Solid electrolytic capacitor

Abstract

A solid electrolytic capacitor (10, 10A, 10B) is provided with a valve metal base (11), a conductive paste layer (14), an insulating layer (15), and an external electrode layer (16). The valve action metal base (11) has dielectric layers (113) on both surfaces thereof in the thickness direction. The conductive paste layers (14) are disposed on both sides of the valve-acting metal base (11) in the thickness direction. The conductive paste layer (14) contains a conductive filler (141). The insulating layer (15) is laminated on the conductive paste layer (14) on the opposite side of the valve action metal base (11). The insulating layer (15) has a via hole (151). The external electrode layer (16) is laminated on the insulating layer (15). The external electrode layer (16) is electrically connected to the conductive paste layer (14) via the via hole (151). Among the conductive fillers (141) contained in the conductive paste layer (14), the external electrode layer (16) is in direct contact with the conductive filler (141) located within the via hole (151) when viewed along the stacking direction of the conductive paste layer (14), the insulating layer (15), and the external electrode layer (16).

Description

Technical Field

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

[0002] For example, as described in Patent Document 1, a solid electrolytic capacitor generally includes a capacitor element and a lead frame. In the solid electrolytic capacitor of Patent Document 1, the capacitor element includes a first electrode as an anode and a second electrode as a cathode. Lead terminals (lead frames) are electrically connected to the first electrode and the second electrode, respectively.

[0003] In patent document 1, the first electrode includes a valve-acting metal as a conductive material. A dielectric layer is formed on the surface of the first electrode. The second electrode includes a solid electrolyte layer, a carbon layer, and a metal paste layer (conductive paste layer). The solid electrolyte layer covers the dielectric layer of the first electrode. The carbon layer and the conductive paste layer are sequentially stacked on the solid electrolyte layer. The carbon layer includes flaky carbon fillers, spherical carbon fillers, and a binder resin. The conductive paste layer includes a metal filler and a binder resin. The conductive paste layer is typically a silver paste layer.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2021 / 172272 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] In the solid electrolytic capacitor of patent document 1, the second electrode as the cathode is electrically connected to the lead frame via an adhesive layer. That is, an adhesive layer containing a thermosetting resin is sandwiched between the metal filler in the conductive paste layer located on the outermost surface of the second electrode and the lead frame as the external electrode layer. In addition, an adhesive resin in the conductive paste layer is also sandwiched between the metal filler and the external electrode layer. The above-mentioned resin is used to block the current between the metal filler and the external electrode layer. Therefore, there is such a problem: when there is a current path in the stacking direction of the conductive paste layer and the external electrode layer, the resistance (equivalent series resistance (ESR)) of the solid electrolytic capacitor increases.

[0009] The problem to be solved by the present disclosure is to provide a solid electrolytic capacitor capable of reducing the resistance of a current path in the lamination direction of a conductive paste layer and an external electrode layer.

[0010] Solutions for solving problems

[0011] The solid electrolytic capacitor disclosed in the present invention includes a valve-acting metal substrate, a conductive paste layer, an insulating layer, and an external electrode layer. The valve-acting metal substrate has a dielectric layer on both surfaces in the thickness direction thereof. The conductive paste layers are respectively arranged on both sides of the valve-acting metal substrate in the thickness direction. The conductive paste layer contains a conductive filler. The insulating layer is stacked on the conductive paste layer on the opposite side of the valve-acting metal substrate. The insulating layer has a via hole. The external electrode layer is stacked on the insulating layer. The external electrode layer is electrically connected to the conductive paste layer via the via hole. The external electrode layer is in direct contact with the conductive filler contained in the conductive paste layer, which is located in the via hole when viewed along the stacking direction of the conductive paste layer, the insulating layer, and the external electrode layer.

[0012] Effects of the Invention

[0013] According to the solid electrolytic capacitor of the present disclosure, it is possible to reduce the resistance of the current path in the lamination direction of the conductive paste layer and the external electrode layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a cross-sectional view schematically showing the structure of the solid electrolytic capacitor according to the first embodiment.

[0015] Figure 2 yes Figure 1 A partial enlarged view of the solid electrolytic capacitor shown.

[0016] Figure 3 It is a partial cross-sectional view showing a schematic structure of a solid electrolytic capacitor according to a second embodiment.

[0017] Figure 4 Yes means Figure 3 Schematic diagram of an example of a conductive filler in a cross-sectional SEM image of a solid electrolytic capacitor shown.

[0018] Figure 5 It is a partial cross-sectional view showing a schematic structure of a solid electrolytic capacitor according to a modified example of the second embodiment.

[0019] Figure 6 It is a partial cross-sectional view showing a schematic structure of a solid electrolytic capacitor according to a third embodiment.

[0020] Figure 7 It is a partial cross-sectional view showing a schematic structure of a solid electrolytic capacitor according to a modified example of the third embodiment. DETAILED DESCRIPTION

[0021] The solid electrolytic capacitor of the embodiment includes a valve-acting metal substrate, a conductive paste layer, an insulating layer, and an external electrode layer. The valve-acting metal substrate has a dielectric layer on both surfaces in the thickness direction thereof. The conductive paste layers are respectively arranged on both sides of the valve-acting metal substrate in the thickness direction. The conductive paste layer contains a conductive filler. The insulating layer is stacked on the conductive paste layer on the opposite side of the valve-acting metal substrate. The insulating layer has a via hole. The external electrode layer is stacked on the insulating layer. The external electrode layer is electrically connected to the conductive paste layer via the via hole. The external electrode layer is in direct contact with the conductive filler contained in the conductive paste layer when the conductive filler located in the via hole is observed along the stacking direction of the conductive paste layer, the insulating layer, and the external electrode layer (the first structure).

