JP2009105171A - Solid-state electrolytic capacitor and its method for manufacturing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable low-impedance solid-state capacitor, and to provide its method for manufacturing. <P>SOLUTION: On the surface of a porous material composed of a sintered compact of valve action metal, an oxide coating of the metal is formed as a dielectric layer, and after a conductive polymer layer is formed as a solid-state electrolytic layer, by chemical oxidation polymerization on an anode body 3, immersion into a conductive high polymer solution and drying are performed. Subsequently, a first solid-state electrolytic layer 201 is formed, and a second solid-state electrolytic layer 202 is formed by chemical oxidation polymerization. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solid electrolytic capacitor and a manufacturing method thereof, and more particularly to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte and a manufacturing method thereof.

  Solid electrolytic capacitors using valve action metals such as tantalum and aluminum are widely used. These solid electrolytic capacitors are characterized in that a large capacity can be obtained by increasing the surface area of the dielectric layer in the form of a sintered body or an etching foil. However, since manganese dioxide or the like is used as the solid electrolyte, there is a disadvantage that impedance at high frequency is large. For this reason, a solid electrolytic capacitor having improved impedance characteristics in a high frequency region using a conductive polymer composed of a functional polymer having higher conductivity as a solid electrolyte has been developed.

  Such a solid electrolytic capacitor not only has excellent characteristics at high frequencies due to the high conductivity of the solid electrolyte, but also does not require any thermal history to form the electrolyte, so that the oxide film is not damaged, and manganese dioxide As compared with a solid electrolytic capacitor using a thermal decomposition product such as the above as a solid electrolyte, it has a feature of excellent reliability.

  As a method for forming a conductive polymer layer to be a solid electrolyte layer, a dense conductive polymer layer is formed inside the capacitor element by chemical oxidative polymerization. Thereafter, techniques for uniformly forming a conductive polymer layer on the outer periphery of the capacitor element using a conductive polymer solution for the capacitor element have been proposed in Documents 1 to 3. Further, when the method for forming the conductive polymer layer is carried out only by chemical oxidative polymerization, there is a drawback that the thickness of the conductive polymer layer film is not uniform and the number of polymerizations is many times.

JP 2005-109252 A JP 2006-1851973 A JP 2002-524868

  FIG. 3 is a schematic cross-sectional view showing a conventional solid electrolytic capacitor element. In the conventional process of forming a solid electrolyte layer, first, a conductive polymer is formed inside the anode body 3 in which a dielectric layer is formed on the surface of the porous body of the valve metal. Thereafter, when the solid electrolyte layer 201 made of a conductive polymer layer is formed on the outer surface of the anode body 3, after immersing the conductive polymer solution in the solid electrolytic capacitor element, the solvent is dried to smooth the surface. The solid electrolyte layer 201 was formed. This surface is smoother than the surface of the solid electrolyte layer formed by chemical oxidative polymerization. This is due to the binder contained in the conductive polymer solution, and there is a problem that the contact area with the graphite paste layer 6 which is a cathode layer to be implemented thereafter is reduced and the interface resistance is increased.

  The binder has a buffering role against mechanical stress during the manufacturing process of the dielectric layer or thermal stress during mounting.

  This invention is made | formed in view of the above problem, and the subject of this invention is providing a solid electrolytic capacitor with low impedance and high reliability, and its manufacturing method.

  The solid electrolytic capacitor of the present invention is formed on the first solid electrolyte layer formed by drying the conductive polymer solution after forming an oxide film of the metal as a dielectric layer on the surface of the sintered body of the valve action metal. A second solid electrolyte layer formed by chemical oxidative polymerization is included.

  Further, it is preferable that the second solid electrolyte layer is formed by attaching a monomer solution after attaching an oxidizing agent.

  The second solid electrolyte layer is preferably made of polythiophene, polypyrrole, polyaniline, polysilane, or a derivative thereof.

  Moreover, it is preferable that the said conductive polymer solution contains the electroconductive particle and solvent which consist of (pi) conjugated system conductive polymer and a binder.

  The π-conjugated conductive polymer is preferably composed of polythiophene, polypyrrole, polyaniline, polysilane, or a derivative thereof, and the binder constituting the conductive polymer solution is acrylic, polyurethane, epoxy, polyphenol, silicon, polyester , Polypropylene, polycarbonate or their derivatives, compounds having ether, lactone, amide or lactam groups, sulfones, sulfoxides, sugars, sugar derivatives, sugar alcohols, furan derivatives and / or di- or polyalcohols.

  The valve metal preferably includes any one of tantalum, aluminum, titanium, niobium, zirconium, hafnium, and vanadium.

