JPH0770439B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a solid electrolytic capacitor having a good equivalent series resistance in a high frequency band.

[Conventional technology]

Generally, in the element of a solid electrolytic capacitor, an oxide film layer is formed on the surface of an anode substrate made of a valve metal, and a semiconductor layer such as manganese dioxide is formed on the outer surface of the oxide film layer as a counter electrode. In order to reduce the amount, a silver paste layer is provided to form a conductor layer.

[Problems to be solved by the invention]

However, the surface of the semiconductor layer is non-uniform even if the material is the same, and the particle size is not uniform, and the surface of the semiconductor layer is covered with particles that are easily peeled off. In that case, there is a problem that the equivalent series resistance in the high frequency band is very large.

[Means for solving problems]

The present invention has been made to achieve the above object, and its gist is to form a dielectric oxide film layer, a semiconductor layer, and a conductor layer in this order on the surface of an anode base made of a metal having a valve action. In the method for producing a solid electrolytic capacitor, the solid electrolytic method in which after forming the semiconductor layer, the surface of the semiconductor layer is ultrasonically cleaned using a solution containing carboxylic acid, oxyacid, carboxylate or oxyacid salt as a medium. There is a method of manufacturing a capacitor. The semiconductor layer is preferably a layer containing lead dioxide as a main component or a layer containing a mixture containing lead dioxide and lead sulfate as a main component.

Hereinafter, a method for manufacturing the solid electrolytic capacitor of the present invention will be described.

As the valve metal substrate used as the anode of the solid electrolytic capacitor manufactured by the method of the present invention, for example, any metal having a valve action such as aluminum, tantalum, niobium, titanium and alloys using these as substrates can be used. .

The oxide film layer on the surface of the anode substrate may be an oxide layer of the substrate itself, or may be a layer of another dielectric oxide provided on the surface of the substrate. Preferably, it is a layer consisting of the oxide of the valve metal itself. In any case, a conventionally known method can be used as a method for providing the oxide layer.

Next, the composition of the semiconductor layer used in the present invention and the manufacturing method are not particularly limited, but in order to enhance the performance of the capacitor, lead dioxide, or lead dioxide and lead sulfate as the main components, is used in the conventional chemical deposition. It is preferable to prepare by the method or the electrochemical deposition method.

Examples of the chemical deposition method include a method of chemically depositing from a solution containing a lead-containing compound and an oxidizing agent.

Examples of the lead-containing compound include oxine, acetylacetone, pyromeconic acid, salicylic acid, alizarin, polyvinyl acetate, porphyrin compounds, crown compounds,
Lead-containing compounds in which lead atoms are coordinate-bonded or ionic-bonded to chelate-forming compounds such as cryptate compounds, lead citrate, lead acetate, basic lead acetate, lead chloride, lead bromide, lead perchlorate, Examples thereof include lead chlorate, lead sulfamate, lead hexafluoride, lead bromate, lead borofluoride, lead acetate hydrate, lead nitrate and the like. These lead-containing compounds are
It is appropriately selected depending on the solvent used for the reaction mother liquor. Moreover, you may use these lead-containing compounds in mixture of 2 or more types.

The concentration of the lead-containing compound in the reaction mother liquor is within the range of 0.05 mol / concentration from the concentration providing the saturated solubility, preferably within the range of 0.1 mol / concentration from the concentration providing the saturated solubility, more preferably the saturated solubility is imparted. The concentration ranges from 0.5 mol / mol. If the concentration of the lead-containing compound in the reaction mother liquor is less than 0.05 mol / mol, a solid electrolytic capacitor having good performance cannot be obtained. Further, when the concentration of the lead-containing compound in the reaction mother liquor exceeds the saturation solubility, the merit of increasing the addition amount is not recognized.

Examples of the oxidizing agent include quinone, chloranil, pyridine-N-oxide, dimethylsulfoxide, chromic acid, potassium permanganate, selenium oxide, mercury acetate, vanadium oxide, sodium chlorate, ferric chloride,
Examples thereof include hydrogen peroxide, benzoyl peroxide, calcium hypochlorite, calcium chlorite, calcium chlorate, calcium perchlorate and the like. These oxidizing agents may be appropriately selected depending on the solvent used. The oxidant is
You may mix and use 2 or more types.

The proportion of the oxidizing agent used is 5 to 5 times the molar amount of the lead-containing compound used.
It is preferably in the range of 0.1 times by mole. If the proportion of the oxidizing agent used is more than 5 times the mole amount of the lead compound used, there is no cost advantage, and if it is less than 0.1 times the mole amount, a solid electrolytic capacitor with good performance cannot be obtained.

As a method of forming a semiconductor layer containing lead dioxide as a main component, for example, a reaction mother liquor is prepared by mixing a solution in which a lead-containing compound is dissolved and a solution in which an oxidizing agent is dissolved, and then the reaction mother liquor is coated with the above-described oxide film. There is a method of immersing the formed chemical foil and chemically depositing it.

