JP3150464B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

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 manufacturing a solid electrolytic capacitor capable of easily manufacturing 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, niobium, etc. To form a manganese dioxide layer, repair the oxide film in a reconversion solution consisting of a phosphoric acid aqueous solution, and repeat the steps of drying, and then a graphite layer and a silver layer for taking out electrodes on the outer periphery of the capacitor element. Is manufactured by a method of forming

However, in the above method, the After repair an oxide film by reformation solution, phosphate ions contained in the re-conversion solution is less likely to evaporate, so remain inside the sintered body, sufficiently washed with water it is necessary to perform a to drying, the manufacturing operation is complicated, moreover the solid electrolytic capacitor to be example, therefore large specific resistance, equivalent series resistance (hereinafter, referred to as ESR) disadvantageously increases Was.

[0004]

In view of the above-mentioned problems, the present inventors have conducted intensive studies in order to obtain a solid electrolytic capacitor having a small specific resistance without requiring complicated operations such as washing and drying. results, in a case where the reformation was carried out using an aqueous solution of an ammonium salt of acid, a
The ammonium salt sublimates easily and evaporates, and does not require complicated operations such as washing with water and drying, but rather does not dry.
By repeating the manganese dioxide layer formation process with
The inventors have found a completely new fact that a solid electrolytic capacitor having a small specific resistance can be obtained, and have completed the present invention.

[0005]

That is, the present invention provides: (A) a molding step of molding a tantalum powder into a predetermined shape; (B) a sintering step of sintering the compact 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; and (D) forming a manganese dioxide layer on the oxide film of the capacitor element obtained in the chemical conversion step. In a method for producing a solid electrolytic capacitor including a step of forming a solid electrolyte layer, and (E) a re-chemical conversion step of repairing the oxide film, the (E) re-chemical conversion step is performed using an aqueous solution of an acidic ammonium salt,
The present invention relates to a method for manufacturing a solid electrolytic capacitor, wherein the step (D) is performed again after the step (E) is performed, and the process is repeated a plurality of times.

[0006]

Operation and Examples As described above, the method for manufacturing the solid electrolytic capacitor of the present invention comprises the steps of (A) forming a metal powder into a predetermined shape, and (B) firing the formed body obtained in the forming step. A sintering step for bonding, (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) a chemical conversion step on the oxide film of the capacitor element obtained in the chemical conversion step. In the method for producing a solid electrolytic capacitor including a step of forming a solid electrolyte layer for forming a manganese dioxide layer, and (E) a re-chemical conversion step of repairing the oxide film, the (E) re-chemical conversion step is performed by using an aqueous solution of an acidic ammonium salt. This is a production method characterized by using

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

Further, according to the method for manufacturing a solid electrolytic capacitor of the present invention, a solid electrolytic capacitor having a small specific resistance can be obtained. Probably, a solid electrolytic capacitor with a small specific resistance is obtained because the capacitor element on which the manganese dioxide layer is formed is immersed in an aqueous solution of an acidic ammonium salt to repair the oxide film, and then the manganese nitrate aqueous solution is used. It is considered that the formation of MnO ₂ is promoted when the manganese dioxide layer is formed, and the formation of Mn ₂ O ₃ is suppressed.

The metal powder constituting the capacitor element used in the present invention is, for example, a metal powder such as tantalum, aluminum, niobium and the like.

[0010] In order to obtain the predetermined shape, the capacitor element is formed by pressing and molding using a molding die having a desired shape in advance (forming step) and then sintering. Made (sintering process).

When the capacitor element is manufactured by sintering, it is preferable that a metal wire forming an electrode is embedded in a 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 exposed surface inside through the hole of the capacitor element, and a partial surface of the metal wire (chemical formation step).

As a method of forming an oxide film by anodic oxidation, 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 a cathode, both are immersed in an electrolyte solution, and a direct current is passed.

Representative examples of the electrolyte solution include, for example, an aqueous solution of an acidic ammonium salt, an aqueous solution of phosphoric acid, and an aqueous solution of ammonium borate. However, the present invention is not limited to these examples. The concentration of the electrolyte in the electrolyte solution cannot be determined unconditionally because it varies depending on the type of the electrolyte and the like. The temperature of the electrolyte solution is not particularly limited, but may be generally 0 to 80 ° C, preferably 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 ,
Preferably, it is about 0.02 to 0.04 mA / cm ² .

Thus, by passing a direct current, the surface of the capacitor element, the inner surface thereof and a part of the surface of the metal wire through the hole of the capacitor element are formed.
An oxide film of a metal constituting the capacitor element and the metal wire is formed.

