JP6187899B2 - 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, and more particularly to a technique for forming a dielectric layer.

  The solid electrolytic capacitor includes a capacitor element, an exterior body that covers the capacitor element, an anode terminal, and a cathode terminal. The capacitor element includes an anode body made of a porous sintered body, an anode lead planted on the anode body, a dielectric layer formed on the surface of the anode body, and an electrolyte layer formed on the surface of the dielectric layer And a cathode layer formed on the outer peripheral surface of the electrolyte layer. Here, the anode body is formed by producing a molded body of valve metal powder in which anode leads are planted, and subjecting this molded body to heat treatment. By heat treatment of the molded body, the valve metal powder is sintered, and the valve metal powder existing on the surface of the anode lead is fused, whereby the anode body and the anode lead are integrated. The dielectric layer is formed by electrochemically oxidizing the surface of the valve metal constituting the anode body (the surface of the porous sintered body).

  The anode terminal is electrically connected to the anode lead, and the cathode terminal is electrically connected to the cathode layer. The exterior body is formed by, for example, a resin mold using a mold so that the anode terminal and the cathode terminal are pulled out from the exterior body.

  In the lead-type solid electrolytic capacitor as described above, stress tends to concentrate on a region of the anode body near the root of the anode lead when the terminal is attached to the capacitor element or during resin molding. For this reason, defects such as cracks are likely to occur in the dielectric layer in that region. Defects generated in the dielectric layer cause an increase in leakage current. Accordingly, it has been proposed to increase the thickness of the dielectric layer in such a region (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 02-277213

  However, during terminal mounting or resin molding, stress is likely to occur in the area including the end face opposite to the end face where the anode lead is planted in the anode body. It was easy to occur. For this reason, even if the technique described in Patent Document 1 is used, it is difficult to sufficiently suppress an increase in leakage current.

  Accordingly, an object of the present invention is to provide a solid electrolytic capacitor in which an increase in leakage current is suppressed and a method for manufacturing the same.

  The method for manufacturing a solid electrolytic capacitor according to the present invention includes steps (a) to (c). In the step (a), an anode body having a first end face on which an anode lead is planted and a second end face opposite to the first end face is prepared. In the step (b), in a state where the entire anode body is immersed in the first chemical conversion liquid, a first voltage is applied between the first chemical conversion liquid and the anode body, and thereby the conductive material constituting the anode body Oxidize the surface. After the step (b), in the step (c), the first region including the first end surface of the anode body is exposed on the liquid surface of the second chemical conversion solution, and the second region including the second end surface of the anode body is included. In a state where the region is immersed in the second chemical conversion solution, a second voltage larger than the first voltage is applied between the second chemical conversion solution and the anode body, and thereby, the surface of the conductive material is applied to the second region. Oxidize. In addition, process (a)-(c) respond | corresponds to the anode preparation process, 1st chemical conversion treatment process, and 2nd chemical conversion treatment process which are demonstrated by below-mentioned embodiment, respectively.

  According to the above manufacturing method, the average film thickness of the dielectric layer formed in the second region of the anode body in steps (b) and (c) is the same as that of the dielectric layer formed in the first region of the anode body. It becomes larger than the average film thickness. Therefore, the thickness of the dielectric layer is increased in the second region. Therefore, even when the anode body receives an external force during manufacture or use of the solid electrolytic capacitor and stress is generated in the second region of the anode body, defects such as cracks are hardly generated in the dielectric layer existing in the second region. As a result, an increase in leakage current is suppressed in the solid electrolytic capacitor.

  In the manufacturing method, in step (c), the liquid surface of the second chemical conversion liquid is adjusted to a position near the lower end surface of the anode lead, or between the lower end surface of the anode lead and the second end surface of the anode body. In the adjusted state, it is preferable to apply a second voltage between the second chemical conversion liquid and the anode body.

  The solid electrolytic capacitor according to the present invention includes an anode body, a dielectric layer, and an electrolyte layer. The anode body has a first end face on which the anode lead is planted, and a second end face opposite to the first end face. The dielectric layer is formed on the surface of the conductive material constituting the anode body. The electrolyte layer is formed on the dielectric layer. And the average film thickness of the dielectric layer in the 2nd area | region which contains a 2nd end surface among anode bodies is larger than the average film thickness of the dielectric layer in the 1st area | region including a 1st end surface among anode bodies.

