Abstract:
A capacitor has a capacitor element, a packaging material, and a sealing material. The capacitor element has an anode foil coupled to an anode terminal, a cathode foil coupled to a cathode terminal, a separator, and an electrolyte layer. The anode foil, the cathode foil and the separator are rolled together. The separator is between the anode foil and the cathode foil. The electrolyte layer is formed between the anode foil and the cathode foil. The packaging material has an opening and packages the capacitor element. The sealing material has a through hole where the anode terminal and the cathode terminal pass through and seals the opening of the packaging material. A given space is provided between the sealing material and the capacitor element. A stopper for securing the space is provided on at least one of the anode terminal and the cathode terminal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention generally relates to a capacitor used in an electronic device and a manufacturing method of the same.  
         [0003]     2. Description of the Related Art  
         [0004]     Recently, there are demands for enhancing capacitance of a capacitor, for downsizing the capacitor, for lowering electrical power consumption of the capacitor and for lowering impedance at high frequencies of the capacitor, as electronics devices are digitalized. A roll-formed electrolytic capacitor is known. The capacitor has a structure in which a capacitor element is packaged in a case such as aluminum case or a resin case having a cylindrical shape and having a bottom, and an opening of the case is sealed.  
         [0005]     Japanese Patent Application Publication No. 2000-114118 (hereinafter referred to as Document 1) and Japanese Patent Application Publication No. 11-3840 (hereinafter referred to as Document 2) disclose a method of putting an epoxy resin or a method of resistance welding with use of an airtight metal, as the sealing method. And the opening is sealed with a sealing material such as a rubber, because the rubber is inexpensive, has sealing activity and has humidity resistance.  
         [0006]     It is necessary to reduce a leakage current from the capacitor as much as possible, because there is a demand for lowering the electrical power consumption of the capacitor. And so, a tab terminal is welded to the electrode foil and a rolled element is energized in an electrolytic solution. The electrode foil and the tab terminal are subjected to a chemical conversion treatment. And the leakage current is reduced. Japanese Patent Application Publication NO. 2001-284175 (hereinafter referred to as Document 3) discloses a method of coating an insulating resin to the tab terminal.  
         [0007]     However, a load intends to be applied to the terminal when the resin is enclosed or the resistance welding is processed, in accordance with the arts of Document 1 and Document 2. Effect of coated layer is reduced because the sealing material limits impregnation of the electrolytic solution to the electrode foil and the terminal, when a chemical coated layer is formed on the electrode foil and the terminal. And a pressure applied to the electrode foil and the terminal breaks the chemically treated layer when the sealing material is put into, in a case where the sealing material is put into after the coated layer is formed. And it is possible that the leakage current is increased. The same goes for the art of Document 3.  
         [0008]     There is a case where the capacitor is subjected to a heat of more than 200 degrees C. as in the case of soldering reflow for few seconds to few minutes. In this case, it is possible that the leakage current is increased and defective appearance is brought about by the deformation of the sealing material, because the inner pressure is increased by the decomposition of the electrolyte and a pressure is applied to the element by the expansion of the sealing material.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides a capacitor limiting an increase of leakage current.  
         [0010]     According to an aspect of the present invention, preferably, there is provided a capacitor including a capacitor element, a packaging material, and a sealing material. The capacitor element has an anode foil coupled to an anode terminal, a cathode foil coupled to a cathode terminal, a separator, and an electrolyte layer. The anode foil, the cathode foil and the separator are rolled together. The separator is between the anode foil and the cathode foil. The electrolyte layer is formed between the anode foil and the cathode foil. The packaging material has an opening and packages the capacitor element. The sealing material has a through hole where the anode terminal and the cathode terminal pass through and seals the opening of the packaging material. A given space is provided between the sealing material and the capacitor element. A stopper for securing the space is provided on at least one of the anode terminal and the cathode terminal.  
