Solid electrolytic capacitor and method for producing solid electrolytic capacitor

Abstract

The present disclosure addresses the problem of providing a solid electrolytic capacitor having ESR characteristics that are less likely to deteriorate. A solid electrolytic capacitor 100 according to the present disclosure comprises: a capacitor element 1; an exterior resin 2 that seals the capacitor element 1; and an external electrode 3 that is disposed on the outer surface of the exterior resin 2. The external electrode 3 is formed of a conductive paste containing a resin and a conductive filler. The outer surface 30 of the external electrode 3 has a plurality of recesses 4. The total area of the plurality of recesses 4 is 1-20% inclusive of the effective area of the external electrode 3.

Description

Solid electrolytic capacitor and method for manufacturing the same

[0001] The present disclosure relates generally to solid electrolytic capacitors and methods for manufacturing solid electrolytic capacitors, and more particularly to solid electrolytic capacitors having external electrodes and methods for manufacturing the same.

[0002] Patent Document 1 describes an electronic component and a method for manufacturing the electronic component. The electronic component is an electrolytic capacitor having first and second end faces opposing each other in a longitudinal direction, first and second main faces opposing each other in a thickness direction perpendicular to the longitudinal direction, and first and second side faces opposing each other in a width direction perpendicular to the longitudinal direction and the thickness direction. The electronic component also includes an element body having an internal electrode, a first external electrode, and a second external electrode. The first external electrode is connected to the internal electrode exposed at the first end face of the element body. The first external electrode is provided on the first end face. The second external electrode is connected to the internal electrode exposed at the second end face of the element body. The second external electrode is provided on the second end face.

[0003] The first external electrode has a resin electrode layer containing a conductive component and a resin component, the resin electrode layer of the first external electrode having a first portion facing the entire first end face of the element body, and a plurality of periodically arranged protrusions on a surface of the first portion of the resin electrode layer of the first external electrode opposite the first end face of the element body.

[0004] In this type of electrolytic capacitor, the ESR characteristics are likely to deteriorate.

[0005] International Publication No. 2021 / 256410

[0006] An object of the present disclosure is to provide a solid electrolytic capacitor in which deterioration of ESR characteristics is unlikely to occur, and a method for manufacturing the solid electrolytic capacitor.

[0007] A solid electrolytic capacitor according to one aspect of the present disclosure includes a capacitor element, an exterior resin that encapsulates the capacitor element, and an external electrode disposed on the exterior surface of the exterior resin. The external electrode is formed from a conductive paste containing a resin and a conductive filler. The exterior surface of the external electrode has a plurality of recesses. The total area of ​​the recesses is 1% to 20% of the effective area of ​​the external electrode.

[0008] A method for manufacturing a solid electrolytic capacitor according to one aspect of the present disclosure includes the steps of: sealing a capacitor element with an exterior resin; supplying a conductive paste containing a resin and a conductive filler on an outer surface of the exterior resin; and curing the conductive paste on the outer surface of the exterior resin to form an external electrode. The conductive paste contains the resin in an amount of 2% by weight to 10% by weight based on the total weight of the resin and the conductive filler.

[0009] Fig. 1 is a schematic cross-sectional view showing an embodiment of a solid electrolytic capacitor according to the present disclosure. Fig. 2 is a graph showing the relationship between the amount of resin contained in the external electrode and the maximum depth of the recesses. Fig. 3 is a graph showing the relationship between the amount of resin contained in the external electrode and the average depth of the recesses. Fig. 4 is a graph showing the relationship between the amount of resin contained in the external electrode and the average total area ratio of multiple recesses. Fig. 5 is a graph showing the relationship between the amount of resin contained in the external electrode and the ESR variation rate after reflow treatment.

[0010] (Embodiments) Hereinafter, solid electrolytic capacitors according to embodiments will be described with reference to the drawings. However, the following embodiment is merely one of various embodiments of the present disclosure. The following embodiment can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved. Furthermore, each figure described in the following embodiments is a schematic diagram, and the ratios of the sizes and thicknesses of the components in the figures do not necessarily reflect the actual dimensional ratios.

[0011] 1. Overview A solid electrolytic capacitor 100 according to this embodiment includes a capacitor element 1, an exterior resin 2, and external electrodes 3 (see FIG. 1). The exterior resin 2 seals the capacitor element 1. The external electrodes 3 are disposed on the outer surface of the exterior resin 2.