After an oxide film is formed 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 forming a manganese dioxide layer on the capacitor element using an aqueous solution of manganese nitrate, it is preferable to wash the capacitor element with pure water, for example, 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 immersed in an aqueous manganese nitrate solution to form a nitric acid solution. After impregnating with a manganese aqueous solution, add 200 g of manganese nitrate.
A method of forming a manganese dioxide layer by pyrolyzing at ~ 300 ° C for 10-20 minutes.

In the method of forming the manganese dioxide layer, it is preferable to sufficiently impregnate the manganese nitrate aqueous solution into the pores inside the capacitor element.

The specific gravity of the manganese nitrate aqueous solution (liquid temperature is 60
The specific gravity at a temperature of ° C., hereinafter the same) is preferably about 1.05 to 1.6 in order to sufficiently impregnate the pores inside the capacitor element with the aqueous solution of manganese nitrate.

When the manganese nitrate in the aqueous manganese nitrate solution impregnated in the capacitor element is decomposed to form a manganese dioxide layer on the capacitor element, the surface tension of the aqueous manganese nitrate solution is reduced in advance to reduce the manganese nitrate aqueous solution. In order to sufficiently infiltrate the aqueous solution of manganese nitrate therein, it is preferable to perform preheating at a temperature range of, for example, 80 to 130 ° C. for about 15 to 20 minutes.

The heating temperature when the manganese nitrate is decomposed to form a manganese dioxide layer on the capacitor element is 200 to 300 ° C., preferably 210 to 300 ° C. in order to sufficiently decompose the manganese nitrate to form the manganese dioxide layer. 230
It is preferable that the temperature be about ° C. The heating time differs depending on the heating temperature and the like, and cannot be unconditionally determined.

Next, the capacitor element on which the manganese dioxide layer has been formed is immersed in an aqueous solution of an acidic ammonium salt in order to repair an oxide film that has been deteriorated by thermal decomposition during the formation of the manganese dioxide layer, and then immersed in the anode again. Oxidation (reformation step).

As described above, the present invention has one major feature in that after forming a manganese dioxide layer on the surface of the capacitor element, the oxide film is repaired using an aqueous solution of an acidic ammonium salt. In the case where an aqueous solution of an acidic ammonium salt is used as described above, it is not necessary to perform a complicated operation of drying after repairing the oxide film as in the related art, and it is necessary to perform manganese nitrate again as described later. When a manganese dioxide layer is formed using an aqueous solution, an 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. .

As the aqueous solution of the acidic ammonium salt, for example, an aqueous solution of an inorganic acid ammonium salt such as ammonium nitrate, ammonium sulfate, ammonium hydrochloride and ammonium carbonate can be mentioned as a typical example.

The concentration of the ammonium salt in the aqueous solution of the acidic ammonium salt is usually about 0.01 to 10% by weight, preferably about 0.01 to 0.05% by weight. The temperature of the aqueous solution of the acidic ammonium salt is not particularly limited, but is usually 0 to 80 ° C.
What is necessary is just about 10-60 degreeC.

In repairing the oxide film by anodizing the capacitor element, a capacitor element is used as an anode, an electrode plate or an electrolytic cell is used as a 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.

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 on the surface of the capacitor element again using a manganese nitrate aqueous solution.

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

In the present invention, in order to form a manganese dioxide layer more evenly 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 to oxidize the element. It is preferable to repeat the operation of restoring the film (re-chemical conversion step) and forming a manganese dioxide layer using an aqueous manganese nitrate solution (solid electrolyte layer forming step). The number of repetitions of such an operation is not particularly limited, but is usually 10 or less, preferably about 3 to 5 times.

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

Before forming the metal layer, it is preferable to form a graphite layer to be an electrode underlayer in advance.

As a method of forming such a graphite layer, for example, the capacitor element is immersed in an aqueous dispersion of graphite powder so that the upper surface of the capacitor element is not immersed, and the graphite powder is adhered to the surface of the capacitor element. A method of forming a graphite layer by baking at a temperature of, for example, about 100 to 130 ° C., and a method of immersing the capacitor element in a kneaded product obtained by kneading graphite powder in a paste so that the upper surface of the capacitor element is not immersed. And then sintering at a temperature of about 100 to 130 ° C. to form a graphite layer.However, the present invention is not limited to only these examples. It is not something to be done.

