JP2003229330A - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor that is appropriate to cope with both high capacity and low ESR (equivalent series resistance). <P>SOLUTION: Two conductive polymer films forming one portion of a conductive polymer layer are formed in two solutions having different pHs due to electrolytic oxidation polymerization or chemical oxidation polymerization. In this manner, in the solid electrolytic capacitor, the conductive polymer layer includes a first conductive polymer film 301 made of a plurality of particles where an average particle size is relatively small, and a second conductive polymer film 302 having an average particle size that is larger than the average particle size of the first conductive polymer film, the second film 302 is formed while covering openings of a plurality of holes 101 formed in an anode conductor 1, and the first film 301 is formed so that at least one portion of the first film 301 is arranged inside the plurality of holes, or is arranged to be the outermost film of the conductive polymer layer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor and its manufacturing method.

[0002]

2. Description of the Related Art In recent years, in electronic equipment in which a solid electrolytic capacitor is used, the frequency of integrated circuits is increasing and the current is increasing significantly. Accordingly, the equivalent series resistance (equivalent series re
There is a demand for a solid electrolytic capacitor having a low sistance (hereinafter abbreviated as “ESR”), a large capacitance, and a small loss.

For a solid electrolytic capacitor, a conventional method for manufacturing an internal electrode (that is, a capacitor element) of the solid electrolytic capacitor will be illustrated. First, the valve metal (valv
e metal; for example, tantalum metal) is anodized in an electrolyte solution such as phosphoric acid, and an oxide film layer (dielectric layer) is formed on the surface.
To form. Next, a solid electrolyte is formed on the surface of this oxide film layer. As a solid electrolyte, for example, manganese dioxide that can be formed by immersing an anode conductor in a manganese nitrate solution, pulling it up, and firing it is known. Finally, a cathode conductor is formed on the solid electrolyte. As the cathode conductor, for example, a laminate of a carbon layer and an exterior silver conductive resin layer is used. To the capacitor element, an anode lead terminal is connected to the anode conductor and a cathode lead terminal is connected to the cathode conductor for electrical connection to the outside.

The ESR can be influenced by the resistance of each of the above-mentioned members, but the solid electrolyte has the most room for consideration of the resistance. In order to lower the resistance of the solid electrolyte, manganese dioxide (conductivity 0.1S
It has been proposed and put into practical use that a conductive polymer material having a conductivity higher than that of the conductive polymer material is used. For example, if polypyrrole is used, a conductivity of about 100 S / cm can be realized. As the monomer for forming the conductive polymer material, aniline, thiophene, 3,4-ethylenedioxythiophene, etc. are known in addition to pyrrole. The method of forming the conductive polymer layer can be roughly classified into chemical oxidative polymerization and electrolytic oxidative polymerization.

Contact resistance between layers also affects the ESR. In Japanese Patent Laid-Open No. 2000-232036 by the applicant, conductive polymer particles are mixed in the conductive polymer layer, and the contact resistance between the conductive polymer layer and the cathode conductor is reduced due to the unevenness formed by the particles. It is disclosed. In the method described in this publication, the conductive polymer layer is formed by chemical oxidative polymerization using a polymerization solution in which conductive polymer particles are dispersed.

It has also been proposed to form the conductive polymer layer in the form of particles in order to increase the capacity of the capacitor. Japanese Unexamined Patent Publication No. 8-45790 discloses that particulate polypyrrole having a particle size of 0.2 μm or less is formed by chemical oxidative polymerization using a polymerization solution in which a mixing molar ratio of a monomer to an oxidizing agent is 1 or more. ing. When the particle size of the conductive polymer layer is suppressed, peeling of this layer is suppressed, and the capacity potentially possessed by the dielectric layer is easily extracted.

It is known that the electroconductive polymer layer formed by electrolytic oxidative polymerization has a higher electric conductivity than the electroconductive polymer layer formed by chemical oxidative polymerization, resulting in a good quality film. However, when the electrolytic oxidation polymerization is repeatedly performed using a single electrolytic solution, the conductivity of the conductive polymer layer gradually changes. Japanese Patent Application Laid-Open No. 11-121279 discloses that in order to suppress this change, electrolytic oxidation polymerization is performed while maintaining the pH of the polymerization solution within a predetermined range.

In Japanese Patent Laid-Open No. 2000-297142,
It is disclosed that the pH of the polymerization solution used for electrolytic oxidation polymerization is 5 or less. Here, the speed of the polymerization reaction is improved by lowering the pH.

[0009]

[Patent Document 1] Japanese Patent Laid-Open No. 2000-232036

[Patent Document 2] Japanese Patent Laid-Open No. 8-45790

[Patent Document 3] Japanese Patent Laid-Open No. 11-112279

[Patent Document 4] Japanese Patent Laid-Open No. 2000-297142

[0010]

As described above, many studies have been conducted on the solid electrolytic capacitor using the conductive polymer layer as the solid electrolyte. However, compatibility between low ESR and large capacitance in a solid electrolytic capacitor and realization of low loss have not yet been sufficiently achieved.

[0011]

Therefore, the present invention is directed to an anode conductor made of a valve metal, a dielectric layer formed on the surface of the anode conductor, and a high conductivity layer formed on the surface of the dielectric layer. A method for producing a solid electrolytic capacitor including a solid electrolyte including a molecular layer, the method comprising: forming a first conductive polymer film, which is a part of the conductive polymer layer, in a first solution; Forming a second conductive polymer film, which is another part of the conductive polymer layer, in a second solution having a pH lower than that of the first solution. Membrane and second
Provided is a method for manufacturing a solid electrolytic capacitor, which comprises forming a conductive polymer film together by electrolytic oxidation polymerization. The first and second conductive polymer films may be formed by chemical oxidative polymerization instead of electrolytic oxidative polymerization.

