JP2003017369A - Method for manufacturing solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid electrolytic capacitor in which the yield can be increased at the time of manufacturing a high withstand voltage capacitor. SOLUTION: An anode foil having an oxide film formed on the surface and a cathode foil are wound through a separator to form a capacitor element which is then subjected to repair formation. Subsequently, the capacitor element is immersed into a mixture liquid prepared by mixing polymeric monomer, an oxidizing agent and a specified solvent in order to cause polymerization of conductive polymer in the capacitor element thus forming a solid electrolytic layer. The capacitor element is inserted into a case which is then sealed by caulking while fixing a sealing rubber to the end part of the opening and then it is subjected to aging to produce a solid electrolytic capacitor. Heat treatment is carried out for a specified time at a temperature not higher than 200 deg.C at an arbitrary time before aging after the conductive polymer is formed in the capacitor element.

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, and more particularly to a method for manufacturing a solid electrolytic capacitor capable of improving the yield of a solid electrolytic capacitor that requires a high withstand voltage. .

[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 follows. 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.

By the way, when mounting such a solid electrolytic capacitor, it is known that when the soldering is performed at a relatively high temperature by a reflow method or the like, the case and the sealing member swell and a problem occurs. Therefore, conventionally, a method has been proposed in which a heat treatment for raising the temperature of the capacitor element to 200 to 300 ° C. is performed before housing the capacitor element in an outer case (Japanese Patent Laid-Open No. 2000-58389).

[0008]

On the other hand, in recent years, the solid electrolytic capacitors as described above have been used for vehicles. Normally, the drive voltage of the in-vehicle circuit is 1.
It is 2V, and a high withstand voltage of 25V is required for the solid electrolytic capacitor. However, when such a high withstand voltage product is manufactured by the conventional manufacturing method as described above, there is a drawback that a short circuit occurs at a high rate in the aging process and the yield is low. 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 above-mentioned problems of the prior art, and its purpose is to improve the yield in the production of high withstand voltage products. It is to provide a method of manufacturing a capacitor.

[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 present invention has been completed.

As described above, when the conductive polymer is used as the solid electrolyte, heat treatment is usually performed in order to remove the monomer and the oxidant solution remaining after the polymerization. In particular, when performing solder reflow under high temperature, heat treatment is important because the electrical characteristics are lowered and the valve is opened due to evaporation of the monomer and oxidant solution remaining after polymerization. However, the inventors of the present invention have conducted a study to develop a high withstand voltage product of 25 V class, and found that the withstand voltage is lowered when the heat treatment temperature is high, and the withstand voltage characteristic is improved and the solderability is improved. The optimum heat treatment temperature condition that can withstand reflow is found.

(Manufacturing Method of Solid Electrolytic Capacitor) An anode foil and a cathode foil having an oxide film layer formed on the surface are wound with a separator interposed therebetween to form a capacitor element, and this capacitor element is subjected to restoration chemical conversion. Subsequently, this capacitor element is immersed in a mixed solution prepared by mixing a polymerizable monomer, an oxidizing agent and a predetermined solvent, and a polymerization reaction of a conductive polymer is generated in the capacitor element to form a solid electrolyte layer. . 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.

After forming the conductive polymer in the capacitor element, heat treatment is performed at a temperature of less than 200 ° C. for a predetermined time before aging. In addition, the conductive polymer is preferably formed by immersing the capacitor element in a mixed liquid of a polymerizable monomer and an oxidant, and then maintaining the condition at 20 to 90 ° C. to cause a polymerization reaction. .

(Conditions for heat treatment) After the conductive polymer is formed and before the aging, the heat treatment temperature is less than 200 ° C.,
The temperature is preferably 150 ° C. or lower, more preferably 125 ° C. or lower, and is preferably room temperature or higher, preferably 80 ° C. or higher. The heat treatment time varies depending on the heat treatment temperature.
If it is about 5 ° C., it is preferably 1 hour or more. The reason why the treatment time is preferably shorter when the heat treatment temperature is higher is considered to be because the solid electrolyte is deteriorated when the treatment time is lengthened, but the withstand voltage characteristic of the solid electrolyte is deteriorated. On the other hand, it is preferable to lengthen the treatment time when the heat treatment temperature is low, because a certain amount of time is required to evaporate the residue.

The heat treatment may be carried out before aging, immediately after polymerization, or before or after storage in the outer case. It is considered that the reason why the short-circuiting in the aging step was reduced by the heat treatment conditions was that the withstand voltage characteristics of the solid electrolyte were improved by lowering the heat treatment temperature.

(Decompression) It is more preferable to reduce the pressure in the polymerization step. The reason is that when heat treatment is performed at a temperature lower than 200 ° C. as in the present invention, a monomer or an oxidant solution may remain, but when the pressure is reduced during heat polymerization, the residue can be evaporated together with the polymerization. Because. In addition, it is desirable that the degree of pressure reduction is such that the pressure is reduced to about 10 to 360 mmHg.

