JPH0727848B2 - 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 excellent stability at high temperatures.

[Prior Art] Generally, in an element of a solid electrolytic capacitor, an oxide film layer is formed on 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. A conductor layer such as paste is formed to reduce the contact resistance.

[Problems to be Solved by the Invention] However, the above-mentioned solid electrolytic capacitor has a drawback that a loss coefficient increases with time when a high temperature long-term life test is performed.

As a result of intensive studies to solve the above problems, the present inventors have found that the high temperature stability is improved by first cleaning the semiconductor layer and subsequently changing various components of the conductor layer.

The present invention has been made based on the above findings, and an object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor in which high temperature stability does not deteriorate for a long period of time.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and its gist is to provide a dielectric oxide film, a semiconductor layer on the surface of an anode base made of a metal having a valve action. In a method of manufacturing a solid electrolytic capacitor in which conductor layers are sequentially formed, a metal oxide powder for forming a semiconductor as the conductor layer and a paste containing metal powder as a main component after cleaning the surface of the semiconductor layer A method of manufacturing a solid electrolytic capacitor comprising a step of forming a layer, and after cleaning the surface of the semiconductor layer, mainly a metal powder as the conductor and a metal oxide powder forming the semiconductor layer, and a metal salt powder. A method for manufacturing a solid electrolytic capacitor, which comprises the step of forming a paste layer as a component.

[Specific Configuration and Action of the Invention] 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 of the present invention, any metal having a valve action such as aluminum, tantalum, niobium, titanium and alloys having these as substrates can be used.

The oxide film layer on the surface of the anode substrate may be an oxide layer of the anode substrate itself provided on the surface layer of the anode substrate, or may be a layer of another dielectric oxide provided on the surface of the anode substrate. It may be present, but it is particularly preferable that the layer is made of an oxide of the anode valve metal itself. In any case, as a method for providing the oxide layer, a conventionally known method such as an anodization method using an electrolytic solution can be used.

Further, the composition of the semiconductor layer used in the present invention and the method for producing the same are not particularly limited, but in order to improve the performance of the capacitor, lead dioxide, or lead dioxide and lead sulfate as main components, and a conventionally known chemical deposition method are used. Alternatively, it is preferably produced by an electrochemical deposition method.

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

As the lead-containing compound, for example, a lead atom is coordinate-bonded or ion-bonded to a chelate-forming compound such as oxine, acetylacetone, pyromeconic acid, salicylic acid, alizarin, polyvinyl acetate, porphyrin compounds, crown compounds, and cryptate compounds. Lead-containing compounds,
Lead citrate, lead acetate, basic lead acetate, lead chloride, lead bromide,
Examples thereof include lead perchlorate, lead chlorate, lead sulfamate, lead hexafluoride, lead bromate, lead borofluoride, lead acetate hydrate, and lead nitrate. These lead-containing compounds are appropriately selected depending on the solvent used in the reaction mother liquor. Water or an organic solvent is used as the solvent. Lead-containing compounds are
You may use it in mixture of 2 or more types.

The concentration of the lead-containing compound in the reaction mother liquor is in the range of 0.05 mol / l from the concentration giving the saturated solubility, preferably in the range of 0.1 mol / l from the concentration giving the saturated solubility, more preferably the saturated solubility. From the concentration giving 0.5 mol / l. If the concentration of the lead-containing compound in the reaction mother liquor is less than 0.05 mol / l, a solid electrolytic capacitor with 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, dimethyl sulfoxide, chromic acid, potassium permanganate, selenium oxide, mercury acetate,
Examples thereof include vanadium oxide, sodium chlorate, ferric chloride, hydrogen peroxide, coconut powder, and benzoyl peroxide.
These oxidizing agents may be appropriately selected depending on the solvent used in the reaction mother liquor. Also, two or more oxidizing agents may be mixed and used.

The amount of the oxidizing agent used is 0.1 to the molar amount of the lead-containing compound used.
It is preferably within a 5-fold molar range. If the proportion of the oxidizing agent used is more than 5 times the mole amount of the lead-containing 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. A method of immersing the provided anode substrate and chemically precipitating it can be mentioned.

On the other hand, as the electrochemical deposition method, for example, the method proposed by the present inventors to deposit lead dioxide by electrolytic oxidation in an electrolytic solution containing a high-concentration lead-containing compound can be mentioned (Japanese Patent Application No. 2000-242242). 61-26952).