Further, the present invention provides an anode conductor made of a valve metal, a dielectric layer formed on the surface of the anode conductor, and a solid electrolyte formed on the surface of the dielectric layer and containing a conductive polymer layer. And a first conductive polymer film including a plurality of holes, wherein the anode conductor includes a plurality of holes, and an average particle size of the plurality of particles. A second conductive polymer film having an average particle size larger than the diameter, the second conductive polymer film is formed to cover the openings of the plurality of holes, and the first conductive polymer film However, at least a part thereof is formed so as to be arranged inside the plurality of holes, or is provided as an outermost film of the conductive polymer layer.

[0013]

According to the present invention, there is provided a solid electrolytic capacitor suitable for achieving both low ESR and large capacitance, and a method for manufacturing the same. The state of the conductive polymer film formed by electrolytic oxidation polymerization is the p of the polymerization solution used for the polymerization.
Depends on H. Similarly, the state of the conductive polymer film formed by the chemical oxidative polymerization also depends on the pH of the polymerization solution used for the polymerization. It should be noted that 2 of a solution containing a monomer (monomer solution) and a solution containing an oxidant (oxidant solution)
When chemical oxidative polymerization is performed using a liquid, p of the monomer solution
When the pH of H and the oxidant solution are different, p of the polymerization solution
H shall refer to the pH of the monomer solution that has a greater effect on the activity of the monomers that form the backbone of the polymer.

Generally, a conductive polymer film formed from a polymerization solution having a relatively high pH has finer particles than a conductive polymer film formed from a polymerization solution having a relatively low pH, and its specific surface area is It becomes relatively large. The conductive polymer film formed from the polymerization solution having a low pH may be observed as one continuous body rather than as a particle. In addition,
In the present specification, the term “average particle size” refers to a single particle, that is, a film observed as a continuous film in which grain boundaries are not observed, and the particle size of the single particle is referred to as “average particle size”. Apply by replacing.

Conventionally, in a polymerization solution for electrolytic oxidative polymerization, in order to keep the characteristics of the membrane constant, as described above,
Was known to be adjusted within a predetermined range. Also,
It was also known that the reaction rate of electrolytic oxidative polymerization was higher in the low pH range. However, using a plurality of polymerization solutions prepared so as to have different pHs, preferably while considering the shape of the pores formed on the surface of the anode conductor, E
It has not been proposed yet to stack a plurality of conductive polymer films whose film shapes are adjusted so that SR lowering and capacity increasing can be pursued at the same time. The conductive polymer film in the form of fine particles is advantageous for filling the pores and expanding the outer surface of the layer. On the other hand, a conductive polymer film in the form of large particles or a continuous film is advantageous for lowering the resistance of the layer.

In consideration of this, in one embodiment of the present invention, the second conductive polymer film having a relatively large average particle size is provided on the first conductive polymer film having a relatively small average particle size. It is formed. In other words, the second conductive polymer film formed from the polymerization solution having a relatively low pH is formed on the first conductive polymer film formed from the polymerization solution having a relatively high pH. In this case, the first conductive polymer film may be formed such that at least a part thereof is arranged inside the plurality of holes formed on the surface of the anode conductor. This is because, in order to increase the capacity of the solid electrolytic capacitor, especially to secure the capacity in the low frequency band, it is preferable to fill the conductive polymer to the deep part of the pores. Further, when the second conductive polymer film is formed so as to cover the openings of the plurality of holes formed in the anode conductor,
It is easy to realize high capacity and low ESR, and it is also easy to secure capacity in a high frequency band.

In another aspect of the present invention, the first conductive polymer film having a relatively small average particle size is formed on the second conductive polymer film having a relatively large average particle size. In other words, the second formed from the polymerization solution having a relatively low pH.
A first conductive polymer film formed of a polymerization solution having a relatively high pH is formed on the conductive polymer film. In this case, the first conductive polymer film may be arranged as the outermost film of the conductive polymer layer, that is, as the film in contact with the cathode conductor.
This is because it is preferable to increase the contact area between the conductive polymer layer and the cathode conductor to reduce the contact resistance in order to reduce the ESR of the solid electrolytic capacitor, particularly in the high frequency band. Here again, the openings of the plurality of holes formed in the anode conductor may be covered with the second conductive polymer film.

In a preferred embodiment of the present invention, a third conductive polymer film, which is another part of the conductive polymer layer, is further formed. This film may be formed in a third solution having a higher pH than the second solution for forming the second conductive polymer film. By using this film forming method, the third conductive polymer film can be composed of a plurality of particles having an average particle size smaller than that of the second conductive polymer film. The third conductive polymer film may also be formed by the same polymerization method (electrolytic oxidation polymerization or chemical oxidation polymerization) as the first and second conductive polymer films.

In the case of forming the third conductive polymer film, for example, first, the first conductive polymer film is formed so that at least a part of the first conductive polymer film is arranged inside the plurality of holes formed in the anode conductor. Then, the second conductive polymer film may be formed to cover the openings of the plurality of holes, and the third conductive polymer film may be formed to be the outermost film of the conductive polymer layer. . According to this preferable mode, it is possible to simultaneously fill the pores with the conductive polymer and increase the contact area with the cathode conductor. In this case, the third conductive polymer film functions as a film for expanding the surface of the second conductive polymer film.

In the production method of the present invention, the difference between the pH of the first solution and the pH of the second solution is, for example, suitably 1.5 or more, preferably 2.5 or more, more preferably 5 or more.
Although not particularly limited, the first solution is preferably alkaline and the second solution is preferably acidic. The solvent contained in the polymerization solution used in the method of the present invention is typically water, but is not limited thereto. A mixed liquid of water and an organic solvent (preferably an organic solvent compatible with water) ), An organic solvent such as alcohol such as ethanol or isopropanol.

The average particle size of the particles forming the conductive polymer film to be formed in the pores depends on the diameter of the pores, but generally 0.1 μm or less is suitable and 0.07 μm or less. Is preferable, and 0.01 μm to 0.1 μm is particularly preferable. More specifically, 30% or less, particularly 20% or less, of the hole diameter corresponding to the mode of the volume distribution ratio of the hole diameters of the plurality of holes formed in the anode conductor is preferable. The volume distribution ratio of pore diameter can be measured by a pore distribution measuring device.

