JPH06196370A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To provide a method able to easily manufacture a solid electrolytic capacitor having small specific resistance. CONSTITUTION:In a manufacturing method of a solid electrytic capacitor including a compacting process compacting metal powder into a prescribed shape (A), a sintering process sintering a compact obtained by the compacting process (B), a forming process forming an oxide film 3 by oxidizing the surface of a capacitor element obtained by the sintering process (C), a forming process of a solid electolyte layer forming a dioxide manganese layer 5 on the oxide film 3 of the capacitor element 1 obtained by the forming process (D) and a reforming process repairing the oxide film 3 (E), and the reforming process (E) is performed by using a water solution of acidic ammonium salt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor. More specifically, the present invention relates to a method for producing a solid electrolytic capacitor which can easily produce a solid electrolytic capacitor having a small specific resistance.

[0002]

2. Description of the Related Art Conventionally, a solid electrolytic capacitor has a metal oxide film formed by anodic oxidation on the surface of a capacitor element obtained by sintering a metal powder such as tantalum, aluminum or niobium, and then a manganese nitrate aqueous solution. To form a manganese dioxide layer, repair the oxide film in a re-forming solution consisting of an aqueous solution of phosphoric acid, and dry it. Then, a graphite layer and a silver layer for electrode extraction are formed on the outer periphery of the capacitor element. Manufactured by the method of forming.

However, in the above method, since the phosphate ion contained in the re-forming solution remains inside the sintered body after the oxide film is repaired in the re-forming solution, it is necessary to perform drying. The manufacturing operation is complicated, and the obtained solid electrolytic capacitor has a large specific resistance, so that it has a drawback that the equivalent series resistance (hereinafter referred to as ESR) becomes large.

[0004]

Therefore, in view of the above-mentioned prior art, the inventors of the present invention have conducted earnest studies to obtain a solid electrolytic capacitor having a small specific resistance without requiring a complicated operation such as drying. However, when re-formation was carried out using an aqueous solution of acidic ammonium salt, we found a completely new fact that solid electrolytic capacitors with low specific resistance can be obtained without the need for complicated operations such as drying. It came to complete the invention.

[0005]

That is, the present invention is
(A) a molding step of molding the metal powder into a predetermined shape,
(B) a sintering step of sintering the molded body obtained in the molding step, (C) a chemical conversion step of oxidizing the surface of the capacitor element obtained in the sintering step to form an oxide film, (D) In the method for producing a solid electrolytic capacitor, which includes a solid electrolyte layer forming step of forming a manganese dioxide layer on an oxide film of the capacitor element obtained in the chemical conversion step, and (E) a re-chemical conversion step of repairing the oxide film, (E) A method for producing a solid electrolytic capacitor, wherein the re-chemical conversion step is performed using an aqueous solution of an acidic ammonium salt.

[0006]

OPERATION AND EXAMPLES As described above, the method for producing a solid electrolytic capacitor according to the present invention comprises: (A) a molding step of molding a metal powder into a predetermined shape; and (B) a molding obtained in the molding step. And (C) a chemical conversion step of oxidizing the surface of the capacitor element obtained in the sintering step to form an oxide film, and (D) an oxide film of the capacitor element obtained in the chemical conversion step. In the method for producing a solid electrolytic capacitor, including the step of forming a solid electrolyte layer for forming a manganese dioxide layer, and (E) the re-forming step for repairing the oxide film, the (E) re-forming step is carried out by adding an aqueous solution of an acidic ammonium salt. It is a manufacturing method characterized by being carried out.

According to the method for producing a solid electrolytic capacitor of the present invention, the complicated operation of drying, which is required in the conventional method, is unnecessary in the re-chemical conversion step.

According to the method for producing a solid electrolytic capacitor of the present invention, a solid electrolytic capacitor having a small specific resistance can be obtained. A solid electrolytic capacitor with such a low specific resistance is probably obtained by immersing the capacitor element on which the manganese dioxide layer is formed in an aqueous solution of an acidic ammonium salt, repairing the oxide film, and then using a manganese nitrate aqueous solution. It is considered that this is based on the fact that the formation of MnO ₂ is promoted when the manganese dioxide layer is formed and the production of Mn ₂ O ₃ is suppressed.

Examples of the metal powder constituting the capacitor element used in the present invention include metal powders such as tantalum, aluminum and niobium.

In order to have a predetermined shape, the above-mentioned capacitor element is prepared by press-molding in advance using a molding die having a desired shape (molding step), followed by sintering. Made (sintering process).

When the capacitor element is produced by sintering, it is preferable that the metal wire forming the electrode is embedded in the metal powder in advance.

In the present invention, first, an oxide film is formed by anodic oxidation on the surface of the capacitor element, the surface exposed inside through the holes of the capacitor element and a part of the surface of the metal wire (chemical conversion step).

