JP3202668B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly to a method for manufacturing a solid electrolytic capacitor using a conductive polymer compound as a solid electrolyte.

[0002]

2. Description of the Related Art Generally, a solid electrolytic capacitor is formed by molding and sintering a fine powder of a valve metal such as aluminum or tantalum, and the resulting porous sintered body is used as an anode. A dielectric oxide film is formed on the surface by electrochemical anodic oxidation or the like, and a solid electrolyte is interposed in close contact with the oxide film to draw out a cathode serving as a counter electrode.

This solid electrolyte has the function of electrically connecting the entire surface of the dielectric oxide film and the cathode to draw out the capacitance of the dielectric oxide film. In addition, when an electrical short circuit occurs due to a defect inside the dielectric oxide film, it is necessary to have a function of repairing the defect.

[0004] As a solid electrolyte meeting the above requirements,
Conventionally, manganese dioxide and 7,7,8,8-tetracyanoquinodimethane complex salt (TCNQ complex salt) have been widely used. However, those using manganese dioxide are not used in a high frequency region because their specific resistance is not low. , The equivalent series resistance (hereinafter referred to as ESR), or the tangent of the dielectric loss angle (hereinafter referred to as tan δ) is high. On the other hand, when the TCNQ complex salt was used for the solid electrolyte, impedance, ES
Although R and tan δ are considerably low, there is a drawback that the heat resistance is poor due to the low thermal decomposition temperature of the TCNQ complex salt, and the above characteristic values cannot be maintained for a long time in a high-temperature atmosphere.

However, in recent years, in the field of polymer chemistry, new solid electrolyte materials have been actively developed, and as a result,
Conductive polymer compounds have been developed in which conjugated polymer compounds having π electrons, such as polypyrrole, polyaniline, polythiophene, and polyfuran, are added with a compound (dopant) having an electron-donating or electron-withdrawing property to impart conductivity.
Many solid electrolytic capacitors using these as a solid electrolyte have been proposed. For example, a pyrrole monomer is polymerized on a dielectric oxide film by a chemical oxidation polymerization method using an oxidizing agent, and a polypyrrole to which a dopant is added is used as a conductive polymer compound layer, and then a graphite layer and a silver paint layer are sequentially formed. Manufacturing methods have been developed.

However, according to this method, the conductive polymer compound layer as the solid electrolyte is thin, and it is not possible to sufficiently secure the fitting with the sintered body as the anode. further,
Since the outer surface of the obtained conductive polymer compound layer is smooth, the fitting between the conductive polymer compound layer and the graphite layer is weak. Therefore, ESR or tan δ in the high frequency region
There was a problem that was large.

As a technique for solving these problems, Japanese Patent Application Laid-Open No. Hei 7-94368 discloses a method of forming an inner conductive polymer compound layer 5 on a dielectric oxide film 2 by chemical oxidation polymerization as shown in FIG. A conductive powder 7 of graphite or the like is mixed therein to form an external conductive polymer compound layer 6 having irregularities on its surface, and further a graphite layer 8 and a silver paint layer 9
Are sequentially formed, and a method for manufacturing the same is disclosed.

FIG. 6 is a flowchart summarizing a series of manufacturing steps of the solid electrolytic capacitor.

[0009]

However, the solid electrolytic capacitor using the conductive polymer compound layer produced by the above method as a solid electrolyte has the following problems.

That is, the first problem is an increase in ESR and tan δ due to thermal shock during mounting. The cause is
The mechanical strength of the outer conductive polymer compound layer and the graphite layer is not always sufficient, and the fitting and adhesion between the inner conductive polymer compound layer and the graphite layer are not sufficient. Is easy to peel off.

The second problem is an increase in leakage current due to thermal stress during mounting. The cause is that, according to the above-described method, it is difficult to form an outer conductive polymer compound layer having a uniform thickness on the outer surface of the anode body made of a sintered body of a valve action metal, and the thickness is partially insufficient. This is because mechanical damage to the dielectric oxide film is likely to be induced at the site. In particular, the thickness of the outer conductive polymer compound layer tends to be insufficient at the edge portion of the anode body, and the leakage current tends to increase.

