JP2005079334A - Method for manufacturing solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a leakage current of a solid electrolytic capacitor. <P>SOLUTION: In a method for manufacturing the solid electrolytic capacitor, a solid electrolytic layer and a cathode layer each composed of a conductive polymer are formed in a capacitor element in which a dielectric oxide film is formed in a sintered body composed of valve metal powder, and further external cladding composed of resin is applied. After the cathode layer is formed before the external cladding composed of resin is applied, or after the external cladding composed of resin is applied, aging is performed in an atmosphere that a peripheral temperature is 20 to 90°C and humidity is 50 to 95% RH. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a solid electrolytic capacitor, and particularly to an aging method for reducing leakage current.

  An electrolytic capacitor is a so-called wound electrolytic capacitor in which an electrolytic solution is impregnated or a solid electrolyte is held in a capacitor element formed by winding an anode foil and a cathode foil made of aluminum or the like through a separator, and tantalum fine powder There is known a sintered type electrolytic capacitor in which a solid electrolyte layer is formed on the surface of a capacitor element formed by sintering.

  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, polyaniline, or derivatives thereof. Among them, polythiophene has higher conductivity and particularly excellent thermal stability than polypyrrole and polyaniline. Has attracted attention in recent years.

  A method for manufacturing such a solid electrolytic capacitor is disclosed in Japanese Patent Application Laid-Open No. 2000-331889. That is, in Japanese Patent Laid-Open No. 2000-331889, a capacitor element in which a dielectric oxide film is formed on a sintered body made of a valve action metal, and a conductive polymer layer and a cathode layer are sequentially laminated on the dielectric oxide film, It describes that an aging treatment is performed by applying a voltage 1.5 to 2.0 times the rated voltage in a high temperature atmosphere in a solid electrolytic capacitor in which an exterior made of resin is formed and then subjected to an aging treatment.

JP 2000-331889 A

  As disclosed in Japanese Patent Application Laid-Open No. 2000-331889, a solid electrolytic capacitor is known to have an increased leakage current value after resin molding. This is presumably because when a conductive polymer is formed on the capacitor element or when the exterior is made of resin, pressure is applied to the dielectric oxide film, and an insulation defect occurs in the dielectric oxide film. For this reason, the leakage current is reduced by aging and repairing and forming fine defects in the dielectric oxide film.

  However, although the conventional aging method can reduce the leakage current to some extent, in recent years, it is required to further reduce the leakage current.

  That is, in order to repair and form a defective portion of the dielectric oxide film, a supply source for supplying oxygen to the defective portion is required. However, when the conductive polymer is a solid electrolyte, Since the oxygen supply source is poor, the aging effect is not great. For this reason, the conventional aging method cannot sufficiently satisfy the recent demand for reducing the leakage current.

  Therefore, the inventors first formed a conductive polymer layer on the capacitor element and then performed aging by immersing the capacitor element in an electrolytic solution. When the leakage current was measured in the state of the capacitor element, It was confirmed that the current can be reduced. However, when a carbon layer and a silver paste layer were subsequently formed on the capacitor element and an external terminal was attached, it was found that the leakage current increased again.

  This is presumably because the heat and mechanical stress applied during the formation of the carbon layer and the silver paste layer became stress, and a defective portion was generated again in the dielectric oxide film of the capacitor element.

  The inventors have further studied, and after forming a cathode layer composed of a carbon layer and a silver layer on the capacitor element, studied an aging method capable of reducing leakage current.

  As an attempt, after forming a carbon layer or silver paste layer, aging was performed in the electrolytic solution, but when immersed in the electrolytic solution, the silver paste layer applied to the capacitor element was deteriorated, and the conductivity of the silver paste layer was increased. It was revealed that it was not practical because of the loss.

  Accordingly, the inventors have studied the aging method in a gas atmosphere under various conditions, and as a result, have come up with a manufacturing method capable of reducing the leakage current of the solid electrolytic capacitor.

