solid electrolytic capacitor

Abstract

A solid electrolytic capacitor (10, 10A, 10B) comprises a valve metal substrate (11), a conductive paste layer (14), an insulating layer (15), and an external electrode layer (16). The valve metal substrate (11) has a dielectric layer (113) on both surfaces in the thickness direction thereof. The conductive paste layer (14) is positioned on both sides of the valve metal substrate (11) in the thickness direction thereof. The conductive paste layer (14) includes a conductive filler (141). The insulating layer (15) is layered on the conductive paste layer (14), on the opposite side from the valve metal substrate (11). The insulating layer (15) has a via hole (151). The external electrode layer (16) is layered 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 filler (141) that is included in the conductive paste layer (14), the external electrode layer (16) is in direct contact with the conductive filler (141) that is located within the via hole (151), as viewed along the layering 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 technology]

[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 which is an anode and a second electrode which is a cathode. A lead terminal (lead frame) is electrically connected to each of the first electrode and the second electrode.

[0003] In Patent Document 1, the first electrode contains a valve metal as a conductive material. A dielectric layer is formed on the surface of the first electrode. The second electrode contains 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 stacked in this order on the solid electrolyte layer. The carbon layer contains a scaly carbon filler, a spherical carbon filler, and a binder resin. The conductive paste layer contains a metal filler and a binder resin. The conductive paste layer is typically a silver paste layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 172272 Summary of the Invention [Problem to be solved by the invention]

[0005] In the solid electrolytic capacitor of Patent Document 1, the second electrode, which is the cathode, is electrically connected to the lead frame via an adhesive layer. That is, an adhesive layer containing a thermosetting resin is interposed between the metal filler in the conductive paste layer on the outermost surface of the second electrode and the lead frame serving as the external electrode layer. In addition, the binder resin in the conductive paste layer is also interposed between the metal filler and the external electrode layer. These resins block the current between the metal filler and the external electrode layer. Therefore, when a current path exists 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.

[0006] An object of the present disclosure is to provide a solid electrolytic capacitor that can reduce the resistance of the current path in the stacking direction of the conductive paste layers and external electrode layers. [Means for solving the problem]

[0007] The solid electrolytic capacitor according to the present disclosure comprises a valve metal substrate, a conductive paste layer, an insulating layer, and an external electrode layer. The valve metal substrate has a dielectric layer on both surfaces in the thickness direction. The conductive paste layer is disposed on each side of the valve metal substrate in the thickness direction. The conductive paste layer contains a conductive filler. The insulating layer is laminated on the conductive paste layer on the opposite side of the valve metal substrate. The insulating layer has via holes. The external electrode layers are laminated on the insulating layer. The external electrode layers are electrically connected to the conductive paste layer through the via holes. The external electrode layers are in direct contact with the conductive filler contained in the conductive paste layer that is located within the via holes when viewed along the lamination direction of the conductive paste layer, the insulating layer, and the external electrode layers. [Effects of the Invention]

[0008] The solid electrolytic capacitor according to the present disclosure can reduce the resistance of the current path in the stacking direction of the conductive paste layers and external electrode layers. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of the solid electrolytic capacitor according to the first embodiment. [Figure 2] FIG. 2 is a partially enlarged view of the solid electrolytic capacitor shown in FIG. [Figure 3] FIG. 3 is a partial cross-sectional view showing a schematic configuration of a solid electrolytic capacitor according to the second embodiment. [Figure 4] FIG. 4 is a schematic diagram showing an example of a conductive filler in a cross-sectional SEM image of the solid electrolytic capacitor shown in FIG. [Figure 5] FIG. 5 is a partial cross-sectional view showing a schematic configuration of a solid electrolytic capacitor according to a modification of the second embodiment. [Figure 6] FIG. 6 is a partial cross-sectional view showing a schematic configuration of a solid electrolytic capacitor according to a third embodiment. [Figure 7] FIG. 7 is a partial cross-sectional view showing a schematic configuration of a solid electrolytic capacitor according to a modification of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] The solid electrolytic capacitor according to the embodiment comprises a valve metal substrate, a conductive paste layer, an insulating layer, and an external electrode layer. The valve metal substrate has a dielectric layer on both surfaces in the thickness direction. The conductive paste layer is disposed on each side of the valve metal substrate in the thickness direction. The conductive paste layer contains a conductive filler. The insulating layer is laminated on the conductive paste layer on the opposite side of the valve metal substrate. The insulating layer has via holes. The external electrode layers are laminated on the insulating layer. The external electrode layers are electrically connected to the conductive paste layers through the via holes. The external electrode layers are in direct contact with the conductive filler contained in the conductive paste layer that is located in the via holes when viewed along the lamination direction of the conductive paste layer, insulating layer, and external electrode layers (first configuration).

