JP2003100557A - Solid electrolytic capacitor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing solid electrolytic capacitor by which the deterioration of the withstand voltage characteristic of a solid electrolytic capacitor caused by lead-free reflow soldering can be prevented, and yield can be improved at the time of manufacturing products having high withstand voltages. SOLUTION: A capacitor element is formed by winding up an anode foil, on the surface of which the oxide coating layer is formed, and cathode foil with a separator containing a compound having a vinyl group between and the formed element is subjected to restorative formation. A link composed of the compound having the vinyl group and a boric acid compound is generated by impregnating the capacitor element with a solution containing the boric acid compound. Thereafter, a solid electrolyte layer is formed by making a conductive polymer to cause a polymerization reaction in the capacitor element by dipping the element in a mixed solution prepared by mixing a polymerizable monomer and oxidizing agent in a prescribed solvent. Finally, the solid electrolytic capacitor is formed by inserting the capacitor element into an encapsulating case through the opened end section of the case and, after the end section is sealed by fitting sealing rubber to the end section and caulking the rubber, aging is conducted to the rubber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same, and more particularly to a solid electrolytic capacitor capable of improving the yield of a solid electrolytic capacitor that requires a high withstand voltage and a method for manufacturing the same. Is.

[0002]

2. Description of the Related Art An electrolytic capacitor using a metal having a valve action, such as tantalum or aluminum, has a valve action metal as a counter electrode on the anode side formed into a sintered body, an etching foil, or the like so that the dielectric is expanded. It is widely used because it is possible to obtain a small size and a large capacity. In particular, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has characteristics such as small size, large capacity, low equivalent series resistance, easy chip formation, and suitability for surface mounting. It is indispensable for downsizing, high functionality, and cost reduction of electronic devices.

In this type of solid electrolytic capacitor, for use in small size and large capacity, generally, an anode foil and a cathode foil made of a valve metal such as aluminum are wound with a separator interposed therebetween to form a capacitor element. The capacitor element is impregnated with a driving electrolytic solution, and the capacitor element is housed in a case made of metal such as aluminum or a case made of synthetic resin, which is hermetically sealed. In addition, aluminum, tantalum, niobium, titanium, etc. are used as the anode material, and the same kind of metal as the anode material is used as the cathode material.

As the solid electrolyte used in the solid electrolytic capacitor, manganese dioxide, 7, 7, 8, 8-
Tetracyanoquinodimethane (TCNQ) complex is known, but in recent years, polyethylenedioxythiophene (hereinafter referred to as PEDT) has a slow reaction rate and excellent adhesion to the oxide film layer of the anode electrode. There is a technique (Japanese Patent Application Laid-Open No. 2-15611) that focuses on the conductive polymer.

PE in such a winding type capacitor element
A solid electrolytic capacitor of the type in which a solid electrolyte layer made of a conductive polymer such as DT is formed is manufactured as shown in FIG. First, the surface of the anode foil made of a valve metal such as aluminum is roughened by electrochemical etching in a chloride aqueous solution to form a large number of etching pits, and then in an aqueous solution of ammonium borate or the like. A voltage is applied to form an oxide film layer that becomes a dielectric (formation). Similar to the anode foil, the cathode foil is also made of a valve metal such as aluminum, but its surface is only subjected to etching treatment.

In this way, the anode foil having the oxide film layer formed on the surface and the cathode foil having only the etching pits are wound around the separator to form a capacitor element. Then, on the capacitor element that has been subjected to repair formation,
A polymerizable monomer such as 3,4-ethylenedioxythiophene (hereinafter referred to as EDT) and an oxidant solution are respectively discharged or immersed in a mixed solution of both to accelerate the polymerization reaction in the capacitor element, and to improve the PEDT. To produce a solid electrolyte layer composed of a conductive polymer such as. Then, the capacitor element is housed in a cylindrical outer case having a bottom to form a solid electrolytic capacitor.

[0007]

By the way, in recent years, the solid electrolytic capacitors as described above have come to be used for vehicles. Usually, the drive voltage of the vehicle-mounted circuit is 12V, and the solid electrolytic capacitor is required to have a high withstand voltage of 25V. However, when such a high withstand voltage product is manufactured by the conventional manufacturing method as described above, the short-circuit rate is high in the aging step,
It had the drawback of low yield.

