JP2792469B2 - Solid electrolytic capacitor and method of manufacturing the same - Google Patents

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 using a conductive polymer as a solid electrolyte and having a low impedance in a high frequency range and excellent reliability, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A solid electrolytic capacitor which uses a conductive polymer as a solid electrolyte of an electrolytic capacitor to reduce the impedance in a high frequency region has been actively developed. FIG. 3 is a sectional view of an example of a conventional solid electrolytic capacitor. A metal pellet 1 serving as an anode has a dielectric film 1a formed on the surface by anodic oxidation, a conductive polymer layer 2 serving as a solid electrolyte is formed thereon, and a carbon layer 4 and a silver layer 5 are formed thereon. Further, an exterior epoxy resin 8 is formed. An anode lead 6 and a cathode lead 7 are connected to the metal pellet 1 and the silver layer 5, respectively.

As this kind of conductive polymer in such a solid electrolytic capacitor, polyacetylene, polypyrrole, polyaniline, polythiophene, polyparaphenylene, and the like are known. Among them, polypyrrole and polyaniline, in particular, have conductivity. Since they are high and have excellent thermal stability, capacitors using these as electrolytes are being developed. For example, Japanese Patent Publication No. 3-6133
No. 1 discloses that a conductive polymer layer is first formed on a dielectric oxide film by a chemical polymerization method, and then a new conductive polymer film is further formed by an electrolytic polymerization method to form a double layer. There is disclosed a solid electrolytic capacitor using the obtained conductive polymer film as a solid electrolyte. In addition, Japanese Patent Publication No. 4-56445
In Japanese Patent Application Laid-Open Publication No. H11-157, a solid electrolytic capacitor in which a conductive polymer is limited to polypyrrole and polypyrrole is used as an electrolyte is disclosed.

Japanese Patent Application Laid-Open No. 62-29124 discloses a solid electrolytic capacitor using polyaniline as an electrolyte, wherein the electrolyte is limited to polyaniline using an arylsulfonic acid or the like as a dopant. As the dopant in this case, arylsulfonic acid (toluenesulfonic acid, benzenesulfonic acid), tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane or quinones is said to be effective.

Further, the present inventors have proposed a solid electrolytic capacitor using a sulfonic acid derivative (such as a mono- or disulfonic acid derivative) as a dopant and using polyaniline synthesized by chemical polymerization as a solid electrolyte, and a method for producing the same. (JP-A-6-234852, Japanese Patent Application No.
192353).

[0006]

By the way, an oxide film formed by anodic oxidation is used as a dielectric on the surface of a film-forming metal serving as an anode, and the oxide film is formed in close contact with the dielectric by a method of electrolytic polymerization or chemical polymerization. The conductive polymer layer is used as a part of the cathode, and the cathode is pulled out from the inside of the pores of the expanded aluminum foil or the inside of the tantalum sintered body in a solid electrolytic capacitor led to the surface mount terminal via solder etc. The formation of a conductive polymer is an important issue, and various techniques as described above have been developed to solve this.

On the other hand, forming a conductive polymer layer having a uniform and controlled thickness on the outer surface of an aluminum foil or a tantalum sintered body is also an important issue. However, when the conductive polymer layer is formed by electrolytic polymerization or chemical polymerization, it is generally difficult to control the film thickness and morphology. That is, when the conductive polymer layer on the outer surface is too thin, the stress at the time of resin coating is directly applied to the capacitor, and the impedance characteristics and the leakage current characteristics of the electrolytic capacitor often fail.

If the conductive polymer layer on the outer surface is too thick, the conductive polymer itself is liable to deteriorate due to the resin sheath. Further, when the conductive polymer layer is formed thick, cracks or peeling are apt to occur on the surface, so that a graphite layer or a silver layer for extracting an electrode lead comes into direct contact with the dielectric film. When defects occur in the dielectric film, these conductive layers have no function of repairing those defects, so that leakage current increases and reliability is insufficient.

