JP2009064960A - Solid electrolytic capacitor and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To strengthen the framework of a sintered compact and its connection with a lead terminal, while controlling its capacity from being lowered, to decrease external stress and stabilize LC even if it is a sheet-like tantalum sintered compact, because the sheet-like tantalum sintered compact is likely to increase a distance between the sintered compact and the lead wire, enough conduction need be secured between one sintered body and another and between the sintered compact and the lead wire, and further, if a sintered compact is assembled by resin-molding, etc., a defective LC product is easily increased by stress and strengthening this aggravates the impregnating property of electrolyte and lowers its capacity. <P>SOLUTION: The solid electrolytic capacitor, whose sintered compact is 0.2 mm to 0.5 mm thick, has a tantalum sintered body with a sintered density of 7.5 g/cm<SP>3</SP>to 8.0 g/cm<SP>3</SP>, and a conductive polymer solid electrolyte layer impregnated into this sintered compact. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a tantalum solid electrolytic capacitor and a method for manufacturing the same. In particular, the present invention relates to a tantalum solid electrolytic capacitor using a thin plate-like tantalum sintered body and a manufacturing method thereof.

The tantalum solid electrolytic capacitor uses a powder obtained by adding and mixing a binder obtained by mixing camphor, acrylic resin, or the like with an organic solvent into tantalum powder, and then volatilizing and removing the organic solvent. And this powder is press-press-molded by embedding one end of a lead wire for an anode made of tantalum valve action metal in advance. After forming, the sintered body is formed by heating and sintering in vacuum at a high temperature. Next, a capacitor element was formed by sequentially forming an oxide film, manganese dioxide or a solid electrolyte layer made of an organic conductive polymer such as polypyrrole or polyaniline, a graphite layer, and a silver layer on the sintered body. Patent Document 1, the tantalum powder of bulk density 0.50~1.85g / cm ^3, a density 4.5~7.0g / cm ^3, a molding step of volume a compact of less than 5 mm ³ It is disclosed that a tantalum solid electrolytic capacitor with a small leakage current and a suppressed capacity reduction can be manufactured by employing a manufacturing method including a small capacitor and a large capacitor.
JP 2002-60803 A

The problem to be solved is that there is a great demand for a thin tantalum solid electrolytic capacitor as well as other electronic components. The anode of a tantalum solid electrolytic capacitor is a sintered body and has a structure in which the lead wire for the anode is drawn out from the central portion. Especially in the case of a thin plate-like tantalum sintered body, the distance between the sintered body and the lead wire is Since the proportion of the distance increases, it is necessary to ensure sufficient conduction between the sintered body and the sintered body and between the sintered body and the lead wire. In particular, in the case of a thin plate-like tantalum sintered body, when the sintered body is assembled by resin molding or the like, leakage current defects are likely to increase due to stress. However, if this is strengthened, the impregnation of the electrolyte deteriorates and the capacity decreases.
Therefore, even with a thin plate-like tantalum sintered body, while suppressing the decrease in capacity, the skeleton of the sintered body, the connection between the sintered body and the lead terminal are strengthened, the external stress is reduced, and the leakage current is stabilized. The problem is to make it easier.

The present invention provides a solid electrolytic capacitor having a tantalum sintered body having a sintered density of 7.5 to 8.0 g / cm ³ and a solid electrolyte layer of a conductive polymer formed on the sintered body. It is to be.
The present invention also provides a tantalum sintered body having a sintered body thickness of 0.2 to 0.5 mm and a sintered density of 7.5 to 8.0 g / cm ³ , and the sintered body. A solid electrolytic capacitor having a conductive polymer solid electrolyte layer.
Further, a tantalum sintered body having a sintered body thickness of 0.2 to 0.5 mm and a sintered density of 7.5 to 8.0 g / cm ³ , an oxidizing agent, and a concentration of 2 to 10 w%. It is to provide a method for producing a solid electrolytic capacitor having a step of forming a solid electrolyte layer of a conductive polymer by impregnating with a monomer-containing solution.