Further, when the semiconductor layer is composed of a layer containing lead dioxide which originally functions as a semiconductor and lead sulfate which is an insulating material as a main component, the leakage current value of the capacitor can be reduced by blending lead sulfate. On the other hand, the compounding of lead sulfate lowers the electric conductivity of the semiconductor layer and thus increases the loss coefficient value, but a high level of performance can be maintained and expressed even when compared with the conventional solid electrolytic capacitor. Therefore, the semiconductor layer is
If it is composed of a mixture of lead dioxide and lead sulfate,
Good capacitor performance can be maintained and expressed in a wide range of composition of 90 parts by weight or less of lead sulfate with respect to 10 parts by weight or more and less than 100 parts by weight, but lead sulfate is preferably used for 20 to 50 parts by weight of lead dioxide. 80 to 50 parts by weight, more preferably 25 to 35 parts by weight of lead dioxide, and 75 to 65 parts by weight of lead sulfate provide a good balance between the leakage current value and the loss coefficient value. 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 / l, preferably from a concentration giving a saturated solubility of 0.
1 mol / l, more preferably from a concentration that gives saturated solubility
Within the range of 0.5 mol / l. If the concentration of lead ions is higher than the saturation solubility, there is no merit by increasing the amount.
When the concentration of lead ions is lower than 0.05 mol / l,
There is a drawback in that the lead ions in the mother liquor are too thin and the number of times of application 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 iron ion species include lead citrate, lead perchlorate, lead nitrate, lead acetate, basic lead acetate, lead chlorate, lead sulfamate, lead hexafluoride, lead bromate, and lead chloride. , Lead bromide and the like. 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 provides the 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.

Further, as the oxidizing agent, for example, hydrogen peroxide, calcium hypochlorite, calcium chlorite, calcium chlorate,
Examples thereof include calcium perchlorate.

Next, the surface of the semiconductor layer formed as described above is cleaned by ultrasonic cleaning.

As a medium used for ultrasonic cleaning, an organic solvent such as water or alcohol is used. Regarding the output, temperature, ultrasonic cleaning time, etc. when performing ultrasonic cleaning,
Since it varies depending on the type of anode substrate used, the type and composition of the formed semiconductor layer, it is determined by preliminary experiments conducted in advance. Further, in order to clean the surface of the semiconductor layer, in addition to ultrasonic cleaning, steps such as cleaning with an organic solvent such as ethyl alcohol and methyl alcohol, water cleaning, etc. may be included, and by adding these cleaning steps, The effect of ultrasonic cleaning is further improved.

Next, in the present invention, the dielectric layer provided on the ultrasonically cleaned semiconductor layer is a paste layer containing metal oxide powder and metal powder as the main components, and particularly as the metal oxide powder, the semiconductor layer is the semiconductor layer. It is desirable to use the metal oxide that forms. Further, the conductor layer provided on the semiconductor layer may be a metal oxide powder forming the semiconductor layer, and a paste layer containing metal salt powder and metal powder as main components. Examples of the metal oxide powder forming a semiconductor (hereinafter simply referred to as “metal oxide powder”) include manganese dioxide, tin dioxide, tungsten dioxide, lead dioxide, copper monoxide, zinc monoxide, nickel monoxide, and monoxide. Examples thereof include cobalt, titanium dioxide, iron sesquioxide, barium titanate, tantalum oxide, vanadium sesquioxide, tungsten trioxide and the like, and lead dioxide is particularly preferable from the viewpoint of good conductivity. As the metal salt powder, for example, manganese sulfate, cobalt sulfate, lead sulfate, copper sulfate,
Examples thereof include nickel sulfate, magnesium carbonate, calcium carbonate, lead carbonate, manganese carbonate, and the like, and lead sulfate is particularly desirable. Further, as the metal powder, for example, silver powder, gold powder, palladium powder, copper powder, nickel powder, alloy powder of silver and copper, alloy powder of silver and nickel, silver-coated copper powder, silver-coated nickel powder,
Examples thereof include silver-coated carbon powder and alloy powders thereof.

The metal powder is preferably in the shape of flakes or corals in order to improve the conductivity of the conductive paste, but may be in the shape of a normal sphere or a shape similar to a sphere.