  In this invention, as a method of manufacturing a solid electrolytic capacitor, a solid electrolyte layer and a cathode layer made of a conductive polymer are formed on a capacitor element in which a dielectric oxide film is formed on a sintered body made of valve metal powder, and a resin In the method for producing a solid electrolytic capacitor having an outer package made of aging, after forming the cathode layer and before applying the outer package made of resin, aging is performed in an atmosphere having an ambient temperature of 20 to 90 ° C. and a humidity of 50 to 95% RH. It is characterized by having gone.

  In the anodizing step and the cathode layer forming step (carbon / silver coating step), it is considered that a fine defect exists in the anodized film layer. In the aging process, it is conceivable that this fine defect portion is repaired and formed, but it is considered that this repair formation is efficiently performed due to the presence of moisture.

  After the cathode layer is formed, when aging is performed in an atmosphere at an ambient temperature of 20 to 90 ° C. and a humidity of 50 to 95% RH, the capacitor element is directly exposed to a high humidity atmosphere, so that the aging takes a short time. It ends with.

  Further, the method for producing a solid electrolytic capacitor of the present invention includes forming a solid electrolyte layer and a cathode layer made of a conductive polymer on a capacitor element in which a dielectric oxide film is formed on a sintered body made of a valve metal powder, A method for producing a solid electrolytic capacitor having a resin exterior, wherein the resin is subjected to aging in an atmosphere having an ambient temperature of 20 to 90 ° C. and a humidity of 50 to 95% RH. To do.

  When aging is performed after the resin sheath is applied, moisture is difficult to reach the capacitor element due to the sheathed resin, but in a high temperature and high humidity atmosphere such as an ambient temperature of 20 to 90 ° C. and a humidity of 50 to 95% RH. Then, it is considered that there is a slight amount of moisture that reaches the capacitor element. Therefore, although the time for aging to reach a predetermined leakage current is long, aging is performed after applying mechanical stress due to the resin sheath, so the leakage current as a solid electrolytic capacitor is Lower than when aged prior to formation.

  From the viewpoint of the presence of moisture, aging in an electrolytic solution using water as a solvent is considered to be equivalent, but in the gas state and the liquid state, the water molecules in the gas state are smaller, so the fineness of the anodized film is small. It is presumed that water molecules easily reach the defective part and the repairability is improved. Moreover, since it is water which contacts a silver paste layer, it also confirmed that deterioration of the silver paste layer by the solute component of electrolyte solution like the aging in electrolyte solution did not generate | occur | produce.

  Manufacture of a solid electrolytic capacitor in which a solid electrolyte layer and a cathode layer made of a conductive polymer are formed on a capacitor element in which a dielectric oxide film is formed on a sintered body made of a valve metal powder, and further, an exterior made of a resin is applied. In the method, after the cathode layer is formed and before the exterior made of resin is applied, the leakage current of the solid electrolytic capacitor is reduced by performing aging in an atmosphere having an ambient temperature of 20 to 90 ° C. and a humidity of 50 to 95% RH. It can be reduced efficiently. In particular, by aging the capacitor element by exposing it to a high temperature and high humidity atmosphere, moisture can be sufficiently supplied to the capacitor element, and leakage current can be reduced by aging in a short time.

  Manufacture of a solid electrolytic capacitor in which a solid electrolyte layer and a cathode layer made of a conductive polymer are formed on a capacitor element in which a dielectric oxide film is formed on a sintered body made of a valve metal powder, and further, an exterior made of a resin is applied. In the method, after the exterior made of resin is applied, the leakage current of the solid electrolytic capacitor can be reduced by performing aging in an atmosphere having an ambient temperature of 20 to 90 ° C. and a humidity of 50 to 95% RH. In particular, by performing aging after the resin coating is applied to the capacitor element, it is possible to repair the insulation defect portion of the dielectric oxide film on the capacitor element generated by applying to the capacitor element during the resin coating. High current reduction effect.

Next, an embodiment of the present invention will be described.

  Niobium fine powder is molded into a rectangular parallelepiped shape and sintered to form a porous sintered body. An anode lead wire 8 made of niobium is implanted in the sintered body and led out to the outside. This sintered body is immersed in an aqueous phosphoric acid solution, anodized, and a dielectric oxide film is formed on the surface of niobium to obtain capacitor element 1.