The tantalum solid electrolytic capacitor of the present invention increases the conductivity by using a conductive polymer in the solid electrolyte layer and increases the sintered density of the tantalum sintered body from 7.5 to 8.0 g / cm ^3. In addition, the connection between the skeleton and the sintered body and the lead terminal can be strengthened, the external stress can be reduced, and the leakage current can be stabilized.
In addition, since it has a step of forming a solid electrolyte layer of a conductive polymer by impregnating with an oxidant and a monomer-containing solution having a concentration of 2 to 10%, the conductive polymer is sufficiently impregnated even if the sintered density is high. Fixing is possible.

The sintered density described in the present invention is the weight per volume of a spongy anode sintered body formed by press-pressing a powder obtained by mixing a binder with a fine tantalum powder and then sintering in vacuum. The unit is expressed in g / cm ³ .

  The thin plate-like tantalum sintered body described in the present invention is a sintered body having a cross section in which the distance from the anode lead made of tantalum embedded in the center of the end face of the sintered body differs in height and width. This refers to a thin tantalum sintered body having a width about three times that of the tantalum.

  The solid electrolyte layer of the conductive polymer described in the present invention is a layer made of a conductive polymer. In addition to polythiophene obtained by chemical oxidative polymerization of a thiophene monomer, for example, polypyrrole or polyaniline can also be used. The forming method is not limited to chemical oxidative polymerization, and can be formed by electrolytic oxidative polymerization.

The monomers described in the present invention are polymerized with a polymerizable compound to become a conductive polymer. In the case of chemical oxidative polymerization, an oxidizing agent such as p-toluenesulfonic acid is used. In the case of electrolytic oxidative polymerization, electrolysis is performed. In this case, polymerization is performed by utilizing an oxidation reaction that occurs in the anode.
In general, a conductive polymer layer formed by electrolytic oxidation polymerization is a high-quality conductive polymer layer having higher strength, higher conductivity, and uniformity than chemical oxidation polymerization. However, it is impossible or very difficult to form the conductive polymer layer directly on the dielectric oxide film by electrolytic oxidation polymerization because the dielectric oxide film is an insulator. Therefore, first, a first conductive polymer layer by chemical oxidative polymerization is formed on the dielectric oxide film, and then a second conductive by electrolytic oxidative polymerization is formed on the first conductive polymer layer. A conductive polymer layer is formed.

  The present invention will be specifically described below.

  The method for producing a tantalum sintered body for an anode of a tantalum solid electrolytic capacitor includes (1) a step of mixing tantalum primary powder, secondary agglomerated powder and an organic binder, (2) a step of compressing and molding it, 3) The process which sinters the obtained molded object is included.

As the tantalum powder used in the present invention, a powder of about 20,000 μF · V / g to 200,000 μF · V / g is used.
As a component other than tantalum, if necessary, at least one element selected from hydrogen, yttrium, zirconium, hafnium, niobium, molybdenum, manganese, tungsten, oxygen, zinc, boron, aluminum, silicon, nitrogen, phosphorus, and the like It is.

  A known organic binder can be used as the binder in the present invention. For example, polyvinyl alcohol, polyvinyl butyral, methyl cellulose, carboxymethyl cellulose or camphor can be used. These binders are usually used after being dissolved in a solution. Examples of the solvent that can be used include water, alcohols, ethers, cellosolves, ketones, aliphatic hydrocarbons, and aromatic hydrocarbons. The usage-amount of an organic binder is 1-15 mass parts normally, when the whole is 100 mass parts, Preferably it is 3-10 mass parts.

Capacitor tantalum powder and organic binder are put in a solvent and mixed thoroughly. As the mixer, a normal mixer such as a shake mixer, a V-type mixer, a bead mixer, and a nauter mixer can be used. The time required for mixing is not particularly limited as long as it is 10 minutes or longer, but is usually 1 to 6 hours.

Next, when the mixture of the tantalum powder and the binder is compression molded, one end of the tantalum wire is embedded together and led out from one end surface of the molded body.
The shape of the molded body is a sintered body having a cross section in which the distance from the lead wire for the anode made of tantalum embedded in the center of the end face of the sintered body is different in height and width. It is about three times as thin as 0.2 to 0.5 mm in height. Molding is performed so that the thickness after sintering is 0.2 to 0.5 mm, and the density after sintering is 7.5 to 8.0 g / cm ³ . If the thickness after sintering is 0.2 to 0.5 mm, the tantalum capacitor can be made thin. If the thickness after sintering is less than 0.2, the manufacturing stress at the time of forming the exterior is gradually weakened, and the leakage current after the formation of the exterior is gradually increased.
The cross section of the tantalum wire is a circle, ellipse, square or rectangle, and the diameter is about half to 90% of the thickness of the sintered body after sintering, so that it does not protrude in the thickness direction of the sintered body. To do.