         [0011]     With the above-mentioned configuration, the space provided between the sealing material and the capacitor element can absorb the expansion of the sealing material caused by a thermal load. And it is possible to restrain the contact of the sealing material and the capacitor element effectively because the stopper is provided. And it is possible to restrain that the capacitor element is subjected to a stress from the sealing material. And it is possible to restrain a break of the edge portion of the anode foil. And the space between the sealing material and the capacitor element absorbs the inner pressure increased because of the vaporization of the solvent remaining in the capacitor element. In this case, it is possible to limit the deformation of the sealing material. And it is possible to limit the increase of the leakage current of the capacitor and defective appearance caused by the deformation of the sealing material.  
         [0012]     According to an aspect of the present invention, preferably, there is provided a manufacturing method. The method includes rolling an anode foil coupled to an anode terminal, a cathode foil coupled to a cathode terminal and a separator together, inserting the anode terminal and the cathode terminal into a sealing material, providing a given space between the sealing material and the anode and the cathode terminals, subjecting the anode terminal, the anode foil, the cathode terminal and the cathode foil to a chemical conversion treatment, forming an electrolyte layer between the anode foil and the cathode foil and thus fabricating the capacitor element, packaging the capacitor element in a packaging material having an opening, and sealing the opening with the sealing material. The separator is between the anode foil and the cathode foil. A stopper for securing the space is provided on at least one of the anode terminal and the cathode terminal.  
         [0013]     With the above-mentioned configuration, the anode foil, the cathode foil and the separator are rolled together. The anode terminal and the cathode terminal are inserted into the sealing material. The space is provided between the sealing material and each electrode foil. The anode terminal, the anode foil, the cathode terminal and the cathode foil are subjected to a chemical conversion treatment. The electrolyte layer is formed between the anode foil and the cathode foil and thus the capacitor element is fabricated. The capacitor element is packaged in the packaging material and the opening is sealed with the sealing material. In this case, an oxide layer is formed on the metal exposed on an end surface (the edge portion) or on an exposed metal surface caused by a chip because of the terminal connection of the anode foil. And it is possible to put the electrolytic solution to the anode terminal sufficiently,because the space is provided between the sealing material and each electrode foil. And it is possible to form an oxide layer on the surface of the anode terminal. Therefore it is possible to limit the increase of the leakage current of the capacitor.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Preferred embodiments of the present invention will be described in detail with reference to the following drawings, wherein:  
         [0015]      FIG. 1A  and  FIG. 1B  illustrate a roll formed capacitor in accordance with a first embodiment of the present invention;  
         [0016]      FIG. 2A  through  FIG. 2D  illustrate details of an anode terminal;  
         [0017]      FIG. 3A  through  FIG. 3D  illustrate a manufacturing flow of the capacitor in accordance with the first embodiment;  
         [0018]      FIG. 4A  through  FIG. 4C  illustrate a manufacturing flow of the capacitor in accordance with the first embodiment;  
         [0019]      FIG. 5  illustrates an external view of a capacitor in accordance with a second embodiment of the present invention;  
         [0020]      FIG. 6A  and  FIG. 6B  illustrate a partially cutout cross sectional view of the capacitor in accordance with the second embodiment;  
         [0021]      FIG. 7A  through  FIG. 7C  illustrate a manufacturing flow of the capacitor in accordance with the second embodiment; and  
         [0022]      FIG. 8A  through  FIG. 8C  illustrate another manufacturing flow of the capacitor in accordance with the second embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     A description will now be given, with reference to the accompanying drawings, of embodiments of the present invention.  
       First Embodiment  
       [0024]      FIG. 1A  and  FIG. 1B  illustrate a roll formed capacitor  100  in accordance with a first embodiment of the present invention.  FIG. 1A  and  FIG. 1B  illustrate a partially cutout cross sectional view of the capacitor  100 .  FIG. 1A  illustrates a front view of the capacitor  100 .  FIG. 1B  illustrates a side view of the capacitor  100 . As shown in  FIG. 1A  and  FIG. 1B , the capacitor  100  has a structure in which a capacitor element  20  is packaged in a metal case  10 . The metal case  10  has a cylindrical shape and has a bottom.  