In recent years, due to environmental problems, high melting point lead-free solder has been used, and the solder reflow temperature is 2
The temperature has further increased from 00 to 220 ° C to 230 to 270 ° C. However, there is a drawback in that the withstand voltage decreases when such solder reflow is performed under high temperature. Therefore, even if high temperature reflow soldering is performed, the development of a solid electrolytic capacitor that does not deteriorate withstand voltage characteristics is desired. It had been. It should be noted that such a problem occurs not only when EDT is used as the polymerizable monomer, but also when other thiophene derivative, pyrrole, aniline, or the like is used.

The present invention has been proposed in order to solve the problems of the prior art as described above, and an object thereof is to prevent deterioration of withstand voltage characteristics due to lead-free reflow and to improve high withstand voltage. It is an object of the present invention to provide a solid electrolytic capacitor and a method for manufacturing the same, which can improve the yield when manufacturing a voltage product.

[0010]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted various studies on the cause of increasing the rate of occurrence of short circuits in the aging process when manufacturing high withstand voltage products. As a result, the following conclusions were reached. That is, normally, in the capacitor element after the formation of the conductive polymer, in addition to the conductive polymer, there are monomers, oxidants and other reaction residues not involved in the polymerization reaction. Since the withstand voltage of the substances other than the conductive polymer is lower than the withstand voltage of the conductive polymer, it is considered that these substances lower the withstand voltage of the solid electrolytic capacitor.

Therefore, the inventors of the present invention have made repeated studies to improve the withstand voltage of the solid electrolytic capacitor and prevent the deterioration of the withstand voltage characteristics due to lead-free reflow even if these reaction residues are present. As a result, it was found that the withstand voltage of the solid electrolytic capacitor can be improved by forming a capacitor element using a separator containing a compound having a vinyl group and incorporating a boric acid compound in the capacitor element. It is a thing.

(Method of Manufacturing Solid Electrolytic Capacitor) The method of manufacturing the solid electrolytic capacitor according to the present invention is as follows. That is, an anode foil and a cathode foil each having an oxide film layer formed on the surface are wound around a separator containing a compound having a vinyl group to form a capacitor element, and the capacitor element is subjected to repair chemical conversion. Subsequently, this capacitor element is impregnated with a solution of a boric acid compound to form a combined body of a compound having a vinyl group and a boric acid compound, and then this capacitor element is treated with a polymerizable monomer and an oxidizing agent. The solid electrolyte layer is formed by immersing in a mixed solution prepared by mixing with a predetermined solvent to cause a polymerization reaction of the conductive polymer in the capacitor element. Then, this capacitor element is inserted into an outer case, a sealing rubber is attached to the opening end, and after sealing by caulking, aging is performed to form a solid electrolytic capacitor.

(Separator) Usually, a separator for a solid electrolytic capacitor, which is mainly composed of synthetic fibers, is composed of synthetic fibers and a binder for joining them. As the binder, a synthetic resin itself is used, or the synthetic resin is made into a fibrous shape and melted in the step of forming the separator to bond the main fibers. In the present invention, good results have been obtained by using a separator using a compound having a vinyl group as the main fiber or binder of such a separator.

The required amount of the compound having a vinyl group to be contained in the main fiber of the separator or the binder is small, but even if it is large, the effect is not reduced. The reason is that the compound having a vinyl group contained in the separator elutes and adheres to the oxide film to obtain the effect of the present invention. Therefore, it may be formed of 100% vinylon fiber like a vinylon separator. In this case, the amount of elution may be controlled so that the compound having a vinyl group does not elute too much during the manufacturing process and the strength of the separator does not decrease. A typical example of the present invention is a separator using a PVA binder, but in this case, the content is 15 in order to obtain a predetermined strength.
-40 wt% is preferable.

Here, as the compound having a vinyl group, polyvinyl alcohol (hereinafter referred to as PVA), polyvinyl acetate, polyvinylpyrrolidone, polyacrylamide and the like can be used, but PVA is more preferable. Specifically, PVA is used as the main fiber of the separator.
Fiber (vinylon) or unstretched vinylon may be used, or PVA polymer or unstretched vinylon may be used as the binder. For example, the fiber diameter is 3.0 to 12.0 μm
It is possible to use a non-woven fabric made of the vinylon fiber of (1) as a short fiber having a predetermined cut length and using a predetermined binder by any means.

As a method of incorporating a compound having a vinyl group into the separator, a method of forming the main fiber or binder as described above from a compound having a vinyl group (in other words, a compound having a vinyl group is constituted of the separator) In addition to the method of containing as a component), a method of immersing the separator in a solution of a compound having a vinyl group,
A method of applying a compound having a vinyl group can also be used.