[0011] In the solid electrolytic capacitor according to the first configuration, the external electrode layer is in direct contact with the conductive filler particles contained in the conductive paste layer that are located within the via holes in a plan view. That is, no resin or other material is interposed between the conductive filler particles located at the via holes and the external electrode layer. This allows a continuous current path to be formed between the conductive filler particles and the external electrode layer. This reduces the resistance of the current path in the stacking direction of the conductive paste layer and the external electrode layer, thereby reducing the equivalent series resistance (ESR) of the solid electrolytic capacitor.

[0012] The external electrode layer may include an external electrode layer main body. The external electrode layer main body is formed on the surface of the insulating layer opposite the conductive paste layer. The conductive paste layer may include, as a main conductive filler, a filler having a core material whose main component is the same metal as the main component of the external electrode layer main body (second configuration).

[0013] When the conductive paste layer and the external electrode layer main body are formed of different metal materials, electromigration, in which metal ions move between the conductive paste layer and the external electrode layer main body, can occur, resulting in poor connection. In contrast, in the second configuration, the core material of the main conductive filler in the conductive paste layer is primarily composed of the same metal as the main component of the external electrode layer main body. This makes it possible to suppress electromigration and ensure stable connection between the conductive paste layer and the external electrode layer.

[0014] The main component of the external electrode layer body may be copper, in which case the main conductive filler is preferably a filler whose core material is mainly copper (third configuration).

[0015] The external electrode layer may further include a via conductor provided in the via hole, and 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 configuration).

[0016] In the fourth configuration, the via conductors, in addition to the external electrode layer itself, are primarily made of the same metal as the core material of the main conductive filler in the conductive paste layer, which further suppresses electromigration and improves the connection stability between the conductive paste layer and the external electrode layer.

[0017] The main component of the external electrode layer body and the main component of the via conductor may both be copper. In this case, the main conductive filler is preferably a filler whose core material is mainly copper (fifth configuration).

[0018] In a cross-sectional view of the solid electrolytic capacitor, the filling rate of the conductive filler relative to the length of the conductive paste layer in the lamination direction may be 50% or more (sixth configuration).

[0019] In the sixth configuration, the filling rate of the conductive filler relative to the length of the conductive paste layer in the stacking direction of the conductive paste layer and the external electrode layer is 50% or more. In other words, the conductive paste layer is sufficiently filled with the conductive filler in the layer thickness direction. This reduces the resistance to the current flowing in the layer thickness direction of the conductive paste layer.

[0020] The conductive filler may include a first conductive filler, which may have, for example, a crushed shape (seventh configuration).

[0021] In a seventh configuration, the conductive paste layer contains first conductive fillers. Because the first conductive fillers have a crushed shape, they tend to overlap each other more easily than, for example, spherical conductive fillers. The overlapping of the first conductive fillers allows a continuous current path to be formed in the thickness direction of the conductive paste layer. As a result, the resistance to the current flowing in the thickness direction of the conductive paste layer can be reduced.

[0022] The first conductive filler may have a flat shape (eighth configuration).

[0023] In the eighth configuration, the first conductive filler particles are arranged in a flat shape. This first conductive filler has a smooth surface with fewer corners than, for example, a crushed shape. This can prevent cracks from occurring in the conductive paste layer, originating from the corners of the conductive filler particles. This can improve the mechanical strength of the conductive paste layer.

[0024] The conductive filler may further include a second conductive filler, and the second conductive filler may have an average particle size smaller than that of the first conductive filler (ninth configuration).

[0025] In the ninth configuration, in addition to the first conductive filler, the conductive paste layer contains a second conductive filler. 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 penetrate between the first conductive filler particles. This makes it easier to form a continuous current path in the thickness direction of the conductive paste layer, thereby further reducing resistance to the current flowing in the thickness direction of the conductive paste layer.

[0026] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0027] First Embodiment [Solid electrolytic capacitor configuration] Fig. 1 is a cross-sectional view showing a schematic configuration of a solid electrolytic capacitor 10 according to a first embodiment. As shown in Fig. 1, the solid electrolytic capacitor 10 is included in a multilayer substrate (package substrate) 20, such as a component-embedded substrate. Fig. 1 shows a partial and schematic cross section of the package substrate 20.

[0028] The package substrate 20 is mounted with, for example, a DC-DC converter 30 and a load 40 which is an integrated circuit (IC). The DC-DC converter 30 is arranged on one surface of the package substrate 20 in the thickness direction. The load 40 is arranged on the surface of the package substrate 20 opposite the DC-DC converter 30 in the thickness direction. In this embodiment, the package substrate 20 includes a plurality of solid electrolytic capacitors 10. The solid electrolytic capacitors 10 may be arranged in an array on the package substrate 20.

[0029] Referring to FIG. 1, each 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.

[0030] The valve metal substrate 11 has a plate or 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.

