JP2002299174A - Manufacturing method for solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for the manufacture of a solid electrolytic capacitor, whereby a solid electrolytic capacitor superior in initial characteristics and reflow characteristics is obtained from a mass production line. SOLUTION: Anode foil and cathode foil are rolled together with separators to form a capacitor element, and the capacitor element is subjected to restoring chemical conversion. Thereafter, the capacitor element is dried at 100 to 150 deg.C for 5 to 30 minutes, and is left in equipment or a workroom conditioned at 60%RH for 0 to 60 minutes. Meanwhile, a specified quantity of EDT and a specified quantity of oxidizer solution are poured into a specified container, to prepared a mixture. The above capacitor element is immersed in the mixture for two or more seconds and is left in equipment or a workroom conditioned at a temperature which is not higher than the polymerization temperature and 10 to 60%RH for 10 to 120 minutes. Thereafter, primary polymerization and secondary polymerization are carried out at a specified temperature to form a solid electrolyte. The capacitor element is placed in a bottomed cylindrical case, and the opening of the case is sealed with rubber. The capacitor element is then subjected to aging, to obtain the solid electrolytic capacitor.

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 in which a method and conditions for impregnating a capacitor element with a monomer solution and an oxidizing agent solution are improved. It is about.

[0002]

2. Description of the Related Art In an electrolytic capacitor using a metal having a valve action such as tantalum or aluminum, a valve action metal as an anode-side counter electrode is formed into a shape of a sintered body or an etching foil to expand a dielectric material. By using such a structure, it is possible to obtain a large capacity with a small size. In particular, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has characteristics that it is small, large-capacity, low equivalent series resistance, easy to chip, and suitable for surface mounting. It is indispensable for miniaturization, high performance, and low cost of electronic devices.

In this type of solid electrolytic capacitor, for small size and large capacity applications, generally, an anode foil and a cathode foil made of 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 electrolyte, and the capacitor element is housed in a metal case such as aluminum or a synthetic resin case, and has a sealed structure. Note that as the anode material, aluminum, tantalum, niobium, titanium, or the like is used, and as the cathode material, the same kind of metal as the anode material is used.

As a solid electrolyte used for a solid electrolytic capacitor, manganese dioxide, 7, 7, 8, 8-
A tetracyanoquinodimethane (TCNQ) complex is known, but recently, polyethylenedioxythiophene (hereinafter, referred to as PEDT), which has a slow reaction rate and excellent adhesion to an oxide film layer of an anode electrode, has been developed. There is a technique (Japanese Patent Laid-Open No. 2-15611) that has been focused on.

[0005] Such a wound-type capacitor element is made of PE.
A solid electrolytic capacitor of the type forming a solid electrolyte layer made of DT is manufactured as follows. First, the surface of the anode foil made of a valve metal such as aluminum is roughened by electrochemical etching treatment in a chloride aqueous solution to form a large number of etching pits, and then, in an aqueous solution such as ammonium borate. A voltage is applied to form an oxide film layer serving as a dielectric (chemical formation). Like the anode foil, the cathode foil is also made of a valve metal such as aluminum, but its surface is only subjected to etching.

[0006] The anode foil having the oxide film layer formed on the surface thereof and the cathode foil having only the etching pits formed thereon are wound through a separator to form a capacitor element. Next, the restoration-formed capacitor element
3,4-Ethylenedioxythiophene (hereinafter referred to as EDT) and an oxidizing agent solution are respectively discharged to accelerate the polymerization reaction of EDT in the capacitor element, and to generate a solid electrolyte layer made of PEDT. In addition to the above-described discharge method, there are also a method of separately impregnating the EDT and the oxidizing agent, and a method of preparing a mixed solution by previously mixing the EDT solution and the oxidizing solution and impregnating the mixed solution into the capacitor element. Used.

[0007]

However, when the above-described manufacturing method is used in an actual mass production process, there is a problem that the ESR varies. Further, there is a problem that the reflow characteristics also vary. That is, when the solid electrolytic capacitor obtained by the conventional manufacturing method as described above is used as a horizontal or vertical surface mounting chip component and subjected to high-temperature reflow soldering, the capacitance decreases during reflow soldering, and the leakage is reduced. There was a problem that the current increased.