(Boric acid compound) As the boric acid compound,
Boric acid, borax, ammonium salts of boric acid, borate salts such as metal salts, borate esters such as triethyl borate, and the like can be used, and among them, boric acid is preferably used. Further, as a solvent for these boric acid compounds,
Any compound in which these compounds can be dissolved may be used, and mainly water, glycerin, or the like can be used. The concentration of the boric acid compound solution is preferably 0.1 wt% to 10 wt%, more preferably 3 wt% to 7 wt%. When the concentration of the boric acid compound solution was outside this range, the effect was reduced. The reason is that the concentration of the boric acid compound solution is 0.1 wt.
If it is less than 10% by weight, the amount of the boric acid compound in the solution is small, so that the amount of the conjugate formed is not sufficient. This is because boric acid adversely affects the ESR.

(Method of Incorporating Boric Acid Compound into Capacitor Element) As a method of incorporating the boric acid compound into the capacitor element, a method of immersing the capacitor element in a solution of the boric acid compound or A method of discharging the solution to the capacitor element can be used.
It was also found that the initial characteristics are improved by heat treatment after the boric acid compound is contained in the capacitor element. It is considered that the reason is that the compound having a vinyl group contained in the separator is eluted into the capacitor element to increase the hydrophobicity of the terminal group, thereby improving the adhesion between the oxide film and the solid electrolyte. The heating temperature is 1
20-250 degreeC is preferable, More preferably, it is 150-2.
It is 00 ° C. When the heating temperature was outside this range, the effect was reduced. The reason is that if the heating temperature is lower than 120 ° C., the reaction such as hydrophobization of the terminal group of the compound having a vinyl group does not proceed sufficiently, while if it exceeds 250 ° C., the thermal deterioration of the compound having a vinyl group occurs. It is thought that this is because the effect occurs and the effect is reduced.

(Time of Incorporation of Boric Acid Compound into Capacitor Element) Further, the present inventors have conducted various studies on the time of incorporation of the boric acid compound into the capacitor element. As a result, it was found that any step can be performed as long as it is a step before the step of forming the conductive polymer. That is, as described above, the time may be before repair formation or may be attached to the electrode foil before forming the capacitor element. For example, the following methods (1) to (3) Can be considered.

The method (1) corresponds to the above-mentioned manufacturing method. In addition, in the following methods (1) to (3),
Anode foil and cathode foil, wound via a separator containing a compound having a vinyl group to form a capacitor element,
After subjecting this capacitor element to restoration chemical conversion, this capacitor element is impregnated with a solution of a boric acid compound to form a combined body of a compound having a vinyl group and a boric acid compound. The method (1) that can form the solid electrolyte layer by causing the polymerization reaction of the conductive polymer to occur is most preferable. The effect of the present invention does not change even if resin sealing is not performed by the following method.

(1) After restoration formation ... See FIG. 1 formation formation → capacitor element formation using a separator containing a compound having a vinyl group → restoration formation → immersion in boric acid compound solution → impregnation with polymerizable monomer and oxidizing agent → Polymerization → Insertion into outer case → Resin sealing → Aging

(2) After capacitor element formation to before repair chemical formation ... See FIG. 2 Chemical formation → Capacitor element formation using separator containing compound having vinyl group → Dip in boric acid compound solution →
Repair formation → Impregnation of polymerizable monomer and oxidizer → Polymerization → Insertion into outer case → Resin encapsulation → Aging

(3) Before Capacitor Element Formation ... See FIG. 3 Chemical formation → Dip at least one of bipolar electrode foils in boric acid compound solution (or after coating and drying treatment) → Separator containing compound having vinyl group Capacitor element formation by using → Repair formation → Impregnation of polymerizable monomer and oxidizer →
Polymerization → insertion into outer case → resin sealing → aging In addition, the concentration, temperature, impregnation time, drying temperature, drying time, etc. of the boric acid compound solution in these methods are the same as those described above.

(EDT and Oxidizing Agent) When EDT is used as the polymerizable monomer, the ED that impregnates the capacitor element
Although EDT monomer can be used as T,
It is also possible to use a monomer solution in which EDT and a volatile solvent are mixed in a volume ratio of 1: 0 to 1: 3. As the volatile solvent, hydrocarbons such as pentane, ethers such as tetrahydrofuran, esters such as ethyl formate, ketones such as acetone, alcohols such as methanol, nitrogen compounds such as acetonitrile and the like can be used. But,
Of these, methanol, ethanol, acetone and the like are preferable.