In addition, the content ratio of the metal oxide powder or the metal oxide powder and the metal salt powder in the paste to the metal powder in the paste is preferably within the range of 1/6 to 6 times that of the metal powder. . If the ratio of the metal oxide powder or the metal oxide powder and the metal salt powder is less than 1/6 of the metal powder, the high temperature stability of the manufactured solid electrolytic capacitor may be insufficient,
Further, if it exceeds 6 times that of the metal powder, the conductivity may become insufficient.

The action of the metal powder and the metal oxide powder or the metal oxide powder and the metal salt powder is presumed as follows. That is, the conductivity of the metal oxide powder or the metal oxide powder and the metal salt powder is about 1/100 to 1/1000 compared to the conductivity of the metal powder,
When dispersed together with the metal powder in the paste, the conductivity is not so deteriorated as compared with the case where only the metal powder is dispersed. On the other hand, regarding the high temperature stability, it is considered that the coefficient of thermal expansion of the paste which is an organic polymer material is large and it is important to make this coefficient small so that thermal stress does not occur. Alternatively, the metal oxide powder and the metal salt powder have the effect of reducing the coefficient of thermal expansion.

The paste containing metal oxide powder and metal powder as a main component, or the paste containing metal oxide powder, metal salt powder, and metal powder as a main component is, for example, lead dioxide as a metal powder, or a semiconductor layer containing lead dioxide as a main component. In the case of such a layer, it is obtained by mixing lead dioxide and a lead-based compound that is an insulator, such as lead sulfate and metal powder, with a suitable resin or oligomer and a solvent.

As the resin or oligomer, a resin or oligomer used in known conductive paste is used,
For example, acrylic resin, alkyd resin, fluororesin, vinyl resin, silicone resin, epoxy resin, urethane resin, novolac, resol and the like can be mentioned. However, of course, it is not limited to these. The solvent used may be any known solvent as long as it can dissolve these resins or oligomers. When the resin or oligomer is liquid, no solvent may be used. Further, in the case of a thermosetting resin or oligomer, a known curing agent may be added, or a liquid containing a curing agent may be separately prepared and used at the time of use.

The ratio of the metal powder and the metal oxide powder, or the metal powder, and the metal oxide powder and the metal salt powder (hereinafter collectively referred to as powder) in the paste is 35 to 95% by weight, and particularly 55 to 95% by weight is preferred. If the content of the powder is less than 35% by weight, the conductivity of the paste is insufficient, and if it exceeds 95% by weight, the adhesiveness of the paste is insufficient, and the performance of the solid electrolytic capacitor is deteriorated.

The solid electrolytic capacitor produced by the method of the present invention is, for example, a resin mold, a resin case, a metal outer case,
General-purpose capacitor products for various applications can be made by dipping resin and packaging with a laminated film.

[Examples] Hereinafter, the present invention will be described 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, the surface of the foil was electrochemically etched by an alternating current, and then the anode terminal was caulked to the etched aluminum foil to connect the anode terminal. Next, it is electrochemically treated in an aqueous solution of boric acid and ammonium borate to form an alumina oxide film, and the low-voltage etched aluminum conversion foil (approx.
1.0 μF / cm ² ) was obtained. Then, lead acetate trihydrate 1 mol / l
Dip the formed foil in an aqueous solution and add 0.5% to lead acetate trihydrate.
A double molar aqueous solution of hydrogen peroxide was added. After standing for 1 hour, the lead dioxide layer deposited on the chemical conversion foil was ultrasonically washed in water for 3 minutes and then dried under reduced pressure at 120 ° C. Further, using this chemical conversion foil, butyl acetate was used as a solvent, and 32 parts by weight of silver powder (hereinafter referred to as “part”), 60 parts of lead dioxide, and urethane resin 8
After being dipped in a paste consisting of parts and pulled up, it was dried at 100 ° C. After connecting the cathode with the above-mentioned paste, the resin was sealed to produce a solid electrolytic capacitor.

Example 2 A portion of the same formed foil as in Example 1 other than the anode terminal was treated with an aqueous solution of lead acetate trihydrate 2.4 mol / l and ammonium persulfate 4
Immerse in a mixed solution (reaction mother liquor) of a mol / l aqueous solution at 80 ℃
After reacting for 30 minutes, the semiconductor layer made of lead dioxide and lead sulfate formed on the dielectric oxide film layer was ultrasonically cleaned in water for 3 minutes and then dried under reduced pressure at 120 ° C. The produced semiconductor layer was composed of lead dioxide and lead sulfate, and it was confirmed by mass spectrometry, X-ray analysis and infrared spectroscopy that lead dioxide was contained in an amount of about 25% by weight.