The third problem is that the solid electrolytic capacitor is required to be used under the condition of practical temperature and humidity, especially under a high temperature atmosphere.
This is a sharp increase in SR and tan δ. As described above, as described above, since the fitting between the inner conductive polymer compound layer, the conductive polymer compound layer, and the graphite layer is weak, peeling or gaps are easily generated between the three members, and these are likely to cause oxygen and moisture. This is considered to be due to a penetration path, in which the oxidative deterioration of the entire conductive polymer compound layer under a high-temperature and high-humidity atmosphere is remarkably accelerated, and the resistance value increases rapidly.

An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor having excellent initial characteristics and reliability by solving the above-mentioned problems of the prior art.

[0014]

A method for manufacturing a solid electrolytic capacitor according to the present invention comprises a step of forming an oxide film on a surface of an anode made of a sintered body of valve metal powder, and a step of forming an oxide film on the oxide film in close contact with the oxide film. A step of forming a first conductive polymer compound layer by oxidative polymerization, immersing in a conductive polymer compound suspension aqueous solution, and a second conductive polymer compound layer on the first conductive polymer compound layer Forming a, and dipped in a graphite powder-containing suspension aqueous solution, after forming a graphite layer on the second conductive polymer compound layer, to form a silver paint layer,
It is configured to include a step of forming a cathode layer.

Here, the second conductive polymer compound layer and the first conductive polymer compound layer are mixed with each other by adding a water-soluble adhesive to the conductive polymer compound aqueous suspension and the graphite powder-containing suspension aqueous solution. The fitting and adhesion between the conductive polymer compound layer and the second conductive polymer compound layer and the graphite layer can be improved.

As the water-soluble adhesive in the aqueous suspension, polyacrylonitrile, methyl cellulose, polyvinyl alcohol, methyl methacrylate and derivatives thereof can be used.

The water-soluble adhesive can be easily prepared as an aqueous suspension in which a desired powder is dispersed in pure water, and dried to remove water, whereby a coating film having a uniform thickness can be formed at a low temperature in a short time. can get. Further, by adjusting the amount of pure water added and changing the concentration of the solid content, it is possible to form a thick film, and there is an advantage that a coating film having a desired thickness can be obtained with a minimum number of treatments.

By using the water-soluble adhesive, the strength of the second conductive polymer compound layer and the graphite layer, and the fitting between these layers can be enhanced. The water-soluble adhesive used for forming the second conductive polymer compound layer and the graphite layer does not have to be the same compound.

In the present invention, as the first conductive polymer compound layer, a polymer of a cyclic organic compound monomer such as pyrrole, aniline, thiophene, and furan, and a polymer of a derivative thereof can be used. These polymers are preferably formed by chemical oxidative polymerization.
The reason for this is that the inside of the pores of the sintered body of the valve action metal is finely enlarged, and in electrolytic oxidation polymerization, a potential difference is easily generated between the inside of the pores and the outer surface when electricity is applied, and the entire surface of the dielectric oxide film This is because it is difficult to uniformly and closely contact the conductive polymer compound layer.

The conductive polymer compound in the aqueous suspension solution for forming the second conductive polymer compound layer in the present invention includes pyrrole, aniline, thiophene, and the like as in the first conductive polymer compound layer. Polymers of furan and their derivatives are used. Note that the first conductive polymer compound layer and the second conductive polymer compound layer need not be the same compound.

According to the present invention, the conductive polymer compound layer has a two-layer structure as described above, and the first conductive polymer compound layer which is in close contact with the dielectric oxide film is formed by chemical oxidation polymerization. After being polymerized, it is immersed in a suspension aqueous solution in which a conductive polymer compound powder doped with a dopant to exhibit conductivity by being doped with a water-soluble adhesive, pulled up, and dried at a predetermined temperature to obtain a graphite layer. A second conductive polymer compound layer having on its surface irregularities for strengthening the fitting was formed. Furthermore, it is immersed in an aqueous suspension of a mixture of graphite powder and a water-soluble adhesive, pulled up and dried at a predetermined temperature to form a graphite layer. In particular, an increase in ESR, tan δ, and leakage current in a high-temperature atmosphere can be suppressed.

