JP4637700B2 - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

  In recent years, with the digitization of electronic equipment, solid electrolytic capacitors have been required to have excellent high frequency characteristics, and conductive polymers have been used for solid electrolytes used in solid electrolytic capacitors for the purpose of reducing ESR. Yes. Generally, conductive polymers used for solid electrolytic capacitors include polythiophene, polypyrrole, polyaniline, or derivatives thereof. Among them, polythiophene has higher conductivity than polypyrrole or polyaniline and has excellent thermal stability. It is often used because of

  Examples of the method for forming the conductive polymer include electrolytic polymerization and chemical oxidation polymerization. When electrolytic polymerization is used, it is necessary to install a polymerization electrode for each capacitor anode body, which is disadvantageous for mass production. On the other hand, chemical oxidative polymerization is widely used among those skilled in the art as a technique that can be easily mass-produced.

  In the conventional solid electrolytic capacitor, a conductive polymer layer is formed by immersing a capacitor anode body in a solution in which a monomer and an oxidant are mixed and performing chemical oxidative polymerization as in the manufacturing process shown in FIG. 2 (for example, , See Patent Document 1).

  Further, a method of forming a conductive polymer layer by alternately immersing a capacitor anode body in a monomer solution and an oxidant solution and performing chemical oxidative polymerization as in the manufacturing process shown in FIG. 3 (for example, Patent Document 2).

In general, since the conductive polymer layer acts as a highly conductive cathode layer, a thinner one is advantageous because it has a lower resistance. However, since the conductive polymer layer also serves to protect the element against mechanical stress applied to the capacitor element from the exterior resin, it is necessary to form a conductive polymer layer having a certain thickness ( For example, see Patent Documents 3 and 4).
Patent No. 3040113 US Pat. No. 4,697,001 Japanese Patent Laid-Open No. 2001-143968 JP 2003-188052 A

  However, the method of performing chemical oxidative polymerization by immersing the capacitor anode body described in Patent Document 1 in a solution in which a monomer and an oxidizing agent are mixed can form a conductive polymer layer in the pore details inside the capacitor anode body. In order to form a sufficient thickness that can reduce short-circuit failure and leakage current, the number of repetitions of chemical oxidative polymerization becomes extremely large, and a solution in which a monomer and an oxidant are mixed is used. There was a problem that the liquid deteriorated rapidly due to the progress of the material, and the material cost was high.

  Further, the method of performing chemical oxidative polymerization by alternately immersing the capacitor anode body described in Patent Document 2 in a monomer solution and an oxidant solution is different from the above, even if the number of repetitions of chemical oxidative polymerization is relatively small. Conductive polymer thickness can be formed, and since monomer solution and oxidant solution are immersed separately, the polymerization reaction in the solution progresses slowly and the liquid life is long. There is a problem that a sufficient capacity cannot be obtained because it is difficult to form fine holes in the anode body.

  The present invention solves the above-mentioned problems, and provides a solid electrolytic capacitor with a small man-hour, a high capacity appearance rate, and good leakage current characteristics and ESR characteristics.

In order to solve the above problems, the solid electrolytic capacitor of the present invention is formed by forming a dielectric oxide film on the surface of a sintered body formed of a valve metal powder or a roughened valve metal foil. In the solid electrolytic capacitor in which a cathode layer made of a conductive polymer is formed on the surface of the dielectric oxide film after forming the capacitor anode body,
On the surface of the capacitor anode body, the first conductive polymer layer formed by chemical oxidative polymerization by immersion in a solution in which a monomer and an oxidant are mixed, and the monomer solution and the oxidant solution are alternately immersed in the chemical A second conductive polymer layer formed by oxidative polymerization,
The solid electrolytic capacitor is characterized in that the coverage of the first conductive polymer layer is 20 to 80%.

In addition, a dielectric oxide film is formed on the surface of a sintered body formed of a valve action metal powder or a roughened valve action metal foil to form a capacitor anode body, and then the dielectric oxide film In the method of manufacturing a solid electrolytic capacitor in which a cathode layer made of a conductive polymer is formed on the surface of the first electrode, the first surface is formed by chemical oxidative polymerization by immersion in a solution in which a monomer and an oxidizing agent are mixed on the surface of the capacitor anode body. A first conductive polymer layer forming step of forming a conductive polymer layer; a second step of alternately immersing in a monomer solution and an oxidant solution and forming a second conductive polymer layer by chemical oxidative polymerization; conductive and a polymer layer forming step, the coverage of the first conductive polymer layer is 20-80%, the second conductive with the first conductive polymer layer formation step Having a re-formation step between the functional polymer layer formation step A method for producing a solid electrolytic capacitor according to symptoms.

With the above configuration, a conductive polymer layer can be easily formed in the pore details inside the capacitor anode body, and a sufficiently thick conductive polymer layer can be formed. A solid electrolytic capacitor with few defects, a low leakage current value, and a low ESR value can be provided.
In addition, since the number of times of chemical oxidation polymerization for forming the first conductive polymer layer in which the polymerization solution is rapidly deteriorated is small, it is possible to provide a solid electrolytic capacitor with stable manufacturing conditions and low material cost.

