JPH0693419B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a solid electrolytic capacitor using a solid electrolyte.

2. Description of the Related Art In recent years, with the digitization of circuits such as electric devices, it has been strongly demanded that capacitors used in the circuits have a low impedance in a high frequency range, a small size, and a large capacity.

Conventionally, as high frequency capacitors, there are plastic film capacitors, mica capacitors, and laminated ceramic capacitors. However, it is difficult to increase the capacity of these capacitors because they are too large in shape.

On the other hand, as capacitors suitable for increasing the capacity, aluminum dry electrolytic capacitors, aluminum solid electrolytic capacitors, and tantalum solid electrolytic capacitors are known.

In an aluminum dry electrolytic capacitor, an etched positive and negative aluminum foil is wound around a paper separator so as to be impregnated with a liquid electrolyte.
However, the aluminum dry electrolytic capacitor has a serious problem of deterioration of characteristics due to electrolyte leakage and evaporation. In order to improve this point, the latter two types of aluminum and tantalum solid electrolytic capacitors were solidified by using manganese dioxide as an electrolyte.

In addition, as the solid stage capacitor, instead of the manganese dioxide layer, 7,7,8,8-tetracyanoquinodimethane complex salt (TCNQ salt) is used for the solid electrolyte (Japanese Patent Publication No. 56-10777). JP-A-58-17609), and further, by conducting electropolymerization using a solution containing a heterocyclic compound monomer such as pyrrole or furan and a supporting electrolyte, a high conductivity containing the anion of the supporting electrolyte as a dovant. There are those using a molecular layer for a solid electrolyte (Japanese Patent Laid-Open Nos. 60-37114 and 60-244017).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in a capacitor using a manganese dioxide layer as a solid electrolyte, the dielectric film is damaged by a plurality of thermal decomposition treatments during the manufacturing process. There is a problem in that the resistivity of the manganese dioxide layer is high and the loss at high frequencies is considerably large.

Capacitors that use TCNQ salt as a solid electrolyte are not practical because they have problems such as an increase in specific resistance when applying TCNQ salt and weak adhesion to the anode metal foil.

On the other hand, in a capacitor using a conductive polymer layer formed by electrolytic polymerization as a solid electrolyte, it is technically difficult to form an electrolytic polymerization layer on a dielectric film. Normal anode (for example,
It has already been known that a highly conductive electrolytic polymerized film can be formed on a platinum (carbon, etc.) by using a solution of a heterocyclic compound such as pyrrole, thiophene, or a derivative thereof and an appropriate supporting electrolyte. This is because it is theoretically difficult to form the electrolytically polymerized conductive polymer layer on the derivative film because the dielectric film, which is a material, does not pass an electric current.

It is possible to form the electropolymerized conductive polymer layer before forming the dielectric film (oxide film) and then form the dielectric film by a chemical conversion reaction. Since the polymerized polymer layer is deteriorated / deteriorated and the polymer layer / metal body is peeled off, a capacitor having sufficient characteristics cannot be obtained in practice and its practicality is low.

Further, an electrode for voltage application is externally contacted with a conductive substance provided on a part of the surface of the metal body having a dielectric film,
It has been proposed to use this as a starting point to deposit and grow an electrolytically polymerized polymer layer (JP-A-62-165313).
Issue).

In addition, after coating a part of the surface of the metal body having the dielectric film with an insulating polymer film, the whole is made conductive, and a metal electrode for an anode is brought into contact with the outside to form an electrolytically polymerized polymer layer. It has also been proposed to precipitate and grow (Japanese Unexamined Patent Publication No.
105523 publication).

However, the former method has a problem that the electropolymerization growth is extremely slow because the portion other than the starting point is in an insulating state. On the other hand, the latter method has a problem that the surface area that can be practically used for the capacitor is reduced. In addition, both methods have a common problem that the obtained capacitor has a large leakage current. This is because the anode electrode brought into contact during electrolytic polymerization damages the dielectric film.

In view of the above circumstances, the present invention can rapidly form an electropolymerized polymer layer for a solid electrolyte having a good film quality without reducing the surface area for a capacitor, and has excellent electrical characteristics with a small leakage current. An object of the present invention is to provide a method capable of obtaining a solid electrolytic capacitor having.

Means for Solving the Problems In order to solve the first problem, the claims (1) to (6)
In the method for producing a solid electrolytic capacitor described above, a metal body (valve metal) formed by forming a dielectric film on the surface by anodic oxidation or anodization, and laminating a conductive layer on the film is used as a heterocyclic compound monomer. Placed in an electrolytic solution containing at least a supporting electrolyte, by contacting the conductive layer to a liquid electrode for voltage application to carry out an electrolytic polymerization reaction of the monomer,
A conductive electropolymerized polymer layer for a solid electrolyte is laminated on the conductive layer.

