JP2001284179A - Solid electrolytic capacitor and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor that can prevent swelling and characteristic deterioration at reflow soldering and is suitable for surface mounting, and to provide a method of manufacturing the same. SOLUTION: A capacitor element is formed by winding a bipolar electrode foil, to which an electrode leading means having a copper-plated external connecting section with a separator composed of vinylon, and the capacitor element is dipped in an aqueous solution of ammonium dihydrogen phosphate for 5-120 minutes for restoration conversion treatment. Subsequently, the capacitor element is subjected to thermal treatment at 175-300 deg.C, preferably, 200-270 deg.C for at least 1 minute or longer, preferably 30 minutes or longer. Then the capacitor element is impregnated with EDT or EDT solution, further impregnated with 30-50% solution of ferric paratoluensulfonate in butanol and heated at 20-180 deg.C for 30 minutes or longer. Then, the capacitor element is coated with a resin on the surface thereof and inserted into a cylindrical aluminium case having a bottom. The opening is sealed with rubber through drawing.

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 of manufacturing the same, and more particularly, to a solid electrolytic capacitor suitable for surface mounting which prevents swelling and characteristic deterioration during reflow soldering, and a method of manufacturing the same. 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] For example, a PED is used for a wound type capacitor element.
As shown in Fig. 2, a solid electrolytic capacitor of the type that forms a solid electrolyte layer made of T is manufactured through a manufacturing process of chemical formation, capacitor element formation, solid electrolyte layer formation, insertion into an outer case, resin sealing, and aging. Is done. Hereinafter, this manufacturing process will be briefly described with reference to FIGS.

First, as shown in FIG. 4, the surface of an anode foil 1 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 8. After formation, a voltage is applied in an aqueous solution of ammonium borate or the like to form oxide film layer 4 serving as a dielectric (chemical formation). Like the anode foil 1, the cathode foil 2 as shown in FIG. 3 is also made of a valve metal such as aluminum, but its surface is only subjected to etching. As shown in FIG. 3, the anode foil 1 and the cathode foil 2 are connected to electrode lead-out means 6 and 7 for connecting the respective electrodes to the outside by known means such as stitching and ultrasonic welding. ing. In addition, the electrode lead means 6, 7
Is composed of a connection portion 11, a round bar portion 12, and an external connection portion (lead wire) 13 inserted into the electrode foil.

Next, as shown in FIG. 3, the anode foil 1 having the oxide film layer 4 formed on the surface thereof and the cathode foil 2 having only the etching pits 8 formed thereon are separated by a separator 3 as shown in FIG.
To form the capacitor element 10 (element formation). Subsequently, 3,4-
Impregnated with ethylenedioxythiophene (hereinafter referred to as EDT) and an oxidizing agent, to produce a solid electrolyte layer 5 made of PEDT as shown in FIG. 4 (solid electrolyte layer formation).

Thereafter, the capacitor element 10 is inserted into an outer case (not shown), and a thermosetting resin such as an epoxy resin is adhered to the outer case and thermally cured, so that the outer periphery of the capacitor element 10 is covered with the outer resin. (Resin sealing) to complete a solid electrolytic capacitor. If the resin sealing is performed in this manner, the oxide film layer 4 is damaged and the leakage current characteristics are deteriorated. Therefore, after the resin sealing, it is necessary to apply a voltage corresponding to the capacitor rated voltage and perform high-temperature aging. The oxide film layer 4 is thereby repaired, and the characteristics are improved.

[0009]

In order to improve the withstand voltage characteristics, a method of further improving the above-mentioned conventional manufacturing method is to provide a solid electrolyte layer to impart an appropriate amount of moisture to the capacitor element. A method has been proposed in which a predetermined amount of moisture is applied to the surface of a capacitor element by leaving the capacitor element in a moisture-resistant tank or the like for a predetermined time after forming the substrate.

That is, in this manufacturing method, after the solid electrolyte layer is formed, the capacitor element is allowed to stand in a moisture-resistant tank or the like filled with water vapor, and moisture is allowed to adhere to the surface of the capacitor element. As described above, the capacitor element 10 is covered with a resin to form a resin layer 14, the capacitor element 10 is inserted into a bottomed cylindrical metal case 15, and the opening is rubber-sealed by drawing. As the moisture-resistant tank, for example, a constant-temperature and constant-humidity chamber having a humidity of 40 to 95% and a temperature of 20 to 85 ° C. is used, and the capacitor element is left in the constant-temperature and constant-humidity tank for 10 to 180 minutes. Moisture on the surface.

