JP2000068159A - Solid electrolytic capacitor electrode foil therefor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a voltage- and heat-resistant film only in the cut end portion of an aluminum electrode foil for solid electrolytic capacitors, by forming a barrier film on the roughened surface of the aluminum electrode foil, cutting the obtained formation foil in a predetermined size subjecting it to a chemical processing, and subjecting further the cut formation foil to another formation processing to form in the cut end portion thereof a porous film having a specific thickness. SOLUTION: Subjecting an aluminum foil 1 to a formation processing after applying a roughening 2 to its surface by etching, a barrier film 3 is formed as a dielectric on its surface subjected to the roughening 2 and it is changed into a formation foil to cut the obtained formation foil in a predetermined size. Then, subjecting further this cut formation foil to another formation processing, there is formed in its cut end portion 5 a porous oxide film 11 having a thickness within the scope of 5-100 times as large as the thickness of its barrier film 3. Also, after forming the porous film 11 in the cut end portion 5, another barrier film (a cut end barrier film) is further formed in the base layer of the porous film 11. Then, this electrode foil 10 is applied to a solid electrolytic capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode foil for a solid electrolytic capacitor which is made of an aluminum conversion foil and whose cut-off portion has improved withstand voltage and heat resistance, a method for manufacturing the same, and a solid electrolytic capacitor using this electrode foil. Related to capacitors.

[0002]

2. Description of the Related Art A solid electrolytic capacitor uses an electrode foil in which a dielectric layer made of an anodic oxide film is formed on the surface of an aluminum foil. Generally, this electrode foil is manufactured by immersing an aluminum foil in an acidic electrolyte, subjecting the surface to a chemical conversion treatment by an anodic oxidation method using the aluminum foil as an anode, and then cutting the aluminum foil into a predetermined size. In recent years, especially in the field of electronic equipment, the miniaturization of low-voltage electrolytic capacitors has progressed,
Since a high capacitance per area is required, when manufacturing the electrode foil for low voltage, conventionally, as shown in FIG. 3, in order to enlarge the effective surface area of the aluminum foil, for example, an electrolytic solution containing chlorine ions is used. , And a surface roughening process for forming a large number of pores 2 having a diameter of, for example, about 0.2 μm is performed on the surface thereof. A chemical conversion treatment for forming a thin, high-density and uniform barrier film (anodic oxide film) 3 of about 1 μm is performed. In the obtained chemical conversion foil, a large number of pores 2 are formed on both surfaces of a core portion 1 made of aluminum ingot, and the barrier film 3 is coated with a dielectric material on a surface having an effective area enlarged by the pores. It is formed as a layer.

[0003] The chemical conversion foil obtained here is then cut into a predetermined size required for each small-sized solid electrolytic capacitor for low voltage, and used as an electrode foil. At this time, the cut portion 5 of the electrode foil cannot be assembled into the solid electrolytic capacitor as it is because the aluminum base metal is exposed, and thus needs to be insulated. Insulation of the cut section 5 is usually performed by subjecting the cut chemical conversion foil to a chemical conversion treatment again (hereinafter referred to as “cut formation”) and forming a barrier film on the cut section 5.

[0004]

However, since the chemical conversion foil is cut by the shearing force of a knife edge, an aluminum base metal is exposed at the cut portion 5 to form a spire portion 6 which is spun. Is done. In this state, a cut film is formed and a barrier film is formed on the cut portion 5. When a voltage is applied, heat is locally generated from the spire shape due to current concentration, and the barrier film is broken by thermal stress.
There is a problem that the voltage resistance and heat resistance of the solid electrolytic capacitor are significantly reduced. When the dielectric layer in the cut portion 5 is strengthened, for example, when the same surface roughening treatment or cut formation under high voltage is performed as described above, the barrier film 3 already formed on the surface of the chemical conversion foil is destroyed. there's a possibility that.

