JP2006108192A - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the leakage current of a solid electrolytic capacitor that has a conductive high polymer as a solid electrolyte. <P>SOLUTION: The solid electrolytic capacitor is manufactured by polymerizing a polymerizing monomer with an oxidant to form a solid electrolyte on the surface of a capacitor element that has a dielectric oxide film formed on the surface of an anode body which is made of a valve action metal. In the manufacturing method, aging is performed by applying voltage of 0.9 to 1.4 times the rated voltage under an atmosphere of 140°C or over after the capacitor element is provided with an external resin, and the solid electrolytic capacitor is completed by bending an external terminal along the external resin. The voltage application is set to start when the surface temperature of the solid electrolytic capacitor reaches 140°C or over. The solid electrolytic capacitor is left in a high temperature state of 140°C or over for a predetermined time period, and the voltage continues to be applied during a cooling-off period, thus performing aging. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  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 polymer as a solid electrolyte.

  Solid electrolytic capacitors are obtained by sintering a so-called wound electrolytic capacitor holding a solid electrolyte or a fine tantalum powder on a capacitor element formed by winding an anode foil and a cathode foil made of aluminum or the like through a separator. A sintered solid electrolytic capacitor in which a solid electrolyte layer is formed on the surface of a capacitor element is known.

  As a solid electrolyte used in such an electrolytic capacitor, in recent years, a conductive polymer has attracted attention for the purpose of reducing ESR, and a solid electrolytic capacitor using the conductive polymer as a solid electrolyte has been put into practical use. In general, these conductive polymers include polythiophene, polypyrrole, or polyaniline. Among them, polythiophene has attracted attention in recent years because it has high electrical conductivity and particularly excellent thermal stability compared to polypyrrole or polyaniline. JP-A-2-15611 discloses a solid electrolytic capacitor using polythiophene as a solid electrolyte.

JP-A-2-15611

  When a solid electrolytic capacitor using a conductive polymer as a solid electrolyte is subjected to a solder reflow process when mounted on a printed circuit board, a leakage current may increase. This is because the dielectric oxide film formed by anodic oxidation of the valve metal has left a fine defect portion, and the fine defect portion of the dielectric oxide film becomes obvious through the reflow process. This is thought to be due to leakage current. This increase in leakage current is characterized by extremely large variations among products.

  By the way, in an electrolytic capacitor using an electrolytic solution, it is known that when an aging treatment is performed, a defective portion of the film is repaired by the electrolytic solution, so that leakage current is reduced. When used, it is considered that oxygen necessary for repairing the film is difficult to be supplied from the conductive polymer, so that the film repair at the defective portion is not sufficient. When a conductive polymer is used for the solid electrolyte, it is considered that the leakage current is reduced by insulating the conductive polymer when a current flows in the insulation defect portion.

  As described above, the conductive polymer is considered to be a mechanism for reducing the leakage current when the solid electrolyte is used, and therefore the degree of insulation of the conductive polymer varies, resulting in leakage of individual products. It is considered that variation occurs to the extent that the current increases.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solid electrolytic capacitor having stable quality with no variation while preventing an increase in leakage current of the solid electrolytic capacitor.

  In the invention according to claim 1 of this application, a solid electrolyte is formed by polymerizing a polymerizable monomer with an oxidizing agent on the surface of a capacitor element in which a dielectric oxide film is formed on the surface of an anode body made of a valve metal. In the manufacturing method for a solid electrolytic capacitor, a capacitor element is provided with a resin sheath, and external terminals are bent along the resin sheath to complete a solid electrolytic capacitor. Aging is performed by applying a voltage of 1.4 times.

  The invention according to claim 2 of the present application is the method for manufacturing a solid electrolytic capacitor according to claim 1, wherein the surface temperature of the solid electrolytic capacitor is set to 140 ° C. or more, and is 0.9 to 1.4 times the rated voltage. A voltage is applied.

  The invention according to claim 3 of this application is the method of manufacturing a solid electrolytic capacitor according to claim 2, wherein the rated voltage is 0.9 during the cooling period in which the solid electrolytic capacitor is cooled from a high temperature state of 140 ° C. or higher to room temperature. Aging is performed by continuously applying a voltage of ˜1.4 times.