Therefore, the electrolytic capacitors using a conductive polymer as a solid electrolyte disclosed above are superior to the conventional solid electrolytic capacitors in that the impedance in a high frequency range is low, but the impedance and the leakage current characteristics are high. The problem remains that the reliability is not yet sufficient.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a solid electrolytic capacitor having improved reliability of leakage current characteristics and impedance characteristics and a method of manufacturing the same.

[0011]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems. As a result, as a solid electrolyte of an electrolytic capacitor, after forming a conductive polymer by electrolytic polymerization or chemical polymerization, a conductive polymer layer containing a conductive polymer and a resin serving as a binder is formed on the outer surface of the capacitor. The present invention has been found that a solid electrolytic capacitor with remarkably improved reliability can be obtained by forming the capacitor again.

FIG. 1 is a sectional view showing the basic structure of a solid electrolytic capacitor according to the present invention, in which a metal pellet 1 serving as an anode is made of a sintered body of fine tantalum powder, and a dielectric film 1a is formed by anodic oxidation. ing. A first layer 2 of a conductive polymer to be a solid electrolyte is formed inside and on the surface of the tantalum pellet 1, a second layer 3 of a conductive polymer is formed thereon, and a carbon layer 4 is further formed thereon. Silver layers 5 are sequentially formed. Then, the anode lead 6 is connected to the tantalum pellet, the cathode lead 7 is connected to the silver layer 5, and these are covered with the exterior epoxy resin 8.

Here, the conductive polymer serving as the electrolyte of the solid electrolytic capacitor of the present invention is not particularly limited, and is obtained by polymerizing a heterocyclic compound or an aromatic compound from a polymerizable monomer.
Alternatively, any conductive polymer obtained by chemical polymerization may be used. For example, polypyrrole, polythiophene, polyfuran, polyaniline, polyparaphenylene, or a dielectric thereof can be used. However, among them, polypyrrole, polyaniline and their dielectrics, which have high conductivity and excellent thermal stability, are more preferable.

FIG. 2 is a flowchart showing a method of manufacturing a solid electrolytic capacitor according to the present invention in the order of steps. When described in conjunction with FIG. 1, first, the film-forming metal pellet 1 is etched (S1). When the film forming metal 1 is an aluminum foil, it is etched to form a large number of pores on the surface. When the film forming metal 1 is a tantalum powder,
The tantalum powder is pressed into a sintered body. Then, a chemical conversion is performed on the surface of the film forming metal 1 to form an oxide film 1a serving as a dielectric (S2). Then, the first conductive polymer layer 2 is formed by electrolytic polymerization or chemical polymerization (S
3), a second conductive polymer layer 3 serving as a binder thereon
Is formed (S4). Thereafter, a carbon paste or a silver paste is applied and baked to form the carbon layer 4 and the silver layer 5, and the leads 6 and 7 are connected (S5).
The exterior 8 is formed and sealing is performed (S6).

In the solid electrolytic capacitor of the present invention, the conductive polymer used for the conductive polymer layer outside the capacitor is synthesized by a chemical polymerization method, and this conductive polymer is formed inside the electrolytic capacitor. The conductive polymer may be the same as the conductive polymer, but does not necessarily have to match. It is preferable to use one having high conductivity and excellent thermal stability. The resin serving as a binder used for the conductive polymer layer on the outside of the capacitor is not particularly limited as long as it acts as a binder, but a resin excellent in heat resistance is preferable, and the size, type, application, and The selection may be made according to, for example, the adhesion to other conductive layers. For a highly reliable solid electrolytic capacitor, use of a fluorine elastomer is particularly preferable.
Examples include vinyl / olefinic fluoroelastomer copolymers, vinyl fluorinated carbon elastomer polymers, fluorinated acrylic polymer resins, and the like. Commercially available fluoroelastomer is Viton: D
upon) and Fluorel:
(Trademark of 3M).

When the resin serving as the binder has a binder resin content of 10% by weight or less, the conductivity of the outer conductive polymer layer is high, but the mechanical properties are significantly reduced. On the other hand, when the content of the binder resin is 85% by weight or more, the mechanical properties of the conductive polymer layer are excellent, but the conductivity is low, which causes an increase in the impedance of the capacitor.