However, when the solid electrolytic capacitor manufactured by the above-described manufacturing method is used as a horizontal or vertical surface mounting chip component and subjected to high-temperature reflow soldering at 200 to 250 ° C., a metal case or a sealing rubber is required. Swelling occurs and the characteristics are degraded.

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned problems of the prior art. It is an object of the present invention to provide a surface mounting method capable of preventing swelling and characteristic deterioration during reflow soldering. It is an object of the present invention to provide a solid electrolytic capacitor and a method for manufacturing the same, which are suitable as the above.

[0013]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors diligently provide a method of manufacturing a solid electrolytic capacitor suitable for surface mounting, which can prevent swelling and characteristic deterioration during reflow soldering. As a result of repeated studies, the present invention has been completed. That is, the present inventor has proposed that a solid electrolytic capacitor obtained by a conventional manufacturing method be used as a horizontal or vertical surface mount chip component,
When performing high-temperature reflow soldering at 0 to 250 ° C,
As a result of conducting various studies on the cause of the swelling of the metal case and the sealing rubber and the deterioration of the characteristics, the following conclusions have been reached.

First, swelling occurs during reflow soldering,
We examined the possibility that one of the causes of the deterioration of the characteristics might be moisture attached to the surface of the capacitor element. That is, in the reflow soldering, the capacitor element is 200
When maintained at a high temperature of about 250 ° C., water present in the capacitor element becomes water vapor. On the other hand, in the conventional method, the resin is coated after moisture is attached to the surface of the capacitor element.However, the capacitor element is not completely sealed with the coated resin. A minute gap exists between the round bar (a terminal made of aluminum) and the resin. Therefore, it was considered that water vapor leaked from these gaps, and as a result, the case swelled, and that the water vapor might have deteriorated the PEDT and, consequently, the characteristics of the capacitor.

Therefore, in order to confirm the possibility that the cause of the swelling during reflow soldering and the deterioration of the characteristics is water vapor, the case where the capacitor element on which the PEDT was formed was dried was examined. It was found that swelling sometimes occurred and the characteristics were deteriorated. This suggests that swelling occurs during reflow soldering, and that the true cause of the deterioration of the characteristics is not moisture adhering to the surface of the capacitor element.

As described above, even when the capacitor element on which the PEDT is formed is dried, it is considered that the reason why the swelling occurs during the reflow soldering and the characteristics are deteriorated is as follows. That is, when vinylon is used as the separator, the terminal group such as -OH group of vinylon is gasified by keeping vinylon at a high temperature or by a reaction with an oxidizing agent remaining in the capacitor element, and the capacitor swells. It is considered that the characteristics deteriorated.

Therefore, the present inventor has found that even when the capacitor element is kept at a high temperature of 200 to 250 ° C. during reflow soldering, the terminal group such as the —OH group of vinylon used as a separator is used. As a result of various studies on the conditions that do not cause gasification, before forming the PEDT, the capacitor element was heated to 175 to 300 ° C, preferably 200 to 300 ° C.
It has been found that good results can be obtained by heat treatment at 270 ° C. for at least 1 minute, preferably 30 minutes or more.

Furthermore, the present inventor also examined the case where ordinary electrolytic paper such as manila paper or kraft paper was used as the separator. As a result, when heat treatment was performed at 280 ° C. or higher, similarly good results could be obtained. found.

The external connection part (lead wire) conventionally used is a steel wire which is plated with copper and further plated with solder or tin.
This external connection part (lead wire) cannot withstand heat treatment at 175 to 300 ° C. For this reason, in the manufacturing method of the present invention, it is preferable to use a steel wire plated with silver as the external connection portion (lead wire). Since the round bar portion and the connection portion are usually made of aluminum, they can withstand a heat treatment at 175 to 300 ° C., so that no change is required.