[0031] The core layer 111 is a layer made of a valve metal. Examples of the valve metal include simple metals such as aluminum, tantalum, niobium, titanium, and zirconium, and alloys containing at least one of these metals. The valve metal is preferably aluminum or an aluminum alloy.

[0032] The porous layer 112 and the dielectric layer 113 are provided on both surfaces of the core layer 111 so as to sandwich the core layer 111 from both sides in the thickness direction. The porous layer 112 and the dielectric layer 113 are laminated in this order on each surface of the core layer 111 in the thickness direction. 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 valve metal foil. Furthermore, the dielectric layer 113 made of an oxide film can be formed on the porous layer 112 by anodizing (chemical conversion treatment).

[0033] 1, 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 metal substrate 11 may be directly connected to the through-hole conductor 22 via the inner wall surface of the through hole 21.

[0034] Through-hole conductor 22 is made of a conductive material. Through-hole conductor 22 is formed at least on the inner wall surface of through-hole 21. For example, through-hole conductor 22 can be formed by metallizing the inner wall surface of through-hole 21 with a material whose main component is a metal such as copper, gold, or silver, or an alloy thereof. Alternatively, through-hole conductor 22 may be formed by filling through-hole 21 with a conductive material.

[0035] The solid electrolyte layer 12, the carbon layer 13, and the conductive paste layer 14 are disposed on both sides of the valve metal substrate 11 in the thickness direction. That is, the solid electrolyte layer 12, the carbon layer 13, and the conductive paste layer 14 are laminated in this order on each surface of the valve metal substrate 11 in the thickness direction. 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.

[0036] The solid electrolyte layer 12 is disposed on the dielectric layer 113 of the valve metal substrate 11. The solid electrolyte layer 12 preferably covers the entire surface of the dielectric layer 113 opposite to the core layer 111 and the porous layer 112. The solid electrolyte layer 12 is typically formed of a conductive polymer material. Examples of conductive polymers include polypyrroles, polythiophenes, and polyanilines. The conductive polymer is preferably a polythiophene, and particularly preferably poly(3,4-ethylenedioxythiophene) known as PEDOT. The conductive polymer material may be one that uses, for example, polystyrene sulfonate (PSS) as a dopant.

[0037] The carbon layer 13 is disposed on the solid electrolyte layer 12. The carbon layer 13 preferably covers the entire surface of the solid electrolyte layer 12 opposite the valve metal substrate 11. The carbon layer 13 contains, for example, a carbon filler and a binder. For example, the carbon layer 13 can be formed by applying a carbon paste containing the carbon filler and a binder in a fluid state onto the solid electrolyte layer 12 by sponge transfer, screen printing, spray coating, a dispenser, inkjet printing, or the like.

[0038] The conductive paste layer 14 is disposed on the carbon layer 13. It is preferable that the conductive paste layer 14 covers the entire surface of the carbon layer 13 that is located opposite the solid electrolyte layer 12. The conductive paste layer 14 is connected to the solid electrolyte layer 12 by the carbon layer 13.

[0039] The insulating layer 15 is laminated on the conductive paste layer 14 on the side opposite the valve metal base 11. The insulating layer 15 preferably covers the entire surface of the conductive paste layer 14 on the side opposite the valve metal base 11. The insulating layer 15 may be provided in common to a plurality of solid electrolytic capacitors 10. That is, the insulating layer 15 may extend across a plurality of solid electrolytic capacitors 10 so as to mask 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 separated by the insulating layer 15.

[0040] The insulating layer 15 is typically made of a resin. For example, the insulating layer 15 can be made of a thermosetting resin. The insulating layer 15 is preferably made of an epoxy-based resin material. Examples of epoxy-based resins include phenol-cured epoxy resins, cyanate ester / epoxy mixed resins, and phenol ester-cured epoxy resins.

[0041] The insulating layer 15 has at least one via hole 151. In this embodiment, a plurality of via holes 151 are formed in the insulating layer 15. Each of the via holes 151 penetrates 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 a laser from a laser processing machine. The laser used in this case is, for example, a CO2 laser.

[0042] For example, in a cross-sectional view of the solid electrolytic capacitor 10, the via hole 151 is formed in a tapered shape that decreases in width toward the conductive paste layer 14. However, the via hole 151 may have a constant width throughout in a cross-sectional view of the solid electrolytic capacitor 10. The cross section of the via hole 151, i.e., the cross section perpendicular to the central axis of the via hole 151, has a circular shape, for example.

[0043] 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 via holes 151. The external electrode layer 16 includes an external electrode layer main body 161 and a via conductor 162.

[0044] The external electrode layer main body 161 is formed on the surface of the insulating layer 15 on the side opposite to the conductive paste layer 14. The external electrode layer main body 161 can function as a wiring layer.