  According to the solid electrolytic capacitor, the thickness of the dielectric layer is increased in the second region where stress is likely to occur in the anode body. Therefore, even when the anode body receives an external force during manufacture or use of the solid electrolytic capacitor and stress is generated in the second region of the anode body, defects such as cracks are hardly generated in the dielectric layer existing in the second region. Therefore, an increase in leakage current is suppressed.

  In the specific configuration of the solid electrolytic capacitor, the average film thickness of the dielectric layer in the region near the end of the anode lead located in the anode body in the second region is in the region near the outer peripheral surface in the first region. It is larger than the average film thickness of the dielectric layer.

  According to the solid electrolytic capacitor and the manufacturing method thereof according to the present invention, an increase in leakage current is suppressed.

1 is a cross-sectional view conceptually showing a solid electrolytic capacitor according to an embodiment of the present invention. It is the figure which showed typically the microstructure of the II area | region shown by FIG. It is a conceptual diagram used for description of the 1st chemical conversion treatment process performed with the manufacturing method of a solid electrolytic capacitor. It is a conceptual diagram used for description of the 2nd chemical conversion treatment process performed with the manufacturing method of a solid electrolytic capacitor.

<Configuration of solid electrolytic capacitor>
FIG. 1 is a cross-sectional view conceptually showing a solid electrolytic capacitor according to an embodiment of the present invention. As shown in FIG. 1, the solid electrolytic capacitor includes a capacitor element 1, an exterior body 2, an anode terminal 3, and a cathode terminal 4. The capacitor element 1 has an anode body 11, an anode lead 12, a dielectric layer 13, an electrolyte layer 14, and a cathode layer 15.

  The anode body 11 is composed of a porous sintered body having conductivity, and has a first end face 11a on which the anode lead 12 is planted, and a second end face 11b opposite to the first end face 11a. doing. Furthermore, the anode body 11 has a first region R1 including the first end surface 11a and a second region R2 including the second end surface 11b. In the present embodiment, the boundary surface Bs between the first region R1 and the second region R2 extends substantially perpendicular to the extending direction of the anode lead 12, and the end surface of the anode lead 12 located in the anode body 11 It is set at the same position as 12a.

  Various shapes such as a rectangular parallelepiped and a cylinder can be adopted as the shape of the anode body 11. The anode lead 12 is composed of a conductive wire. As the conductive material constituting the anode body 11 and the anode lead 12, the same kind or different kinds of materials are used. As the conductive material, valve metals such as titanium (Ti), tantalum (Ta), aluminum (Al), and niobium (Nb) are used. In particular, titanium, tantalum, aluminum, and niobium are suitable materials to be used because an oxide film (dielectric layer 13) having a higher dielectric constant is formed by oxidizing their surfaces. In addition, you may use the alloy which contains valve metals as a main component, such as an alloy which consists of two or more types of valve metals, an alloy which consists of a valve metal and another substance, for an electroconductive material.

  The dielectric layer 13 is formed on the surface of the conductive material constituting the anode body 11 (the surface of the porous sintered body). The dielectric layer 13 is an oxide film formed by oxidizing the surface of the conductive material constituting the anode body 11. Therefore, the dielectric layer 13 is formed on the outer peripheral surface of the anode body 11 and the inner wall surface of the minute hole H existing in the anode body 11 (see FIG. 2). In FIG. 1, only the portion of the dielectric layer 13 formed on the outer peripheral surface of the anode body 11 is schematically shown.

  Next, the film thickness of the dielectric layer 13 will be described. FIG. 2 is a diagram schematically showing the fine structure of the II region shown in FIG. As shown in FIG. 2, the average film thickness of the dielectric layer 13 in the second region R2 is larger than the average film thickness of the dielectric layer 13 in the first region R1. Here, in the first region R1, it is considered that the film thickness T1 of the dielectric layer 13 changes according to the position. And in 1st area | region R1, it is thought that the film thickness T1 of the dielectric material layer 13 is comparatively large in area | region Ra (refer FIG. 1) near the outer peripheral surface. Similarly, in the second region R2, it is considered that the film thickness T2 of the dielectric layer 13 changes according to the position. And in 2nd area | region R2, it thinks that the film thickness T2 of the dielectric material layer 13 is comparatively small in area | region Rb (refer FIG. 1) near the edge part 121 of the anode lead 12 located in the anode body 11. FIG. It is done. In the present embodiment, even when such regions Ra and Rb are compared, the average film thickness of the dielectric layer 13 in the region Rb is larger than the average film thickness of the dielectric layer 13 in the region Ra.