Therefore, a method of covering and insulating the cut portion with a resin or the like without using an anodic oxide film (for example, Japanese Utility Model Publication No. 6-14)
No. 465) has been proposed, but in these methods, the resin layer goes around the surface of the electrode foil and reduces the capacitance as a capacitor, which is against the demand for miniaturization, and the process is difficult. The production cost increases because of the complexity. The present invention has been made in order to solve the above-mentioned problems, and therefore, an object of the present invention is to form a voltage-resistant and heat-resistant film only on a cut portion without reducing an effective area of an electrode foil. An object of the present invention is to provide a method of manufacturing an inexpensive electrode foil for a solid electrolytic capacitor, an electrode foil for a solid electrolytic capacitor manufactured by the manufacturing method, and a solid electrolytic capacitor using the electrode foil.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method of forming a surface of an aluminum foil by etching and roughening the surface, forming a dielectric layer on the roughened surface. The chemical conversion foil on which the film is formed is cut into a predetermined size, and the cut chemical conversion foil is subjected to a chemical conversion treatment, and a cut portion thereof is a porous oxide film having a thickness of 5 times or more the thickness of the barrier film. Provided is a method for manufacturing an electrode foil for a solid electrolytic capacitor that forms a porous film having a thickness of 100 times. In the above, it is preferable that after forming the porous film, a chemical conversion treatment is further performed to form a cut barrier film on the base layer of the porous film. The present invention also provides an electrode foil for a solid electrolytic capacitor manufactured by any of the above manufacturing methods, and a solid electrolytic capacitor manufactured using the electrode foil for a solid electrolytic capacitor. Hereinafter, the electrode foil for solid electrolytic capacitors is referred to as "electrode foil",
A solid electrolytic capacitor is called a “capacitor”.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to preferred embodiments. When manufacturing the present electrode foil, first, the aluminum foil is etched and roughened as in the conventional case. Thereafter, a chemical conversion treatment is performed, a barrier film is formed as a dielectric layer on the surface of the roughened aluminum foil to form a chemical conversion foil, and the obtained chemical conversion foil is cut into a predetermined size required as an electrode foil of a capacitor. .

[0008] Next, the cut chemical conversion foil is subjected to a chemical conversion treatment (cut formation), and the cut portion has a porous oxide film having a thickness of 5 to 100 times the thickness of the barrier film. A porous film formed inside is formed. More preferably, a porous film having a thickness in the range of 20 to 100 times the thickness of the barrier film is formed.

In the present invention, the cut chemical conversion foil is formed by immersing a cut chemical conversion foil in an electrolytic solution containing an acid such as phosphoric acid, oxalic acid, sulfuric acid or the like, and using the aluminum core as an anode for a constant current. Is applied.

As shown in FIG. 1, in the electrode foil 10 of the present invention obtained here, a large number of pores 2 are formed on the surface of a core portion 1 made of aluminum metal, and the effective area is formed by the pores. The barrier film 3 is formed as a dielectric layer on both enlarged surfaces. Then, an oxide film covering the surface where the aluminum base metal is exposed and a porous film 11 made of aluminum oxide having a hole in the center and grown in a columnar shape from the oxide film are formed on the cut portion 5,
The porous film 11 covers the cut portion 5 thickly.
The thickness tp of the porous film 11 is 5 to 100 times, preferably 20 to 1 times the thickness tb of the barrier film 3.
It is within the range of 00 times.

It has been found that by performing the above-mentioned cut chemical conversion treatment, a part of the spire portion 6 shown in FIG. 3 disappears from the cut portion 5 of the present electrode foil 10, and the spire shape of the cut portion is relaxed. . It is considered that this is because at the time of the cut formation in the present invention, at least a part of the spire portion is dissolved in the acidic electrolyte before the porous film 11 is formed on the cut portion 5.

The porous film 11 is formed by energization using the aluminum core 1 of the chemical conversion foil as an anode.
By properly selecting the energization conditions, the barrier film 3 formed on the effective surface of the chemical conversion foil can be selectively formed only on the exposed portion of the cut metal 5 without damaging the barrier film 3. Therefore, even if the porous film 11 is formed, the effective area of the present electrode foil 10 as a capacitor does not decrease and the insulating property does not decrease.