[0045] The external electrode layer main body 161 may extend from the solid electrolytic capacitor 10 to one of the through-hole conductors 22. Of the external electrode layer main bodies 161 arranged on both sides in the thickness direction of the solid electrolytic capacitor 10, one of the external electrode layer main bodies 161 may be electrically connected to the through-hole conductor 22 connected to GND.

[0046] 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 .

[0047] Fig. 2 is an enlarged view of the via hole 151 and its vicinity in the cross section of the solid electrolytic capacitor 10 shown in Fig. 1. Hereinafter, the configurations of the conductive paste layer 14 and the external electrode layer 16 will be described in more detail with reference to Fig. 2.

[0048] As shown in FIG. 2, the conductive paste layer 14 includes a conductive filler 141 and a binder 142.

[0049] The conductive filler 141 has conductivity. The conductive filler 141 may be a metal filler or a non-metal filler. Each of the conductive fillers 141 includes a core material. Each of the conductive fillers 141 may include a coating layer that covers 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, or the like. The main component of the core material of the conductive filler 141 refers to the element that is contained in the largest amount (for example, by mass %) in the chemical composition of the core material.

[0050] The conductive paste layer 14 preferably contains a filler whose core material is mainly composed of copper as the main conductive filler 141. More specifically, the conductive paste layer 14 preferably contains a metal filler whose core material is copper particles or copper alloy particles as the main conductive filler 141.

[0051] The conductive fillers 141 contained in the conductive paste layer 14 may all be fillers of the same material. The conductive paste layer 14 may also contain a mixture of conductive fillers 141 of different materials. For example, the conductive paste layer 14 may contain only copper fillers whose core material is copper particles or copper alloy particles, or may contain a mixture of copper fillers and silver fillers whose core material is silver particles or silver alloy particles. When the conductive paste layer 14 contains a mixture of fillers of different materials, the main conductive filler 141 is the filler with the highest content in the conductive paste layer 14. When the fillers in the conductive paste layer 14 are all of the same type, this filler is the main conductive filler 141.

[0052] The main conductive filler 141 in the conductive paste layer 14 can be identified, for example, using 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 acquired and subjected to necessary image processing to distinguish the conductive filler 141 from the binder 142. Furthermore, if fillers of different materials are mixed in the conductive paste layer 14, the conductive fillers 141 are distinguished by material. Then, from 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 (vol%), and the filler with the highest content in the cross-sectional SEM image can be determined as the main conductive filler 141. The total content of the conductive filler 141 in the conductive paste layer 14 is, for example, 30 vol% or more and 80 vol% or less. Although it depends on the total content of the conductive filler 141, the content of the main conductive filler 141 in the conductive paste layer 14 is preferably 50 vol% or more.

[0053] The binder 142 contains conductive filler 141. That is, a large number of conductive fillers 141 are dispersed in the binder 142. The conductive filler 141 located within the via hole 151 when viewed along the stacking direction of the conductive paste layer 14 and the insulating layer 15 and present in the outermost layer of the conductive paste layer 14 has at least a portion exposed from the binder 142. More specifically, in the portion of the conductive paste layer 14 located within the via hole 151 when viewed along the stacking direction, the binder 142 in the outermost layer is burned and disappeared by irradiation with a laser when forming the via hole 151 in the insulating layer 15. Therefore, in that portion, the conductive filler 141 is exposed from the binder 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 binder 142 and the insulating layer 15.

[0054] In a cross-sectional view of the solid electrolytic capacitor 10, the filling rate of the conductive filler 141 relative to the length (layer thickness) of the conductive paste layer 14 in the stacking direction 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 acquired at an arbitrary position of the solid electrolytic capacitor 10, the layer thickness L0 of the conductive paste layer 14 and the length L1 in the layer thickness direction of each conductive filler 141 present at the same position are measured at each of 10 equally spaced points, and the total S of L1 is calculated. L1 Then, calculate the S L1 The average value of / L0×100 is calculated, and this average value can be used as the filling rate (%) of the conductive filler 141 in the thickness direction of the conductive paste layer 14.

[0055] The conductive paste layer 14 can be formed by applying a conductive paste containing a conductive filler 141 and a binder 142 in a fluid state onto the carbon layer 13. The conductive paste is applied to the carbon layer 13 by, for example, sponge transfer, screen printing, spray application, a dispenser, or inkjet printing. The applied conductive paste becomes the conductive paste layer 14 when the binder 142 is hardened by, for example, firing.

[0056] 2, the external electrode layer 16 is electrically connected to the conductive paste layer 14 by a via conductor 162. The via conductor 162 includes an electroless plated layer 163 and an electrolytic plated layer 164.