[0022] In the solid electrolytic capacitor of the first structure, the external electrode layer is in direct contact with the conductive filler located in the via hole when viewed from above, among the conductive fillers included in the conductive paste layer. That is, there is no resin or the like between the conductive filler located at the position of the via hole and the external electrode layer. Therefore, a continuous current path can be formed between the conductive filler and the external electrode layer. As a result, the resistance of the current path in the stacking direction of the conductive paste layer and the external electrode layer can be reduced, and the equivalent series resistance (ESR) of the solid electrolytic capacitor can be reduced.

[0023] The external electrode layer may also include an external electrode layer body. The external electrode layer body is formed on the surface of the insulating layer on the opposite side of the conductive paste layer. The conductive paste layer may include a filler having a core material whose main component is the same metal as the main component of the external electrode layer body as the main conductive filler (second structure).

[0024] When the conductive paste layer and the external electrode layer body are formed of different metal materials, electromigration of metal ions may occur between the conductive paste layer and the external electrode layer body, resulting in connection failure. In contrast, in the second structure, the core material of the main conductive filler of the conductive paste layer has the same metal as the main component of the external electrode layer body as the main component. Therefore, electromigration can be suppressed, thereby ensuring the connection stability between the conductive paste layer and the external electrode layer.

[0025] The main component of the external electrode layer body may be copper. In this case, it is preferable that the main conductive filler is a filler having copper as the main component of the core material (third structure).

[0026] The external electrode layer may further include a via conductor. The via conductor is provided in the via hole. The main component of the via conductor may be the same metal as the main component of the core material of the main conductive filler (fourth structure).

[0027] In the fourth structure, in addition to the external electrode layer body, the via conductor also has the same metal as the core material of the main conductive filler of the conductive paste layer as the main component. This can further suppress electromigration and improve the connection stability between the conductive paste layer and the external electrode layer.

[0028] The main component of the external electrode layer body and the main component of the via conductor may both be copper. In this case, it is preferable that the main conductive filler is a filler having copper as the main component of the core material (fifth configuration).

[0029] When the solid electrolytic capacitor is viewed in cross section, the filling rate of the conductive filler in the stacking direction relative to the length of the conductive paste layer may be 50% or more (sixth configuration).

[0030] In the sixth structure, in the stacking direction of the conductive paste layer and the external electrode layer, the filling rate of the conductive filler relative to the length of the conductive paste layer is 50% or more. That is, in the conductive paste layer, the conductive filler is fully filled in the layer thickness direction. Thus, the resistance can be reduced for the current flowing in the layer thickness direction of the conductive paste layer.

[0031] The conductive filler may include a first conductive filler. The first conductive filler has, for example, a crushed shape (seventh structure).

[0032] In the seventh configuration, the conductive paste layer includes a first conductive filler. The first conductive filler has a fragmented shape and is therefore easier to overlap than, for example, a spherical conductive filler. By overlapping the first conductive filler, a current path that is continuous in the thickness direction of the conductive paste layer can be formed. As a result, the resistance can be reduced for the current flowing in the thickness direction of the conductive paste layer.

[0033] The first conductive filler may have a flat shape (eighth configuration).

[0034] In the eighth structure, the first conductive filler is adjusted to a flat shape. The first conductive filler has a smooth surface with fewer corners than a crushed shape. Therefore, in the conductive paste layer, the generation of cracks starting from the corners of the conductive filler can be suppressed. Therefore, the mechanical strength of the conductive paste layer can be improved.

[0035] The conductive filler may further include a second conductive filler. The second conductive filler may have an average particle diameter smaller than the average particle diameter of the first conductive filler (ninth structure).

[0036] In the ninth structure, in addition to the first conductive filler, the second conductive filler is also included in the conductive paste layer. The average particle size of the second conductive filler is smaller than the average particle size of the first conductive filler. Therefore, the second conductive filler can enter between the first conductive fillers. As a result, it is easier to form a continuous current path in the thickness direction of the conductive paste layer, and the resistance can be further reduced for the current flowing in the thickness direction of the conductive paste layer.

[0037] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In each of the drawings, the same reference numerals are given to the same or corresponding structures, and the same description will not be repeated.

[0038] <First embodiment>

[0039] [Structure of solid electrolytic capacitor]

[0040] Figure 1 1 is a cross-sectional view showing a schematic structure of a solid electrolytic capacitor 10 according to the first embodiment. Figure 1 As shown, the solid electrolytic capacitor 10 is included in a multilayer substrate (package substrate) 20 such as a component-embedded substrate. Figure 1 2 shows a partial and schematic cross section of the package substrate 20 .

[0041] For example, a DC-DC converter 30 and a load 40 as an integrated circuit are mounted on the package substrate 20. The DC-DC converter 30 is arranged on a surface on one side in the thickness direction of the package substrate 20. The load 40 is arranged on a surface on the opposite side of the DC-DC converter 30 in the thickness direction of the package substrate 20. In the example of the present embodiment, the package substrate 20 includes a plurality of solid electrolytic capacitors 10. The solid electrolytic capacitors 10 can be arranged in an array in the package substrate 20.

[0042] Reference Figure 1 The solid electrolytic capacitor 10 includes a valve metal substrate 11 , a solid electrolyte layer 12 , a carbon layer 13 , a conductive paste layer 14 , an insulating layer 15 , and an external electrode layer 16 .

[0043] The valve metal substrate 11 has a plate shape or a foil shape. The valve metal substrate 11 functions as an anode of the solid electrolytic capacitor 10. The valve metal substrate 11 includes a core layer 111, a porous layer 112, and a dielectric layer 113. The valve metal substrate 11 has the dielectric layer 113 on both surfaces in the thickness direction thereof.

[0044] The core layer 111 is a layer made of a valve metal. Examples of the valve metal include a single metal such as aluminum, tantalum, niobium, titanium, or zirconium, or an alloy containing at least one of the above metals. The valve metal is preferably aluminum or an aluminum alloy.

