JP2002289474A - Manufacturing method for solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid electrolytic capacitor wherein leakage current characteristics and frequency characteristics are improved. SOLUTION: In the method for manufacturing the solid electrolytic capacitor 14, a dielectric film 4 is formed on a sintered body 1 made of impalpable powder of valve action metal and then a conductive layer made of conductive polythiophene or a derivative thereof is formed on the surface of the dielectric film 4. The manufacturing method for the solid electrolytic capacitor 14 uses a process in which after the formation of the dielectric film 4, a solution containing thiophene or a derivative thereof, oxidizer, and dopant is applied to the sintered body 1 to form a first conductive layer 5 made of the conductive polythiophene or the derivative thereof, and a subsequent process in which the solution containing the thiophene or the derivative thereof and the dopant and the solution containing the oxidizer and the dopant are alternately applied to the surface of the first conductive layer 5 to form a second conductive layer 6 made of the conductive polythiophene or the derivative thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a solid electrolytic capacitor, and more particularly, to a method for manufacturing a solid electrolytic capacitor using a conductive layer made of conductive pothiophene or a derivative thereof as a cathode.

[0002]

2. Description of the Related Art In a solid electrolytic capacitor, for example, a sintered body made of a fine powder of a valve action metal such as tantalum or aluminum is anodized to form a dielectric film, and then a dielectric film is formed on the surface of the dielectric film. There is an element having a structure in which a manganese dioxide layer is laminated, and further, a carbon layer and a silver layer are sequentially laminated.

Incidentally, the manganese dioxide layer has a function of directly contacting the dielectric film and acting as a cathode, and electrically connecting the dielectric film to an external cathode portion via the carbon layer and the silver layer. ing. It also has a function to cut off leakage current caused by defects in the dielectric film.

However, since manganese dioxide has a relatively low conductivity, the impedance of the capacitor in a high-frequency region increases.

Conventionally, in order to reduce high-frequency impedance, for example, instead of manganese dioxide, a compound having an electron-donating property or an electron-withdrawing property to an electron conjugated polymer such as polyaniline, polypyrrole, polythiophene or a derivative thereof ( Hereinafter, a conductive polymer to which conductivity is imparted by adding a dopant may be used.

That is, conductive polymers such as conductive polythiophene and derivatives thereof have higher conductivity than manganese dioxide. Therefore, the high-frequency impedance of the capacitor can be reduced. If there is a break in the dielectric film, a leakage current flows. Joule heat is generated due to the leakage current. The Joule heat causes the dopant to be released from the conductive polythiophene or its derivative, the conductive polythiophene or its derivative to be cross-linked, or the conductive polythiophene or its derivative or the dopant to be decomposed, and the conductive polythiophene to be decomposed. And its derivatives lose conductivity. As a result, the leakage current is suppressed. In particular, conductive polythiophene and its dielectric have an advantage of being superior in heat resistance and moisture resistance as compared with other conductive polymers.

Conventionally, in order to form a conductive layer made of conductive polythiophene or its dielectric on the surface of a dielectric film, means such as electrolytic polymerization and chemical oxidation polymerization have been used. However, in the former electrolytic polymerization method, since the dielectric film is insulative, it is impossible to carry out the polymerization reaction by energizing the dielectric film as it is. First, manganese dioxide is laminated on the surface of the dielectric film, or chemical oxidation is performed. It is necessary to laminate conductive polymers by a polymerization method or the like to act as an electrode,
The process becomes very complicated. On the other hand, the latter chemical oxidative polymerization method has a relatively simple process and has been widely studied. The chemical oxidation polymerization method includes the following two methods. That is, one method is to immerse the element after forming the dielectric film in a solution in which thiophene or a derivative thereof, an oxidizing agent and dopan are dissolved, impregnate the liquid, and perform a chemical oxidative polymerization reaction to conduct the conductive polythiophene or the conductive polythiophene. This is a method of forming a derivative. Another method is to alternately immerse the element after forming the dielectric film in two kinds of solutions, a solution in which thiophene or a derivative thereof and a dopant are dissolved, and a solution in which an oxidizing agent and a dopant are dissolved. Thiophene and its derivatives are chemically oxidized and polymerized to form conductive polythiophene and its derivatives.