The average particle size of the particles forming the conductive polymer film formed as the outermost film is generally 5 μm or less, and more preferably 1 μm or less.

The particle size of the particles constituting the conductive polymer film is
For example, in the case of electrolytic oxidative polymerization, it is also affected by the composition and types of the solvent of the polymerization solution, the dopant, the monomer, etc., and the difference in the polymerization rate depending on the applied voltage. However, the adjustment of the particle size by pH has a wider range that can be performed without impairing the preferable manufacturing conditions of the solid electrolytic capacitor than the adjustment by these other factors, and has the advantage that it can be performed in addition to the adjustment by different compositions and types. is there.

Generally, the improvement of the filling rate of the conductive polymer in the pores becomes more important as the depth of the pores becomes deeper. The average depth of the holes formed in the anode conductor is 4
If it exceeds 0 μm, the average particle size is relatively small,
The necessity of the conductive polymer film formed so that at least a part thereof is arranged inside the plurality of holes becomes high. on the other hand,
The average depth of the holes formed in the anode conductor is 40μ.
When it is m or less, a great effect may not be expected in the formation of the conductive polymer film. In the latter case,
Emphasizing reduction of manufacturing cost, the opening of the pores is covered with a conductive polymer film having a relatively large average particle size as the first step of electrolytic oxidation polymerization, and the conductive layer having a relatively small average particle size is used as the second step. In some cases, the contact resistance with the cathode conductor should be reduced by the conductive polymer film.

That is, according to another aspect of the present invention, an anode conductor made of a valve metal, a dielectric layer formed on the surface of this anode conductor, and a conductive layer formed on the surface of this dielectric layer are provided. A method for producing a solid electrolytic capacitor including a solid electrolyte including a molecular layer, wherein at least a part of the conductive polymer layer is formed by electrolytic oxidation polymerization, and a depth of a plurality of holes formed in the anode conductor. When the average value of is more than 40 μm, as a first step of the electrolytic oxidative polymerization, at least a part of the first conductive polymer film, which is a part of the conductive polymer layer, in the first solution is As a second step of the electrolytic oxidative polymerization, a second conductive polymer film, which is another part of the conductive polymer layer, is formed so as to be arranged inside the plurality of holes, and the second solution is formed from the first solution. Second with a very low pH
When it is formed so as to cover the openings of the plurality of holes in the solution and the average value of the depth of the plurality of holes is 40 μm or less, as the first step of the electrolytic oxidation polymerization, the conductive polymer layer First part of the second conductive polymer film that becomes a part
In the solution, a plurality of holes formed in the anode conductor are formed so as to cover the openings of the plurality of holes, and as a second step of the electrolytic oxidation polymerization, the first conductive high layer serving as another part of the conductive polymer layer is formed. Provided is a method for manufacturing a solid electrolytic capacitor, which comprises forming a molecular film as an outermost film of the conductive polymer layer in a second solution having a higher pH than the first solution. Here again, the first and second conductive polymer films may be formed by chemical oxidative polymerization instead of electrolytic oxidative polymerization.

Hereinafter, preferred embodiments of the present invention will be further described with reference to the drawings.

As shown in FIG. 1, a capacitor element generally has a structure in which a dielectric layer 2, a solid electrolyte 3, and a cathode conductor 4 are laminated in this order on an anode conductor 1. The cathode conductor 4 may have a two-layer structure including a carbon layer 5 and an exterior silver conductive resin layer 6. The anode conductor 1 is formed of a metal plate having a valve action, a foil or a sintered body made of fine particles of a wire and a metal having a valve action, or a metal foil subjected to surface expansion treatment by etching, for example. Valve metals include tantalum, aluminum, titanium, niobium, zirconium or alloys of these metals, preferably tantalum,
At least one selected from aluminum and niobium
The seed may be used, and for example, a capacitor using tantalum powder and niobium foil or wire may be used.

The dielectric layer 2 is an oxide film obtained by electrolytically oxidizing the surface of the anode conductor 1, and is also formed in voids such as a sintered body and an etching foil. The thickness of the oxide film can be adjusted by the voltage of electrolytic oxidation.

The solid electrolyte 3 contains at least a conductive polymer layer. The conductive polymer layer is, for example, polypyrrole, polythiophene, polyaniline, poly-3, 4,
-Ethylenedioxythiophene, in particular pyrrole, thiophene and at least one polymer selected from 3,4-ethylenedioxythiophene and derivatives thereof,
It is preferable to include. The conductive polymer layer can be formed by chemical oxidative polymerization using a monomer such as pyrrole, a dopant such as alkylnaphthalenesulfonic acid, and an oxidizing agent such as iron (III) sulfate and ammonium persulfate.
Instead of chemical oxidative polymerization, or together with chemical oxidative polymerization, it may be formed by electrolytic oxidative polymerization whose details will be described later.

The solid electrolyte 3 includes, for example, an oxide conductor such as manganese dioxide or ruthenium oxide, TCNQ.
An organic semiconductor such as a complex (7,7,8,8-tetracyanoquinodimethane complex salt) may be contained.

FIG. 2 shows an enlarged view of the vicinity of the pores 101 of the anode conductor 1. In this solid electrolytic capacitor, the solid electrolyte contains a first conductive polymer film 301 and a second conductive polymer film 302 both formed by electrolytic oxidation polymerization in addition to the conductive film 300 formed by chemical oxidation polymerization. , And a third conductive polymer film 303. The conductive film 300 is, for example, manganese dioxide formed by thermal decomposition of manganese nitrate, or a conductive polymer film formed by, for example, chemical oxidative polymerization. Three membranes 301
The electro-oxidative polymerization to form ~ 303 is performed utilizing the conductivity of the membrane 300.