[0012] The external electrode 3 is formed of a conductive paste containing a resin and a conductive filler. The outer surface 30 of the external electrode 3 has a plurality of recesses 4. The total area of ​​the plurality of recesses 4 is 1% to 20% of the effective area of ​​the external electrode 3.

[0013] The solid electrolytic capacitor 100 of this embodiment is soldered when mounted on another component such as a circuit board. In this case, the solder is bonded to the outer surface 30 of the external electrode 3, and because the outer surface 30 of the external electrode 3 has a plurality of recesses 4 formed at a predetermined area ratio, the anchor effect makes it difficult for the solder to peel from the external electrode 3. Therefore, the electrical conductivity between the solder and the solid electrolytic capacitor 100 is unlikely to decrease, and the ESR characteristics are unlikely to deteriorate. As a result, the product life of the solid electrolytic capacitor 100 is unlikely to be shortened.

[0014] In the solid electrolytic capacitor 100, if the ratio of the total area of ​​the multiple recesses 4 to the effective area of ​​the external electrode 3 is outside the range of 1% or more and 20% or less, the anchor effect will not be sufficient, peeling will easily occur between the solder and the external electrode 3, and the ESR characteristics will easily deteriorate.

[0015] In the solid electrolytic capacitor 100 of this embodiment, the depth of each of the plurality of recesses 4 is preferably 1% to 40% of the thickness of the external electrode 3. This makes it more difficult for peeling to occur between the solder and the external electrode 3.

[0016] In the solid electrolytic capacitor 100 of this embodiment, the plurality of recesses 4 preferably include a plurality of types of recesses 4 having irregularly different shapes, which makes it more difficult for peeling to occur between the solder and the external electrode 3.

[0017] 2. Details The solid electrolytic capacitor 100 of this embodiment includes a capacitor element 1, an exterior resin 2, and external electrodes 3 (see FIG. 1). The solid electrolytic capacitor 100 also includes a lead frame 5. The solid electrolytic capacitor 100 has an end-face current collection structure.

[0018] The capacitor element 1 includes a metal foil 10, a dielectric layer 11, a solid electrolyte layer 12, a carbon layer 13, and a silver layer 14. In the present disclosure, the direction in which the metal foil 10, the dielectric layer 11, the solid electrolyte layer 12, the carbon layer 13, and the silver layer 14 are stacked is defined as a first direction. The external electrodes 3 include a first external electrode 31 and a second external electrode 32. The direction perpendicular to the first direction and in which the first external electrode 31 and the second external electrode 32 face each other is defined as a second direction. The first and second directions are used for convenience in explaining the present disclosure and do not define the usage state, etc., of the solid electrolytic capacitor 100 of this embodiment.

[0019] (1) Capacitor Element The capacitor element 1 is a main component that functions as the solid electrolytic capacitor 100. The capacitor element 1 has a metal foil 10, a dielectric layer 11, a solid electrolyte layer 12, a carbon layer 13, and a silver layer 14. The metal foil 10, the dielectric layer 11, the solid electrolyte layer 12, the carbon layer 13, and the silver layer 14 are stacked in a first direction. Therefore, the capacitor element 1 is a laminate. The capacitor element 1 has an anode and a cathode as internal electrodes. The anode is made of the metal foil 10, and the cathode is made of the solid electrolyte layer 12, the carbon layer 13, and the silver layer 14.

[0020] The metal foil 10 is a foil made of aluminum or an aluminum alloy. The thickness of the metal foil 10 is not particularly limited, but may be, for example, 15 μm or more and 300 μm or less, or 80 μm or more and 250 μm or less. Both surfaces of the metal foil 10 in the first direction (the upper and lower surfaces in FIG. 1 ) are preferably rough surfaces having fine irregularities to increase the surface area. Such rough surfaces are formed by etching the metal foil 10 with an acidic solution such as hydrochloric acid.

