JPH097894A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE: To provide a method of manufacturing a solid electrolytic capacitor where a manganese dioxide layer is used as a negative counter electrode, wherein a manganese dioxide layer is lessened in manufacturing man-hours, the capacitor is enhanced in withstand voltage and lessened in leakage current, and failures such as short circuits are lessened in frequency of occurrence. CONSTITUTION: A positive electrode previously coated with an oxide film is dipped into a manganese nitrate solution, a manganese nitrate solution film attached to the positive electrode is thermally decomposed into a manganese dioxide layer, whereby a first manganese dioxide layer is formed on a dielectric oxide film (step 5). Then, the positive electrode is dipped into a manganese nitrate solution where manganese dioxide particles whose average grain diameter is smaller than the diameter of voids in the porous anode are contained, a solution film attached to the positive electrode is thermally decomposed into a second manganese dioxide layer (step 6). Furthermore, the positive electrode is dipped into a manganese nitrate solution where manganese dioxide particles whose average grain diameter is larger than the diameter of voids in the porous positive electrode are contained, and a solution film attached to the positive electrode is thermally decomposed into a third manganese dioxide layer (step 7).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a solid electrolytic capacitor, and more particularly to the formation of a manganese dioxide layer in the production of a solid electrolytic capacitor having a structure using a manganese dioxide layer as a counter electrode formed on a dielectric oxide film. Regarding the method.

[0002]

2. Description of the Related Art FIG. 3 schematically shows a basic structure of a solid electrolytic capacitor of this type in an enlarged manner. Referring to FIG. 3, in the structure of this capacitor, an anode lead wire 2 also having a valve action is erected on an anode body 1 made of a metal having a valve action, and a dielectric oxide film 3, 3 is formed on the surface of the anode body 1. It has a structure in which a manganese dioxide (MnO ₂ ) layer 4, a graphite layer 8 and a silver coating layer 9 are sequentially formed (however, the exterior structure is not shown). Tantalum is well known as a valve action metal used for the anode body 1 and the anode lead wire 2, but there are also aluminum, niobium, titanium and the like. The anode body 1 is a porous body obtained by press-molding valve-action metal powder having a particle size on the order of micron meters and sintering it in vacuum in order to increase the surface area and increase the capacitance. A quality sintered body is used. Therefore, when the anode body 1 is observed microscopically, a very large number of holes are complicatedly intricately formed inside the anode body. Dielectric oxide film 3
Is usually formed by an anodic oxidation method. The manganese dioxide layer 4 is on the dielectric oxide film layer and functions as a counter electrode on the cathode side in the capacitor, and is generally formed by thermal decomposition of a manganese nitrate solution. That is, the anode body 1 on which the oxide film 3 has been formed is dipped in a manganese nitrate solution, and the manganese nitrate solution is filled into the pores inside the anode body 1 and then heated to be thermally decomposed and converted into a manganese dioxide layer. Usually, the immersion in the manganese nitrate solution and the thermal decomposition are repeated a plurality of times. This is to form the manganese dioxide layer 4 reliably and in a sufficient thickness in the numerous holes inside the anode body 1. Both the graphite 8 on the manganese dioxide layer and the silver coating layer 9 thereon function as a lead electrode layer for an external cathode terminal (not shown), and the graphite layer 8 serves as a manganese dioxide layer as a cathode side counter electrode. It is provided to reduce the contact resistance between layer 4 and the external cathode terminal.