Next, the molded body thus obtained is sintered. A step of removing the organic binder is provided before the sintering temperature is reached. The removal of the organic binder can be performed, for example, by treating at 200 to 600 ° C., which is lower than the sintering temperature, for 10 minutes to 10 hours under reduced pressure (10 to 10 ³ Pa). The sintering conditions depend on the melting point of the tantalum powder and the boiling point of the organic binder, but in the presence of an inert gas such as argon or helium, or under a high vacuum (for example, 10 ⁻⁴ to 10 ⁻¹ Pa), 700 ° C. It is performed by heating at ˜2000 ° C. for 1 minute to 100 hours. A preferable sintering temperature is 800 ° C to 1500 ° C, and a more preferable sintering temperature is 1000 ° C to 1300 ° C. After completion of the sintering, the tantalum sintered body is cooled and taken out until the temperature reaches about room temperature.

  Next, production of a capacitor element using the above tantalum sintered body for anode will be described. A capacitor element is formed by sequentially forming an oxide film, a solid electrolyte layer made of a conductive polymer, a graphite layer, and a silver layer on the sintered body.

First, a disc-shaped insulating plate made of polytetrafluoroethylene, silicone rubber, silicone resin, or the like is disposed at the root of the anode lead wire. The insulating plate has a thickness of, for example, less than 0.2 mm, preferably about 0.1 mm. That is, when the insulating plate is thinner, the size of the sintered body can be increased without changing the overall size of the capacitor, the capacity can be increased, and the capacitor can be reduced in size when the capacity is constant.
Next, it is immersed in a chemical conversion solution such as nitric acid or phosphoric acid to a predetermined level by visual observation or the like, and a direct current voltage corresponding to the rated voltage is applied thereto for chemical conversion treatment. By this chemical conversion treatment, an oxide film is generated at a rate of about 16 Å / V, and finally an oxide film having a thickness of about 200 to 6000 Å is formed.

Next, a solid electrolyte layer made of an organic conductive polymer is provided on the surface of the oxide film. As a conductive polymer, a substance that imparts a dopant to an electron conjugated polymer such as polyacetylene, polyparaphenylene, polypyrrole, poly-p-phenylene vinylene, polyaniline, polythiophene, polyimidazole, polythiazole, polyfuran, and derivatives thereof. Is included.
As the substance imparting the dopant, a sulfonic acid compound, a carboxylic acid compound, a phosphoric acid compound, sulfuric acid, or the like is used. In particular, examples of the sulfonic acid compound include P-toluenesulfonic acid, sulfoneisophthalic acid and sulfosuccinic acid, methanesulfonic acid, phenolsulfonic acid, sulfosalicylic acid, benzenesulfonic acid, benzenedisulfonic acid, alkylbenzenesulfonic acid and derivatives thereof, camphorsulfone. Acids such as acid, sulfonic acetic acid, diphenol sulfonic acid, naphthalene sulfonic acid and its derivatives, anthraquinone sulfonic acid and its derivatives are used. The concentration of the acid compound is about 0.05 to 1.0 mol / L. In addition, ammonium salts, sodium salts, and potassium salts of the aforementioned acid compounds are used as the salt compound used as the dopant-imparting substance. That is, in the case of sulfonic acid compounds, ammonium sulfoisophthalate, ammonium sulfosuccinate, ammonium methanesulfonate, ammonium phenolsulfonate, ammonium sulfosalicylate, ammonium benzenesulfonate, ammonium benzenedisulfonate, ammonium alkylbenzenesulfonate as ammonium salts. And derivatives thereof, salts of ammonium camphorsulfonate, ammonium sulfonate acetate, ammonium diphenolsulfonate, and the like. Sodium salts include sodium sulfoisophthalate, sodium sulfosuccinate, sodium methanesulfonate, sodium phenolsulfonate, sodium sulfosalicylate, sodium benzenesulfonate, sodium benzenedisulfonate, sodium alkylbenzenesulfonate and its derivatives, camphorsulfonic acid. Salts such as sodium, sodium sulfonate acetate, sodium diphenolsulfonate are used. Further, potassium salts include potassium sulfoisophthalate, potassium sulfosuccinate, potassium methanesulfonate, potassium phenolsulfonate, potassium sulfosalicylate, potassium benzenesulfonate, potassium benzenedisulfonate, potassium alkylbenzenesulfonate and derivatives thereof, camphorsulfone. Salts of potassium acid, potassium sulfonate, sulfoaniline, potassium diphenolsulfonate, etc. are used. And the density | concentration of these ammonium salt, sodium salt, and the compound of potassium salt shall also be about 0.05-1.00 mol / L. Hydrochloric acid or sulfuric acid may be added to increase the solubility of the salt compound and reduce the concentration in the liquid. These compounds can be used alone or in admixture of two or more.