As the oxidant, an aqueous solution of ferric p-toluenesulfonate, periodate or iodic acid dissolved in ethanol can be used, and the concentration of the oxidant in the solvent is preferably 40 to 57 wt%. 45-5
7 wt% is more preferable. The higher the concentration of oxidant to solvent, the lower the ESR. As the solvent for the oxidizing agent, the volatile solvent used for the monomer solution can be used, and among them, ethanol is preferable. It is considered that ethanol is suitable as a solvent for the oxidant because it has a low vapor pressure and is likely to evaporate, and a small amount remains.

(Decompression) It is more preferable to reduce the pressure in the polymerization step. The reason is that when the pressure is reduced during the heat polymerization, the residue can be evaporated together with the polymerization. In addition, it is desirable that the degree of pressure reduction is such that the pressure is reduced to about 10 to 360 mmHg.

(Dip Step) The time for immersing the capacitor element in the mixed solution depends on the size of the capacitor element, but for a capacitor element of about φ5 × 3L, 5 seconds or more, φ
For a capacitor element of about 9 × 5 L, 10 seconds or more is desirable, and it is necessary to soak for at least 5 seconds. It should be noted that even if it is immersed for a long time, there is no adverse effect on the characteristics. Moreover, it is preferable to hold in a reduced pressure state after soaking.
It is considered that the reason is that the residual amount of the volatile solvent decreases. The reduced pressure conditions are the same as the reduced pressure conditions in the above-mentioned polymerization step.

(Chemical conversion solution for repair chemical conversion) As chemical conversion solution for repair chemical conversion, phosphoric acid-based chemical conversion solutions such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, boric acid-based chemical conversion solutions such as ammonium borate, Adipic acid-based chemical conversion solutions such as ammonium adipate can be used, but above all,
It is desirable to use ammonium dihydrogen phosphate. The immersion time is preferably 5 to 120 minutes.

(Other Polymerizable Monomer) As the polymerizable monomer used in the present invention, in addition to the above EDT, EDT
Other thiophene derivatives, aniline, pyrrole, furan, acetylene or their derivatives, which are oxidatively polymerized by a predetermined oxidant to form a conductive polymer, can be applied. As the thiophene derivative, one having the following structural formula can be used.

[Chemical 1]

(Operation / Effect) As described above, by forming a capacitor element by using a separator containing a compound having a vinyl group, and by adding a boric acid compound to the capacitor element at a predetermined time, lead It is possible to prevent deterioration of withstand voltage characteristics due to free reflow, and it is possible to significantly reduce the rate of occurrence of a short circuit in the aging process.

The reason why such an effect is obtained is that the compound having a vinyl group contained in the separator is eluted during the manufacturing process to form a bonded body with the boric acid compound in the capacitor element by hydrogen bonding or the like. Adhesion between the solid electrolyte and the oxide film is improved by forming a layer by bonding the bonded body on the oxide film of the electrode foil. Furthermore, the withstand voltage of this layer is high, thus improving the withstand voltage of the capacitor. it is conceivable that.

Further, the compound having a vinyl group contained in the separator as in the present invention elutes more than the compound having a vinyl group contained in the device after the formation of the capacitor element is bound to the boric acid compound. There is also the advantage that the body adheres evenly to the oxide film. In particular, when PVA and boric acid are used, a bond consisting of an ester compound is formed, and the ester compound does not penetrate into the dielectric film and adheres to the film surface to form a good layer. It is considered that good characteristics can be obtained.

Then, as described above, when the boric acid compound is added and then the heat treatment is performed, the bondability between the terminal group of the compound having a vinyl group eluted from the separator and the dielectric oxide film or the conductive polymer. Improves the initial characteristics,
In particular, it is considered that the capacitance and ESR characteristics are improved.