[0008]

However, in the former chemical oxidation polymerization method, the liquid is easily impregnated into the sintered body and easily adhered to the surface of the dielectric film, but the concentration of thiophene or its derivative is increased. Therefore, it is difficult to form a thick conductive layer made of conductive polythiophene or a derivative thereof. Further, since a brittle polymer in the form of a film is generated, the polymer is easily peeled off by a physical force. For this reason, there is a disadvantage that the leakage current characteristics, the frequency characteristics, and the like are easily deteriorated due to the shrinkage force of the resin at the time of forming the outer package and the heat at the time of heat treatment after forming the outer package.

In the latter chemical oxidation polymerization method, there is an advantage that a conductive layer made of conductive polythiophene or a derivative thereof is easily thickened. However, two kinds of solutions used for this treatment usually have a viscosity and a dielectric constant. Each has different wettability to the film. Therefore, it is difficult to uniformly laminate a conductive layer made of conductive polythiophene or a derivative thereof on the surface of the dielectric film, and a portion where the conductive polythiophene or a derivative thereof is not laminated tends to be formed, and the thickness thereof is also apt to vary. When heated during the manufacturing process or after the manufacturing process, a dielectric film or a conductive layer made of conductive thiophene or a derivative thereof,
The exterior contracts or expands to generate physical stress.
As a result, in a portion where the conductive thiophene or its derivative is not laminated or a portion where the thickness is small, the dielectric film is easily subjected to stress and easily deteriorates. Further, the deterioration of the dielectric film deteriorates the leakage current characteristics of the capacitor and causes a problem that the high-frequency characteristics cannot be sufficiently improved.

An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor which can improve the above-mentioned drawbacks and improve the leakage current and the frequency characteristics.

[0011]

According to a first aspect of the present invention, a dielectric film is formed on a sintered body made of a fine powder of a valve action metal, and then the dielectric film is formed. In a method for manufacturing a solid electrolytic capacitor in which a conductive layer made of conductive polythiophene or a derivative thereof is laminated on the surface,
Adhering a solution containing thiophene or a derivative thereof, an oxidizing agent, and a dopant to the sintered body after forming the dielectric film to form a first conductive layer made of conductive polythiophene or a derivative thereof; A solution containing thiophene or a derivative thereof and a dopant and a solution containing an oxidizing agent and a dopant are alternately attached to the surface of the first conductive layer to form a second conductive layer made of conductive polythiophene or a derivative thereof. Process.

Further, according to a second aspect of the present invention, after a dielectric film is formed on a sintered body made of a fine powder of valve metal, a conductive layer made of conductive polythiophene or a derivative thereof is formed on the surface of the dielectric film. In a method for manufacturing a solid electrolytic capacitor to be laminated, a solution containing thiophene or a derivative thereof, an oxidizing agent, and a dopant is attached to a sintered body after forming a dielectric film to form a first conductive polythiophene or a derivative thereof.
And a solution containing two types selected from thiophene, an oxidizing agent and a dopant, and a solution containing the remaining one type are alternately formed on the surface of the first conductive layer after this step. And laminating a second conductive layer made of conductive pothiophene or a derivative thereof.

In the present invention, first, a solution containing thiophene or a derivative thereof, an oxidizing agent, and a dopant is used.
A first conductive layer made of conductive polythiophene or a derivative thereof, which is relatively uniformly laminated on the surface of the dielectric film, can be formed. Next, a solution containing thiophene or a derivative thereof and a dopant and a solution containing an oxidizing agent and a dopant are used alternately, or a solution containing two types of thiophene or a derivative thereof, an oxidizing agent and a dopant, and Of 1
Since the solutions containing the types are alternately used, the second conductive layer made of conductive polythiophene having a relatively large thickness or a derivative thereof can be stacked on the surface of the first conductive layer. That is, a first conductive layer capable of relatively uniformly laminating a conductive layer laminated on the surface of a dielectric film, and a second conductive layer having a relatively large thickness laminated on the surface of the first conductive layer. And a conductive layer. Therefore, it is possible to prevent the leakage current characteristics and the frequency characteristics from being deteriorated by the stress caused by the contraction or expansion of the exterior or the like during the heat treatment, and to improve these characteristics.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First, a metal such as tantalum, aluminum, niobium, or titanium is used as the valve action metal. Then, a cylindrical or rectangular parallelepiped sintered body is formed using the fine powder of the valve metal such as tantalum.