In the present electrode foil 10, the spire shape of the cut portion 5 is relaxed, and the porous film 11 formed on the cut portion 5 is sufficiently thicker than a normal barrier film and formed on these films. It has a buffering property for the solid electrolyte layer and the conductive layer to be formed. Therefore, the present electrode foil 1
A value of 0 is not only high in insulation properties but also high in resistance to mechanical stress and thermal stress, and can prevent deterioration of the withstand voltage and heat resistance of the capacitor caused by the cut portion 5.

In a further preferred embodiment of the present invention, as shown as an electrode foil 15 in FIG. 2, a porous film 11 is formed on the cut portion 5 and then subjected to a chemical conversion treatment to form a barrier film ( A cut barrier film 12 is formed. In this chemical conversion treatment, for example, the electrode foil 10 on which the porous film 11 is formed is immersed in an electrolytic solution containing an acid such as adipic acid, boric acid or phosphoric acid, and a constant current is applied using the aluminum core 1 as an anode. Can be performed. During this anodic oxidation, the electrolyte penetrates into the holes 13 in the column of the porous film 11 and forms a cut barrier film 12 in the base layer of the porous film 11. The formed cut barrier film 12 has substantially the same withstand voltage as the barrier film 3.

In the obtained electrode foil 15, the cut portion 5 is firstly covered with a high-density and uniform cut barrier film 12, and then the outside thereof is double-covered with a thick cushioning porous film 11. The protection of the film is enhanced, and both the voltage resistance and the heat resistance are significantly improved. The enhanced protection of this membrane
This is particularly important for a solid electrolytic capacitor that does not use an electrolytic solution, since self-repair of the barrier film cannot be expected very much.

In the capacitor manufactured using the present electrode foil 10 or the present electrode foil 15, the spire shape of the cut portion 5 is relaxed only by repeating the anodic oxidation, which is a simple manufacturing process. A high density, uniform and high strength cut barrier coating 12 is formed on the high porous coating 11 and more preferably on its base layer. As a result, the present capacitor can be manufactured at low cost, and is excellent in voltage resistance, heat resistance and impact resistance, and can meet the demand for miniaturization because the capacitance is not reduced.

Although the electrode foil of the present invention can be applied to a solid electrolytic capacitor, a solid electrolyte can be formed by a known method. Preferably, a conductive polymer is suitable, and a polymerization method such as a chemical polymerization method or an electrolytic polymerization method can be used. More preferably, in a chemical polymerization method, resistance to thermal stress and mechanical stress when a polymer is formed by immersing the polymer in a monomer solution or an oxidizing agent solution is increased.

The dopant may be any compound as long as it has a doping ability, and examples thereof include organic sulfonic acids, inorganic sulfonic acids, organic carboxylic acids, and salts thereof. As a compound that can bring out particularly excellent capacitor performance, a compound having at least one sulfonic acid group and a quinone structure in a molecule, a heterocyclic sulfonic acid, an anthracene monosulfonic acid, and a salt thereof may be used.

Hereinafter, the present invention will be described in more detail. When manufacturing the present electrode foil, first, the aluminum foil is roughened. This method of surface roughening is known, and particularly for an electrode foil used for a small-sized low-voltage solid electrolytic capacitor, for example, a roll of aluminum foil having a width of 500 mm and a thickness of 100 μm is formed by using a chlorine ion such as hydrochloric acid or aluminum chloride. AC etching in an electrolytic solution containing Thereby, for example, pores having a depth of about 35 μm and an average diameter of about 0.2 μm are formed on both surfaces of the foil, whereby the effective area of the foil is enlarged about 100 times.

Next, the roughened aluminum foil is subjected to a chemical conversion treatment using a relatively mild acidic electrolytic solution such as adipic acid, boric acid, phosphoric acid or the like according to a conventional method, so that the enlarged surface is formed. For example, a barrier film 2 having a thickness of about 0.03 μm
To form The obtained chemical conversion foil is cut into a predetermined size as an electrode foil.

