electrolytic capacitor

Abstract

This electrolytic capacitor is provided with: a capacitor element that is provided with a positive electrode part and a negative electrode part; an outer case that seals the capacitor element; a first external electrode that is electrically connected to the positive electrode part; and a second external electrode that is electrically connected to the negative electrode part. At least one of an end face of the positive electrode part and an end face of the negative electrode part of the capacitor element is exposed from the outer case, and is electrically connected to the first external electrode or the second external electrode. The end face exposed from the outer case is covered by an electroless Ni plating layer; and the electroless Ni plating layer is covered by an electroless Ag plating layer. Since the electroless Ag plating layer is covered by the first external electrode or the second external electrode, the ESR of this electrolytic capacitor is reduced.

Description

[Technical Field]

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

[0002] The electrolytic capacitor includes a capacitor element, an exterior body that seals the capacitor element, and external electrodes that are electrically connected to the anode and cathode sides of the capacitor element. The capacitor element includes an anode body having a first portion (also referred to as an anode lead portion) that includes a first end and a second portion (also referred to as a cathode forming portion) that includes a second end, a dielectric layer formed on the surface of at least the second portion of the anode body, and a cathode portion that covers at least a portion of the dielectric layer.

[0003] Regarding a method for electrically connecting an anode body to an external electrode, Patent Document 1 proposes a method for electrically connecting an anode body to an external electrode at the end face of a resin molded body, which includes a first external electrode formed on a first end face of the resin molded body and electrically connected to the anode exposed from the first end face, and a second external electrode formed on a second end face of the resin molded body and electrically connected to the cathode exposed from the second end face. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-141059 Summary of the Invention

[0005] One aspect of the present disclosure provides a capacitor including a capacitor element having an anode portion and a cathode portion, an exterior body that seals the capacitor element, a first external electrode electrically connected to the anode portion, and a second external electrode electrically connected to the cathode portion. ,before The anode part End face of At least one of the end faces of the cathode portion is exposed from the exterior body, and the first external electrode or the second external electrode How to deal withthe end surface exposed from the outer casing is covered with an electroless Ni plating layer, the electroless Ni plating layer is covered with an electroless Ag plating layer, and the electroless Ag plating layer is electrically connected to the first external electrode or the second external electrode. How to deal with Regarding electrolytic capacitors, [Effects of the Invention]

[0006] According to the present disclosure, an electrolytic capacitor with reduced ESR and high reliability can be realized. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an electrolytic capacitor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view schematically illustrating the structure of a capacitor element that constitutes an electrolytic capacitor. [Figure 3A] 2 is an enlarged schematic cross-sectional view showing a part of the structure of the electrolytic capacitor shown in FIG. 1. [Figure 3B] 2 is an enlarged schematic cross-sectional view showing a part of the structure of the electrolytic capacitor shown in FIG. 1. [Figure 4] FIG. 10 is a cross-sectional view schematically illustrating another example of the structure of the electrolytic capacitor according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] Prior to describing the embodiments, the problems in the prior art will be briefly described below.

[0009] In conventional solid electrolytic capacitors, the external electrodes have an inner plating layer, a resin electrode layer, and an outer plating layer, and the exposed end surfaces of the anode and cathode are covered with an inner plating layer consisting of an electroless Ni plating layer and an electrolytic Ag plating layer. However, in this case, it is difficult to form the electrolytic Ag plating layer with a thin and uniform thickness, which can result in exposure of the underlying Ni plating layer or the occurrence of pinholes. To prevent exposure of the underlying Ni plating layer and the occurrence of pinholes, the electrolytic Ag plating layer must be made thicker than necessary, which increases manufacturing costs.

[0010] When the underlying Ni plating layer is exposed, oxidation of the surface increases the ESR. In addition, pinholes that can occur in the electrolytic Ag plating can affect the electrical characteristics and oxygen barrier properties of the electrolytic capacitor. In view of the above problems, the present disclosure provides an electrolytic capacitor with reduced ESR and high reliability.

[0011] [Electrolytic capacitor] An electrolytic capacitor according to one embodiment of the present disclosure comprises a capacitor element having an anode portion and a cathode portion, an exterior body that seals the capacitor element, a first external electrode electrically connected to each of the anode portions, and a second external electrode electrically connected to each of the cathode portions.

[0012] Anode part of capacitor element End face of At least one of the end faces of the cathode portion is exposed from the outer casing, and the first external electrode or the second external electrode How to deal with In other words, the end face of the anode part exposed from the exterior housing may be electrically connected to the first external electrode, and / or the end face of the cathode part exposed from the exterior housing may be electrically connected to the second external electrode. When only one end face of the anode part or the cathode part of the capacitor element is exposed from the exterior housing, the other end face of the anode part or the cathode part may be connected to a lead terminal such as a lead frame inside the exterior housing.

[0013] The end faces of the anode and / or cathode exposed from the outer casing are covered with an electroless Ni plating layer. The electroless Ni plating layer is covered with an electroless Ag plating layer. The electroless Ag plating layer is covered with the first external electrode or the second external electrode. The electroless Ni plating layer and the electroless Ag plating layer are contact layers that ensure electrical connection between the end faces and the external electrodes. The use of contact layers can improve the reliability of the electrolytic capacitor.

[0014] However, when using electrolytic plating to plate end surfaces with Ag, it is difficult to form a thin, uniform Ag electroplating layer. In Ag electroplating, dummy balls are typically used to ensure electrical conductivity and agitate the plating. When the dummy balls are not in contact with the plating area, there is no current flowing, and plating does not proceed. This can lead to oxidation of the surface of the Ni plating layer, which increases ESR and reduces the adhesion strength of the plating layer. Furthermore, Ag electroplating is prone to pinhole formation. Furthermore, because Ag electroplating also forms a plating layer on the surface of the dummy balls, the amount of silver used increases, which tends to increase manufacturing costs. To prevent pinhole formation and exposure of the Ni plating layer (the underlayer), the Ag electroplating layer must be thicker than necessary, resulting in increased silver consumption.

[0015] In contrast, forming an Ag plating layer by electroless plating makes it easier to control the thickness of the plating layer, resulting in a thin, uniform plating layer. This suppresses the oxidation of the electroless Ni plating layer surface and the formation of pinholes due to the exposure of the underlying electroless Ni plating layer. As a result, the ESR of the electrolytic capacitor is reduced, resulting in an electrolytic capacitor with excellent reliability. Furthermore, the electroless Ag plating layer is less likely to deposit on the surface of the outer casing where the end faces are exposed. In other words, even if an electroless Ni plating layer accidentally forms on the surface of the outer casing, more of the electroless Ag plating layer is formed on the end faces of the anode or cathode. This means that the electroless Ag plating layer can be selectively formed on the surface of the electroless Ni plating layer rather than on the surface of the outer casing where the end faces are exposed, thereby reducing the amount of silver used. Furthermore, the electroless Ag plating layer forms a denser film than the electrolytic Ag plating layer, improving adhesion between the plating layer and the external electrodes and improving the electrical properties and oxygen barrier properties of the electrolytic capacitor.

[0016] Whether a Ni plating layer is an electrolytic Ni plating layer or an electroless Ni plating layer, and whether an Ag plating layer is an electrolytic Ag plating layer or an electroless Ag plating layer, can be determined by analyzing the components other than the plating metal contained in the plating layer.