As described above, in the production of this type of solid electrolytic capacitor, when forming the manganese dioxide layer, immersion in a manganese nitrate solution and thermal decomposition are repeated a plurality of times. In that case, if the specific gravity of the manganese nitrate solution used is small, the manganese dioxide layer 4 can be formed even at the tips of the pores in the anode body 1, so that the capacitance can be sufficiently drawn out. However, since the manganese dioxide layer formed by one immersion and pyrolysis is thin, the above immersion and pyrolysis must be repeated a very large number of times in order to form a manganese dioxide layer having a sufficient thickness. Inefficient and difficult to reduce manufacturing cost. Further, since the thermal stress is repeatedly received, the dielectric oxide film 3 is damaged and the withstand voltage of the capacitor is lowered. Also, the leakage current increases. Further, contact resistance is generated between successively formed manganese dioxide layers, and dielectric loss (tan δ) and equivalent series resistance increase. Further, bubbles are likely to remain in the completed manganese dioxide layer 4 due to gas generation during thermal decomposition.
An δ and an equivalent series resistance increase. On the other hand, when the specific gravity of the manganese nitrate solution used for forming the manganese dioxide layer is large, the manganese nitrate solution cannot be filled up to the tips of the pores inside the anode body 1, so that a sufficient capacitance expression rate is obtained. I can't. In a high temperature and high humidity environment, the silver particles in the silver coating layer 9 migrate to the incompletely covered portion of the dielectric oxide film 3 that is not covered with the manganese dioxide layer, and the withstand voltage of the capacitor decreases. There are problems such as increase of leakage current and occurrence of short circuit failure.

Therefore, in recent years, attempts have been made to solve the above problems by forming the manganese dioxide layer into a two-layer structure instead of a single layer. For example, JP-A-58-107622
In the publication, the first manganese dioxide layer is formed on the dielectric oxide film by thermal decomposition of manganese nitrate as before, and then the manganese dioxide fine powder and the organic polymer binder are further formed thereon. There is disclosed a solid electrolytic capacitor having a structure in which a second manganese dioxide layer is formed by applying a coating material consisting of According to this technique, it is possible to form a uniform manganese dioxide layer having a small number of bubbles and a small number of thermal decompositions during the formation of the manganese dioxide layer, so that the withstand voltage of the capacitor can be increased.

Further, in JP-A-61-166020, in forming a manganese dioxide layer, as a first step, a high concentration (specific gravity = 1. The manganese nitrate solution of 8) is used to form a first manganese dioxide layer, and as a second step, a higher concentration (specific gravity;
By forming the second manganese dioxide layer using the manganese nitrate solution of 1.9), the manganese dioxide layer is formed up to the tip of the pores in the anode body with less dipping and thermal decomposition times than before. Therefore, a solid electrolytic capacitor in which leakage current is reduced without reducing tan δ and capacitance is disclosed.

Further, in the solid electrolytic capacitor having a two-layer structure of a manganese dioxide layer disclosed in Japanese Patent Laid-Open No. 62-226617, a specific gravity of 1.10 to 1. In a low specific gravity manganese nitrate solution of 40, manganese dioxide particles having an average particle size of 10 μm or less are mixed and dispersed in a volume ratio of 1: 1 to 1: 0.1. Then, the above dispersion liquid is flowed at a flow rate of 2 m / min or more to immerse the anode body therein, and simultaneously filling the pores with the manganese nitrate solution and adhering manganese dioxide to the outer surface of the anode body are performed. The operation of drying and pyrolyzing is repeated several times to form the first manganese dioxide layer. Then, the second manganese dioxide layer is formed by immersing the anode body in a solution containing only manganese nitrate and thermally decomposing it in the same manner as the conventional manganese dioxide layer formation in the manufacture of capacitors. The invention described in this publication can also reduce the leakage current of the solid electrolytic capacitor and improve the withstand voltage.

[0007]

As disclosed in the above-mentioned three publications, by forming the manganese dioxide layer into a two-layer structure instead of a single layer, the formation of the manganese dioxide layer can be performed with a smaller number of thermal decompositions than ever. Moreover, it is possible to form even the tip of the hole inside the anode body. This makes it possible to prevent damage to the dielectric oxide film caused by thermal stress during thermal decomposition, and to prevent a decrease in withstand voltage and an increase in leakage current due to the damage. It has become possible to prevent an increase in leakage current due to a decrease in capacitance and migration of silver particles to the uncoated portion due to the formation of the manganese layer.

[0008] However, in recent years, as the technical application of electronic circuits has expanded their uses, the demands for improving the performance and reliability of the electronic circuits and by extension the circuit elements used for them have been increasing. Such requirements are, of course, no exception to solid electrolytic capacitors.