On the other hand, as the electrochemical deposition method, for example, a method previously proposed by the present inventors to deposit lead dioxide by electrolytic oxidation in an electrolytic solution containing high-concentration lead ions (Japanese Patent Laid-Open No. 62-62). -185307 publication).

Further, when the semiconductor layer is composed of lead dioxide which originally functions as a semiconductor and a layer containing lead sulfate which is an insulating material as a main component, the leakage current of the capacitor can be reduced by mixing lead sulfate. On the other hand, the compounding of lead sulfate lowers the electrical conductivity of the semiconductor layer and thus increases the loss coefficient.
A high level of performance can be maintained and exhibited even when compared with conventional solid electrolytic capacitors. Therefore, when the semiconductor layer is composed of a mixture of lead dioxide and lead sulfate, 10% lead dioxide is used.
Maintains good capacitor performance in a wide range of compositions, where lead sulfate is 90 parts by weight or less for parts by weight or more and less than 100 parts by weight,
Although it can be expressed, preferably in the range of 80 to 50 parts by weight of lead sulfate to 20 to 50 parts by weight of lead dioxide, more preferably in the range of 75 to 65 parts by weight of lead sulfate to 25 to 35 parts by weight of lead dioxide. The balance between leakage current and loss factor is particularly good.
If the amount of lead dioxide is less than 10 parts by weight, the conductivity is deteriorated, the loss factor increases, and the capacity does not appear sufficiently.

The semiconductor layer containing lead dioxide and lead sulfate as main components can be formed by chemical deposition using, for example, an aqueous solution containing lead ions and persulfate ions as a reaction mother liquor. Also, a suitable oxidizing agent containing no persulfate ion may be added.

The concentration of lead ion in the mother liquor is calculated from
0.05 mol / preferably from the concentration that gives saturated solubility
It is within the range of 0.1 mol / percent, and more preferably 0.5 mol / percent from the concentration providing the saturated solubility. If the concentration of lead ions is higher than the saturation solubility, there is no merit by increasing the amount. Further, when the concentration of lead ions is lower than 0.05 mol / mol, the concentration of lead ions in the mother liquor is too low, so that the number of times the semiconductor layer is deposited must be increased.

On the other hand, the concentration of persulfate ions in the mother liquor is in the range of 5 to 0.05 in terms of molar ratio with respect to lead ions. If the concentration of persulfate ion is more than 5 with respect to the lead ion, unreacted persulfate ion remains, resulting in higher cost, and the concentration of persulfate ion is less than 0.05 with respect to the lead ion. If so, unreacted lead ions remain and the conductivity deteriorates, which is not preferable.

Examples of compounds that give lead ion species include lead citrate, lead perchlorate, lead sulfate, lead acetate, basic lead acetate, lead chlorate, lead sulfamate, lead hexafluoride, lead bromate, and chloride. Examples thereof include lead and lead bromide. Two or more kinds of compounds that give these lead ion species may be mixed and used.
On the other hand, examples of the compound that gives a persulfate ion species include potassium persulfate, sodium persulfate, and ammonium persulfate. Two or more kinds of these compounds giving the persulfate ion species may be mixed and used.

On the other hand, examples of the oxidizing agent include hydrogen peroxide, hypochlorite, chlorite, chlorate, and perchlorate.

Next, the semiconductor layer formed as described above is treated with a solution containing a carboxylic acid, an oxyacid, a carboxylic acid salt or an oxyacid salt on the surface thereof in order to make good contact with the conductor layer. Ultrasonic cleaning is performed using the mixed solution of.

Representative examples of carboxylic acid, oxyacid, carboxylic acid salt and oxyacid salt are acetic acid, propionic acid, butyric acid, propenoic acid,
Valeric acid, oxalic acid, succinic acid, adipic acid, acrylic acid, crotonic acid, fumaric acid, maleic acid, benzoic acid, phthalic acid, glycolic acid, glyceric acid, hydroxypropionic acid, hydroxybutyric acid, tartaric acid, malic acid, glycolic acid , Salicylic acid and ammonium salts of these acids,
Examples thereof include sodium salt and potassium salt.

The output, frequency, temperature and ultrasonic cleaning time during ultrasonic cleaning will vary depending on the type of anode substrate used, the type and composition of the semiconductor layers formed, etc. To be done.

In the present invention, a metal layer or a carbon layer is formed on the semiconductor layer cleaned as described above, or a conductor layer is formed by forming a metal layer on the carbon layer. . The method of forming the carbon layer on the semiconductor layer is not particularly limited, a conventionally known method,
For example, a method of applying carbon paste is adopted. Examples of the method of providing the metal layer on the carbon layer include a method of applying a paste containing silver, nickel, copper, silver-coated copper, or the like, or a method of plating or vapor-depositing silver, nickel, copper, or the like. .