         [0025]     The capacitor element  20  is a cylindrical capacitor element, in which an anode foil  21 , a cathode foil  22  and a separator  23  are rolled together, the separator  23  being between the anode foil  21  and the cathode foil  22 . An electrolyte layer  24  is formed between the anode foil  21  and the separator  23  and is formed between the cathode foil  22  and the separator  23 . The anode foil  21  and the cathode foil  22  are composed of a metal such as aluminum, tantalum, niobium, or titanium. The cathode foil  22  may be composed of a metal as same as that of the anode foil  21 . The cathode foil  22  may be composed of a metal material having a valve metal deposited on the surface thereof or a metal material having a carbon absorbed to the surface thereof. In the embodiment, the anode foil  21  and the cathode foil  22  are composed of an aluminum having a dielectric oxide layer formed on the surface thereof.  
         [0026]     The separator  23  may be a cellulose electrolytic paper mainly formed of manila hemp or may be a nonwoven fabric mainly formed of such as acrylic resin, polyethylene terephthalate (PET). The separator  23  may be a mixture of the nonwoven and the cellulose electrolytic paper. In the embodiment, the separator  23  is composed of an electrolytic paper mainly formed of manila hemp. In this case, it is possible to fill the separator  23  with an electrolyte, because the manila hemp is carbonized in a thermal treatment in a chemical conversion treatment and a density of the manila hemp is reduced.  
         [0027]     The electrolyte layer  24  may be an electrolytic solution in which a carboxylic acid is solved in a solvent such as water or may be a complex salt such as TCNQ complex. In the embodiment, the electrolyte layer  24  may be composed of a conductive polymer that has a low resistance and is stable in a high temperature condition. The conductive polymer may be a polymer of polyethylene dioxythiophene or the like. In this case, a resistivity and ESR of the capacitor  100  is reduced.  
         [0028]     The capacitor element  20  has an anode terminal  30  and a cathode terminal  40  acting as electrode extracting portion. The anode terminal  30  is coupled to the anode foil  21 . The cathode terminal  40  is coupled to the cathode foil  22 . A description will be given later of the anode terminal  30  and the cathode terminal  40 .  
         [0029]     The metal case  10  is composed of a metal material that can be formed into a cylinder having a bottom. In the embodiment, the metal case  10  is composed of aluminum that is inexpensive and can be processed easily. A concave portion  12  is formed along a circumference near an opening of the metal case  10 . The opening of the metal case  10  is filled with a sealing material  11 . The sealing material  11  is fixed by the concave portion  12 . The metal case  10  is sealed with the sealing material  11 . Two through holes are formed in the sealing material  11 . The anode terminal  30  passes through one of the through holes, and the cathode terminal  40  passes through the other. And the anode terminal  30  and the cathode terminal  40  are extracted outside of the metal case  10 .  
         [0030]     The sealing material  11  may be composed of a metal that can be resistance-welded with the metal case  10  or may be composed of epoxy resin or the like being formed easily. In the embodiment, a rubber is used as the sealing material  11 . In this case, a drawing process or a curling process is possible and airtightness of the sealing material  11  is secured. The rubber may be a rubber composed of isobutylene-isopropylene copolymer (IIR), ethylene-propylene copolymer (EPT), or a blend of the IIR and the EPT.  
         [0031]     Airspace of approximately 1.0 mm to 3.0 mm is provided between the sealing material  11  and the capacitor element  20 . In this case, it is possible to absorb an expansion of the sealing material  11  caused by a thermal load or the like. And it is possible to restrain that the sealing material  11  presses the capacitor element  20 . It is therefore possible to restrain that a defect is formed in a dielectric oxide layer at an edge portion of the anode foil  21 . The airspace between the sealing material  11  and the capacitor element  20  absorbs an inner pressure caused by a vaporization of a solvent remaining in the capacitor element  20 . In this case, it is possible to restrain a deformation of the sealing material  11 . And it is possible to limit an increase of a leakage current of the capacitor  100 .  
         [0032]     Next, a description will be given of the anode terminal  30 , with reference to  FIG. 1A ,  FIG. 1B  and  FIG. 2A  through  FIG. 2D .  FIG. 2A  through  FIG. 2D  illustrate details of the anode terminal  30 .  FIG. 2A  illustrates a side view of the anode terminal  30 .  FIG. 2B  illustrates a bottom view of the anode terminal  30  viewing from a reduced portion  31  side.  FIG. 2C  illustrates a top view of the anode terminal  30  viewing from a lead portion  33  side.  FIG. 2D  illustrates a front view of the anode terminal  30 .  