[0021] An anode lead layer 62 is provided on the metal foil 10. The anode lead layer 62 protrudes to the outside of the exterior resin 2. The anode lead layer 62 protrudes to the outside of the exterior resin 2 from the second end surface 22 of the exterior resin 2. The anode lead layer 62 is located inside the second external electrode 32 formed on the second end surface 22. The anode lead layer 62 is in contact with and electrically connected to the second external electrode 32. The anode lead layer 62 can be formed by metal plating such as copper plating or nickel-silver plating.

[0022] The dielectric layer 11 is provided on the metal foil 10. The dielectric layer 11 is an electrically insulating layer, thereby ensuring electrical insulation between the metal foil 10 and the cathode. The dielectric layer 11 covers almost the entire surface of the metal foil 10. Therefore, the dielectric layer 11 is formed so as to face both sides of the metal foil 10 in the first direction.

[0023] The dielectric layer 11 is preferably an oxide film of the metal that constitutes the metal foil 10. When the metal foil 10 is made of aluminum or an aluminum alloy, the dielectric layer 11 is preferably made of aluminum oxide (Al ２ O ３ The dielectric layer 11 of the oxide film can be formed by anodizing the metal foil 10. The thickness of the dielectric layer 11 is set according to the required withstand voltage, capacitance, etc.

[0024] The solid electrolyte layer 12 is provided on the dielectric layer 11. The capacitor element 1 has two solid electrolyte layers 12 facing each other in the first direction, and the metal foil 10 and the dielectric layer 11 are disposed between the two solid electrolyte layers 12.

[0025] The solid electrolyte layer 12 is formed in a layer shape containing a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, and polyaniline. The thickness of the solid electrolyte layer 12 is set according to the required capacitance, etc.

[0026] The carbon layer 13 is provided on the solid electrolyte layer 12. The capacitor element 1 has two carbon layers 13 facing each other in the first direction, and the metal foil 10, the dielectric layer 11, and the two solid electrolyte layers 12 are disposed between the two carbon layers 13.

[0027] The carbon layer 13 is formed in a layer shape containing carbon particles. The carbon layer 13 can be formed by applying a carbon paste or the like onto the solid electrolyte layer 12 and then curing the paste. The thickness of the carbon layer 13 is set according to the required conductivity, etc.

[0028] The silver layer 14 is provided on the carbon layer 13. The capacitor element 1 has two silver layers 14 facing each other in a first direction, and the metal foil 10, the dielectric layer 11, the two solid electrolyte layers 12, and the two carbon layers 13 are disposed between the two silver layers 14.

[0029] The silver layer 14 is formed in a layer shape containing silver particles. The silver layer 14 can be formed by applying a silver paste or the like onto the carbon layer 13 and curing it. The thickness of the silver layer 14 is set depending on the required conductive performance, and may be, for example, 0.1 μm to 50 μm, or 1 μm to 20 μm.

[0030] (2) Lead Frame The lead frame 5 is a support substrate that supports the capacitor element 1. The lead frame 5 can be made of a conductive metal material, for example, by processing a copper plate. The lead frame 5 has a support portion 50 and a connection portion 51.

[0031] The support part 50 is formed in a flat plate shape and is disposed opposite the surface (lower surface) of one of the two silver layers 14 (the lower silver layer 14). The support part 50 and one of the silver layers 14 are bonded together with a silver-containing adhesive 52. The silver-containing adhesive 52 is an adhesive containing silver particles and is electrically conductive. Therefore, the support part 50 and one of the silver layers 14 are electrically connected by the silver-containing adhesive 52.

[0032] The connection portion 51 is formed in a flat plate shape and extends from the support portion 50 in the first direction. The connection portion 51 is located closer to the first external electrode 31 than the center of the support portion 50 in the second direction. The connection portion 51 is disposed opposite one end face of the capacitor element 1 in the second direction (the end face closer to the first external electrode 31). The connection portion 51 and the one end face of the capacitor element 1 are bonded together with an adhesive 52 containing silver. This electrically connects the two solid electrolyte layers 12, the two carbon layers 13, and the two silver layers 14 of the capacitor element 1 to the lead frame 5. On the other hand, the metal foil 10 of the capacitor element 1 is not electrically connected to the lead frame 5 because the dielectric layer 11 is interposed between the adhesive 52 containing silver and the metal foil 10.