[0017] The first external electrode and / or the second external electrode may include a conductive paste layer and a Ni / Sn plating layer covering the conductive paste layer. The Ni / Sn plating layer is a layer containing Ni and Sn, and includes, for example, two layers: a Ni plating layer and a Sn plating layer formed on the Ni plating layer. In the Ni / Sn plating layer, Ni in the Ni plating layer is replaced by Sn plating. layer The Sn in the Sn-plated layer may diffuse toward the Ni-plated layer, and the Sn in the Sn-plated layer may diffuse toward the Ni-plated layer, forming an alloy layer of Ni and Sn. Of the first external electrode or the second external electrode, at least the external electrode covering the electroless Ag-plated layer may include a conductive paste layer and a Ni / Sn-plated layer. The use of the conductive paste layer improves adhesion between the electroless Ag-plated layer and the external electrode, significantly reducing ESR.

[0018] The electroless Ni plating layer contains phosphorus (P) and / or boron (B) due to the reducing agent (sodium hypophosphite, dimethylamine-borane, etc.) added to the plating bath. )but In the electroless Ni plating layer, phosphorus (P )teeth For example, boron (B )teeth For example, it can be contained in the plating layer at a ratio of 0.1 mass % to 5 mass %. In particular, the inclusion of phosphorus (P) in the electroless Ni plating layer improves corrosion resistance and oxidation resistance.

[0019] The electroless Ni plating layer may consist essentially of Ni. Here, "the electroless Ni plating layer consists essentially of Ni" means that the proportion of elements other than Ni in the electroless Ni plating layer is less than 0.1 mass%. In this case, although plating takes time, a dense plating layer with excellent corrosion resistance is obtained, and the ESR is significantly reduced. The composition ratio of elements in each plating layer can be determined, for example, by an electron probe microanalyzer (EPMA).

[0020] The thickness of the electroless Ni plating layer is preferably 0.1 to 10 μm. When the thickness of the electroless Ni plating layer is 0.1 μm or more, a plating layer of uniform thickness can be formed, and the end faces of the cathode or anode parts are prevented from being partially uncovered by the electroless Ni plating layer, resulting in exposure of the end faces. When the thickness of the electroless Ni plating layer is 10 μm or less, a decrease in productivity due to an increase in the thickness of the plating layer can be prevented.

[0021] Similarly, the thickness of the electroless Ag plating layer is preferably 0.1 to 1 μm. When the thickness of the electroless Ag plating layer is 0.1 μm or more, a plating layer of uniform thickness can be formed, and exposure of the electroless Ni plating layer, which serves as the base layer, in some regions can be suppressed. Furthermore, when the thickness of the electroless Ag plating layer is 1 μm or less, a decrease in productivity due to an increase in the thickness of the Ag plating layer can be suppressed, and an increase in manufacturing costs due to an increase in the amount of Ag used can be suppressed.

[0022] The thickness of the plating layer is determined by arbitrarily selecting 10 or more locations on the end face based on the cross-sectional image of the end face and calculating the average thickness.

[0023] An adhesion improving layer may be disposed between the electroless Ni plating layer and the electroless Ag plating layer. The adhesion improving layer is formed on the electroless Ni plating layer and can improve the adhesion of the electroless Ag plating layer. The adhesion improving layer can be formed, for example, by strike Ag plating. The strike Ag plating can be formed by electroless plating or electrolytic plating. Formation by electroless plating is preferred because a uniform film can be formed by controlling the chemical solution concentration and reaction conditions.

[0024] The electrolytic capacitor may have an element stack including a plurality of capacitor elements. In this case, the anode portion of the capacitor element End face of At least one end face of the cathode part is exposed from the outer casing, and the first external electrode or the second external electrode is formed through the electroless Ni plating layer and the electroless Ag plating layer. How to deal with and are electrically connected to each other. That is, when the exposed end surface is an end surface of an anode part, the anode part and the first external electrode can be electrically connected to each other at that end surface via an electroless Ni plating layer and an electroless Ag plating layer. When the exposed end surface is an end surface of a cathode part, the cathode part and the second external electrode can be electrically connected to each other at that end surface via an electroless Ni plating layer and an electroless Ag plating layer. The multiple capacitor elements may face in the same direction or in different directions. For example, the anode part and the cathode part may be stacked so that they alternately face in opposite directions, or the anode part and the cathode part may be stacked so that they face in opposite directions in any order.

[0025] The electrolytic capacitor may be configured such that only the end face of the anode unit is exposed from the exterior housing and electrically connected to the first external electrode, or such that only the end face of the cathode unit is exposed from the exterior housing and electrically connected to the second external electrode, or such that both the end face of the anode unit and the end face of the cathode unit are exposed from the exterior housing and electrically connected to the first external electrode or the second external electrode, respectively. The electroless Ni plating layer and the electroless Ag plating layer are formed to cover at least one of the exposed end faces of the anode unit and the exposed end face of the cathode unit. The end face of the anode unit and the first external electrode may be electrically connected via the electroless Ni plating layer and the electroless Ag plating layer, or the end face of the cathode unit and the second external electrode may be electrically connected via the electroless Ni plating layer and the electroless Ag plating layer, or both the end face of the anode unit and the first external electrode and the end face of the cathode unit and the second external electrode may be electrically connected via the electroless Ni plating layer and the electroless Ag plating layer. In addition, an adhesion improving layer may be disposed between the electroless Ni plating layer and the electroless Ag plating layer.

[0026] In the case of an element stack in which end faces of anode portions of a plurality of capacitor elements are exposed from the exterior housing and electrically connected to the first external electrode, the end faces of the anode portions may be exposed on the first main surface of the exterior housing. The end faces of the anode portions may be electrically connected to the first external electrode via an electroless Ni plating layer and an electroless Ag plating layer. The first external electrode may be disposed so as to cover the first main surface. Alternatively, an adhesion improving layer may be disposed between the electroless Ni plating layer and the electroless Ag plating layer.

[0027] Furthermore, when the element stack is provided and end faces of the anode portions of the plurality of capacitor elements are exposed from the exterior body and electrically connected to the first external electrode, an end face of the anode portion of at least one first capacitor element is exposed on the first main surface of the exterior body, Other than at least one first capacitor elementAn end face of the anode portion of at least one second capacitor element may be exposed on a second main surface opposite the first main surface of the exterior package. The end faces of the anode portions of the first capacitor element and the second capacitor element may be electrically connected to the first external electrode via an electroless Ni plating layer and an electroless Ag plating layer, respectively. In this case, two first external electrodes are provided, spaced apart from each other, one of which is disposed so as to cover the first main surface and electrically connect to the first capacitor element, and the other of which is disposed so as to cover the second main surface and electrically connect to the second capacitor element. In this case, an adhesion improving layer may be disposed between the electroless Ni plating layer and the electroless Ag plating layer.

[0028] The cathode section may also include a cathode foil. In this case, an end face of the cathode foil may be exposed from the exterior body and electrically connected to the second external electrode via an electroless Ni plating layer and an electroless Ag plating layer. When an element stack including multiple capacitor elements is used, the cathode foil may be provided on at least one of the multiple capacitor elements.

[0029] Fig. 1 is a cross-sectional view schematically illustrating the structure of an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view illustrating the structure of a capacitor element constituting the electrolytic capacitor of Fig. 1. However, the electrolytic capacitor according to the present disclosure is not limited to this.

