JP2003109866A - Solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor having low ESR characteristics. SOLUTION: The solid electrolytic capacitor in which a conductive polymer is formed in a capacitor element which winds an anodic electrode and a cathodic electrode via a separator. An anodic electrode foil or a cathodic foil has a depressed etching layer, and the resistivity of foil per unit area is 0.237 to 0.7 mΩ, a foil width is 1.5 to 4 mm or over, and a foil area is 150 mm<2> or over. Therefore the resistance of the electrode foil is reduced, the resistance of electrolyte between electrodes is reduced, and the contact resistance at a bonded portion of the electrode foil and electrode leading terminal is also reduced. The solid electrolytic capacitor provided in this manner has a low ESR characteristic.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solid electrolytic capacitor using a conductive polymer as an electrolyte.

[0002]

2. Description of the Related Art In recent years, electronic information devices have been digitized,
Further, the drive frequency of the microprocessor (MPU), which is the heart of these electronic information devices, is being increased. Along with this, the increase in power consumption has progressed, and the problem of reliability due to heat generation has become apparent. As a countermeasure, the drive voltage has been reduced. Here, a DC-DC converter called a voltage control module (VRM) is widely used as a circuit for supplying high-precision power to a microprocessor, and a series equivalent resistance ( Many capacitors with low ESR are used. As the capacitor having this low ESR characteristic, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has been put into practical use, and is widely used as a capacitor suitable for these applications.

However, the driving frequency of the microprocessor is remarkably increased, the power consumption is increased accordingly, and in order to cope with the increase in the power consumption, it is required to increase the power supplied from the capacitor to prevent the voltage drop. That is, it is necessary to be able to supply a large amount of electric power in a short time. Therefore, the solid electrolytic capacitor is required to have a large capacity, a small size, a low voltage, and an ESR characteristic lower than ever. To be done.

On the other hand, downsizing and high functionality of electronic information equipment,
In order to improve productivity, surface mounting of electronic parts has progressed, and the above solid electrolytic capacitor is also required to be of the surface mounting type.

The solid electrolytic capacitor will be described below. A valve metal foil such as aluminum, tantalum or niobium is etched to increase its surface area, and then an anode foil having an anodic oxide film formed thereon, aluminum, tantalum or niobium, etc. Etching is applied to the valve action metal foil of to form a cathode foil. Kraft paper, manila paper, glass separator or vinylon between the electrode foil, a separator such as non-woven fabric made of synthetic fiber such as polyester fiber is interposed, and the lead terminals are attached to arbitrary portions of the electrode foil. A wound capacitor element is formed. A solid electrolyte is formed on this capacitor element and stored in a metal case, and the metal case opening is sealed with a sealing resin such as epoxy resin, or a sealing rubber is inserted and sealed by caulking. is there.

The surface mount type solid electrolytic capacitor is formed by mounting the solid electrolytic capacitor prepared as described above on a pedestal. Since the surface mounting type solid electrolytic capacitor is required to be downsized, the foil width and foil length of the electrode foil should not be made as small as possible.

The solid electrolytic capacitor having the above-mentioned structure uses as the electrolyte a solid electrolyte having a low specific resistance of 10's Ω · cm or less as compared with a conventional electrolytic solution having a specific resistance of 100 Ω · cm. It is a capacitor with excellent ESR characteristics.

By the way, as the solid electrolyte, manganese dioxide having a specific resistance of 10 Ω · cm or less has been conventionally used, and thereafter, a solid using an organic semiconductor such as TCNQ complex or polypyrrole having a specific resistance of 10 Ω · cm or less. Electrolytic capacitors have been put to practical use, but the specific resistance is 0.1Ω.
-Solid electrolytic capacitors using thiophene dielectric polymers of cm or less are being put to practical use. The use of this thiophene dielectric polymer is suitable for reducing the ESR of a small surface mount solid electrolytic capacitor. However, as the drive frequency of MPU is further increased,
There is a demand for a capacitor having a smaller size, a larger capacity, and a lower ESR. According to the study by the inventors, the effect of reducing the ESR of the capacitor is not sufficient in such a solid electrolytic capacitor, although the specific resistance of the electrolyte is low.