[0022]

Embodiments of the present invention will be described with reference to the drawings.

FIGS. 1A and 1B are schematic sectional views of a solid electrolytic capacitor for illustrating a method of manufacturing a solid electrolytic capacitor according to an embodiment of the present invention. FIG. 1A is an overall sectional view, and FIG. FIG. 3 is an enlarged sectional view of a dielectric oxide film portion of the solid electrolytic capacitor of FIG.

First, the valve action metal 1 which is an anode made of a sintered body of the valve action metal powder is anodized to form a dielectric oxide film 2 along the pore wall surface of the sintered body. A first conductive polymer compound layer 3 is formed on the surface of the dielectric oxide film 2 by chemical oxidation polymerization to manufacture a capacitor element.

Next, the capacitor element is immersed in an aqueous solution of a conductive polymer compound suspension to form a second conductive polymer compound layer 4 on the first conductive polymer compound layer 3.
Here, as the conductive polymer compound suspension aqueous solution for forming the second conductive polymer compound layer 4, a suspension solution obtained by mixing a conductive polymer compound powder and a water-soluble adhesive is used. You. The second conductive polymer compound layer is formed by immersing in this liquid, pulling it up, and drying it at a predetermined temperature. Since the outer surface of the second conductive polymer compound layer 4 has many irregularities made of the conductive polymer compound powder,
The fit with the graphite layer formed thereon can be improved.

Further, the capacitor element is immersed in a graphite powder-containing aqueous suspension to form a graphite layer 8 so as to cover the outer surface of the second conductive polymer compound layer 4.

As the water-soluble adhesive in the aqueous suspension, it is preferable to use polyacrylonitrile, methylcellulose, polyvinyl alcohol, methyl methacrylate and derivatives thereof. The mixing ratio of these water-soluble adhesives is not particularly strictly limited, but from the results of resistance value, adhesive strength, workability and various reliability evaluations, 0.5 to 3 wt. % Is most preferred. When the mixing ratio is 0.5 wt. %, The adhesive strength is slightly weak and 3 w
t. %, There was a tendency for the resistance to increase.

Next, a silver paint layer 9 is formed on the graphite layer 8.
Are sequentially formed to form a cathode layer.

Further, the electrode terminals 10 are formed by a conventionally known method.
Is mounted with an exterior resin 11 to produce the solid electrolytic capacitor of FIG. FIG. 2 is a flowchart summarizing the series of manufacturing steps.

[0030]

The present invention will be described below in more detail with reference to examples. In each of the embodiments, a sintered body of columnar fine tantalum powder having a diameter of 1 mm and a length of 1 mm was used as the valve metal in the above embodiment. The CV product (product of capacitance per gram of powder and anodic oxidation voltage) of the sintered body after anodization was 48000 μF · V / g.

Example 1 A tantalum fine powder sintered body pellet was anodized at 60 V in a 0.2 M aqueous nitric acid solution to form a dielectric oxide film 2.
Was formed. This pellet was immersed in a 0.1 M solution of ferric dodecylbenzenesulfonate in methanol for 1 minute, immersed in a methanol solution of 0.1 M pyrrole monomer for 1 minute, and then kept at room temperature for 15 minutes to perform chemical oxidation. Polymerization and doping were performed simultaneously. Impregnation of these oxidants,
By repeating a series of operations of polymerization and doping 15 times, polypyrrole as the first conductive polymer compound layer 3 was formed so as to be in close contact with the dielectric oxide film.

Next, as a polymerization solution, pyrrole: 0.1
A methanol solution was prepared by mixing so that M, 2-naphthalenesulfonic acid: 0.2 M and ferric nitrate: 0.2 M, kept at −40 ° C. or lower, and sufficiently stirred. Thereafter, the solution was left at room temperature for 5 hours to undergo chemical oxidation polymerization. In addition, excess pyrrole using methanol,
After removing 2-naphthalene sulfonic acid and ferric nitrate, the resultant was dried at room temperature for 24 hours to obtain powdered boropyrrole.

