JP7806906B2 - Solid electrolytic capacitor and method for manufacturing the solid electrolytic capacitor - Google Patents

Description

The present invention relates to an electrolytic capacitor having a laminated structure of a capacitor element having a dielectric layer and a solid electrolyte layer formed on a valve metal body, and a cathode film.

The solid electrolytic capacitor in Patent Document 1 comprises an element stack consisting of first layers that function as capacitors and second layers that function as cathodes. The first layer consists of a valve metal element with a dielectric layer formed on its surface, and a solid electrolyte layer provided on this dielectric layer. The second layer consists of metal foil.

A carbon paste layer is formed between the first and second layers, i.e., between the solid electrolyte layer and the metal foil. The solid electrolyte layer and the metal foil are electrically connected and physically bonded by the carbon paste layer.

Japanese Patent Application Laid-Open No. 2019-079866

However, with the configuration of Patent Document 1, there is a possibility that corrosion of the cathode made of metal foil may occur due to the intrusion of moisture from the outside. Furthermore, with the configuration of Patent Document 1, due to the difference in the linear expansion coefficient between the metal foil and the solid electrolyte layer, there is a possibility that insulation may peel off due to expansion and contraction stress caused by thermal history between the metal foil and the solid electrolyte layer.

Therefore, the present invention aims to provide a solid electrolytic capacitor that suppresses cathode corrosion and internal insulation peeling.

The solid electrolytic capacitor of this invention comprises a plurality of capacitor elements and a plurality of cathodes. Each of the plurality of capacitor elements comprises a film-like valve metal body, a dielectric layer, and a solid electrolyte layer. The cathode includes a second resin substrate and a second conductive material. The plurality of capacitor elements and the plurality of cathodes are alternately stacked with the solid electrolyte layer and the cathode in contact. The region where the solid electrolyte layer and the cathode contact each other has a portion where the solid electrolyte layer and the cathode are mixed.

In this configuration, the solid electrolyte layer and cathode are primarily made of the same type of resin, and the solid electrolyte layer and cathode are mixed at the contact point. This increases the contact area between the solid electrolyte layer and the cathode, improving the adhesive strength between them. Furthermore, the occurrence of a clear interface due to differences in physical properties is suppressed, and peeling is suppressed. Furthermore, because the cathode is not a metal foil, corrosion is suppressed.

This invention can prevent cathode corrosion and internal insulation peeling.

FIG. 1 is a perspective view showing the appearance of a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 2 is a side cross-sectional view showing the configuration of a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 3A is a plan view of the capacitor element, and FIG. 3B is a side cross-sectional view of the capacitor element. FIG. 4 is a cross-sectional view showing the structure of the cathode film. FIG. 5 is an enlarged cross-sectional view of the contact portion between the outer layer CP and the cathode film. FIG. 6 is a flowchart showing an example of a schematic flow of the method for manufacturing the solid electrolytic capacitor according to this embodiment. FIG. 7A is a perspective view of the appearance of a capacitor element sheet, and FIG. 7B is a perspective view of the appearance of a cathode sheet. FIG. 8 is a perspective view showing the appearance of a laminate (sheet-type capacitor laminate) of a capacitor element sheet and a cathode sheet.

The solid electrolytic capacitor according to an embodiment of the present invention and a method for manufacturing the solid electrolytic capacitor will be described with reference to the figures.

(Description of the Structure of Solid Electrolytic Capacitor 10)
Fig. 1 is an external perspective view of a solid electrolytic capacitor according to an embodiment of the present invention. Fig. 2 is a side cross-sectional view showing the configuration of a solid electrolytic capacitor according to an embodiment of the present invention. Fig. 2 is a cross-sectional view taken along a plane perpendicular to the top, bottom, and end faces of the body of the solid electrolytic capacitor. Note that in Fig. 2, to clearly illustrate the configuration, dimensions in each direction are appropriately emphasized, and dimensions in the height direction (z-axis direction in the drawing) are particularly emphasized (exaggerated).

As shown in Figures 1 and 2, the solid electrolytic capacitor 10 comprises a base body 11, a resin electrode 71, a resin electrode 72, an external electrode 81, and an external electrode 82.

