JPH1012497A - Manufacture of solid electrolytic capacitor using conductive polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the converage factor of a solid electrolytic capacitor using conductive polymer and reduce the variations in strength of a capacitance against a temperature change and in electrical characteristics which are caused in the manufacturing process. SOLUTION: A material having high wettability is, in advance, made to adhere to fine hollow holes in porous unit on which a dielectric oxide film is formed (steps S1A and S1B). A certain quantity, enough to the volumes of the hollow holes of the porous unit, of oxidant solution is dropped onto a capacitor element (step S2). A necessary quantity of monomer solution is dropped onto the capacitor element (step S3). As the oxidant solution and the monomer solution are diffused in the solvent of the high wettability material adhering to the surfaces of the fine hollow holes in advance, uniform and defect-free conductive polymer layer are formed on the inner surface and whole outer surface of the porous unit. As the oxidant quantity and the monomer quantity can be controlled to be stoichiometric mol ratios securely, the conductive polymer layer which shows a primary high conductivity can be formed with high reproducibility. Unlike an immersion method, the consumption of the reaction solution itself can be reduced and the replacement of the solution because of the deterioration of the solution is not necessary, so that the manufacturing cost can be reduced.

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 using a conductive polymer as a solid electrolyte, and more particularly to a method for manufacturing a solid electrolytic capacitor in which a conductive polymer layer is formed by a chemical oxidation polymerization method. About.

[0002]

2. Description of the Related Art In recent years, along with demands for miniaturization, high performance, and high frequency of electronic equipment, the size and improvement of high frequency performance of solid electrolytic capacitors have been remarkable. Incidentally, the solid electrolytic capacitor is manufactured by the following manufacturing process, for example. First, as an example, a fine powder of an oxide film-forming metal such as tantalum is formed into a columnar body such as a cylinder or a prism,
After sintering, it has a myriad of fine cavities (pores) inside the column,
A broadened sintered pellet is obtained. Next, a metal oxide (in this case, tantalum oxide Ta ₂₎ is used as a dielectric layer on the inner surface, that is, the surface of the pores and the outer surface of the sintered body.
O ₅ ) is formed. Anodization or the like is used for forming the film. Next, a solid electrolyte layer is formed on the dielectric oxide film, and a cathode conductor layer is formed on the solid electrolyte layer. The cathode conductor layer connects the cathode terminal for external connection to be attached later and the above-mentioned solid electrolyte layer with low resistance, and is formed by, for example, laminating a silver paste layer and a solder layer. Thereafter, a capacitor is completed through mounting of a cathode terminal and an anode terminal for external connection, sealing exterior with a mold resin layer and the like, and terminal molding.

[0003] Here, inorganic semiconductors such as manganese dioxide and lead dioxide have been frequently used as solid electrolytes of solid electrolytic capacitors. However, since those substances have a considerably high resistivity, they are used in a high frequency region. Has a large impedance, and it is becoming difficult to apply such a capacitor to a high-frequency compatible electronic device. Therefore, a solid electrolytic capacitor using a conductive polymer having a low resistivity has been developed, and the impedance characteristics in a high frequency region have been improved.

[0004] The method for obtaining the above-mentioned conductive polymer layer includes the following:
There are a method of electrolytic polymerization of a monomer and a method of chemical oxidation polymerization.In the electrolytic polymerization method, for example, a method of applying an electric field using a mixed solution of a polymerizable monomer and a supporting electrolyte as an electrolytic solution is known. ing. In the chemical oxidative polymerization method, a method of mixing a polymerizable monomer and an oxidizing agent mainly in a liquid phase is known. The present invention relates to a method for manufacturing a solid electrolytic capacitor in which a conductive polymer layer is formed by chemical oxidation polymerization among the above two polymerization methods.

When a solid electrolytic capacitor is manufactured using chemical oxidation polymerization, a capacitor element on which a dielectric film has been formed is immersed in an oxidizing solution stored in a tank, and the oxidizing solution is converted into a dielectric material. A method of applying a monomer solution after attaching it to a body film is general. Also when applying the monomer solution, an immersion method in which the capacitor element is immersed in the monomer solution stored in the tank is used. However, such a manufacturing method using the immersion method requires a large amount of solution since the capacitor element must be surely immersed in each solution. Since the immersion immersion, the oxidizing agent is mixed into the monomer solution on the side to be immersed, and an oxidation reaction occurs. In addition to the decrease with the passage of time, the concentration also changes due to repetition of immersion, so that it is necessary to frequently change the liquid. Also, in this method, the controllability of the amount of the oxidizing agent and the monomer attached to the capacitor element is poor. In other words, the molar ratio between the oxidizing agent and the monomer is strictly controlled to the stoichiometric molar ratio. However, it is difficult to obtain the originally expected high conductivity with good reproducibility, and the stability of the electrical characteristics of the capacitor is lacking.