  Examples of a method for producing a solid electrolyte layer made of a conductive polymer include polymerizable compounds of acetylene, paraphenylene, pyrrole, p-phenylene vinylene, aniline, thiophene, imidazole, thiazole, furan, or substituted derivatives thereof. A method in which a monomer is dissolved in a solvent and polymerized by the action of an oxidizing agent is employed.

Specific examples of the oxidizing agent include Fe (III) compounds such as FeCl ³ and FeClO ⁴ , Fe (organic acid anion) salts, or anhydrous aluminum chloride / cuprous chloride, alkali metal persulfates, Manganese such as ammonium persulfate, peroxides, potassium permanganate, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetrachloro-1,4-benzoquinone, tetracyano- Quinones such as 1,4-benzoquinone, halogens such as iodine and bromine, peracid, sulfuric acid, fuming sulfuric acid, sulfur trioxide, sulfonic acid such as chlorosulfuric acid, fluorosulfuric acid and amidosulfuric acid, ozone and the like A combination of oxidizing agents may be mentioned.
Among these, examples of the basic compound of the organic acid anion that forms the Fe (organic acid anion) salt include organic sulfonic acid or organic carboxylic acid, organic phosphoric acid, and organic boric acid. Specific examples of the organic sulfonic acid include benzenesulfonic acid, p-toluenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, α-sulfo-naphthalene, β-sulfo-naphthalene, naphthalene disulfonic acid, alkylnaphthalenesulfonic acid (alkyl group). As butyl, triisopropyl, di-t-butyl, etc.).
On the other hand, specific examples of the organic carboxylic acid include acetic acid, propionic acid, benzoic acid, oxalic acid and the like. Furthermore, in the present invention, polyelectrolyte anions such as polyacrylic acid, polymethacrylic acid, polystyrene sulfonic acid, polyvinyl sulfonic acid, polyvinyl sulfate poly-α-methyl sulfonic acid, polyethylene sulfonic acid, and polyphosphoric acid are also used. These organic sulfonic acids or organic carboxylic acids are merely examples, and are not limited thereto. Examples of the counter cation of the anion include alkali metal ions such as H ⁺ , Na ⁺ , K ⁺ , or ammonium ions substituted with hydrogen atoms, tetramethyl groups, tetraethyl groups, tetrabutyl groups, tetraphenyl groups, or the like. Although illustrated, it is not limited to these. Of the above oxidizing agents, particularly preferred are oxidizing agents containing trivalent Fe compounds, or cuprous chloride, alkali persulfates, ammonium persulfates, and quinones.

  As the solvent, an alcohol-based, glycol-based, ether-based, ketone-based solvent or the like with water added thereto is used. As the alcohol solvent, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, or the like is used. As the glycol solvent, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, or the like is used. The ether solvents are methyl cellosolve and ethyl cellosolve, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol Diethyl ether, diethylene glycol ethyl methyl ether, diglyme, triglyme, tetraethylene glycol dimethyl ether, tetrahydrofuran, dioxane, etc. are used. As the ketone solvent, acetone or the like is used.