Therefore, the present invention is a method for manufacturing a solid electrolytic capacitor using a manganese dioxide layer as a counter electrode on the cathode side, which has a capacitance and a tan δ of the capacitor.
It is an object of the present invention to provide a manufacturing method capable of further increasing the withstand voltage and reducing the leakage current without deteriorating the above.

[0010]

A method of manufacturing a solid electrolytic capacitor according to the present invention comprises a step of forming a dielectric oxide film on the surface of a porous anode body of valve action metal on which anode leads are erected, and the dielectric body thereof. In the method for producing a solid electrolytic capacitor, comprising a step of forming a manganese dioxide layer on the surface of an oxide film, and a step of forming a cathode-side conductor layer including at least a graphite layer directly covering the manganese dioxide layer on the manganese dioxide layer, Forming the manganese dioxide layer,
The operation of immersing the oxide film-formed anode body in a manganese nitrate solution and then thermally decomposing it into a manganese dioxide layer is repeated a plurality of times to form a first manganese dioxide layer on the dielectric oxide film. The first manganese dioxide layer forming step and the anode body on which the manganese dioxide layer of the first layer has been formed are treated with a manganese nitrate solution to obtain a dioxide having an average particle diameter smaller than the pore diameter of the porous anode body. After soaking in the mixed mother liquor obtained by containing the manganese powder, pyrolysis,
A second manganese dioxide layer forming step of forming a second manganese dioxide layer on the first manganese dioxide layer and an anode body on which the second manganese dioxide layer has been formed are treated with manganese nitrate. The solution was mixed with a manganese dioxide powder having an average particle diameter larger than the pore diameter of the porous anode body to obtain a mixed mother liquor, which was then thermally decomposed to produce the second layer of manganese dioxide. And a third manganese dioxide layer forming step of forming a third manganese dioxide layer on the layer.

The object of the present invention is to replace the use of the mixed mother liquor consisting of the manganese nitrate solution containing the manganese dioxide powder in the third step of forming the manganese dioxide layer in the above-mentioned manufacturing method. It is also achieved by a method for producing a solid electrolytic capacitor, which is characterized by using a solution containing only manganese nitrate.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart showing the manufacturing process of one embodiment of the present invention. FIG. 2 is a schematic enlarged cross-sectional view showing the structure of the tantalum solid electrolytic capacitor obtained in this example. The macroscopic appearance of the capacitor according to this embodiment is the same as that shown in the lower part of FIG. Referring to FIG. 1, FIG. 2 and partial FIG. 3,
First, a pressure-molded body of tantalum metal powder was formed (step S1). This pressure-molded body will later be used as the tantalum anode body 1.
100 mg of metal tantalum powder having an average particle diameter of 2 μm was molded into a cylindrical shape having a diameter of 2 mm and a height of 3 mm.

Next, after the metal tantalum wire 2 is planted in the above tantalum metal powder compact (step S2), 160
It vacuum-sintered at 0 degreeC (step S3). By this vacuum sintering, a tantalum porous sintered anode body 1 having a metal tantalum anode lead wire 2 and a pore diameter of 1.0 to 1.5 μm was obtained.

Further, a tantalum oxide (Ta ₂ O ₅ ) film 3 is formed on the surface of the tantalum anode body 1 (step S).
4). The oxide film is formed by anodic oxidation at 80 ° C,
A direct current voltage of 100 V was applied in a 0.1 mol / l phosphoric acid aqueous solution.

Thereafter, the first manganese dioxide layer 5 was formed (step S5). The anode body having the tantalum oxide film 3 formed thereon was immersed in an aqueous solution of manganese nitrate having a specific gravity of 1.3 and a temperature of 25 ° C., pulled up, and then thermally decomposed at 200 to 400 ° C. to convert to manganese dioxide. The number of repetitions is the minimum number of times for filling the first manganese dioxide layer 5 and the surface of the oxide film 3 at the tips of the holes in the anode body, and is four in this embodiment.