In order to improve such a problem, the techniques disclosed in Japanese Patent Application Laid-Open Nos. 3-198315 and 6-45197 have been invented. That is, the monomer solution and the oxidizing agent solution are separately adjusted, and a certain amount of the monomer solution and a certain amount of the oxidizing agent solution are alternately dropped onto the chemical conversion foil portion to be subjected to the chemical oxidative polymerization. Then, chemical oxidation polymerization is performed to form a conductive polymer layer.

[0007]

The method of forming a conductive polymer layer by chemical oxidation polymerization described in the above-mentioned publication includes a method of forming a conductive polymer layer by covering the capacitor (the total area of the dielectric oxide film, (The ratio of the area of the formed dielectric oxide film) is small.

[0008] This is because the surface tension of the air, the monomer solution or the oxidant solution contained in the pores in the capacitor element is reduced by the monomer solution or the oxidant solution dropped on the outer surface of the capacitor element. This is because it impedes penetration into the pores and causes a portion where the conductive polymer layer is not formed on the dielectric oxide film. If the coverage is small, as will be described later, the capacitance value of the capacitor is likely to change depending on the environment, particularly the ambient humidity, and the stability is lacking.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solid electrolytic capacitor using a conductive polymer as a solid electrolyte, which has a high covering rate and a high stability against a change in capacitance value due to humidity. It is assumed that.

Another object of the present invention is to form a conductive polymer exhibiting the original high conductivity with higher reproducibility than by the immersion method, and to reduce variations in the characteristics of the capacitor during manufacturing. Things.

Another object of the present invention is to reduce the amount of a monomer solution and an oxidizing agent solution used in forming a conductive polymer layer as compared with the immersion method, thereby enabling a reduction in manufacturing cost. .

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention has made intensive studies on a method of manufacturing a solid electrolytic capacitor using a conductive polymer as a solid electrolyte. As a result, the invention of this application was reached.

That is, in the method for manufacturing a solid electrolytic capacitor of the present invention, a step of forming a porous body having a large number of fine pores therein using a metal having an oxide film formation; A step of forming a metal oxide film as a dielectric, and a step of forming a conductive polymer layer as a solid electrolyte layer on the metal oxide film by chemical oxidation polymerization,
Forming a cathode conductor layer on the conductive polymer layer,
A method of manufacturing a solid electrolytic capacitor, comprising: attaching an external terminal and providing an exterior, wherein the step of forming the conductive polymer layer comprises applying a highly wettable liquid to the metal oxide film on the surface of the fine pores in the porous body. A first step of attaching, a second step of dropping an oxidizing agent solution or a monomer solution in an amount equal to or less than the pore volume of the porous body to the porous body after the completion of the first step; In response to the dropping of the oxidizing agent solution or the monomer solution in the first step, the porous body after the step 2 is completed,
Dropping a monomer solution or an oxidizing agent solution in an amount equal to or less than the pore volume of the porous body.

The amount of the monomer solution and the oxidizing agent solution to be dropped is preferably not more than the pore volume of the porous material, and the stoichiometric molar ratio between the oxidizing agent and the monomer determined by the polymerization reaction formula. It is desirable that the amount of the monomer be within 1 to 15 times the ratio.

The substance having high wettability to be formed in advance is not limited, but is preferably an oxidizing agent or a good solvent for a monomer, for example, water or an organic solvent such as an alcohol solvent.

The monomer is preferably an aromatic monomer or a five-membered heterocyclic monomer, such as pyrrole, aniline, thiophene, furan or a derivative thereof.

The porous body is preferably a sintered body, but may be a foil shape.

According to the present invention, the reaction liquid dropped later diffuses into the solvent of the substance having a high wettability, which is previously adhered to the entire dielectric oxide film on the surface of the pores in the porous body. The reaction liquid uniformly adheres to the entire surface of the dielectric oxide film on the surface of the pores in the porous body. Thereby, a solid electrolytic capacitor having a high coverage can be manufactured.

The supply of the reaction liquid to the capacitor element is performed by dripping using a nozzle having a thin tip. Therefore, it is possible to supply a required amount of the reaction solution having an excellent controllability of the supply amount and a stoichiometric molar ratio corresponding to the vacant volume of the porous body. Therefore, the obtained conductive polymer layer has high conductivity which can be expected by chemical reaction theory, and has good reproducibility. In addition, the use amount of the reaction solution itself is small, and there is no deterioration of the reaction solution itself due to repeated mixing and immersion of the reaction solution in the tank. Can be reduced.