Next, the cut chemical conversion foil is subjected to a cut chemical conversion treatment. In the present invention, the porous film 11 is formed on the surface where the aluminum base metal is exposed such that the thickness is within a range of 5 to 100 times, preferably 20 to 100 times the barrier film 3 on the exposed surface of the aluminum metal. Perform under the conditions that The formation conditions for forming the porous film 11 are not particularly limited. For example, an electrolytic solution containing at least one of phosphoric acid, oxalic acid, and sulfuric acid is used, and the concentration of the electrolytic solution is 0.1% by weight or more. for 30 wt%, temperature of 0 ° C. to 80 ° C., a current density of ^{0.1mA / cm 2 ~1000mA / cm 2} , the constant current conversion core portion 1 of the foil in the chemical conversion time is within hundredths conditions as the anode . More preferably, the electrolyte concentration is 1
% To 20 wt%, temperature of 20 ° C. to 50 ° C., a current density is ^{1mA / cm 2 ~400mA / cm 2} , the chemical conversion time 60
Select conditions within the range of minutes. Thereby, the porous film 11 having a thickness of about 0.5 μm to several μm is formed.

Although the above-mentioned chemical conversion conditions are suitable for an industrial method, various conditions such as the type of the electrolytic solution, the electrolytic solution concentration, the temperature, the current density, the chemical conversion time and the like have already been formed on the surface of the chemical conversion foil. The barrier film 3 can be arbitrarily selected as long as the barrier film 3 is not destroyed or deteriorated.

The thickness of the porous film 11 to be formed is in the range of 5 to 100 times the thickness of the barrier film 3 formed on the surface of the chemical conversion foil. If the thickness is less than 5 times, the effect of forming a porous film cannot be expected. When the film thickness exceeds 100 times, the effect is not further improved, and conversely, it is difficult to set conditions for forming a thick film without destroying or deteriorating the barrier film of the chemical conversion foil, so that it is industrially necessary. Disadvantageous. In particular, when the thickness of the porous film 11 is selected to be in the range of 20 to 100 times the barrier film 3, both the withstand voltage and the heat resistance of the obtained electrode foil are significantly improved.

The porous film has been conventionally used in the past for the purpose of forming a high-pressure resistant barrier film on the effective surface of an aluminum foil particularly in an aluminum electrolytic capacitor for medium to high pressures (for example, JP-A-1-18491).
No. 2, Japanese Patent Publication No. 3-65010, etc.). However, all of these are electrolytic solution type capacitors, and most of the pores 13 (FIG. 2) of the formed porous film are filled with oxide and do not exist as a porous film. In this regard, the electrode foil of the present invention, in which the porous film is present as it is and has a buffering effect, is significantly different from the conventional one.

According to the invention of claim 2 of the present invention, the cut portion 5 after the formation of the porous film 11 is further subjected to a chemical conversion treatment to form a base layer of the porous film with the cut barrier film 1.
Form 2 The conditions for this chemical conversion treatment are not particularly limited, but for example, an electrolytic solution containing at least one of adipic acid, boric acid, phosphoric acid and the like is used, and the concentration of the electrolytic solution is 0.05% by weight to 20% by weight. , the temperature is 0 ° C. to 90 ° C., a current density makes the constant current conversion ^{0.1mA / cm 2 ~2000mA / cm 2} , the core 1 of the foil under the conditions of within 60 minutes Chemical time as an anode. More preferably the electrolyte solution concentration is 0.1% by weight to 15% by weight, temperature is 20 ° C. to 70 ° C., conditions within a current density of ^{1mA / cm 2 ~1200mA / cm 2} , the chemical conversion time is within 30 minutes Is selected.