  The film thicknesses T1 and T2 of the dielectric layer 13 can be examined by observing the cross section of the anode body 11 using, for example, a scanning electron microscope (SEM). Moreover, the average film thickness of the dielectric layer 13 is calculated | required by the following methods, for example. That is, the film thickness of the dielectric layer 13 is measured at a plurality of locations (for example, 5 locations) in the cross section of the anode body 11, and the average value of these thicknesses is obtained as the average film thickness. By such a method, the average film thickness of the dielectric layer 13 in the first region R1 and the average film thickness of the dielectric layer 13 in the second region R2 can be obtained and compared.

  In the present embodiment, the boundary surface Bs between the first region R1 and the second region R2 is set at the same position as the end surface 12a of the anode lead 12, but the present invention is not limited to this. The boundary surface Bs may be set at a position in the vicinity of the end face 12a of the anode lead 12, or may be set at a position between the end face 12a and the second end face 11b. By setting the boundary surface Bs in this way, a decrease in the capacitance of the solid electrolytic capacitor can be suppressed.

  The electrolyte layer 14 is formed on the surface of the dielectric layer 13. Specifically, the electrolyte layer 14 is formed on the outer peripheral surface of the dielectric layer 13 and the inner wall of fine holes H (see FIG. 2) present in the anode body 11. In FIG. 1, only the portion of the electrolyte layer 14 formed on the outer peripheral surface of the dielectric layer 13 is schematically shown. In FIG. 2, the illustration of the electrolyte layer 14 is omitted. As the electrolyte material constituting the electrolyte layer 14, a conductive inorganic material such as manganese dioxide, or a conductive organic material such as a TCNQ (Tetracyano-quinodimethane) complex salt or a conductive polymer is used. Note that various materials that are not limited to these conductive inorganic materials and conductive organic materials can be used as the electrolyte material.

  The cathode layer 15 is formed on the outer peripheral surface of the electrolyte layer 14. Specifically, the cathode layer 15 includes a carbon layer (not shown) formed on the outer peripheral surface of the electrolyte layer 14 and a silver paint layer (not shown) formed on the outer peripheral surface of the carbon layer. Has been. The cathode layer 15 is not limited to such a configuration, and various configurations having a current collecting function can be employed.

  As shown in FIG. 1, the exterior body 2 covers the capacitor element 1. An electrical insulating material such as an epoxy resin is used as a constituent material of the exterior body 2. The anode terminal 3 is electrically connected to the anode lead 12 and pulled out from the side surface 2a (the left side surface in FIG. 1) of the exterior body 2. Furthermore, the anode terminal 3 is bent along the side surface 2 a and the lower surface 2 c of the exterior body 2, and the end 31 of the anode terminal 3 is disposed on the lower surface 2 c of the exterior body 2. The cathode terminal 4 is electrically connected to the cathode layer 15 via the conductive adhesive 5 and is drawn out from the side surface 2b (the right side surface in FIG. 1) of the exterior body 2. Furthermore, the cathode terminal 4 is bent along the side surface 2 b and the lower surface 2 c of the exterior body 2, and the end 41 of the cathode terminal 4 is disposed on the lower surface 2 c of the exterior body 2. In this way, the end portions 31 and 41 constitute the lower surface electrode of the solid electrolytic capacitor.

<Method for manufacturing solid electrolytic capacitor>
Next, a method for manufacturing the solid electrolytic capacitor according to the present embodiment will be specifically described. In the manufacturing method of the present embodiment, the element manufacturing process, the connecting process, and the exterior body forming process are sequentially performed. Further, in the element manufacturing process, an anode manufacturing process, a first chemical conversion process, a second chemical conversion process, an electrolyte layer forming process, and a cathode layer forming process are sequentially performed.

  In the anode manufacturing step, first, a molded body of valve metal powder is manufactured. Specifically, the anode lead 12 is inserted into the mold so that the valve metal powder is filled in the mold and the anode lead 12 is planted in the molded body. Thereafter, pressure is applied to the mold to compress the valve metal powder into a predetermined shape (such as a rectangular parallelepiped or a cylinder). After producing the molded body, the valve metal powder is sintered by subjecting the molded body to a heat treatment, thereby producing a porous sintered body that becomes the anode body 11. At this time, the valve metal powder existing on the surface of the anode lead 12 is fused, whereby the anode body 11 and the anode lead 12 are integrated. In the anode preparation step, conductive powder such as an alloy containing a valve metal as a main component may be used instead of the valve metal powder. Such an alloy preferably contains 50 atom% or more of valve metal.

  In order to realize a large capacity of the solid electrolytic capacitor, it is preferable to produce a porous sintered body using a valve metal powder of 100000 μF · V / g or more in the anode production process.