(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 55 wt%. 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.

(Mixing ratio of EDT and oxidizer) The mixing ratio of EDT and oxidizer (excluding solvent) is 1: 0.5 by weight.
A range of 1: 2.5 is preferred, 1: 1.0 to 1: 2.
The range of 0 is more preferable. ESR rises outside this range. The reason is considered to be as follows.
That is, if the amount of the oxidant with respect to the monomer is too large,
Since the amount of impregnated monomer is relatively low, the amount of PEDT formed is low and the ESR is high. On the other hand, if the amount of the oxidant is too small, the amount of the oxidant necessary for polymerizing the monomer is insufficient, the amount of PEDT formed is decreased, and the ESR is increased.

(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 × 2L, 5 seconds or more, φ
For a capacitor element of about 8 × 4 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 the 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, after the conductive polymer is formed in the capacitor element, heat treatment is performed at a temperature of less than 200 ° C. for a predetermined time before aging, so that a short circuit occurs in the aging process. Can be significantly reduced. It is considered that the reason is that the withstand voltage characteristic of the solid electrolyte was improved by lowering the heat treatment temperature.

[0024]

EXAMPLES Next, the present invention will be described in more detail based on Examples and Comparative Examples produced as follows. (Example 1) An electrode lead-out means was connected to an anode foil and a cathode foil having an oxide film layer formed on the surface, and both electrode foils were wound with a separator interposed therebetween to form a capacitor element having an element shape of 3φ x 4L. did. Then, this capacitor element was immersed in an aqueous solution of ammonium dihydrogen phosphate for 40 minutes to carry out repair formation. On the other hand, EDT and 45% ferric paratoluene sulfonate ethanol solution were poured into a predetermined container so that the weight ratio thereof was 1: 2, and the capacitor element was immersed in the mixed solution for 10 seconds, It was held under a reduced pressure of about 250 mmHg, and then heated at 60 ° C. for 60 minutes under the same conditions to cause a polymerization reaction of PEDT in the capacitor element to form a solid electrolyte layer. Then, heat treatment was performed at 190 ° C. for 10 minutes. 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 solid electrolytic capacitor has a rated voltage of 25 WV and a rated capacity of 6.8 μF.

(Example 2) After polymerization, at 150 ° C. for 30 minutes,
Heat treatment was performed. The other conditions and steps are the same as in Example 1. (Example 3) After polymerization, heat treatment was performed at 125 ° C for 1 hour. The other conditions and steps are the same as in Example 1. (Embodiment 4) Heat treatment is performed after housing in an outer case, and 1
Heat treatment was performed at 25 ° C. for 1 hour. The other conditions and steps are the same as in Example 1. (Comparative Example) After polymerization, heat treatment was performed at 200 ° C. for 5 minutes. The other conditions and steps are the same as in Example 1.

[Comparison Results] For each of the 50 solid electrolytic capacitors of Examples 1 to 4 and Comparative Example obtained by the above method, the number of short circuits during aging was examined, and as shown in Table 1. The results were obtained.

[Table 1]

As is clear from Table 1, the heat treatment temperature is set to 2
In the comparative example in which the temperature was 00 ° C., short-circuit occurred in all 50 pieces. In contrast, in each of the examples in which the heat treatment temperature was lowered, it was found that the lower the heat treatment temperature, the smaller the number of shorts. In particular, in Examples 3 and 4 in which the heat treatment temperature was 125 ° C., short-circuit did not occur in all 50 regardless of the heat treatment timing.

When a reflow test was conducted on each of the solid electrolytic capacitors which did not short-circuit during aging among Examples 1 to 4, the characteristics were good in all of them. The reflow test conditions are a peak temperature of 250 ° C. and a holding time of 230 ° C. or higher for 30 seconds.

[0029]

As described above, according to the present invention, it is possible to provide a method of manufacturing a solid electrolytic capacitor which can improve the yield when manufacturing a high withstand voltage product.

Claims (3)

[Claims] 1. A solid obtained by forming a solid electrolyte layer made of a conductive polymer by impregnating a capacitor element obtained by winding an anode electrode foil and a cathode electrode foil via a separator and impregnating a polymerizable monomer and an oxidizing agent. In the electrolytic capacitor, a method for producing a solid electrolytic capacitor, characterized in that, after forming a conductive polymer in the capacitor element, heat treatment is performed at a temperature of less than 200 ° C. before aging. 2. The method for producing a solid electrolytic capacitor according to claim 1, wherein the polymerizable monomer is a thiophene derivative. 3. The method for producing a solid electrolytic capacitor according to claim 2, wherein the thiophene derivative is 3,4-ethylenedioxythiophene.