250A in the conventional configuration shown in FIG. The distance measured along the roughened surface of the first surface 201A from the first end 20E1 to the second end 20E2 in the present invention is defined as distance d3. Similarly, the distance measured along the non-roughened surface of the first surface 201A from the first end 20E1 to the second end 20E2 in the conventional configuration is defined as distance d2, as in the first embodiment. Since the first surface 201A in the present invention is roughened, d3 > d2.

[0063] In addition, the method of forming the openings 250A in the cathode electrode sheet is different from that of the first embodiment in the configuration of step S14. More specifically, it is as follows.

[0064] The surface of the cathode electrode sheet (the surface corresponding to the first surface 201A and the second surface 202A in FIG. 11 ) is roughened by electrolytic etching or chemical etching. The roughening of the cathode electrode sheet forms an opening 250A. At this time, the opening depth dp1 is formed by grinding the cathode electrode sheet in the depth direction.

[0065] In the first embodiment, the thickness of the cathode electrode sheet is increased by wet plating or dry plating, but in the second embodiment, the opening 250A is preferably formed by electrolytic etching or chemical etching.

[0066] Even with this configuration, the adhesion between the outer layer CP 132 and the cathode electrode 20A can be improved. This allows for low resistance of the solid electrolytic capacitor 1A. Furthermore, by roughening the first surface 201A and the second surface 202A of the cathode electrode 20A, the distance d3 from the first end 20E1 to the second end 20E2 of the cathode electrode 20A can be further increased. Therefore, even if impurities such as moisture or gas penetrate through the interface, this distance d3 can more reliably prevent moisture, gas, or the like from penetrating into the capacitor element 10A. This means that a solid electrolytic capacitor 1A with excellent long-term reliability can be provided.

[0067] (Explanation of an example of specific materials, etc., of each component of the solid electrolytic capacitor 1) (Capacitor element 10) The capacitor element 10 is realized, for example, with the following materials and thicknesses.

[0068] The anode 11 is made of a metal such as aluminum, tantalum, niobium, titanium, zirconium, or magnesium, or an alloy containing any of these metals. The anode 11 is preferably made of aluminum or an aluminum alloy. The anode 11 may be made of any valve metal that exhibits a so-called valve action.

[0069] The anode 11 is preferably flat, and the thickness of the core (the center portion not reached by the pores of the porous body) of the anode 11 is preferably 5 μm or more and 100 μm or less. The thickness (thickness of one side) of the porous portion (the portion where the pores of the porous body are formed) is preferably 5 μm or more and 200 μm or less.

[0070] The dielectric layer 12 is preferably made of an oxide film of the anode electrode 11. For example, when an aluminum foil is used for the anode electrode 11, the dielectric layer 12 is formed by oxidizing the aluminum foil in an aqueous solution containing boric acid, phosphoric acid, adipic acid, or their sodium salts or ammonium salts. The thickness of the dielectric layer 12 is preferably 1 nm or more and 100 nm or less.

[0071] The inner layer CP131 may be a PEDOT:PSS layer realized by, for example, a conductive polymer having a skeleton of pyrroles, thiophenes, anilines, or the like, or a conductive polymer having a skeleton of thiophenes, such as PEDOT [poly(3,4-ethylenedioxythiophene)], and composited with polystyrene sulfonic acid (PSS) as a dopant. The inner layer CP131 may be formed, for example, by a method of forming a polymer film of poly(3,4-ethylenedioxythiophene) or the like on the surface of the dielectric layer 12 using a treatment liquid containing a monomer such as 3,4-ethylenedioxythiophene, or by a method of applying a dispersion of a polymer such as poly(3,4-ethylenedioxythiophene) to the surface of the dielectric portion and drying it.

[0072] The thickness of the outer layer CP 132 is preferably 2 μm or more and 20 μm or less. The material of the outer layer CP 132 is the same as the material of the inner layer CP 131.

[0073] The cathode electrode 20 is preferably made of aluminum or an aluminum alloy. The thickness of the cathode electrode 20 is, for example, approximately the same as the thickness of the anode electrode 11.

[0074] The insulating resin 50 may contain a filler. Examples of suitable resins include epoxy resin, phenol resin, polyimide resin, silicone resin, polyamide resin, and liquid crystal polymer. Examples of suitable fillers include insulating oxide particles such as silica particles, alumina particles, titania particles, and zirconia particles. The maximum diameter of the filler is preferably 30 μm or more and 40 μm or less. For example, a material containing silica particles in a solid epoxy resin is more preferable.

[0075] DESCRIPTION OF SYMBOLS d1, d2, d3... distance dp, dp1... opening depth w, w1... opening width 1, 1A... solid electrolytic capacitor 10... capacitor element 10E1, 20E1... first end 10E2, 20E2... second end 11... anode electrode 12... dielectric layer 131... inner layer CP 132... outer layer CP 13... CP layer 14... CP dam 19C... anode through-hole 19L... anode through-hole 20, 20A... cathode electrode 29C... cathode through-hole 29L... cathode through-hole 50... insulating resin 61... external electrode 62... external electrode 100... capacitor element laminate 101... top surface 102... bottom surface 201, 201A... first surface 202, 202A... second surface 250, 250A...opening

Claims

1. A solid electrolytic capacitor comprising: a plurality of flat film capacitor elements each having a flat film anode electrode foil on which a dielectric layer and a solid electrolyte layer are successively formed; a plurality of flat film cathode electrode foils; and an insulating resin sealing a sheet laminate formed by alternately stacking the plurality of flat film capacitor elements and the cathode electrode foil, wherein the solid electrolyte layer and the cathode electrode foil are directly bonded to each other, a bonding surface at which the cathode electrode foil is bonded to the solid electrolyte layer is roughened, and a ratio of an opening width formed in the bonding surface by the roughening in a plan view to an opening depth of the opening perpendicular to the bonding surface is 1 or more.

2. The solid electrolytic capacitor according to claim 1, wherein the ratio of said opening width to said opening depth is 5 or less.

3. The solid electrolytic capacitor according to claim 1, wherein the ratio of the opening width to the opening depth is greater than 5.

4. The solid electrolytic capacitor according to claim 1, wherein the opening width is 10 μm.

5. A method for manufacturing a solid electrolytic capacitor, comprising: a capacitor element forming step of forming a plurality of flat film capacitor elements each having a dielectric layer and a solid electrolyte layer sequentially formed on a surface of a flat film anode electrode foil; a cathode electrode foil forming step of forming a plurality of flat film cathode electrode foils; and a sealing step of sealing a sheet laminate formed by alternately stacking the plurality of flat film capacitor elements and the cathode electrode foil with an insulating resin, wherein the solid electrolyte layer and the cathode electrode foil are directly bonded to each other, a bonding surface at which the cathode electrode foil is bonded to the solid electrolyte layer is roughened, and a ratio of an opening width, when viewed in plan, of an opening formed on the bonding surface by the roughening to an opening depth perpendicular to the bonding surface in the opening is 1 or more.

6. The method for producing a solid electrolytic capacitor according to claim 5, wherein the ratio of the opening width to the opening depth is 5 or less.

7. The method for manufacturing a solid electrolytic capacitor according to claim 5, wherein the ratio of the opening width to the opening depth is greater than 5.

8. The method for manufacturing a solid electrolytic capacitor according to claim 5, wherein the opening width is 10 μm.

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