  FIG. 3 is a conceptual diagram used for explaining the first chemical conversion treatment step. As shown in FIG. 3, in the first chemical conversion treatment step, chemical conversion treatment is performed on the entire anode body 11. Specifically, first, the tip 122 of the anode lead 12 is fixed to the metal frame 81. As a result, the anode body 11 is held by the metal frame 81 with the first end face 11a facing upward. Next, the entire anode body 11 is immersed in a first chemical conversion solution 61 such as a phosphoric acid aqueous solution or an adipic acid aqueous solution with the first end face 11a facing upward. As a result, the first chemical conversion liquid 61 penetrates inside the fine holes H present in the anode body 11. Next, the first voltage V <b> 1 is applied between the cathode plate 71 provided in the first chemical conversion liquid 61 and the anode lead 12. Thereby, the surface of the conductive material constituting the anode body 11 (the surface of the porous sintered body) is electrochemically oxidized (anodic oxidation). As a result, an oxide film to be the dielectric layer 13 is formed on the surface of the conductive material constituting the anode body 11. In addition, it is preferable that the density | concentration of the electrolyte in the 1st chemical conversion liquid 61 is 0.001-10 wt%. Moreover, it is preferable that the 1st voltage V1 is a voltage more than twice a rated voltage.

  FIG. 4 is a conceptual diagram used for explaining the second chemical conversion treatment step. As shown in FIG. 4, in the second chemical conversion treatment step, chemical conversion treatment is performed on the second region R <b> 2 of the anode body 11. Specifically, first, the tip 122 of the anode lead 12 is fixed to the metal frame 82. As a result, the anode body 11 is held by the metal frame 82 with the first end face 11a facing upward. Next, the anode body 11 is immersed in the second chemical conversion solution 62 such as a phosphoric acid aqueous solution or an adipic acid aqueous solution with the first end face 11a facing upward. At this time, the first region R1 of the anode body 11 is exposed on the liquid surface 62a of the second chemical liquid 62, and the second region R2 of the anode body 11 is immersed in the second chemical liquid 62. In the present embodiment, the anode body 11 is immersed in the second chemical forming liquid 62 so that the end face 12a (the lower end face in FIG. 4) of the anode lead 12 and the liquid level 62a of the second chemical forming liquid 62 are aligned in substantially the same plane. It is done. As a result, the second chemical liquid 62 penetrates into the fine holes H existing in the second region R2 of the anode body 11. In the second chemical conversion treatment step, the liquid level 62a of the second chemical conversion liquid 62 may be adjusted to a position in the vicinity of the end face 12a of the anode lead 12, or adjusted between the end face 12a and the second end face 11b. May be. By adjusting the liquid level 62a in this way, a decrease in the capacitance of the solid electrolytic capacitor can be suppressed.

  Next, in a state where the second region R2 is immersed in the second chemical formation liquid 62, a second voltage V2 is applied between the cathode plate 72 provided in the second chemical formation liquid 62 and the anode lead 12. . As a result, in the second region R2 of the anode body 11, the surface of the conductive material (the surface of the porous sintered body) is further electrochemically oxidized (anodic oxidation). As a result, the thickness of the oxide film increases in the second region R2.

  In addition, it is preferable that the film thickness of the oxide film in 2nd area | region R2 is 1.05-2.5 times the film thickness of the oxide film in 1st area | region R1 after a 2nd chemical conversion treatment process. In order to advance the oxidation in the second region R2 so as to have such a film thickness, the concentration of the electrolyte in the second chemical conversion liquid 62 is preferably 0.001 to 10 wt%. The second voltage V2 is preferably set to be higher than the first voltage V1, and particularly preferably set to a voltage 1.05 to 2.5 times the first voltage V1. According to these preferable conditions, the thickness of the oxide film can be easily controlled by a control factor such as a voltage application time.

  As the second chemical conversion liquid 62, the first chemical conversion liquid 61 used in the first chemical conversion treatment process may be used, or a chemical conversion liquid different from the first chemical conversion liquid 61 may be used. When using the 1st chemical conversion liquid 61 as the 2nd chemical conversion liquid 62, without moving up the anode body 11 whole from the 1st chemical conversion liquid 61 after a 1st chemical conversion liquid process, it moves to the following 2nd chemical conversion treatment process. I can do it. That is, after the first chemical conversion treatment step, the anode region 11 is pulled up by a predetermined distance, so that the first region R1 is exposed on the liquid surface 62a of the second chemical conversion solution 62 and the second region R2 is converted into the second chemical conversion solution. It can be immersed in the liquid 62. On the other hand, when a chemical conversion liquid different from the first chemical conversion liquid 61 is used as the second chemical conversion liquid 62, it is necessary to replace the chemical conversion liquid into the processing tank or to prepare another processing tank, but the type and concentration of the electrolyte are changed. It becomes possible to do.