[0030] 1, electrolytic capacitor 100 includes a plurality of capacitor elements, an exterior body 14 that seals the capacitor elements, a first external electrode 21, and a second external electrode 22. The plurality of capacitor elements are stacked to form an element stack.

[0031] As shown in FIG. 2, capacitor element 10 includes an anode body 3, which is an anode portion, and a cathode portion 6. Anode body 3 is, for example, a foil (anode foil). Anode body 3 has a porous portion 5 on its surface, and a dielectric layer (not shown) is formed on at least a portion of the surface of porous portion 5. Cathode portion 6 covers at least a portion of the dielectric layer. Cathode portion 6 includes a solid electrolyte layer 7, a cathode extraction layer, and cathode foil 20.

[0032] Capacitor element 10 has one end (first end) 1a where anode body 3 is exposed without being covered with cathode portion 6, while the other end (second end) 2a is covered with cathode portion 6. Hereinafter, the portion of anode body 3 that is not covered with a cathode portion will be referred to as first portion 1, and the portion of anode body 3 that is covered with a cathode portion will be referred to as second portion 2. The end of first portion 1 is first end 1a, and the end of second portion 2 is second end 2a. A dielectric layer is formed on at least the surface of porous portion 5 formed in second portion 2. First portion 1 of anode body 3 is also referred to as an anode lead-out portion. Second portion 2 of anode body 3 is also referred to as a cathode-forming portion.

[0033] More specifically, the second portion 2 has a core 4 and a porous portion (porous body) 5 formed on the surface of the core 4 by roughening (etching, etc.). On the other hand, the first portion 1 may or may not have the porous portion 5 on its surface. The dielectric layer is formed along the surface of the porous portion 5. At least a portion of the dielectric layer covers the inner wall surfaces of the pores of the porous portion 5 and is formed along those inner wall surfaces.

[0034] The cathode section 6 includes a solid electrolyte layer 7 that covers at least a portion of the dielectric layer, and a cathode extraction layer that covers at least a portion of the solid electrolyte layer 7. The surface of the dielectric layer has an uneven shape that corresponds to the shape of the surface of the anode body 3. The solid electrolyte layer 7 can be formed to fill in the unevenness of the dielectric layer. The cathode extraction layer includes, for example, a carbon layer 8 that covers at least a portion of the solid electrolyte layer 7, and a silver paste layer 9 that covers the carbon layer 8. The cathode extraction layer may be only the carbon layer 8 that covers at least a portion of the solid electrolyte layer 7.

[0035] A cathode foil 20 is interposed between the cathode lead layers of capacitor elements 10 adjacent to each other in the stacking direction of the element stack. The cathode foil 20 constitutes part of the cathode section 6 and is shared by capacitor elements 10 adjacent to each other in the stacking direction of the element stack. A conductive adhesive layer may be interposed between the cathode foil 20 and the capacitor element 10. The adhesive layer may be, for example, a conductive adhesive. The adhesive layer may contain, for example, silver. Alternatively, the adhesive layer may contain, for example, carbon.

[0036] The portion of the anode body 3 where the solid electrolyte layer 7 is formed on the anode body 3 via a dielectric layer (porous portion 5) is the second portion 2, and the portion of the anode body 3 where the solid electrolyte layer 7 is not formed on the anode body 3 via a dielectric layer (porous portion 5) is the first portion 1.

[0037] Of the region of the anode body 3 that does not face the cathode part 6, at least a portion adjacent to the cathode part 6 may have an insulating separation layer (or insulating member) 12 formed to cover the surface of the anode body 3. This prevents contact between the cathode part 6 and the exposed portion (first portion 1) of the anode body 3. The separation layer 12 is, for example, an insulating resin layer.

[0038] The exterior housing 14 has a substantially rectangular parallelepiped outer shape, and the electrolytic capacitor 100 also has a substantially rectangular parallelepiped outer shape. The exterior housing 14 has a first surface 14a and a second surface 14b opposite the first surface 14a. In the element stack, first ends 1a of the capacitor elements 10 are exposed on the first surface 14a. Furthermore, end surfaces 20a of the cathode foils 20 are exposed from the exterior housing on the second surface 14b. Each end surface of the cathode foils 20 exposed from the exterior housing 14 is electrically connected to a second external electrode 22 extending along the second surface 14b.

[0039] In the electrolytic capacitor 100, each of the multiple first end portions 1a (first portions) exposed from the outer casing 14 is electrically connected to a first external electrode 21 extending along the first surface 14a. In this case, it is not necessary to bundle the multiple first portions 1 to form the anode of the electrolytic capacitor, and there is no need to ensure the length required to bundle the multiple first portions 1. Therefore, compared to when multiple first portions are bundled together, the proportion of the first portions in the anode body can be reduced, thereby increasing the capacitance. In addition, the contribution of the first portions to the ESR and ESL is reduced.

[0040] The end faces of the multiple first ends 1a exposed from package 14 and the multiple end faces 20a of cathode foil 20 exposed from package 14 are each covered with contact layer 15. First ends 1a are electrically connected to first external electrode 21 via contact layer 15. Cathode foil 20 is electrically connected to second external electrode 22 via contact layer 15.

[0041] 3A and 3B are enlarged schematic cross-sectional views of a portion of the structure of electrolytic capacitor 100. Fig. 3A is an enlarged cross-sectional view of the vicinity of the connection portion between first end 1a of capacitor element 10 in Fig. 1 and first external electrode 21, and Fig. 3B is an enlarged cross-sectional view of the vicinity of the connection portion between cathode foil 20 and second external electrode 22. Contact layer 15 includes electroless Ni plating layer 15A and electroless Ag plating layer 15B.

[0042] As shown in Fig. 3A, an electroless Ni plating layer 15A covers the end face of the first end portion 1a, and an electroless Ag plating layer 15B covers the electroless Ni plating layer 15A. In Fig. 3A, the electroless Ag plating layer 15B is covered with a first external electrode 21. Similarly, as shown in Fig. 3B, the electroless Ni plating layer 15A covers the end face of the cathode foil 20, and the electroless Ag plating layer 15B covers the electroless Ni plating layer 15A. In Fig. 3B, the electroless Ag plating layer 15B is covered with a second external electrode 22.

[0043] By forming an electroless Ag plating layer covering the electroless Ni plating layer, the thickness of the electroless Ag plating layer can be easily controlled, resulting in a uniform, thin plating layer. This reduces the amount of silver used, while suppressing oxidation due to exposure of the underlying electroless Ni plating layer and the formation of pinholes in the Ag plating layer. As a result, the ESR of the electrolytic capacitor is reduced, and a highly reliable electrolytic capacitor can be obtained at low cost. Although not shown, an adhesion-improving layer may be disposed between the electroless Ni plating layer and the electroless Ag plating layer.

[0044] The first external electrode 21 includes a silver paste layer 21A and a Ni / Sn plating layer 21B. The silver paste layer 21A covers the contact layer 15 (electroless Ag plating layer 15B) that covers the end face of the first end portion 1a and the first surface 14a of the package 14. The Ni / Sn plating layer 21B covers the silver paste layer 21A. The second external electrode 22 includes a silver paste layer 22A and a Ni / Sn plating layer 22B. The silver paste layer 22A covers the contact layer 15 that covers the end face of the cathode foil 20 and the second surface 14b of the package 14. The Ni / Sn plating layer 22B covers the silver paste layer 22A.