[0033] A cathode lead layer 61 is provided on the lead frame 5. The cathode lead layer 61 protrudes to the outside of the exterior resin 2. The cathode lead layer 61 protrudes to the outside of the exterior resin 2 from a first end surface 21 of the exterior resin 2. The cathode lead layer 61 is located inside a first external electrode 31 formed on the first end surface 21. The cathode lead layer 61 is in contact with and electrically connected to the first external electrode 31. The cathode lead layer 61 can be formed by metal plating such as copper plating or nickel-silver plating.

[0034] (3) Exterior Resin The exterior resin 2 seals the capacitor element 1. The exterior resin 2 also seals the lead frame 5. Therefore, the capacitor element 1 and the lead frame 5 are covered with the exterior resin 2.

[0035] The exterior resin 2 is a resin molded body, and contains, for example, a thermosetting resin such as an epoxy resin and a filler such as alumina particles. The exterior resin 2 is formed by a molding method such as transfer molding.

[0036] The exterior resin 2 has an outer shape like a rectangular parallelepiped. That is, the exterior resin 2 has a first end face 21 and a second end face 22 that face each other in the second direction. The exterior resin 2 also has a first main surface 23 and a second main surface 24 that face each other in the first direction. The exterior resin 2 also has two side surfaces (not shown) that are parallel to both the second direction and the first direction. The exterior surface of the exterior resin 2 is made up of the first end face 21, the second end face 22, the first main surface 23, the second main surface 24, and the two side surfaces. The first end face 21, the second end face 22, the first main surface 23, the second main surface 24, and the two side surfaces are each approximately flat.

[0037] (4) External Electrode The external electrode 3 is disposed on the exterior resin 2. The external electrode 3 has a first external electrode 31 provided on a first end surface 21 of the exterior resin 2 and a second external electrode 32 provided on a second end surface 22 of the exterior resin 2. The first external electrode 31 is electrically connected to the lead frame 5 by a cathode lead layer 61. The second external electrode 32 is electrically connected to the metal foil 10 by an anode lead layer 62.

[0038] The external electrode 3 is formed from a conductive paste containing a resin and a conductive filler. The external electrode 3 can be formed from a cured product of the conductive paste. The resin contained in the conductive paste can be a thermosetting resin, and among these, epoxy resin, which has good heat resistance and rigidity, is preferably used. The conductive filler contained in the conductive paste can be conductive metal particles, and among these, silver particles, which have good conductive properties, are preferably used. Examples of conductive particles that can be used include metal particles such as silver and copper, and particles of conductive inorganic materials such as carbon. The conductive paste may contain an appropriate solvent to adjust viscosity. The external electrode 3 may also be formed from multiple different layers or multiple different materials.

[0039] The external electrodes 3 can be formed by supplying a conductive paste to the outer surface of the exterior resin 2 and then curing the resin in the conductive paste. For example, a screen printing method can be used to supply the conductive paste to the outer surface of the exterior resin 2. If the conductive paste contains a solvent, the resin in the conductive paste is cured after the solvent in the conductive paste is removed by evaporation or the like.

[0040] Of the external electrodes 3, the first external electrode 31 can be formed by supplying a conductive paste over the entire first end surface 21 of the exterior resin 2 and then hardening the conductive paste. The second external electrode 32 can be formed by supplying a conductive paste over the entire second end surface 22 of the exterior resin 2 and then hardening the conductive paste.

[0041] The external electrode 3 preferably contains 2% by weight or more and 10% by weight or less of resin relative to the total amount. This makes it easier to form an external electrode 3 having a plurality of recesses 4. If the resin content of the external electrode 3 is less than 2% by weight relative to the total amount, the amount of resin is too small, and the heat resistance and rigidity of the external electrode 3 are likely to decrease. If the resin content of the external electrode 3 exceeds 10% by weight relative to the total amount, the amount of resin is too large, and the conductivity of the external electrode 3 is likely to decrease. The external electrode 3 more preferably contains 2.5% by weight or more and 9% by weight or less of resin relative to the total amount. Furthermore, the external electrode 3 still more preferably contains 3% by weight or more and 8.5% by weight or less of resin relative to the total amount.