Further, in the solid electrolytic capacitor of the present invention, the method of forming the conductive polymer layer outside the capacitor is not particularly limited, but the conductive polymer and the resin serving as the binder are dispersed and coated in an appropriate solvent. Can be sprayed. The thickness is usually 2 to 20 μm, but is not particularly limited, and is set according to the size and type of the electrolytic capacitor.

In the solid electrolytic capacitor of the present invention, the film-forming metal is tantalum, aluminum, niobium, titanium, zirconium, magnesium, silicon, or the like, and can be used in the form of a rolled foil or a fine powder sintered product. . The film-forming metal is anodized in an electrolyte solution to form an oxide film serving as a dielectric. The electrolyte and solvent used are not particularly limited, and conventionally known ones can be used.
In addition, a constant voltage method or a constant current method can be applied as a method of anodic oxidation, and the voltage, the method of increasing the current, the holding time after the voltage becomes constant, the temperature, and the like are not limited, and if necessary Can be set.

In the solid electrolytic capacitor according to the present invention, a coating metal provided with a dielectric is heat-treated at a predetermined temperature and a predetermined atmosphere to improve characteristics such as a capacitance appearance ratio and an equivalent series resistance of the capacitor. Can be subjected to various surface treatments.

The method for synthesizing the electrolyte conductive polymer during the production of the solid electrolytic capacitor of the present invention is not particularly limited. It can be synthesized by a method of electrolytic polymerization or chemical polymerization (in a gas phase or a liquid phase). In the case of electrolytic polymerization, in a suitable solution in which a polymerizable monomer and an electrolyte or, if necessary, a proton oxide compound are dissolved, a porous formed body of a film-forming metal having an oxide film formed thereon is used as an anode. Polymerization can be performed by a current method or a constant voltage method. In order to smoothly perform the electrolytic polymerization, the electrolytic polymerization may be performed after forming a precoat film on the oxide film surface.

In the case of chemical polymerization, an oxidizing agent or a mixture of an oxidizing agent and a protonic acid compound is introduced as it is or after being introduced into a porous forming body of a film forming metal having an oxide film formed by dissolving in an appropriate solvent. Contacting with a gas or a solution of a polymerizable monomer or a mixture of a polymerizable monomer and a protonic acid compound; Then, it is introduced into a porous formed body of a film-forming metal and then brought into contact with an oxidizing agent or a mixture of an oxidizing agent and a protonic acid compound. After completion of the polymerization, the capacitor element is washed with water or a solvent in which the oxidizing agent is easily soluble to remove the oxidizing agent that does not contribute to the conductivity.

When the electrolyte is polyaniline or its derivative, the conductivity and reliability of the electrolyte strongly depend on the dopant concentration of polyaniline or its derivative. At high dopant concentrations, the conductivity of the electrolyte is high,
There is a possibility that the moisture resistance, particularly the reflow resistance when mounting a solid electrolytic capacitor, may be reduced. On the other hand, at a low dopant concentration, the conductivity of the electrolyte decreases and the equivalent series resistance of the capacitor increases. Therefore, after forming the electrolyte polyaniline or a derivative thereof, the dopant concentration of the electrolyte polyaniline is adjusted according to the specifications of the capacitor. The method of adjusting the dopant concentration is not particularly limited, but a simple method of re-doping in a protonic acid solution having an appropriate concentration is a simple method.

After the formation of the electrolyte conductive polymer, drying is performed if necessary, and a conductive polymer layer containing the conductive polymer and a resin serving as a binder is formed. A graphite layer and a silver layer are further formed thereon. Is formed, and a lead electrode is provided by a usual method to assemble the capacitor. In the present invention, the graphite layer and the silver layer are not particularly limited, and conventionally known layers can be used.

[0024]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. Here, Examples 1 and 2 described below illustrate examples of electrolytic capacitors using polyaniline as an electrolyte.
Examples 3 to 5 show examples of electrolytic capacitors using polypyrrole as an electrolyte. Reference Examples 1 to 4 show examples in which a conductive polymer layer made of a conductive polymer and a resin serving as a binder is not formed.