[0045] 1 and 3A, the end face of first end portion 1a is flush with first surface 14a. Also, in FIGS. 1 and 3B, end face 20a of cathode foil 20 is flush with second surface 14b. However, the end faces of first end portion 1a and cathode foil 20 do not necessarily have to be flush with the main surface of package 14, and the end face of first end portion 1a may be protruding or recessed relative to first surface 14a. Similarly, end face 20a of cathode foil 20 may be protruding or recessed relative to second surface 14b.

[0046] 3A, the electroless Ni plating layer 15A and the electroless Ag plating layer 15B may cover the end face of the separation layer 12 exposed from the first surface 14a. Department In this case, the electroless Ni plating layer 15A and the electroless Ag plating layer 15B may extend to the first surface 14a. Department 5 may be formed to cover it.

[0047] The element stack is supported by a substrate 17. The substrate is, for example, an insulating substrate. It may be a metal substrate or a printed circuit board with a wiring pattern, as long as it can electrically isolate the first external electrode 21 and the second external electrode 22. A cathode foil may be disposed between the cathode lead layer located on the bottom surface of the element stack and the substrate 17. The substrate 17 is, for example, a laminated substrate with conductive wiring patterns formed on its front and back surfaces. The wiring patterns on the front surface and the back surface may be electrically connected via through holes. The wiring pattern on the front surface may be electrically connected to the cathode portion 6 of the capacitor element stacked in the bottom layer, and the wiring pattern on the back surface may be electrically connected to a third external electrode (not shown). In this case, the third external electrode is electrically connected to the cathode portion 6 of each capacitor element in the element stack via the substrate 17. In this case, depending on the wiring pattern on the back surface, it is possible to arbitrarily position the third external electrode (cathode) in the central region of the bottom surface of the electrolytic capacitor. For example, by arranging the third external electrode close to the first external electrode, the ESL can be reduced.

[0048] The substrate 17 is a metal plate, and may have a lead frame structure in which a metal plate processed into a predetermined shape is bent. A part of the metal plate is exposed from the exterior body, and the exposed part is electrically connected to an external terminal.

[0049] A portion of the first external electrode 21 is bent along the bottom surface of the exterior housing 14 and is exposed at the bottom surface of the electrolytic capacitor 100. Similarly, a portion of the second external electrode 22 is bent along the bottom surface of the exterior housing 14 so as to face the bent portion of the first external electrode 21 and is exposed at the bottom surface of the electrolytic capacitor 100. The exposed portions of the first external electrode 21 and the second external electrode 22 at the bottom surfaces respectively constitute the anode terminal and cathode terminal of the electrolytic capacitor.

[0050] Fig. 4 is a cross-sectional view schematically illustrating another example of the structure of an electrolytic capacitor according to an embodiment of the present disclosure. The electrolytic capacitor 101 shown in Fig. 4 includes multiple capacitor elements, an exterior housing 14 that seals the capacitor elements, first external electrodes 25 and 26, and a second external electrode 22. The multiple capacitor elements are stacked to form an element stack. The first external electrodes 25 and 26 are spaced apart from each other, with the first external electrode 25 covering the first surface 14a of the exterior housing 14 and the first external electrode 26 covering the second surface 14b of the exterior housing 14.

[0051] The multiple capacitor elements include a first capacitor element 10a in which the first portion 1 of the anode body 3 faces in one direction (toward the first surface 14a of the exterior body 14) relative to the second portion 2, and a second capacitor element 10b in which the first portion 1 of the anode body 3 faces in the opposite direction from the first capacitor element 10a (toward the second surface 14b of the exterior body 14) relative to the second portion 2. A first end 1a of the first capacitor element 10a is exposed from the exterior body at the first surface 14a and is electrically connected to a first external electrode 25 via a contact layer 15. A first end 1a of the second capacitor element 10b is exposed from the exterior body at the second surface 14b and is electrically connected to a first external electrode 26 via a contact layer 15. On the other hand, although not shown, on a third surface intersecting with first surface 14a and second surface 14b and / or a fourth surface opposite to the third surface, the end surfaces of cathode foil 20 are exposed from outer casing 14 and are electrically connected to second external electrode 22 via contact layer 15.

[0052] Similar to the electrolytic capacitor 100 shown in FIG. 1 , the contact layer 15 includes an electroless Ni-plated layer covering the end face of the first end portion 1a or the end face of the cathode foil 20, and an electroless Ag-plated layer covering the electroless Ni-plated layer (not shown). This allows the electroless Ag-plated layer to be formed thin and uniformly thick, reducing the amount of silver used while suppressing oxidation due to exposure of the underlying electroless Ni-plated layer and the formation of pinholes in the Ag-plated layer. As a result, the ESR of the electrolytic capacitor is reduced, and a low-cost, highly reliable electrolytic capacitor can be obtained. Although not shown, an adhesion-improving layer may be disposed between the electroless Ni-plated layer and the electroless Ag-plated layer.

[0053] 1, the first external electrode 25 (26) includes a silver paste layer 25A (26A) covering the contact layer 15 (electroless Ag plating layer) and a Ni / Sn plating layer 25B (26B) covering the silver paste layer. Similarly, although not shown, the second external electrode 22 includes a silver paste layer covering the contact layer 15 (electroless Ag plating layer) and a Ni / Sn plating layer covering the silver paste layer.

[0054] In the electrolytic capacitor 101, the direction of current flow within the first capacitor element 10a and the second capacitor element 10b is different. Therefore, the direction of the magnetic field generated by the current is different, and the magnetic flux generated within the element stack is reduced. This makes it possible to reduce ESL. Preferably, the first surface and the second surface may be surfaces of the exterior body that face each other.

[0055] 4, first capacitor elements 10a and second capacitor elements 10b are alternately stacked within the element stack. However, the first capacitor elements 10a and second capacitor elements 10b do not necessarily have to be alternately stacked, and the element stack may have a portion where the first capacitor elements 10a are stacked adjacent to each other and / or a portion where the second capacitor elements 10b are stacked adjacent to each other. Stacking the first capacitor elements and the second capacitor elements alternately is preferable because it effectively reduces the magnetic flux generated within the element stack and effectively reduces ESL.

[0056] In the electrolytic capacitors 100 and 101, the electroless Ni plating layer, the electroless Ag plating layer, the adhesion improving layer (strike Ag plating layer), and the Ni / Sn plating layer can be formed by known plating methods.

[0057] The components of the electrolytic capacitor according to the above embodiment will be described in more detail below.

[0058] (anode body) The anode body can contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal (such as an intermetallic compound), or the like. These materials can be used alone or in combination. Examples of the valve metal include aluminum, tantalum, niobium, and titanium. The anode body can be a foil of a valve metal, an alloy containing a valve metal, or a compound containing a valve metal, or a porous sintered body of a valve metal, an alloy containing a valve metal, or a compound containing a valve metal.

[0059] When a metal foil is used for the anode body, a porous portion is usually formed on the surface of at least the second portion of the anode foil to increase the surface area. The second portion has a core and a porous portion formed on the surface of the core. The porous portion may be formed by roughening the surface of at least the second portion of the anode foil by etching or other methods. A predetermined masking member may be placed on the surface of the first portion, followed by a roughening treatment such as etching. Alternatively, the entire surface of the anode foil may be roughened by etching or other methods. In the former case, an anode foil having no porous portion on the surface of the first portion but a porous portion on the surface of the second portion is obtained. In the latter case, a porous portion is formed on the surface of the first portion as well as the surface of the second portion. Known etching methods, such as electrolytic etching, may be used. The masking member is not particularly limited, but is preferably an insulator such as a resin. The masking member needs to be removed before the solid electrolyte layer is formed, but it may be a conductor containing a conductive material.