[0042] If the external electrodes 3 contain 2% to 10% by weight of resin relative to the total amount, the conductive paste forming the external electrodes 3 preferably contains 2% to 10% by weight of resin relative to the total amount of resin and conductive filler. Similarly, if the external electrodes 3 contain 2.5% to 9% by weight of resin relative to the total amount of resin, the conductive paste forming the external electrodes 3 preferably contains 2.5% to 9% by weight of resin relative to the total amount of resin and conductive filler. Furthermore, if the external electrodes 3 contain 3% to 8.5% by weight of resin relative to the total amount of resin, the conductive paste forming the external electrodes 3 preferably contains 3% to 8.5% by weight of resin relative to the total amount of resin and conductive filler.

[0043] The outer surface 30 of the external electrode 3 has a plurality of recesses 4. The recesses 4 are formed on the surface opposite to the surface facing the outer surface of the exterior resin 2. That is, of the external electrodes 3, the first external electrode 31 has a plurality of recesses 4 on the outer surface 30 opposite to the surface that contacts the first end surface 21 of the exterior resin 2. The second external electrode 32 has a plurality of recesses 4 on the outer surface 30 opposite to the surface that contacts the second end surface 22 of the exterior resin 2. The outer surface 30 is formed to be substantially flat except for the portions of the recesses 4, and the recesses 4 are recessed toward the exterior resin 2 with respect to the flat portion of the outer surface 30.

[0044] The multiple recesses 4 include multiple types of recesses that have irregularly different shapes. Here, "irregular" means that the multiple recesses 4 are arranged irregularly in terms of position and shape. That is, the multiple recesses 4 each have a different recess shape. Furthermore, the recess shapes of the multiple recesses 4 are not uniform but random. The recess shape of the recess 4 is defined by the opening shape of the recess 4 on the outer surface 30 (the shape of the recess 4 as viewed from the second direction) and the depth dimension from the flat portion of the outer surface 30. Therefore, the multiple recesses 4 each have a different opening shape on the outer surface 30 and a different depth dimension from the flat portion of the outer surface 30.

[0045] Furthermore, the multiple recesses 4 are not formed concentratedly in one location on the outer surface 30, but are formed scattered over the entire outer surface 30. The positions of the multiple recesses 4 when viewed from the second direction are not constant but random. In other words, there is no regularity between the positions of the multiple recesses 4 formed on the outer surface 30 of the first external electrode 31 and the positions of the multiple recesses 4 formed on the outer surface 30 of the second external electrode 32, and they are random. Furthermore, the positions of the multiple recesses 4 on the outer surface 30 differ for each solid electrolytic capacitor 100.

[0046] The total area of ​​the plurality of recesses 4 is 1% to 20% of the effective area of ​​the external electrode 3. This ensures adhesion between the outer surface 30 of the external electrode 3 and the solder, and the anchor effect allows the outer surface 30 of the external electrode 3 and the solder to be firmly joined, making peeling less likely to occur.

[0047] Here, the total area of ​​the plurality of recesses 4 is the sum of the areas of the plurality of recesses 4 formed on the outer surface 30 of one external electrode 3 (the first external electrode 31 or the second external electrode 32). The effective area of ​​the external electrode 3 is the entire area of ​​the outer surface 30 of one external electrode 3 (the first external electrode 31 or the second external electrode 32). The solid electrolytic capacitor 100 is solder-bonded when mounted on another component such as a circuit board. At this time, the solder adheres to the entire outer surface 30. Therefore, the surface of the solid electrolytic capacitor 100 that effectively functions for solder bonding is the entire outer surface 30, and the area of ​​this surface is defined as the effective area.

[0048] If the total area of ​​the plurality of recesses 4 is less than 1% of the effective area of ​​the external electrode 3, the number of recesses 4 is too small or the opening area of ​​the recesses 4 is too small, so that the solder does not sufficiently penetrate into the plurality of recesses 4, making it difficult to obtain an anchor effect.If the total area of ​​the plurality of recesses 4 exceeds 20% of the effective area of ​​the external electrode 3, the number of recesses 4 is too large or the opening area of ​​the recesses 4 is too large, so that the heat resistance and rigidity of the external electrode 3 are likely to decrease.

[0049] The total area of ​​the plurality of recesses 4 is preferably 2% to 16% of the effective area of ​​the external electrode 3, and more preferably 4% to 12%.

[0050] The total area of ​​the recesses 4 and the effective area of ​​the external electrode 3 can be determined by measuring the two-dimensional area using a 3D shape measuring device.