[0057] The electroless plating layer 163 is provided directly on the side wall of the via hole 151. The electroless plating layer 163 is a metal film deposited by a chemical reaction. In the example shown in FIG. 2, the electroless plating layer 163 extends to the outer surface of the insulating layer 15 of the via hole 151. That is, the electroless plating layer 163 constitutes not only a part of the via conductor 162 but also a part of the external electrode layer main body 161, which is a wiring layer. In the external electrode layer main 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 photolithographic etching.

[0058] Electrolytic plated layer 164 is provided on electroless plated layer 163. Electrolytic plated layer 164 covers the entire electroless plated layer 163. Electrolytic plated layer 164 is a metal coating deposited using electricity.

[0059] 2, a so-called filled via is used to connect the conductive paste layer 14 and the external electrode layer 16, and a 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. In other words, the conductive paste layer 14 and the external electrode layer 16 may be connected by a so-called conformal via.

[0060] The external electrode layer 16 is in direct contact with the conductive fillers 141 contained in the conductive paste layer 14 that are located within the via holes 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 that is located within the via holes 151 in a plan view of the solid electrolytic capacitor 10, some of the conductive fillers 141 are exposed from the binder 142. Therefore, the via conductors 162 of the external electrode layer 16 can be in direct contact with the conductive fillers 141 exposed from the binder 142. The via conductors 162 may be joined to the conductive fillers 141.

[0061] When the main conductive filler 141 in the conductive paste layer 14 is a metal filler, it is preferable that the external electrode layer body 161 contains 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 uses a certain metal or its alloy as the core material, it is preferable that the external electrode layer body 161 is also formed from the same metal or an alloy of this metal. More preferably, the main conductive filler 141 is a filler whose core material is mainly copper, and the main component of the external electrode layer body 161 is copper.

[0062] It is preferable that the via conductors 162 also have as their main component the same metal as the main component of the core material of the main conductive filler 141. For example, if the main conductive filler 141 has a certain metal or its alloy as its core material, it is preferable that the via conductors 162 are also formed of the same metal or an alloy of this metal. More preferably, the main conductive filler 141 is a filler whose main component of the core material is copper, and the main component of both the external electrode layer main body 161 and the via conductors 162 is copper. The main components of the external electrode layer main body 161 and the via conductors 162 refer to the elements that are contained in the largest amounts (e.g., by mass%) in the chemical compositions of the external electrode layer main body 161 and the via conductors 162, respectively.

[0063] When main conductive filler 141 has copper particles or copper alloy particles as the core material, electroless plating layer 163 can be an electroless copper plating layer, and electrolytic plating layer 164 can be an electrolytic copper plating layer. In this case, seed layer 165 can be formed of copper or a copper alloy.

[0064] [effect] In the solid electrolytic capacitor 10 according to this embodiment, the external electrode layer 16 is in direct contact with the conductive fillers 141 contained in the conductive paste layer 14 that are located within the via holes 151 in a plan view. More specifically, inside the via holes 151, the via conductors 162 of the external electrode layer 16 are in direct contact with the conductive fillers 141 exposed from the binder 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 through metal contact between the conductive fillers 141 and the external electrode layer 16, rather than through a contact point (interface) of the conductive fillers 141 with the insulator. This reduces the resistance when a current path exists in the stacking direction of the conductive paste layer 14 and the external electrode layer 16, thereby reducing the equivalent series resistance (ESR) of the solid electrolytic capacitor 10.

[0065] However, the conductive paste layer 14 is electrically connected to the carbon layer 13 via the contact point (interface) of the conductive filler 141 with the binder 142, etc. In other words, the method of connecting the conductive paste layer 14 to the carbon layer 13 is different from the method of connecting the conductive paste layer 14 to the external electrode layer 16.

[0066] In this embodiment, the core material of the main conductive filler 141 in the conductive paste layer 14 preferably contains the same metal as the main component of the external electrode layer body 161. The main component of the core material of the main conductive filler 141 is also preferably the same metal as the main component of the via conductors 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 conductors 162 are copper. In this case, 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.

[0067] In the stacking direction of the conductive paste layers 14 and the external electrode layers 16, the filling rate of the conductive filler 141 relative to the length of the conductive paste layers 14 is preferably 50% or more. In this case, the conductive paste layers 14 are sufficiently filled with the conductive filler 141 in the stacking direction of the conductive paste layers 14 and the external electrode layers 16, i.e., in the direction of the current path of the solid electrolytic capacitor 10. This allows the ESR of the solid electrolytic capacitor 10 to be further reduced.

[0068] Second Embodiment 3 is a partial cross-sectional view showing a schematic configuration 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 contained in the conductive paste layer 14. FIG. 3 shows an enlarged view of the conductive paste layer 14 and its vicinity in the solid electrolytic capacitor 10A.

[0069] 3, the conductive filler 141 includes a first conductive filler 141a and a second conductive filler 141b. In the example shown in FIG. 3, the conductive filler 141 is made up of the first conductive filler 141a and the second conductive filler 141b.