In particular, in recent years, lead-free solders having a high melting point have been used due to environmental problems, and the solder reflow temperature has been reduced to two.
Since the temperature is further increased from 00 to 220 ° C to 230 to 270 ° C, the development of a solid electrolytic capacitor that does not cause swelling of the metal case or the sealing rubber and does not deteriorate the characteristics even when high-temperature reflow soldering is performed. Longed for. Incidentally, such a problem is caused by the fact that EDT is used as a polymerizable monomer.
Not only in the case of using thiophene, but also in the case of using other thiophene derivatives, pyrrole, aniline and the like.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object thereof is to obtain a solid electrolytic capacitor having excellent initial characteristics and reflow characteristics in a mass production process. It is an object of the present invention to provide a method for manufacturing a solid electrolytic capacitor that can be used.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, during the normal mass-production process, the products may stay or be left unattended. The humidity at that time varied from 15% to 70% RH, and it was found that the characteristics deteriorated as the humidity increased. Thus, the present inventors have completed the present invention by assuming that such environmental conditions in each step may have an adverse effect on the capacitor element.

(Environmental conditions before the impregnation step)
First, the conditions before the impregnation process were examined. After the capacitor element was repair-formed and dried, the humidity was reduced to 60% RH.
It was found that the characteristics could be adversely affected in about 30 minutes if the apparatus was left in a work process exceeding 30 minutes. In this case, it was found that this adverse effect can be reduced by performing drying at 100 ° C. for 60 minutes or more before the impregnation step.

In addition, various studies have revealed that it is desirable to maintain the humidity conditions before the impregnation step at 60% RH or less. The humidity condition is more preferably 45% RH or less, and further preferably 30% RH or less. Outside this range, the ESR increases and the reflow heat resistance decreases. The reason is that the capacitor element absorbs moisture,
It is considered that this moisture inhibits the formation of PEDT. The condition under which the characteristics are not adversely affected is 60% R
H for 20 minutes and 30% RH for about half a day.

(Impregnation step) EDT is applied to this capacitor element.
And an oxidizing agent. The impregnation method may be either individual impregnation or mixed liquid impregnation.
C is preferred. As the impregnation method, mixed impregnation is more preferable than individual impregnation.

(After the impregnating step) After the impregnating step, it is desirable to keep the temperature below the polymerization temperature and under the condition of 10 to 60% RH. Since the polymerization temperature is usually around 60 ° C., the holding temperature is preferably at most 60 ° C. The reason is that the polymerization proceeds during the holding, and the state of formation of PEDT after the subsequent polymerization step deteriorates. Therefore, if the temperature is maintained at 60 ° C. or lower for a long period of time, the polymerization proceeds. If the temperature is maintained for a long period, the temperature is preferably 30 ° C. or lower.

The humidity condition is more preferably 15 to 45% RH, and further preferably 20 to 30% RH. Outside this range, the ESR increases and the reflow heat resistance decreases.
The reason is that if it exceeds this range, the polymerization liquid absorbs moisture,
It is considered that the water content of the polymerization liquid was increased, and this water inhibited the formation of PEDT. The conditions under which the characteristics are not adversely affected are as follows: 60% RH for about 10 minutes, 10%
It took about 2 hours at RH.

Therefore, the capacitor element kept in a dry state after the repair formation is replaced with the capacitor element satisfying the above conditions of 15 to 30.
C. and 10% to 60% RH are stored in a room or in an apparatus, then impregnated, and the capacitor element is further stored to produce a solid electrolytic capacitor having good characteristics. It has been found that an efficient integrated line can be formed.

(Method of Manufacturing Solid Electrolytic Capacitor) An anode foil and a cathode foil are wound through a separator to form a capacitor element, and after the capacitor element is subjected to restoration formation,
The capacitor element is dried at 100 to 150 ° C. for 5 to 30 minutes, and stored for 0 to 60 minutes in an apparatus or a working room maintained at a condition of 60% RH. On the other hand, a certain amount of EDT and a certain amount of the oxidizing agent solution are poured into a predetermined container to prepare a mixed solution, and the capacitor element is immersed in the mixed solution for 2 seconds or more. The solution is stored for 10 to 120 minutes in an apparatus or a working room maintained under the condition of% RH, and thereafter, primary polymerization and secondary polymerization are performed at a predetermined temperature to form a solid electrolyte. Then, the capacitor element is housed in a bottomed cylindrical case, the opening is sealed with rubber, and aging is performed to produce a solid electrolytic capacitor.