[0051] The depth d of each of the plurality of recesses 4 is preferably 1% to 40% of the thickness D of the external electrode 3. In other words, the value calculated by d / D×100 is in the range of 1% to 40%. This ensures adhesion between the outer surface 30 of the external electrode 3 and the solder, and the anchor effect allows the outer surface 30 of the external electrode 3 and the solder to be firmly joined, making peeling less likely to occur.

[0052] Here, the depth d of each of the recesses 4 refers to the dimension from the opening to the bottom of each recess 4. The thickness D of the external electrode 3 refers to the dimension from the flat portion of the outer surface 30 to the outer surface of the exterior resin 2 (the first end surface 21 or the second end surface 22).

[0053] If the depth d of each of the plurality of recesses 4 is less than 1% of the thickness D of the external electrode 3, the recesses 4 are too shallow, the solder does not sufficiently penetrate into the recesses 4, and it is difficult to obtain an anchor effect. If the depth d of each of the plurality of recesses 4 is more than 40% of the thickness D of the external electrode 3, the recesses 4 are too deep, and the heat resistance and rigidity of the external electrode 3 are likely to decrease.

[0054] The depth d of each of the plurality of recesses 4 is more preferably 1% to 35% of the thickness D of the external electrode 3, and even more preferably 1% to 30%.

[0055] The depth d of the recess 4 can be measured using a 3D shape measuring device.

[0056] The external electrode 3 may have a plating layer formed of nickel-copper plating or the like on the outer surface 30. In this case, the plating layer is formed to conform to the shape of the outer surface 30, so that multiple recesses 4 are also formed in the plating layer. Furthermore, solder adheres to the plating layer, and is electrically and mechanically joined to the external electrode 3.

[0057] In the solid electrolytic capacitor 100 of this embodiment, the ratio of the total area of ​​the plurality of recesses 4 to the effective area of ​​the external electrode 3 and the ratio of the depth d of each of the plurality of recesses 4 to the thickness D of the external electrode 3 can be adjusted by changing the amount of resin contained in the external electrode 3. The amount of resin contained in the external electrode 3 can be adjusted by changing the compounding ratio of the resin and conductive filler contained in the conductive paste.

[0058] 2 is a graph showing the relationship between the amount of resin relative to the total amount of external electrode 3 and the maximum value of the depth (in-plane average depth) of recesses 4. The external electrode 3 was a cured product of a conductive paste containing epoxy resin and silver particles, and the amount of resin contained in the external electrode 3 was varied between 3.0 wt %, 3.5 wt %, 4.5 wt %, 5.0 wt %, and 7.0 wt %. Seventeen samples were taken for each resin amount. The in-plane average depth was calculated as the depth of recesses 4. The in-plane average depth was calculated as the ratio of the depth of the recess to the thickness D of the external electrode 3. FIG. 2 is a graph plotting the maximum values ​​of the calculated in-plane average depths.

[0059] 2, the maximum value of the in-plane average depth tends to decrease as the resin content of the external electrode 3 increases. In other words, as the resin content of the external electrode 3 increases, the number of recesses 4 with small depths (shallow recesses) increases, making it easier to flatten the outer surface 30.

[0060] Fig. 3 is a graph showing the relationship between the amount of resin relative to the total amount of external electrode 3 and the average value (arithmetic mean value) of the depth (in-plane average depth) of recesses 4. Fig. 3 is a graph plotting the average values ​​of the in-plane average depth calculated in the same manner as above.

[0061] 3 also shows that the average value of the in-plane average depth tends to decrease as the resin content of the external electrode 3 increases. In other words, as the resin content of the external electrode 3 increases, the number of recesses 4 with small depths (shallow recesses) increases, making it easier to flatten the outer surface 30.

[0062] Fig. 4 is a graph showing the relationship between the amount of resin relative to the total amount of external electrode 3 and the average value (arithmetic mean value) of the total area ratio (area ratio of recessed portions) of the plurality of recesses 4. The samples are the same as those in Figs. 2 and 3. The total area ratio of the plurality of recesses 4 is the ratio of the total area of ​​the plurality of recesses 4 to the effective area of ​​external electrode 3. Fig. 4 is a graph plotting the average value of the total area ratio of the plurality of recesses 4 of each sample for each amount of resin.