[0045] The porous layer 112 and the dielectric layer 113 are provided on both surfaces of the core layer 111 in such a manner as to sandwich the core layer 111 from both sides in the thickness direction thereof. The porous layer 112 and the dielectric layer 113 are sequentially stacked on each surface in the thickness direction of the core layer 111. For example, the porous layer 112 can be formed on the surface of the core layer 111 by etching the surface of a valve metal plate or a valve metal foil. Furthermore, the dielectric layer 113 composed of an oxide film can be formed on the porous layer 112 by performing an anodic oxidation treatment (chemical conversion treatment).

[0046] exist Figure 1 In the example shown, the package substrate 20 has a plurality of through holes 21. A through hole conductor 22 is provided in each through hole 21. The core layer 111 of the valve-acting metal substrate 11 can be directly connected to the through hole conductor 22 via the inner wall surface of the through hole 21.

[0047] The through-hole conductor 22 is made of a conductive material. The through-hole conductor 22 is formed at least on the inner wall surface of the through-hole 21. For example, the through-hole conductor 22 can be formed by metallizing the inner wall surface of the through-hole 21 with a material mainly composed of a metal such as copper, gold, silver, or an alloy thereof. Alternatively, the through-hole conductor 22 can be formed by filling the through-hole 21 with a conductive material.

[0048] The solid electrolyte layer 12, the carbon layer 13, and the conductive paste layer 14 are respectively arranged on both sides of the thickness direction of the valve metal substrate 11. That is, the solid electrolyte layer 12, the carbon layer 13, and the conductive paste layer 14 are sequentially stacked on each surface in the thickness direction of the valve metal substrate 11. The solid electrolyte layer 12, the carbon layer 13, and the conductive paste layer 14 function as the cathode of the solid electrolytic capacitor 10.

[0049] The solid electrolyte layer 12 is arranged on the dielectric layer 113 of the valve-acting metal substrate 11. Preferably, the solid electrolyte layer 12 covers the entire surface of the dielectric layer 113 located on the opposite side of the core layer 111 and the porous layer 112. The solid electrolyte layer 12 is typically formed of a conductive polymer material. As conductive polymers, for example, polypyrroles, polythiophenes, polyanilines, etc. can be cited. The conductive polymer is preferably a polythiophene, and poly(3,4-ethylenedioxythiophene) called PEDOT is particularly preferred. The conductive polymer material can also be a material formed by using, for example, polystyrene sulfonic acid (PSS) as a dopant.

[0050] The carbon layer 13 is disposed on the solid electrolyte layer 12. Preferably, the carbon layer 13 covers the entire surface of the solid electrolyte layer 12 on the opposite side of the valve metal substrate 11. The carbon layer 13 includes, for example, a carbon filler and a binder. For example, the carbon layer 13 can be formed by applying a carbon slurry including a carbon filler and a fluid binder on the solid electrolyte layer 12 using sponge transfer, screen printing, spray coating, a dispenser, or inkjet printing.

[0051] The conductive paste layer 14 is disposed on the carbon layer 13. Preferably, the conductive paste layer 14 covers the entire surface of the carbon layer 13 on the opposite side to the solid electrolyte layer 12. The conductive paste layer 14 is connected to the solid electrolyte layer 12 via the carbon layer 13.

[0052] The insulating layer 15 is stacked on the conductive paste layer 14 on the opposite side of the valve-acting metal substrate 11. Preferably, the insulating layer 15 covers the entire surface of the conductive paste layer 14 on the opposite side of the valve-acting metal substrate 11. The insulating layer 15 may be provided in common for a plurality of solid electrolytic capacitors 10. That is, the insulating layer 15 may extend over the range of the plurality of solid electrolytic capacitors 10 in a manner that shields the plurality of solid electrolytic capacitors 10. In this case, the area of ​​the conductive paste layer 14 is smaller than the effective capacitance portion of the solid electrolytic capacitor 10 divided by the insulating layer 15.

[0053] The insulating layer 15 is typically formed of a resin. For example, the insulating layer 15 can be formed of a thermosetting resin. Preferably, the insulating layer 15 is formed of an epoxy resin material. Examples of the epoxy resin include phenolic curing epoxy resin, cyanate / epoxy mixed resin, and novolac curing epoxy resin.

[0054] The insulating layer 15 has at least one via hole 151. In the example of the present embodiment, a plurality of via holes 151 are formed in the insulating layer 15. The via holes 151 penetrate the insulating layer 15 in the stacking direction of the valve metal substrate 11, the solid electrolyte layer 12, the carbon layer 13, the conductive paste layer 14, and the insulating layer 15. The via holes 151 can be formed by irradiating the insulating layer 15 with laser light from a laser processing machine. The laser light at this time is, for example, a CO2 laser.

[0055] The via hole 151 is formed in a tapered shape, for example, with a width decreasing toward the conductive paste layer 14 when the solid electrolytic capacitor 10 is viewed in cross section. However, the via hole 151 may have a constant width over the entire range when the solid electrolytic capacitor 10 is viewed in cross section. The shape of the cross section of the via hole 151, that is, the cross section perpendicular to the central axis of the via hole 151, is, for example, a circular shape.

[0056] The external electrode layer 16 is provided on the insulating layer 15. The external electrode layer 16 is electrically connected to the conductive paste layer 14 through the via hole 151. The external electrode layer 16 includes an external electrode layer body 161 and a via conductor 162.

[0057] The external electrode layer main body 161 is formed on the surface of the insulating layer 15 on the opposite side to the conductive paste layer 14. The external electrode layer main body 161 can function as a wiring layer.

[0058] External electrode layer bodies 161 may extend from solid electrolytic capacitor 10 to any through-hole conductor 22. Any one of external electrode layer bodies 161 disposed on both sides of solid electrolytic capacitor 10 in the thickness direction may be electrically connected to through-hole conductor 22 connected to GND.