[0009]

As described above, the ES of the capacitor cannot be improved by only improving the solid electrolyte by lowering the specific resistance.
There is a problem in that there is a limit in reducing R and it is difficult to further reduce ESR.

The present invention has been made to solve the above-mentioned problems, and provides a solid electrolytic capacitor using a conductive polymer having a low specific resistance, which realizes further low ESR. Is.

[0011]

In order to solve the above-mentioned problems, as a result of intensive studies by the inventors, in a solid electrolytic capacitor using an organic semiconductor having a low specific resistance, an electrode foil having a reduced etching layer is used. To optimize the resistance value per unit area of the electrode foil, that is, the resistance value between the end faces of the square-shaped electrode foil (hereinafter referred to as foil resistivity), and the foil width and foil area. It has been found that the ESR can be reduced.

That is, although the ESR of the capacitor can be reduced by using the conductive polymer as described above, there is a limit to the reduction of the electrolyte, and the level of the ESR reduced by the conductive polymer as described above. Then, it was found that the foil resistivity, foil width and foil area of the electrode foil contribute to the ESR of the capacitor. Therefore, by optimizing these values, the ESR of the capacitor can be significantly reduced. Then, in the present invention, by using the electrode foil having the reduced etching layer, the foil thickness is reduced, the foil length is increased, and the optimum foil area is obtained.

The present invention uses a conductive polymer having a specific resistance of 0.1 Ω · cm or less, and by using the following electrode foil, it is possible to maximize the low specific resistance characteristics of the conductive polymer. This is the realization of a solid electrolytic capacitor having a low ESR characteristic not found in other products. The electrode foil used in the present invention has a reduced etching layer and has a foil resistivity of 0.2.
7 to 0.7 mΩ, more preferably 0.34 to 0.55
It is mΩ. By using the electrode foil in this range, the resistance of the electrode foil is reduced and the ESR is reduced. If it is less than this range, the effect of reducing ESR is small, and if it exceeds this range, the reduction rate of ESR is lowered.

The foil width is 1.5 to 4 mm, preferably 2 to 3 mm. Below this range, even if the foil resistivity is reduced, the contribution of the resistance component of the electrolyte becomes large and the ESR is not reduced. If it exceeds this range, the reduction rate of ESR is lowered, and the height of the capacitor is increased to exceed the allowable range of the surface mount type.

The foil area must be 150 mm ² or more, preferably 200 mm ² or more. If it is less than this range, the area of the electrode foil and the electrolyte is small and the resistance value is not reduced, so that the ESR is not reduced. Since the solid electrolytic capacitor of the present invention uses the capacitor element formed by winding the electrode foil having the rolled down etching layer through the separator, the electrode foil having a long foil length can be used. This allows a sufficient foil area to be obtained and the ESR to be reduced.

As described above, the foil resistivity of the electrode foil is 0.27 to 0.7 mΩ, more preferably 0.34 to
Remaining core thickness is 40 to 100 μm for 0.55 mΩ
m, more preferably 50 to 80 μm electrode foil can be used.

The electrode foil for electrolytic capacitors of the present invention is prepared as follows. First, the surface of the aluminum foil is roughened in an etching solution containing an aqueous solution of hydrochloric acid or the like to form sponge-like etching pits. The etching foil thus formed is pressed to reduce the foil thickness, that is, a so-called reduction treatment is performed. This rolled foil is used as a cathode foil.

Then, as the anode foil, this rolled foil is further energized in a chemical conversion solution containing an aqueous solution of phosphoric acid or the like to form an oxide film on its surface to form an anode foil. Therefore, such an electrode foil is not etched in the aluminum part (hereinafter,
(Residual core) and an etched part, and in the case of an anode foil, it further comprises an oxide film part.
By setting it to be μm, more preferably 50 to 80 μm, the foil resistivity can be set to 0.27 to 0.7 mΩ, and more preferably 0.34 to 0.55 mΩ.

