JP2504182B2 - Solid electrolytic capacitor - Google Patents

Description

The present invention relates to a solid electrolytic capacitor, and more particularly to the structure of a cathode layer.

[Conventional technology]

As shown in FIG. 2, the conventional solid electrolytic capacitor has an anode body 11 formed by pressure-molding a metal powder having a valve action.
A metal wire 12 having a valve action is preliminarily erected as an anode lead and sintered in a vacuum.
An oxide film layer is formed on the outer peripheral surface of 11, a semiconductor layer of manganese dioxide or the like is formed on the outer peripheral surface of the oxide film layer as a counter electrode, and a graphite layer for further reducing the contact resistance.
A silver paste layer 14 is deposited via 13 to form a cathode conductor layer to form a capacitor element.

[Problems to be Solved by the Invention]

Since the above-described conventional capacitor element has a silver paste layer, it has a drawback that silver migration occurs when left in a moist atmosphere and leakage current increases.

Further, the conventional capacitor element has a drawback that the cost of the product becomes high because an expensive silver paste is used. As a solution to these two points, there has been proposed a method of forming a graphite layer containing palladium powder or silver-palladium alloy powder and then forming a plating layer of copper, nickel or the like by an electroless plating method. However, the solid electrolytic capacitor having such a structure uses a small amount of palladium powder instead of using a silver paste, and thus has a drawback that the cost is not reduced so much. Further, if palladium is contained in the cathode layer, the leakage current significantly increases in a pressure cooker test or the like, though not so much as migration of silver.

The object of the present invention is to reduce the product cost significantly, and without the occurrence of silver migration even in a humid atmosphere,
Another object of the present invention is to provide a solid electrolytic capacitor of excellent quality capable of significantly improving the increase in leakage current in the pressure cooker test.

[Means for solving the problem]

The solid electrolytic capacitor of the present invention is a solid electrolytic capacitor in which a dielectric oxide film layer, a semiconductor oxide layer, and a cathode layer are sequentially formed on an anode body made of a valve metal in which anode leads are erected. In a solid electrolytic capacitor having a structure in which a layer includes a conductor layer containing graphite, metal powder and resin, and a base metal layer formed on the dielectric layer, the metal powder in the conductor layer is copper, Any one of iron, zinc, nickel and tin powders and alloy powders of these metals, or a mixed powder of at least two kinds of powders selected from the plurality of kinds of powders. It is an electrolytic capacitor.

〔Example〕

Next, the present invention will be described with reference to the drawings. First
The figure is a cross-sectional view of a resin-molded solid electrolytic capacitor manufactured by an embodiment of the solid electrolytic capacitor of the present invention.

As shown in FIG. 1, an anode body 1 in which tantalum powder, which is one of the metals having a valve action, is pressure-molded and vacuum-sintered.
An anode lead 2 of tantalum material is erected on the outer surface of the anode body 1. An oxide film layer and a manganese dioxide layer (not shown) are formed on the outer peripheral surface of the anode body 1. One conductor layer 4 is formed. A coating resin layer 5 is formed by applying a polybutadiene resin to the surface of the anode lead on which the anode leads are set and heating the same. Further, a second conductor layer 6 containing copper powder and a base metal layer 7 made of nickel plating or the like are sequentially formed on the outer peripheral surface of the anode body other than the anode lead planting surface. An external anode terminal 3 is welded to the tip of the anode lead 2, and an external cathode terminal 9 is connected to a base metal layer 7 made of nickel plating or the like by a solder layer 8 so that the entire capacitor element is made of a thermosetting resin. Insulating resin layer
A resin-molded solid electrolytic capacitor is formed by being packaged by 10.

Next, a manufacturing process of the resin mold type tantalum solid electrolytic capacitor having such a configuration will be described. After the pressure-molded tantalum powder was vacuum-sintered at a high temperature, the anode body 1 on which the anode lead 2 of tantalum material was planted was anodized in a phosphoric acid aqueous solution at a formation voltage of 100 V and a tantalum oxide film was formed on the entire outer peripheral surface. Formed and then immersed in a manganese nitrate solution
A manganese dioxide layer is formed by thermal decomposition in an atmosphere of 250 to 300 ° C. This dipping and pyrolysis is performed multiple times to obtain a uniform manganese dioxide layer.

Next, the anode body 1 having the manganese dioxide layer formed thereon is immersed in a graphite solution prepared by suspending graphite powder in an aqueous solution of a water-soluble polymer material, and dried in an atmosphere of 150 to 200 ° C. to obtain the first conductivity. The body layer 4 is formed.

Next, a polybutadiene resin is applied to the anode lead lead surface with a dispenser and then dried in an atmosphere of 150 to 200 ° C. to form a coating resin layer 5.