[0060] When the entire surface of the anode foil is roughened, the surface of the first portion has a porous portion. This may result in insufficient adhesion between the porous portion and the outer casing, allowing air (specifically, oxygen and moisture) to enter the electrolytic capacitor through the contact area between the porous portion and the outer casing. To prevent this, the porous first portion may be compressed in advance to crush the pores in the porous portion. This prevents air from entering the electrolytic capacitor through the porous portion from the first end exposed from the outer casing, and prevents a decrease in the reliability of the electrolytic capacitor due to this air intrusion.

[0061] (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 using a 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 where the porous portion is formed (including the inner wall surfaces of the pores of the porous portion). Note that the method for 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, on the porous portion of the surface of the first portion).

[0062] (cathode) The cathode section includes a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer. The cathode section may include a cathode foil. The cathode foil is electrically connected to the cathode extraction layer, and electrical connection with the cathode terminal is established via the cathode foil, facilitating electrical connection between the cathode extraction layer and the cathode terminal.

[0063] (solid electrolyte layer) The solid electrolyte layer contains, for example, a conductive polymer. Examples of the conductive polymer that can be used include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The solid electrolyte layer can be formed, for example, by chemically polymerizing and / or electrolytically polymerizing raw material monomers on the dielectric layer. Alternatively, the solid electrolyte layer can be formed by applying a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed to the dielectric layer. The solid electrolyte layer may contain a manganese compound.

[0064] (Cathode extraction layer) The cathode extraction layer includes, for example, a carbon layer and a silver paste layer. The carbon layer may be made of any conductive carbon material, such as graphite. The carbon layer may be formed, for example, by applying a carbon paste to at least a portion of the surface of the solid electrolyte layer. The silver paste layer may be formed, for example, by applying a composition containing silver powder and a binder resin (such as an epoxy resin). The silver paste layer may be formed, for example, by applying a silver paste to the surface of the carbon layer. The configuration of the cathode extraction layer is not limited to this, and may be any configuration that has a current collecting function.

[0065] (cathode foil) The cathode foil is, for example, a metal foil, and may be a sintered foil, a vapor-deposited foil, or a coated foil. The cathode foil may also be a sintered foil, a vapor-deposited foil, or a coated foil in which the surface of a metal foil (e.g., Al foil, Cu foil) is coated with a conductive film by vapor deposition or coating. The vapor-deposited foil may be an Al foil with Ni vapor-deposited on its surface. Examples of the conductive film include Ti, TiC, TiO, and C (carbon) films. The conductive film may also be a carbon coating.

[0066] (separation layer) An insulating separation layer may be provided to electrically separate the first portion from the cathode portion. The separation layer may be provided adjacent to the cathode portion so as to cover at least a portion of the surface of the first portion. The separation layer is preferably in close contact with the first portion and the exterior body. This can prevent air from entering the electrolytic capacitor. The separation layer may be disposed on the first portion via a dielectric layer.

[0067] The separation layer may contain, for example, a resin, and may be one of those exemplified for the exterior body described later. The dielectric layer formed in the porous portion of the first part may be compressed and densified to provide insulation.

[0068] The separation layer that adheres to the first portion can be obtained, for example, by attaching a sheet-like insulating member (such as a resin tape) to the first portion. When using an anode foil with a porous portion on its surface, the porous portion of the first portion may be compressed and flattened before the insulating member is adhered to the first portion. The sheet-like insulating member preferably has an adhesive layer on the surface that is attached to the first portion.

[0069] Alternatively, a liquid resin may be applied to or impregnated into the first portion to form an insulating member that adheres closely to the first portion. In a method using a liquid resin, the insulating member is formed so as to fill the irregularities on the surface of the porous portion of the first portion. The liquid resin easily penetrates into the recesses on the surface of the porous portion, making it easy to form an insulating member in the recesses as well. As the liquid resin, a curable resin composition exemplified in the fourth step described below can be used.

[0070] (exterior body) The exterior body preferably contains, for example, a cured product of a curable resin composition, and may contain a thermoplastic resin or a composition containing the same.

[0071] The exterior body can be formed using a molding technique such as injection molding, for example, by filling a curable resin composition or a thermoplastic resin (composition) into predetermined locations using a predetermined mold so as to cover the capacitor element.

[0072] The curable resin composition may contain, in addition to the curable resin, a filler, a curing agent, a polymerization initiator, and / or a catalyst. 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.

[0073] As the curable resin composition and the thermoplastic resin (composition), those exemplified in the fourth step described below can be used.

[0074] From the viewpoint of adhesion between the separation layer and the outer casing, it is preferable that the insulating member and the outer casing each contain a resin, since the outer casing is more likely to adhere to the insulating member containing a resin than the first portion containing a valve metal or the dielectric layer containing an oxide of a valve metal.

[0075] It is more preferable that the separation layer and the outer casing contain the same resin. In this case, the adhesion between the separation layer and the outer casing is further improved, thereby further suppressing the intrusion of air into the electrolytic capacitor. Examples of the same resin contained in the separation layer and the outer casing include epoxy resin.

[0076] From the viewpoint of increasing the strength of the exterior body, the exterior body preferably contains a filler.

[0077] On the other hand, the separation layer preferably contains a filler having a particle size smaller than that of the outer casing, and more preferably does not contain a filler. When the separation layer is formed by impregnating the first portion with a liquid resin, the liquid resin preferably contains a filler having a particle size smaller than that of the outer casing, and more preferably does not contain a filler. In this case, the liquid resin can be easily impregnated deep into the recesses on the surface of the porous portion of the first portion, making it easy to form a separation layer. In addition, it is easy to form a separation layer with a small thickness so that multiple capacitor elements can be stacked.

[0078] (contact layer) The contact layer includes an electroless Ni plating layer and an electroless Ag plating layer and can be formed to cover the end surface of the first end of the anode body and / or the end surface of the cathode foil. Preferably, the contact layer can be selectively formed to cover only the surface of the first end and the surface of the cathode foil exposed from the exterior body, while minimizing coverage of the surface of the resin exterior body (and the separation layer). To enhance the adhesion of the electroless plating layer and facilitate the selective formation of the electroless Ni plating layer and the electroless Ag plating layer on the surface of the first end and the surface of the cathode foil exposed from the exterior body, it is preferable to perform a zincate treatment before forming the electroless Ni plating layer. Furthermore, an adhesion-improving layer can be formed between the electroless Ni plating layer and the electroless Ag plating layer by strike Ag plating. Forming the adhesion-improving layer can improve the adhesion of the electroless Ag plating layer.

[0079] (external electrode) The first external electrode and / or the second external electrode preferably includes 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 spraying, or thermal spraying.

[0080] The first external electrode and / or the second external electrode may include, for example, a laminated structure of a Ni layer and a Sn layer. At least the outer surface of the first external electrode and / or the second external electrode may be made of a metal that has excellent wettability with solder. Examples of such metals include Sn, Au, Ag, and Pd.

[0081] The first external electrode and / or the second external electrode preferably includes a laminate structure of a conductive paste layer and a plating layer. The plating layer may be a Ni / Sn plating layer, which has excellent wettability with solder.