[0020]

Next, an embodiment of the present invention will be described with reference to the drawings. First, FIG. 1 is a process flow chart sequentially showing the manufacturing steps of the method for manufacturing a solid electrolytic capacitor according to the present invention. 2 and 3 are views showing a cross section of the capacitor in accordance with the process order of FIG.
FIG. 3 is a diagram showing a cross section of a completed capacitor. In the embodiment described below, a tantalum solid electrolytic capacitor whose sectional view is shown in FIG. 4 was manufactured by the manufacturing process shown in FIG. 1, FIG. 2 or FIG. Hereinafter, embodiments of the present invention will be specifically described based on some examples and comparative examples.

Example 1 In this example, a tantalum solid electrolytic capacitor was manufactured based on the process flow shown in FIG. 1, specifically, by the method shown in FIG.

First, a tantalum sintered body 2 was prepared using tantalum fine powder. This sintered body 2 is 3.2 mm ×
An anode lead wire 1 made of tantalum wire is planted on one end face in advance of a 1.8 mm × 3.4 mm prism. The porosity is 70% and the porosity volume is 12 μl. Next, a tantalum oxide (Ta ₂ O ₅ ) film 3 was formed as a dielectric film on the inner surface and the outer surface of the sintered body 2. The film is formed by anodic oxidation in a phosphoric acid aqueous solution at a voltage of 27 V
Was applied. This state is hereinafter referred to as a capacitor element 4.

Next, the obtained capacitor element 4 was immersed in methanol to fill the pores with methanol (step S1A, FIG. 2 (b)).

Thereafter, the capacitor element was pulled out of methanol, a part of the filled methanol was dried, and a methanolic solution of ferric p-toluenesulfonate as an oxidizing agent was dropped on the capacitor element (step S2).
Ferric methanol solution of p-toluenesulfonic acid has a concentration of 40
wt. %, And the drop amount is 5 μl (0.45 mmol) per capacitor element.

Next, the solvent was dried, and subsequently pyrrole, which was a monomer solution, was dropped on the capacitor element, dried and polymerized, and then the element was washed with methanol (step S3). The amount of pyrrole dropped was 1.5 μl (0.23 mmol) per capacitor element. still,
The stoichiometric molar ratio between the oxidizing agent and pyrrole determined by the chemical reaction formula is 2: 1, and the molar ratio in the present example substantially matches the value.

The operations of steps S1A, S2 and S3 were repeated five times to form a polypyrrole film 5 on the tantalum oxide film 3.

Thereafter, a cathode conductor layer 6 is formed on the polypyrrole film 5, an external anode terminal 7 is welded to the anode lead wire 1, and an external cathode terminal 9 is formed on the cathode side by using a conductive adhesive 8.
After fixing, the tantalum solid electrolytic capacitor of the present example was obtained by coating the resin with the mold resin 10.

The obtained capacitor was subjected to a high-temperature and high-humidity test, and the capacitance value was compared before and after the test. The test conditions are
It is left unloaded for 100 hours in an atmosphere of a temperature of 65 ° C. and a humidity of 90 to 95% RH. The capacitance value is 1k
The value in Hz was measured. Table 1 shows the test results. The capacitance value ratio before and after the test (capacity value after the test / capacity value after the test) was 1.08, and it was confirmed that the coverage was high. It is generally known that when a high-temperature and high-humidity test is performed on a capacitor, the capacitance value after the test becomes larger than the capacitance value before the test. This is because moisture is adsorbed on a portion of the dielectric oxide film that is not covered with the conductive polymer layer, and that portion contributes to capacity development. From this, it can be determined that the smaller the above-mentioned capacitance value ratio, the higher the coverage ratio, and the capacitance value ratio is specified as 1.2 or less as a product standard for commercial capacitors.

Embodiment 2 In this embodiment, a tantalum solid electrolytic capacitor was manufactured based on the process flow shown in FIG. 1, specifically, by the method shown in FIG. That is, although the same capacitor element as in the first embodiment is used, the method of filling the pores in the capacitor element with methanol is different from the first embodiment. In the present embodiment, filling with methanol (Step S1B; FIG. 3B)
At this time, a sufficient amount of methanol was dropped on the capacitor element.

The obtained capacitor was subjected to a high-temperature and high-humidity test under the same conditions as in Example 1, and the capacitance value was measured before and after the test. Table 1 shows the test results. The capacitance value ratio before and after the test was 1.05, confirming that the coverage was high.