  Furthermore, the method for producing a solid electrolytic capacitor of the present invention includes a step of drying a conductive polymer solution to form a first solid electrolyte layer and a step on the first solid electrolyte layer in the step of forming the solid electrolyte layer. The method for producing a solid electrolytic capacitor is characterized by including a step of forming a second solid electrolyte layer by chemical oxidative polymerization.

  According to the present invention, after forming a metal oxide film as a dielectric layer on the surface of a porous body made of a sintered body of valve action metal, and forming a conductive polymer layer by chemical oxidative polymerization as a solid electrolyte layer After immersing and drying in a conductive polymer solution to complete the first solid electrolyte layer, the second solid electrolyte layer is formed again by chemical oxidative polymerization, so that the surface of the solid electrolyte layer has irregularities. In addition, since the anchor effect and the contact area with the graphite paste layer are increased, it is possible to provide a solid electrolytic capacitor having a low impedance and a method for manufacturing the same.

  Next, an embodiment of the present invention will be described with reference to the drawings, taking a tantalum solid electrolytic capacitor as an example. FIG. 2 is a cross-sectional view of the solid electrolytic capacitor of the present invention.

First, the formation process of the porous body 2 consists of 1) powder preparation, and 2) pressing and sintering. 1) For powder preparation, a tantalum powder as a valve metal is added and mixed with a binder to improve press formability. 2) For pressing / sintering, the anode lead 2a is inserted into the tantalum mixed powder and press-molded into a cylindrical shape or a rectangular parallelepiped shape. Subsequently, the press-molded product is sintered by heating to 1300 to 2000 ° C. in a high vacuum (10 ⁻⁴ Pa or less) to form the porous body 2.

  The dielectric layer 4 is formed by immersing the porous body 2 made of tantalum as an anode in an electrolyte solution such as phosphoric acid together with the counter electrode, and applying a voltage to the dielectric layer 4 on the surface of the porous body 2. A tantalum oxide film is formed to form anode body 3.

  The formation of the solid electrolyte layer mainly comprises a step of forming inside the anode body 3 and a step of forming mainly outside. The formation of the solid electrolyte layer inside is formed on the dielectric layer inside the anode body formed in the previous step. A solid electrolyte layer is formed by chemical oxidative polymerization of polyaniline, polypyrrole, polythiophene, or the like.

  FIG. 1 is a schematic cross-sectional view showing the structure of the solid capacitor element in the solid electrolyte layer forming step. The solid electrolyte layer of the present invention is formed by forming the solid electrolyte layer inside the anode body 3 and then forming the second solid electrolyte layer 201 after the formation of the first solid electrolyte layer 201 by drying the conductive polymer solution as the external solid electrolyte layer. A solid electrolyte layer 202 is formed. The second solid electrolyte layer has irregularities due to chemical oxidative polymerization. This is because, during the formation of the second solid electrolyte layer, as the solvent evaporates after immersion in the oxidant, crystals of the metal salt are deposited and adhered to form irregularities, and if a monomer adheres to that part, a polymerization reaction occurs. Thus, an uneven conductive polymer layer is obtained. In this case, the oxidant to be applied may be either water or a non-aqueous solvent, and the volume% of the metal salt contained is preferably 10% by volume to 50% by volume.

  The first solid electrolyte layer preferably contains at least a π-conjugated conductive polymer and a binder, and the weight ratio of the binder constituting the first solid electrolyte layer is preferably 0.1 to 90% by weight. More preferably, it is 1-80 weight%, More preferably, it is 5-60 weight%. This is because when the amount of the binder is increased, the bonding force of the conductive polymer layer is enhanced, but the conductivity is remarkably reduced.

  As the π-conjugated conductive polymer constituting the first solid electrolyte layer, polypyrrole, polythiophene, polyaniline, polyfuran, or derivatives thereof can be used.

  The binder constituting the first solid electrolyte layer is acrylic, polyurethane, epoxy, polyphenol, silicone, polyester, polypropylene, polycarbonate or a derivative thereof, a compound having an ether, lactone, amide or lactam group, sulfone, sulfoxide, sugar, Sugar derivatives, sugar alcohols, furan derivatives or dialcohols, polyalcohols or their derivatives can be used.

  The first solid electrolyte layer can be formed by applying and drying a solution in which a π-conjugated conductive polymer, a binder, and additives constituting the first solid electrolyte layer are dispersed in a solvent.

  The viscosity of the solution in which the π-conjugated conductive polymer, the binder, and the additive constituting the first solid electrolyte layer are dispersed in a solvent is preferably 10 mPa · s or more. More preferably, it is 50 mPa * s or more, More preferably, it is 100 mPa * s or more, Most preferably, it is 200 mPa * s or more. This is because if the viscosity is small, it is difficult to form the first solid electrolyte layer at the end of the capacitor element.

  The solid content of the solution in which the conductive polymer, binder, and additive constituting the first solid electrolyte layer are dispersed in a solvent is preferably 1% by weight or more. More preferably, it is 3% by weight or more, and further preferably 5% by weight or more. This is because it is difficult to produce a highly viscous solution when the solid content is small.