[0082] (Conductive paste layer) The conductive paste layer is formed to cover the main surface of the exterior body and to be electrically connected to the first ends of the (plurality of) capacitor elements and / or the cathode foil via the contact layer.

[0083] The conductive paste layer includes a conductive resin layer mixed with conductive particles. The conductive resin layer can be formed by applying a conductive paste containing conductive particles and a resin material to the main surface of the exterior body and drying it. The resin material is suitable for bonding to the exterior body and the contact layer, and can increase the bonding strength through chemical bonding (e.g., hydrogen bonding). Examples of the conductive particles that can be used include metal particles such as silver or copper, and particles of a conductive inorganic material such as carbon.

[0084] The conductive paste layer may cover a portion of the surface (eg, top or bottom surface) that intersects with the first end of the capacitor element and / or the main surface of the exterior body from which the cathode foil is exposed.

[0085] [Manufacturing method of electrolytic capacitors] An electrolytic capacitor according to an embodiment of the present disclosure may be manufactured by a manufacturing method including, for example, a first step of preparing an anode body, a second step of obtaining a plurality of capacitor elements, a third step of obtaining an element stack by stacking the plurality of capacitor elements, a fourth step of covering the element stack with an exterior body, a fifth step of forming an end face of the first portion and exposing it from the exterior body, and a sixth step of electrically connecting the end face of the first portion to a first external electrode. The manufacturing method may further include a step of arranging a separation layer (insulating member) on a portion of the anode body (a separation layer arranging step).

[0086] Each step of the method for manufacturing an electrolytic capacitor will be described below.

[0087] (1st step) In the first step, an anode body having a dielectric layer formed on its surface is prepared. More specifically, an anode body is prepared that includes a first portion including one end and a second portion including the other end opposite the one end, with the dielectric layer formed on at least the surface of the second portion. The first step includes, for example, a step of forming a porous portion on the surface of the anode body and a step of forming a dielectric layer on the surface of the porous portion. More specifically, the anode body used in the first step has a first portion including the end to be removed (the one end) and a second portion including the second end (the other end). It is preferable to form a porous portion on at least the surface of the second portion.

[0088] The porous portion on the surface of the anode body may be formed by forming irregularities on the surface of the anode body, and may be formed, for example, by roughening the surface of the anode foil by etching (for example, electrolytic etching).

[0089] The dielectric layer may be formed by chemical conversion treatment of the anode body. The chemical conversion treatment may be performed, for example, by immersing the anode body in a chemical conversion solution to impregnate the surface of the anode body with the chemical conversion solution, and applying a voltage between the anode body as an anode and a cathode immersed in the chemical conversion solution. When the anode body has a porous portion on its surface, the dielectric layer is formed to conform to the uneven shape of the surface of the porous portion.

[0090] (Separation layer arrangement process) When manufacturing an electrolytic capacitor having a separation layer (insulating member), the step of disposing the separation layer (insulating member) may be performed after the first step and before the second step. In this step, the insulating member is disposed on a part of the anode body. More specifically, in this step, the insulating member is disposed on the first part of the anode body via a dielectric layer. The insulating member is , th The first portion is arranged to separate the cathode portion that will be formed in a later process.

[0091] In the separation layer arranging step, a sheet-like insulating member (such as a resin tape) may be attached to a part (for example, the first part) of the anode body. Even when an anode body having a porous portion formed on its surface is used, the insulating member can be firmly adhered to the first part by compressing and flattening the irregularities on the surface of the first part. The sheet-like insulating member preferably has an adhesive layer on the surface that is attached to the first part.

[0092] In addition to the above, in the separation layer arranging step, a liquid resin may be applied to or impregnated into a portion of the anode body (e.g., the first portion) to form the insulating member. For example, the liquid resin may be applied to or impregnated into the anode body and then cured. In this case, an insulating member that adheres closely to the first portion can be easily formed. As the liquid resin, a curable resin composition exemplified in the fourth step (forming the outer casing), a resin solution in which a resin is dissolved in a solvent, or the like can be used.

[0093] When a porous portion is formed on the surface of the anode body, it is preferable to apply or impregnate a liquid resin to a portion of the surface of the porous portion of the anode body (for example, the surface of the first portion). In this case, an insulating member can be easily formed so as to fill in the irregularities on the surface of the porous portion of the first portion. The liquid resin easily enters the recesses on the surface of the porous portion, and the insulating member can be easily formed in the recesses as well. This protects the porous portion on the surface of the anode body with the insulating member, which prevents the porous portion of the anode body from collapsing when the anode body is partially removed together with the outer casing in the fourth step. Because the surface of the porous portion of the anode body and the insulating member are firmly adhered to each other, the insulating member is prevented from peeling off from the surface of the porous portion of the anode body when the anode body is partially removed together with the outer casing in the fourth step.

[0094] (2nd process) In the second step, a cathode portion is formed on the anode body to obtain a capacitor element. If an insulating member is provided in the first step, a cathode portion is formed in a portion of the anode body where no insulating member is provided in the second step to obtain a capacitor element. More specifically, in the second step, at least a portion of the dielectric layer formed on the surface of the second portion of the anode body is covered with the cathode portion.

[0095] The step of forming the cathode portion includes, for example, a step of forming a solid electrolyte that covers at least a part of the dielectric, and a step of forming a cathode extraction layer that covers at least a part of the solid electrolyte layer.

[0096] The solid electrolyte layer can be formed, for example, by chemically polymerizing and / or electrolytically polymerizing raw material monomers on the dielectric layer. Alternatively, the solid electrolyte layer may be formed by applying a treatment liquid containing a conductive polymer and then drying it. The treatment liquid may further contain other components such as a dopant. For the conductive polymer, for example, a polymerization liquid containing pyrrole (a monomer of a conjugated polymer), naphthalenesulfonic acid (a dopant), and water is prepared. Electrolytic polymerization is performed using the obtained polymerization liquid.

[0097] The cathode extraction layer can be formed, for example, by sequentially laminating a carbon layer and a silver paste layer on a solid electrolyte layer.

[0098] (3rd step) In the third step, multiple capacitor elements are stacked to obtain an element stack. The element stack may be obtained by sandwiching a cathode foil between the capacitor elements. In the element stack, the first portions of the multiple capacitor elements may be oriented in the same direction or different directions. The element stack may be obtained by alternately stacking the cathode portions of the multiple capacitor elements with a conductive adhesive interposed between them so that the first portions of adjacent capacitor elements face opposite directions.

[0099] The element stack is then placed on a substrate via a conductive adhesive. The substrate may be an insulating substrate, a metal substrate, or a laminated substrate with wiring patterns formed on its front and back surfaces. When a laminated substrate is used, a third external electrode 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 third external electrode, the third external electrode can be electrically connected to the cathodes of the capacitor elements constituting the element stack via the wiring pattern formed on the laminated substrate and through holes connecting the wiring pattern on the front surface and the wiring pattern on the back surface.

[0100] Alternatively, for example, an external lead terminal in the form of a plate bent into a predetermined shape may be attached to the surface of the cathode portion exposed in the bottom or top layer of the element stack via a conductive paste or the like, thereby electrically connecting the element stack and the lead terminal.