  After the solid electrolytic capacitor is completed, the temperature of the entire solid electrolytic capacitor rises by leaving it in an atmosphere of 140 ° C. or higher. For this reason, the temperature of the dielectric oxide film of the capacitor element also rises, and the electrical resistance of the film is reduced. Then, by applying a voltage 0.9 to 1.4 times the rated voltage in this state, a current flows even in a minute defect portion. For this reason, more current flows than in a state where the solid electrolytic capacitor is normally used, and it is considered that the conductive polymer is insulated by this current. When the voltage is less than 0.9 times the rated voltage, the aging effect is not sufficient, and the leakage current of the solid electrolytic capacitor is not reduced. On the other hand, when the voltage exceeds 1.4 times the rated voltage, a short circuit occurs during aging, and a current runaway occurs.

  In this way, an increase in leakage current after reflow of the solid electrolytic capacitor is suppressed by flowing current even in a minute defect portion and insulating the conductive polymer formed on the defect portion. Can do.

  In particular, when the surface temperature of the solid electrolytic capacitor is 140 ° C. or higher and a voltage of 0.9 to 1.4 times the rated voltage is applied, the insulation of the conductive polymer is performed smoothly, which is preferable. .

  In addition, the solid electrolytic capacitor is allowed to stand at a high temperature of 140 ° C. or higher for a predetermined time and then cooled to room temperature, and during the cooling period to room temperature, a voltage 0.9 to 1.4 times the rated voltage is applied for aging. If it does, insulation of a conductive polymer will progress further and the reduction effect of a leakage current will become a big thing.

  In the method for manufacturing a solid electrolytic capacitor according to the present invention, the leakage current can be reduced. In addition, the solid electrolytic capacitor can be provided in a stable quality with no variation without causing the solid electrolytic capacitor to be short-circuited.

Next, embodiments of the present invention will be described in detail.
FIG. 1 is a cross-sectional view showing the internal structure of the solid electrolytic capacitor. Reference numeral 1 denotes a capacitor element, in which fine tantalum powder is molded into a predetermined shape, and an anode lead wire such as a tantalum wire is embedded and further sintered to obtain a tantalum sintered body, which is further immersed in a phosphoric acid aqueous solution or the like. A predetermined voltage is applied to form an anodic oxide film serving as a dielectric on the surface of the fine tantalum powder. The sintered body is not limited to tantalum, and valve action metals such as aluminum, niobium, and titanium can be used.

  2 is a conductive polymer layer formed on the anodized film. The conductive polymer layer includes a step of immersing the capacitor element in a monomer solution obtained by diluting 3,4-ethylenedioxythiophene with a predetermined solvent, and further immersing in a oxidant solution in which a predetermined oxidant is dissolved in the predetermined solvent. By repeating, 3,4-ethylenedioxythiophene is formed by oxidative polymerization.

  3 is a carbon layer formed on the conductive polymer layer 2, and 4 is a silver paste layer formed on the carbon layer.

  Reference numeral 5 denotes an anode lead wire, which is welded to the anode lead-out line of the capacitor element and is in electrical communication with the outside. Reference numeral 6 denotes a cathode lead wire, which is connected by a silver paste layer and is in electrical communication with the outside. Further, the whole is molded with a resin and a resin sheath 7 is applied. Further, the anode lead wire 5 and the cathode lead wire 6 are bent along the resin sheath 7.

  The solid electrolytic capacitor as described above can be produced by a known method, and the details of the manufacturing process are omitted here. Such a solid electrolytic capacitor is subjected to an aging treatment in order to further stabilize its characteristics. In the aging treatment, an electrode is attached to each of the anode lead wire and the cathode lead wire, and aging is performed by applying a predetermined DC voltage to the solid electrolytic capacitor so that the anode lead wire is positive and the cathode lead wire is negative.

  When performing this aging, the solid electrolytic capacitor is previously placed in a thermostatic oven or the like and heated to 140 ° C. or higher. Aging is performed by applying a voltage 0.9 to 1.4 times the rated voltage while the surface temperature of the solid electrolytic capacitor is 140 ° C. or higher. Although this aging time varies depending on the size of the solid electrolytic capacitor, for example, in the case of a solid electrolytic capacitor having a size of about 3.5 mm × 2.8 mm × 1.2 mm, a voltage is applied for about 60 minutes. Further, the solid electrolytic capacitor is cooled by taking out the solid electrolytic capacitor from the thermostat or by forced air cooling of the thermostat. In this cooling process, a voltage is continuously applied to the solid electrolytic capacitor.

