JP4548730B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a method for manufacturing a solid electrolytic capacitor used in various electronic devices, and more particularly to an anodizing method for forming an oxide film layer.

  In the conventional solid electrolytic capacitor, a metal powder having a valve action such as tantalum or niobium is pressed and then sintered to form a porous sintered body, and further, an oxide film layer serving as a dielectric, a cathode, After sequentially forming a cathode electrolyte layer such as a conductive polymer or manganese dioxide, a graphite layer, and a cathode silver layer, the anode lead wire and the anode lead frame are connected by resistance welding, and the cathode lead layer And a cathode lead frame are connected via a conductive adhesive, and an exterior resin is formed by transfer molding.

  In general, in the step of forming an oxide film layer, a method is used in which a porous sintered body is immersed in an acidic electrolyte solution such as phosphoric acid, which is an anodizing solution, and a voltage is applied in the electrolyte solution. However, in the conventional method, when anodizing a porous sintered body having a small pore diameter, the inside of the porous sintered body has high electrical resistance, and the anodizing current hardly flows. Had to be done.

Therefore, in order to make the anodic oxidation current flow easily, a method of increasing the solute concentration of the anodic oxidation solution to increase the electrical conductivity, or supplying the anodic oxidation solution to the inside of the porous sintered body by vibrating the anodic oxidation solution Is used to promote the formation of an oxide film layer (see, for example, Patent Document 1).
JP-A-9-283380

  However, in the above-described method for increasing the electrical conductivity of the anodic oxidation solution, the oxide film layer takes in more solute ions in the anodic oxidation solution, and many defects are generated in the oxide film, resulting in leakage current characteristics. There was a problem of getting worse.

Moreover, in the method of patent document 1 which vibrates an anodic oxidation liquid, it was necessary to attach an ultrasonic generator to an anodic oxidation tank, and caused the increase in equipment cost.
Furthermore, when performing anodization, the anode lead protruding from the porous sintered body is connected to a metal bar and immersed in an anodizing solution, and a voltage is applied to the porous sintered body through the metal bar. In addition, the anodizing solution rises up to the metal bar due to the vibration of the anodizing tank, and the current flows directly from there to the anodizing solution, so that there is a problem that the formation of the oxide film layer becomes insufficient. In order to prevent this, it is necessary to lengthen the anode lead, resulting in an increase in production cost.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method of manufacturing a solid electrolytic capacitor having good leakage current characteristics and withstand voltage characteristics without incurring long-term anodic oxidation and an increase in production cost. .

  In order to solve the above-mentioned problem, the present invention performs the anodic oxidation a plurality of times in the step of forming an oxide film layer by anodic oxidation on a porous sintered body made of a valve action metal, at least once, for the first time. A method for producing a solid electrolytic capacitor, characterized in that anodization is performed with an anodizing solution having higher electrical conductivity.

  Said structure WHEREIN: The said valve action metal is a tantalum or niobium, The manufacturing method of the solid electrolytic capacitor characterized by the above-mentioned.

  According to the present invention configured as described above, an oxide film layer having no defect is formed by the first anodic oxidation, and then the inside of the pores of the porous sintered body is sufficiently filled with the anodic oxidation liquid having high electrical conductivity. Since a simple oxide film layer can be formed, a solid electrolytic capacitor having good leakage current characteristics and withstand voltage characteristics can be manufactured without anodizing for a long time and an increase in production cost.

  Hereinafter, several examples of the present invention will be described, and these characteristics and the characteristics of the conventional example will be compared and examined.

[Example 1]
A tantalum powder embedded with one of the anode leads is pressed and then sintered in a vacuum at a high temperature, and then an anodic oxidation voltage in a phosphoric acid aqueous solution having an electrical conductivity of 3 mS / cm. A first anodic oxidation was performed by applying 30 V for 2 hours.
Subsequently, the porous sintered body was subjected to a second anodic oxidation by applying an anodic oxidation voltage of 30 V for 1 hour in an aqueous phosphoric acid solution having an electric conductivity of 6 mS / cm, thereby forming an oxide film layer. .
And after impregnating the said porous sintered compact in manganese nitrate aqueous solution, thermal decomposition at 200-400 degreeC was performed in multiple times, and the solid electrolyte layer which consists of manganese dioxide was fully formed on the dielectric oxide film layer.
Furthermore, after immersing in a graphite liquid in which graphite powder was suspended and drying in a high-temperature bath to form a carbon layer, a cathode silver layer was formed to form a cathode lead layer. After that, the anode lead and the anode terminal are connected by resistance welding, the cathode lead layer and the cathode terminal are connected by a conductive adhesive, and the exterior resin is covered with a transfer mold, and then the anode terminal and the cathode terminal are packaged. The chip-shaped tantalum solid electrolytic capacitor of Example 1 was obtained by bending along the resin.

[Example 2]
In a phosphoric acid aqueous solution with an electrical conductivity of 3 mS / cm, an anodic oxidation voltage of 30 V is applied for 2 hours to perform the first anodic oxidation, and then in an aqueous phosphoric acid solution with an electrical conductivity of 15 mS / cm, A chip-shaped tantalum solid electrolytic capacitor of Example 2 was obtained in the same manner as in Example 1 except that the oxidation voltage of 30 V was applied for 1 hour and the second anodic oxidation was performed.

