JP2002110464A - Solid-state electrolytic capacitor and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state electrolytic capacitor which can be prevented from expanding and degrading in characteristics at the time of flow soldering and therefore is suitable for surface mounting, and also to provide a method of manufacturing the same. SOLUTION: A bipolar electrode foil connected by an electrode extraction means having an external connection is wound through a separator fabricated using unwoven cloth formed of PET fiber whose main fiber's diameter is 1-12 μm, to form a capacitor element. Then, the capacitor element is dipped in an ammonium dihydrogenphosphate aqueous solution for 5 to 120 minutes for recovery chemical conversion treatment. Next, the capacitor element is impregnated with EDT or a EDT solution, and then with a butanol solution containing 30 to 50% of ferric paratoluenesulfonic acid, and then is heated to 20-180 deg.C at least for 30 minutes. Thereafter, the capactor element is inserted into an aluminum case of a cylindrical shape having a bottom and the opening is sealed by drawing with 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 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. Further, as a separator, in order to be able to obtain a precise and uniform solid electrolyte layer, a technique that focuses on a separator composed of a nonwoven fabric mainly composed of vinylon fibers (Japanese Patent Laid-Open No.
0-340829).

[0005] Such a wound-type capacitor element is made of PE.
A solid electrolytic capacitor of the type that forms a solid electrolyte layer made of DT is usually formed by chemical formation → formation of a capacitor element → formation of a solid electrolyte layer → resin coating of the capacitor element → insertion into a bottomed cylindrical metal case → drawing of the opening It is produced by a manufacturing process called rubber sealing.

However, when the solid electrolytic capacitor manufactured by the above manufacturing method is used as a horizontal or vertical surface mounting chip component and subjected to high-temperature reflow soldering, the metal case and the sealing rubber swell. There is a problem that characteristics are also deteriorated.

Therefore, the present inventor has proposed that a solid electrolytic capacitor obtained by the above-described conventional manufacturing method be used as a horizontal or vertical surface mount chip component at a temperature of 200 to 250 ° C.
When high-temperature reflow soldering was performed, swelling of the metal case and the sealing rubber occurred, and as a result of conducting various studies on the cause of deterioration of the characteristics, the following invention was completed, and a patent application was filed earlier. .

That is, when vinylon, paper, or the like is used as the separator, the oxidizing agent remaining in the capacitor element after polymerization reaction or the oxidizing agent is generated by maintaining vinylon, paper, or the like at a high temperature. It was considered that the terminal group such as -OH group of vinylon or paper was gasified by the reaction with the acid, causing swelling and deterioration of characteristics of the capacitor.

Therefore, the present inventor has found that even when the capacitor element is maintained 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 under which gasification does not occur, it was concluded that good results could be obtained by heat-treating the capacitor element at 175 to 300 ° C. for at least 1 minute before forming PEDT.

That is, the manufacturing method shown in the earlier application is as follows. First, a bipolar electrode foil connected to an electrode lead means having an external connection portion is wound together with a separator made of vinylon to form a capacitor element, and the capacitor element is immersed in an aqueous solution of ammonium dihydrogen phosphate for 5 to 120 minutes. And perform repair formation. Thereafter, this capacitor element is heat-treated at 175 to 300 ° C. for at least one minute.

Subsequently, the capacitor element is impregnated with EDT or an EDT solution, and further impregnated with a 30 to 50% ferric paratoluenesulfonate butanol solution.
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.

[0012]

However, in the conventional manufacturing method as described above, after repair formation, PED
Before forming T, the capacitor element is heated to 175-300 ° C.
When the heat treatment of the separator is performed by performing the heat treatment for at least one minute or more, the electrical characteristics are improved to some extent, but have not been satisfactory yet. Further, when the capacitor element is subjected to a high temperature treatment as described above, the lead wire has to be plated with silver or the like in order to withstand the high temperature treatment.

In particular, in recent years, lead-free solder having a high melting point has 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 250 to 270 ° C., when the high-temperature reflow soldering is performed, the above-mentioned problem that the metal case and the sealing rubber swells and the characteristics are deteriorated is as follows. It is even more remarkable.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object of the present invention is 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.

[0015]

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. In other words, the present inventor has found that the capacitor element is 200
A separator that does not decompose, or a separator that does not react at a high temperature with an oxidizing agent remaining after the polymerization reaction or an acid generated by decomposition of the oxidizing agent, even when the separator is kept at a high temperature of up to 260 ° C. As a result of various studies on the material of the above, it has been found that good results can be obtained when the separator is made of a heat-resistant resin.

(Separator) The separator used in the present invention is made of a heat-resistant resin. Here, the separator composed of a heat-resistant resin refers to a non-woven fabric using fibers made of a heat-resistant resin, a separator composed of a porous film using a heat-resistant resin, or the like. Further, as these separators, it is preferable to use a resin which does not react at high temperature with an oxidizing agent remaining after the polymerization reaction or an acid generated by decomposition of the oxidizing agent. Examples of the resin include polyester, nylon, polyimide, and aramid. In particular, a separator made of a nonwoven fabric made of polyethylene terephthalate (PET) fiber is preferable.