As the conductive polymer,
When the thiophene dielectric polymer shown by
Since it has a low specific resistance characteristic of Ω · cm or less, the ESR of the capacitor is reduced and the heat resistance characteristic of the capacitor is improved, which is preferable. Among them, 3,4 with good reactivity and good electrical properties
-Ethylenedioxythiophene is preferred.

[Chemical 1] Here, X is O or S, when X is O, A is alkylene or polyoxyalkylene, and when at least one of X is S, A is alkylene, polyoxyalkylene,
A substituted alkylene, a substituted polyoxyalkylene, where
The substituents are an alkyl group, an alkenyl group and an alkoxy group.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described. An aluminum foil is roughened by AC etching in an etching solution composed of an aqueous solution of hydrochloric acid or the like to form an etching foil, and then a reduction treatment is performed to form a reduction foil. Such reduction treatment is generally performed by rolling. That is, rolling is continuously performed while unwinding the coiled aluminum foil. Here, a treatment for improving etching characteristics such as surface layer removal, oxide film formation, and annealing may be performed before the etching treatment. Further, it is preferable to carry out usual post-treatments such as surface cleaning and drying after the etching treatment. The rolled foil thus formed is used as a cathode foil.

Here, the reduction rate (reduction rate) of the foil thickness is 3 to 6
0%, preferably 5-55%, below this range ESR
The effect of reduction is small, and if it exceeds this range, the capacitance decreases.

Further, in order to form a dielectric film on the surface of this rolled foil, it is subjected to chemical conversion in a chemical conversion solution composed of an aqueous solution of phosphoric acid or the like and used as an anode foil. In the present invention, the foil resistance per unit area of such an electrode foil is set to 0.
27 to 0.7 mΩ, more preferably 0.34 to 0.5
It is set to 5 mΩ.

Here, the thickness of the unetched portion of the aluminum foil, that is, the residual core portion, is set to 40 at the time of etching.
It is possible to obtain an electrode foil having the foil resistivity as described above by setting the thickness to -100 μm, and more preferably 50 to 80 μm.

Then, these electrode foils are cut to form electrode foils for electrolytic capacitors, and the foil width at this time is 1.5.
-4 mm, preferably 2-3 mm. Further, the foil area needs to be 150 mm ² or more, preferably 200 mm ² or more.

Further, it is preferable to form a chemical conversion coating film of 0.1 to 10 V, preferably 0.3 to 5 V on the cathode foil because the ESR is reduced and the high temperature life characteristics are improved.

Further, it is preferable to form a layer made of a metal compound or metal having a low oxidizing property such as titanium nitride or titanium on the surface of the cathode foil because the capacitance increases. Here, it is more preferable to form a chemical conversion film on the cathode foil and to form a layer made of the above-mentioned metal or metal compound having low oxidizing property on the chemical conversion film.

An anode lead terminal and a cathode lead terminal are attached to the above anode foil and cathode foil, and they are wound via a separator. After that, a voltage is applied in the chemical conversion liquid to repair the dielectric oxide film damaged in the previous steps. The effects of the present invention can be obtained by using the above-described anode foil of the present invention and the conventional cathode foil, the conventional anode foil and the cathode foil of the present invention, and both the anode foil and the cathode foil of the present invention can be obtained. The maximum effect can be obtained by using.

Here, as the separator, manila paper,
Kraft paper, glass separator, etc., or vinylon,
A nonwoven fabric made of synthetic fiber such as polyester, and a porous separator can be used.

When attaching the lead-out terminal to the electrode foil, the use of the electrode foil having an increased conductive portion according to the present invention lowers the contact resistance of the joint portion between the electrode foil and the lead-out terminal, which also contributes to the solid state. The effect of reducing the ESR of the electrolytic capacitor is increased.