Then, a second manganese dioxide layer 6 was formed (step S6). In this step, a mixed mother liquor containing manganese nitrate solution containing fine manganese dioxide powder having an average particle diameter of 0.5 μm, which is finer than the pore diameter (= 1.0 to 1.5 μm) of the anode body, is prepared. An operation of immersing the anode body of the first layer manganese dioxide layer-forming stack in the mixed mother liquor and pulling it up, and then thermally decomposing at 200 to 400 ° C. was repeated. The number of repetitions is 3 times. By this operation, the entire space of the pores of the anode body was almost completely filled with the manganese dioxide layer, and fine irregularities due to the second layer manganese dioxide layer 6 were formed on the outer surface of the anode body 1.

Then, a third manganese dioxide layer 7 was formed (step S7). In this step, a mixed mother liquor consisting of a manganese dioxide powder having an average particle diameter of 5.0 μm and a manganese nitrate solution, which is larger than the pore diameter of the anode body, is used, and the anode body on which the second manganese dioxide layer is formed is The operation of immersing in the mixed mother liquor, pulling it up, and then thermally decomposing at 200 to 400 ° C. was repeated. 3 repetitions
Times. By this operation, the outer surface of the anode body 1 was covered with the third manganese dioxide layer 7 having large irregularities. The large unevenness is caused by the third manganese dioxide layer 7
And the graphite layer 8 formed in the next step are firmly adhered to each other to enhance the adhesive force between them.

Finally, a graphite layer 8 and a silver coating layer 9 were sequentially formed on the third manganese dioxide layer 7 by a known method (step S8) to obtain a solid electrolytic capacitor of this example. In the present embodiment, electrolytic manganese dioxide is heat-treated at 350 to 400 ° C. in each mixed mother liquor when forming the second and third manganese dioxide layers in step S6 and step S7 in the above process. The manganese dioxide powder obtained from the product converted to β-MnO ₂ was used in a weight ratio of 30 to 40%. Manganese dioxide produced by the electrolytic method has a crystal structure of γ-MnO ₂ containing a large amount of adsorbed water and structured water, and has an electric resistance of 10 ³ Ω · cm.
And high. By heat-treating this γ-MnO ₂ , it is possible to convert it to β-MnO ₂ which has a small resistance value and excellent chemical conversion ability, so that the internal resistance of the capacitor is lowered,
A solid electrolytic capacitor having a small tan δ and an equivalent series resistance can be obtained.

The electrical characteristics of the tantalum solid electrolytic capacitor according to this embodiment will be described below in comparison with the characteristics of a capacitor manufactured by a conventional manufacturing method.

[Comparative Example 1] A tantalum solid electrolytic capacitor different from this example in that the manganese dioxide layer has a single layer structure. That is, the anode body 1 is manufactured and the anode lead wire 2 is manufactured.
The manganese dioxide layer 4 (see FIG. 3) was transformed into a manganese nitrate (including only) solution by using an anode body in which planting, vacuum sintering, and formation of the tantalum oxide film 3 were performed under the same conditions as in this example. Was formed by repeating immersion and thermal decomposition 18 times. This number of repetitions is the number of times required to make the capacitances equal in Comparative Example 1 and this example.

FIG. 4 shows the results of a withstand voltage test in which 20 capacitors were arbitrarily extracted from each of the capacitors according to this example and the capacitors according to Comparative Example 1. Referring to FIG. 4, the withstand voltage of the capacitor of this example is higher than that of the capacitor of Comparative example 1. This is because the thermal stress applied to the anode body during the formation of the manganese dioxide layer was four times during the formation of the first manganese dioxide layer and three times during the formation of the second manganese dioxide layer in this example. The total number of times when forming the third layer of manganese dioxide layer was 10 times, which was 18 times in Comparative Example 1, which is about 1/2 of that of Comparative Example.
It is thought that this is due to the reduction in The reduction in the number of repetitions of dipping in the manganese nitrate solution (or the mixed mother liquor) and the thermal decomposition required for forming the manganese dioxide layer significantly contributes to the reduction of manufacturing man-hours, the improvement of productivity, and the reduction of cost. .