As a method of forming an oxide film by the anodization, for example, a capacitor element is used as an anode,
In addition, there is a method in which an electrode plate or an electrolytic cell is used as the cathode, and both are immersed in an electrolyte solution to pass a direct current.

Representative examples of the electrolyte solution include an aqueous solution of an acidic ammonium salt, an aqueous solution of phosphoric acid, an aqueous solution of ammonium borate and the like, but the present invention is not limited to these examples. The concentration of the electrolyte in the electrolyte solution cannot be unconditionally determined because it varies depending on the type of the electrolyte and the like, but it is usually 0.01 to 0.1% by weight, preferably 0.05 to 0.1% by weight. Further, the liquid temperature of the electrolyte solution is not particularly limited, but it is usually 0 to 80 ° C, especially about 10 to 60 ° C.

When passing a direct current, the current density in the capacitor element is usually 0.01 to 0.05 mA / cm ² ,
It is preferably about 0.02 to 0.04 mA / cm ^2, especially.

Thus, by passing a direct current, not only the surface of the capacitor element, but also the inner surface of the capacitor element and the partial surface of the metal wire through the holes of the capacitor element,
An oxide film of metal forming the capacitor element and the metal wire is formed.

After forming an oxide film on the surface of the capacitor element by anodic oxidation, a manganese dioxide layer is formed on the oxide film using a manganese nitrate aqueous solution (solid electrolyte layer forming step).

When the manganese dioxide layer is formed on the capacitor element by using an aqueous solution of manganese nitrate, it is preferable to wash the capacitor element with, for example, pure water in advance and then dry it.

As a typical example of a method of forming a manganese dioxide layer on an oxide film formed on the surface of a capacitor element using the manganese nitrate aqueous solution, for example, the capacitor element is dipped in an aqueous manganese nitrate solution to form the nitric acid. After impregnating with the manganese aqueous solution, add 200 manganese nitrate.
A method of forming a manganese dioxide layer by thermally decomposing at ~ 300 ° C for 10 to 20 minutes can be mentioned.

In the method of forming the manganese dioxide layer, it is preferable that the pores inside the capacitor element are sufficiently impregnated with the manganese nitrate aqueous solution.

Specific gravity of the manganese nitrate aqueous solution (liquid temperature is 60
The specific gravity at the temperature of ° C (the same applies hereinafter) is preferably about 1.05 to 1.6 so that the pores inside the capacitor element are sufficiently impregnated with the aqueous manganese nitrate solution.

When manganese nitrate in the manganese nitrate aqueous solution impregnated in the capacitor element is decomposed to form a manganese dioxide layer on the capacitor element, the surface tension of the manganese nitrate aqueous solution is lowered in advance. In order to sufficiently permeate the aqueous manganese nitrate solution, it is preferable to carry out preheating in the temperature range of 80 to 130 ° C. for about 15 to 20 minutes.

The heating temperature for decomposing the manganese nitrate to form the manganese dioxide layer on the capacitor element is 200 to 300 ° C. for the sufficient decomposition of the manganese nitrate to form the manganese dioxide layer. 230
It is preferable to set the temperature to about ° C. The heating time cannot be unconditionally determined because it depends on the heating temperature and the like, but it is usually about 10 to 15 minutes.

Next, the capacitor element having the manganese dioxide layer formed thereon is immersed in an aqueous solution of an acidic ammonium salt in order to restore the oxide film deteriorated by the thermal decomposition at the time of forming the manganese dioxide layer, and the anode is again made. Oxidize (reformation process).

As described above, one of the major features of the present invention is that after the manganese dioxide layer is formed on the surface of the capacitor element, the oxide film is repaired using an aqueous solution of an acidic ammonium salt. Thus, when an aqueous solution of an acidic ammonium salt is used in this manner, it is not necessary to perform the complicated operation of drying after repairing the oxide film as in the conventional case, and as described later, manganese nitrate is again used. When a manganese dioxide layer is formed using an aqueous solution, a MnO ₂ film having a low content of impurities such as Mn ₂ O ₃ and having a low specific resistance of, for example, about 1 to 10 Ω · cm can be formed. .

Typical examples of the aqueous solution of the acidic ammonium salt include aqueous solutions of inorganic acid ammonium salts such as ammonium nitrate, ammonium sulfate, ammonium chloride and ammonium carbonate.

The concentration of the ammonium salt in the aqueous solution of the acidic ammonium salt is usually 0.01 to 10% by weight, preferably 0.01 to 0.05% by weight. The temperature of the acidic ammonium salt aqueous solution is not particularly limited, but it is usually 0 to 80 ° C.
It may be about 10 to 60 ° C.