         [0033]     As shown in  FIG. 2A  and  FIG. 2D , the anode terminal  30  has a tab terminal structure. In detail, the anode terminal  30  has the reduced portion  31 , a round bar portion  32 , and the lead portion  33 . The round bar portion  32  and the lead portion  33  are coupled through a welding portion  34 . The reduced portion  31  and the round bar portion  32  are composed of a material as same as that of the anode foil  21 . An oxide layer may be formed on a surface of the reduced portion  31  and the round bar portion  32  with a chemical conversion treatment, as is case of the anode foil  21 . An insulating resin such as polyimide may be coated on the surface of the reduced portion  31  and the round bar portion  32 . In the embodiment, the reduced portion  31  and the round bar portion  32  are composed of aluminum of which surface is subjected to a chemical conversion treatment. The lead portion  33  is composed of a copper wire of which surface is subjected to a tinned treatment.  
         [0034]     The reduced portion  31  has a stopper  35  and a connector  36  in order from the round bar portion  32  side. The stopper  35  is positioned between the sealing material  11  and the capacitor element  20 , in the capacitor  100 . The stopper  35  has a width larger than a diameter of the round bar portion  32 , as shown in  FIG. 2D . In this case, it is possible to restrain the contact of the sealing material  11  and the capacitor element  20 , even if the sealing material  11  expands because of a thermal load. It is therefore possible to restrain that a defect is formed in the dielectric oxide layer at the edge portion of the anode foil  21 . The connector  36  has a plate shape. The anode terminal  30  is coupled to the anode foil  21  through the connector  36 .  
         [0035]     The width of the stopper  35  is, preferably, more than 1.2 times of the diameter of the round bar portion  32 . The thickness of the stopper  35  is, preferably, 2.5 times of that of the connector  36 . In this case, it is possible to fabricate the capacitor  100  stably. It is possible to limit an influence of the increase of the inner pressure caused by the vaporization of the remaining solvent. And it is possible to restrain the contact of the sealing material  11  and the capacitor element  20  caused by the expansion of the sealing material  11 . In addition, it is possible to form the stopper  35  by reducing a part of the round bar portion  32 . It is possible to form the connector  36  by reducing a part of the stopper  35 .  
         [0036]     The cathode terminal  40  has a structure as same as that of the anode terminal  30 . In the embodiment, the reduced portion  31  and the round bar portion  32  of the cathode terminal  40  are composed of aluminum of which surface is subjected to the chemical conversion treatment. The lead portion  33  of the cathode terminal  40  is composed of a copper wire of which surface is subjected to a tinned treatment.  
         [0037]     Next, a description will be given of a manufacturing method of the capacitor  100 .  FIG. 3A  through  FIG. 3D  and  FIG. 4A  through  FIG. 4C  illustrate a manufacturing flow of the capacitor  100 . As shown in  FIG. 3A , the connector  36  of the anode terminal  30  is coupled to the anode foil  21 . The connector  36  of the cathode terminal  40  is coupled to the cathode foil  22 . In this case, it is possible to use an ultra sonic welding method, a resistance welding method, a caulking press method or the like. In the embodiment, the caulking press method is used. In this case, more metallurgical bonds are formed between the connector and the electrode foil. And the connector and the electrode foil are strong against an external force loaded in the rolling. It is therefore possible to limit a resistance change. Next, as shown in  FIG. 3B , the anode foil  21 , the cathode foil  22  and the separator  23  are rolled together, the separator  23  being between the anode foil  21  and the cathode foil  22 . Then, as shown in  FIG. 3C , the round bar portion  32  of the anode terminal  30  and the cathode terminal  40  are inserted into the through holes of the sealing material  11 . And airspace is provided between the sealing material  11  and each electrode foil.  