[Comparative Example 2] A tantalum solid electrolytic capacitor different from this example is that a manganese dioxide layer is formed based on the technique described in the above-mentioned JP-A-61-166020. That is, the anode body 1 was manufactured, the anode lead 2 was planted, the vacuum sintering was performed, and the tantalum oxide film 3 was formed under the same conditions as in this embodiment. The first manganese dioxide layer was formed by repeating the immersion in the high-concentration manganese nitrate solution of No. 8 and the thermal decomposition, and then the second manganese dioxide layer was formed by repeating the immersion in the high-concentration manganese nitrate solution with a specific gravity of 1.9 and the thermal decomposition. This was done by forming a second layer manganese dioxide layer. The number of repetitions of the immersion in the manganese nitrate solution and the thermal decomposition was the same as the total number of repetitions in this example, 1 in total.
0 times.

[Comparative Example 3] A tantalum solid electrolytic capacitor different from this example is that a manganese dioxide layer is formed based on the technique described in Japanese Patent Laid-Open No. 62-226617. That is, the anode body 1 was manufactured, the anode lead wire 2 was planted, the vacuum sintering was performed, and the tantalum oxide film 3 was formed under the same conditions as in this embodiment. The first manganese dioxide layer is formed by repeating immersion of a manganese dioxide powder having an average particle size of about 10 μm in the solution and thermal decomposition, and then immersion in a solution containing only manganese nitrate and heat treatment. This was performed by forming a second manganese dioxide layer by repeating decomposition. The number of repetitions of immersion in the dispersion liquid (or a solution containing only manganese nitrate) and thermal decomposition was 10 times in the same manner as in the present example and comparative example 2.

FIG. 5 (a) shows the temporal transition of tan δ when 50 capacitors were arbitrarily sampled from the capacitors according to this example, the capacitors according to Comparative Example 2 and the capacitors according to Comparative Example 3 and subjected to a no-load moisture resistance test. Shown in.
In addition, FIG. 5B shows the result of spotting the cumulative short-circuit failure rate in this test on a Weibull probability sheet. The test conditions were
It was left unloaded under conditions of an ambient temperature of 65 ° C. and a relative humidity of 95% or more, and continued for up to 1000 hours. Tan δ was measured at 120 Hz.

Referring to FIG. 5 (a), the capacitor of this embodiment has a tan δ in comparison with the capacitors of Comparative Examples 2 and 3.
Both the absolute value and the distribution width (variation) are small. Moreover, the change over time is small. Further, referring to FIG. 5 (b),
The capacitor of the present embodiment has a smaller number of cumulative short-circuit failures than the capacitors of Comparative Examples 2 and 3, and the increase over time is slower. That is, the capacitor of the present embodiment is a so-called failure reduction type failure mode capacitor in which the Weibull shape parameter m for occurrence of a short-circuit failure is m = 0.7 and the failure rate decreases with the passage of time. .
On the other hand, the capacitors of Comparative Examples 2 and 3 are both in the shape parameter m = 1.0, and the failure mode of the wear failure type in which the failure rate increases with the passage of time.