When the oxide film is restored by anodizing the capacitor element, the capacitor element is used as the anode, the electrode plate or the electrolytic cell is used as the cathode, and both are immersed in an aqueous solution of an acidic ammonium salt. .

[0029] between the said capacitor element and the cathode is lead direct current, that this time, the current density in the capacitor element is usually 0.01~1μA / cm ^2, inter alia 0.1 to 0.3 .mu.A / cm ² of about Is preferred.

Thus, by passing a direct current for about 5 to 30 minutes, especially about 15 to 30 minutes, the oxide film of the capacitor element is repaired using an aqueous solution of an acidic ammonium salt.

After the capacitor element is immersed in an aqueous solution of an acidic ammonium salt to repair the oxide film, a manganese dioxide layer is formed again on the surface of the capacitor element by using an aqueous solution of manganese nitrate.

As a method of forming the manganese dioxide layer on the surface of the capacitor element again using the manganese nitrate aqueous solution, for example, there is a method of forming the manganese dioxide layer on the oxide film by using the manganese nitrate aqueous solution. . In this method, it is preferable that the manganese nitrate aqueous solution is sufficiently permeated into the pores inside the capacitor element.

In the present invention, in order to more uniformly form the manganese dioxide layer on the capacitor element, the capacitor element on which the manganese dioxide layer is formed is immersed in an aqueous solution of an acidic ammonium salt and oxidized. It is preferable to repeat the operation of repairing the film (reforming step) and forming a manganese dioxide layer using an aqueous solution of manganese nitrate (solid electrolyte layer forming step). The number of times such an operation is repeated is not particularly limited, but is usually 10 times or less, preferably about 3 to 5 times.

Next, a metal layer is formed around the capacitor element on which the manganese dioxide layer is formed.

Before forming the metal layer, it is preferable to previously form a graphite layer as an electrode underlayer.

As a method for forming such a graphite layer, for example, the capacitor element is immersed in an aqueous dispersion of graphite powder to such an extent that the upper surface of the capacitor element is not dipped, and the graphite powder is attached to the surface of the capacitor element. After squeezing, for example, a method of firing at a temperature of about 100 to 130 ° C. to form a graphite layer, such that the upper surface of the capacitor element is not soaked in a kneaded product obtained by kneading graphite powder into a paste. A method of forming a graphite layer by immersing the kneaded material in the surface of the capacitor element to adhere the kneaded material to the surface of the capacitor element, and then calcining the material at a temperature of about 100 to 130 ° C. It is not something that will be done.

The thickness of the graphite layer is not particularly limited as long as the manganese dioxide layer is completely covered.

Examples of the metal used for the metal layer include silver and nickel, but the present invention is not limited to these examples.

When a silver layer is formed as a metal layer on the capacitor element on which the manganese dioxide layer is formed, silver is added to an aqueous dispersion or paste of silver powder as in the case of forming the graphite layer. The powder is kneaded, and the capacitor element is dipped in these so that the upper surface of the capacitor element is not soaked to adhere to the surface of the capacitor element, and then baked at a temperature of, for example, 210 to 230 ° C. to form a silver layer. Should be formed.

When a nickel layer is formed as the metal layer, the nickel layer may be formed by a commonly used nickel plating method.

The thickness of the metal layer is not particularly limited as long as the manganese dioxide layer or the graphite layer is completely covered.

Thus, a solid electrolytic capacitor can be obtained. Before using the solid electrolytic capacitor, external lead terminals are usually connected to the anode and cathode, respectively, and sealed with a resin such as epoxy resin. It is preferable.

Next, the method for producing the solid electrolytic capacitor of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Example 1 Tantalum powder was used as the metal powder, pressure-molded into a cubic shape with one side of about 1 mm, and a part of the tantalum wire (diameter: 0.2 mm, length: 7 mm) was embedded inside from the upper surface. Then, heat it at about 1500 ℃ for 20 minutes, sinter it, and
A capacitor element 1 as shown in (a) was obtained.

The obtained capacitor element 1 was used as an anode, and as shown in FIG. 1 (b), a part of the capacitor element 1 and the tantalum wire 2 was changed to a 0.1 wt% phosphoric acid aqueous solution (liquid temperature: 60 ° C.) 4. Immersion, the current density of the capacitor element 1
DC current is passed for 5 hours to perform anodic oxidation while adjusting to 0.0364 mA / cm ^2, and tantalum pentoxide (Ta ₂ O ₅ ) is formed as oxide film 3 on the surface of capacitor element 1.
Was formed.

Next, the capacitor element 1 having the oxide film 3 formed thereon is washed with water and dried, and then a manganese nitrate aqueous solution having a specific gravity of 1.6 is impregnated into the inside of the capacitor element,
Then, the capacitor element 1 was taken out from the manganese nitrate aqueous solution and heated at 230 ° C. for 10 minutes to form a manganese dioxide layer 5 on the surface of the capacitor element 1 as shown in FIG. 1 (c).