The element body 11 has a rectangular parallelepiped shape and has a top surface, a bottom surface, an end surface 111, an end surface 112, and two side surfaces. The element body 11 includes a plurality of capacitor elements 20, a plurality of cathode films 30, an insulating resin 50, and an insulator layer 500.

(Capacitor element 20)
Fig. 3A is a plan view of the capacitor element, and Fig. 3B is a side cross-sectional view of the capacitor element, and Fig. 3B is a cross-sectional view taken along a plane perpendicular to the flat film surface and end surface of the capacitor element.

As shown in Figures 3(A) and 3(B), the capacitor element 20 comprises an anode electrode 21, an inner layer CP22, and an outer layer CP23. The inner layer CP22 and the outer layer CP23 form a solid electrolyte layer SEL.

The anode electrode 21 is flat and has end surfaces 211, 212, flat membrane surfaces 213, and flat membrane surfaces 214. While detailed structural details are omitted in Figure 3, the anode electrode 21 has numerous holes recessed from the flat membrane surfaces 213 and 214. In other words, a predetermined thickness of the anode electrode 21 near the flat membrane surfaces 213 and 214 is porous. The ratio of the thickness of the porous material and core metal portion on one side of the anode electrode 21 to the thickness of the porous material on the other side is approximately 1:1:1. The dielectric layer 210 covers the outer surface of the anode electrode 21. Because detailed structural details of the anode electrode 21 are omitted in Figure 3, the dielectric layer 210 is shown schematically as covering the macroscopic surface (flat membrane surfaces 213 and 214) of the anode electrode 21. However, in reality, the dielectric layer 210 covers not only the macroscopic surface (flat membrane surfaces 213 and 214 ) of the anode electrode 21 , but also the inner surfaces of the numerous pores of the anode electrode 21 .

The anode electrode 21 is made of a metal such as aluminum, tantalum, niobium, titanium, zirconium, magnesium, or silicon, or an alloy containing these metals. It is preferable that the anode electrode 21 is made of aluminum or an aluminum alloy. The anode electrode 21 may be any valve metal that exhibits so-called valve action.

The inner layer CP22 covers the surface of the dielectric layer 210. The inner layer CP22 is made of a conductive polymer. The inner layer CP22 fills the fine recesses in the porous portion.

The outer layer CP23 covers the surface of the inner layer CP22. In other words, for example, the outer layer CP23 is a layer formed to cover the entire dielectric layer 210 after the inner layer CP22 is formed to fill the fine recesses in the porous portion. The outer layer CP23 is made of the same material as the inner layer CP22. The outer layer CP23 may be made of a material (including composition) different from that of the inner layer CP22 as long as it contains a resin material.

The insulator layer 500 is formed near the end faces 211, 212 of the flat membrane surfaces 213, 214 of the anode electrode 21. The insulator layer 500 is a frame body that limits the formation area of the inner layer CP22 and the outer layer CP23. As a result, for example, the inner layer CP22 and the outer layer CP23 do not reach the end face 211 of the anode electrode 21.

With this configuration, the anode electrode 21 and the solid electrolyte layer (a laminate of an inner layer CP22 and an outer layer CP23) face each other across the dielectric layer 210, and the capacitor element 20 functions as a capacitor with a predetermined capacitance.

(Cathode film 30)
Fig. 4 is a cross-sectional view showing the configuration of the cathode film. As shown in Fig. 4, the cathode film 30 includes an insulating substrate 31 and a plurality of conductive fillers 32. The insulating substrate 31 is a film having a predetermined thickness and contains a resin material. The conductive fillers 32 are metal particles. Note that the conductive fillers 32 are not limited to metal, but are preferably metal.

With this configuration, the cathode film 30 is electrically conductive while the main body is insulating. Furthermore, because the cathode film 30 is not a metal foil, corrosion due to moisture, etc. is suppressed.

The insulating substrate 31 of the cathode film 30 may be thermosetting or thermoplastic, each with its own advantages. The advantages of each will be described later.