[0059] The via conductor 162 is provided in the via hole 151 . The via conductor 162 electrically connects the external electrode layer main body 161 to the conductive paste layer 14 .

[0060] Figure 2 Yes Figure 1 FIG. 1 is an enlarged view of a via hole 151 and its vicinity in a cross section of a solid electrolytic capacitor 10. Figure 2 , in particular, the structures of the conductive paste layer 14 and the external electrode layer 16 are described in more detail.

[0061] like Figure 2 As shown, the conductive paste layer 14 includes a conductive filler 141 and a binder 142 .

[0062] The conductive filler 141 has conductivity. The conductive filler 141 may be a metal filler or a non-metal filler. The conductive filler 141 includes a core material. Alternatively, the conductive filler 141 includes a coating covering the core material. When the conductive filler 141 is a metal filler, the main component of the core material of the conductive filler 141 may be copper, nickel, silver, etc. The main component of the core material of the conductive filler 141 refers to the element with the largest content (e.g., mass %) in the chemical composition of the core material.

[0063] Preferably, the conductive paste layer 14 contains a filler having copper as a main component of the core material as the main conductive filler 141. More specifically, preferably, in the conductive paste layer 14, a metal filler having copper particles or copper alloy particles as a core material exists as the main conductive filler 141.

[0064] The conductive fillers 141 included in the conductive paste layer 14 may all be fillers of the same material. Conductive fillers 141 of different materials may also be mixed in the conductive paste layer 14. For example, the conductive paste layer 14 may contain only copper fillers with copper particles or copper alloy particles as core materials, or copper fillers and silver fillers with silver particles or silver alloy particles as core materials. In the case where fillers of different materials are mixed in the conductive paste layer 14, the main conductive filler 141 is the filler with the highest content in the conductive paste layer 14. In the case where all the fillers in the conductive paste layer 14 are of the same type, the filler is the main conductive filler 141.

[0065] The main conductive filler 141 of the conductive paste layer 14 can be determined using, for example, a cross-sectional SEM image of the solid electrolytic capacitor 10. Specifically, a cross-sectional SEM image at an arbitrary position of the solid electrolytic capacitor 10 is obtained and necessary image processing is applied to set the conductive filler 141 and the binder 142 to be distinguishable. In addition, when fillers of different materials are mixed in the conductive paste layer 14, the conductive filler 141 is set to be distinguishable according to its material. Then, based on the cross-sectional SEM image after image processing, the ratio of the area of ​​each filler to the area of ​​the conductive paste layer 14 is calculated as the content (volume %), and the filler with the largest content in the cross-sectional SEM image can be determined as the main conductive filler 141. The overall content of the conductive filler 141 in the conductive paste layer 14 is, for example, 30% by volume or more and 80% by volume or less. It also depends on the overall content of the conductive filler 141, but the content of the main conductive filler 141 in the conductive paste layer 14 is preferably 50% by volume or more.

[0066] The adhesive 142 contains the conductive filler 141. That is, a large amount of the conductive filler 141 is dispersed in the adhesive 142. The conductive filler 141 located in the via hole 151 and present in the outermost layer of the conductive paste layer 14 when viewed along the stacking direction of the conductive paste layer 14 and the insulating layer 15 is at least partially exposed from the adhesive 142. More specifically, in the portion of the conductive paste layer 14 located in the via hole 151 when viewed along the stacking direction, the adhesive 142 of the outermost layer is burned and disappears by irradiating the laser when the via hole 151 is formed in the insulating layer 15. Therefore, in this portion, the conductive filler 141 is exposed from the adhesive 142. On the other hand, the conductive filler 141 located outside the via hole 151 when viewed along the stacking direction is covered by the adhesive 142 and the insulating layer 15.

[0067] When the solid electrolytic capacitor 10 is cross-sectioned, the filling rate of the conductive filler 141 in the stacking direction relative to the length (thickness) of the conductive paste layer 14 is preferably 50% or more. The filling rate of the conductive filler 141 can be measured using a cross-sectional image of the solid electrolytic capacitor 10. For example, in a cross-sectional SEM image obtained at an arbitrary position of the solid electrolytic capacitor 10, the thickness L0 of the conductive paste layer 14 and the length L1 of each conductive filler 141 in the thickness direction at ten equally spaced locations are measured, and the total length S of L1 is calculated. L1 Then, calculate the S of the ten parts L1 The average value of / L0×100 can be used as the filling rate (%) of the conductive filler 141 in the thickness direction of the conductive paste layer 14 .

[0068] The conductive paste layer 14 can be formed by applying a conductive paste including a conductive filler 141 and a fluid binder 142 onto the carbon layer 13. The conductive paste is applied to the carbon layer 13 by, for example, sponge transfer, screen printing, spray coating, a dispenser, or inkjet printing. The applied conductive paste is cured by, for example, firing the binder 142 to form the conductive paste layer 14.

[0069] Continue to refer to Figure 2 The external electrode layer 16 is electrically connected to the conductive paste layer 14 by means of the via conductor 162. The via conductor 162 includes an electroless plating layer 163 and an electrolytic plating layer 164.

[0070] The electroless plating layer 163 is directly provided on the side wall of the via hole 151. The electroless plating layer 163 is a metal film deposited by a chemical reaction. Figure 2 In the example shown, the electroless plating layer 163 extends to the surface outside the via hole 151 in the insulating layer 15. That is, the electroless plating layer 163 constitutes a part of the external electrode layer body 161 as a wiring layer in addition to constituting a part of the via conductor 162. Alternatively, in the external electrode layer body 161, a seed layer 165 may be provided between the electroless plating layer 163 and the insulating layer 15. The seed layer 165 can be formed, for example, by forming a metal film on the insulating layer 15 by electrolytic plating or electroless plating and then removing a part of the metal film by photolithography etching.