Next, epoxy resin 20-50%, graphite powder 5-
30%, calcium carbonate powder 5-20%, copper powder 5-60%,
The second conductor layer 6 is formed by immersing the anode body 1 in a mixed solution in which butyl cellosolve is mixed in a weight ratio of 10 to 40% and thermally curing it in an atmosphere of 150 to 200 ° C. The copper powder in the second conductor layer acts as a plating catalyst and has the effect of enhancing the plating depositability of the base metal layer 7 made of nickel plating, which will be described later. The calcium carbonate powder has an effect of forming unevenness on the surface to increase the adhesion of the plating film by the anchor effect and an effect of increasing the heat resistance of the second conductor layer 6 containing resin. If the amount of copper is large, the plating depositability will be good, but if it is too large, the adhesion to the plating film will be poor. This second conductor layer 6 requires both graphite powder and copper powder. This is because the copper powder alone has good plating depositability, but the copper powder oxidizes in a humid atmosphere, etc., and the dielectric loss of the solid electrolytic capacitor increases. Therefore, it is necessary to add graphite powder so that the resistivity of the second conductor layer 6 does not deteriorate even in a humid atmosphere. As a result of examining the above, a conductor layer having a ratio of 23% of epoxy resin, 19% of graphite powder, 4.5% of calcium carbonate powder and 53.5% of copper powder was suitable.

Next, anode body 1 is immersed in dilute hydrochloric acid of 2 to 10% for pretreatment, and then washed with pure water to perform electroless plating. Since the anode body 1 is covered with the coating resin layer 5 and the second conductor layer 6, the manganese dioxide layer and the oxide film are protected from the gas during the reaction. As a plating solution, for example, an electroless nickel plating solution (pH = 6.7 at room temperature) using dimethylaminoborane as a reducing agent is used, plating is performed at 65 ° C. for 40 minutes, and a base metal layer 7 made of nickel plating of about 4 to 5 μm is used. Is formed. After plating, the whole is thoroughly washed and 120 to 1
It is dried in an atmosphere at 50 ° C to evaporate the water.

Further, the external anode terminal 3 made of a solderable material is welded to the anode lead 2, and the external cathode terminal 9 is placed on the base metal layer 7 made of nickel plating via a solder paste.
Then, infrared reflow is performed to form a solder paste as the solder layer 8, and the base metal 7 made of nickel plating and the external cathode terminal 9 are electrically connected.

Finally, the capacitor element is molded and packaged by the exterior insulating resin layer 10 made of a thermosetting resin, and the external anode terminal 3 and the external cathode terminal 9 are bent to form a resin-molded fixed electrolytic capacitor.

Although polybutadiene resin was used in the formation of the coating resin layer 5 in this example, since the coating resin layer is provided to protect the manganese dioxide layer and the oxide film from the gas during the plating reaction, epoxy, acrylic, polyester, Resins such as polyvinyl chloride and polypropylene, and mixed resins thereof may be used.

Further, in this example, calcium carbonate was used when forming the second conductor layer, but calcium carbonate is an inorganic filler for the purpose of improving the adhesion of the plating film and improving the heat resistance of the second conductor layer. In addition to these, inorganic substances such as iron oxide, barium carbonate, and copper oxide, and mixtures thereof may be used.

〔The invention's effect〕

As described above, the present invention has the following effects by not using the silver paste for the cathode layer and including the metal powder such as copper in the second conductor layer.

(1) Since the expensive silver paste is not used at all, the product cost can be reduced significantly, and the quality of the solid electrolytic capacitor is improved without migration of silver in a humid atmosphere.

(2) Since the second conductor layer uses metal powder such as copper instead of palladium powder or silver-palladium alloy powder, the product cost can be significantly reduced.

(3) In addition, since a metal powder such as copper is used for the second conductor layer, a pressure cooker test (125 ° C 100%
The increase in leakage current at RH) can be greatly improved as shown in FIG.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a resin-molded tantalum solid electrolytic capacitor which is an embodiment of the solid electrolytic capacitor of the present invention, FIG. 2 is a vertical sectional view of an example of a conventional tantalum solid electrolytic capacitor, and FIG. FIG. 6 is a comparison diagram of leakage current in a pressure cooker test when the metal powder in the conductor layer of is changed. 1 ... Anode body, 2 ... Anode lead, 3 ... External anode terminal, 4 ... First conductor layer, 5 ... Coating resin layer, 6 ...
Second conductor layer, 7 ... Base metal layer, 8 ... Solder layer, 9
...... External cathode terminal, 10 …… External insulating resin layer, 11 …… Anode body, 12 …… Anode lead, 13 …… Graphite layer, 14 ……
Silver paste layer.

Claims (1)

(57) [Claims] 1. A solid electrolytic capacitor in which a dielectric oxide film layer, a semiconductor oxide layer, and a cathode layer are sequentially formed on an anode body made of a valve metal in which anode leads are set up, the cathode layer comprising: In a solid electrolytic capacitor having a structure including a conductor layer containing graphite, metal powder and resin, and a base metal layer formed on the dielectric layer, the metal powder in the conductor layer is copper, iron or zinc. , Nickel, tin powder and alloy powders of these metals, or at least 2 selected from the above-mentioned plural kinds of powders.
A solid electrolytic capacitor, which is a mixed powder of at least one kind of powder.