In the electrolytic oxidative polymerization, the first and third conductive polymer films 301, 30 are prepared from a polymerization solution having a relatively high pH.
3, the second conductive polymer film 302 is formed from a polymerization solution having a relatively low pH. As a result, the membrane 30
1, 303 is a fine grain, the film 302 has a large grain size,
In some cases, the whole is formed into one particle, that is, a continuous film. The second conductive polymer film 301 is such that at least a part of the first conductive polymer film 301 enters the inside of the pores 101 and preferably substantially covers the surface of the dielectric layer 2 in the pores 101. The third conductive polymer film 303 is formed in this order as an outermost film in contact with the cathode conductor 4 so that 302 covers the opening of the pore 101.

When the conductive polymer film is arranged in this way,
The first conductive polymer film 301 can bring out the capacitance originally possessed by the dielectric film 2, and the second conductive polymer film 30
2 can reduce the resistance of the solid electrolyte, and the third conductive polymer film 303 can reduce the contact resistance with the cathode conductor 4.

The first conductive polymer film 301 has a great effect on its formation when the average value of the depths 102 of the pores exceeds 40 μm. In a capacitor having a structure in which a powder using tantalum or niobium as a valve metal is combined with a lead wire or a foil, the average depth of pores often exceeds 40 μm. Therefore, when tantalum or niobium is used as the valve metal, the formation of the first conductive polymer film 301 often brings a remarkable effect to increase the capacity. As described above, the average particle size of the film 301 is preferably determined in relation to the mode of the pore size of the pores 101, but is generally 0.1 μm or less. In order to realize this average particle diameter, the pH of the polymerization solution for forming the first conductive polymer film 301 depends on the polymerization method and the kind of the monomer, but is 7 or more, for example, by electrolytic oxidation polymerization. Sometimes 7
It is recommended to set to 10.

When an aluminum etching foil is used as the valve metal, the average depth of the pores may be 40 μm or less depending on the method of forming the pores. In this case, the formation of the first conductive polymer film 301 may be omitted.

The second conductive polymer film 302 covers the openings of the plurality of holes, and in other words, the outer surface of the film is always higher than the outermost (highest position) of the dielectric layer 2. Then, the film may be deposited to such an extent that the outer surface of the film does not enter the inside of the pores (see FIG. 2). The second conductive polymer film 302 has few grain boundaries and is the anode conductor 1.
The whole is wrapped as a continuous film to reduce the resistance of the entire conductive polymer layer. The pH of the polymerization solution for forming the second conductive polymer film 302 depends on the polymerization method and the like, but may be set to 7 or less, for example, 2 to 7 in the case of electrolytic oxidation polymerization.

Since the outer surface of the second conductive polymer film 302 is relatively flat, it is desirable to form the third conductive polymer film 303 to reduce the contact resistance with the cathode conductor. The average particle diameter of the third conductive polymer film 303 is the same as the first conductive polymer film 3
It is not necessary to limit the average particle size to 01, and generally 5 μm or less can achieve the purpose of surface enlargement. Third
PH of polymerization solution for forming conductive polymer film 303
Depends on the polymerization method and the like, but is preferably set to 4.5 or more, for example, 4.5 to 10 when electrolytic oxidation polymerization is performed.

The ratio of the respective conductive polymer films 301 to 303 is not particularly limited, but when the second conductive polymer film is 1, it is expressed by the weight ratio and the first conductive polymer film 301 is displayed. Is 0.5 to 2 and the third conductive polymer film 303 is 0.
It is preferably 1 to 0.5. In the case of electrolytic oxidative polymerization, the weight ratio of each film is substantially proportional to the amount of current consumed to form the film, and can be controlled by this amount of current.

Due to the formation of the second conductive polymer film 302 having a relatively large average particle size, depletion 103 not filled with the conductive polymer may remain inside the pores 101. However, the characteristics of the solid electrolytic capacitor are better when the conductive polymer film 302 having a low resistance is formed at a relatively low pH, rather than continuously forming the fine conductive polymer particles and filling the pores. improves.

Here, the solid electrolytic capacitor in which the first to third conductive polymer films are formed by electrolytic oxidation polymerization has been described. However, it is possible to obtain the same effect as described above by chemical oxidative polymerization in which the pH is adjusted appropriately. However, the change in the characteristics of the conductive polymer film due to pH becomes more remarkable by electrolytic oxidative polymerization than by chemical oxidative polymerization.

The cathode conductor 4 may be, for example, a laminated body composed of a carbon layer 5 and an exterior silver conductive resin layer 6. The carbon layer 5 contains carbon particles as conductive particles,
The carbon particles maintain close electrical connection between the silver powder contained in the conductive resin layer 6 and the solid electrolyte layer 3.

Although omitted in FIG. 1, the capacitor element is
An anode lead terminal is connected to the anode conductor 1 and a cathode lead terminal is connected to the cathode conductor 4, and further sealed in an exterior resin such as an epoxy resin to form a solid electrolytic capacitor.

The arrangement of polymerizing electrodes in electrolytic oxidation polymerization will be described below with reference to FIGS.

3 to 7 show various examples of arrangement of polymerization electrodes in electrolytic oxidation polymerization. As shown in these figures, electrolytic oxidation polymerization involves immersing a film-forming matrix 10, a polymerization anode (positive electrode) 7 and a polymerization cathode (negative electrode) 8 on which a film is to be formed, in a polymerization solution 9. Then do. The anode 7 and the cathode 8 are connected to the power supply 12. Membrane forming base 10
Is specifically an anode conductor on which at least a dielectric layer is formed. Usually, the anode 7 is fixed near the film forming base 10. At this time, as shown in FIGS. 3 and 4, the anode 7 and the cathode 8 are preferably arranged such that at least a part of the film forming matrix 10 is interposed between the electrodes 7 and 8. In the arrangement shown in FIG. 7, the film forming base 10
The conductive polymer formed on the surface 11 of the cathode 8 side is easily grown on the cathode side, that is, in the direction away from the surface of the matrix 10. The direction of this film growth is the conductive polymer film on this surface. May affect the adhesion. The influence of the electrode arrangement becomes remarkable in a polymerization solution having a relatively low pH, for example, an acidic polymerization solution. This is because in a polymerization solution having a low pH (for example, less than 7), the conductive polymer grows quickly and the conductive polymer film is likely to be a continuous film.