(Layered structure of multiple capacitor elements 20 and multiple cathode films 30)
The plurality of capacitor elements 20 and the plurality of cathode films 30 are arranged so that their respective flat film surfaces are approximately parallel to the top and bottom surfaces of the element body 11. The plurality of capacitor elements 20 and the plurality of cathode films 30 are alternately stacked in a direction perpendicular to the top and bottom surfaces (the height direction of the element body 11 (z-axis direction in the figure)). Note that, although the number of the plurality of capacitor elements 20 is three and the number of the plurality of cathode films 30 is four in FIG. 2, this is not a limitation.

At this time, the capacitor element 20 and the cathode film 30 adjacent to each other in the stacking direction are in contact. More specifically, the flat film surface of the cathode film 30 is in contact with the outer surface 230 of the outer layer CP23 of the capacitor element 20.

(Configuration of element body 11)
This laminate of the plurality of capacitor elements 20 and the plurality of cathode films 30 is covered with insulating resin 50. In this way, element body 11 is formed.

The end faces 211 of the multiple capacitor elements 20 are exposed to the outside of the element body 11 from the end face 111 of the element body 11. Furthermore, the end faces 311 of the multiple cathode films 30 are exposed to the outside of the element body 11 from the end face 112 of the element body 11.

(Configuration of terminal conductors)
The resin electrode 71 abuts against and covers the end face 111 of the element body 11. In this way, the resin electrode 71 is connected to the end faces 211 of the plurality of capacitor elements 20. The external electrode 81 has a laminated structure of an electrode film 811 and an electrode film 812. The electrode film 811 covers the outer surface of the resin electrode 71, and the electrode film 812 covers the outer surface of the electrode film 811. The resin electrode 71 and the external electrode 81 form a first terminal conductor.

The resin electrode 72 abuts against and covers the end face 112 of the element body 11. This connects the resin electrode 72 to the end faces 311 of the multiple cathode films 30. The external electrode 82 has a laminated structure of electrode films 821 and 822. The electrode film 821 covers the outer surface of the resin electrode 72, and the electrode film 822 covers the outer surface of the electrode film 821. The resin electrode 72 and the external electrode 82 form a second terminal conductor.

The above configuration realizes the solid electrolytic capacitor 10.

(Connection structure between solid electrolyte layer and cathode film 30)
In the above configuration, the contact portion between the outer layer CP 23 and the cathode film 30 has the following structure: Fig. 5 is an enlarged cross-sectional view of the contact portion between the outer layer CP and the cathode film.

As shown in Figure 5, in the region 323 where the outer layer CP23 and the cathode film 30 contact each other, the outer layer CP23 and the cathode film 30 are mixed together. "Mixed together" here means that the ratio of the resin portions originating from the outer layer CP23 to the resin portions originating from the cathode film 30 in the stacking direction of the outer layer CP23 and the cathode film 30 (the z-axis direction in Figure 5) is not uniform in a plane perpendicular to the stacking direction (the two-dimensional region determined by the x-axis and y-axis directions in Figure 5), and the portions originating from the outer layer CP23 and the portions originating from the cathode film 30 are intertwined. In other words, a resin solid solution region is formed.

In addition, when the resin material constituting the outer layer CP23 is the same as the resin material constituting the cathode film 30, as shown by the solid line in Figure 5, no clear boundary line is visible, but in reality, the outer layer CP23 and the cathode film 30 are mixed together.

This configuration increases the contact area between the outer layer CP23 and the cathode film 30, improving adhesive strength. Furthermore, the occurrence of a clear interface between the outer layer CP23 and the cathode film 30 due to differences in physical properties is suppressed, and interfacial peeling between the outer layer CP23 and the cathode film 30 is suppressed.

This allows the solid electrolytic capacitor 10 to suppress corrosion of the cathode and prevent separation and insulation between the cathode and the solid electrolyte layer. While it is preferable that the resin material of the outer layer CP23 and the resin material of the cathode film 30 are exactly the same, they may have similar compositions as long as they achieve the above-mentioned effects.

The multiple cathode films 30 are also connected to a resin electrode 72. In this configuration, both the cathode films 30 and the resin electrode 72 contain a resin material (resin component). This reduces the difference in physical properties between the cathode films 30 and the resin electrode 72, preventing separation and insulation between the cathode films 30 and the resin electrode 72.