Then, poly- (3,4-ethylenedioxythiophene) (PED), which is a polymer of 3,4-ethylenedioxythiophene (EDT), is used as a conductive polymer.
The case of using T) will be described. Capacitor element is EDT
The solid electrolyte layer made of PEDT is formed by immersing it in a mixed solution prepared by mixing an oxidizing agent and a predetermined solvent to cause a polymerization reaction of EDT in the capacitor element. Then, this capacitor element is inserted into a metal case, a sealing rubber is inserted into the opening end portion, and a caulking process is performed to seal the solid electrolytic capacitor.

As the EDT, an EDT monomer can be used, but the EDT and the volatile solvent are 1: 0.
It is also possible to use a monomer solution mixed in a volume ratio of ˜1: 3. As the volatile solvent, hydrocarbons such as pentane, ethers such as tetrahydrofuran, esters such as ethyl formate, ketones such as acetone, alcohols such as methanol, nitrogen compounds such as acetonitrile and the like can be used. However, among them, methanol, ethanol, acetone and the like are preferable. Also, as the oxidant,
Ferric p-toluenesulfonate dissolved in butanol,
Periodic acid or an aqueous solution of iodic acid can be used, and the concentration of the oxidizing agent in the solvent is preferably 40 to 55 wt%. If it is less than this range, the ESR increases, and if it exceeds this range, the capacitance decreases.

The mixing ratio of EDT and the oxidizing agent (excluding the solvent) is preferably in the range of 1: 0.9 to 1: 2.2 by weight, and 1: 1.3 to 1: 2.0. Is more preferable.
ESR rises outside this range. The reason is considered to be as follows. That is, when the amount of the oxidant with respect to the monomer is too large, the amount of the impregnated monomer relatively decreases, so that 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 oxidizing agent necessary for polymerizing the monomer will be insufficient,
The amount of PEDT formed decreases and the ESR increases.

In addition to the EDT described here, a polymerizable monomer can be used. As the polymerizable monomer,
Aniline, pyrrole, furan, acetylene or their derivatives, which are oxidatively polymerized by a predetermined oxidizing agent,
Any material can be applied as long as it forms a conductive polymer.

The solid electrolytic capacitor of the present invention as described above is a solid electrolytic capacitor using a conductive polymer having a specific resistance of 0.1 Ω · cm or less, and the ESR of the capacitor is reduced to 80 to 60% of the conventional value. It is possible to obtain an ESR of 6 mΩ or less, which has never been achieved.
On the other hand, the ESR of the electrolytic capacitor using the electrolytic solution having a specific resistance of several tens of Ω · cm and the solid electrolytic capacitor using the solid electrolyte of several Ω · cm is 30.
It is very high, about 50 mΩ, and even when the electrode foil of the present invention is used, it is reduced to only about 90% at maximum, and it is not possible to obtain the effect of greatly reducing ESR as in the present invention.

Further, since the solid electrolytic capacitor of the present invention can reduce the ESR even in the range where the foil width is small, it is difficult to reduce the ESR in the surface mounting type solid electrolytic capacitor which is difficult to reduce because of the small foil width. The characteristics can be realized.

[0036]

EXAMPLES Specific examples of the solid electrolytic capacitor of the present invention will be described below. PED as a conductive polymer
An example using T will be described. While coiling the coiled aluminum foil with a purity of 99.9%,
Etching was performed with a 15 Hz AC rectangular wave in a 10 wt% hydrochloric acid bath. This etching foil was rolled at a rolling speed of 10 m / min and a rolling mill temperature of room temperature to produce a rolled foil. And 0.4V to this rolled foil
Was formed, and a layer made of titanium nitride was formed on the chemical conversion film to form a cathode foil, while a 8 V conversion film was formed to form an anode foil. A separator made of non-woven vinylon fiber is interposed between the anode foil and the cathode foil, and an anode lead terminal and a cathode lead terminal are attached and wound at arbitrary positions. After that, a voltage is applied in the chemical conversion liquid to restore the chemical conversion of the dielectric oxide film damaged by the winding.