[0071] The electrolytic plating layer 164 is provided on the electroless plating layer 163. The electrolytic plating layer 164 covers the entire electroless plating layer 163. The electrolytic plating layer 164 is a metal film deposited using electricity.

[0072] exist Figure 2In the example shown, the conductive paste layer 14 and the external electrode layer 16 are connected using a so-called filled via, and the via conductor 162 is filled in the via hole 151. However, the via conductor 162 may be formed so as to be recessed along the via hole 151. That is, the conductive paste layer 14 and the external electrode layer 16 may be connected using a so-called conformal via.

[0073] The external electrode layer 16 is in direct contact with the conductive filler 141 included in the conductive paste layer 14, which is located in the via hole 151 when viewed along the stacking direction of the conductive paste layer 14 and the insulating layer 15. More specifically, in the portion of the conductive paste layer 14 located in the via hole 151 when the solid electrolytic capacitor 10 is viewed from above, part of the conductive filler 141 is exposed from the adhesive 142. Therefore, the via conductor 162 of the external electrode layer 16 can be in direct contact with the conductive filler 141 exposed from the adhesive 142. The via conductor 162 can also be bonded to the conductive filler 141.

[0074] When the main conductive filler 141 in the conductive paste layer 14 is a metal filler, it is preferred that the external electrode layer body 161 has as its main component the same metal as the main component of the core material of the main conductive filler 141. For example, when the main conductive filler 141 has as its core material a certain metal or its alloy, it is preferred that the external electrode layer body 161 is also formed of the metal or the alloy of the metal. It is more preferred that the main conductive filler 141 is a filler having as its main component the core material of copper, and the main component of the external electrode layer body 161 is copper.

[0075] Preferably, the via conductor 162 also has as its main component the same metal as the main component of the core material of the main conductive filler 141. For example, in the case where the main conductive filler 141 has as its core material a certain metal or its alloy, preferably, the via conductor 162 is also formed of the metal or the alloy of the metal. More preferably, the main conductive filler 141 is a filler having as its main component copper as its core material, and the main components of the external electrode layer body 161 and the via conductor 162 are both copper. The main components of the external electrode layer body 161 and the via conductor 162 refer to the elements having the largest content (e.g., mass %) in the chemical composition of the external electrode layer body 161 and the via conductor 162, respectively.

[0076] When the main conductive filler 141 has copper particles or copper alloy particles as the core material, for example, the electroless plating 163 can be electroless copper plating, and the electrolytic plating 164 can be electrolytic copper plating. In this case, the seed layer 165 can be formed of copper or a copper alloy.

[0077] [Effect]

[0078] In the solid electrolytic capacitor 10 of the present embodiment, the external electrode layer 16 is in direct contact with the conductive filler 141 included in the conductive paste layer 14, which is located in the via hole 151 when viewed from above. More specifically, inside the via hole 151, the via conductor 162 of the external electrode layer 16 is in direct contact with the conductive filler 141 exposed from the adhesive 142. In the current path from the conductive paste layer 14 to the external electrode layer 16, there is no interface between a conductor such as a metal and an insulator such as a resin. That is, electricity is drawn from the conductive paste layer 14 to the external electrode layer 16 not through the contact point (interface) of the conductive filler 141 with the insulator, but through the metal contact of the conductive filler 141 with the external electrode layer 16. Therefore, the resistance is reduced when the current path in the stacking direction of the conductive paste layer 14 and the external electrode layer 16 exists, and the equivalent series resistance (ESR) of the solid electrolytic capacitor 10 can be reduced.

[0079] However, the conductive paste layer 14 is electrically connected to the carbon layer 13 via the contact (interface) of the conductive filler 141 and the binder 142. That is, the connection method of the conductive paste layer 14 to the carbon layer 13 is different from the connection method of the conductive paste layer 14 to the external electrode layer 16.

[0080] In this embodiment, it is preferred that the core material of the main conductive filler 141 of the conductive paste layer 14 has the same metal as the main component of the external electrode layer body 161 as the main component. In addition, it is preferred that the main component of the core material of the main conductive filler 141 is also the same metal as the main component of the via conductor 162. For example, the main component of the core material of the main conductive filler 141 is copper, and the main components of the external electrode layer body 161 and the via conductor 162 are copper. In this case, the electromigration between the conductive paste layer 14 and the external electrode layer 16 can be suppressed, and the connection stability between the conductive paste layer 14 and the external electrode layer 16 can be ensured.

[0081] In the stacking direction of the conductive paste layer 14 and the external electrode layer 16, the filling rate of the conductive filler 141 relative to the length of the conductive paste layer 14 is preferably 50% or more. In this case, the conductive filler 141 is sufficiently filled in the stacking direction of the conductive paste layer 14 and the external electrode layer 16, that is, in the direction of the current path of the solid electrolytic capacitor 10. Therefore, the ESR of the solid electrolytic capacitor 10 can be further reduced.

[0082] <Second embodiment>

[0083] Figure 31 is a partial cross-sectional view showing a schematic structure of a solid electrolytic capacitor 10A according to the second embodiment. The solid electrolytic capacitor 10A differs from the solid electrolytic capacitor 10 according to the first embodiment only in the shape of the conductive filler 141 included in the conductive paste layer 14. Figure 3 , the conductive paste layer 14 and its vicinity in the solid electrolytic capacitor 10A are shown in an enlarged manner.

[0084] Reference Figure 3 The conductive filler 141 includes a first conductive filler 141a and a second conductive filler 141b. Figure 3 In the illustrated example, the conductive filler 141 is composed of a first conductive filler 141 a and a second conductive filler 141 b .