         [0038]     Next, as shown in  FIG. 3D , the anode foil  21 , the cathode foil  22 , the anode terminal  30  and the cathode terminal  40  are energized in an electrolytic solution and are subjected to a chemical conversion treatment. A dissolved substance in the electrolytic solution is, for example phosphoric acid that is conductive in an aqueous solution. In the embodiment, ammonium adipate is used as the electrolytic solution. The chemical conversion treatment is carried out at a voltage near a formation voltage of a dielectric oxide layer, using chemical liquid mainly containing 0.5% to 2% ammonium adipate. After that, a thermal treatment is carried out and the chemical conversion treatment is carried out few times. It is therefore possible to form a strong dielectric oxide layer. The thermal treatment is carried out in temperature range 200 degrees C. to 320 degrees C. for few minutes to few tens of minutes.  
         [0039]     An oxide layer is therefore formed on the valve metal exposed on an end surface (the edge portion) or on an exposed metal surface caused by a chip because of the terminal connection of the anode foil  21 . And it is possible to put the anode terminal  30  in the electrolytic solution sufficiently, because the airspace is provided between the sealing material  11  and the each electrode foil. It is therefore possible to form the oxide layer on the surface of the anode terminal  30  sufficiently. Accordingly, it is possible to limit the increase of the leakage current of the capacitor  100 .  
         [0040]     In the chemical conversion treatment, an oxide layer is formed on the surface of the cathode foil  22  and the cathode terminal  40 . The insulation property of the cathode foil  22  and the cathode terminal  40  is, however, independent of the leakage current of the capacitor  100 . Therefore, the oxide layer may not be formed on the surface of the cathode foil  22  and the cathode terminal  40 .  
         [0041]     Next, as shown in  FIG. 4A , polymerizable monomers and an oxidizing reagent are impregnated into the separator  23 , and the electrolyte layer  24  is formed. The electrolyte layer  24  is composed of a conductive polymer of polyethylene dioxythiophene. It is possible to form the conductive polymer by polymerizing polymerizable polymer such as 3,4-ethylene dioxythiophene with use of an oxidizing reagent.  
         [0042]     Instead of the polymerizable monomer, a monomer solution, in which the polymerizable monomer and a volatility liquid solution are blended at a ratio 1:1 to 1:3, can be used. The volatility liquid may be hydrocarbon such as pentane, ether such as tetrahydrofuran, ester such as ethyl formate, ketone such as acetone, alcohol such as methanol, nitrogen compound such as acetonitrile, a mixture thereof. It is preferred to use methanol, ethanol or acetone.  
         [0043]     It is possible to use ferric p-toluene sulfonate, a mixture of ferric p-toluene sulfonate and ferric dodecylbenzenesulfonate, or a mixture of ferric p-toluene sulfonate and ferric methoxybenzenesulfonate or the like that are dissolved in a solvent and are suitable for formation of a polymer having high conductivity, as the oxidizing reagent. In particular, in a case where a mixed oxidizing reagent like the latter two examples is used, dopants in the polymer is stabilized and the heat resistance is stabilized. It is preferable to use butanol or a mixture of butanol and alcohol having more than one carbon as the solvent mentioned above. In this case, oxidizing reagent elements are dispersed and polymerization reaction of the polymerizable monomer is promoted. And it is possible to shorten polymerization time.  
         [0044]     The ratio of the solvent mentioned above and the acid ferric may be optional. It is preferable to use a liquid solution containing 40% to 70% of the acid ferric by weight. In this case, the concentration of the oxidizing reagent is high. And a polymer that is denser and has a high yield point, is formed through the polymerization reaction of the polymerizable monomer mentioned above. The conducting polymer therefore excels in conductivity. And it is possible to reduce the ESR. In addition, preferably the compounding ratio of the polymerizable monomer and the oxidizing reagent is 1:3 to 1:6.  
         [0045]     After the polymerization, the capacitor element  20  is subjected to a thermal treatment. The thermal treatment is carried out in a temperature of 240 degrees C. to 320 degrees C. for 3 minutes to 20 minutes. In this case, it is possible to eliminate the monomer, the oxidizing reagent, and the solvent dissolving the monomer and the oxidizing reagent not used in the polymerizing reaction. It is therefore possible to limit the increase of the inner pressure caused by the vaporization of the solvent or the like. Accordingly, it is possible to limit the deformation of the metal case  10  and the sealing material  11 .  