[0063] 4, the average value of the total area ratio (area ratio of the recessed portions) of the plurality of recesses 4 tends to decrease as the resin content of the external electrode 3 increases. In other words, as the resin content of the external electrode 3 increases, the number of recesses 4 decreases, making it easier to flatten the outer surface 30.

[0064] 5 is a graph showing the relationship between the amount of resin relative to the total amount of external electrodes 3 and the ESR variation rate after reflow treatment. The samples were the same as those in FIGS. 2, 3, and 4, and the number of samples was 18 to 20. The ESR variation rate was calculated by measuring the initial ESR of the solid electrolytic capacitor 100 and the ESR after reflow treatment using an LCR meter, and calculating the rate of change in ESR after reflow treatment relative to the initial ESR. The solid electrolytic capacitor 100 was initially baked (conditions: 155°C, 24 hours), then further subjected to a moisture absorption treatment (conditions: 85°C, 85% RH, 12 hours), and then subjected to a reflow treatment (conditions: 260°C max).

[0065] As is clear from FIG. 5, the solid electrolytic capacitor 100 of this embodiment has a small ESR variation rate after reflow treatment, and the ESR variation rate after reflow treatment tends to be small particularly when the resin amount in the external electrode 3 is in the range of 3% by weight or more and 5% by weight or less.

[0066] 3. The modified embodiment is merely one of various embodiments of the present disclosure. The embodiment can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0067] Solid electrolytic capacitor 100 can include one or more capacitor elements 1. When solid electrolytic capacitor 100 includes multiple capacitor elements 1, the multiple capacitor elements 1 may be stacked in the first direction and bonded together with a conductive adhesive such as a silver-containing adhesive.

[0068] The metal foil 10 can be a foil formed of a valve metal, and in addition to aluminum or its alloy, examples include metals such as tantalum, titanium, niobium, and tungsten, or alloys containing at least one of these metals.

[0069] Instead of the silver-containing adhesive 52, a carbon adhesive containing carbon particles may be used.

[0070] The solid electrolytic capacitor 100 does not need to include the lead frame 5. In this case, a metal foil connected to the cathode can be used instead of the lead frame.

[0071] In addition to epoxy resin, thermosetting resins such as phenolic resin or melamine resin can be used as the resin contained in the external electrodes 3. In addition to silver particles, the conductive filler contained in the external electrodes 3 may also be particles of copper, nickel, tin, or an alloy containing one or more of these metals.

[0072] The external electrode 3 may be provided on an outer surface other than the first end surface 21 and the second end surface 22 of the exterior resin 2, for example, the external electrode 3 may be provided on either the first main surface 23, the second main surface 24, or one of the two side surfaces.

[0073] (Summary) As described above, the solid electrolytic capacitor (100) according to the first aspect comprises a capacitor element (1), an exterior resin (2) that seals the capacitor element (1), and an external electrode (3) disposed on the outer surface of the exterior resin (2). The external electrode (3) is formed from a conductive paste containing a resin and a conductive filler. The outer surface (30) of the external electrode (3) has a plurality of recesses (4). The total area of ​​the plurality of recesses (4) is 1% or more and 20% or less of the effective area of ​​the external electrode (3).

[0074] According to this embodiment, the anchor effect makes it difficult for peeling to occur between the solder and the external electrode (3). Therefore, the electrical conductivity between the solder and the solid electrolytic capacitor (100) is unlikely to decrease, and the ESR characteristics are unlikely to deteriorate. As a result, the product life of the solid electrolytic capacitor (100) is unlikely to be shortened.

[0075] A second aspect is the solid electrolytic capacitor (100) according to the first aspect, wherein the depth of each of the plurality of recesses (4) is 1% to 40% of the thickness of the external electrode (3).

[0076] According to this embodiment, the anchor effect makes it even more difficult for peeling to occur between the solder and the external electrode (3), and the ESR characteristics are less likely to deteriorate, so that the product life of the solid electrolytic capacitor (100) is less likely to be shortened.

[0077] A third aspect is the solid electrolytic capacitor (100) according to the first or second aspect, wherein the plurality of recesses (4) includes a plurality of types of recesses having irregularly different shapes.