  A method for providing a solid electrolyte layer on a tantalum sintered body having a dielectric layer formed thereon is a method in which an oxidant, a dopant, and a monomer are mixed and immersed in a solution in which polymerization is in progress, and a monomer, a dopant, and an oxidant. Can be divided into the following two types of solutions, and the sintered body can be alternately immersed and polymerized. The two methods are: a) a solution in which a monomer and a dopant are dissolved and a solution in which an oxidizing agent is dissolved, b) a solution in which a monomer is dissolved and a solution in which an oxidizing agent and a dopant are dissolved, and c) a monomer and a dopant. There are three types: a dissolved solution and a solution in which an oxidizing agent and a dopant are dissolved. The immersed tantalum sintered body is left to stand in the air and the polymerization is completed during drying, and the solid electrolyte is fixed on the surface of the tantalum sintered body. Further, the third method is a method of stacking another solid electrolyte layer made of a conductive polymer on the surface of the solid electrolyte layer by combining the above two methods. The operation of such a polymerization step is repeated once or more, preferably 5 to 20 times, whereby a dense and layered conductive polymer layer can be easily formed.

In the case of the tantalum sintered body of the present invention having a sintered density as high as 7.5 to 8.0 g / cm ³ , it is impregnated by impregnating with a monomer-containing solution having a viscosity concentration of 1 to 10 w% of the solution to be immersed. However, if the amount of the solute with respect to the solvent is reduced for that purpose, the monomer, the dopant and the oxidizing agent are divided into two types of solutions, and the sintered body 2 is alternately immersed and polymerized, Since the oxidizing agent or monomer fixed on the sintered body may be washed away by a large amount of solvent by the following operation, preferably, the oxidizing agent, the dopant and the monomer are mixed and immersed in a solution in which polymerization is in progress. The method is preferred. More preferably, the impregnation is performed in a monomer-containing solution having a concentration of 1 to 10% by weight so that the polymerization does not proceed. When the conductive polymer layer is fixed in the back of the tantalum sintered body, the monomer-containing concentration may be gradually increased. By doing so, the number of impregnations can be reduced.

  After forming the conductive polymer layer, a carbon paste is applied to the surface to form a carbon layer. Thereafter, a silver paste is applied to the surface of the carbon layer to form a silver layer. After forming the silver layer, the sintered body is connected to a lead frame or the like by conductive paste or welding at each of the silver layer and the anode lead wire, and the resin layer is coated with a resin, or the silver layer is a cathode terminal In addition, an anode terminal is connected to the anode lead wire, and a resin is coated by a resin dipping method to form an exterior, thereby obtaining a solid electrolytic capacitor.

Examples of the present invention will be described below.
Example 1 A method for manufacturing a tantalum chip type solid electrolytic capacitor having a rating of 10 V and 100 μF will be described. As a valve metal, tantalum fine powder (40000 μF · V / g) was used, and fine powder obtained by adding acrylic resin as a binder was embedded in one end of a tantalum lead wire having a diameter of 0.2 mm. Then, compression molding is performed with a press. Then, the compact is heat-treated in a vacuum, sintered, and sintered in a thin plate shape having a width of 2.0 mm, a height of 0.4 mm, a length of 2.5 mm, and a sintered density of 7.7 g / cm ^3. Form the body.
Next, a plurality of the sintered bodies are welded and integrated at equal intervals to a stainless steel plate having a width of 2 cm and a length of 10 cm at the location of the anode lead wire. And in the state welded to this stainless steel plate, a sintered compact is immersed in a dilute phosphoric acid liquid, DC voltage 30V is applied, and a dielectric film is formed.
Oxidant and dopan comprising 50 ml of 3,4-ethylenedioxythiophene having a concentration of 5 w% cooled to 0 ° C. to 10 ° C. and 16 mmol of ferric p-toluenesulfonate ferric butanol after forming the dielectric film The sintered body is immersed in the mixed solution for 1 minute. This immersion treatment is performed within 10 minutes after the solution is prepared. After immersion, the sintered body is left in the air for 20 minutes. Then, the steps from immersion to standing are repeated 30 times to obtain a solid electrolyte layer made of conductive polythiophene or a derivative thereof. After this drying, the sintered body is immersed in a 5 w% aqueous solution of p-toluenesulfonic acid, and a voltage of 14 V is applied. After this voltage application treatment, the sintered body is taken out of the liquid and dried in air at a temperature of 110 ° C. for 30 minutes.
After heat drying, the sintered body is immersed in colloidal carbon, and carbon is adhered to the surface of the solid electrolyte layer. Thereafter, the device is taken out and dried at a temperature of 150 ° C. in a nitrogen gas atmosphere to form a carbon layer. After the carbon layer is formed, a silver paste is applied and dried by heating at a temperature of 150 ° C. in a nitrogen gas atmosphere to form a silver paste layer.
After forming the silver layer, the silver layer of the element is connected to the cathode terminal portion of the lead frame with a silver conductive paste, and the anode lead wire is welded to the anode terminal portion of the lead frame, and the sintered body is used as the lead frame. Install.
After the element is attached to the lead frame, an exterior is formed by transfer molding using epoxy resin. After forming the exterior, aging treatment is performed, the lead frame is cut and removed, the cathode terminal and the anode terminal are formed, and a chip-type solid electrolytic capacitor is obtained.