The metal of the metal body on the surface of which a dielectric film (oxide film) is formed by anodic oxidation or anodization in this invention is
As in the invention according to claim (5), for example, at least one of aluminum, tantalum, and titanium can be used. The metal body is, more specifically, an aluminum foil,
The conductivity of the conductive layer laminated on the dielectric film such as tantalum foil, titanium foil, or alloy foil of these metals does not need to be so high, and substantial growth of electrolytic polymerized film is possible. It can be used as long as it has a conductivity (normally 10 ^-3 S / cm or more). As a specific conductive layer, considering the chemical conversion of the dielectric film on the surface of the metal body, for example,
A layer containing a manganese oxide such as manganese dioxide is preferable as in the invention of claim (6).

As the heterocyclic compound monomer contained in the electrolytic solution used in the electrolytic polymerization of the present invention, for example, at least proline, thiophene, or a derivative thereof (for example, N-methylpyrrole) can be used as in the invention of claim (4). Examples thereof include furan and selenophene, and examples of the supporting electrolyte include sodium p-toluenesulfonate and tetra-n-butylammonium p.
-Toluene sulfonate, tetra-n-butylammonium perchlorate and the like can be mentioned. Of course, the present invention is not limited to these, as long as electrolytic polymerization is possible and an electrolytic polymerization film having a conductivity of about 1 S / cm or more can be obtained.
The monomers and the supporting electrolytes may not be used alone, but a plurality of supporting electrolytes may be mixed and used, or a plurality of the above monomers may be used in combination, such as prol and thiophene mixed with respective derivatives.

In addition to the heterocyclic compound monomer and the supporting electrolyte, the electrolytic solution may also contain an additive for improving adhesion, an oxidation inhibitor for the electrolytic solution, and the like. Of course, it may not be included.

The liquid electrode used in the present invention is claimed in claim (2).
As in the invention described above, a metal that is in a molten state near room temperature at which electrolytic polymerization is usually performed is preferable, and specifically, as in the invention described in claim (3), it is in a molten state near room temperature. Examples of such a metal include mercury and an indium-gallium eutectic. In short, it is sufficient that the liquid state is maintained without being substantially dissolved in the electrolytic solution during the electrolytic polymerization.

Of course, the present invention is not limited to the above-exemplified compounds and treatment methods. It goes without saying that other compounds and treatment methods other than those exemplified above may be used.

Action In the production method of the present invention, since the electrode to be brought into contact during electrolytic polymerization is a liquid, the dielectric film, which is extremely thin and vulnerable to mechanical shock, is not damaged. Therefore, a capacitor with a small leakage current can be obtained.

The obtained capacitor is also excellent in frequency characteristics and loss characteristics, because the conductive layer is provided with a solid electrolyte composed of an electropolymerized conductive polymer layer having a good film quality.

The conductivity of the conductive layer does not necessarily have to be high. The electropolymerized conductive polymer layer in this invention is, for example, 10 ² S / cm.
Since it is possible to easily form a material with high conductivity, the thickness of the conductive layer is made sufficiently thin compared to the thickness of the electropolymerized conductive polymer layer so that the solid electrolyte as a whole has high conductivity and loss. This is because the coefficient can be kept low.

The electropolymerized conductive polymer layer is not formed in the portion in contact with the liquid electrode. Since the anode lead can be taken out from the portion where the electropolymerized conductive polymer layer is not formed after the electropolymerization, there is an advantage that, for example, a chip structure can be easily obtained.

Examples Hereinafter, specific examples of the method for manufacturing a solid electrolytic capacitor according to the present invention will be described.

-Example 1- Fig. 1 shows a state of an electrolytic polymerization step in a method for producing a solid electrolytic capacitor according to the present invention.

First, 3 pieces of aluminum etched foil 1 of length 8mm x width 10mm
% An aqueous solution of ammonium adipate to form a dielectric film 2 on the surface of the etched foil 1 by anodizing at about 70 ° C. and an applied voltage of 35 V.
% Aqueous solution and heated at 250 ° C. for 10 minutes for thermal decomposition to form a conductive layer 3 of manganese oxide. However, as shown in FIG. 1, the conductive layer 3 is not formed in most of the region buried in the liquid electrode 6. This is for connecting the anode lead later.

Then, the etched foil 1 is pyrrole (0.3mol / l), p-
It is placed in an electrolyte solution 5 consisting of sodium toluene sulfonate (0.1 mol / l) and water, and a mercury liquid electrode 6
The cathode 7 was placed in the electrolytic solution 5 while being brought into contact with. Four
Is an electrolytic solution tank. Then, between both electrodes 6,7
A voltage of 3V is applied to carry out electrolytic polymerization and p
-The electropolymerized conductive polymer layer 8 doped with the toluenesulfonic acid anion was laminated. Then, after washing with water and drying, the anode lead is attached by caulking, the carbon paste and the silver paste are applied on the polymer layer 8, the cathode lead is taken out, and further the exterior is covered with an epoxy resin to obtain a solid electrolytic capacitor. . Five pieces are manufactured.