The above-mentioned chemical conversion conditions are suitable for an industrial method, but the point is that the barrier film 12 having a withstand voltage equal to or higher than that of the barrier film 3 formed on the effective surface of the electrode foil is formed in the cut portion 5. Therefore, various conditions such as the type of the electrolytic solution, the concentration of the electrolytic solution, the temperature, the current density, and the formation time do not destroy or deteriorate the barrier film 3 already formed on the surface of the formation foil. As long as it can be selected arbitrarily.

Before or after any of the above chemical conversion treatments, if necessary, for example, a phosphoric acid immersion treatment for improving water resistance, a heat treatment for strengthening the film, or a immersion treatment in boiling water can be performed. In addition, these ancillary treatments and any of the above barrier film conversion treatments, porous film conversion treatments,
Each of them can be repeated alone or in combination. Although the above description has been directed to a low-voltage solid electrolytic capacitor, it goes without saying that the present invention can also be applied to a medium to high-voltage solid electrolytic capacitor.

[0028]

(Example 1) An aluminum foil roughened by AC etching was placed in an aqueous solution of ammonium adipate.
A chemical conversion treatment was performed at a voltage of 32 V, and the resulting chemical conversion foil for a low-voltage capacitor was cut into a size of 3 × 7 mm. One short side of this chemical conversion foil piece was welded to an electrode bar, and the entire periphery of the foil at a distance of 5 mm from the opposite end of the weld was masked with an insulating resin to a width of 0.6 mm. Then, the three sides under the mask were subjected to a chemical conversion treatment under the following conditions to form a porous film. Electrolyte solution; 7.5% by weight oxalic acid aqueous solution Temperature; 35 ° C. Voltage; 32 V Current density; Current density 180 mA / cm ² Formation time: 13 minutes

Next, after a heat treatment at 350 ° C. for 30 minutes, a chemical conversion treatment was carried out under the following conditions to form a cut barrier film on the base layer of the porous film. Electrolyte solution; adipic acid 10% by weight aqueous solution temperature; 45 ° C. voltage; 32 V current density; current density 180 mA / cm ² formation time; 10 minutes

After washing with water and drying, the surface of the obtained electrode foil is
After immersion in a 1 mol / l solution of 3,4-ethylenedioxythiophene in isopropyl alcohol, the mixture is allowed to stand for 2 minutes, and then oxidized (ammonium persulfate; 1.8 mol / l).
1) and a dopant (sodium 4-morpholinepropanesulfonate; 0.06 mol / l) in a mixed aqueous solution and left at 45 ° C. for 5 minutes. This step was repeated 25 times and washed with water to form a conductive polymer layer, on which a carbon paste and a silver paste were sequentially laminated to form a conductive layer. Next, this foil piece is separated from the electrode bar, and four sheets are laminated on the silver paste application part to form a cathode part, which is adhered to a lead frame, and the opposite side where a conductive polymer is not formed is welded to a lead frame. The anode was used. Then, the entire capacitor element was sealed with an epoxy resin and aged at 105 ° C. and 20 V for 3 hours to manufacture a capacitor.

(Example 2) Instead of the chemical conversion time of 13 minutes in the porous film chemical conversion treatment of Example 1, the chemical conversion time was set to 1
A capacitor of Example 2 was manufactured in the same manner as in Example 1 except that the time was 0 minutes.

(Example 3) Instead of the chemical conversion time of 13 minutes in the porous film chemical conversion treatment of Example 1, the chemical conversion time was 7
A capacitor of Example 3 was manufactured in the same manner as in Example 1 except that the amount was changed.

(Example 4) Instead of the chemical conversion time of 13 minutes in the porous film chemical conversion treatment of Example 1, the chemical conversion time was set to 4
A capacitor of Example 4 was manufactured in the same manner as Example 1 except that the amount was changed.

(Example 5) Instead of the chemical conversion time of 13 minutes in the porous film chemical conversion treatment of Example 1, the chemical conversion time was changed to 2
A capacitor of Example 5 was manufactured in the same manner as Example 1 except that the amount was changed.