For example, when a fine powder of tantalum is used, a binder obtained by dissolving an acrylic resin or the like in an organic solvent is added to the fine powder of tantalum, mixed, and then heated to volatilize and remove the organic solvent. To be fine powder. Then, this fine powder is compression-molded into a cylindrical shape or the like by a press or the like. At this time, one end of an anode lead wire made of a valve metal such as tantalum is inserted into the fine powder, and the other end is drawn out. After compression molding, sintering is performed at a high temperature in an atmosphere such as a vacuum to form a sintered body 1 as shown in FIG. Thereafter, a disk-shaped insulating plate 3 made of Teflon (registered trademark), silicone rubber, silicone resin, or the like is arranged at the root of the anode lead wire 2.

Next, this sintered body 1 is immersed in a chemical solution such as nitric acid or phosphoric acid, and anodized by applying a predetermined voltage to form a dielectric film 4 as shown in FIG. Form.

After the dielectric film 4 is formed, a solution containing thiophene or a derivative thereof, an oxidizing agent, and a dopant is attached to the sintered body 1 to form a first conductive layer. To adhere the solution, the sintered body 1 is immersed in the solution or sprayed with the solution. Then, in an atmosphere containing oxygen such as air,
The polymerization reaction is completed by being left in either one of an atmosphere of an inert gas such as nitrogen or argon. The process from the application of this solution to the sintered body 1 to the completion of the polymerization reaction is repeated a predetermined number of times, and the conductive film having a predetermined thickness is formed on the surface of the dielectric film 4 as shown in FIG. A first conductive layer 5 made of conductive polythiophene or a derivative thereof is laminated.

The thiophene derivative is represented by the formula

Embedded image 3,4-ethylenedioxythiophene represented by

Embedded image Isothianaphthene represented by the formula

Embedded image3-alkylthiophene represented by (R: alkyl group)
(Alkyl group is CH₃ , C₂H₅ , C₃H ₇ Etc.)
Which is used.

As the oxidizing agent, potassium dichromate, sodium dichromate, ammonium peroxodisulfate, hydrogen peroxide, ferric chloride, potassium permanganate, manganese dioxide, lead dioxide and the like can be used.
Particularly, ferric chloride is preferable.

As the dopant, halides, halogens, sulfonic acids, alkali metals and the like can be used, and hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and sulfonic acid are particularly preferable. The ferric sulfonic acid salt can be used as a dopant and an oxidizing agent.

Further, as a solvent for dissolving thiophene or its derivative, an oxidizing agent and a dopant, an alcohol-based, glycol-based, ether-based or ketone-based solvent or a mixture thereof with water is used. Alcohol solvents include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,
Use t-butyl alcohol or the like. As the glycol solvent, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, or the like is used. Ether solvents include methyl cellosolve and ethyl cellosolve, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol. Diethyl ether, diethylene glycol ethyl methyl ether, diglyme, triglyme, tetraethylene glycol dimethyl ether, tetrahydrofuran, dioxane and the like are used. Acetone or the like is used as the ketone solvent.

After forming the first conductive layer 5 made of conductive polythiophene or its derivative, as one method, a solution containing thiophene or its derivative and a dopant,
A solution containing an oxidizing agent and a dopant is alternately attached to the sintered body 1. Either may be attached first. Also,
Alternatively, thiophene or its derivatives, oxidants,
A solution containing two kinds of substances selected from dopants and a solution containing the remaining one kind of substance are alternately attached to the sintered body 1. Thiophene or its derivative, oxidizing agent,
As a combination of two kinds of substances selected from dopants, thiophene or a derivative thereof and an oxidizing agent, thiophene or a derivative thereof and a dopant, and an oxidizing agent and a dopant are used.
There are types. Then, in order to attach each solution, the sintered body 1 is immersed in the solution or sprayed with the solution as in the case of forming the first conductive layer 5. After the application of the solution, the sintered body 1 is allowed to stand in either an atmosphere containing oxygen such as air or an inert gas atmosphere to complete the polymerization reaction. The process from the application of the solution to the completion of the polymerization reaction is repeated a predetermined number of times.
As shown in (2), a second conductive layer 6 made of conductive polythiophene or a derivative thereof is laminated on the surface of the first conductive layer 5. After laminating the second conductive layer 6, a heat treatment is performed if necessary.

The solvent used for each solution may be the same as the solvent used for dissolving all of thiophene or its derivative, oxidizing agent and dopant.

After forming the second conductive layer 6 made of conductive polythiophene or a derivative thereof, a carbon paste is applied to the surface of the second conductive layer 6, and then a carbon paste is applied.
As shown in (e), a carbon layer 7 is formed. afterwards,
Silver paste is applied to the surface of the carbon layer 7 and FIG.
The silver layer 8 is formed as shown in FIG.