As described above, the solid electrolytic capacitor manufactured by the method of the present invention includes, for example, a resin mold, a resin case,
It can be used as a general-purpose capacitor product for various purposes by using a metal outer case, resin dipping, a laminate film outer case, and the like.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 An aluminum foil having a length of 2 cm and a width of 0.5 cm was used as an anode, and the surface of the foil was electrochemically etched by an alternating current. Then, an anode terminal was caulked to the etched aluminum foil, and an anode lead wire was connected. Then, it was electrochemically treated in an aqueous solution of boric acid and ammonium borate to form an oxide film of alumina to obtain a low-pressure etched aluminum chemical conversion foil (about 10 μF / cm ² ). After winding the chemical conversion foil, the part of the chemical conversion foil other than the anode lead wire was immersed in 1.0 mol of lead acetate trihydrate / aqueous solution. This chemical conversion foil was used as the anode side, and the usual unetched aluminum foil was used as the cathode side, and electrolytic oxidation was performed at 15V. After 4 hours, the semiconductor layer made of lead dioxide formed on the chemical conversion foil was washed with water to remove unreacted materials, and then the chemical conversion foil was immersed in a 10 wt% aqueous solution of tartaric acid except for the anode lead wire, and output 35w. The surface of the semiconductor layer was ultrasonically cleaned by applying an ultrasonic cleaner having a frequency of 41 kHz for 3 minutes at room temperature. It was visually observed that the surface of the semiconductor layer after ultrasonic cleaning was glossy. Next, a commercially available silver paste was applied to the semiconductor layer to form a conductor layer. Subsequently, a cathode lead wire was connected with this paste and a resin was sealed to produce a solid electrolytic capacitor.

Example 2 A chemical conversion foil similar to that in Example 1 was prepared by mixing lead acetate trihydrate with 2.4 mol / mol.
It was immersed in a mixed solution of an aqueous solution of 4 and an aqueous solution of ammonium persulfate 4 mol /, and reacted at 80 ° C for 30 minutes. The generated semiconductor layer was washed with water to remove unreacted substances. Then, dip it in a 25% by weight aqueous solution of ammonium acetate, except for the anode lead wire, together with the chemical conversion foil, and place it in an ultrasonic cleaner with an output of 60 w and a frequency of 45 kHz
The surface of the semiconductor layer was ultrasonically cleaned at 2 ° C. for 2 minutes. Then, a conductor layer was formed in the same manner as in Example 1 to produce a solid electrolytic capacitor. The surface of the semiconductor layer after ultrasonic cleaning was visually observed to be glossy. The semiconductor layer contains lead dioxide of about 34% by weight and lead sulfate of about 66% by weight.
It was confirmed by X-ray analysis and infrared spectroscopy.

Example 3 A solid electrolytic capacitor was produced in the same manner as in Example 2 except that the solution for cleaning the surface of the semiconductor layer in Example 2 was a 5 wt% aqueous solution of propionic acid, and the ultrasonic cleaning time was 3 minutes at room temperature. did.

Example 4 A solid electrolytic capacitor was produced in the same manner as in Example 2 except that the solution for cleaning the surface of the semiconductor layer was an aqueous solution of 10% by weight ammonium lactate and the ultrasonic cleaning time was 3 minutes.

Comparative Example 1 A solid electrolytic capacitor was produced in the same manner as in Example 2 except that ultrasonic cleaning treatment in an aqueous solution of ammonium acetate was not performed in Example 2.

Comparative Example 2 In Example 2, the ultrasonic cleaning treatment in an ammonium acetate aqueous solution was stopped, and an ammonium acetate aqueous solution having the same concentration was used at 40 ° C. for 2 hours.
A solid electrolytic capacitor was produced in the same manner as in Example 2 except that it was immersed in the solution for a minute and then taken out, followed by continuous ultrasonic cleaning in water for 2 minutes.

Table 1 collectively shows the characteristic values of the solid electrolytic capacitors produced in Examples 1 to 4 and Comparative Examples 1 and 2.

[Effects of the Invention] In the method for producing a solid electrolytic capacitor in which the electric oxide film, the semiconductor layer, and the conductor layer are sequentially formed on the surface of an anode substrate made of a metal having a valve action, the semiconductor layer is formed. Later, the surface of this semiconductor layer is ultrasonically cleaned using a solution containing a carboxylic acid, an oxyacid, a carboxylic acid salt or an oxyacid salt as a medium, so that a solid electrolytic capacitor having a small equivalent series resistance and good performance in a high frequency band. Can be manufactured.

Claims (3)

[Claims] 1. A method for producing a solid electrolytic capacitor comprising a dielectric oxide film layer, a semiconductor layer and a conductor layer sequentially formed on a surface of an anode substrate made of a metal having a valve action, wherein the semiconductor layer is formed. After that, the surface of this semiconductor layer is ultrasonically cleaned using a solution containing a carboxylic acid, an oxy acid, a carboxylic acid salt or an oxy acid salt as a medium, and a method for producing a solid electrolytic capacitor. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the semiconductor layer is a layer containing lead dioxide as a main component. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein the semiconductor layer is a layer containing lead dioxide and lead sulfate as main components.