  A cleaning step may be provided after the first chemical conversion treatment step and before the second chemical conversion treatment step. In the cleaning process, the first chemical liquid 61 attached to the anode body 11 is removed by cleaning the anode body 11. Thereby, in the first region R1 of the anode body 11, it is prevented that the thickness of the oxide film is increased in the second chemical conversion treatment process due to the remaining of the first chemical conversion liquid 61. Alternatively, the second chemical conversion treatment step may be performed in a state where the anode body 11 is impregnated with an aqueous solution not containing an electrolyte such as phosphoric acid after the first chemical conversion solution 61 is removed in the cleaning step. Thereby, in 1st area | region R1 of the anode body 11, it can suppress that the film thickness of an oxide film becomes large at a 2nd chemical conversion treatment process.

  In the electrolyte layer forming step, the electrolyte layer 14 is formed on the surface of the dielectric layer 13 using a polymerization method or a coating method. As the polymerization method, there are methods such as a chemical polymerization method and an electrolytic polymerization method. When forming the electrolyte layer 14 using a polymerization method, first, the tip 122 of the anode lead 12 is fixed to a metal frame. Thereby, the anode body 11 is hold | maintained at a metal frame in the state which orient | assigned the 1st end surface 11a upwards. Next, the anode body 11 is immersed in a polymerization solution for generating a conductive polymer. As a result, the polymerization solution permeates inside the fine holes H present in the anode body 11. Thereafter, by polymerizing the monomer in the polymerization solution, a conductive polymer is generated on the outer peripheral surface of the dielectric layer 13 and the inner walls of the fine holes H, and the electrolyte layer 14 is formed by the conductive polymer.

  When forming the electrolyte layer 14 using the coating method, first, the front end portion 122 of the anode lead 12 is fixed to a metal frame. Thereby, the anode body 11 is hold | maintained at a metal frame in the state which orient | assigned the 1st end surface 11a upwards. Next, the anode body 11 is immersed in a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed. As a result, the solution or dispersion penetrates inside the fine holes H existing in the anode body 11. Thereafter, the anode body 11 is pulled up from the solution or dispersion liquid, and the solution or dispersion liquid adhered to the anode body 11 is dried. As a result, the conductive polymer remains on the outer peripheral surface of the dielectric layer 13 and the inner walls of the fine holes H, and the electrolyte layer 14 is formed by the conductive polymer.

  In the cathode layer forming step, a carbon layer and a silver paint layer to be the cathode layer 15 are formed on the outer peripheral surface of the electrolyte layer 14. Specifically, the carbon layer is formed on the outer peripheral surface of the electrolyte layer 14 by immersing the anode body 11 in the carbon paste. Next, the anode body 11 is immersed in a silver paste to form a silver paint layer on the outer peripheral surface of the carbon layer. Thereby, the capacitor element 1 is completed.

  In the connection step, the anode terminal 3 and the anode lead 12 are electrically and mechanically connected to each other by performing processing such as welding on these connection portions. Further, the cathode terminal 4 and the cathode layer 15 are electrically and mechanically connected to each other by interposing a conductive adhesive 5 between them.

  In the exterior body forming step, the exterior body 2 is molded using a resin such as an epoxy resin to cover the capacitor element 1 with the exterior body 2. At this time, the exterior body 2 is formed so that the anode terminal 3 and the cathode terminal 4 are pulled out from the side surfaces 2a and 2b of the exterior body 2, respectively. After forming the exterior body 2, the anode terminal 3 is bent along the side surface 2 a and the lower surface 2 c of the exterior body 2. Further, the cathode terminal 4 is bent along the side surface 2 b and the lower surface 2 c of the exterior body 2. Thereby, the solid electrolytic capacitor shown in FIG. 1 is completed.