[0101] (4th step) In the fourth step, the element stack is covered with an exterior body. When a third external electrode is provided, the third external electrode is not entirely covered with the exterior body, but at least a portion of the third external electrode is exposed. The exterior body can be formed using injection molding or the like. The exterior body can be formed, for example, by using a predetermined mold to fill a curable resin composition or a thermoplastic resin (composition) into predetermined locations so as to cover the element stack.

[0102] The curable resin composition may contain, in addition to the curable resin, a filler, a curing agent, a polymerization initiator, and / or a catalyst. Examples of the curable resin include epoxy resin, phenolic 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.

[0103] The filler is preferably, for example, insulating particles and / or fibers. Examples of insulating materials constituting the filler include insulating compounds (oxides, etc.) such as silica and alumina, glass, and mineral materials (talc, mica, clay, etc.). The outer casing may contain one type of these fillers or a combination of two or more types.

[0104] (5th step) In the fifth step, after the fourth step, an end face of the first portion is formed and exposed from the exterior housing. More specifically, at least the anode body is partially removed along with the exterior housing on the end side of the element stack to expose at least the first end of the anode body (specifically, the end face of the first end) from the exterior housing. Examples of methods for exposing the first end from the exterior housing include covering the capacitor element with the exterior housing, and then polishing the surface of the exterior housing or cutting off a portion of the exterior housing so that the first end is exposed from the exterior housing. Alternatively, a portion of the first portion may be cut off together with a portion of the exterior housing. In this case, the first end, which does not include a porous portion and has a surface free of a native oxide film, can be easily exposed from the exterior housing, resulting in a connection between the first portion and the external electrode with low resistance and high reliability. Dicing is a preferred method for cutting the exterior housing. As a result, an exposed end face of the first end of the first portion appears on the cut surface. At least one of the cut surfaces becomes the first surface. If the element stack has two types of capacitor elements with first portions oriented in different directions, cutting the first portion together with the outer casing requires cutting at two locations, one of which becomes the first surface and the other becomes the second surface.

[0105] When the element stack includes a cathode foil, the cathode foil is partially removed together with the exterior housing to expose the end of the cathode foil from the exterior housing. The method for exposing the end of the cathode foil from the exterior housing can be the same as the method for exposing the first end of the anode body from the exterior housing. The surface of the end of the cathode foil exposed from the exterior housing is preferably a surface different from the surface of the exterior housing where the first end of the anode body is exposed. Note that by appropriately designing the shapes of the anode body and the cathode foil, the end of the cathode foil and the first end of the anode body can be exposed at different locations on the surface of the same exterior housing.

[0106] In the fifth step, the anode body and the insulating member may be partially removed along with the exterior body at the end of the element stack to expose the end face of the first end and the end face of the insulating member from the exterior body. In this case, the anode body and the insulating member each have a flush end face that is exposed from the exterior body. This makes it possible to easily expose the end face of the anode body and the end face of the insulating member, which are flush with the surface of the exterior body, from the exterior body.

[0107] The fifth step makes it possible to easily expose the end surface of the anode body (first end portion) (and the end surface of the cathode foil) on which no natural oxide film is formed from the outer casing, thereby achieving a connection state with low resistance and high reliability between the anode body (more specifically, the first portion) and the external electrode.

[0108] (6th step) In the sixth step, the end face of the anode body (first end) exposed from the exterior housing is electrically connected to the first external electrode. In this step, for example, the first external electrode is formed to cover the exposed surface of the first end of the exterior housing, and the first external electrode is electrically connected to the end face of the first end. For example, if the end faces of the anode body (first end) are exposed on the first and second faces, the first external electrode covering the first face and the first external electrode covering the second face may be formed separately. Furthermore, if the element stack includes a cathode foil, the end face of the cathode foil exposed from the exterior housing is electrically connected to the second external electrode. For example, the second external electrode is formed to cover the exposed surface of the cathode foil of the exterior housing, and the second external electrode is electrically connected to the end face of the cathode foil. The first external electrode and / or the second external electrode includes, for example, a conductive paste layer and a Ni / Sn plating layer covering the conductive paste layer.

[0109] Prior to forming the first and second external electrodes, a step of forming a contact layer is performed on the surface that is the end face of the first end portion and / or the end face of the cathode foil. The step of forming the first and second external electrodes may include a step of forming a conductive paste layer so as to cover the main surface of the exterior body where the end face of the first end portion and / or the end face of the cathode foil are exposed. When forming a contact layer, the conductive paste layer may be formed so as to cover the contact layer and the main surface of the exterior body.

[0110] (Process for forming contact layer) The contact layer is preferably formed by plating. The contact layer preferably includes two layers: an electroless Ni plating layer and an electroless Ag plating layer covering the electroless Ni plating layer. This allows for the formation of a uniform, thin electroless Ag plating layer, reducing the amount of silver used while suppressing oxidation due to exposure of the underlying electroless Ni plating layer and pinhole formation in the Ag plating layer. As a result, the ESR of the electrolytic capacitor is reduced, and a low-cost, highly reliable electrolytic capacitor can be obtained. The specific plating methods, such as the components of the plating baths used for electroless Ni plating and electroless Ag plating, can be determined by known methods.

[0111] The electroless Ni plating layer and the electroless Ag plating layer are formed so as to selectively cover the end face of the first end portion and / or the end face of the cathode foil, while minimizing coverage of the exposed resin portion of the exterior body. To enhance the selectivity of the electroless Ni plating layer, a zincate treatment may be performed before the electroless Ni plating. The electroless Ag plating layer may be selectively formed on the surface of the electrolytic Ni plating layer. Furthermore, an adhesion-improving layer may be formed between the electroless Ni plating layer and the electroless Ag plating layer by strike Ag plating. Forming the adhesion-improving layer can improve the adhesion of the electroless Ag plating layer.

[0112] (Process for forming a conductive paste layer) The conductive paste layer can be formed to cover the end face of the first end portion and / or the end face of the cathode foil (the contact layer if a contact layer is formed), the exposed surface of the outer casing where the end face of the first end portion and / or the end face of the cathode foil is exposed, and, if a separation layer is provided, the end face of the separation layer (insulating member).

[0113] The conductive paste layer can be formed by applying a conductive paste containing conductive particles and a resin material. Specifically, the conductive paste (e.g., silver paste) is applied to each end surface by a dipping method, a transfer method, a printing method, a dispensing method, or the like, and then cured at a high temperature to form the conductive paste layer.

[0114] To fabricate an electrolytic capacitor similar to the electrolytic capacitor 100 shown in Figure 1, a capacitor element with a carbon layer formed as a cathode lead layer was laminated with a cathode foil via a conductive adhesive to obtain an element laminate. The element laminate was covered with an outer casing, and the above manufacturing method was carried out up to step 5 to obtain electrolytic capacitor X0 for evaluation. The end faces of the anode body and cathode foil exposed from the outer casing of electrolytic capacitor X0 were connected to a resistance measuring device, and the resistance value at 100 kHz was evaluated as the ESR value. The ESR of electrolytic capacitor X0 was 0.18 mΩ.

[0115] Next, contact layers consisting of an electroless Ni-P plating layer (5 μm thick) and an electroless Ag plating layer (0.3 μm thick) were formed on the end faces of the anode body and the cathode foil of electrolytic capacitor X0, yielding electrolytic capacitor X1A for evaluation. Here, the electroless Ni-P plating layer refers to an electroless Ni plating layer containing phosphorus (P). The contact layers of electrolytic capacitor X1A were connected to a resistance measuring device, and the ESR was similarly measured. The ESR of electrolytic capacitor X1A was 0.21 mΩ.