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

The metal used for the metal layer includes, for example, silver, nickel and the like, but the present invention is not limited only 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, a silver powder aqueous dispersion or paste is added to the silver powder as in the case of forming the graphite layer. Using a kneaded powder, the capacitor element is immersed in these so that the upper surface thereof is not immersed, and adhered to the surface of the capacitor element. May be formed.

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

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 is obtained. Before using the solid electrolytic capacitor, external lead terminals are usually connected to the anode and the cathode, respectively, and sealed using a resin such as an epoxy resin. Is preferred.

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

Example 1 Tantalum powder was used as a metal powder, pressed into a cubic shape having a side of about 1 mm, and a part of a tantalum wire (diameter: 0.2 mm, length: 7 mm) was buried from the upper surface. After that, heat at about 1500 ℃ for 20 minutes, sinter and
A capacitor element 1 as shown in FIG.

Using the obtained capacitor element 1 as an anode, as shown in FIG. 1B, the capacitor element 1 and a part of the tantalum wire 2 were converted to a 0.1% by weight phosphoric acid aqueous solution (liquid temperature: 60 ° C.) 4. Immersion, the current density of the capacitor element 1
Anodizing is performed by applying a direct current for 5 hours while adjusting to 0.0364 mA / cm ^2, and tantalum pentoxide (Ta ₂ O ₅ ) is formed as an oxide film 3 on the surface of the capacitor element 1.
Was formed.

Next, the capacitor element 1 on which the oxide film 3 has been formed is washed with water and dried, and then impregnated with an aqueous solution of manganese nitrate having a specific gravity of 1.6 into the inside of the capacitor element.
Then, the capacitor element 1 was taken out of the aqueous manganese nitrate 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.

Next, the capacitor element on which the manganese dioxide layer was formed was used as an anode, and an electrolytic bath made of stainless steel was used as a cathode. (Liquid temperature: 25 ° C.), and a DC current was supplied for 30 minutes while adjusting the current density of the capacitor element to be 0.2 μA / cm ² to treat the surface of the capacitor element.

Next, the capacitor element whose surface was treated was immersed in an aqueous solution of manganese nitrate having a specific gravity of 1.6 to sufficiently impregnate the aqueous solution of manganese nitrate into the interior of the capacitor element. The manganese dioxide layer 5 was formed again by heating in the electric oven at 230 ° C. for 10 minutes.

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

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

Thus, as shown in FIG. 1 (e), the external lead terminals were respectively connected to the tantalum wire and the silver layer of the solid electrolytic capacitor obtained by forming the graphite layer 9 and the silver layer 10, and then using a resin. The exterior was completed to obtain a solid electrolytic capacitor.

The obtained 50 solid electrolytic capacitors 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 1.08Ω.

Comparative Example 1 The procedure of Example 1 was repeated, except that a 0.1% by weight aqueous solution of phosphoric acid was used instead of the 0.05% by weight aqueous solution of ammonium nitrate, treated with the aqueous solution of phosphoric acid, and then dried.
A solid electrolytic capacitor was obtained in the same manner as described above.

The ESR of the obtained 50 solid electrolytic capacitors was examined in the same manner as in Example 1. The result is shown in FIG. The average value of the ESR of 50 such solid electrolytic capacitors was 3.83Ω.

As is clear from the comparison between Example 1 and Comparative Example 1, when a solid electrolytic capacitor was manufactured by the method of Example 1, the capacitor element was treated with an aqueous solution of ammonium nitrate and then dried. It can be seen that a solid electrolytic capacitor which 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 an aqueous solution of 0.01% by weight of ammonium carbonate was used instead of the aqueous solution of 0.05% by weight of ammonium nitrate.

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

[0058]

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

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a manufacturing process of a solid electrolytic capacitor in Embodiment 1 of the present invention.

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

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

[Explanation of symbols]

 Reference Signs List 1 capacitor element 3 oxide film 5 manganese dioxide layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01G 9/04 307 H01G 9/032

Claims (2)

(57) [Claims] 1. (A) a molding step of molding a tantalum powder into a predetermined shape; (B) a sintering step of sintering the compact obtained in the molding step; and (C) a sintering step. Forming a oxide film by oxidizing the surface of the capacitor element obtained, (D) forming a solid electrolyte layer to form a manganese dioxide layer on the oxide film of the capacitor element obtained in the chemical conversion step, and (E) ) A method for producing a solid electrolytic capacitor comprising a re-chemical conversion step of repairing the oxide film.
A method for producing a solid electrolytic capacitor, characterized in that the re-chemical conversion step is performed using an aqueous solution of an acidic ammonium salt, and the step (E) is performed, then the step (D) is performed again, and each of the steps is repeated a plurality of times. 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.