  As described above, in FIG. 1, the outermost conductive polymer layer, that is, the second solid electrolyte layer 202 is uneven as compared with the conventional FIG. 3, and the anchor effect with the graphite paste layer 6 formed thereafter is obtained. And the contact area increases.

  As shown in FIG. 2, the cathode layer is formed by forming a graphite paste layer 6 on the solid electrolyte layer 5 as a cathode layer and further forming a silver paste layer 7 thereon.

  Next, as shown in FIG. 2, the lead frame 9 is joined to the anode and the cathode by spot welding, and the cathode part of the lead frame 9 is joined to the silver paste layer 7 by the conductive adhesive 8. . Finally, the whole is molded with the exterior resin 10 and the lead frame 9 is bent to complete a tantalum solid electrolytic capacitor having the structure shown in FIG.

  Next, a specific embodiment according to the present invention will be described with reference to FIGS. As an embodiment of the present invention, a solid electrolytic capacitor having a rated voltage of 4 V and a rated capacity of 47 μF is manufactured by the following process.

Using a tantalum powder (about 80 kCV / g), a press body in which a tantalum wire (diameter 0.23 mm) is embedded in a 1.10 × 1.10 × 1.16 mm ³ rectangular parallelepiped adjusted to a press density of 6.0, The porous body 2 was produced by sintering at about 1200 to 1300 ° C.

  A porous body 2 made of tantalum is used as an anode, immersed in an electrolyte such as phosphoric acid at 0.6 wt% and 85 ° C. together with a counter electrode, and a dielectric is applied to the surface of the porous body 2 by applying a voltage of 10V. A tantalum oxide film to be the layer 4 is formed, and this is used as the anode body 3.

  Next, the anode body is immersed in an oxidant solution. As the oxidizing agent solution, a solution in which 20 wt% of a sulfonate was dissolved in a predetermined solvent such as pure water was used.

  After immersing in an oxidizer aqueous solution for 5 minutes, the capacitor element is pulled up from the oxidizer solution and further left at room temperature for 30 minutes. Then, after immersing in 3,4-ethylenedioxythiophene as a polymerizable monomer solution for 1 second, the capacitor element was pulled up from the polymerizable monomer solution and allowed to stand at room temperature for 60 minutes or longer to perform chemical oxidative polymerization.

  After forming a conductive polymer layer on the anodized film constituting the capacitor element inside the anode body in this way, polythiophene and acrylic resin mixed in a weight ratio of 1: 1 are dispersed in diethylene glycol, and the solid content Was immersed in a conductive polymer solution adjusted to 5 wt% and the viscosity was adjusted to 100 mPa · s for 1 minute and then dried at 150 ° C. for 30 minutes to form the first solid electrolyte layer 201.

  It is immersed again in the oxidizing agent solution. As the oxidizing agent solution, a solution in which 35 wt% of sulfonate was dissolved in a predetermined solvent such as ethyl alcohol was used.

  After immersing in the relevant oxidant solution for 1 minute, the anode body is pulled up from the oxidant solution and further left at room temperature for 60 minutes. Then, after being immersed in 3,4-ethylenedioxythiophene as a polymerizable monomer solution for 1 second, it is pulled up from the polymerizable monomer solution and allowed to stand at room temperature for 60 minutes to perform chemical oxidative polymerization. Layer 202 was formed.

  Next, a graphite paste layer 6 was formed on the conductive polymer layer of the capacitor element by ink jet coating, and a silver paste layer 7 was further formed thereon to a thickness of 10 μm. Next, the lead frame 9 is spot welded to the anode portion, and the cathode portion is further formed with the conductive adhesive 8 and the lead frame 9 is taken out and then covered with an epoxy exterior resin 10, and the lead frame along the exterior resin. Was folded to complete the solid electrolytic capacitor 1.

(Comparative example)
Hereinafter, a comparative example will be described with reference to FIG. Using a tantalum powder (about 80 kCV / g), a press body in which a tantalum wire (diameter 0.23 mm) is embedded in a 1.10 × 1.10 × 1.16 mm ³ rectangular parallelepiped adjusted to a press density of 6.0, The porous body 2 was produced by sintering at about 1200 to 1300 ° C.

  A porous body 2 made of tantalum is used as an anode, immersed in an electrolyte such as phosphoric acid at 0.6 wt% and 85 ° C. together with a counter electrode, and a dielectric is applied to the surface of the porous body 2 by applying a voltage of 10V. A tantalum oxide film to be the layer 4 is formed, and this is used as the anode body 3.

  Next, the anode body is immersed in an oxidant solution. As the oxidizing agent solution, a solution in which 20 wt% of a sulfonate was dissolved in a predetermined solvent such as pure water was used.