  Further, after the coverage of the first conductive polymer layer is set to 20 to 80%, the dielectric oxide film deteriorated by the chemical oxidative polymerization is repaired by re-forming, thereby forming the second conductive polymer layer. By doing so, the leakage current can be further reduced without degrading the ESR.

[Example 1]
Specific embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a manufacturing process in Examples 1 to 3.
Anode lead wire is embedded in tantalum powder, pressed into a predetermined shape, sintered to a porous body of 0.60 mm x 1.00 mm x 0.60 mm, and anodized at an applied voltage of 15 V in a phosphoric acid aqueous solution Then, a dielectric oxide film layer was formed on the surface of the porous body to obtain a capacitor anode body.

  Next, a monomer solution containing 2,4-ethylenedioxythiophene (hereinafter abbreviated as EDT) and an oxidizer solution containing ferric dodecylbenzenesulfonate are mixed, and the mixture solution maintained at −5 ° C. is mixed with the above solution. After immersing the capacitor anode body, it was pulled up and chemically oxidized and polymerized at 20 ° C. to form a first conductive polymer layer. Then, it wash | cleaned with alcohol and dried at 85 degreeC. The above operation was performed twice, and the coverage (impregnation rate) of the first conductive polymer layer was measured and found to be 20%.

Here, the coverage (impregnation rate) indicates the ratio of the coating of the conductive polymer layer or solid electrolyte layer formed on the dielectric oxide film layer to the dielectric oxide film layer. Specifically, a capacitance value (capacitance value inherent to the capacitor element) after sufficiently containing the conductive solution in the capacitor element after the formation of the conductive polymer layer or the solid electrolyte layer, and the inside of the capacitor element From the capacitance value after washing the conductive solution and sufficiently drying the water (the capacitance value actually possessed by the capacitor element after the formation of the conductive polymer layer or the solid electrolyte layer).
The formula for calculating the coverage is shown below.

[Equation 1]

  Further, the capacitor element was immersed in an EDT monomer solution maintained at 25 ° C., and then pulled up and dried. Then, after being immersed in an oxidant solution containing ferric dodecylbenzenesulfonate held at 25 ° C., it was pulled up and chemically oxidized and polymerized at 20 ° C. to form a second conductive polymer layer. Then, it wash | cleaned with alcohol and dried at 85 degreeC. The above operation was repeated 4 times.

  Next, a carbon paste and a silver paste are applied on the conductive polymer layer of the capacitor element to sequentially form a carbon layer and a silver layer, and a cathode lead terminal is formed on the silver layer. After connecting the anode terminal to the anode lead drawn out from each, an exterior resin was applied by transfer molding to produce a solid electrolytic capacitor.

[Example 2]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the chemical polymerization was repeated so that the coverage (impregnation rate) of the first conductive polymer layer was 50%.

[Example 3]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the chemical polymerization was repeated so that the coverage (impregnation rate) of the first conductive polymer layer was 80%.

[Examples 4 to 6]
FIG. 4 shows the manufacturing process in Examples 4-6.
Under the manufacturing conditions of Examples 1 to 3, after forming the first conductive polymer layer, re-formation was performed in an aqueous solution of phosphoric acid having a concentration of 0.01 wt% at an applied voltage of 14 V and a liquid temperature of 40 ° C. A solid electrolytic capacitor was produced in the same manner as in Examples 1 to 3 except that the coating layer was repaired.

[Comparative Example 1]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the chemical polymerization was repeated so that the coverage (impregnation rate) of the first conductive polymer layer was 10%.

[Comparative Example 2]
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the chemical polymerization was repeated so that the coverage (impregnation rate) of the first conductive polymer layer was 90%.

(Conventional example 1)
FIG. 2 shows a manufacturing process in Conventional Example 1.
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the second conductive polymer layer was not formed and the chemical oxidation polymerization for forming the first conductive polymer layer was repeated 20 times. .

(Conventional example 2)
FIG. 3 shows a manufacturing process in Conventional Example 2.
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the chemical oxidation polymerization for forming the second conductive polymer layer was repeated 5 times without forming the first conductive polymer layer. .

  The polymer layer thickness and electric characteristics of the solid electrolytic capacitors produced in Examples 1 to 6, Comparative Examples 1 and 2 and Conventional Examples 1 and 2 were measured. The polymer layer thickness was an average value of the side surface portion and the bottom surface portion of the capacitor element. The results are shown in Table 1.

  As can be seen from Table 1, Examples 1 to 3 can reduce the number of chemical oxidative polymerizations compared to Conventional Example 1, and the polymer layer is thick, the short-circuit failure is small, and the leakage current is low. It was.

In addition, Examples 1 to 3 had a higher capacitance than Conventional Example 2, and exhibited substantially the same values for leakage current and ESR. Here, when the coverage (impregnation rate) is less than 20% (Comparative Example 1), the electrostatic capacity becomes small,
Furthermore, when the coverage (impregnation rate) exceeds 80% (Comparative Example 2), the ESR becomes high. Therefore, the coverage (impregnation rate) of the first conductive polymer layer is desirably 20 to 80%.
In addition, the present invention can provide a solid electrolytic capacitor with a reduced man-hour and low material cost because the number of times of chemical oxidation polymerization in forming the first conductive polymer layer in which the polymerization solution is severely deteriorated is small.