  Due to the aging of the solid electrolytic capacitor, insulation of the conductive polymer occurs due to the current flowing in the defective portion of the dielectric oxide film of the solid electrolytic capacitor, and the leakage current of the solid electrolytic capacitor can be reduced.

  The solid electrolytic capacitor is completed through the steps as described above.

Specific examples will be described below.
The solid electrolytic capacitor has a rated voltage of 4 V and an outer diameter of 3.5 mm × 2.8 mm × 1.2 mm. This solid electrolytic capacitor was aged. The aging conditions were an applied voltage of 5.2V and 1.3 times the rated voltage. The aging atmosphere was performed at four levels of 175 ° C., 140 ° C., 130 ° C., and 105 ° C. Aging at 105 ° C. and 130 ° C. is a comparative example.

  Further, during aging, aging was performed by changing the temperature of the solid electrolytic capacitor at the start of voltage application and at the end of voltage application. More specifically, the solid electrolytic capacitor is housed in a constant temperature bath at room temperature, and then heated to a constant temperature, and then the constant temperature bath is opened and cooled to room temperature, and then the solid electrolytic capacitor is taken out from the constant temperature bath. However, the effect of investigating the effect of changing the timing of starting or ending voltage application in this process was investigated.

  Table 1 below summarizes the aging conditions.

  After aging under the above conditions, the leakage current characteristics of the solid electrolytic capacitor were investigated. The survey item was the average leakage current. Some samples have a solid electrolytic capacitor in a short-circuit state, and the short-circuited state is regarded as a failure due to a large leakage current. In this case, the average value of the leakage current is obtained by calculating the average value of the other non-defective samples except for the one having a large leakage current. The results are shown in Table 2 below.

  As can be seen from Table 2, in Examples 1 to 4, the average value of the leakage current is a low value of 0.4 to 0.6 μA, whereas the comparative example was aged at a relatively low temperature. 1. In Comparative Example 2, the average value of the leakage current is as high as 0.9 to 1.0 μA. Therefore, it can be seen that leakage current can be reduced by performing aging at 140 ° C. or higher.

  In addition, when the aging was performed after the surface temperature of the solid electrolytic capacitor was increased (Example 1, Example 3, Example 4), no defect due to a large leakage current occurred, whereas aging was performed at room temperature. In the case of performing more (Example 2), a defect due to a large leakage current occurred. Therefore, it can be seen that aging is preferably performed after the surface temperature of the solid electrolytic capacitor is increased.

  Furthermore, when the aging is performed after the surface temperature of the solid electrolytic capacitor is increased until it is cooled to room temperature (Example 1), the aging is completed in a state where the surface temperature of the solid electrolytic capacitor is increased (implementation). Compared with Example 3), the average value of the leakage current is small. From this, it can be seen that it is more preferable to perform aging after the surface temperature of the solid electrolytic capacitor rises until it is cooled to room temperature.

It is sectional drawing which shows the internal structure of a solid electrolytic capacitor.

Explanation of symbols

1 Capacitor Element 2 Solid Electrolyte Layer 3 Carbon Layer 4 Silver Paste Layer 5 Anode Lead Wire 6 Cathode Lead Wire 7 Resin Exterior

Claims (3)

A solid electrolyte is formed by polymerizing a polymerizable monomer with an oxidizing agent on the surface of a capacitor element in which a dielectric oxide film is formed on the surface of an anode body made of a valve metal, and a resin sheath is applied to the capacitor element to provide an external terminal. A method for producing a solid electrolytic capacitor, wherein the aging is performed by applying a voltage of 0.9 to 1.4 times the rated voltage in an atmosphere of 140 ° C. or higher after being bent along the resin sheath . The method for producing a solid electrolytic capacitor according to claim 1, wherein a voltage 0.9 to 1.4 times the rated voltage is applied after the surface temperature of the solid electrolytic capacitor is 140 ° C. or higher. The aging is performed by continuously applying a voltage of 0.9 to 1.4 times the rated voltage during a cooling period in which the solid electrolytic capacitor is cooled from a high temperature state of 140 ° C or higher to room temperature. 2. A method for producing a solid electrolytic capacitor according to 2.