Then, a paste consisting of 30 parts of silver powder, 60 parts of lead dioxide and 10 parts of acrylic resin was applied on the semiconductor layer and dried, and then the cathode was taken out in the same manner as in Example 1 and the resin was sealed to produce a solid electrolytic capacitor. did.

Example 3 A semiconductor layer was produced in the same manner as in Example 2 except that 0.05 mol / l of hydrogen peroxide solution was further added to the reaction mother liquor at the time of semiconductor formation in Example 2. It was confirmed that the semiconductor layer at this time was a composition composed of lead dioxide and lead sulfate, and contained about 50% by weight of lead dioxide.

Furthermore, silver powder 25 is applied to the chemical conversion foil on which this semiconductor layer is formed.
Part, lead dioxide 65 parts, and acrylic resin 10 parts were applied and dried, and then a solid electrolytic capacitor was prepared in the same manner as in Example 2.

Example 4 After a semiconductor layer made of lead dioxide and lead sulfate was formed in the same manner as described in Example 2, ultrasonic cleaning was performed in water for 3 minutes. It was confirmed that the lead dioxide content was about 25% by weight.

On this semiconductor layer, 30 parts of silver powder, 50 parts of lead dioxide, 10 parts of lead sulfate
Parts and 10 parts of acrylic resin were applied and dried, and then the cathode was taken out and the resin was sealed in the same manner as in Example 1 to prepare a solid electrolytic capacitor.

Comparative Example 1 In Example 1, the lead dioxide content in the paste was eliminated and the silver powder 92
Section, and a solid electrolytic capacitor was prepared in the same manner as in Example 1 except that a conductor layer was formed as 8 parts of urethane resin.

Comparative Example 2 A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the semiconductor layer was not cleaned with ultrasonic waves in Example 1.

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] As described above, according to the method for producing a solid electrolytic capacitor of the present invention, the surface of the formed semiconductor layer is cleaned, and thereafter, the metal oxide powder and the metal powder are used as the main components. The step of forming a paste layer as a conductor layer or a step of forming a paste layer containing metal powder, metal oxide powder, and metal salt powder as main components as a conductor layer is performed, so that the surface of the semiconductor layer is cleaned. The solid electrolytic capacitor having extremely excellent high-temperature stability can be manufactured by the synergistic effect of combining the step of forming and the step of forming the paste layer on the conductor layer.

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Claims (11)

[Claims] 1. A method of manufacturing a solid electrolytic capacitor comprising a dielectric oxide film, a semiconductor layer, and a conductor layer sequentially formed on the surface of an anode substrate made of a metal having a valve action, and the surface of the semiconductor layer is cleaned. After that, the method for producing a solid electrolytic capacitor, which comprises the step of forming a metal oxide powder for forming a semiconductor layer as the conductor layer and a paste layer containing metal powder as a main component. 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. 4. The method for producing a solid electrolytic capacitor according to claim 1, wherein the metal oxide powder is lead dioxide powder. 5. The method for producing a solid electrolytic capacitor according to claim 1, wherein the surface of the semiconductor layer is cleaned with ultrasonic waves. 6. A method for producing a solid electrolytic capacitor, which comprises sequentially forming a dielectric oxide film, a semiconductor layer and a conductor layer on the surface of an anode substrate made of a metal having a valve action, and cleaning the surface of the semiconductor layer. And a metal oxide powder forming a semiconductor layer as the conductor layer, and a step of forming a paste layer containing metal salt powder as a main component. . 7. The method for producing a solid electrolytic capacitor according to claim 6, wherein the semiconductor layer is a layer containing lead dioxide as a main component. 8. The method for producing a solid electrolytic capacitor according to claim 6, wherein the semiconductor layer is a layer containing lead dioxide and lead sulfate as main components. 9. The method for producing a solid electrolytic capacitor according to claim 6, wherein the metal oxide powder is lead dioxide powder. 10. The method for producing a solid electrolytic capacitor according to claim 6, wherein the metal salt powder is lead sulfate powder. 11. The method for producing a solid electrolytic capacitor according to claim 6, wherein the surface of the semiconductor layer is cleaned with ultrasonic waves.