Thus, the separator is made of a heat-resistant resin,
Among these, good results were obtained by using a resin that does not react at high temperature with an oxidizing agent remaining after the polymerization reaction or an acid generated by the decomposition of the oxidizing agent. It is considered that as a result, the separator itself does not decompose, so that no gas is generated and no swelling occurs during reflow.

When a non-woven fabric made of the above polyethylene terephthalate (PET) fiber is used, the non-woven fabric preferably has the following configuration. That is, PET fibers having a softening temperature of 240 to 280 ° C are used as main fibers, and unstretched PET fibers having a softening temperature of 90 to 130 ° C are used as a binder. The fiber diameter of the main fiber is 1 to 12 μm, preferably 2 to 9 μm,
The fiber length is 3 to 12 mm, preferably 4 to 10 mm. Outside this range, a suitable separator for a solid electrolytic capacitor, such as strength and thickness, cannot be obtained.

Then, these main fibers and binder fibers are dispersed in water, dehydrated and dried,
A nonwoven fabric is formed by compressing with a roller under heating conditions of 240 ° C., bonding the main fiber and the binder fiber by softening the undrawn fiber, and adjusting the thickness. The thickness of this non-woven fabric is 10
It is 200 μm, preferably 30 to 50 μm. Below the lower limit, the withstand voltage decreases, and above the upper limit, miniaturization cannot be achieved.

The separator has a density of 0.1 to 1 g / cm ³ , preferably 0.2 to 0.6 g / cm ³ .
cm ³ , basis weight 10-30 g / m ² , preferably 15-2
5 g / m ² . Below this lower limit, the strength and withstand voltage decrease, while above this upper limit, a sufficient solid electrolyte is not formed in the separator, and the electrical properties deteriorate.

(Chemical solution for repair chemical formation) As a chemical solution for repair chemical formation, a phosphate-based chemical solution such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a boric acid-based chemical solution 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 in 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. 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. 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 between EDT and oxidizing agent is preferably in the range of 1: 3 to 1: 6.

(Method of Manufacturing Solid Electrolytic Capacitor) Next, an example of a method of manufacturing the wound solid electrolytic capacitor according to the present invention will be described. That is, the bipolar electrode foil to which the electrode lead means having the external connection portion is connected is wound around a separator made of a nonwoven fabric made of PET fiber having a main fiber having a fiber diameter of 1 to 12 μm to form a capacitor element. Then, the capacitor element is immersed in an aqueous solution of ammonium dihydrogen phosphate for 5 to 120 minutes to perform repair formation.

Subsequently, the capacitor element was impregnated with EDT or an EDT solution, and further impregnated with a 30 to 50% ferric paratoluenesulfonate butanol solution.
Heat at ~ 180 ° C for 30 minutes or more. Then, it is inserted into a bottomed cylindrical aluminum case, and the opening is sealed with rubber by drawing. As a method of 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 with a syringe or the like at room temperature.

(Operation / Effect) In the solid electrolytic capacitor according to the present invention manufactured by the above-described manufacturing method, since the separator is made of a heat-resistant resin, even when high-temperature reflow soldering is performed, Since the separator itself does not decompose, no gas is generated, and no swelling occurs during reflow. Furthermore, when the separator is made of a resin that does not react with an acid generated by decomposing the oxidizing agent remaining after the polymerization reaction or the oxidizing agent, the separator does not react with the oxidizing agent or the acid. No gas is generated, and no swelling occurs during reflow.

Further, since the generation of gas can be prevented as described above, it is possible to prevent the solid electrolyte layer from peeling off from the dielectric film and the dielectric film from being damaged due to the stress caused by the gas generation. As a result, it is also possible to suppress deterioration of electrical characteristics such as a decrease in capacitance and an increase in leakage current, which are considered to be caused by them. Further, conventionally, the generation of gas has been suppressed by coating the capacitor element with a resin. However, in the present invention, since the generation of gas itself can be prevented, it is not necessary to perform resin coating. The process can be simplified and shortened. Further, in the present invention, since it is not necessary to perform a high-temperature treatment during the manufacturing process, it is not necessary to perform a special treatment such as silver plating on the lead wire.

[0027]

Hereinafter, the present invention will be described in more detail with reference to examples. In addition, the Example which concerns on this invention was produced as follows using the nonwoven fabric which consists of PET fiber as a separator, without performing resin coating. Also, in the conventional example,
Using a nonwoven fabric made of vinylon fiber as a separator,
The resin coating was performed, and the other conditions were the same as in the example. Further, in the comparative example, a nonwoven fabric made of vinylon fiber was used as a separator in the same manner as in the related art.
Heat treatment was performed at 30 ° C., resin coating was performed, and other conditions were the same as in the example.