After aging the obtained solid electrolytic capacitor for 1 hour at 13 V, the initial capacity (120 Hz), loss (120 Hz), impedance (1 MHz), and leakage current 2 minutes after the start of voltage application of 10 V were measured. Table 1 shows the measurement results (average value of 5 samples).

-Comparative Example 1-As shown in FIG. 2, the anode lead 9 is attached in advance, and a stainless steel electrode for the anode is used instead of the liquid electrode.
A solid electrolytic capacitor was obtained in the same manner as in Example 1 except that 10 was applied. Table 1 shows the measurement results of each property.

-Example 2-Acetonitrile and tetra-n-butylammonium p-toluenesulfonate were used in place of water and sodium p-toluenesulfonate, and indium gallium eutectic was used in the same manner as in Example 1. A solid electrolytic capacitor was obtained. Table 1 shows the measurement results of each property.

In addition, in Example 2, pyrrole was used as pyrrole and N.
-A solid electrolytic capacitor was obtained in the same manner except that a mixture containing equimolar amount of -methylpyrrole was obtained, and the same results as in Example 2 were obtained.

-Example 3-A solid electrolytic capacitor was obtained in the same manner as in Example 2 except that thiophene was used in place of pyrrole, and the electrolytic solution tank 4 was entirely placed in a dry box to carry out electrolytic polymerization. Table 1 shows the measurement results of each property.

-Example 4-After embossing, using a 10% phosphoric acid aqueous solution, 90 ° C, 35V
8mm in length with anodized under the conditions of
A solid electrolytic capacitor was obtained in the same manner as in Example 1 except that a tantalum foil having a width of 10 mm was used. Table 1 shows the measurement results of each property.

-Comparative Example 2-As shown in Fig. 2, the anode lead 9 is attached in advance, and a stainless steel electrode for the anode is used instead of the liquid electrode.
A solid electrolytic capacitor was obtained in the same manner as in Example 4 except that 10 was contacted. Table 1 shows the measurement results of each property.

Comparing the leakage current values of Example 1 and Comparative Example 1 or Example 4 and Comparative Example 2, it is clear that the liquid electrode exhibits the leakage current reducing function. Further, as can be seen from the data of the capacity, loss (tan δ) and impedance of each example, it is well understood that a capacitor with low loss and excellent frequency characteristics is obtained.

EFFECTS OF THE INVENTION As described above, in the manufacturing method according to claims (1) to (6), in order to bring the liquid electrode into contact during the formation of the electropolymerized conductive polymer layer, the dielectric film Not only can a solid electrolytic capacitor with excellent electrical characteristics with less leakage current be obtained without causing damage, but a conductive layer is pre-formed on the dielectric film to form a good electrolytic polymerized conductive polymer. The layer is formed quickly, and is also highly practical.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a state of an electrolytic polymerization step in an example of the production method according to the present invention, and FIG.
It is a schematic explanatory view showing a state of an electrolytic polymerization step in a conventional method. 1 ... Aluminum etched foil (metal body), 2 ... Dielectric film, 3 ... Conductive layer, 4 ... Electrolyte bath, 5 ... Electrolyte, 6 ... Liquid electrode, 7 ... Cathode, 8 ...... Electropolymerized conductive polymer layer, 9 ...... Anode lead, 10 ...... Stainless steel electrode for anode.

Claims (6)

[Claims] 1. A metal body having a dielectric coating formed on the surface and a conductive layer laminated on the coating is placed in an electrolytic solution containing at least a heterocyclic compound monomer and a supporting electrolyte,
A method for producing a solid electrolytic capacitor in which a conductive electrolytically polymerized polymer layer for a solid electrolyte is formed on the conductive layer by bringing the conductive layer into contact with a liquid electrode for voltage application to carry out an electrolytic polymerization reaction of the monomer. . 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the liquid electrode is made of a metal which is in a molten state near room temperature. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein the metal that is in a molten state near room temperature is one of mercury and an indium-gallium eutectic. 4. The method for producing a solid electrolytic capacitor according to claim 1, wherein the heterocyclic compound monomer is at least one of pyrrole, thiophene and derivatives thereof. 5. The metal of the metal body is at least one of aluminum, tantalum and titanium.
5. A method for manufacturing a solid electrolytic capacitor as described in any one of 1. 6. The method for producing a solid electrolytic capacitor according to claim 1, wherein the conductive layer contains manganese oxide.