That is, in the method of the present invention, the anode and the cathode are arranged so that at least a part of the film-forming matrix including the anode conductor and the dielectric layer is interposed between these electrodes, and the anode and the cathode are arranged. It is possible to form at least one film forming a conductive polymer layer, for example, at least one selected from a first conductive polymer film and a second conductive polymer film, by carrying out electrolytic oxidative polymerization. preferable.

As shown in FIGS. 5 and 6, a plurality of cathodes 8
In the case of arranging a and 8b, not only at least a part of the film forming base 10 is interposed between the anode 7 and one of the cathodes 8a (8b) (FIGS. 5 and 6), It should be arranged such that at least a part of the film forming base 10 is interposed between the anode 7 corresponding to the film forming base 10 and the cathode 8a closest to the anode 7 (FIG. 5). According to this arrangement, the electric field can be applied more effectively than when the film forming base 10 is arranged between the anode 7 and the cathode 8b relatively far (FIG. 6).

This arrangement is important in the actual manufacturing process when electrolytic oxidation polymerization is carried out using the same polymerization solution for a plurality of film-forming bases (FIG. 8). That is, a plurality of film forming bases 10 and a plurality of anodes (positive electrodes) 7 respectively corresponding to the plurality of film forming bases 10 are prepared, and for each of the plurality of anodes 7, the cathode (closest to the anode 7 It is preferable to interpose at least a part of the film-forming base 10 corresponding to the anode 7 between the negative electrode) 8 and the anode 7. This arrangement forms another aspect of the invention.

That is, the present invention provides an anode conductor made of a valve metal, a dielectric layer formed on the surface of the anode conductor, and a solid electrolyte formed on the surface of the dielectric layer and containing a conductive polymer layer. A method of manufacturing a solid electrolytic capacitor comprising: a plurality of film forming bases, and a plurality of film forming bases corresponding to each of the plurality of film forming bases, wherein the anode conductor on which at least the dielectric layer is formed in advance is used as a film forming base. An anode of, and for each of the plurality of anodes, by electrolytic oxidation polymerization by an arrangement in which at least a part of the film forming matrix corresponding to the anode is interposed between the cathode closest to the anode and the anode, Also provided is a method of manufacturing a solid electrolytic capacitor that forms at least a portion of a conductive polymer layer. According to this manufacturing method, a conductive polymer layer having excellent adhesion can be efficiently formed.

[0049]

[Examples] (Example 1) [Preliminary experiment] The influence of the difference in pH in electrolytic oxidation polymerization was confirmed. The produced solid electrolytic capacitor has the same configuration as that shown in FIG.

First, 1.4% of fine powder having a specific surface area of tantalum metal having a valve action of 70,000 μF · V / g was prepared.
mm × 3.0 mm × 3.8 mm, and vacuum-sintered in a form equipped with a tantalum wire lead for drawing out an anode to produce an anode conductor made of a sintered pellet. Next, this anode conductor was formed in a 5 wt% phosphoric acid aqueous solution at 90 ° C. under the condition of an applied voltage of 30 V to form a tantalum oxide film as a dielectric layer on the surface of the anode conductor. The average depth of the pores of this anode conductor is the thickness of the molded body (1.4 m
m), that is, 700 μm.

After washing and drying the anode conductor, a solid electrolyte was formed. Here, as the conductive polymer, poly-3,
It was decided to form 4-ethylenedioxythiophene. First, chemical oxidative polymerization was performed to impart conductivity to the dielectric layer. The polymerization solution was 3 g of 3,4-ethylenedioxythiophene, 70 g of an n-butanol solution containing 40% by weight of iron (III) alkylnaphthalenesulfonate, and n.
Prepared by mixing 10 g butanol. Chemical oxidation polymerization was performed by repeating the operation of immersing the anode conductor in this polymerization solution and drying it in the air at 40 ° C. to 150 ° C. three times. Sequentially, at a reforming voltage of 18 V, the concentration is about 0.0
The dielectric layer was repaired by re-chemical conversion in a 5% phosphoric acid solution.
Furthermore, the anode conductor is washed in pure water at about 90 ° C.
It was dried in the atmosphere at 0 ° C. Thus, an anode conductor having a dielectric layer and a conductive polymer film formed by chemical oxidative polymerization as a film-forming matrix for electrolytic oxidative polymerization was obtained.

The arrangement of electrodes for electrolytic oxidative polymerization is shown in FIG.
As shown in. Carbon fiber having a wire diameter of 50 μm was fixed in the vicinity of the film-forming base as an anode, and this was immersed in a polymerization solution together with the cathode. The polymerization solution was 100 g of a 40 wt% sodium alkylnaphthalene sulfonate aqueous solution,
3,4-ethylenedioxythiophene 10g, water 500
g and a predetermined amount of sulfuric acid were mixed and prepared. Here, the sulfuric acid was added so that the pH would be a predetermined value (2, 4.5, 7 or 10).

The electrolytic oxidative polymerization was carried out at an applied voltage of 2.5V. The polymerization time was adjusted so that the thickness of the conductive polymer layer on the surface layer of the film-forming matrix was about 20 μm.

Subsequently, the anode conductor on which the conductive polymer layer was formed was dipped in an aqueous suspension solution containing carbon fine particles and allowed to stand in the atmosphere at 130 ° C. for 30 minutes to dry and solidify the suspension solution. Thus, a carbon layer was formed on the conductive polymer layer. Furthermore, it is immersed in a silver paint solution, left at room temperature for 1 hour, and then pulled up to 145 ° C.
It was left to stand in the atmosphere for 1 hour to dry and solidify the silver paint solution. Thus, the exterior silver conductive resin layer was formed on the carbon layer.

Further, a cathode lead terminal was connected to a cathode conductor composed of a carbon layer and an exterior silver conductive resin layer with a silver conductive adhesive, and a tantalum wire pulled out from the anode conductor was welded to the anode lead terminal. Finally, the capacitor element was covered with epoxy resin to complete the solid electrolytic capacitor.