[0085] The first conductive fillers 141a each have a broken shape. The first conductive filler 141a having a broken shape means that there are broken surfaces on the surface of the first conductive filler 141a. Each of the first conductive fillers 141a has, for example, five or more corners when the solid electrolytic capacitor 10A is cross-sectionally viewed. The second conductive fillers 141b are, for example, substantially spherical or roughly spherical. There are no broken surfaces on the surface of the second conductive filler 141b. Preferably, the second conductive filler 141b does not have corners when the solid electrolytic capacitor 10A is cross-sectionally viewed. The second conductive filler 141b may also have corners, but the number of corners in each second conductive filler 141b is four or less. The second conductive filler 141b has a relatively small particle size.

[0086] In a cross-sectional view of the solid electrolytic capacitor 10A, the conductive fillers 141a and 141b both have an aspect ratio of less than 4.0. The aspect ratio of each of the conductive fillers 141a and 141b can be obtained by dividing the length of the major axis by the length of the minor axis.

[0087] The major axis and minor axis of the conductive fillers 141 a and 141 b can be defined as follows. Figure 4 Schematic diagram showing an example of the first conductive filler 141 a in a cross-sectional SEM image taken at an arbitrary position of the solid electrolytic capacitor 10A. Figure 4, the major axis A1 of the first conductive filler 141a is set to be the longest line segment among the line segments connecting any two points located at the interface of the first conductive filler 141a relative to the adhesive 142 in the cross-sectional SEM image. The minor axis A2 of the first conductive filler 141a is set to be the longest line segment among the line segments that are perpendicular to the major axis A1 and connect any two points located at the interface of the first conductive filler 141a in the cross-sectional SEM image. The aspect ratio of the first conductive filler 141a is calculated by the length of the major axis A1 / the length of the minor axis A2. Although not shown in the figure, the major axis and the minor axis of the second conductive filler 141b can also be determined by the same method as the first conductive filler 141a to calculate the aspect ratio. In the cross-sectional SEM image, the conductive fillers 141 a and 141 b can be distinguished by defining the conductive filler 141 having a fracture surface as the first conductive filler 141 a and defining the conductive filler 141 not having a fracture surface as the second conductive filler 141 b .

[0088] The particle size of the conductive fillers 141a and 141b can be set to the length of the major axis determined as described above. The average particle size of the first conductive filler 141a can be obtained by averaging the particle sizes of the first conductive filler 141a included in the cross-sectional SEM image of the solid electrolytic capacitor 10A. Similarly, the average particle size of the second conductive filler 141b can be obtained by averaging the particle sizes of the second conductive filler 141b included in the cross-sectional SEM image. The average particle size of the first conductive filler 141a is greater than 0.2 times and less than 1.0 times the maximum layer thickness of the conductive paste layer 14 obtained from the same cross-sectional SEM image. The average particle size of the second conductive filler 141b is greater than 0.1 times and less than 0.5 times the maximum layer thickness of the conductive paste layer 14. The average particle size of the second conductive filler 141b is smaller than the average particle size of the first conductive filler 141a. The average particle size of the second conductive filler 141 b is, for example, 50% or less, or preferably 40% or less of the average particle size of the first conductive filler 141 a .

[0089] The main component of the core material of the first conductive filler 141a may be the same as or different from the main component of the core material of the second conductive filler 141b. In addition, in the conductive paste layer 14, the main component of the core material of all the first conductive fillers 141a may be the same, or the first conductive fillers 141a having different main components of the core material may be mixed. Similarly, in the conductive paste layer 14, the main component of the core material of all the second conductive fillers 141b may be the same, or the second conductive fillers 141b having different main components of the core material may be mixed.

[0090] The solid electrolytic capacitor 10A of the present embodiment also has the same structure as the solid electrolytic capacitor 10 of the first embodiment, and thus can achieve the same effect as the solid electrolytic capacitor 10 of the first embodiment. In addition, in the solid electrolytic capacitor 10A of the present embodiment, the conductive paste layer 14 includes the first conductive filler 141a having a fragmented shape. The first conductive filler 141a is easier to overlap with each other than a conductive filler having a spherical shape, and thus it is easier to form a current path that is continuous in the thickness direction of the conductive paste layer 14. As a result, the resistance to the current flowing in the thickness direction of the conductive paste layer 14 can be reduced.

[0091] In this embodiment, in addition to the first conductive filler 141a, the second conductive filler 141b is also included in the conductive paste layer 14. The second conductive filler 141b has a smaller average particle size than the first conductive filler 141a, and can enter between the first conductive fillers 141a. As a result, it is easier to form a continuous current path in the thickness direction of the conductive paste layer 14, and the resistance of the conductive paste layer 14 can be further reduced.

[0092] exist Figure 3 In the example shown, the conductive paste layer 14 includes a first conductive filler 141a and a second conductive filler 141b. Figure 5 As shown in FIG. 1 , the conductive paste layer 14 may not include the second conductive filler 141 b . The conductive paste layer 14 may include only the first conductive filler 141 a having a fragmented shape as the conductive filler 141 .

[0093] <Third embodiment>

[0094] Figure 6 1 is a partial cross-sectional view showing a schematic structure of a solid electrolytic capacitor 10B according to a third embodiment. The solid electrolytic capacitor 10B differs from the solid electrolytic capacitors 10 and 10A according to the above embodiments only in the shape of the conductive filler 141 included in the conductive paste layer 14. Figure 6 , the conductive paste layer 14 and its vicinity in the solid electrolytic capacitor 10B are shown in an enlarged manner.

[0095] Reference Figure 6 The conductive filler 141 includes a first conductive filler 141c and a second conductive filler 141b. Figure 6 In the illustrated example, the conductive filler 141 is composed of a first conductive filler 141 c and a second conductive filler 141 b .

[0096] The second conductive filler 141b has the same structure as the second conductive filler 141b used in the solid electrolytic capacitor 10A of the second embodiment. On the other hand, the first conductive filler 141c is different from the first conductive filler 141a used in the solid electrolytic capacitor 10A of the second embodiment.