EXAMPLE 6 An aluminum foil roughened by AC etching was subjected to a chemical conversion treatment in an aqueous solution of ammonium adipate at a voltage of 23 V, and the chemical conversion treatment for the porous film was performed except that the chemical conversion time was 9 minutes. A capacitor of Example 6 was manufactured in the same manner as in Example 1.

Example 7 A capacitor of Example 7 was manufactured in the same manner as in Example 6, except that the chemical conversion time in the porous film chemical conversion treatment of Example 6 was changed to 7 minutes instead of 9 minutes. .

Example 8 The capacitor of Example 8 was manufactured in the same manner as in Example 6, except that the chemical conversion time in the porous film chemical conversion treatment of Example 6 was changed to 4 minutes instead of 9 minutes. .

(Example 9) The capacitor of Example 9 was manufactured in the same manner as in Example 6, except that the chemical conversion time in the porous film chemical conversion treatment of Example 6 was changed to 2 minutes instead of 9 minutes. .

(Example 10) Instead of the chemical conversion time of 9 minutes in the porous film chemical conversion treatment of Example 6, the chemical conversion time was set to 1
A capacitor of Example 10 was manufactured in the same manner as Example 6 except that the amount was changed.

Example 11 A capacitor of Example 11 was prepared in the same manner as in Example 1 except that sodium anthraquinone-2-sulfonate was used instead of sodium 4-morpholinepropanesulfonate in the dopant of Example 1. Was manufactured.

(Example 12) N-methylpyrrole was used in place of 3,4-ethylenedioxythiophene in Example 1, and sodium 1-naphthalenesulfonate was used instead of sodium 4-morpholinepropanesulfonate in the dopant. Example 12 A capacitor of Example 12 was manufactured in the same manner as Example 1 except for using.

Example 13 Isothianaphthene was used in place of 3,4-ethylenedioxythiophene of Example 1, and an oxidizing agent (ammonium persulfate; 1.8 mol /
l) and an aqueous solution of a dopant (sodium 4-morpholinepropanesulfonate; 0.06 mol / l) instead of an aqueous solution of an oxidizing agent (2,3-dichloro-5,6-dicyanobenzoquinone; 1.8 mol / l) Solution and dopant (sodium anthracene-1-sulfonate;
A capacitor of Example 13 was produced in the same manner as in Example 1, except that a mixture of aqueous solutions of 0.06 mol / l) was used.

Example 14 An aluminum foil roughened by AC etching was subjected to a chemical conversion treatment in an aqueous solution of ammonium adipate at a voltage of 23 V, and the chemical conversion treatment for the porous film was performed except that the chemical conversion time was 9 minutes. The capacitor of Example 14 was manufactured in the same manner as in Example 11.

Example 15 An aluminum foil roughened by AC etching was subjected to a chemical conversion treatment in an aqueous solution of ammonium adipate at a voltage of 23 V, and the chemical conversion treatment for the porous film was performed except that the chemical conversion time was 9 minutes. The capacitor of Example 15 was manufactured in the same manner as in Example 12.

Example 16 An aluminum foil roughened by AC etching was subjected to a chemical conversion treatment in an aqueous solution of ammonium adipate at a voltage of 23 V and the chemical conversion treatment for the porous film was performed except that the chemical conversion time was 9 minutes. A capacitor of Example 16 was manufactured in the same manner as in Example 13.

Comparative Example 1 Comparative Example 1 was performed in the same manner as in Example 1 except that the porous film conversion treatment of Example 1 was omitted.
Was manufactured.

(Comparative Example 2) Instead of the formation time of 13 minutes in the porous film conversion treatment of Example 1, the formation time was changed to 2
A capacitor of Comparative Example 2 was manufactured in the same manner as in Example 1, except that the time was set to 0 second.

(Comparative Example 3) Instead of the formation time of 13 minutes in the porous film conversion treatment of Example 1, the formation time was changed to 2
A capacitor of Comparative Example 3 was manufactured in the same manner as in Example 1, except that the time was 0 minutes.