For each of the solid electrolytic capacitors thus obtained, the electrostatic capacity at frequencies of 120 Hz and 100 kHz and the E at frequencies of 100 kHz and 1 MHz.
SR and was measured. Furthermore, a voltage of 10 V was applied to each solid electrolytic capacitor, and the current after 1 minute was measured to obtain the leakage current. The results are shown in (Table 1). In (Table 1), the maximum value and the minimum value for 20 samples are shown in the upper part, and the average value is shown in the lower part.

[0057]

[Table 1]

As shown in (Table 1), the capacity at 120 Hz increased as the pH increased, and the capacity at 100 kHz increased as the pH decreased. This is 120Hz
It is possible to draw out the capacity in the high resistance region inside the pores in a low frequency band of about a certain degree, but when the frequency increases up to around 100 kHz, only the capacity in the low resistance region can be drawn out, and the resistance value of the conductive polymer itself is This is probably because the impact was relatively high. The fine granular conductive polymer formed at a high pH is likely to be filled in the pores, and peeling of the film due to film shrinkage due to drying hardly occurs. In contrast, low pH
The conductive polymer formed in step 1 has a low resistance value.

The ESR at 100 kHz was smaller as the pH was lower, and the ESR at 1 MHz was smaller as the pH was higher. As a result, it is more advantageous to lower the resistance value of the conductive polymer in the band of about 100 kHz to keep the current collecting effect high, but in the high frequency band of about 1 MHz, the influence of the contact resistance with the cathode conductor is more important. Suggests something to do.

When the electroconductive polymer layer actually formed by using each polymerization solution was observed by a scanning electron microscope (SEM), the electroconductive polymer layer became finer as the pH of the polymerization solution was higher. It could be confirmed. According to SEM observation, when the pH is 2, 7 and 10, the average particle diameters of the particles constituting each conductive polymer layer are 1.5 μm, 0.5 μm and 0.07 μm, respectively, and the maximum particle diameter is 20μ each
m, 5 μm and 1 μm. The film formed at pH 2 was substantially free of particles having a particle size equal to or smaller than the maximum particle size (1 μm) of the film formed at pH 10.
As described above, the conductive polymer film formed from the polymerization solution having a relatively low pH has a particle size larger than the maximum particle size of the plurality of particles forming the film formed of the relatively high conductive polymer film. It is preferable that it is composed of particles having the above or is formed as a single particle (in the form of a continuous film).

The leakage current decreased at low pH. It is considered that this is because a conductive polymer film having a large particle size is more excellent as a protective film against mechanical stress generated during terminal connection or molding of the exterior resin.

The pore distribution of the anode conductor produced above was measured using an automatic porosimeter. Specifically, it was measured using "Autopore IV9520 type" manufactured by Shimadzu Corporation.
The results are shown in Fig. 9. The mode of the pore size of this anode conductor is
It was about 0.35 μm. In order to further increase the specific surface area for increasing the capacity, for example, 100,000 μF · V
It is desirable to use a fine metal powder having a large specific surface area of up to / g or more. In this case, in order to draw out the capacity, the conductive polymer layer is further made into fine particles, for example, the maximum particle diameter is
m or less, and the average particle size is preferably 0.07 μm or less.

[Preparation of Sample] Based on the above results,
Electrolytic oxidative polymerization was carried out using two kinds of polymerization solutions having different pH.

Up to the formation of the conductive polymer film by chemical oxidative polymerization, the same procedure as in the above preliminary experiment was performed.

In the electrolytic oxidative polymerization, the polymerization solution, the arrangement of electrodes, the applied voltage, etc. were the same as in the above preliminary experiment.
However, here, electrolytic oxidative polymerization was carried out by sequentially using polymerization solutions having different pHs.

First, electrolytic oxidation polymerization was carried out for 40 minutes using a polymerization solution having a pH of 10 to form a first conductive polymer film,
Next, electrolytic oxidation polymerization was carried out for 15 minutes using a polymerization solution of pH 2 to form a second conductive polymer film. Hereinafter, in the same manner as the above preliminary experiment, a solid electrolytic capacitor (Sample 1)
Got

Separately from this, a first conductive polymer film was formed by performing electrolytic oxidative polymerization for 40 minutes using a polymerization solution having a pH of 10, and then performing electrolytic oxidative polymerization for 12 minutes using a polymerization solution having a pH of 2. A second conductive polymer film was formed, and electrolytic oxidation polymerization was further performed for 5 minutes using a polymerization solution having a pH of 7 to form a third conductive polymer film. Hereinafter, a solid electrolytic capacitor (Sample 2) was obtained in the same manner as the above preliminary experiment.

The total amount of electric current used for electrolytic oxidation polymerization was substantially the same in Samples 1 and 2. Regarding Sample 1, the amount of current consumed for electrolytic oxidation polymerization was 1 for the first conductive polymer film and 1 for the formation of the second conductive polymer film. Regarding Sample 2, the amount of current consumed for electrolytic oxidation polymerization was 1.25 for the first conductive polymer film, and 1.25 for the first conductive polymer film, similarly with the current amount for forming the second conductive polymer film being 1. The polymer film was 0.3. The ratio of the consumed current amount corresponds to the weight ratio of each conductive polymer film.

The samples 1 and 2 were measured in the same manner as in the preliminary experiment. The results are shown in (Table 2).

[0070]

[Table 2]

From Table 2, in both Samples 1 and 2, the capacitance was large and the ESR was small from the low frequency band to the high frequency band, and the leakage current was also suppressed.

Further, an ink containing tantalum powder as a paint was formed on both sides of a tantalum foil having a thickness of 25 μm so as to have a thickness of about 40 μm, and binder removal and vacuum sintering were performed to produce an anode conductor. The average depth of the pores of this anode conductor is 4
It is 0 μm. Using this anode conductor, a solid electrolytic capacitor was prepared in the same manner as in Sample 2 (Sample 3),
Further, another solid electrolytic capacitor was prepared in the same manner as in Sample 2 except that the same amount of the first conductive polymer film was formed using the same polymerization solution as the second conductive polymer film (Sample 4). Comparing the characteristics of both capacitors, Sample 4 was slightly inferior at a capacity of 120 Hz. However, the degree of deterioration of the characteristics due to the omission of the fine granular first conductive polymer film was much smaller than that of the solid electrolytic capacitor having deep tantalum valve metal pores.