Among the capacitors of Comparative Examples 2 and 3, those having a short circuit failure in the above-mentioned moisture resistance test were cross-section polished and subjected to high-magnification electron microscope observation to find that on the tantalum oxide film 3 inside the pores of the anode body 1. In addition, a large number of uncoated portions were confirmed together with silver ions. This is probably due to the following reasons. In the capacitor of Comparative Example 2, when forming the first layer of manganese dioxide, a high-concentration manganese nitrate solution having a specific gravity of 1.8, which is the upper limit for filling the manganese dioxide layer in the pores, is used. Therefore, the number of repetitions of immersion and thermal decomposition is reduced, and the thermal stress on the tantalum oxide film 3 is reduced, so that the decrease in withstand voltage and the increase in leakage current due to the thermal stress are reduced. However, on the other hand, it is difficult to fill the manganese dioxide layer up to the tips of the holes in the anode body,
An uncoated portion is likely to remain on the tantalum oxide film 3. As a result, in an atmosphere of high temperature and high humidity, silver particles migrate from the silver coating layer 9 which is one of the cathode-side conductor layers to the above-mentioned uncoated portion, increasing leakage current with time, and causing short circuit failure. Reach On the other hand, in Comparative Example 3, a dispersion liquid in which manganese dioxide powder is dispersed in a manganese nitrate solution having a relatively low specific gravity of 1.1 to 1.4 is used to form the first manganese dioxide layer. The average particle diameter of the manganese dioxide powder to be dispersed is 10 μm or less, and the pore diameter of the anode body is 1.0 to
Since it is much larger than 1.5 μm, it becomes difficult to impregnate the pores with the dispersion liquid in the second and subsequent immersions (in the repeated operation in forming the first manganese dioxide layer). As a result, the tantalum oxide film is not covered with the manganese dioxide layer at the tip of the holes, and an uncoated portion remains. As in Comparative Example 2, the leakage current increases and a short circuit failure occurs in the uncoated portion. .

As described above, according to this example, the manganese dioxide layer was formed by immersing it in a solution containing only manganese nitrate and repeating thermal decomposition, which is the same as in Comparative Example 1 having a single layer structure. To get the capacitance, dip,
The thermal stress can be reduced by reducing the number of repeated thermal decompositions.
Further, as compared with the solid electrolytic capacitors having the two-layer structure of the manganese dioxide layer as in Comparative Examples 2 and 3, increase of tan δ and leakage current due to incomplete coating of the dielectric oxide film and short circuit. Failure occurrence can be reduced.

From the above description, even if the method of forming the third manganese dioxide layer in the present invention is changed to a method of forming the third manganese dioxide layer by dipping it in a solution containing only manganese nitrate and repeating pyrolysis, As in the example, it will be apparent that the effects of improving the withstand voltage by reducing the thermal stress, reducing the leakage current, and reducing the leakage current by improving the coverage of the pores inside the anode body can be obtained. This has the advantage that the manufacturing process can be simplified as compared with the present embodiment, and the degree of freedom in manufacturing process design is increased. On the other hand, when a manganese nitrate solution containing manganese dioxide powder is used as in this example, the unevenness of the formed manganese dioxide layer is appropriately increased to improve the adhesion with the graphite layer thereon and the contact resistance. Therefore, tan δ can be made smaller.

Although the tantalum solid electrolytic capacitor has been described in this embodiment, the present invention is not limited to this. For example, solid electrolytic using another metal having a valve action, such as aluminum, niobium, or titanium. It goes without saying that the same effect as in this embodiment can be obtained even when applied to a capacitor.

[0030]

As described above, according to the present invention, a manganese dioxide layer is formed up to the tips of the pores by immersion in a low-concentration manganese nitrate solution and thermal decomposition. By immersing in a manganese nitrate solution containing various manganese dioxide powders and thermal decomposition, the manganese dioxide layer is surely filled in all the spaces inside the pores.

As a result, according to the present invention, the thermal stress received when the manganese dioxide layer is formed can be reduced to about half that of the conventional capacitor having a single-layered manganese dioxide layer. It is possible to prevent film damage and decrease in withstand voltage of capacitors. Also, the productivity can be significantly increased.

In addition, since the manganese dioxide layer can improve the coverage of the dielectric oxide film with the manganese dioxide layer as compared with a capacitor having a two-layer structure, the migration of the conductive metal particles to the uncoated portion and this can be prevented. It is possible to prevent the increase of leakage current and the occurrence of short circuit failure.

Further, by using a manganese nitrate solution containing manganese dioxide powder having an average particle diameter larger than the pore diameter to form the uppermost layer of the three-layered manganese dioxide layer,
Since it is possible to reduce the contact resistance between the manganese dioxide layer surface and the graphite layer by providing the surface with appropriate irregularities,
A solid electrolytic capacitor having a small tan δ can be manufactured.

According to the present invention, it is possible to manufacture a solid electrolytic capacitor having excellent productivity, high withstand voltage, small leakage current, small tan δ, short-circuit failure and excellent characteristics and reliability.