[0097] The first conductive fillers 141c each have a flat shape. The first conductive fillers 141c are formed, for example, in a plate shape. Unlike the first conductive fillers 141a of the second embodiment, there is no fracture surface on the surface of the first conductive fillers 141c of this embodiment. Preferably, the first conductive fillers 141c do not have corners when the solid electrolytic capacitor 10B is cross-sectionally viewed. The first conductive fillers 141c may also have corners, but the number of corners in each first conductive filler 141c is four or less.

[0098] In a cross-sectional view of the solid electrolytic capacitor 10B, the first conductive filler 141c has an aspect ratio of 4.5 or more. The aspect ratio of the second conductive filler 141b is less than 4.0, similarly to the second embodiment. The aspect ratio of each of the first conductive filler 141c and the second conductive filler 141b can be obtained by dividing the length of the major axis by the length of the minor axis.

[0099] The length of the major axis, the length of the minor axis, and the aspect ratio of the first conductive filler 141 c and the second conductive filler 141 b can be obtained by the method described in the second embodiment using a cross-sectional SEM image of the solid electrolytic capacitor 10B.

[0100] The particle sizes of the first conductive filler 141c and the second conductive filler 141b are the lengths of the major axes of the first conductive filler 141c and the second conductive filler 141b, respectively. The average particle size of the first conductive filler 141c can be obtained by averaging the particle sizes of the first conductive filler 141c included in the cross-sectional SEM image of the solid electrolytic capacitor 10B. Similarly, the average particle size of the second conductive filler 141b can be obtained by averaging the particle sizes of the second conductive filler 141b included in the cross-sectional SEM image. The average particle size of the first conductive filler 141c is greater than 0.5 times and less than 2.0 times the maximum layer thickness of the conductive paste layer 14 obtained from the same cross-sectional SEM image. The average particle size of the second conductive filler 141b is greater than 0.1 times and less than 0.5 times the maximum layer thickness of the conductive paste layer 14. The average particle size of the second conductive filler 141b is smaller than the average particle size of the first conductive filler 141c. The average particle size of the second conductive filler 141 b is, for example, 50% or less, or preferably 40% or less of the average particle size of the first conductive filler 141 c .

[0101] The main component of the core material of the first conductive filler 141c may be the same as or different from the main component of the core material of the second conductive filler 141b. In addition, in the conductive paste layer 14, the main component of the core material of all the first conductive fillers 141c may be the same, or the first conductive fillers 141c having different main components of the core material may be mixed. Similarly, in the conductive paste layer 14, the main component of the core material of all the second conductive fillers 141b may be the same, or the second conductive fillers 141b having different main components of the core material may be mixed.

[0102] The solid electrolytic capacitor 10B of the present embodiment also has the same structure as the solid electrolytic capacitor 10 of the first embodiment, and thus can achieve the same effect as the solid electrolytic capacitor 10 of the first embodiment. In addition, in the solid electrolytic capacitor 10B of the present embodiment, the conductive paste layer 14 includes a first conductive filler 141c having a flat shape. The first conductive filler 141c has a relatively smooth surface with few or no corners. Therefore, in the conductive paste layer 14, the generation of cracks starting from the corners of the conductive filler can be suppressed. Therefore, the mechanical strength of the conductive paste layer 14 and the solid electrolytic capacitor 10B can be improved.

[0103] In this embodiment, in addition to the first conductive filler 141c, the second conductive filler 141b is also included in the conductive paste layer 14. The second conductive filler 141b has a smaller average particle size than the first conductive filler 141c, and can enter between the first conductive fillers 141c. As a result, a continuous current path in the thickness direction of the conductive paste layer 14 is easily formed, so that the resistance of the conductive paste layer 14 can be reduced.

[0104] exist Figure 6 In the example shown, the conductive paste layer 14 includes a first conductive filler 141c and a second conductive filler 141b. Figure 7 As shown, the conductive paste layer 14 may not include the second conductive filler 141 b . For example, the conductive paste layer 14 may include only the first conductive filler 141 c having a flat shape as the conductive filler 141 .

[0105] As mentioned above, although embodiment of this disclosure was described, this disclosure is not limited to the said embodiment, Various changes can be made within the range which does not deviate from the summary.

[0106] The solid electrolytic capacitor of the present disclosure is as follows.

[0107] <1>

[0108] A solid electrolytic capacitor, wherein:

[0109] The solid electrolytic capacitor includes:

[0110] A valve-action metal substrate having dielectric layers on both surfaces in a thickness direction;

[0111] Conductive paste layers, which are respectively arranged on both sides of the valve-acting metal substrate in the thickness direction and contain conductive fillers;

[0112] an insulating layer, which is laminated on the conductive paste layer on the side opposite to the valve metal substrate and has a via hole; and

[0113] an external electrode layer, which is stacked on the insulating layer and is electrically connected to the conductive paste layer through the via hole,

[0114] The external electrode layer is in direct contact with the conductive filler included in the conductive paste layer, which is located in the via hole when viewed along a lamination direction of the conductive paste layer, the insulating layer, and the external electrode layer.

[0115] <2>

[0116] A solid electrolytic capacitor according to <1>, wherein:

[0117] The external electrode layer includes an external electrode layer body formed on the surface of the insulating layer on the opposite side of the conductive paste layer.

[0118] The conductive paste layer contains a filler having a core material mainly composed of the same metal as the main component of the external electrode layer main body as a main conductive filler.

[0119] <3>

[0120] A solid electrolytic capacitor according to <2>, wherein:

[0121] The main component of the external electrode layer body is copper,

[0122] The main conductive filler is a filler having copper as a main component of the core material.