  After immersing in an oxidizer aqueous solution for 5 minutes, the capacitor element is pulled up from the oxidizer solution and further left at room temperature for 30 minutes. Then, after immersing in 3,4-ethylenedioxythiophene as a polymerizable monomer solution for 1 second, the capacitor element was pulled out from the polymerizable monomer solution and left at room temperature for 60 minutes or longer to perform chemical oxidative polymerization. .

  After forming a conductive polymer layer on the anodized film constituting the capacitor element in this way, polythiophene and acrylic resin mixed at a weight ratio of 1: 1 are dispersed in diethylene glycol, and the solid content is 5% by weight. The first solid electrolyte layer 201 was formed by applying and drying a solution whose viscosity was adjusted to 100 mPa · s.

  Next, a graphite paste layer 6 was formed on the conductive polymer layer of the capacitor element by ink jet coating, and a silver paste layer 7 was further formed thereon to a thickness of 10 μm. Further, after forming a conductive adhesive and taking out the lead frame, the lead frame was covered with an epoxy outer resin, and the lead frame was bent along the outer resin to complete the solid electrolytic capacitor 1.

   In the embodiment, the second solid electrolyte layer 202 is formed, whereas in the comparative example, the second solid electrolyte layer is not formed. Except for the above points, a conventional solid electrolytic capacitor was obtained in the same manner as in Example, structure and manufacturing method.

(Evaluation 1)
In the examples and comparative examples manufactured as described above, the equivalent series resistance (ESR) before and after the reflow soldering history of the solid electrolytic capacitor was measured. The results are shown in Table 1. As the reflow conditions, the temperature was set at a peak of 260 ° C., and a keep temperature of 240 ° C. for 10 to 30 seconds.

  The solid electrolytic capacitor manufactured in the example of the present invention can obtain a solid electrolytic capacitor having a lower equivalent series resistance (ESR) than the solid electrolytic capacitor manufactured in the comparative example.

  The present invention may also be used for aluminum capacitors and niobium capacitors.

The schematic cross section of the solid electrolytic capacitor element of this invention. Sectional drawing of a solid electrolytic capacitor. The schematic cross section of the conventional solid electrolytic capacitor element.

Explanation of symbols

1 Solid Electrolytic Capacitor 2 Porous Body 2a Anode Lead
3 Anode body 4 Dielectric layer 5 Solid electrolyte layer 6 Graphite paste layer 7 Silver paste layer 8 Conductive adhesive 9 Lead frame 10 Epoxy exterior resin 201 (first) solid electrolyte layer 202 (second) solid electrolyte layer

Claims (8)

  In a solid electrolytic capacitor having a solid electrolytic capacitor element in which a solid electrolyte layer and a cathode layer are sequentially formed on an anode body in which a dielectric layer is formed on a columnar porous body of valve action metal from which an anode lead is derived, A solid electrolytic capacitor comprising a second solid electrolyte layer formed by chemical oxidation polymerization on a first solid electrolyte layer formed by drying a conductive polymer solution.   The solid electrolytic capacitor according to claim 1, wherein the second solid electrolyte layer is formed by attaching a monomer solution after attaching an oxidizing agent.   3. The solid electrolytic capacitor according to claim 1, wherein the second solid electrolyte layer is made of polythiophene, polypyrrole, polyaniline, polysilane, or a derivative thereof.   The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the conductive polymer solution contains conductive particles composed of a π-conjugated conductive polymer and a binder and a solvent.   The solid electrolytic capacitor according to claim 4, wherein the π-conjugated conductive polymer is made of polythiophene, polypyrrole, polyaniline, polysilane, or a derivative thereof.   The binder constituting the conductive polymer solution is acrylic, polyurethane, epoxy, polyphenol, silicon, polyester, polypropylene, polycarbonate or a derivative thereof, a compound having an ether, lactone, amide or lactam group, sulfone, sulfoxide, sugar, The solid electrolytic capacitor according to claim 4, comprising a sugar derivative, a sugar alcohol, a furan derivative and / or a di- or polyalcohol.   The solid electrolytic capacitor according to any one of claims 1 to 6, wherein the valve metal includes any one of tantalum, aluminum, titanium, niobium, zirconium, hafnium, and vanadium.   In the method of manufacturing a solid electrolytic capacitor, the anode body in which a dielectric layer is formed on a columnar porous body of a valve action metal from which an anode lead is derived has a step of sequentially forming a solid electrolyte layer and a cathode layer. In the step of forming the solid electrolyte layer, the step of forming the first solid electrolyte layer by drying the conductive polymer solution and the formation of the second solid electrolyte layer by chemical oxidative polymerization on the first solid electrolyte layer The manufacturing method of the solid electrolytic capacitor characterized by including the process to do.

Images