[Brief description of drawings]

FIG. 1 is a process flowchart showing a manufacturing process according to an embodiment of the present invention.

FIG. 2 is a schematic enlarged cross-sectional view showing the structure of a tantalum solid electrolytic capacitor according to an embodiment of the present invention.

FIG. 3 is a schematic enlarged cross-sectional view showing the basic structure of a solid electrolytic capacitor using a manganese dioxide layer as a cathode side counter electrode.

FIG. 4 is a diagram showing a comparison of withstand voltages of a tantalum solid electrolytic capacitor according to an example of the present invention and a tantalum solid electrolytic capacitor of Comparative Example 1 according to a conventional technique.

FIG. 5 is a graph showing a temporal transition of tan δ and a cumulative short circuit when a tantalum solid electrolytic capacitor according to an embodiment of the present invention and a tantalum solid electrolytic capacitor of Comparative Examples 2 and 3 according to the related art are subjected to a no-load humidity resistance test. It is a figure which compares and shows the Weibull plot of a failure rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode body 2 Anode lead wire 3 Dielectric oxide film 4 Manganese dioxide layer 5 First layer manganese dioxide layer 6 Second layer manganese dioxide layer 7 Third layer manganese dioxide layer 8 Graphite layer 9 Silver coating layer

Claims (5)

[Claims] 1. A step of forming a dielectric oxide film on the surface of a porous anode body of a valve metal in which anode leads are planted, a step of forming a manganese dioxide layer on the surface of the dielectric oxide film, A step of forming a cathode-side conductor layer including at least a graphite layer that directly covers the manganese dioxide layer on the manganese layer, the method of manufacturing a solid electrolytic capacitor, wherein the formation of the manganese dioxide layer, the oxide film-formed anode body Is immersed in a manganese nitrate solution and then pyrolyzed to be converted into a manganese dioxide layer, which is repeated a plurality of times to form a first manganese dioxide layer on the dielectric oxide film. Step, the anode body of the first layer of manganese dioxide layer has been formed,
The manganese nitrate solution was soaked in a mixed mother liquor obtained by containing a manganese dioxide powder having an average particle diameter smaller than the pore diameter of the porous anode body, and then pyrolyzed to form the first layer. A second manganese dioxide layer forming step of forming a second manganese dioxide layer on the manganese dioxide layer, the anode body having the second manganese dioxide layer formed,
The manganese nitrate solution is soaked in a mixed mother liquor obtained by including a manganese dioxide powder having an average particle diameter larger than the pore diameter of the porous anode body, and then thermally decomposed to form the second layer. And a third manganese dioxide layer forming step of forming a third manganese dioxide layer on the manganese dioxide layer. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the pore diameter of the porous anode body is 1.0.
˜1.5 μm, and the average particle size of the manganese dioxide powder used for forming the second manganese dioxide layer is 0.5 μm.
The following is a method for producing a solid electrolytic capacitor, characterized in that the manganese dioxide powder used for forming the third manganese dioxide layer has an average particle size of 5.0 μm or less. 3. The method for producing a solid electrolytic capacitor according to claim 2, wherein the manganese dioxide powder used for forming the second manganese dioxide layer and the manganese dioxide used for forming the third manganese dioxide layer. As powder, β-MnO ₂
A method of manufacturing a solid electrolytic capacitor, characterized by using. 4. The solid electrolytic capacitor manufacturing method according to claim 3, wherein the manganese dioxide powder occupies the mixed mother liquor used in the second manganese dioxide layer forming step and the mixed mother liquor used in the third manganese dioxide layer forming step. The method for producing a solid electrolytic capacitor, characterized in that the content of is 30% or more and 40% or less in terms of weight ratio. 5. The method for producing a solid electrolytic capacitor according to claim 1, wherein in the third manganese dioxide layer forming step, a mixed mother liquor made of a manganese nitrate solution containing the manganese dioxide powder is used, A method of manufacturing a solid electrolytic capacitor, which comprises using a solution of only manganese nitrate containing no manganese powder.