For each of the obtained capacitors, the thickness of the porous film (measured by scanning electron microscope observation), the ratio of the thickness of the porous film to the barrier film, the withstand voltage failure rate, and the reflow failure rate were measured. Here, the withstand voltage failure rate is as follows. After applying a voltage of 1.25 times the rated voltage to 85 capacitors at 85 ° C. and repeating a cycle of charging time 30 seconds and discharging time 30 seconds 1,000 times, 0.04 CV [CV is the nominal capacitance C (μ
F) and the rated voltage V (v)] or more, and the result was expressed as (defective number / test number). In addition, the reflow defect rate was such that after 30 capacitors were treated at 230 ° C. for 30 seconds using a reflow furnace, the leakage current was 0.1%.
Those having a value of 04 CV or more were regarded as defective, and represented by (number of defectives / number of tests). Table 1 shows the test results.

[0050]

[Table 1]

In Table 1, Examples 1 to 5, Example 11 to Example 13, and Comparative Examples 1 to 3 all have a barrier film formation voltage of 32 V on the foil surface and Examples 6 to Each of Example 10 and Examples 14 to 16 is a capacitor using a low-voltage conversion foil having a barrier film formation voltage of 23 V on the foil surface, and the film thickness ratio of the porous film is 5 times that of the barrier film. Examples 1 to 16 in the range of 100 times have better withstand voltage failure rate and reflow failure than Comparative Example 1 having no porous film and Comparative Example 2 having a film thickness magnification of less than 5 times. Rate. In particular, in Examples 1 to 4 and Examples 6 to 16 in which the film thickness magnification is in the range of 20 to 100 times, both the withstand voltage failure rate and the reflow failure rate are zero. A remarkable effect was observed as compared with Comparative Examples 1 and 2. In Comparative Example 3, the porous film conversion treatment was performed for a long time, and the film thickness magnification exceeded 100 times. Although there is no difference in the performance of Comparative Example 3 from that of the embodiment, the film forming conditions cannot be industrially employed because the cost is not suitable for the performance.

[0052]

According to the electrode foil for a solid electrolytic capacitor of the present invention, a porous film having a thickness in the range of 5 to 100 times the thickness of the barrier film formed on the surface of the electrode foil is provided at the cut portion. Is formed, a solid electrolytic capacitor with significantly improved withstand voltage and heat resistance of the electrode foil can be obtained by a simple and inexpensive manufacturing method without reducing the effective area of the electrode foil.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention.

FIG. 2 is a sectional view showing another embodiment of the present invention.

FIG. 3 is a sectional view showing a cut chemical conversion foil.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Core part 2 ... Pore 3 ... Barrier film 5 ... Cut part 6 ... Spire part 10 ... Electrode foil 11 ... Porous film 12 ... Cut-off barrier film 13 ... Hole (of porous film) 15 ... Electrode foil tb ... Barrier film thickness Sa tp… porous film thickness

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Sakai 6850 Omachi Omachi, Omachi City, Nagano Prefecture Showa Denko Corporation Omachi Plant (72) Inventor Hiroshi Onuma 5-1 Yawata Kaigandori, Ichihara City, Chiba Prefecture Showa Denko KK HD factory

Claims (4)

[Claims] An aluminum foil surface is etched and roughened to form a surface, and then subjected to a chemical conversion treatment. The formed foil having a barrier film formed as a dielectric layer on the roughened surface is cut into a predetermined size. Forming a porous oxide film having a thickness in the range of 5 to 100 times the thickness of the barrier film on the cut portion of the formed chemical conversion foil. Of manufacturing an electrode foil for a solid electrolytic capacitor. 2. The production of an electrode foil for a solid electrolytic capacitor according to claim 1, wherein after forming the porous film, a chemical conversion treatment is further performed to form a cut barrier film on a base layer of the porous film. Method. 3. An electrode foil for a solid electrolytic capacitor manufactured by the manufacturing method according to claim 1. 4. A solid electrolytic capacitor manufactured using the electrode foil for a solid electrolytic capacitor according to claim 3.