[0070] Each of the first conductive fillers 141a has a crushed shape. The crushed shape of the first conductive fillers 141a means that there are fractures on the surface of the first conductive fillers 141a. Each of the first conductive fillers 141a has, for example, five or more corners in a cross-sectional view of the solid electrolytic capacitor 10A. Each of the second conductive fillers 141b is, for example, substantially or roughly spherical. There are no fractures on the surface of the second conductive fillers 141b. The second conductive fillers 141b preferably have no corners in a cross-sectional view of the solid electrolytic capacitor 10A. The second conductive fillers 141b may have corners, but each second conductive filler 141b has four or fewer corners. The second conductive fillers 141b have a relatively small particle size.

[0071] In a cross-sectional view of the solid electrolytic capacitor 10A, the conductive fillers 141a and 141b each have an aspect ratio of less than 4.0. The aspect ratio of each of the conductive fillers 141a and 141b can be calculated by dividing the length of its major axis by the length of its minor axis.

[0072] The major and minor axes of the conductive fillers 141a and 141b can be defined as follows. FIG. 4 is a schematic diagram showing an example of a first conductive filler 141a in a cross-sectional SEM image acquired at an arbitrary position of the solid electrolytic capacitor 10A. Referring to FIG. 4, the major axis A1 of the first conductive filler 141a is defined as the longest line segment among the line segments connecting any two points on the interface of the first conductive filler 141a with the binder 142 in the cross-sectional SEM image. The minor axis A2 of the first conductive filler 141a is defined as the longest line segment among the line segments connecting any two points on the interface of the first conductive filler 141a that are perpendicular to the major axis A1 in the cross-sectional SEM image. The aspect ratio of the first conductive filler 141a is calculated by dividing the length of the major axis A1 by the length of the minor axis A2. Although not shown, the long and short axes of the second conductive filler 141b can be determined in the same manner as for the first conductive filler 141a, and the aspect ratio can be calculated. In the cross-sectional SEM image, the conductive filler 141 having a fracture surface is referred to as the first conductive filler 141a, and the conductive filler 141 not having a fracture surface is referred to as the second conductive filler 141b, so that the conductive fillers 141a and 141b can be distinguished.

[0073] The particle diameters of the conductive fillers 141a and 141b can be the length of their major axes determined as described above. The average particle diameter of the first conductive filler 141a can be determined by averaging the particle diameters of the first conductive filler 141a included in a cross-sectional SEM image of the solid electrolytic capacitor 10A. Similarly, the average particle diameter of the second conductive filler 141b can be determined by averaging the particle diameters of the second conductive filler 141b included in the cross-sectional SEM image. The average particle diameter of the first conductive filler 141a is 0.2 times or more and less than 1.0 times the maximum layer thickness of the conductive paste layer 14 determined from the same cross-sectional SEM image. The average particle diameter of the second conductive filler 141b is 0.1 times or more and less than 0.5 times the maximum layer thickness of the conductive paste layer 14. The average particle diameter of the second conductive filler 141b is smaller than the average particle diameter of the first conductive filler 141a. The average particle size of the second conductive filler 141b is, for example, 50% or less, and preferably 40% or less, of the average particle size of the first conductive filler 141a.

[0074] 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. Furthermore, 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 first conductive fillers 141a having different main components of their 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 second conductive fillers 141b having different main components of their core material may be mixed.

[0075] The solid electrolytic capacitor 10A according to this embodiment has a similar configuration to the solid electrolytic capacitor 10 according to the first embodiment, and therefore can achieve the same effects as the solid electrolytic capacitor 10 according to the first embodiment. Furthermore, the solid electrolytic capacitor 10A according to this embodiment includes first conductive fillers 141a having a crushed shape in the conductive paste layer 14. The first conductive fillers 141a are more likely to overlap with each other than, for example, spherical conductive fillers, and are therefore more likely to form continuous current paths in the thickness direction of the conductive paste layer 14. This reduces the resistance to current flowing in the thickness direction of the conductive paste layer 14.

[0076] In this embodiment, in addition to the first conductive filler 141a, second conductive filler 141b is contained in the conductive paste layer 14. The second conductive filler 141b has a smaller average particle size than the first conductive filler 141a, and therefore can penetrate between the first conductive filler 141a. This makes it 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.

[0077] 3, the conductive paste layer 14 includes first conductive filler 141a and second conductive filler 141b. However, as shown in FIG. 5, the conductive paste layer 14 does not necessarily include the second conductive filler 141b. The conductive paste layer 14 may include only the first conductive filler 141a having a crushed shape as the conductive filler 141.

[0078] <Third embodiment> 6 is a partial cross-sectional view showing a schematic configuration 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 contained in the conductive paste layer 14. FIG. 6 shows an enlarged view of the conductive paste layer 14 and its vicinity in the solid electrolytic capacitor 10B.