(Method of Manufacturing Solid Electrolytic Capacitor) Next, an example of a method of manufacturing a wound solid electrolytic capacitor according to the present invention will be described. That is, as shown in FIG. 1, a bipolar electrode foil to which an electrode lead means having an external connection portion subjected to silver plating is connected is wound together with a separator made of vinylon to form a capacitor element. Restoration formation is performed by immersion in an aqueous solution of ammonium dihydrogen phosphate for 5 to 120 minutes. Thereafter, the capacitor element is heated to 175 to 300 ° C., preferably 200 to 300 ° C.
Heat treatment is performed at 270 ° C. for at least 1 minute, preferably 30 minutes or more.

Subsequently, the capacitor element is impregnated with EDT or an EDT solution, and further impregnated with a 30 to 50% ferric paratoluenesulfonate butanol solution to give 20%.
Heat at ~ 180 ° C for 30 minutes or more. Then, after covering the surface of the capacitor element with resin, it is inserted into a bottomed cylindrical aluminum case, and the opening is sealed with rubber by drawing.

As a method for impregnating the capacitor element with the EDT and the oxidizing agent, it goes without saying that an immersion method can be used in addition to an injection method in which a fixed amount is injected at normal temperature using a syringe or the like. Further, the heat treatment temperature is set to 175 to 300
℃, preferably 200-270 ℃ is 175 ℃
If it is less than the above, the decomposition of the terminal group of vinylon does not proceed to obtain the desired effect, and if it exceeds 300 ° C., the decomposition proceeds too much, and the decomposition of the portion serving as the skeleton of the vinylon molecule also starts, and vinylon itself Is decomposed and no longer functions as a separator fiber. Further, the reason why the heat treatment time is at least 1 minute or more, preferably 30 minutes or more is that if the treatment is performed at a high temperature close to 300 ° C., the terminal group of vinylon can be decomposed in about 1 minute.

As described above, the capacitor element is used between 175 to 300 between the step of forming the oxide film and the step of forming the PEDT while using the separator made of vinylon.
The reason why good results were obtained by performing the heat treatment at 200C, preferably 200 to 270C is considered as follows. That is, 200 ° C. is the decomposition temperature of vinylon, and most of the terminal groups such as the —OH group of vinylon are decomposed by heat treatment after repair formation, so that the capacitor element is kept at a high temperature during reflow soldering. This is considered to be because the terminal group such as -OH group of vinylon does not react and gasify.

(Separator) The separator used in the present invention is formed by converting vinylon fibers having a fiber diameter of 3.0 to 12.0 μm into short fibers having a predetermined cut length, and using a predetermined binder to form a nonwoven fabric by any means. It was done. The separator has a basis weight of 5 to 30 g /
m ² , thickness 10 to 200 μm, density 0.1 to 0.5
It is preferably 6 g / cm ³ .

(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.

(EDT, Oxidizing Agent) As the EDT to be impregnated into the capacitor element, an EDT monomer can be used, and the EDT and the volatile solvent are mixed in a ratio of 1: 1 to 1: 3.
Can be used. Examples of the volatile solvent include 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. However, among them, methanol, ethanol, acetone and the like are preferable. As the oxidizing agent, ferric paratoluenesulfonate dissolved in butanol is used. In this case, the ratio between butanol and ferric paratoluenesulfonate may be arbitrary, but in the present invention, the ratio is 30 to
A 50% solution is used. The mixing ratio of EDT and oxidizing agent is preferably in the range of 1: 3 to 1: 6.

[0027]

Hereinafter, the present invention will be described in more detail with reference to examples. The solid electrolytic capacitor according to the present invention was made as in Example 1 below. Comparative Example 1
A solid electrolytic capacitor having a solid electrolyte layer formed without heat treatment was used.

(Example 1) An anode foil having an oxide film layer formed on its surface and an electrode lead-out means having an external connection portion with silver plating applied to a cathode foil are connected.
Wound through a separator made of vinylon non-woven fabric mainly composed of 5 μm vinylon fiber, the element shape is 4φ × 7
An L capacitor element was formed. Then, the capacitor element was immersed in an aqueous solution of ammonium dihydrogen phosphate for 40 minutes to perform repair formation, and then heat-treated at 230 ° C. for 1 hour. Subsequently, E is injected into this capacitor element by an injection method.
Impregnated with DT monomer, and 40% as oxidizing agent solution
Of butanol solution of ferric paratoluenesulfonate, and heated at 100 ° C. for 1 hour to form a solid electrolyte layer made of PEDT. Thereafter, the surface of the capacitor element was coated with a resin, inserted into a bottomed cylindrical aluminum case, and the opening was sealed with rubber by drawing to form a solid electrolytic capacitor. The mixing ratio between the EDT monomer and the oxidizing agent was 1: 5. The solid electrolytic capacitor has a rated voltage of 6.3 WV and a rated capacity of 33 μm.
F.