Then, the solid electrolyte was formed as follows. A mixed solution was prepared by injecting EDT and 45% ferric paratoluenesulfonate butanol solution into a cup-shaped container at a weight ratio of 1: 0.8.
Then, the capacitor element was immersed in the mixed solution for 10 seconds. And it heated at 120 degreeC for 1 hour, the polymerization reaction of PEDT was generated within the capacitor element, and the solid electrolyte layer was formed. Then, this capacitor element was inserted into a bottomed cylindrical aluminum case, the opening was rubber-sealed by drawing, and aging was performed to prepare a solid electrolytic capacitor.

Then, the foil resistivity, foil width, foil area, and residual core thickness of the anode foil and cathode foil used in Examples 1 to 3 and Comparative Examples 1 to 4 of the solid electrolytic capacitors thus formed, respectively, The ESR of the solid electrolytic capacitor (1) is shown in (Table 1). The foil thicknesses of Examples 1 to 3 were 95 μm and 90 μm, respectively.
m and 120 μm. The reduction ratio of the used reduction foil was 25 to 40%.

[0039]

[Table 1]

As is clear from (Table 1), the solid electrolytic capacitors of Examples 1 to 3 of the present invention have a low ESR of 15 mΩ or less, which shows the effect of the present invention.
On the other hand, Comparative Example 1 having a foil resistivity of 0.7 mΩ or more has a high value of 19 mΩ even though the foil area is 180 mm ² which is larger than that of Example 3. In Comparative Example 2 in which the foil width is 1.5 mm or less, the foil resistivity is 0.32 mΩ.
And lower than Examples 1 to 3, and the foil area is 360 mm.
Despite being larger than ² and Examples 1 and 3, 19 mΩ
And shows a high value. Further, in Comparative Example 3 in which the foil area is 150 mm ² or less, the foil resistivity is 0.31 mΩ, which is smaller than those in Examples 1 to 3, but the ESR is as large as 19 mΩ.

Further, as Comparative Examples 4 and 5, capacitor elements were formed in the same manner as in Example 1, and TCNQ complex and manganese dioxide were respectively formed as solid electrolytes on the capacitor elements. The obtained ESR is 17 mΩ,
The value was as high as 61 mΩ, and it was found that the effect of the present invention could not be obtained even if the electrode foil of the present invention was used, unless a conductive polymer having low specific resistance characteristics was used as an electrolyte.

[0042]

As described above, according to the present invention, there is provided a solid electrolytic capacitor in which a conductive polymer is formed in a capacitor element formed by winding an anode foil and a cathode foil with a separator interposed therebetween. Alternatively, the cathode foil has a rolled down etching layer and the foil resistivity per unit area is 0.27.
~ 0.7 mΩ, foil width 1.5 ~ 4 mm, foil area 150
By setting it to be ² mm ² or more, it is possible to provide a solid electrolytic capacitor having a low ESR characteristic which has not been obtained conventionally.

Continued front page    (72) Inventor Akio Ishii             One day at 1-167 Higashi Ome, Ome City, Tokyo             Inside this Chemi-Con Corporation (72) Inventor Ichidai Saegusa             One day at 1-167 Higashi Ome, Ome City, Tokyo             Inside this Chemi-Con Corporation F term (reference) 4J032 BA04 BB01 BC12

Claims (3)

[Claims] 1. A solid electrolytic capacitor in which a conductive polymer is formed in a capacitor element formed by winding an anode foil and a cathode foil with a separator interposed therebetween, the anode foil or the cathode foil having an etching layer which is pressed down. And the foil resistance per unit area is 0.27 to 0.7 mΩ, the foil width is 1.5 to 4 mm,
A solid electrolytic capacitor having a foil area of 150 mm ² or more. 2. The residual core thickness of the anode foil or cathode foil is 40.
The solid electrolytic capacitor according to claim 1, wherein the solid electrolytic capacitor has a thickness of about 100 μm. 3. The solid electrolytic capacitor according to claim 1, wherein polyethylenedioxythiophene is used as the conductive polymer.