After the silver layer 8 is formed, the sintered body is connected to a lead frame by a conductive paste 9 or welding at the silver layer and the anode lead wire, respectively, and the resin is coated by a resin molding method, The cathode terminal is connected to the layer 8, the anode terminal is connected to the anode lead wire, and the resin is coated by a resin dipping method, as shown in FIG.
0 is formed.

After the exterior 10 is formed, the cathode terminal 11 and the anode terminal 12 are formed by forming or the like to form a solid electrolytic capacitor 13.
And

[0027]

Embodiments of the present invention will be described below. Example 1 A method for manufacturing a tantalum chip type solid electrolytic capacitor rated at 10 V and 100 μF will be described. Tantalum fine powder (CV value 30000) was used as a valve metal, and the fine powder obtained by adding an acrylic resin as a binder to the fine powder was embedded in one end of a tantalum anode lead wire and compressed by a press machine. Molding. The molded body is heat-treated in a vacuum, sintered, and has a width of 1.5 mm.
A rectangular parallelepiped sintered body having a thickness of 3.0 mm and a length of 4.0 mm is formed. Next, a plurality of the sintered bodies are welded and integrated at equal intervals on a stainless steel plate having a width of 2 cm and a length of 10 cm at the location of the lead wire for the anode. Then, in a state of being welded to the stainless steel plate, the sintered body is immersed in a dilute phosphoric acid solution, and a DC voltage of 30 V is applied to form a dielectric film. After forming the dielectric film, 14 mmol of 3, cooled to 0 ° C. to 10 ° C.
4-ethylenedioxythiophene and 16 mmol of p-
The sintered body 1 is immersed for 1 minute in a mixed solution of an oxidizing agent and dopan consisting of 50 ml of a butanol solution of ferric toluenesulfonic acid. This immersion treatment is performed within 10 minutes after the preparation of the solution. After immersion, the sintered body is left in the air for 20 minutes. Then, the process from immersion to standing is repeated 10 times, and a first conductive layer made of conductive polythiophene or a derivative thereof is laminated. After laminating the first conductive layer, the sintered body is immersed for 1 minute in a solution composed of 50 mmol of a 100 mmol 3,4-ethylenedioxythiophene butanol solution. After this, 50 mM of a 35 mmol ferric p-toluenesulfonate butanol solution was added.
1 for 1 minute. After immersion,
The sintered body is left in the air for 30 minutes. The process from immersion to standing is repeated five times. After the repetition, the sintered body is dried by heating in air at a temperature of 40 ° C. for 30 minutes, and a second layer made of conductive polythiophene or a derivative thereof is formed.
Are laminated. After the drying, the sintered body is immersed in a 5 wt% aqueous solution of p-toluenesulfonic acid, and a voltage of 14 V is applied. After the voltage application, the sintered body is taken out of the liquid and dried in air at 110 ° C. for 30 minutes. After the heating and drying, the sintered body is immersed in colloidal carbon to attach carbon to the surface of the second conductive layer. After that, the device is taken out and heated to a temperature of 150 in a nitrogen gas atmosphere.
Dry at ℃ to form a carbon layer. After forming a carbon layer, a silver paste is applied, and the paste is applied in a nitrogen gas atmosphere.
Heat drying at a temperature of 50 ° C. to form a silver paste layer.
After the silver layer is formed, the silver layer of the element is connected to the cathode terminal of the lead frame with a silver conductive paste, and the anode lead wire is welded to the anode terminal of the lead frame to form a sintered body on the lead frame. Attach. After attaching the element to the lead frame, an exterior is formed by a transfer molding method using an epoxy resin. After forming the exterior, perform aging treatment, cut and remove the lead frame,
The cathode terminal and the anode terminal are formed into a chip-type solid electrolytic capacitor.

Examples 2 to 5: In Example 1,
When forming the first conductive layer and the second conductive layer, except that the number of repetitions of the treatment from dipping the sintered body in the solution to leaving it in the air as shown in Table 1, It shall be manufactured under the same conditions.

Next, with respect to the tantalum solid electrolytic capacitors of Examples 1 to 5, together with the conventional example, after forming the silver layer and before forming the package, after forming the package, and after forming the package and after heat treatment. Leakage current and 1
The impedance at a frequency of 00 KHz is measured.

In the conventional example 1, the process of immersing the sintered body in the same solution as used in forming the first conductive layer in the embodiment 1 and leaving the sintered body in the air was repeated 15 times.
Thereafter, the semiconductor device is manufactured under the same conditions except that the conductive layer is formed by heating and drying at a temperature of 80 ° C. in air to form a second conductive layer.