(Comparative Example 1) After performing repair formation in the same manner as in Example 1, the capacitor element was dried at 100 ° C for 1 hour. Other conditions were the same as in Example 1 to form a solid electrolytic capacitor.

[Comparative Results] The initial characteristics of the solid electrolytic capacitors of Example 1 and Comparative Example 1 obtained by the above method and the characteristics after reflow soldering at 230 ° C. for 40 seconds were examined. The result as shown in FIG. 1 was obtained.

[Table 1]

As is evident from Table 1, in Example 1 in which the heat treatment was performed at 230 ° C. after the repair formation was performed, the ESR (equivalent series resistance) after the reflow test was 1.03 times the initial characteristic, which was almost 1.03 times. Did not change. Further, the reduction rate of the capacitance was only 1.5%, and no swelling was observed in the metal case and the sealing rubber after the reflow test.

On the other hand, in Comparative Example 1 in which the heat treatment was not performed after the repair formation was performed, the ESR (equivalent series resistance) after the reflow test was increased to 1.19 times the initial characteristic. In addition, the rate of decrease in capacitance is as large as 5.0%,
After the reflow test, swelling was observed in the metal case and the sealing rubber.

As described above, the two electrode foils are wound through the separator made of vinylon to form a capacitor element.
After the repair formation, if heat treatment is performed at 230 ° C,
It was found that swelling and characteristic deterioration during reflow soldering can be prevented.

[0034]

As described above, according to the present invention, it is possible to prevent swelling and characteristic deterioration during reflow soldering.
A solid electrolytic capacitor suitable for surface mounting and a method for manufacturing the same can be provided.

[Brief description of the 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 conventional solid electrolytic capacitor manufacturing process.

FIG. 3 is a perspective view showing a wound state of a capacitor element.

FIG. 4 is an enlarged sectional view showing an anode foil of the capacitor element of FIG. 3;

FIG. 5 is a sectional view showing an example of a solid electrolytic capacitor obtained by a conventional manufacturing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Anode foil 2 ... Cathode foil 3 ... Separator 4 ... Oxide film layer 5 ... Solid electrolyte layer 6, 7 ... Electrode lead-out means 8 ... Etching pit 10 ... Capacitor element 11 ... Connection part 12 ... Round bar part 13 ... External connection part (Lead wire) 14 ... Resin layer 15 ... Metal case

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01G 9/00 H01G 9/05 C 9/24 A CB

Claims (4)

[Claims] 1. A solid electrolytic capacitor comprising a capacitor element in which a bipolar electrode foil connected to an electrode lead-out means is wound via a separator and a solid electrolyte layer made of polyethylene dioxythiophene is formed between the bipolar electrode foils. In the above, the electrode lead-out means has a silver-plated external connection part, uses a separator made of vinylon as the separator, and heat-treats at 175 to 300 ° C. for at least 1 minute before forming the solid electrolyte layer. A solid electrolytic capacitor characterized by the following. 2. The solid electrolytic capacitor according to claim 1, wherein the separator made of vinylon is made of a nonwoven fabric mainly composed of vinylon fibers having a fiber diameter of 3.0 to 12.0 μm. 3. A step of winding a bipolar electrode foil connected to an electrode lead means having an external connection portion together with a separator to form a capacitor element; a step of performing a repair formation on the capacitor element; In a method for manufacturing a solid electrolytic capacitor having a step of forming a solid electrolyte layer made of polyethylene dioxythiophene by impregnating dioxythiophene and an oxidizing agent, silver plating is applied to an external connection part of the electrode lead means, and the separator is used as the separator. A method for manufacturing a solid electrolytic capacitor, comprising using a separator made of vinylon, and after the step of performing the repair formation, a step of heat-treating the capacitor element at 175 to 300 ° C. for at least one minute. 4. The solid electrolytic capacitor according to claim 3, wherein the separator made of vinylon is made of a nonwoven fabric mainly composed of vinylon fibers having a fiber diameter of 3.0 to 12.0 μm. Production method.