(Method for manufacturing solid electrolytic capacitor 10)
The solid electrolytic capacitor 10 having the above-described configuration is manufactured, for example, as follows. Fig. 6 is a flowchart showing an example of a schematic flow of a method for manufacturing a solid electrolytic capacitor according to this embodiment. Fig. 7(A) is an external perspective view of a capacitor element sheet, and Fig. 7(B) is an external perspective view of a cathode sheet. Fig. 8 is an external perspective view of a laminate (sheet-type capacitor laminate) of a capacitor element sheet and a cathode sheet.

A capacitor element sheet 20M is formed (S11). As shown in Figure 7(A), the capacitor element sheet 20M is a sheet in which a plurality of capacitor elements 20 are arranged two-dimensionally. The specific configuration of the plurality of capacitor elements 20 is as described above, and includes an anode electrode 21, a dielectric layer 210, an inner layer CP22, and an outer layer CP23, with an insulator layer 500 formed for the inner layer CP22 and the outer layer CP23.

A cathode sheet 30M is formed (S12). As shown in Figure 7(B), the cathode sheet 30M is a sheet in which multiple cathode films 30 are arranged two-dimensionally. The arrangement pitch of the multiple cathode films 30 is the same as the arrangement pitch of the multiple capacitor elements 20.

The plurality of capacitor element sheets 20M and the plurality of cathode sheets 30M are stacked in order and heated and pressed together (S13). More specifically, the plurality of capacitor element sheets 20M and the plurality of cathode sheets 30M are stacked so that the outer surfaces 230 of the plurality of outer layers CP23 of the capacitor element sheets 20M adjacent in the stacking direction face and abut against the cathode film 30 of the cathode sheet 30M. This forms a sheet-type capacitor laminate.

This sheet-type capacitor laminate is then heated and pressurized. This heating and pressurization deforms the portion at a predetermined depth from the contact surface between the outer layer CP23 and the cathode film 30, resulting in a state in which the portion originating from the outer layer CP23 and the portion originating from the cathode film 30 are intertwined and mixed (resin solid solution region: see Figure 5).

The sheet-type capacitor laminate is cut along cutting lines CL1 and CL2 as shown in Figure 8 to separate the capacitors (S14). Because the cathode sheet 30M (cathode film 30) is made of resin, burrs on the cut surface are minimized. This helps prevent undesirable short circuits.

The individualized capacitor laminate is coated with insulating resin 50 (S15). At this time, the insulating resin 50 is heated and pressurized. This solidifies the insulating resin 50, forming the element body 11 of the solid electrolytic capacitor 10. At this time, by appropriately adjusting the temperature during the thermocompression bonding of the insulating resin 50, the thermocompression bonding of the insulating resin 50 can be used to appropriately adjust the intricately mixed state of the portion based on the outer layer CP23 and the portion based on the cathode film 30.

Terminal conductors are formed on the end faces 111 and 112 of the element body 11 (S16). More specifically, a resin electrode 71 is formed on the end face 111 of the element body 11, and electrode films 811 and 812 are formed on the surface of the resin electrode 71. A resin electrode 72 is formed on the end face 112 of the element body 11, and electrode films 821 and 822 are formed on the surface of the resin electrode 72.

By using the manufacturing method described above, the solid electrolytic capacitor 10 can be manufactured without using a conductive adhesive between the outer layer CP23 and the cathode film 30. This makes it possible to easily and reliably manufacture a solid electrolytic capacitor 10 that has strong adhesive strength between the outer layer CP23 and the cathode film 30 and suppresses peel insulation.

(Physical properties of cathode film 30)
(When the insulating substrate 31 is made of a thermosetting resin and the content of the conductive filler 32 is low)
Since the insulating substrate 31 has high fluidity before heating, the resin solid solution region becomes large (in the thickness direction), and the adhesive strength between the outer layer CP 23 and the cathode film 30 becomes high.

In addition, because the insulating substrate 31 is a thermosetting resin, the shape of the cathode film 30 is highly retained when it is heated and compressed and cooled, i.e., after the resin has dissolved. This increases the stability of the adhesion between the cathode film 30 and the outer layer CP23, and improves the long-term reliability of the solid electrolytic capacitor 10.