Next, a capacitor element having a manganese dioxide layer formed thereon was used as an anode, and an electrolytic cell made of stainless steel was used as a cathode. The surface of the capacitor element was treated by immersing it in (liquid temperature: 25 ° C.) and applying a direct current for 30 minutes while adjusting the current density of the capacitor element to 0.2 μA / cm ² .

Next, the surface-treated capacitor element is immersed in a manganese nitrate aqueous solution having a specific gravity of 1.6 to sufficiently impregnate the manganese nitrate aqueous solution into the inside of the capacitor element, and then the capacitor element is removed from the manganese nitrate aqueous solution. It was taken out, placed in an electric oven and heated at 230 ° C. for 10 minutes to form the manganese dioxide layer 5 again.

The operation of immersing the capacitor element in an ammonium nitrate aqueous solution to restore the oxide film, and forming a manganese dioxide layer using the manganese nitrate aqueous solution is repeated 5 times, and as shown in FIG. After forming the manganese layer 5, the graphite powder is dipped so that its upper surface is not dipped, and the capacitor element is taken out of the graphite dispersion liquid and placed in an electric oven.
Firing was performed by heating at 30 ° C. for 30 minutes.

Next, the capacitor element is dipped in a dispersion liquid of silver powder so that the upper surface thereof is not soaked, and then the capacitor element is taken out of the silver dispersion liquid and placed in an electric oven. Firing was performed by heating at 60 ° C. for 60 minutes.

Thus, external lead terminals were connected to the tantalum wire and silver layer of the solid electrolytic capacitor obtained by forming the graphite layer 9 and the silver layer 10 as shown in FIG. It was packaged to obtain a solid electrolytic capacitor.

50 solid electrolytic capacitors thus obtained were prepared, and as physical properties, ESR at a frequency of 100 kHz was measured using an LCR meter. The result is shown in FIG. Further, the average value of ESR of 50 such solid electrolytic capacitors was calculated and found to be 1.08Ω.

Comparative Example 1 Example 1 was repeated except that a 0.1% by weight phosphoric acid aqueous solution was used in place of the 0.05% by weight ammonium nitrate aqueous solution, and the treatment was carried out with the phosphoric acid aqueous solution followed by drying.
A solid electrolytic capacitor was obtained in the same manner as in.

As the physical properties of the 50 solid electrolytic capacitors thus obtained, the ESR was examined in the same manner as in Example 1. The result is shown in FIG. Further, the average value of ESR of 50 such solid electrolytic capacitors was calculated and found to be 3.83Ω.

As is clear from comparison between Example 1 and Comparative Example 1, when the solid electrolytic capacitor was manufactured by the method of Example 1, the capacitor element was treated with the aqueous ammonium nitrate solution and then dried. It can be seen that a solid electrolytic capacitor that does not need to be applied and has a small ESR can be obtained.

Example 2 A solid electrolytic capacitor was obtained in the same manner as in Example 1, except that the 0.01 wt% ammonium carbonate aqueous solution was used instead of the 0.05 wt% ammonium nitrate aqueous solution.

As the physical properties of the obtained 50 solid electrolytic capacitors, ESR was examined in the same manner as in Example 1, and the same results as in Example 1 were obtained.

[0058]

According to the method for producing a solid electrolytic capacitor of the present invention, a solid electrolytic capacitor having a small specific resistance can be easily obtained without requiring a complicated operation such as drying.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a manufacturing process of a solid electrolytic capacitor according to a first embodiment of the present invention.

FIG. 2 is a graph showing the ESR of 50 solid electrolytic capacitors obtained in Example 1 of the present invention.

FIG. 3 is a graph showing the ESR of 50 solid electrolytic capacitors obtained in Comparative Example 1.

[Explanation of symbols]

 1 Capacitor element 3 Oxide film 5 Manganese dioxide layer

Claims (2)

[Claims] 1. (A) a molding step of molding a metal powder into a predetermined shape; (B) a sintering step of sintering the molded body obtained in the molding step; and (C) a sintering step. A step of oxidizing the surface of the capacitor element to form an oxide film, (D) a step of forming a solid electrolyte layer for forming a manganese dioxide layer on the oxide film of the capacitor element obtained in the chemical conversion step, and (E) ) In the method for producing a solid electrolytic capacitor, which comprises a re-chemical conversion step of repairing the oxide film,
A method for producing a solid electrolytic capacitor, characterized in that the re-forming step is performed using an aqueous solution of an acidic ammonium salt. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the chemical conversion step (C) is performed using an aqueous solution of an acidic ammonium salt.