(Example) An electrode drawing means is connected to an anode foil and a cathode foil each having an oxide film layer formed on the surface, and both electrode foils are produced using a nonwoven fabric made of PET fiber having a main fiber diameter of 7 μm. The capacitor was wound with the separator interposed therebetween to form a capacitor element having an element shape of 10φ × 8 L. Then, the capacitor element was immersed in an aqueous solution of ammonium dihydrogen phosphate for 40 minutes to perform repair formation. continue,
This capacitor element was impregnated with an EDT monomer by an injection method, and further impregnated with a 40% butanol solution of ferric paratoluenesulfonate as an oxidizing agent solution.
C. for 1 hour to form a solid electrolyte layer made of PEDT. Thereafter, the capacitor element was inserted into a bottomed cylindrical aluminum case without resin coating, 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 rated voltage of this solid electrolytic capacitor is 16 WV and the rated capacity is 180 μF.

(Comparative Example) An anode foil having an oxide film layer formed on its surface and an electrode lead-out means having an external connection portion in which a cathode foil is plated with silver were connected, and both electrode foils had a fiber diameter of 7.5.
It is wound through a separator made of vinylon non-woven fabric mainly composed of a vinylon fiber of μm, and the element shape is 10φ × 8
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 16 WV and a rated capacity of 180 μm.
F.

(Conventional example) A capacitor element was formed in the same manner as in the comparative example, and after performing repair formation, a solid electrolytic capacitor was formed under the same conditions as in the comparative example without performing heat treatment.

[Comparative Results] The initial characteristics and the characteristics after the reflow test of each of the solid electrolytic capacitors of the example, the comparative example, and the conventional example obtained by the above method were examined.
The results as shown in Table 1 were obtained. The reflow test conditions were as follows: peak temperature 250 ° C, 230 ° C or higher for 30 seconds,
The reflow soldering is performed twice.

[Table 1]

As is clear from Table 1, in the conventional example in which the vinylon separator was used and the heat treatment was not performed after the repair formation, the ESR (equivalent series resistance) after the reflow test was 1.4 as the initial characteristics. It increased twice, and the rate of decrease in capacitance showed a large value of 15.0%. Furthermore, the change in the diameter of the metal case after the reflow test (試 験 L)
Was as large as 0.75 mm, and swelling was also observed in the sealing rubber.

On the other hand, in a comparative example in which a vinylon separator was used for repair formation and then heat treatment at 230 ° C., the ESR (equivalent series resistance) after the reflow test was almost unchanged at 1.12 times the initial characteristics. Was. In addition, the rate of decrease in capacitance was 6%, which was reduced to about 40% of the conventional example.
It was not enough yet. Furthermore, the amount of change (ΔL) in the diameter of the metal case after the reflow test was 0.40 mm. Although this was improved compared to the conventional example, it was not sufficient, and swelling was observed in the sealing rubber.

On the other hand, in the embodiment according to the present invention, the ESR (equivalent series resistance) after the reflow test shows the same value as the initial characteristic, and the capacitance reduction rate is 2.0%.
%, Which is significantly reduced as compared with the conventional example and the comparative example. Furthermore, the change in the diameter of the metal case after the reflow test (試 験 L)
Is 0.02 mm, and the increase is 2.7 times that of the conventional example.
%, Only 5% of the comparative example, and no swelling was observed in the sealing rubber.

As described above, when a capacitor element is formed by winding both electrode foils through a separator formed by using a non-woven fabric made of PET fiber, and a solid electrolytic capacitor is manufactured without resin coating, It was found that swelling and characteristic deterioration during reflow soldering can be prevented. Further, since no resin coating is performed, the manufacturing process is shortened.

[0036]

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.

Claims (8)

[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. 3. The solid electrolytic capacitor according to claim 1, wherein the separator is made of a heat-resistant resin. 2. The method according to claim 1, wherein the separator is made of an oxidizing agent for forming a solid electrolyte or a resin which does not react at high temperature with an acid generated by decomposition of the oxidizing agent. The solid electrolytic capacitor as described. 3. The solid electrolytic capacitor according to claim 1, wherein the separator is made of a non-woven fabric made of polyethylene terephthalate fiber. 4. The solid electrolytic capacitor according to claim 3, wherein the polyethylene terephthalate fiber has a fiber diameter of 1 to 12 μm. 5. A capacitor element is formed by winding a bipolar electrode foil to which an electrode lead means having an external connection portion is connected together with a separator, and the capacitor element is subjected to repair formation. A method for manufacturing a solid electrolytic capacitor in which a solid electrolyte layer made of polyethylene dioxythiophene is formed by impregnating thiophene and a predetermined oxidizing agent, wherein a separator made of a heat-resistant resin is used as the separator. Production method. 6. The solid electrolytic capacitor according to claim 5, wherein a separator made of a resin that does not react at high temperature with the oxidizing agent or an acid generated by decomposition of the oxidizing agent is used as the separator. Production method. 7. The method for manufacturing a solid electrolytic capacitor according to claim 5, wherein the separator is made of a non-woven fabric made of polyethylene terephthalate fiber. 8. The method according to claim 7, wherein the polyethylene terephthalate fiber has a fiber diameter of 1 to 12 μm.