Next, this powdery polypyrrole was added to 25 w
t. %, 1.5 wt.% Of polyvinyl alcohol as a water-soluble adhesive. %, Pure water (remainder) was mixed to a composition of 73.5 wt% to prepare a suspension aqueous solution, and the pellet after forming the first conductive polymer compound layer was immersed in the aqueous solution for 3 seconds and pulled up. By drying at 120 ° C. for 15 minutes, a thick film of polypyrrole was formed as a second conductive polymer compound layer.

Further, a graphite powder (having an average particle size of about 0.
3 μm) 10 wt%, polyvinyl alcohol 1.5 wt
%, Pure water (remainder): 88.5 wt%, a suspension aqueous solution was prepared, and the pellet after the formation of the second conductive polymer compound layer was immersed in the aqueous solution for 3 seconds and pulled up.
By drying at 120 ° C. for 15 minutes, a graphite layer was formed.

Further, a silver paint layer was formed on the graphite layer, and after extracting the electrode terminals, it was sealed with an exterior resin to complete a solid electrolytic capacitor.

Example 2 The procedure up to the formation of the dielectric oxide film was carried out in the same manner as in Example 1. The pellet was immersed in a 0.1 M aqueous solution of 2-peroxodisulfate for 1 minute, then immersed in a 0.1 M aqueous solution of aniline monomer for 1 minute, and dried at room temperature for 15 minutes. To form undoped polyaniline. Next, this was immersed in an ethanol solution of 0.1 M p-toluenesulfonic acid for 1 hour to dope polyaniline to impart conductivity. A series of operations including the impregnation of the oxidizing agent, the contact with the aniline monomer, and the doping was repeated 10 times to form polypyrrole as the first conductive polymer compound layer so as to be in close contact with the dielectric oxide film. did.

Next, the pellet after forming the first conductive polymer compound layer was immersed in an aqueous suspension containing polypyrrole powder prepared in the same manner as in Example 1, pulled up, and pulled up at 120 ° C. for 15 minutes. By drying, a thick film of polypyrrole as a second conductive polymer compound layer was formed.

Further, after a graphite layer and a silver paint layer were sequentially formed in the same manner as in Example 1, the electrode terminals were taken out and sealed with an exterior resin to complete a solid electrolytic capacitor.

Example 3 The procedure up to the formation of the dielectric oxide film was carried out in the same manner as in Examples 1 and 2. Next, 0.1M thiophene / 0.1M citric acid / 0.1M p-toluenesulfonic acid / 0.2M
Prepare an ethanol solution to be M ferric nitrate,
It was kept at 50 ° C. The pellet after the formation of the dielectric oxide film was immersed therein for 1 minute, pulled up, and kept at room temperature for 1 hour to carry out chemical oxidation polymerization. Further, excess thiophene, citric acid, P-toluenesulfonic acid, and ferric nitrate were removed using ethanol. By repeating the above series of operations of immersion of the polymerization solution, drying at room temperature, and washing with ethanol eight times, the doped polythiophene film as the first conductive polymer compound layer closely contacts the dielectric oxide film. Was formed. Next, the pellet after forming the first conductive polymer compound layer is immersed in an aqueous suspension containing polypyrrole powder prepared in the same manner as in Example 1, pulled up, and dried at 120 ° C. for 5 minutes. As a result, a thick film of polypyrrole was formed as the second conductive polymer compound layer.

Further, after a graphite layer and a silver paint layer were sequentially formed in the same manner as in Example 1, the electrode terminals were taken out and sealed with an exterior resin to complete a solid electrolytic capacitor.

Example 4 An operation up to the formation of the second conductive polymer layer was performed under the same conditions as in Example 1. Next, graphite powder (average particle size: about 0.3 μm) 10 wt. %, Carboxymethylcellulose 0.8 wt. %, Pure water (remainder) 89.2
wt. % Of the suspension is prepared, and the pellet after forming the second conductive polymer compound layer is immersed in the suspension for 3 seconds, pulled up, and dried at 100 ° C. for 5 minutes to obtain graphite. A layer was formed.

Further, a silver paint layer was formed, and after the electrode terminals were drawn out, they were sealed with an exterior resin to complete a solid electrolytic capacitor.