(When the insulating substrate 31 is made of a thermosetting resin and the content of the conductive filler 32 is high)
Because the insulating base material 31 is a thermosetting resin, the shape of the cathode film 30 is highly maintainable when the insulating base material 31 is heated and compressed and then cooled, i.e., after the resin has dissolved. This improves the stability of the adhesion between the cathode film 30 and the outer layer CP 23, and increases the long-term reliability of the solid electrolytic capacitor 10.

In addition, since the content of conductive filler 32 is high, the cathode film 30 has high strength and can be firmly adhered even in areas with a small amount of resin solid solution.

The specific values indicating whether the conductive filler 32 content is low or high can be set appropriately based on the fluidity and strength of the cathode film 30. As an example, from the perspective of improving fluidity, a conductive filler 32 content of 30 volume percent or less is defined as a low conductive filler 32 content, and from the perspective of improving strength, a conductive filler 32 content of 70 volume percent or more is defined as a high conductive filler 32 content. Note that these are merely examples and can be adjusted appropriately depending on, for example, the physical properties and thickness of the insulating substrate 31, and can be set appropriately depending on the impact of the conductive filler 32 content on the fluidity or strength of the cathode film 30.

(When the insulating substrate 31 is made of thermoplastic resin)
Since the insulating base material 31 has high fluidity when heated, the resin solid solution region becomes larger (in the thickness direction), and the adhesive strength between the outer layer CP 23 and the cathode film 30 increases. In addition, no additional processing is required on the material side for heat melting.

10: Solid electrolytic capacitor 11: Body 20: Capacitor element 20M: Capacitor element sheet 21: Anode electrode 22: Inner layer CP
23: Outer layer CP
30: Cathode film 30M: Cathode sheet 31: Insulating substrate 32: Conductive filler 50: Insulating resin 71, 72: Resin electrodes 81, 82: External electrodes 111, 112: End surface 210: Dielectric layers 211, 212: End surfaces 213, 214: Flat film surface 230: Outer surface 311: End surface 323: Region 500: Insulator layers 811, 812, 821, 822: Electrode film

Claims (7)

a plurality of capacitor elements each including a film-like valve metal element, a dielectric layer, and a solid electrolyte layer;
a plurality of cathodes;
Equipped with
the cathode includes a second resin base material and a second conductive material,
the plurality of capacitor elements and the plurality of cathodes are alternately stacked in a state in which the solid electrolyte layer and the cathode are in contact with each other,
a region where the solid electrolyte layer and the cathode are in contact with each other includes a portion where the solid electrolyte layer and the cathode are mixed;
Solid electrolytic capacitor. The second resin base material is a thermosetting resin.
The solid electrolytic capacitor according to claim 1 . The second resin substrate is a thermoplastic resin.
The solid electrolytic capacitor according to claim 1 . a capacitor laminate in which the plurality of capacitor elements and the plurality of cathodes are laminated;
an insulating resin that insulates and seals the capacitor laminate, exposing the valve metal elements at one end surface and the cathodes at the other end surface;
a first terminal conductor formed on the one end surface and connected to the plurality of valve metal elements;
a second terminal conductor formed on the other end surface and connected to the cathode;
Equipped with
the second terminal conductor includes a resin electrode in contact with the other end surface;
4. The solid electrolytic capacitor according to claim 1. forming a capacitor element sheet in which capacitor elements each including a film-like valve metal element, a dielectric layer, and a solid electrolyte layer are arranged;
forming a cathode sheet on which a plurality of cathodes are arranged;
laminating the capacitor element sheet and the cathode sheet;
a step of heat-pressing the laminated capacitor element sheet and the cathode sheet together;
The method for manufacturing a solid electrolytic capacitor includes the steps of: The cathode sheet includes a resin substrate made of a thermosetting resin.
The method for manufacturing the solid electrolytic capacitor according to claim 5 . The cathode sheet includes a resin substrate made of a thermoplastic resin.
The method for manufacturing the solid electrolytic capacitor according to claim 5 .