(Embodiment 3) This embodiment is different from Embodiment 1 in that
The difference is that the solvent used is changed from methanol to isopropyl alcohol. Other manufacturing methods and conditions are:
This is the same as the first embodiment.

The obtained capacitor was subjected to a high-temperature and high-humidity test under the same conditions as in Example 1, and the capacitance value was measured before and after the test. Table 1 shows the test results. The capacitance ratio before and after the test was 1.10, confirming that the coverage was high.

(Embodiment 4) This embodiment is different from Embodiment 1 in that
The difference is that the amount of pyrrole dropped in step S3 is quadrupled to 6.0 μl. That is, the molar ratio between the oxidizing agent and pyrrole was changed from 2: 1 to 1: 2 in Example 1.
Has been changed to. Other manufacturing methods and conditions are described in Example 1.
Is the same as

The obtained capacitor was subjected to a high-temperature and high-humidity test under the same conditions as in Example 1, and the capacitance value was measured before and after the test. Table 1 shows the test results. The capacitance value ratio before and after the test was 1.04, and it was confirmed that the coverage was high.

Comparative Example 1 This comparative example is different from Example 1 in that
Filling the capacitor element with methanol (Step S1A)
Is omitted. That is, the oxidizing agent was directly dropped on the capacitor element on which the tantalum oxide film had been formed (Step S2). Other manufacturing methods and conditions are the same as those in the first embodiment.

The obtained capacitor was subjected to a high-temperature and high-humidity test under the same conditions as in Example 1, and the capacitance value was measured before and after the test. Table 1 shows the test results. The capacitance value ratio before and after the test was 1.27, indicating that the coverage was worse than that of the examples described above.

Comparative Example 2 This comparative example is different from Example 1 in that
The difference is that the amount of the oxidizing agent solution dropped in step S2 and the amount of the pyrrole dropped in step S3 are increased to be larger than the pore volume of the tantalum sintered body while the manufacturing process flow is the same. ing. In this embodiment, the drop amount of the oxidizing agent solution in Step S2 is set to 15 μL, and Step S3
The amount of pyrrole dropped in the above was 4.5 μl. Other manufacturing methods and conditions are the same as those in the first embodiment.

The obtained capacitor was subjected to a high-temperature and high-humidity test under the same conditions as in Example 1, and the capacitance value was measured before and after the test. Table 1 shows the test results. The ratio of the capacitance values before and after the test was 1.25, indicating that the coverage was worse than in the previous examples. This is because when the amount of the oxidizing agent solution and the monomer solution is more than the volume of the pores, the dropped solution covers the pores in the sintered body and blocks the escape path of the air in the pores. It is presumed.

(Embodiment 5) This embodiment is different from Embodiment 1 in that
The difference is that the monomer in step S3 was changed from pyrrole to thiophene, and the amount of thiophene dropped was set to 2 μl according to the molecular weight, while the production process flow was the same. Other manufacturing methods and conditions are the same as those in the first embodiment.

The obtained capacitor was subjected to a high-temperature and high-humidity test under the same conditions as in Example 1, and the capacitance value was measured before and after the test. Table 1 shows the test results. The capacitance ratio before and after the test was 1.09, confirming that the coverage was high.

[0041]

[Table 1]

In Example 4 described above, the effect of increasing the coverage was obtained by increasing the amount of the monomer (pyrrole) to be dropped by four times the amount determined by the stoichiometric molar ratio. It was confirmed that the same effect as in Example 4 could be obtained even when the amount was increased to twice. However, when the amount of the monomer was smaller than 1, the deterioration of the coverage was observed. Therefore, the drop amount of the monomer is
It can be said that the amount is preferably 1 to 15 times the amount determined by the stoichiometric molar ratio.

In the above-described embodiments, the oxidizing agent solution was deposited in step S2, and then the monomer was deposited in step S3. However, this process was replaced, and the monomer was deposited first. By attaching an oxidizing agent after
It was confirmed that the same effect as in each example was obtained.

Further, in the present embodiment, pyrrole or thiophene is used as a monomer, but the monomer is not limited to them.
Any π-conjugated molecule may be used. However, aromatic or hetero-five-membered ring monomers such as pyrrole, aniline, thiophene, N-methylpyrrole, furan, etc. are suitable because of their high heat resistance. Methanol or isopropyl alcohol was used as the substance having high wettability, but is not limited thereto.