[0079] 6, the conductive filler 141 includes a first conductive filler 141c and a second conductive filler 141b. In the example shown in FIG. 6, the conductive filler 141 is made up of the first conductive filler 141c and the second conductive filler 141b.

[0080] The second conductive filler 141b has a configuration similar to that of the second conductive filler 141b used in the solid electrolytic capacitor 10A in accordance with the second embodiment, while the first conductive filler 141c is different from the first conductive filler 141a used in the solid electrolytic capacitor 10A in accordance with the second embodiment.

[0081] Each of the first conductive fillers 141c has 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, the first conductive fillers 141c of this embodiment do not have any fractured surfaces. The first conductive fillers 141c preferably do not have any corners in a cross-sectional view of the solid electrolytic capacitor 10B. The first conductive fillers 141c may have corners, but each first conductive filler 141c has four or fewer corners.

[0082] 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, as in the second embodiment. The aspect ratios of the first conductive filler 141c and the second conductive filler 141b can be calculated by dividing the length of their major axes by the length of their minor axes.

[0083] The length of the major axis, the length of the minor axis, and the aspect ratio of the first conductive filler 141c and the second conductive filler 141b can be determined using a cross-sectional SEM image of the solid electrolytic capacitor 10B by the method described in the second embodiment.

[0084] The particle diameters 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 diameter of the first conductive filler 141c can be determined by averaging the particle diameters of the first conductive filler 141c included in the cross-sectional SEM image of the solid electrolytic capacitor 10B. Similarly, the average particle diameter of the second conductive filler 141b can be determined by averaging the particle diameters of the second conductive filler 141b included in the cross-sectional SEM image. The average particle diameter of the first conductive filler 141c is 0.5 times or more and less than 2.0 times the maximum layer thickness of the conductive paste layer 14 determined from the same cross-sectional SEM image. The average particle diameter of the second conductive filler 141b is 0.1 times or more and less than 0.5 times the maximum layer thickness of the conductive paste layer 14. The average particle diameter of the second conductive filler 141b is smaller than the average particle diameter of the first conductive filler 141c. The average particle size of the second conductive filler 141b is, for example, 50% or less, and preferably 40% or less, of the average particle size of the first conductive filler 141c.

[0085] 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. Furthermore, 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 first conductive fillers 141c having core materials with different main components 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 second conductive fillers 141b having core materials with different main components may be mixed.

[0086] The solid electrolytic capacitor 10B according to this embodiment has a similar configuration to the solid electrolytic capacitor 10 according to the first embodiment, and therefore can achieve the same effects as the solid electrolytic capacitor 10 according to the first embodiment. Furthermore, in the solid electrolytic capacitor 10B according to this embodiment, the conductive paste layer 14 contains first conductive fillers 141c having a flat shape. The first conductive fillers 141c have a relatively smooth surface with few or no corners. This can prevent cracks from occurring in the conductive paste layer 14, originating from the corners of the conductive fillers. This can improve the mechanical strength of the conductive paste layer 14 and the solid electrolytic capacitor 10B.

[0087] In this embodiment, in addition to the first conductive filler 141c, the conductive paste layer 14 also contains second conductive filler 141b. The second conductive filler 141b has a smaller average particle size than the first conductive filler 141c, and therefore can penetrate between the first conductive filler 141c. This makes it 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 reduced.

[0088] 6, the conductive paste layer 14 includes a first conductive filler 141c and a second conductive filler 141b. However, as shown in Fig. 7, the conductive paste layer 14 does not necessarily include the second conductive filler 141b. For example, the conductive paste layer 14 may include only the first conductive filler 141c having a flat shape as the conductive filler 141.

[0089] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0090] The solid electrolytic capacitor according to the present disclosure is as follows.

[0091] <1> a valve metal substrate having dielectric layers on both surfaces in the thickness direction; a conductive paste layer containing a conductive filler, the conductive paste layer being disposed on each side of the valve metal base in the thickness direction; an insulating layer having a via hole and laminated on the conductive paste layer on the opposite side of the valve metal substrate; an external electrode layer laminated on the insulating layer and electrically connected to the conductive paste layer through the via hole; Equipped with a solid electrolytic capacitor in which the external electrode layer is in direct contact with, among the conductive fillers contained in the conductive paste layer, the conductive filler that is located within the via hole when viewed along the stacking direction of the conductive paste layer, the insulating layer, and the external electrode layer.

[0092] <2> <1> The solid electrolytic capacitor according to claim 1, the external electrode layer includes an external electrode layer body formed on a surface of the insulating layer opposite to the conductive paste layer, The conductive paste layer contains, as a main conductive filler, a filler having a core material whose main component is the same metal as that of the main component of the external electrode layer body.