[0034]

EXAMPLE Next, an example manufactured as follows,
The present invention will be described in more detail based on comparative examples and conventional examples. (Example) A main fiber contains 49 wt% of PET fiber, and P
A solid electrolytic capacitor was prepared as follows using a separator using VA polymer as a binder.
An electrode lead-out means was connected to the anode foil and the cathode foil having an oxide film layer formed on the surface, and both electrode foils were wound with the above separator interposed therebetween to form a capacitor element having an element shape of 5φ × 2.8L. . Then, this capacitor element was immersed in an aqueous solution of ammonium dihydrogen phosphate for 40 minutes to carry out repair formation. After restoration formation, this capacitor element is 5 wt%
It was dipped in the boric acid aqueous solution and heat treated at 175 ° C. On the other hand, EDT and 45% ferric p-toluenesulfonate ethanol solution were mixed in a predetermined container, the capacitor element was immersed in the mixed solution for 10 seconds, and kept under a reduced pressure of about 250 mmHg. 120 ° C under 6
After heating for 0 minutes, a polymerization reaction of PEDT was generated in the capacitor element to form a solid electrolyte layer. Then, this capacitor element was inserted into an outer case having a bottomed cylindrical shape, a sealing rubber was attached to the opening end, and sealing was performed by caulking. After that, aging was performed by applying a voltage of 33 V at 150 ° C. for 120 minutes to form a solid electrolytic capacitor. The rated voltage of this solid electrolytic capacitor is 25
The WV and rated capacity are 15 μF.

(Comparative Example 1) After the repair formation, a conductive polymer was formed without immersing in a boric acid aqueous solution. Other conditions and steps are the same as those in the example. (Comparative Example 2) Main fiber contains 49 wt% of PET fiber,
A separator using PET polymer as a binder was used. Other conditions and steps are the same as those in the example. (Comparative Example 3) After the repair formation, the capacitor element was immersed in a 5 wt% boric acid aqueous solution and was not subjected to heat treatment. Other conditions and steps are the same as those in the example.

[Comparison Results] The initial characteristics and the number of short-circuits during aging were examined for each of the 50 solid electrolytic capacitors of the examples and comparative examples obtained by the above method. The results were obtained.
In addition, for a good product in which no short circuit occurred, a lead-free reflow with a peak temperature of 250 ° C and a retention time of 230 ° C for 30 seconds or more was performed, and then a surge test was performed in which 32.5V charge / discharge was performed 1000 times at 125 ° C. When the short circuit voltage was measured, the results shown in Table 1 were obtained.

[Table 1]

As is clear from Table 1, in the examples in which the separator containing the PVA polymer was used and the capacitor element contained the aqueous boric acid solution, the initial characteristics, the number of short circuits after aging, and the short voltage after surge were All were better than Comparative Examples 1 to 3. On the other hand, the characteristics of Comparative Example 1 in which the boric acid treatment was not performed and Comparative Example 2 in which the separator containing no compound having a vinyl group was used were worse than those of the Examples. Further, in Comparative Example 3 in which the heat treatment was not performed, a better result was obtained than in Comparative Example 1 or Comparative Example 2, but the effect was lower than that of the Example.

[0038]

As described above, according to the present invention, it is possible to prevent the deterioration of withstand voltage characteristics due to lead-free reflow and to improve the yield when manufacturing high withstand voltage products. Further, it is possible to provide a solid electrolytic capacitor having good initial characteristics and a method for manufacturing the same.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of a manufacturing process of a solid electrolytic capacitor according to the present invention.

FIG. 2 is a flowchart showing an example of a manufacturing process of a solid electrolytic capacitor according to the present invention.

FIG. 3 is a flowchart showing an example of a manufacturing process of a solid electrolytic capacitor according to the present invention.

FIG. 4 is a flowchart showing an example of a manufacturing process of a conventional solid electrolytic capacitor.

Claims (6)

[Claims] 1. A solid electrolytic capacitor in which a solid electrolytic layer made of a conductive polymer is formed by impregnating a capacitor element in which an anode foil and a cathode foil are wound via a separator with a polymerizable monomer and an oxidizer. In, containing a compound having a vinyl group in the separator,
A solid electrolytic capacitor, characterized in that the capacitor element contains a combination of a compound having a vinyl group and a boric acid compound. 2. The solid electrolytic capacitor according to claim 1, wherein the compound having a vinyl group is polyvinyl alcohol. 3. The solid electrolytic capacitor according to claim 1, wherein the boric acid compound is boric acid or borax. 4. The solid electrolytic capacitor according to claim 1, wherein the polymerizable monomer is a thiophene derivative. 5. The solid electrolytic capacitor according to claim 4, wherein the thiophene derivative is 3,4-ethylenedioxythiophene. 6. An anode foil and a cathode foil are wound around a separator containing a compound having a vinyl group to form a capacitor element, and the capacitor element is impregnated with a solution of a boric acid compound to form a vinyl group. A method for producing a solid electrolytic capacitor, comprising: forming a combined body of a compound having the compound and a boric acid compound, and then forming a solid electrolyte layer made of a conductive polymer.