  In order to form such a capacitor element 1, a powder of a valve action metal such as aluminum, tantalum, or titanium can be used in addition to niobium.

  In order to form the conductive polymer layer 2 to be a solid electrolyte layer on the capacitor element 1, first, the capacitor element 1 is immersed in a polymerizable monomer solution. The polymerizable monomer solution is obtained by diluting 3,4-ethylenedioxythiophene with isopropyl alcohol at a predetermined ratio. By diluting, the viscosity of the polymerizable monomer solution becomes low, and the polymerizable monomer is easily impregnated into the capacitor element 1. The capacitor element 1 is immersed in the polymerizable monomer solution for about 30 seconds to 1 minute.

  After the capacitor element 1 is immersed in the polymerizable monomer solution for a predetermined time, the capacitor element 1 is pulled up from the polymerizable monomer solution, and then the capacitor element 1 is immersed in the oxidant solution. As the oxidizing agent solution 12, a solution obtained by dissolving a persulfate such as ammonium persulfate or a sulfonate in a predetermined solvent such as pure water can be used.

  By dipping in the oxidant solution, the polymerizable monomer comes into contact with the oxidant, and the polymerization of the polymerizable monomer starts to proceed. The conductive polymer can be formed inside the capacitor element 1 by the process as described above.

  And the capacitor | condenser element which complete | finished superposition | polymerization of the conductive polymer is wash | cleaned with the flowing water by a pure water. Thereafter, the capacitor element is dried, and one polymerization is completed.

  Next, the steps from immersion in the polymerizable monomer solution to drying are repeated a predetermined number of times to form the conductive polymer layer 2 inside and on the surface of the capacitor element 1.

  Furthermore, after performing pure water washing and drying, a carbon layer 3 and a silver paste layer 4 are formed on the conductive polymer layer 2. Further, the anode lead wire 5 is welded to the anode lead wire 8 and the cathode lead wire 6 is attached on the silver paste layer 4 using a silver adhesive.

  Next, the capacitor element 1 to which the anode lead wire 5 and the cathode lead wire 6 are joined is aged in an environment having an ambient temperature of 20 to 95 ° C. and a humidity of 50% RH or more. As conditions for the ambient temperature, a higher temperature is preferable, but when it exceeds 95 ° C, it becomes difficult to maintain a high humidity state, and therefore a range of 70 to 95 ° C is preferable.

  Moreover, it is preferable that humidity is also a high-humidity condition, and since the effect of water | moisture content is little at the humidity below 50% RH, the reduction effect of leakage current is small. In particular, a humidity of 70% RH or higher is preferable. Under a humidity condition of 70% RH or higher, variation in leakage current among individual solid electrolytic capacitors is reduced.

  Aging is performed by applying a voltage 1.5 to 2.0 times the rated voltage. In the aging, the capacitor element 1 to which the anode lead wire 5 and the cathode lead wire 6 are joined is left in an environment having an ambient temperature of 20 to 95 ° C. and a humidity of 50% RH or more for a predetermined time. It is preferable to start applying the voltage after the temperature has risen. Since the aging current has a relatively large number of insulation defects in the dielectric oxide film of the capacitor element 1 at the beginning of aging, a relatively large current flows to repair the aging current, but the repair of the insulation defects proceeds. As it goes on, the aging current also decreases. However, since there is also a current flowing through the dielectric oxide film itself, the aging current does not become completely zero, but shows a substantially constant value. Therefore, it is preferable to perform the aging time until the aging current flowing during aging decreases to a predetermined value. This aging time varies depending on the frequency of defects in the film of the capacitor element.

  Then, the resin is coated with the exterior resin 7 and the anode lead wire 5 and the cathode lead wire 6 are bent along the exterior resin 7 to obtain a solid electrolytic capacitor.

  Aging is performed by applying a resin sheath to the capacitor element to complete the solid electrolytic capacitor, and then leaving it in an environment with an ambient temperature of 20 to 95 ° C. and a humidity of 50% RH or more for a predetermined time, and the inside of the capacitor element rises to the ambient temperature. After that, it is preferable to apply an aging voltage.