         [0046]     Next, as shown in  FIG. 4B , the capacitor element  20  is packaged in the metal case  10 . Then, as shown in  FIG. 4C , the opening of the metal case  10  is filled with the sealing material  11 . The opening of the metal case  10  is subjected to a drawing process and a curling process. And the concave portion  12  is formed. In this case, a pressure is not applied to the capacitor element  20 , because airspace is provided between the sealing material  11  and the capacitor element  20 . It is therefore possible to restrain a break of the chemically treated layer of the anode foil  21 . Through the processes, the capacitor  100  is fabricated.  
         [0047]     There is a case where the capacitor  100  is subjected to a heat of more than 200 degrees C. as in the case of soldering reflow for few seconds to few minutes. The dielectric oxide layer is, however, formed on the upper portion of the capacitor element  20 , the reduced portion  31  of the anode terminal  30  and the round bar portion  32  in the re-chemical conversion treatment. It is therefore possible to limit the leakage current even if the inner pressure is increased. The capacitor element  20  is subjected to a given voltage treatment at 120 degrees C. to 180 degrees C. If necessary, the lead portion  33  is processed, and the capacitor  100  is fabricated. For example, the lead portion  33  may be pressed and may be subjected to a bending process after a board is inserted, when the capacitor  100  is surface-mounted.  
         [0048]     In the embodiment, the metal case  10  corresponds to the packaging material. The round bar portion  32  corresponds to the first material. The connector  36  corresponds to the second material. The concave portion  12  corresponds to the first concave portion.  
       Second Embodiment  
       [0049]      FIG. 5  illustrates an external view of a capacitor  100   a  in accordance with a second embodiment of the present invention. As shown in  FIG. 5 , a concave portion  13  is formed along the circumference near the opening of the metal case  10 .  FIG. 6A  and  FIG. 6B  illustrate a partially cutout cross sectional view of the capacitor  10   a.    FIG. 6A  illustrates is a front view of the capacitor  100   a.    FIG. 6B  illustrates a side view of the capacitor  100   a.  As shown in  FIG. 6A  and  FIG. 6B , the capacitor  100   a  has the concave portion  13  between the sealing material  11  and the capacitor element  20  on the metal case  10 , being different from the capacitor  100  in  FIG. 1A  and  FIG. 1B .  
         [0050]     In this case, the sealing material  11  is fixed by the concave portion  12  and the concave portion  13 . It is therefore possible to restrain the contact of the sealing material  11  and the capacitor element  20  effectively, even if the sealing material  11  expands because of a thermal load. It is therefore possible to effectively restrain that a defect is formed in the dielectric oxide layer at the edge portion of the anode foil  21  and the cathode foil  22 . And it is possible to restrain the deformation of the sealing material  11  effectively.  
         [0051]     Next, a description will be given of a manufacturing method of the capacitor  100   a.    FIG. 7A  through  FIG. 7C  illustrate a manufacturing flow of the capacitor  100   a.  The capacitor element  20  is fabricated through the processes shown in  FIG. 3A  through  FIG. 3C  and  FIG. 4A . Next, the capacitor element  20  is packaged in the metal case  10  as shown in  FIG. 7A . Then, as shown in  FIG. 7B , the opening of the metal case  10  is filled with the sealing material  11 . A part of the metal case  10  between the sealing material  11  and the capacitor element  20  is subjected to a drawing process. The concave portion  13  is thus formed. In this case, a pressure is not applied to the capacitor element  20 , because airspace is provided between the sealing material  11  and the capacitor element  20 . It is therefore possible to restrain a break of the chemically treated layer of the anode foil  21  and the cathode foil  22 .  
         [0052]     Next, a part of the metal case  10 , where the sealing material  11  is provided, is subjected to a drawing process and a curling process as shown in  FIG. 7C . The concave portion  12  is thus formed. In this case, the sealing material  11  is fixed by the concave portion  12 . Through the processes mentioned above, the capacitor  100   a  is fabricated.  