In the second conventional example, the process of forming the first conductive layer in the first embodiment is omitted, and the number of repetitions of the process from immersion to standing when forming the second conductive layer is one.
Manufacturing is performed under the same conditions except that the conductive layer is formed as zero times.

The leakage current is a value after a lapse of one minute from the application of a DC voltage of 10 V. In addition, the heat treatment is performed by leaving the sample after forming the exterior in air and heating it at a temperature of 125 ° C. for 10 hours. Table 1 shows the measurement results.

[0033]

[Table 1]

As is clear from Table 1, after the silver layer is formed, the leakage current and the impedance of the first to fifth embodiments are almost the same as those of the first and second conventional examples. I have.

Then, after forming the exterior, Examples 1 to
Example 5 has a leakage current of 3 to 5 μA and an impedance of 32 to 36 mΩ, and is 0.75 to 1.5 times and 1 to 1 times as large as the values of the same example after the silver layer is formed. 0.09 times. On the other hand, in the conventional examples 1 and 2, the leakage current is 44 to 64 μA and the impedance is 49 to 53 mΩ. 13 times and 1.25 to 1.33 times.

Further, after the heat treatment, Examples 1 to
Example 5 has a leakage current of 3 to 6 μA and an impedance of 33 to 38 mΩ, which are 0.75 to 2.5 times and about 1.06 times, respectively, as compared with the values of the same example after forming the silver layer. About 1.13 times. On the other hand, in the conventional examples 1 and 2, the leakage current was 78 to 110 μA and the impedance was 55 to 59 mΩ, which was 10.5 to 10.5, respectively, as compared with the same conventional example after the silver layer was formed. About 1
1.3 times and about 1.58 to about 1.66 times.

That is, as is clear from Table 1, Examples 1 to 5 suppress the increase in the leakage current and the impedance after the outer package is formed and after the heat treatment, as compared with Conventional Examples 1 and 2. it can.

[0038]

As described above, according to the production method of the present invention, a solution containing thiophene or a derivative thereof, an oxidizing agent, and a dopant is attached to the sintered body after the formation of the dielectric film to form conductive polythiophene or a conductive polythiophene. A first conductive layer made of a derivative is laminated, and thereafter, a solution containing thiophene or a derivative thereof and a dopant and a solution containing an oxidizing agent and a dopant are alternately attached to each other, or thiophene or a derivative thereof,
A solution containing two kinds selected from an oxidizing agent and a dopant and a solution containing the remaining one kind are alternately attached to each other to form a second layer made of conductive polythiophene or a derivative thereof on the surface of the first conductive layer. Since the conductive layers are stacked, a solid electrolytic capacitor having improved leakage current characteristics and frequency characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 shows a process chart of an embodiment of the present invention.

[Explanation of symbols]

1 ... sintered body, 4 ... dielectric film, 5 ... first conductive layer,
6 ... second conductive layer, 13 ... solid electrolytic capacitor. Reference number P2566

Claims (2)

[Claims] 1. Production of a solid electrolytic capacitor in which a dielectric film is formed on a sintered body made of fine powder of a valve metal and a conductive layer made of conductive polythiophene or a derivative thereof is laminated on the surface of the dielectric film. A method of depositing a solution containing thiophene or a derivative thereof, an oxidizing agent, and a dopant on the sintered body after forming the dielectric film to form a first conductive layer made of conductive polythiophene or a derivative thereof; After the process, a solution containing thiophene or a derivative thereof and a dopant, and a solution containing an oxidizing agent and a dopant are alternately attached to the surface of the first conductive layer to form a second conductive layer made of conductive polythiophene or a derivative thereof. And a step of laminating the layers. 2. Production of a solid electrolytic capacitor in which a dielectric film is formed on a sintered body made of a fine powder of a valve action metal and a conductive layer made of conductive polythiophene or a derivative thereof is laminated on the surface of the dielectric film. A method of depositing a solution containing thiophene or a derivative thereof, an oxidizing agent, and a dopant on the sintered body after forming the dielectric film to form a first conductive layer made of conductive polythiophene or a derivative thereof; After the process, a solution containing two kinds selected from thiophene, an oxidizing agent, and a dopant and a solution containing the remaining one kind are alternately attached to the surface of the first conductive layer to form a conductive polythiophene or a derivative thereof. And a step of laminating a second conductive layer.