[Example 3]
An anodizing voltage of 30 V is applied for 2 hours in an aqueous nitric acid solution having an electric conductivity of 3 mS / cm, and the first anodizing is performed. Subsequently, an anodizing voltage is applied in an aqueous nitric acid solution having an electric conductivity of 6 mS / cm. A chip-shaped tantalum solid electrolytic capacitor of Example 3 was obtained in the same manner as in Example 1 except that 30 V was applied for 1 hour and the second anodic oxidation was performed.

[Example 4]
Anodization voltage of 30V is applied for 2 hours in an aqueous nitric acid solution having an electrical conductivity of 3 mS / cm for the first time, followed by anodization in an aqueous phosphoric acid solution having an electrical conductivity of 6 mS / cm. A chip-like tantalum solid electrolytic capacitor of Example 4 was obtained in the same manner as in Example 1 except that the voltage 30 V was applied for 1 hour and the second anodic oxidation was performed.

[Example 5]
The first anodic oxidation is performed by applying an anodic oxidation voltage of 30 V for 2 hours in a phosphoric acid aqueous solution having an electric conductivity of 3 mS / cm, and then an anodic oxidation in an aqueous nitric acid solution having an electric conductivity of 6 mS / cm. A chip-like tantalum solid electrolytic capacitor of Example 5 was obtained in the same manner as in Example 1 except that the voltage 30 V was applied for 1 hour and the second anodic oxidation was performed.

[Comparative Example 1]
In a phosphoric acid aqueous solution having an electrical conductivity of 3 mS / cm, an anodic oxidation voltage of 30 V is applied for 2 hours to perform the first anodic oxidation, followed by an anodic oxidation in an aqueous phosphoric acid solution having an electrical conductivity of 3 mS / cm. A chip-like tantalum solid electrolytic capacitor of Comparative Example 1 was obtained in the same manner as in Example 1, except that the oxidation voltage of 30 V was applied for 1 hour and the second anodic oxidation was performed.

[Comparative Example 2]
In a phosphoric acid aqueous solution having an electric conductivity of 6 mS / cm, an anodic oxidation voltage of 30 V is applied for 2 hours to perform the first anodic oxidation, and then in an aqueous phosphoric acid solution having an electric conductivity of 3 mS / cm, A chip-shaped tantalum solid electrolytic capacitor of Comparative Example 2 was obtained in the same manner as in Example 1, except that the oxidation voltage of 30 V was applied for 1 hour and the second anodic oxidation was performed.

[Conventional example 1]
In the same manner as in Example 1, except that the anodic oxidation was performed only once by applying an anodic oxidation voltage of 30 V for 8 hours in a phosphoric acid aqueous solution having an electrical conductivity of 3 mS / cm, A chip-shaped tantalum solid electrolytic capacitor was obtained.

[Conventional example 2]
In the same manner as in Example 1, except that the anodic oxidation was performed only once by applying an anodic oxidation voltage of 30 V for 3 hours in a phosphoric acid aqueous solution having an electrical conductivity of 6 mS / cm. A chip-shaped tantalum solid electrolytic capacitor was obtained.

  Leakage current value of the above chip-shaped tantalum solid electrolytic capacitor (applied 10V, 1 minute), withstand voltage, leakage current value after high temperature load test (applied at 85 ° C, 10V, 1000 hours) (applied 10V, 1 minute) Table 1 shows the results of the comparison.

  As is clear from Table 1, in Examples 1 to 5 in which the electrical conductivity of the second anodic oxidation solution was higher than the electrical conductivity of the first anodic oxidation solution, the leakage current value was reduced by short-term anodic oxidation. In the withstand voltage and the leakage current value after the high-temperature load test, characteristics equal to or higher than those of the conventional example 1 can be obtained.

  In addition, when the electrical conductivity of the second anodic oxidation liquid was set to be equal to or lower than the electrical conductivity of the first anodic oxidation liquid by comparing Example 1 with Comparative Examples 1 and 2, the anodic oxidation was performed a plurality of times. It can also be seen that none of the leakage current value, withstand voltage, or leakage current value after the high temperature load test is improved.

  Furthermore, even if the liquid type of the first and second anodic oxidation is changed by comparing the examples 3 to 5 with the conventional example 1, the second anodic oxidation liquid is more than the electric conductivity of the first anodic oxidation liquid. By increasing the electrical conductivity, the characteristics equivalent to or higher than those of Conventional Example 1 can be obtained in the leakage current value, the withstand voltage, and the leakage current value after the high temperature load test.

  In the examples of the present invention, phosphoric acid and nitric acid were used as the anodizing solution, but the same effect can be obtained by using adipic acid, citric acid, acetic acid, oxalic acid, tartaric acid, and boric acid.

  In the embodiment, the anodic oxidation is performed twice. However, the anodic oxidation may be performed three or more times and at least once with an anodic oxidation liquid having higher electrical conductivity than the first time. The electric conductivity of the liquid is made higher than the first time, the electric conductivity of the third anodizing liquid is made lower than the second time, the electric conductivity of the second anodizing liquid is made higher than the first time, and the third time The electrical conductivity of the anodizing liquid is made higher than the second time, the electric conductivity of the second anodizing liquid is made higher than the first time, and the electric conductivity of the third anodizing liquid is made the same as the second time. In this case, the same effect as in the above embodiment can be obtained.

Claims (2)

In the process of forming an oxide film layer by anodic oxidation for a porous sintered body made of a valve metal,
A method for producing a solid electrolytic capacitor, wherein the anodization is performed a plurality of times, and anodization is performed at least once with an anodizing solution having a higher electrical conductivity than the first time.   The method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the valve metal is tantalum or niobium.