[0078] According to this embodiment, the anchor effect makes it even more difficult for peeling to occur between the solder and the external electrode (3), and the ESR characteristics are less likely to deteriorate, so that the product life of the solid electrolytic capacitor (100) is less likely to be shortened.

[0079] A fourth aspect is the solid electrolytic capacitor (100) according to any one of the first to third aspects, wherein the external electrodes (3) contain the resin in an amount of 2% by weight to 10% by weight based on the total amount.

[0080] According to this embodiment, the outer surface (30) of the external electrode (3) is less likely to be flattened, and a plurality of recesses (4) are more likely to be formed.

[0081] A fifth aspect is a solid electrolytic capacitor (100) according to any one of the first to fourth aspects, in which the capacitor element (1) has a metal foil (10) that serves as an anode, a dielectric layer (11) provided on the metal foil (10), and a cathode provided on the dielectric layer (11). One or more capacitor elements (1) are bonded to a lead frame (5) with a silver-containing adhesive (52). The metal foil (10) is provided with an extraction layer (anode extraction layer (62)) that protrudes outside the exterior resin (2) and is electrically connected to the external electrode (3).

[0082] According to this embodiment, the electrical conductivity between the solder and the solid electrolytic capacitor 100 is less likely to decrease, and the ESR characteristics are less likely to deteriorate, resulting in less shortening of the product life of the solid electrolytic capacitor 100.

[0083] A method for manufacturing a solid electrolytic capacitor according to a sixth aspect includes the steps of: sealing a capacitor element (1) with an exterior resin (2), supplying a conductive paste containing a resin and a conductive filler on the outer surface of the exterior resin (2), and hardening the conductive paste on the outer surface of the exterior resin (2) to form an external electrode (3). The conductive paste contains the resin in an amount of 2% by weight to 10% by weight based on the total weight of the resin and the conductive filler.

[0084] According to this embodiment, a solid electrolytic capacitor (100) is obtained in which the outer surface (30) of the external electrode (3) has a plurality of recesses (4), and the total area of ​​the plurality of recesses (4) is 1% to 20% of the effective area of ​​the external electrode (3). Therefore, the anchor effect makes it difficult for peeling to occur between the solder and the external electrode (3). This makes it difficult for the electrical conductivity between the solder and the solid electrolytic capacitor (100) to decrease, and the ESR characteristics to deteriorate. As a result, the product life of the solid electrolytic capacitor (100) is unlikely to be shortened.

[0085] REFERENCE SIGNS LIST 1 capacitor element 2 exterior resin 3 external electrode 4 recess 5 lead frame 10 metal foil 11 dielectric layer 30 outer surface 52 adhesive containing silver 100 solid electrolytic capacitor

Claims

1. A solid electrolytic capacitor comprising: a capacitor element; an exterior resin that seals the capacitor element; and an external electrode disposed on the outer surface of the exterior resin, wherein the external electrode is formed from a conductive paste containing resin and a conductive filler; the outer surface of the external electrode has a plurality of recesses, and the total area of ​​the plurality of recesses is 1% or more and 20% or less of the effective area of ​​the external electrode.

2. The solid electrolytic capacitor according to claim 1, wherein the depth of each of the plurality of recesses is 1% to 40% of the thickness of the external electrode.

3. The solid electrolytic capacitor according to claim 1 or 2, wherein the plurality of recesses includes a plurality of types of recesses having irregularly different shapes.

4. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the external electrodes contain 2% by weight or more and 10% by weight or less of the resin based on the total weight of the external electrodes.

5. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the capacitor element comprises a metal foil serving as an anode, a dielectric layer provided on the metal foil, and a cathode provided on the dielectric layer, one or more of the capacitor elements are bonded to a lead frame with an adhesive containing silver, and the metal foil is provided with an extraction layer that protrudes outside the exterior resin and is electrically connected to the external electrode.

6. A method for manufacturing a solid electrolytic capacitor, comprising: a step of sealing a capacitor element with an exterior resin; a step of supplying a conductive paste containing a resin and a conductive filler onto the outer surface of the exterior resin; and a step of hardening the conductive paste on the outer surface of the exterior resin to form an external electrode, wherein the conductive paste contains 2% by weight or more and 10% by weight or less of the resin relative to the total weight of the resin and the conductive filler.

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