(EDT and Oxidizing Agent) When EDT is used as the polymerizable monomer, the
As T, an EDT monomer can be used,
A monomer solution in which EDT and a volatile solvent are mixed at a volume ratio of 1: 0 to 1: 3 can also be used. 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, and nitrogen compounds such as acetonitrile can be used. But,
Among them, methanol, ethanol, acetone and the like are preferable. Further, as the oxidizing agent, an aqueous solution of ferric paratoluenesulfonate, periodic acid or iodic acid dissolved in butanol can be used, and the concentration of the oxidizing agent in the solvent is preferably 40 to 55 wt%.

(Mixing ratio of EDT and oxidizing agent) The mixing ratio of EDT and oxidizing agent (not including the solvent) is 1: 0.9 to weight ratio.
A range of 1: 2.2 is preferred, with a ratio of 1: 1.3 to 1: 2.
A range of 0 is more preferred. Outside this range, the ESR increases. The reason is considered as follows.
That is, if the amount of the oxidizing agent relative to the monomer is too large,
As the amount of monomer impregnated relatively decreases, the amount of PEDT formed decreases and the ESR increases. On the other hand, if the amount of the oxidizing agent is too small, the amount of the oxidizing agent necessary for polymerizing the monomer will be insufficient, and the amount of the formed PEDT will decrease and the ESR will increase.

(Immersion time) The time for immersing the capacitor element in the mixed solution is determined by the size of the capacitor element.
For a capacitor element of about 8 × 4 L, the time is preferably 10 seconds or more, and it is necessary to soak for at least 5 seconds. It should be noted that there is no adverse effect on the characteristics even when immersed for a long time.

(Chemical solution for repair chemical formation) As a chemical solution for repair chemical formation, a chemical solution of phosphoric acid such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a chemical solution of boric acid such as ammonium borate, An adipic acid-based chemical solution such as ammonium adipate can be used.
It is desirable to use ammonium dihydrogen phosphate. Also, the immersion time is desirably 5 to 120 minutes.

(Other Polymerizable Monomers) The polymerizable monomers used in the present invention include, in addition to the above-mentioned EDT, EDT
Any other thiophene derivative, aniline, pyrrole, furan, acetylene or a derivative thereof, which is oxidatively polymerized with a predetermined oxidizing agent to form a conductive polymer, can be applied. As the thiophene derivative, one having the following structural formula can be used.

Embedded image

(Operation / Effect) As described above, by properly controlling the environmental conditions before and after the step of impregnating the capacitor element with the polymerizable monomer and the oxidizing agent, the capacitor element absorbs moisture before impregnation. , This water is PE
Inhibition of the formation of DT can be prevented, and after the impregnation step, the polymerization solution absorbs moisture and the water content of the polymerization solution increases, thereby preventing the water from inhibiting the formation of PEDT. Therefore, a solid electrolytic capacitor having good characteristics can be obtained.

[0024]

Next, the present invention will be described in more detail based on examples and comparative examples manufactured as follows. Example 1 satisfies the optimum manufacturing conditions of the present invention both before and after the impregnation.
And Example 3 satisfies the manufacturing conditions of the present invention before impregnation, but does not satisfy the manufacturing conditions of the present invention after impregnation. Although the production conditions are not satisfied, after impregnation, the production conditions of the present invention are satisfied. On the other hand, the comparative examples do not satisfy the production conditions of the present invention both before and after the impregnation.