In the following, the conductivity of the conductive polymer was measured as follows. 3. Using IR tablet former.
After applying a pressure of 5 × 104 ton / m ² to produce a conductive polymer pellet, the conductive polymer pellet was cut out into a 10 mm × 1 mm strip and subjected to conductivity measurement. The conductivity was measured by a four-terminal method. A constant current was passed from the stabilized power supply to the current terminals, and the voltage between the voltage terminals was measured to determine the conductivity. The measurement was performed at room temperature.
Performed under reduced pressure. The frequency characteristics of the capacitors were measured using an impedance analyzer 4194A manufactured by Yokogawa Hewlett-Packard Co., Ltd.

(Example 1) "Synthesis of polyaniline" 1.4 g (5 mmol) of m-xylylenedisulfonic acid was weighed in an eggplant type flask (for 300 ml) with a dropping funnel, and 100 ml of pure water was added. While stirring the above solution, 0.93 g of aniline (1
(0 mmol) was added and dissolved. While maintaining the temperature of the reaction system at 0 ° C. or lower, a solution in which 0.94 g (3.3 mmol) of ammonium dichromate and 3.2 g (12 mmol) of m-xylylenedisulfonic acid were previously dissolved in 30 ml of pure water was dropped from the dropping funnel. It was added dropwise over 2 hours. After completion of the dropwise addition, polymerization was carried out with stirring for further 3 hours. After completion of the polymerization, the product was filtered, washed with 1 l of pure water and 0.5 l of ethanol, and dried. Yield 1.7 g. Conductivity 15.
6s / cm.

"Preparation of conductive paste comprising polyaniline and resin serving as binder" 1.0 g of polyaniline synthesized as described above and 0.6 g of viton (fluorinated elastomer manufactured by Dupont, Inc.) serving as a binder were added to methyl ethyl ketone. , And thoroughly mixed with a homogenizer, so that the concentration of polyaniline is 30 wt%.
A conductive polyaniline paste was prepared. The conductivity of the thin film cast from the paste is 11.5 s / c
m.

[Preparation of Capacitor Using Polyaniline as Solid Electrolyte] CV value of powder (product of capacity and formation voltage) per gram is 1.5 mm, height is 2 mm and gram is 30,000 /
g of cylindrical sintered tantalum powder
Anodized at 95 V in a t% nitric acid aqueous solution, washed and dried. This tantalum pellet was first immersed in a 5 wt% aniline water: ethanol = 1: 1 solution for 30 seconds at room temperature with an equivalent amount of aniline and m-xylylenedisulfonic acid.
After 5 minutes, an aqueous solution of an oxidizing agent containing ammonium chromate and m-xylylene disulfonic acid (the molar ratio of ammonium dichromate / m-xylylene disulfonic acid is 1: 1.5 and the content of nichrome acid is 10 wt%) is added. It was immersed in the solution cooled to 0 ° C. for 30 seconds. The tantalum pellets were taken out and kept in the air for further 10 minutes to carry out polymerization. Thereafter, when the substrate was washed and dried with water and ethanol, black polyaniline was formed on the surface of the dielectric.

A series of operations of charging the aniline, contacting the mixed solution of the oxidizing agent and m-xylylenedisulfonic acid, polymerization, washing and drying were repeated five times. Then, 0.1M
Was treated with an m-xylylenedisulfonic acid solution for 10 minutes, further washed with an ethanol solution, and then dried at 85 ° C. in the air for 2 hours. The conductive paste was applied to the tantalum electrolytic capacitor on which the electrolyte polyaniline was formed and dried at 85 ° C. in the air for 1 hour to form a conductive polymer layer made of a conductive polymer and a resin serving as a binder. . The thickness of the conductive polymer layer was 7 μm. Then, attach the silver paste and pull out the cathode lead,
The capacitor was completed by sealing with epoxy resin.