  As shown in FIG. 1, the first region R1 has many portions where the anode body 11 is bonded to the anode lead 12, while the second region R2 has almost no such portion. Accordingly, when the anode body 11 receives an external force, stress is easily generated in the second region R2. On the other hand, according to the present embodiment, the average film thickness of the dielectric layer 13 formed in the second region R2 of the anode body 11 by the first chemical conversion treatment process and the second chemical conversion treatment process is the first film thickness of the anode body 11. It becomes larger than the average film thickness of the dielectric layer 13 formed in the region R1. Accordingly, the thickness of the dielectric layer 13 is increased in the second region R2. Therefore, even when the anode body 11 receives an external force during manufacture or use of the solid electrolytic capacitor and a stress is generated in the second region R2 of the anode body 11, the dielectric layer 13 existing in the second region R2 is cracked or the like. As a result, an increase in leakage current is suppressed in the solid electrolytic capacitor.

  As described above, in the electrolyte layer forming step, the polymerization method or the coating method is performed in a state where the tip 122 of the anode lead 12 is fixed to the metal frame (the first end surface 11a of the anode body 11 is directed upward). Is used to form the electrolyte layer 14. However, according to such a forming method, there is a possibility that a protrusion made of a conductive polymer (hereinafter referred to as “conductive polymer protrusion”) is formed on the second end face 11 b of the anode body 11. . Specifically, it is as follows.

  In the case of the chemical polymerization method, when the anode body 11 is pulled up from the polymerization liquid after being immersed in the polymerization liquid, a part of the polymerization liquid adhering to the anode body 11 hangs down from the second end surface 11 b of the anode body 11. Then, due to dripping or pooling, conductive polymer protrusions are formed on the second end face 11b. Similarly, also in the case of the coating method, when the anode body 11 is pulled up from the solution or dispersion, conductive polymer protrusions are formed on the second end surface 11b due to dripping or pooling.

  In the case of the electrolytic polymerization method, when the anode body 11 is immersed in the polymerization solution, the cathode plate provided at the bottom of the treatment tank and the second end face 11b of the anode body 11 face each other. For this reason, on the second end face 11b, the electrolyte layer 14 partially grows toward the cathode plate, thereby forming a conductive polymer protrusion.

  The protrusion of the conductive polymer is easily subjected to external force in the manufacturing process after the electrolyte layer forming step. When the protrusion receives an external force, stress is easily generated in the second region R2 of the anode body 11. Accordingly, the conductive polymer protrusions may cause defects such as cracks in the dielectric layer 13 in the second region R2. Therefore, when such a protrusion is generated, it can be considered to remove the protrusion. However, when removing the protrusion, a large force is applied to the anode body 11 to generate stress in the second region R2 of the anode body 11, which causes a crack in the dielectric layer 13 in the second region R2. There is a risk of the occurrence of defects.

  According to the present embodiment, as described above, the average film thickness of the dielectric layer 13 in the second region R2 of the anode body 11 is larger than the average film thickness of the dielectric layer 13 in the first region R1 of the anode body 11. Become. Therefore, even when a conductive polymer protrusion exists on the second end surface 11b of the anode body 11 and stress is generated in the second region R2 due to the protrusion, the dielectric layer existing in the second region R2 is present. Defects such as cracks are hardly generated in 13. Further, even when a stress is generated in the second region R2 when the protrusion is removed, the dielectric layer 13 existing in the second region R2 is unlikely to have a defect such as a crack. Therefore, an increase in leakage current is suppressed in the solid electrolytic capacitor.

  When a porous sintered body (anode body 11) is produced using a valve metal powder of 100000 μF · V / g or more, it is possible to realize a large capacity of the solid electrolytic capacitor, while the strength of the anode body 11 is high. Will be reduced. This is considered to be because the bonding area between the valve metal particles is reduced by reducing the particle size of the valve metal powder constituting the anode body 11. For this reason, when the anode body 11 receives external force at the time of manufacture and use of the solid electrolytic capacitor, stress is generated at the grain boundary between the valve metal particles, so that the bonding force of the grain boundary is weakened. Defects such as cracks are likely to occur in the nearby dielectric layer 13. According to the present embodiment, as described above, the thickness of the dielectric layer 13 increases in the second region R2 where stress is likely to occur. Therefore, even when stress is generated in the second region R2, the dielectric layer 13 existing in the second region R2 is unlikely to have defects such as cracks. Therefore, an increase in leakage current is suppressed in the solid electrolytic capacitor. That is, according to the present embodiment, an increase in leakage current can be suppressed while realizing a large capacity by using a valve metal powder of 100000 μF · V / g or more.