Comparative Example A solid electrolytic capacitor manufactured by a known method in Japanese Patent Application Laid-Open No. 7-94368 will be described as a representative comparative example.

A dielectric oxide film was formed by the same pellets and the same method as in the above embodiment of the present invention. The pellet was immersed in a 0.1 M solution of ferric dodecylbenzenesulfonate in ethanol for 1 minute, immersed in a methanol solution of 0.1 M pyrrole monomer for 1 minute, and kept at room temperature for 10 minutes to simultaneously carry out chemical oxidation polymerization and doping. Done.
A series of operations including the above-described impregnation of the oxidizing agent, contact with the pyrrole monomer, and polymerization / doping was repeated 10 times to form a polypyrrole as an internal conductive polymer layer in close contact with the dielectric oxide film. .

Next, 5 g of a polyaniline powder soluble in an organic solvent prepared by a conventionally known method was used as a conductive powder, and the solution was added little by little to 95 g of N-methyl-2-pyrrolidone to form a solution. The pellet after the formation of the inner conductive polymer compound layer is held in the solution for 1 minute, and then immersed in a sulfuric acid aqueous solution for 30 minutes to dope the outer conductive layer containing polypyrrole powder as a conductive powder. Polyaniline was formed as a molecular compound layer.

Further, a graphite layer containing no organic binder and a silver paint layer were sequentially formed thereon, and after the electrode terminals were drawn out, they were sealed with an exterior resin to complete a solid electrolytic capacitor of a comparative example.

The four types of solid electrolytic capacitors of the present invention completed by the above-described method and 100 solid electrolytic capacitors of the comparative example were each subjected to a solder immersion test (immersion at 270 ° C. for 10 seconds).
Was served. Tanδ before and after the test (measured at 1 kHz),
The distribution of ESR (measured at 100 KHz) and leakage current (LC rated voltage, 1 minute value) are shown in comparison with FIG. While the solid electrolytic capacitors manufactured by the manufacturing method of the comparative example significantly deteriorated in various characteristics after the test, the four types of solid electrolytic capacitors manufactured by the examples of the present invention had tan δ,
Almost no increase in ESR is observed. Further, the distribution of the leakage current hardly changes. That is, according to the method for manufacturing a solid electrolytic capacitor of the present invention, it was confirmed that a solid electrolytic capacitor having stable heat resistance characteristics without deterioration of various characteristics due to heat history and thermal stress applied at the time of solder mounting can be provided. .

Four types of solid electrolytic capacitors manufactured according to the embodiment of the present invention and 20 solid electrolytic capacitors manufactured according to the comparative example were each subjected to a solder immersion test (270 ° C., 1
FIG. 4 shows a change with time of ESR (measured at 100 KHz) when the sample was left in a hot air atmosphere at 125 ° C. after subjecting the sample to 0 ° immersion. Here, the value after solder immersion was set to 1 (initial value), and the average value of the ESR change magnification of 20 samples was plotted against time.

According to the results shown in FIG. 4, the solid electrolytic capacitor manufactured according to the comparative example of the related art has an ESR after 1000 hours that is nine times as large as the initial value. In the case of the solid electrolytic capacitors manufactured according to the examples, the ESR after the lapse of 1000 hours was less than twice the initial value, showing good thermal stability.

[0050]

As described above, the present invention solves the problems of a conventional solid electrolytic capacitor using a conductive polymer compound, and produces a solid electrolytic capacitor having excellent initial characteristics and reliability. It is possible to provide a method.

That is, an increase in ESR and tan δ due to thermal history during mounting, which is a first problem in the prior art, is suppressed. In this method, the conductive polymer compound layer has a two-layer structure, and the second conductive polymer compound layer and the graphite layer on the outer peripheral portion of the element are formed using a suspension aqueous solution made of a water-soluble adhesive. And delamination between layers which causes tan δ deterioration is suppressed. Further, since the outer surface of the second conductive polymer compound has a large number of irregularities made of the conductive polymer compound powder, the fitting between the two is more reliable.