[0045]

As described above, according to the present invention, a substance having a high wettability is attached to the surface of the fine pores in the porous body on which the dielectric oxide film is formed before the reaction liquid is attached. Let me. Therefore, the reaction solution dropped on the outer surface of the porous body diffuses in the solvent of the substance having high wettability and adheres to the entire surface of the fine pores inside the porous body. As a result, according to the present invention, it is possible to provide a solid electrolytic capacitor having an excellent environmental protection property, in which the coverage ratio is improved and the capacitance value does not change even when the ambient humidity changes.

In the present invention, the oxidizing agent solution and the monomer solution are supplied dropwise. Therefore, it is easy to control the amount of each solution attached, and the molar ratio of the oxidizing agent and the monomer can be controlled strictly to the stoichiometric molar ratio with good reproducibility. Thus, according to the present invention, a conductive polymer having an original high conductivity expected from the stoichiometry can be formed with good reproducibility, so that variations in the electrical characteristics of the capacitor during manufacturing can be reduced.

Moreover, the reaction solution is dropped in an amount corresponding to the pore volume of the porous body, so that the reaction solution is compared with the conventional manufacturing method in which the capacitor element is immersed in the reaction solution stored in the tank. The use amount can be reduced, and the manufacturing cost can be reduced.

In addition, since there is no deterioration of the monomer due to mixing of the oxidizing agent and the monomer in the reaction solution tank and a decrease in the oxidizing power due to repeated immersion, the frequency of replacement of the reaction solution is reduced. However, manufacturing costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a manufacturing process flow chart of a method for manufacturing a solid electrolytic capacitor according to the present invention.

FIG. 2 is a diagram showing a cross section of the capacitor according to the embodiment of the present invention in the order of manufacturing steps.

FIG. 3 is a diagram showing a cross section of the capacitor according to the embodiment of the present invention in the order of manufacturing steps.

FIG. 4 is a sectional view of a tantalum solid electrolytic capacitor according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode lead wire 2 Tantalum sintered body 3 Tantalum oxide film 4 Capacitor element 5 Polypyrrole film 6 Cathode conductor layer 7 External anode terminal 8 Conductive adhesive 9 External cathode terminal 10 Mold resin

Claims (9)

[Claims] 1. A step of forming a porous body having a large number of fine pores therein using a metal capable of forming an oxide film, and oxidizing the porous body to form a metal oxide film as a dielectric on the surface. A step of forming a conductive polymer layer as a solid electrolyte layer on the metal oxide film by chemical oxidation polymerization, a step of forming a cathode conductor layer on the conductive polymer layer, and attaching external terminals. In the method for manufacturing a solid electrolytic capacitor including a step of providing an exterior, the step of forming the conductive polymer layer includes the step of first adhering a highly wettable liquid to the metal oxide film on the surface of the fine pores in the porous body. And dropping an oxidizing agent solution or a monomer solution in an amount equal to or less than the pore volume of the porous body to the porous body after the completion of the first step.
And a step of adding the oxidizing agent solution or the monomer solution in the first step to the porous body after the completion of the second step. A method of dropping a dimer solution or an oxidizing agent solution. 2. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the amount of the oxidizing agent solution and the amount of the monomer solution dropped in the second step and the third step of forming the conductive polymer layer are: A method for producing a solid electrolytic capacitor, characterized in that the amount of the monomer solution is in the range of 1 to 15 times the molar ratio determined stoichiometrically by the polymerization reaction formula. 3. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein in the first step of forming the conductive polymer layer, when the liquid having a high wettability is attached, A method for manufacturing a solid electrolytic capacitor, characterized by immersing a porous body in the liquid having high wettability stored in a tank. 4. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein in the first step of forming the conductive polymer layer, the liquid having high wettability is adhered after the formation of the metal oxide film. A method for manufacturing a solid electrolytic capacitor, characterized in that the liquid having high wettability is dropped on a porous body. 5. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein in the first step of forming the conductive polymer layer, any one of water and an organic solvent is used as the liquid having a high wettability. A method for manufacturing a solid electrolytic capacitor. 6. The method for manufacturing a solid electrolytic capacitor according to claim 5, wherein an alcohol is used as the organic solvent in the first step of forming the conductive polymer layer. Method. 7. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein any one of an aromatic monomer and a five-membered heterocyclic monomer is used as the monomer. Manufacturing method of capacitor. 8. The method for manufacturing a solid electrolytic capacitor according to claim 7, wherein the monomers include pyrrole, aniline, thiophene,
A method for producing a solid electrolytic capacitor, comprising using one of furan and a derivative thereof. 9. The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein a sintered body of a fine powder of the oxide film-forming metal is used as the porous body.