(Example 2) "Preparation of capacitor using polyaniline as solid electrolyte"
5% of aluminum foil with a thickness of 150 μm and 1 × 0.5 cm ² whose surface area is enlarged almost 20 times by etching
Anodize at 100V in ammonium borate aqueous solution,
Washed and dried. A capacitor was completed in exactly the same manner except that the aluminum foil was used in place of the tantalum fine powder sintered compact pellets of Example 1.

(Example 3) "Synthesis of polypyrrole" In an eggplant type flask (for 300 ml) equipped with a dropping funnel, 150 ml of a 30 wt% ethanol solution of iron (III) dodecylbenzenesulfonate was added, and the mixture was stirred at room temperature while stirring the pyrrole 8 g to about 30
It was added dropwise over a period of minutes. After completion of the dropwise addition, polymerization was carried out with stirring for another 2 hours. After the polymerization is completed, the product is filtered, and 1
It was washed with 1 l of pure water and 2 l of ethanol and dried. Yield 2.3 g. Conductivity 31.7 S / cm.

[Preparation of Conductive Paste Consisting of Polypyrrole and Resin as Binder] 1.0 g of polypyrrole synthesized as described above and Viton as a binder resin (Viton, fluorine elastomer manufactured by Dupont)
0.6 g was dissolved in methyl ethyl ketone and sufficiently mixed with a homogenizer to prepare a conductive polypyrrole paste having a polypyrrole concentration of 30 wt%. The conductivity of the thin film cast from the paste was 24.5 S / cm.

[Preparation of Capacitor Using Polypyrrole as Solid Electrolyte] Tantalum pellets similar to those in Example 1 were prepared. The tantalum pellet was first immersed in a 60 wt% pyrrole ethanol solution at room temperature for 30 seconds. After 5 minutes, 35 wt% of iron (III) dodecylbenzenesulfonate
% Ethanol solution for 30 seconds. The tantalum pellets were taken out and kept in the air for further 10 minutes to carry out polymerization. Thereafter, when washing and drying were performed with ethanol, black polypyrrole could be formed on the dielectric surface. A series of operations of filling with pyrrole, contact with an oxidizing agent solution, polymerization, washing and drying was repeated a total of seven times. When a conductive paste of the polypyrrole was applied to a tantalum electrolytic capacitor formed with the electrolyte polypyrrole and dried at 85 ° C. for 1 hour in the air, a conductive polymer layer composed of a conductive polymer and a resin serving as a binder was formed. Formed. The thickness of the conductive polymer layer was 10 μm. Then, a silver paste was applied, the cathode lead was pulled out, and the package was sealed with epoxy resin to complete the capacitor.

(Example 4) "Preparation of capacitor using polypyrrole as solid electrolyte"
In Example 3, after forming the electrolyte polypyrrole,
The polyaniline conductive paste of Example 1 was formed. Otherwise, the capacitor was completed in exactly the same manner as in Example 3.

(Example 5) "Preparation of capacitor using polypyrrole as solid electrolyte"
An aqueous solution was prepared such that the concentration of pyrrole was 1 M and the concentration of iron (III) dodecylbenzenesulfonate was 0.3 M. The aluminum foil of Example 2 was immersed in the above electrolyte,
The counter electrode was placed in the electrolytic solution immediately below the aluminum foil, and a gold wire auxiliary electrode was brought into contact with the upper surface of the aluminum foil. First, a fractal was grown on the surface of the aluminum foil by applying a voltage of 10 V for about 5 minutes, and then electrolytic polymerization was performed at a voltage of 2 V for about 2 hours. After completion of the polymerization, the substrate was washed by immersion in ethanol and dried under reduced pressure at 85 ° C. for 4 hours. Applying the conductive paste of polypyrrole to the aluminum electrolytic capacitor on which the electrolyte polypyrrole is formed,
After drying at 5 ° C. in the air for 1 hour, a conductive polymer layer composed of a conductive polymer and a resin serving as a binder was formed. The thickness of the conductive polymer layer was 10 μm. Then, a silver paste was applied, the cathode lead was pulled out, and the package was sealed with epoxy resin to complete the capacitor.