(Example 1) An electrode drawing means was connected to an anode foil and a cathode foil each having an oxide film layer formed on the surface, and both electrode foils were wound via a separator to form an element having a shape of 6.3φ.
A × 5.4 L capacitor element was formed. Then, the capacitor element is placed in an aqueous solution of ammonium dihydrogen phosphate for 4 hours.
Restoration was performed by immersion for 0 minutes. After the repair formation, the capacitor element was dried at 100 ° C. for 10 minutes,
It was stored for 30 minutes in an apparatus maintained under the condition of 0 to 30% RH. Subsequently, a certain amount of EDT and a certain amount of a 45% solution of butanol of ferric paratoluenesulfonate in butanol are poured into a predetermined container to prepare a mixed solution, and the capacitor element is immersed in the mixed solution for 10 seconds. Then, at 25 ° C, 10-30
It was stored for 30 minutes in the same apparatus maintained under the condition of% RH. Thereafter, primary polymerization was performed at 60 ° C., and secondary polymerization was performed at 150 ° C. to form a solid electrolyte. Thereafter, the capacitor element was housed in a bottomed cylindrical case, the opening was sealed with rubber, and aging was performed to produce a solid electrolytic capacitor. The solid electrolytic capacitor has a rated voltage of 6.3 WV and a rated capacity of 100 μF.

Example 2 After impregnation with the above mixed solution,
Stored at 5 ° C., 5% RH. Other conditions were the same as those in Example 1. (Example 3) After impregnation with the above mixed solution, 25 ° C, 70%
Stored at RH. Other conditions were the same as those in Example 1. Example 4 25 ° C., 70 ° C. before impregnation with the mixed solution
Stored at% RH. Other conditions were the same as those in Example 1. (Comparative Example) 25 ° C., 70%
Stored at RH and after impregnation, stored at 25 ° C., 75% RH. Other conditions were the same as those in Example 1.

[Comparative Results] The solid electrolytic capacitors of Examples 1 to 4 and Comparative Example obtained by the above method were examined for initial characteristics and reflow characteristics. The results shown in Table 1 were obtained. Was. The reflow test conditions are a peak temperature of 250 ° C. and a holding temperature of 230 ° C. or more for 30 seconds.

[Table 1]

As is clear from Table 1, in the comparative example prepared outside the range of the conditions of the present invention, desired characteristics were not obtained in both initial characteristics and reflow characteristics. On the other hand, in Examples 2 and 3 in which the holding conditions before the impregnation were performed under the conditions of the present invention, the initial characteristics were improved and the reflow characteristics were also better as compared with the comparative example. Similar results were obtained in Example 4 in which the holding conditions after the impregnation were performed under the conditions of the present invention. Furthermore, in Example 1 in which the holding conditions before and after the impregnation were both performed under the conditions of the present invention, both of the initial characteristics and the reflow characteristics were further improved due to the synergistic effect.

Incidentally, comparing Example 1 and Example 2 with the same conditions before impregnation but different conditions after impregnation, Example 1 in which the humidity after impregnation is 10% RH or more is better. After the impregnation,
It was found that better results were obtained when the humidity was higher than% RH.

[0030]

As described above, according to the present invention, it is possible to provide a method of manufacturing a solid electrolytic capacitor capable of obtaining a solid electrolytic capacitor having excellent initial characteristics and reflow characteristics in a mass production process.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4J002 CE001 DE196 EV256 FD206

Claims (4)

[Claims] 1. A solid electrolytic capacitor in which a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator is impregnated with a polymerizable monomer and an oxidizing agent to form a solid electrolyte layer made of a conductive polymer. In the method for producing a capacitor element, before the step of impregnating the capacitor element with a polymerizable monomer and an oxidizing agent, the capacitor element is subjected to 60% RH.
A method for producing a solid electrolytic capacitor, characterized in that the method is maintained under the following environment. 2. A solid electrolytic capacitor in which a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator is impregnated with a polymerizable monomer and an oxidizing agent to form a solid electrolyte layer made of a conductive polymer. In the manufacturing method, after the capacitor element is impregnated with a polymerizable monomer and an oxidizing agent, the capacitor element is cooled to a polymerization temperature of 10 to 6 or less.
A method for producing a solid electrolytic capacitor, wherein the method is maintained in an environment of 0% RH. 3. The method for producing a solid electrolytic capacitor according to claim 1, wherein the polymerizable monomer is a thiophene derivative. 4. The method according to claim 3, wherein the thiophene derivative is 3,4-ethylenedioxythiophene.