Example 2 In Example 2, chemical oxidative polymerization was used as the polymerization method.

0.1 mol of pyrrole was used as a monomer in an aqueous solution containing 10% by volume of isopropyl alcohol.
/ L and alkyl naphthalene sulfonic acid 0.02 mol /
1 of Na salt was dissolved and sulfuric acid or sodium hydroxide was added thereto to prepare a monomer solution having a pH of 2, 4.5, 7, 10. On the other hand, isopropyl alcohol 10
Sodium persulfate 0.1 mol / l and Na salt of alkylnaphthalene sulfonic acid 0.05 mol / l were dissolved as an oxidizing agent in an aqueous solution containing 10% by volume, and sulfuric acid or sodium hydroxide was added thereto to adjust pH. 2, 4.
5, 7, and 10 oxidant solutions were prepared.

The anode conductor on which the dielectric layer was formed in the same manner as in Example 1 was immersed in the above-mentioned monomer solution of pH 2 and
A polypyrrole film was formed on the dielectric layer by immersing it in the oxidant solution of pH 2 described above, and further washed and dried. While repeating this polypyrrole film forming step 40 times, the anode conductor was appropriately re-formed in a phosphoric acid solution having a concentration of about 0.05% to restore the dielectric layer. Reforming voltage is 18
It was set to V. Next, the anode conductor was washed in pure water at about 90 ° C. and dried in the atmosphere at about 120 ° C. to form a conductive polymer layer. Hereinafter, a solid electrolytic capacitor was obtained in the same manner as in Example 1. In addition, a solid electrolytic capacitor was similarly obtained for each pH.

When the characteristics of these solid electrolytic capacitors were measured in the same manner as described above, the tendency of the characteristic changes of the solid electrolytic capacitors depending on the pH of the polymerization solution was found to be that of Example 1.
It became the same as. Here, the pH of the monomer solution and the oxidant solution are set to be the same in order to control the polymerization rate to be constant, but the form in which the present invention is applied to the chemical oxidative polymerization is not limited to this. The same tendency as above can be obtained only by adjusting the pH of the monomer solution.

Further, when poly-3,4-ethylenedioxythiophene is used instead of polypyrrole as the conductive polymer, the tendency of change in film quality depending on the pH of the polymerization solution for chemical oxidative polymerization is the same. became. However, poly-
Since the polymerization rate of 3,4-ethylenedioxythiophene is very slow, it is necessary to adjust the pH for forming the conductive polymer layer of each layer to be relatively small as compared with the case of pyrrole.

This poly-3,4-ethylenedioxythiophene film was prepared by mixing 100 g of a 40 wt% sodium alkylnaphthalenesulfonate aqueous solution, 10 g of 3,4-ethylenedioxythiophene and 500 g of water, and adding sulfuric acid as appropriate. Monomer solution and isopropyl alcohol 10
Oxidizing agent prepared by dissolving 0.1 mol / l of sodium persulfate and 0.05 mol / l of Na salt of alkylnaphthalenesulfonic acid as an oxidizing agent in an aqueous solution containing 10% by volume, and adding sulfuric acid or sodium hydroxide thereto. Formed with the solution.

[0079]

According to the present invention, it is easy to achieve both low ESR and large capacitance in a solid electrolytic capacitor and to realize low loss.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of internal electrodes (capacitor elements) in a solid electrolytic capacitor according to the present invention.

FIG. 2 is a partially enlarged view of the cross-sectional view of FIG.

FIG. 3 is a diagram showing an example of arrangement of polymerization electrodes used for carrying out the method of the present invention.

FIG. 4 is a diagram showing another example of arrangement of polymerization electrodes used for carrying out the method of the present invention.

FIG. 5 is a diagram showing another example of arrangement of the polymerization electrodes used for carrying out the method of the present invention.

FIG. 6 is a view showing still another example of the arrangement of the polymerization electrodes used for carrying out the method of the present invention.

FIG. 7 is a view showing still another example of the arrangement of the polymerization electrodes used for carrying out the method of the present invention.

FIG. 8 is a diagram showing an example of the arrangement of polymerization electrodes when the method of the present invention is simultaneously applied to a plurality of film-forming bases.

FIG. 9 is a diagram showing an example of a volume content distribution of pore diameters of pores formed in the anode conductor.

[Explanation of symbols]

1 Anode conductor 2 Dielectric layer 3 Solid electrolyte 4 cathode conductor 5 carbon layer 6 Exterior silver conductive resin layer 7 Polymerization anode (positive electrode) 8 Polymerization cathode (cathode) 9 Polymerization solution 10 Film forming matrix 301 First conductive polymer film 302 Second conductive polymer film 303 Third conductive polymer film

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiko Nakata             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd.