  Furthermore, the conditions under which the re-formation was performed (Examples 4 to 6) were compared with the conditions under which the re-formation was not performed (Examples 1 to 3), respectively, and the short circuit failure was observed without affecting the capacitance and ESR. Rate and leakage current can be further reduced.

  Moreover, although the formation method of the 2nd conductive polymer layer was immersed in the oxidant solution after being immersed in the monomer solution, the same effect is acquired even if it is immersed in the monomer solution after being immersed in the oxidant solution.

  Furthermore, EDT and ferric dodecylbenzene sulfonate were used as the monomer and oxidant. Known monomers such as pyrrole and aniline were used as the monomer, and ferric butyl naphthalene sulfonate and p-toluene sulfone were used as the oxidant. The same effect can be obtained by using a known oxidizing agent such as ferric acid.

  In the present invention, an aqueous phosphoric acid solution is used for re-chemical conversion, but the same effect can be obtained by using a known anodizable aqueous solution such as adipic acid, citric acid, acetic acid, succinic acid, tartaric acid, nitric acid, boric acid. Is obtained.

  Further, although tantalum is used as the capacitor anode material, the same effect can be obtained by using a valve metal such as niobium or aluminum.

  Further, in the formation of the first conductive polymer layer in which the capacitor anode body is immersed in a solution in which the monomer and the oxidant are mixed and chemically oxidatively polymerized, the monomer solution and the oxidant solution containing ferric dodecylbenzenesulfonate are added. The mixed solution was maintained at −5 ° C., but it is preferable that the temperature is low enough not to freeze the solution in order to suppress the progress of the polymerization reaction in the solution and to increase the life of the solution.

  Further, in the formation of the second conductive polymer layer, the monomer solution containing thiophene was kept at 25 ° C. and the oxidant solution containing ferric dodecylbenzenesulfonate was kept at 25 ° C., but the temperature is limited to this. is not.

  Further, in the formation of the first conductive polymer layer, chemical oxidative polymerization was performed at 20 ° C., and then in the formation of the second conductive polymer layer, chemical oxidative polymerization was performed at 20 ° C., but the temperature was limited to this. Is not something

  Furthermore, in the formation of the first conductive polymer layer, a mixed solution of a monomer and an oxidizing agent containing ferric dodecylbenzenesulfonate having a dopant action was used, but the monomer and a dopant such as dodecylbenzenesulfonate were used. The same effect can be obtained by polymerization using a mixed solution with an oxidizing agent such as ammonium persulfate.

  In addition, after the first conductive polymer layer was formed, re-chemical conversion was performed at a liquid temperature of 40 ° C. in a phosphoric acid aqueous solution having a concentration of 0.01 wt%, but the chemical conversion liquid type, concentration, and liquid temperature are limited to this. It is not a thing.

  Furthermore, although the present invention is applied to a tantalum solid electrolytic capacitor, the same effect can be obtained when applied to a wound aluminum solid electrolytic capacitor, a laminated aluminum solid electrolytic capacitor or a niobium solid electrolytic capacitor.

It is the schematic of the solid electrolytic capacitor manufacturing process of this invention. It is the schematic of the solid electrolytic capacitor manufacturing process of the prior art example 1. It is the schematic of the solid electrolytic capacitor manufacturing process of the prior art example 2. It is the schematic of the solid electrolytic capacitor manufacturing process of Examples 4-6.

Claims (2)

A dielectric oxide film is formed on the surface of a sintered body formed of a valve action metal powder or a roughened valve action metal foil to form a capacitor anode body, and then the surface of the dielectric oxide film In a solid electrolytic capacitor that forms a cathode layer made of a conductive polymer in
On the surface of the capacitor anode body, the first conductive polymer layer formed by chemical oxidative polymerization by immersion in a solution in which a monomer and an oxidant are mixed, and the monomer solution and the oxidant solution are alternately immersed in the chemical A second conductive polymer layer formed by oxidative polymerization,
The solid electrolytic capacitor, wherein the coverage of the first conductive polymer layer is 20 to 80%. A dielectric oxide film is formed on the surface of a sintered body formed of a valve action metal powder or a roughened valve action metal foil to form a capacitor anode body, and then the surface of the dielectric oxide film In the method for producing a solid electrolytic capacitor in which a cathode layer made of a conductive polymer is formed,
A first conductive polymer layer forming step of forming a first conductive polymer layer by chemical oxidative polymerization by immersion in a solution in which a monomer and an oxidant are mixed on the surface of the capacitor anode body;
A second conductive polymer layer forming step of alternately immersing in a monomer solution and an oxidant solution and forming a second conductive polymer layer by chemical oxidative polymerization;
Have
The coverage of the first conductive polymer layer is 20 to 80%,
Method of manufacturing a solid electrolytic capacitor characterized by having a re-formation process between the first conductive polymer layer formation step and the second conductive polymer layer formation step.

Images