Reference Example 1 "Preparation of Capacitor Using Polyaniline as Solid Electrolyte"
In Example 1, after forming the electrolyte polyaniline,
A conductive polymer layer composed of a conductive polymer and a resin serving as a binder was not formed. Otherwise, the capacitor was completed in exactly the same manner as in Example 1.

Reference Example 2 "Preparation of Capacitor Using Polyaniline as Solid Electrolyte"
In Example 2, after forming the electrolyte polyaniline,
A conductive polymer layer composed of a conductive polymer and a resin serving as a binder was not formed. Otherwise, the capacitor was completed in exactly the same manner as in Example 2.

Reference Example 3 "Preparation of Capacitor Using Polypyrrole as Solid Electrolyte"
In Example 3, after forming the electrolyte polypyrrole,
A conductive polymer layer composed of a conductive polymer and a resin serving as a binder was not formed. Otherwise, the capacitor was completed in the same manner as in Example 3.

Reference Example 4 "Preparation of Capacitor Using Polypyrrole as Solid Electrolyte"
In Example 5, after forming the electrolyte polypyrrole,
A conductive polymer layer composed of a conductive polymer and a resin serving as a binder was not formed. Otherwise, the capacitor was completed in the same manner as in Example 5.

[0040]

In each of the embodiments, 200 solid electrolytic capacitors were prototyped. When the standard values of the leakage current and the impedance at 100 kHz of the obtained solid electrolytic capacitor were 0.5 μA and 0.4 Ω, respectively, immediately after the capacitor was manufactured (after resin sheathing) and at 260 ° C.
Tables 1 and 2 show the defect occurrence rates of the capacitors after a lapse of 300 hours under a condition of 125 ° C. after performing the solder test for 10 seconds. From these results, it was confirmed that the capacitors obtained according to the examples of the present invention had low equivalent series resistance, good high frequency characteristics, and excellent reliability.

[0041]

[Table 1]

[0042]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a diagram showing a sectional structure of an embodiment of a solid electrolytic capacitor of the present invention.

FIG. 2 is a flowchart showing a method for manufacturing a solid electrolytic capacitor of the present invention.

FIG. 3 is a diagram showing a cross-sectional structure of an example of a conventional solid electrolytic capacitor.

[Explanation of symbols]

 Reference Signs List 1 metal pellet 1a dielectric film 2 conductive polymer layer (first layer) 3 conductive polymer layer (second layer) 4 carbon layer 5 silver layer 6 anode lead 7 concealed lead 8 exterior epoxy resin

Claims (5)

(57) [Claims] 1. A film-forming metal serving as an anode, an oxide film serving as a dielectric formed on the surface thereof, a conductive polymer layer formed in close contact with the dielectric, the anode and the conductive polymer layer In a solid electrolytic capacitor including an anode connected to each of the leads of the cathode, the conductive polymer layer,
A first conductive polymer layer formed on a dielectric by a method of electrolytic polymerization or chemical polymerization, and a second conductive polymer including a conductive polymer formed thereon and a fluorine elastomer serving as a binder A solid electrolytic capacitor comprising a layer. 2. The solid electrolytic capacitor according to claim 1, wherein the conductive polymer used for the first conductive polymer layer is mainly composed of polypyrrole, polyaniline, or a dielectric material thereof. 3. The solid electrolyte according to claim 1, wherein the conductive polymer used for the second conductive polymer layer is mainly composed of polypyrrole, polyaniline, or a dielectric thereof synthesized by chemical polymerization. Capacitors. 4. The content of a fluorine elastomer as a binder used in the second conductive polymer layer is 10 to 85.
4. The solid electrolytic capacitor according to claim 1, which is in weight percent. 5. A step of forming an oxide film as a dielectric on the surface of a film-forming metal serving as an anode by anodic oxidation, and forming a first conductive film on the oxide film by electrolytic polymerization or chemical polymerization. Forming a second conductive polymer layer by applying a conductive polymer paste containing a conductive polymer and a fluorine-containing elastomer serving as a binder to form a second conductive polymer layer; A step of connecting an anode lead and a cathode lead to the first and second conductive polymer layers, respectively, and a step of sealing with an exterior material.