[0116] Next, the contact layer of electrolytic capacitor X1A was covered with a silver paste layer, and first and second external electrodes were formed to obtain electrolytic capacitor X2A for evaluation. The first and second external electrodes of electrolytic capacitor X2A were connected to a resistance measuring device, and the ESR was similarly measured. The ESR of electrolytic capacitor X2A was 1.21 mΩ, a sufficiently low ESR.

[0117] Next, a contact layer consisting of an electroless Ni-P plating layer (5 μm thick), an adhesion-improving layer formed by electroless strike Ag plating, and an electroless Ag plating layer (0.3 μm thick) was formed on the end faces of the anode body and the cathode foil of electrolytic capacitor X0, yielding electrolytic capacitor X1B for evaluation. The contact layer of electrolytic capacitor X1B was connected to a resistance measuring device, and the ESR was similarly measured. The ESR of electrolytic capacitor X1B was 0.21 mΩ.

[0118] Next, the contact layer of electrolytic capacitor X1B was covered with a silver paste layer, and first and second external electrodes were formed to obtain electrolytic capacitor X2B for evaluation. The first and second external electrodes of electrolytic capacitor X2B were connected to a resistance measuring device, and the ESR was similarly measured. The ESR of electrolytic capacitor X2B was 1.21 mΩ, a sufficiently low ESR.

[0119] The product ESR variation (σ) of the evaluation electrolytic capacitor X2A was 2.570, and the product ESR variation (σ) with the evaluation electrolytic capacitor X2B was 1.813, confirming that the product ESR variation (σ) can be reduced by placing an adhesion-improving layer.

[0120] Next, contact layers consisting of an electroless Ni-B plating layer (5 μm thick) and an electroless Ag plating layer (0.3 μm thick) were formed on the end faces of the anode body and the cathode foil of electrolytic capacitor X0, yielding electrolytic capacitor X1C for evaluation. Here, the electroless Ni-B plating layer refers to an electroless Ni plating layer containing boron (B). The contact layers of electrolytic capacitor X1C were connected to a resistance measuring device, and the ESR was similarly measured. The ESR of electrolytic capacitor X1C was 0.19 mΩ.

[0121] Next, the contact layer of electrolytic capacitor X1C was covered with a silver paste layer, and first and second external electrodes were formed to obtain electrolytic capacitor X2C for evaluation. The first and second external electrodes of electrolytic capacitor X2C were connected to a resistance measuring device, and the ESR was similarly measured. The ESR of electrolytic capacitor X2C was 1.22 mΩ, a sufficiently low ESR.

[0122] On the other hand, contact layers consisting of an electroless Ni plating layer (5 μm thick) and an electrolytic Ag plating layer (1 μm thick) were formed on the end faces of the anode body and the cathode foil of electrolytic capacitor X0, to obtain electrolytic capacitor Y1 (comparative example) for evaluation. The contact layers of electrolytic capacitor Y1 were connected to a resistance measuring device, and the ESR was similarly measured. The ESR of electrolytic capacitor Y1 was 0.28 mΩ, which was higher than that of electrolytic capacitors X1A, X1B, and X1C.

[0123] The contact layer of electrolytic capacitor Y1 was covered with a silver paste layer, and first and second external electrodes were formed to obtain electrolytic capacitor Y2 (comparative example) for evaluation. The first and second external electrodes of electrolytic capacitor Y2 were connected to a resistance measuring device, and the ESR was similarly measured. The ESR of electrolytic capacitor Y2 was 1.95 mΩ, significantly higher than that of electrolytic capacitors X2A, X2B, and X2C. [Industrial Applicability]

[0124] The electrolytic capacitor according to the present disclosure can be used in a variety of applications that require high capacitance and low ESR. [Explanation of symbols]

[0125] 1 1st part (anode extraction part), 1a 1st end 2 Second part (cathode forming part) 2a Second end 3 Anode body 4 core 5 Porous part 6 Cathode 7 Solid electrolyte layer 8 carbon layers 9 Silver paste layer 10 Capacitor element 10a First capacitor element 10b Second capacitor element 11 Electrolytic capacitors 12 Separation layer (insulating material) 14 Exterior body 14a First surface of exterior body 14b Second surface of the exterior body 15 Contact layer 16 Anode electrode layer 17 PCB 20 Cathode foil 20a end face 21, 25, 26 First external electrodes 21A, 25A, 26A silver paste layer 21B, 25B, 26B Ni / Sn plating layer 22 second external electrode 22A Silver paste layer 22B Ni / Sn plating layer 100, 101 Electrolytic capacitors

Claims

1. a capacitor element having an anode portion and a cathode portion; an exterior body that seals the capacitor element; a first external electrode electrically connected to the anode portion; a second external electrode electrically connected to the cathode portion, at least one of an end face of the anode portion and an end face of the cathode portion is exposed from the exterior body and is electrically connected to the corresponding one of the first external electrode and the second external electrode; the end surface exposed from the exterior body is covered with an electroless Ni plating layer, the electroless Ni plating layer is covered with an electroless Ag plating layer; the electroless Ag plating layer is covered with the corresponding one of the first external electrode and the second external electrode; an element stack including a plurality of capacitor elements each of which is the capacitor element; the end face of the anode portion of at least one first capacitor element among the plurality of capacitor elements is exposed on a first main surface of the exterior body and is electrically connected to the first external electrode via the electroless Ni plating layer and the electroless Ag plating layer; an electrolytic capacitor, wherein the end face of the anode portion of at least one second capacitor element other than the at least one first capacitor element is exposed on a second main surface opposite the first main surface of the outer casing, and is electrically connected to the first external electrode via the electroless Ni plating layer and the electroless Ag plating layer.

2. 2. The electrolytic capacitor according to claim 1, wherein at least one of the first external electrode and the second external electrode includes a conductive paste layer and a Ni / Sn plating layer covering the conductive paste layer.

3. 3. The electrolytic capacitor according to claim 1, wherein the electroless Ag plating layer is selectively formed on the surface of the electroless Ni plating layer rather than on the surface of the outer casing where the end face is exposed.

4. 4. The electrolytic capacitor according to claim 1, wherein an adhesion improving layer is disposed between the electroless Ni plating layer and the electroless Ag plating layer.

5. 5. The electrolytic capacitor according to claim 1, wherein the electroless Ni plating layer contains at least one of phosphorus (P) and boron (B).

6. 5. The electrolytic capacitor according to claim 1, wherein the electroless Ni plating layer consists essentially of Ni.

7. 7. The electrolytic capacitor according to claim 1, wherein the electroless Ni plating layer has a thickness of 0.1 to 10 μm.

8. 8. The electrolytic capacitor according to claim 1, wherein the electroless Ag plating layer has a thickness of 0.1 to 1 μm.

9. An electrolytic capacitor described in any one of claims 1 to 8, wherein at least one end face of the cathode portion of each of the plurality of capacitor elements in the element stack is exposed from the outer casing and is electrically connected to the second external electrode via the electroless Ni plating layer and the electroless Ag plating layer.

10. the cathode portion includes a cathode foil, 10. The electrolytic capacitor according to claim 1, wherein an end surface of the cathode foil is exposed from the exterior body and is electrically connected to the second external electrode via the electroless Ni plating layer and the electroless Ag plating layer.

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