[0123] <4>

[0124] A solid electrolytic capacitor according to <2>, wherein:

[0125] The external electrode layer further includes a via conductor disposed in the via hole,

[0126] The main component of the via conductor is the same metal as the main component of the core material of the main conductive filler.

[0127] <5>

[0128] A solid electrolytic capacitor according to <4>, wherein:

[0129] The main component of the external electrode layer body and the main component of the via conductor are copper,

[0130] The main conductive filler is a filler having copper as a main component of the core material.

[0131] <6>

[0132] The solid electrolytic capacitor according to any one of <1> to <5>, wherein

[0133] In a cross-sectional view of the solid electrolytic capacitor, a filling rate of the conductive filler relative to a length of the conductive paste layer in the stacking direction is 50% or more.

[0134] <7>

[0135] The solid electrolytic capacitor according to any one of <1> to <6>, wherein

[0136] The conductive filler includes a first conductive filler having a crushed shape.

[0137] <8>

[0138] The solid electrolytic capacitor according to any one of <1> to <6>, wherein

[0139] The conductive filler includes a first conductive filler having a flat shape.

[0140] <9>

[0141] A solid electrolytic capacitor according to <7> or <8>, wherein:

[0142] The conductive filler further includes a second conductive filler having an average particle diameter smaller than an average particle diameter of the first conductive filler.

[0143] [Example]

[0144] In order to confirm the difference in effect due to the shape of the conductive filler 141, a Figure 3 , Figure 5 , Figure 6 as well as Figure 7 The solid electrolytic capacitors 10A and 10B shown in the figure were used to measure the equivalent series resistance (ESR). In addition, the filling rate of the conductive filler 141 in the layer thickness direction of the conductive paste layer 14 (the stacking direction of the conductive paste layer 14, the insulating layer 15, and the external electrode layer 16) was measured using the cross-sectional SEM images of the solid electrolytic capacitors 10A and 10B. More specifically, Figure 3 , Figure 5 , Figure 6 as well as Figure 7 The cross-sectional SEM images of the solid electrolytic capacitors 10A and 10B shown in the figure are obtained, and necessary image processing is performed. Then, the total length L1 of the conductive filler 141 in the layer thickness direction is measured at ten locations arranged at equal intervals in a direction perpendicular to the layer thickness direction in the cross-sectional SEM image. L1 , and divided it by the thickness L0 of the conductive paste layer 14 to obtain the filling rate (%) of the conductive filler 141. By averaging the above filling rates, the filling rates (%) of the conductive filler 141 in the conductive paste layer 14 in the layer thickness direction are obtained for the solid electrolytic capacitors 10A and 10B, respectively. The measurement results are shown in Table 1.

[0145] [Table 1]

[0146] Table 1

[0147]

[0148] In any of Examples 1 to 4, the filling rate of the conductive filler 141 in the layer thickness direction is 50% or more, and it can be said that the conductive filler 141 is fully filled in the layer thickness direction of the conductive paste layer 14. In Examples 1 to 4, the ESR is reduced by about 10% compared with the general chip-type electrolytic capacitor. Compared with Example 1 ( Figure 5 ), Example 3 using only the flat first conductive filler 141c ( Figure 7 ) compared to Example 2 ( Figure 3 ) and Example 4 ( Figure 6 ) has a lower ESR.

[0149] Description of Reference Numerals

[0150] 10, 10A, 10B, solid electrolytic capacitor; 11, valve-acting metal substrate; 113, dielectric layer; 14, conductive paste layer; 141, conductive filler; 141a, 141c, first conductive filler; 141b, second conductive filler; 15, insulating layer; 151, via hole; 16, external electrode layer; 161, external electrode layer body; 162, via conductor.

Claims

1. A solid electrolytic capacitor, wherein: The solid electrolytic capacitor includes: A valve-action metal substrate having dielectric layers on both surfaces in a thickness direction; Conductive paste layers, which are respectively arranged on both sides of the valve-acting metal substrate in the thickness direction and contain conductive fillers; an insulating layer, which is laminated on the conductive paste layer on the side opposite to the valve metal substrate and has a via hole; and an external electrode layer, which is stacked on the insulating layer and is electrically connected to the conductive paste layer through the via hole, The external electrode layer is in direct contact with the conductive filler included in the conductive paste layer, which is located in the via hole when viewed along the lamination direction of the conductive paste layer, the insulating layer, and the external electrode layer.

2. The solid electrolytic capacitor according to claim 1, wherein: The external electrode layer includes an external electrode layer body formed on the surface of the insulating layer on the opposite side of the conductive paste layer. The conductive paste layer contains a filler having a core material mainly composed of the same metal as the main component of the external electrode layer main body as a main conductive filler.

3. The solid electrolytic capacitor according to claim 2, wherein: The main component of the external electrode layer body is copper, The main conductive filler is a filler having copper as a main component of the core material.

4. The solid electrolytic capacitor according to claim 2, wherein: The external electrode layer further includes a via conductor disposed in the via hole, The main component of the via conductor is the same metal as the main component of the core material of the main conductive filler.

5. The solid electrolytic capacitor according to claim 4, wherein: The main component of the external electrode layer body and the main component of the via conductor are copper, The main conductive filler is a filler having copper as a main component of the core material.

6. The solid electrolytic capacitor according to any one of claims 1 to 5, wherein: In a cross-sectional view of the solid electrolytic capacitor, a filling rate of the conductive filler relative to a length of the conductive paste layer in the stacking direction is 50% or more.

7. The solid electrolytic capacitor according to any one of claims 1 to 6, wherein: The conductive filler includes a first conductive filler having a crushed shape.

8. The solid electrolytic capacitor according to any one of claims 1 to 6, wherein The conductive filler includes a first conductive filler having a flat shape.

9. The solid electrolytic capacitor according to claim 7 or 8, wherein: The conductive filler further includes a second conductive filler having an average particle diameter smaller than an average particle diameter of the first conductive filler.

Images