  Furthermore, according to this embodiment, in the first region R1 of the anode body 11, the surface of the conductive material hardly oxidizes in the second chemical conversion treatment step. Therefore, even after the second chemical conversion treatment step, the film thickness of the dielectric layer 13 formed in the first chemical conversion treatment step is maintained in the first region R1 of the anode body 11, and accordingly, the film thickness of the dielectric layer 13 is maintained. Remains small. Therefore, a capacitor component having a large capacitance is generated in the first region R1 of the anode body 11, and as a result, a decrease in the capacitance of the solid electrolytic capacitor is suppressed.

  Then, in the second chemical conversion treatment step of the present embodiment, the anode body 11 so that the end surface 12a (the lower end surface in FIG. 4) of the anode lead 12 and the liquid surface 62a of the second chemical conversion liquid 62 are aligned in substantially the same plane. Is immersed in the second chemical conversion liquid 62. Accordingly, the first region R1 and the second region R2 have the boundary surface Bs at the same position as the end surface 12a of the anode lead 12 or a position in the vicinity thereof. That is, the region (second region R2) where the thickness of the dielectric layer 13 is increased is limited to the region of the anode body 11 where stress is likely to occur. Therefore, according to the present embodiment, a decrease in capacitance is suppressed and an increase in leakage current is suppressed.

  Further, according to the present embodiment, when the anode body 11 is immersed in the second chemical forming liquid 62, the portion to be immersed in the second chemical forming liquid 62 by a simple control such as adjusting the distance at which the anode body 11 is lowered or raised. The height of (second region R2) can be adjusted. Therefore, even when the second chemical conversion treatment step is executed, the manufacturing method of the solid electrolytic capacitor is not complicated.

  In addition, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim.

  As an example of the above embodiment, a solid electrolytic capacitor (rated voltage 6.3 V, rated capacitance 220 μF) was produced under the following conditions (Example 1). That is, in the anode preparation step, a porous sintered body was prepared using tantalum powder of 100000 μF · V / g or more as the anode body 11. A tantalum wire was used as the anode lead 12. In the first chemical conversion treatment step, a phosphoric acid aqueous solution was used as the first chemical conversion solution 61, and the first voltage V1 was set to 16V. In the second chemical conversion treatment step, a phosphoric acid aqueous solution was used as the second chemical conversion solution 62, and the second voltage V2 was set to 20V. In the electrolyte layer forming step, polypyrrole was generated as the conductive polymer contained in the electrolyte layer 14.

  For comparison with Example 1, two types of solid electrolytic capacitors (rated voltage 6.3 V, rated capacitance 220 μF) were produced without performing the second chemical conversion treatment step (Comparative Examples 1 and 2). In Comparative Example 1, the first voltage V1 in the first chemical conversion treatment step was set to 16 V, which is the same as the applied voltage in the first chemical conversion treatment step of Example 1. On the other hand, in Comparative Example 2, the first voltage V1 in the first chemical conversion treatment step was set to 20 V, which is the same as the applied voltage in the second chemical conversion treatment step of Example 1. Other conditions are the same as those in the first embodiment.

  For comparison with the first embodiment, the first voltage V1 and the second voltage V2 are set to the same voltage when the first and second chemical conversion treatment steps are performed, and two types of solid electrolytic capacitors (rated voltage) are used. 6.3 V, rated capacitance 220 μF) (Comparative Examples 3 and 4). In Comparative Example 3, the first voltage V1 and the second voltage V2 were set to 16 V, which is the same as the applied voltage in the first chemical conversion treatment process of Example 1. In Comparative Example 4, the first voltage V1 and the second voltage V2 were set to 20 V, which was the same as the applied voltage in the second chemical conversion treatment process of Example 1. Other conditions are the same as those in the first embodiment.

  Furthermore, for comparison with Example 1, the order of the first chemical conversion treatment step and the second chemical conversion treatment step was changed to produce a solid electrolytic capacitor (rated voltage 6.3 V, rated capacitance 220 μF) (Comparative Example). 5). In Comparative Example 5, the first voltage V1 and the second voltage V2 were set to 16 V, which is the same as the applied voltage in the first chemical conversion treatment process of Example 1. Other conditions are the same as those in the first embodiment.

  As another example of the above embodiment, a solid electrolytic capacitor (rated voltage: 6.3 V, rated capacitance: 220 μF) was manufactured under the following conditions (Example 2). That is, in the anode production step, a porous sintered body was produced using tantalum powder of 200000 μF · V / g or more as the anode body 11. In the first chemical conversion treatment step, the first voltage V1 was set to 19V, and in the second chemical conversion treatment step, the second voltage V2 was set to 23V. Other conditions are the same as those in the first embodiment.