Claims (20)

[Claims] 1. A solid including an anode conductor made of a valve metal, a dielectric layer formed on the surface of the anode conductor, and a solid electrolyte formed on the surface of the dielectric layer and containing a conductive polymer layer. A method of manufacturing an electrolytic capacitor, comprising a step of forming a first conductive polymer film which is a part of the conductive polymer layer in a first solution, and another part of the conductive polymer layer. And a second conductive polymer film having a pH lower than the pH of the first solution.
A step of forming in a solution, wherein the first conductive polymer film and the second conductive polymer film are both formed by electrolytic oxidation polymerization. 2. The first conductive polymer film and the second conductive polymer film.
The method for producing a solid electrolytic capacitor according to claim 1, wherein both of the conductive polymer films are formed by chemical oxidative polymerization instead of electrolytic oxidative polymerization. 3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the second conductive polymer film is formed on the first conductive polymer film. 4. The first conductive polymer film is formed such that at least a part of the first conductive polymer film is arranged inside a plurality of holes formed in the anode conductor, and the second conductive polymer film is formed as described above. The method for manufacturing a solid electrolytic capacitor according to claim 3, wherein the solid electrolytic capacitor is formed so as to cover the openings of the plurality of holes. 5. The third conductive polymer film, which is another part of the conductive polymer layer, has a higher pH than that of the second solution.
The method for producing a solid electrolytic capacitor according to claim 3, further comprising a step of forming the second conductive polymer film on the second conductive polymer film in a third solution containing 6. The first conductive polymer film is formed such that at least a part of the first conductive polymer film is arranged inside a plurality of holes formed in the anode conductor, and the second conductive polymer film is formed by the method described above. The method for producing a solid electrolytic capacitor according to claim 5, wherein the third conductive polymer film is formed so as to cover the openings of the plurality of holes, and the third conductive polymer film is formed as an outermost film of the conductive polymer layer. 7. The method for producing a solid electrolytic capacitor according to claim 1, wherein the first conductive polymer film is formed on the second conductive polymer film as an outermost film of the conductive polymer layer. 8. The pH of the first solution and the p of the second solution
The method for producing a solid electrolytic capacitor according to claim 1, wherein the difference from H is 2.5 or more. 9. The method for producing a solid electrolytic capacitor according to claim 1, wherein the first solution is alkaline and the second solution is acidic. 10. A positive electrode and a negative electrode are arranged such that at least a part of a film forming matrix including the anode conductor and the dielectric layer is interposed between these electrodes, and the positive electrode and the negative electrode. The method for producing a solid electrolytic capacitor according to claim 1, wherein at least one selected from the first conductive polymer film and the second conductive polymer film is formed by performing electrolytic oxidation polymerization using. 11. A plurality of film forming bases and a plurality of positive electrodes corresponding to each of the plurality of film forming bases are prepared, and for each of the plurality of positive electrodes, a negative electrode closest to the positive electrode and The method for producing a solid electrolytic capacitor according to claim 10, wherein at least a part of the film forming matrix corresponding to the positive electrode is interposed between the positive electrode and the positive electrode. 12. A solid comprising an anode conductor made of a valve metal, a dielectric layer formed on the surface of the anode conductor, and a solid electrolyte formed on the surface of the dielectric layer and containing a conductive polymer layer. A method of manufacturing an electrolytic capacitor, wherein at least a part of the conductive polymer layer is formed by electrolytic oxidation polymerization, and when the average value of the depths of the plurality of holes formed in the anode conductor exceeds 40 μm, As a first step of electrolytic oxidative polymerization, a first conductive polymer film, which is a part of the conductive polymer layer, is arranged so that at least a part thereof is arranged inside the plurality of holes in the first solution. And forming a second conductive polymer film, which is another part of the conductive polymer layer, in a second solution having a pH lower than that of the first solution as a second step of the electrolytic oxidation polymerization. To cover the openings of the plurality of holes in When the average value of the depths of the plurality of holes formed in the anode conductor is 40 μm or less, as the first step of the electrolytic oxidative polymerization, the second conductive layer that becomes a part of the conductive polymer layer is formed. A conductive polymer film is formed in the second solution so as to cover the openings of the plurality of holes formed in the anode conductor, and as the second step of the electrolytic oxidation polymerization, another conductive polymer layer is formed. The first electroconductive polymer film that becomes a part is formed as an outermost film of the electroconductive polymer layer in a first solution having a pH higher than that of the second solution. Production method. 13. An anode conductor made of a valve metal, a dielectric layer formed on the surface of the anode conductor, and a solid electrolyte formed on the surface of the dielectric layer and containing a conductive polymer layer. A solid electrolytic capacitor, wherein the anode conductor includes a plurality of holes, the conductive polymer layer is larger than a first conductive polymer film composed of a plurality of particles and an average particle size of the plurality of particles. A second conductive polymer film having an average particle diameter, the second conductive polymer film is formed to cover the openings of the plurality of holes, and the first conductive polymer film is at least A solid electrolytic capacitor, wherein a part of the solid electrolytic capacitor is formed so as to be arranged inside the plurality of holes or is arranged as an outermost film of the conductive polymer layer. 14. The conductive polymer layer further comprises a third conductive polymer film composed of a plurality of particles having an average particle size smaller than that of the second conductive polymer film, The first conductive polymer film is formed so that at least a part thereof is arranged inside the plurality of holes, and the third conductive polymer film is arranged as the outermost film of the conductive polymer layer. The solid electrolytic capacitor according to claim 13, which has been applied. 15. The first conductive polymer film is disposed as an outermost film of the conductive polymer layer, and a plurality of particles forming the first conductive polymer film has an average particle size of 5 μm or less. The solid electrolytic capacitor according to claim 13. 16. The plurality of particles forming the first conductive polymer film, wherein the first conductive polymer film is formed so that at least a part thereof is arranged inside the plurality of holes. The solid electrolytic capacitor according to claim 13, which has an average particle diameter of 0.1 μm or less. 17. The plurality of particles forming the first conductive polymer layer, wherein the first conductive polymer film is formed so that at least a part thereof is arranged inside the plurality of holes. The solid electrolytic capacitor according to claim 13, wherein the average particle diameter is 20% or less of the pore diameter corresponding to the mode of the volume content distribution regarding the pore diameters of the plurality of pores. 18. The first conductive polymer film is formed such that at least a part thereof is disposed inside the plurality of holes, and the average depth of the plurality of holes exceeds 40 μm. Item 13. The solid electrolytic capacitor as described in Item 13. 19. The solid electrolytic capacitor according to claim 13, wherein the valve metal is at least one selected from aluminum, tantalum and niobium. 20. At least one selected from the first conductive polymer film and the second conductive polymer film is at least one selected from pyrrole, thiophene, 3,4-ethylenedioxythiophene and derivatives thereof. 14. The solid electrolytic capacitor of claim 13, which comprises a polymer of a species.