  In the environment of high temperature and high humidity as described above, even if the capacitor element is resin-coated, moisture slightly reaches the capacitor element through the gap between the external terminal and the outer resin or the outer resin itself. It is considered a thing. Therefore, it becomes an oxygen supply source for repairing the dielectric oxide film, and the leakage current is reduced. In such a high temperature and high humidity environment, an epoxy resin is suitable as the exterior resin that easily transmits moisture.

Next, specific examples of the present invention will be described.
As Example 1, a niobium capacitor having a case size of 7.3 × 4.3 × 2.8 mm was obtained according to the manufacturing method described above. The rated voltage is 2.5V and the rated capacitance is 220 μF.
In this manufacturing process, an aging treatment was performed after a solid electrolyte layer was formed on the capacitor element, and an anode lead wire and a cathode lead wire were joined to the capacitor element.
As the aging treatment, the capacitor element joined with the external lead wire is left in an atmosphere of 85 ° C. and 90% RH for 30 minutes, and after the capacitor element rises to the same temperature as the ambient temperature, a voltage of DC 3.5V is applied. Aging was performed. This aging was performed until the aging current flowing through the solid electrolytic capacitor during aging became a substantially constant value.
Then, after finishing the aging treatment, a resin sheath was further applied to complete a solid electrolytic capacitor.

As Example 2, a niobium capacitor having a case size of 7.3 × 4.3 × 2.8 mm was obtained according to the manufacturing method described above. The rated voltage is 2.5V and the rated capacitance is 220 μF.
In this manufacturing process, after the capacitor element was resin-sealed, an aging treatment was performed. As the aging treatment, the solid electrolytic capacitor is left in an atmosphere of 85 ° C. and 90% RH for 120 minutes, and after the solid electrolytic capacitor rises to the same temperature as the ambient temperature, a voltage of DC 3.5V is applied to perform aging. went. This aging was performed until the aging current flowing through the solid electrolytic capacitor during aging became a substantially constant value.

(Conventional example)
As a conventional example, the same capacitor element as in Example 1 was aged at 85 ° C. in an air atmosphere. The conventional example was performed under the same conditions as in Example 1 except for the aging atmosphere.

The capacitance and leakage current of the solid electrolytic capacitors of Examples 1 and 2 and the conventional example were measured. The leakage current is a value 5 minutes after applying the rated voltage.
The results are shown in Table 1 below. Note that the number of samples is 10 in each of Example 1, Example 2, and the conventional example.

  As can be seen from this result, the leakage currents of Example 1 and Example 2 are greatly reduced as compared with the conventional example. Moreover, in Example 1 and Example 2, the leakage current of the solid electrolytic capacitor is smaller in Example 2. However, it can be seen that the aging time (time until the aging current becomes a substantially constant value) is shorter in the first embodiment than in the second embodiment.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Conductive polymer layer 3 Carbon layer 4 Silver paint layer 5 Anode lead terminal 6 Cathode lead terminal 7 Resin exterior layer

Claims (2)

Manufacture of a solid electrolytic capacitor in which a solid electrolyte layer and a cathode layer made of a conductive polymer are formed on a capacitor element in which a dielectric oxide film is formed on a sintered body made of a valve metal powder, and further, an exterior made of a resin is applied. In the method
A method for producing a solid electrolytic capacitor, characterized in that aging is performed in an atmosphere at an ambient temperature of 20 to 90 ° C. and a humidity of 50 to 95% RH after forming a cathode layer and before applying an exterior made of resin. Manufacture of a solid electrolytic capacitor in which a solid electrolyte layer and a cathode layer made of a conductive polymer are formed on a capacitor element in which a dielectric oxide film is formed on a sintered body made of a valve metal powder, and further, an exterior made of a resin is applied. In the method
A method for producing a solid electrolytic capacitor, characterized by performing aging in an atmosphere at an ambient temperature of 20 to 90 ° C. and a humidity of 50 to 95% RH after applying an exterior made of resin.