[0093] <3> <2> The solid electrolytic capacitor according to claim 1, The main component of the external electrode layer body is copper, The solid electrolytic capacitor, wherein the main conductive filler is a filler containing copper as a main component of the core material.

[0094] <4> <2> The solid electrolytic capacitor according to claim 1, the external electrode layer further includes a via conductor provided in the via hole, A solid electrolytic capacitor, wherein the via conductor is mainly made of the same metal as the main component of the core material of the main conductive filler.

[0095] <5> <4> The solid electrolytic capacitor according to claim 1, the main component of the external electrode layer body and the main component of the via conductor are copper, The solid electrolytic capacitor, wherein the main conductive filler is a filler containing copper as a main component of the core material.

[0096] <6> <1> from <5> 10. The solid electrolytic capacitor according to claim 9, A solid electrolytic capacitor, wherein in a cross-sectional view of the solid electrolytic capacitor, a filling rate of the conductive filler relative to the length of the conductive paste layers in the stacking direction is 50% or more.

[0097] <7> <1> from <6> 10. The solid electrolytic capacitor according to claim 9, The solid electrolytic capacitor, wherein the conductive filler includes a first conductive filler having a crushed shape.

[0098] <8> <1> from <6> 10. The solid electrolytic capacitor according to claim 9, The solid electrolytic capacitor, wherein the conductive filler includes a first conductive filler having a flat shape.

[0099] <9> <7> or <8> The solid electrolytic capacitor according to claim 1, The solid electrolytic capacitor, wherein the conductive filler further includes a second conductive filler having an average particle size smaller than that of the first conductive filler. [Example]

[0100] To confirm the difference in effect depending on the shape of the conductive filler 141, the solid electrolytic capacitors 10A and 10B shown in FIGS. 3, 5, 6, and 7 were actually fabricated and their equivalent series resistance (ESR) was measured. Furthermore, the filling rate of the conductive filler 141 in the 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 from the cross-sectional SEM images of the solid electrolytic capacitors 10A and 10B. More specifically, cross-sectional SEM images were obtained for each of the solid electrolytic capacitors 10A and 10B shown in FIGS. 3, 5, 6, and 7, and the necessary image processing was performed. Then, the total length L1 of the conductive filler 141 in the thickness direction was measured for each of 10 equally spaced locations in the cross-sectional SEM images, which were aligned perpendicular to the thickness direction. L1 was measured and divided by the thickness L0 of the conductive paste layer 14 to determine the filling rate (%) of the conductive filler 141. These filling rates were averaged to obtain the filling rate (%) of the conductive filler 141 in the thickness direction of the conductive paste layer 14 for each of the solid electrolytic capacitors 10A and 10B. The measurement results are shown in Table 1.

[0101] [Table 1]

[0102] In all of Examples 1 to 4, the filling rate of the conductive filler 141 in the layer thickness direction was 50% or more, which means that the conductive filler 141 was sufficiently filled in the layer thickness direction of the conductive paste layer 14. In Examples 1 to 4, the ESR was reduced by approximately 10% compared to a typical chip-type electrolytic capacitor. Compared to Example 1 (FIG. 5), which used only crushed first conductive filler 141a, and Example 3 (FIG. 7), which used only flat first conductive filler 141c, Example 2 (FIG. 3) and Example 4 (FIG. 6), which added small-diameter second conductive filler 141b, had reduced ESR. [Explanation of symbols]

[0103] 10, 10A, 10B: Solid electrolytic capacitor 11: Valve 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: Beer hall 16: External electrode layer 161: External electrode layer body 162: Via conductor

Claims

1. a valve metal substrate having dielectric layers on both surfaces in the thickness direction; a conductive paste layer containing a conductive filler, the conductive paste layer being disposed on each side of the valve metal base in the thickness direction; an insulating layer having a via hole and laminated on the conductive paste layer on the opposite side of the valve metal substrate; an external electrode layer laminated on the insulating layer and electrically connected to the conductive paste layer through the via hole; Equipped with a solid electrolytic capacitor in which the external electrode layer is in direct contact with, among the conductive fillers contained in the conductive paste layer, the conductive filler that is located within the via hole when viewed along the stacking direction of the conductive paste layer, the insulating layer, and the external electrode layer.

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

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

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

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

6. 6. The solid electrolytic capacitor according to claim 1, In a cross-sectional view of the solid electrolytic capacitor, a filling rate of the conductive filler relative to the length of the conductive paste layers in the stacking direction is 50% or more.

7. 2. The solid electrolytic capacitor according to claim 1, The conductive filler includes a first conductive filler having a crushed shape.

8. 2. The solid electrolytic capacitor according to claim 1, The conductive filler includes a first conductive filler having a flat shape.

9. 9. The solid electrolytic capacitor according to claim 7, The conductive filler further includes a second conductive filler having an average particle size smaller than that of the first conductive filler.

Images