Further, an increase in leakage current due to thermal stress during mounting, which is the second problem, can be suppressed. This is achieved by using a suspension aqueous solution in which a conductive polymer compound powder and a water-soluble adhesive are mixed, immersing the element in the suspension, pulling it up, and drying it at a predetermined temperature, so that a uniform and sufficient peripheral part of the element is formed. This is because a second conductive polymer compound layer having a thickness can be formed, and mechanical damage to the dielectric oxide film due to thermal stress during mounting is suppressed.

Further, it is possible to suppress the third problem, that is, a sharp increase in ESR and tan δ associated with use of the solid electrolytic capacitor under practical temperature and humidity conditions, particularly under a high temperature atmosphere.
The reason for this is that the above method uniformly and
A second conductive polymer compound layer and a graphite layer having a sufficient thickness are sequentially formed, and the fitting between the two is strengthened, thereby causing an increase in the resistance value of the entire conductive polymer compound layer in a high-temperature atmosphere. This is because it is possible to block the entry path of oxygen and moisture,

As described above, according to the present invention, a solid electrolytic capacitor having excellent initial characteristics and thermal stability during solder mounting, and having a stable performance with a small change in equivalent series resistance value over a long period of time even in a high-temperature atmosphere. Is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a solid electrolytic capacitor for describing a method of manufacturing a solid electrolytic capacitor according to an embodiment of the present invention, where (a) is an overall cross-sectional view and (b) is a solid state of (a). It is an expanded sectional view of the dielectric oxide film part of an electrolytic capacitor.

FIG. 2 is a flowchart summarizing a series of manufacturing steps of the solid electrolytic capacitor of FIG.

FIG. 3 shows a solder immersion test ta of a solid electrolytic capacitor manufactured according to the present invention and a solid electrolytic capacitor of a comparative example.
It is a measurement result of nδ, ESR and leakage current.

FIG. 4 is a measurement result of a change over time in ESR of a solid electrolytic capacitor manufactured according to the present invention and a solid electrolytic capacitor of a comparative example when left at a high temperature of 125 ° C.

FIG. 5 is an enlarged schematic cross-sectional view of a conventional solid electrolytic capacitor using a conductive polymer compound solid electrolyte;
(A) is an overall sectional view, and (b) is an enlarged sectional view of a dielectric oxide film portion of the solid electrolytic capacitor of (a).

6 is a flowchart summarizing a series of manufacturing steps of the conventional solid electrolytic capacitor of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Valve metal 2 Dielectric oxide film 3 First conductive polymer compound layer 4 Second conductive polymer compound layer 5 Internal conductive polymer compound layer 6 External conductive polymer compound layer 7 Conductive powder 8 Graphite layer 9 Silver paint layer 10 Electrode terminal 11 Exterior resin

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01G 9/028 H01G 9/04

Claims (6)

(57) [Claims] 1. A step of forming a dielectric oxide film on the surface of an anode made of a sintered body of a valve metal powder, and forming a first conductive polymer compound layer on the oxide film by chemical oxidation polymerization. Forming, immersing in a conductive polymer compound suspension aqueous solution, forming a second conductive polymer compound layer on the first conductive polymer compound layer, and a graphite powder-containing suspension aqueous solution And forming a graphite layer on the second conductive polymer compound layer, then forming a silver paint layer, and forming a cathode layer. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the aqueous conductive polymer compound suspension is an aqueous suspension obtained by mixing a conductive polymer compound powder and a water-soluble adhesive. 3. The conductive polymer compound powder in the conductive polymer compound suspension aqueous solution is a conductive polymer compound powder that has been polymerized in advance and then doped with a dopant to exhibit conductivity. Item 3. A method for manufacturing a solid electrolytic capacitor according to Item 2. 4. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein said first and second conductive polymer compound layers are polymers of pyrrole, aniline, thiophene, furan, and derivatives thereof. 5. The method for producing a solid electrolytic capacitor according to claim 1, wherein said graphite powder-containing suspension aqueous solution contains a water-soluble adhesive. 6. A method according to claim 2, wherein polyacrylonitrile, methylcellulose, polyvinyl alcohol, methyl methacrylate and derivatives thereof are used as a water-soluble adhesive for the aqueous conductive polymer compound suspension and the graphite powder-containing aqueous suspension. A method for manufacturing a solid electrolytic capacitor according to claim 5.