Example 2 and Example 3 As shown in Table 1, the sintered density is manufactured under the same conditions as in Example 1 except that the density is 7.5 g / cm ³ and 8.0 g / cm ³ .
Examples 4 and 5: Manufactured under the same conditions as in Example 1 except that the monomer concentration is 2 w% and 8 w% as shown in Table 1.
Comparative Example 1 and Comparative Example 2: As shown in Table 1, the sintered density is manufactured under the same conditions as in Example 1 except that the sintered density is set to 7.3 g / cm ³ and 8.2 g / cm ³ .
Comparative Example 4 and Comparative Example 5: Manufacture under the same conditions as in Example 1 except that the monomer concentration is 1 w% and 12 w% as shown in Table 1.

Next, with respect to the tantalum solid electrolytic capacitors of Examples 1 to 5, together with the conventional examples, the drawing strength, the capacity achievement rate, the leakage current, and the deflection strength are measured.
The pullout strength is the ratio between the sintered body and the anode lead wire when the sintered body is fixed after sintering and the anode lead wire embedded in the center of the end face of the sintered body is pulled up. It indicates the adhesion strength between.
The capacity achievement rate refers to the ratio of the measured capacitance value of the capacitor element when the solid electrolyte layer is provided to the measured capacitance value of the capacitor element in a 30% sulfuric acid aqueous solution.
In addition, the bending strength refers to strength resistance when a pillow portion is provided at both bottoms of the sintered body and a force is applied downward from the center upper surface of the sintered body.
The leakage current is measured by leaving the sample in the air and heating at 125 ° C. for 10 hours after the exterior is formed. Apply a DC voltage of 10V and set the value after 1 minute.
The measurement results are shown in Table 1.

As is clear from Table 1, the comparative example 1 having a sintered density of 7.3 g / cm ³ smaller than 7.5 g / cm ³ compared to the example has a small pulling strength and deflection strength, and the sintered body Since the thickness is as thin as 0.2 to 0.5 mm, it is weak against manufacturing stress during the formation of the exterior, and the leakage current after the formation of the exterior is increased.
Further, as compared with the embodiment, when the sintered density but Comparative Example 2 of 8.0 g / cm ³ greater than 8.2 g / cm ^3, the capacity achievement ratio deteriorates, the leakage current for the increases.
Further, compared with Example 1, in Comparative Example 3 in which the monomer concentration is 1 w% smaller than 2 w%, the impregnation amount of the conductive polymer is small and the capacity achievement rate is deteriorated, so that the leakage current is increased. .
Further, compared with Example 1, in Comparative Example 4 in which the monomer concentration is 12 w% which is larger than 8 w%, the impregnating property of the conductive polymer is deteriorated and the capacity achievement rate is deteriorated, and thus the leakage current is increased. Yes.

Claims (3)

A solid electrolytic capacitor comprising a tantalum sintered body having a sintered density of 7.5 to 8.0 g / cm ³ and a solid electrolyte layer of a conductive polymer formed on the sintered body. A tantalum sintered body having a sintered body thickness of 0.2 to 0.5 mm and a sintered density of 7.5 to 8.0 g / cm ³ , and a conductive polymer formed on the sintered body. A solid electrolytic capacitor having a solid electrolyte layer. A tantalum sintered body having a sintered body thickness of 0.2 to 0.5 mm and a sintered density of 7.5 to 8.0 g / cm ³ , containing an oxidizing agent and a monomer having a concentration of 2 to 10 w% A method for producing a solid electrolytic capacitor comprising a step of impregnating with a solution to form a solid electrolyte layer of a conductive polymer.