  Further, for comparison with Example 2, a solid electrolytic capacitor (rated voltage 6.3 V, rated capacitance 220 μF) was produced without performing the second chemical conversion treatment step (Comparative Example 6). In Comparative Example 6, the first voltage V1 in the first chemical conversion treatment step was set to 19 V, which is the same as the applied voltage in the first chemical conversion treatment step of Example 2. Other conditions are the same as in the second embodiment.

  About the solid electrolytic capacitor of Examples 1 and 2 and Comparative Examples 1-6, the electrostatic capacitance and the leakage current were measured. As a measurement condition of the capacitance, the frequency at the time of measurement was 120 Hz. The leakage current was measured after a rated voltage was applied to the solid electrolytic capacitor for 5 minutes. The measurement results for Example 1 and Comparative Examples 1 to 5 are shown in Table 1. The measurement results for Example 2 and Comparative Example 6 are shown in Table 2. In Tables 1 and 2, the capacitance of each example is shown as a ratio (capacitance ratio) based on the capacitance of the example. Further, the leakage current of each example is indicated by a ratio (leakage current ratio) based on the leakage current of the example.

※比較例５では、第１化成処理工程と第２化成処理工程の順序を他の例とは逆にした。

* In Comparative Example 5, the order of the first chemical conversion treatment step and the second chemical conversion treatment step was reversed from the other examples.

  As shown in Table 1, the leakage current of Comparative Example 1 is significantly larger than that of Example 1. This is presumably because the increase in leakage current could not be suppressed because the thickness of the dielectric layer 13 is the same in the second region R2 where stress is likely to occur and other regions. In Comparative Example 2, although the increase in leakage current is suppressed, the capacitance is significantly smaller than that in Example 1. This is presumably because the film thickness of the dielectric layer 13 is increased as a whole. In contrast to the comparative examples 1 and 2 described above, in the example 1, a decrease in electrostatic capacity is suppressed and an increase in leakage current is suppressed. From the measurement results shown in Table 2, the same can be said for Example 2.

  As shown in Table 1, the leakage current is larger in Comparative Example 3 than in Example 1. This is presumably because the second voltage V2 was small in the second chemical conversion treatment step, and thus the film thickness of the dielectric layer 13 in the second region R2 was not sufficiently large. Therefore, by comparing Example 1 and Comparative Example 3, it is confirmed that setting the second voltage V2 higher than the first voltage V1 as in Example 1 greatly contributes to the suppression of the increase in leakage current. I was able to do it.

  In Comparative Example 4, although the increase in leakage current is suppressed, the capacitance is significantly smaller than that in Example 1. This is considered to be because the film thickness of the dielectric layer 13 is increased overall as in Comparative Example 2.

  Furthermore, as shown in Table 1, the leakage current of Comparative Example 5 is significantly larger than that of Example 1. Therefore, by comparing Example 1 and Comparative Example 5, the second chemical conversion treatment step (the step of subjecting the anode body 11 to partial chemical conversion treatment) is changed to the first chemical conversion treatment step (the chemical conversion of the entire anode body 11). It was confirmed that what is performed after the step of applying the treatment greatly contributes to the suppression of the increase in leakage current.

DESCRIPTION OF SYMBOLS 1 Capacitor element 11 Anode body 11a 1st end surface 11b 2nd end surface 12 Anode lead 12a End surface 13 Dielectric layer 14 Electrolyte layer 15 Cathode layer 61 1st chemical liquid 62 2nd chemical liquid 62a Liquid surface 121 End R1 1st area | region R2 Second region V1 First voltage V2 Second voltage

Claims (2)

(A) preparing an anode body having a first end face on which an anode lead is planted and a second end face opposite to the first end face;
(B) In a state where the entire anode body is immersed in the first chemical conversion liquid, a first voltage is applied between the first chemical conversion liquid and the anode body, and thereby the conductivity constituting the anode body. Oxidizing the surface of the material;
(C) After the step (b), the first region including the first end face of the anode body is exposed on the liquid surface of the second chemical liquid, and the second end face of the anode body is included. In a state where the second region is immersed in the second chemical conversion solution, a second voltage higher than the first voltage is applied between the second chemical conversion solution and the anode body, and thereby the second region. Oxidizing the surface of the conductive material in
A method for producing a solid electrolytic capacitor.   In the step (c), the liquid level of the second chemical conversion liquid is adjusted to a position near the lower end surface of the anode lead, or is adjusted between the lower end surface of the anode lead and the second end surface 2. The method of manufacturing a solid electrolytic capacitor according to claim 1, wherein the second voltage is applied between the second chemical conversion liquid and the anode body.

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