         [0053]      FIG. 8A  through  FIG. 8C  illustrate another manufacturing flow of the capacitor  100   a.  The capacitor element  20  is fabricated through the processes shown in  FIG. 3A  through  FIG. 3C  and  FIG. 4A . Next, the capacitor element  20  is packaged in the metal case  10  as shown in  FIG. 8A . The concave portion  12  is formed on the metal case  10  through a drawing process in advance. Then, as shown in  FIG. 8B , the opening of the metal case  10  is filled with the sealing material  11 . The opening of the metal case  10  is subjected to a drawing process and a curling process. The concave portion  12  is thus formed. In this case, a pressure is not applied to the capacitor element  20 , because airspace is provided between the sealing material  11  and the capacitor element  20 . It is therefore possible to restrain a break of the chemically treated layer of the anode foil  21  and the cathode foil  22 . Through the processes mentioned above, the capacitor  100   a  is fabricated.  
         [0054]     In the embodiment, the concave portion  13  corresponds to the second concave portion.  
       EXAMPLES  
     Example  
       [0055]     In an example, the capacitor  100  shown in  FIG. 1  was manufactured. Aluminum foil, which was subjected to an etching treatment and a chemical conversion treatment, was used as the anode foil  21  and the cathode foil  22 . A copper material subjected to a tinned treatment was used as the lead portion  33  of the anode terminal  30  and the cathode terminal  40 . Aluminum was used as the reduced portion  31  and the round bar portion  32  of the anode terminal  30  and the cathode terminal  40 . An electrolytic paper mainly composed of a manila hemp was used as the separator  23 . Aluminum having a resin coated on both faces thereof was used as the metal case  10 . The IIR was used as the sealing material  11 . The normal rated voltage of the capacitor in accordance with the example is 2.5 WV.  
         [0056]     At first, the capacitor element  20  was fabricated. The anode foil  21  is coupled to the anode terminal  30 , and the cathode foil  22  was coupled to the cathode terminal  40  by a caulking press method. After that, the anode foil  21 , the cathode foil  22  and the separator  23  were rolled together, the separator being between the anode foil  21  and the cathode foil  22 . Each round bar portion  32  of the anode terminal  30  and the cathode terminal  40  was inserted to each of the through holes of the sealing material  11 . And the anode terminal  30  and the cathode terminal  40  were attached to the capacitor element  20 .  
         [0057]     The anode foil  21 , the cathode foil  22 , and each reduced portion  31  of the anode terminal  30  and the cathode terminal  40  were subjected to a chemical conversion treatment at a voltage near a formation voltage of the oxide layer of the anode foil  21  using chemical liquid mainly containing 0.5% to 2% ammonium adipate by weight, and were subjected to a thermal treatment in a temperature range 200 degrees C. to 320 degrees C. for 3 minutes to 20 minutes. The chemical conversion treatment and the thermal treatment were repeated 3 times to 7 times. The foils and the reduced portions were cleaned with purified water for more than 5 minutes, and were dried in an atmosphere of more than 100 degrees C. for 30 minutes to 90 minutes.  
         [0058]     Next, the electrolyte layer  24  was formed. 3,4-ethylene dioxythiophene and 1-butanol solution containing ferric p-toluene sulfonate were impregnated into the separator  23 . The separator  23  was kept 16 hours in the atmosphere in temperature range 40 degrees C. to 150 degrees C. The conductive polymer layer formed of polyethylene dioxythiophene was formed and the electrolyte layer  24  was formed. Next, the capacitor element  20  was subjected to a thermal treatment in a temperature range 240 degrees C. to 320 degrees C. for 3 minutes to 20 minutes. The capacitor element  20  was packaged in the metal case  10 . The metal case  10  was subjected to a drawing process. The metal case  10  was thus closed. After that, an aging treatment was carried out in an atmosphere of more than 125 degrees C. at more than 2.5 V. The capacitor  100  having 8 mm diameter and 11.5 mm length was fabricated.  
       Comparative Example  
       [0059]     In a comparative example, a capacitor not having airspace between the capacitor element  20  and the sealing material  11  was fabricated. At first, the anode foil  21 , the cathode foil  22  and the separator  23  were rolled together, the separator  23  being between the anode foil  21  and the cathode foil  22 . The sealing material  11  was compressed to the top face of the capacitor element  20 . The chemical conversion treatment was repeated. Other material and other processes were as same as those of the capacitor in accordance with the example mentioned above. The normal rated voltage of the capacitor in accordance with the comparative example is 2.5 WV.  
         [0000]     (Analysis)  
         [0060]     Table 1 shows an electrical capacitance at 120 Hz frequency, the tan δ, the ESR at 100 kHz frequency, the leakage current after energization of normal rated voltage two minutes of the capacitor in accordance with the example and the comparative example. Fifty capacitors in accordance with the example and the comparative example were fabricated, and each value in Table 1 shows average value thereof.  
                                                         TABLE 1                                   Electrical                       capacitance   tanδ   ESR   Leakage current           (μF)   (—)   (mΩ)   (μA/2 minutes)                                    Example   Ave 558.3   Ave 0.011   Ave 5.7   Ave 4.23           σ 27.7   σ 0.004   σ 0.55   σ 5.85       Comparative   Ave 560.2   Ave 0.010   Ave 5.5   Ave 31.4       example   σ 29.1   σ 0.004   σ 0.85   σ 124.0                  
 
         [0061]     As shown in Table 1, there was little difference between each electrical capacitance, between each tan δ and between each ESR. The dispersion and the average of the leakage current of the capacitor in accordance with the example were reduced considerably, compared to those of the capacitor in accordance with the comparative example.  
         [0062]     Airspace was provided between the sealing material  11  and the capacitor element  20  in the capacitor in accordance with the example, being different from the capacitor in accordance with the comparative example. And the electrolytic solution was provided to the reduced portion  31  and the round bar portion  32  sufficiently in the chemical conversion treatment. A strong dielectric oxide layer was formed on the surface of the reduced portion  31  and the round bar portion  32 . It is thought that the insulation property when a voltage was applied to the capacitor  100  was improved and accordingly the leakage current was reduced.  
         [0063]     Next, property change caused by a thermal load was measured. In detail, the capacitors in accordance with the example and the comparative example were impregnated into a solder bath (at 240 degrees C. for 90 seconds). The external views were measured and the leakage current after energization of normal rated voltage two minutes was measured. The results are shown in Table 2. Average values of fifty capacitors in accordance with the example and the comparative example are shown in Table 2. And external conditions after examination, average value Ave of the leakage currents, and dispersion a thereof are shown in Table 2.  
                                             TABLE 2                                   External condition   Leakage current           after thermal load   (μA/2 minutes)                                        Example   External deformation   Ave 20.23               is not remarkable. 50/50   σ 16.85           Comparative   Center of sealing member   Ave 470.8           example   is expanded a little. 6/50   σ 166.7               External deformation               is not remarkable. 44/50                      
 
         [0064]     As shown in Table 2, an increasing amount of the leakage current of the capacitor in accordance with the example was reduced, compared to the capacitor in accordance with the comparative example. The shape of the capacitor in accordance with the example was not changed remarkably after the thermal load, compared to the capacitor in accordance with the comparative example.  
         [0065]     The inner pressure of the metal case  10  was increased during the thermal load, because of the vaporization of the unreacted oxidizing reagent, the monomer, and the remaining solvent in the electrolyte. In the capacitor in accordance with the comparative example, the capacitor element  20  was stressed by the deformation of the sealing material  11  in addition to the increase of the inner pressure. Therefore, it is thought that the oxide layer on the edge of the anode foil  21  and the cathode foil  22  was broken, a defect was formed, and the leakage current was accordingly increased.  
         [0066]     In the capacitor in accordance with the example, the airspace was provided in the metal case  10 . And the vapor was absorbed in the airspace after the inner pressure was increased. Therefore, it is thought that the leakage current was not increased. And it is supposed that it is one of the reasons that the deformation of the sealing material  11  was limited because the sealing material  11  was held by the concave portion  12  and the reduced portion  31  in a substantially equal strength.  
         [0067]     As mentioned above, the initial leakage current was reduced in the capacitor in accordance with the example. And the increasing of the leakage current and the shape change were limited.  
         [0068]     While the preferred embodiments of the prevent invention have been illustrated in detail, the invention is not limited to the specific embodiments above. In addition, it will be appreciated that the invention is susceptible of modification, variation and change without departing from the proper and fair meaning of the accompanying claims.  
         [0069]     The present invention is based on Japanese Patent Application No. 2006-005440 filed on Jan. 12, 2006, the entire disclosure of which is hereby incorporated by reference.