JPH07120613B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an improvement of a solid electrolytic capacitor using lead dioxide as an electrolyte.

[Prior art]

Solid electrolytic capacitors use a so-called valve metal, such as aluminum, tantalum, and niobium, on the surface of which an insulating oxide film is formed, as the anode. The body is formed as a solid electrolyte layer, and a conductive layer for drawing out a cathode is further provided on the outer surface of the body. As a metal oxide used for the solid electrolyte, manganese dioxide obtained by heating and modifying manganese nitrate is well known. Lead dioxide as a solid electrolyte is disclosed, for example, in Japanese Examined Patent Publication No.
As described in Japanese Patent Publication No. 4, the electric conductivity is higher than that of manganese dioxide. Also in the solid electrolyte formation process, there is no need for heat treatment such as manganese nitrate heating to convert manganese dioxide to manganese dioxide, and the heating may be performed at room temperature or at most 100 ° C. or lower in order to accelerate the precipitation reaction. Therefore, it is possible to obtain a highly reliable solid electrolytic capacitor with low loss of the dielectric oxide film, low loss. As means for forming lead dioxide as a solid electrolyte on a dielectric oxide film, as described in JP-B-49-29374, lead acetate, lead chloride, lead bromide, lead nitrate, A solution containing lead ions, such as lead borofluoride, dissolved in water or another solvent, and an oxidizing agent such as ammonium persulfate, hydrogen peroxide, potassium permanganate, dimethyl sulfoxide, or quinone in water or There is a method of immersing the anode body in a mixed solution with a solution dissolved in another solvent and precipitating lead dioxide by a chemical oxidation reaction. Further, as in Japanese Patent Publication No. 39-285, there is generally known an electrochemical method in which an anode is immersed in a lead ion solution such as a lead nitrate solution and electrolytically oxidized.

[Problems to be Solved by the Invention]

When lead dioxide is deposited by a chemical method, a lead dioxide layer having a predetermined thickness can be formed once or relatively few times. However, the surface of the solid electrolyte layer formed by this chemical method is rough, and the bonding with the cathode extraction layer such as the colloidal carbon layer or the conductive paste formed on the outer surface is often incomplete. In addition, when used for a long time, there is a drawback that the peeling occurs locally at the joint surface, resulting in an increase in loss and internal resistance. Also, the lead dioxide layer formed by electrochemical means is
A denser layer can be formed as compared with the case of using a chemical means, the state of joining with the cathode extraction layer is good, and inconveniences such as peeling hardly occur even after long-term use. However, the formation rate of lead dioxide is slower than that of the chemical method, and it takes a long time to obtain a solid electrolyte layer having a sufficient thickness. The present invention improves the above-mentioned drawbacks, takes advantage of both the chemical method and the electrochemical method, and does not deteriorate the characteristics.
The object of the present invention is to provide a solid electrolytic capacitor that is easy to manufacture.

[Means for Solving the Problems]

As a method for manufacturing a solid electrolytic capacitor, the present invention forms a first lead dioxide layer by chemical means on the upper surface of a dielectric oxide film layer of a valve metal anode having a dielectric oxide film layer formed on the surface thereof. At the same time, a second lead dioxide layer is formed on the upper surface of the first lead dioxide layer by electrochemical means. That is, according to the present invention, a solid electrolyte layer made of lead dioxide is formed by sequentially using both chemical means and electrochemical means. The figure schematically shows the structure of the electrode and the solid electrolyte layer of the solid electrolytic capacitor manufactured according to the present invention. The formed dielectric oxide film layer 2 is formed. A first lead dioxide layer 3 is first formed on this upper surface by chemical means, and a second lead dioxide layer 4 is formed on it by electrochemical means. Then, a cathode lead-out means composed of conductive layers such as a conductive carbon layer 5 and a silver paste layer 6 for drawing out the cathode is provided in contact with the second lead dioxide layer. It should be noted that the valve metal anode 1 and the silver paste layer 6 are respectively provided with lead wires 7 and 8 for leading out to the outside so that electrical connection with the outside can be obtained.

[Action]

According to the present invention, the solid electrolyte of lead dioxide is first formed by the chemical method in the first step, so that the solid electrolyte having a desired thickness is formed once or in a relatively small number of times. Next, as a second step, since a dense second lead dioxide layer is formed by an electrochemical method, the subsequent bondability between the colloidal carbon layer or the conductive paste layer and the solid electrolyte layer is improved. Further, the occurrence of peeling phenomenon on the joint surface due to long-term use is reduced.

【Example】

Next, the results of making a solid electrolytic capacitor by the method of the present invention and comparing the characteristics with those of the conventional method will be shown. First, as the anode foil, a high-purity aluminum foil having a thickness of 80 μm was prepared. This aluminum foil has been subjected to an etching treatment in advance to expand its surface area. 70 this foil
It was anodized in a boric acid bath at a voltage of V to form a dielectric insulating oxide film on the surface. Next, this foil was cut to a size of 1 cm ² , and an anode lead wire was connected by ultrasonic welding. To form the lead dioxide layer, first dip this foil in a mixed solution of 50 g of lead acetate in 40 g of water and 60 g of ammonium persulfate in 100 g of water at 70 ° C for 20 minutes. Lead was chemically deposited. Next, after washing this foil with water, this foil was immersed in a solution with a concentration of 1Mol / l lead acetate, and the silver / silver chloride reference electrode ratio was + 2V at a constant voltage and a temperature of 20 ° C.
The lead dioxide was electrochemically deposited for 20 minutes. Then, the foil was washed with water and dried at 100 ° C. for 2 hours, a silver paste was applied to the foil surface, and a cathode lead wire was connected to complete the solid electrolytic capacitor of the present invention. Further, as Comparative Example 1, the same foil as that of the embodiment of the present invention was used, and the formation of lead dioxide was performed only by the first-step chemical method. As Comparative Example 2, the same foil was similarly used.
A lead dioxide layer was formed by applying only the stepwise electrochemical method. Also in these comparative examples, a silver paste was applied and a cathode lead wire was connected to obtain a solid electrolytic capacitor. When the characteristics of these solid electrolytic capacitors were measured, the results shown in the following table were obtained. The measurement is the capacitance,
Loss (Tanδ), Equivalent series resistance value (ESR) at 100KHz
There are three items. As can be seen from these results, the capacitance of the chemical method of Comparative Example 1 alone is not so different, but both Tan δ and ESR are inferior to those of the present invention. In addition, Tan δ of Comparative Example 2 only by the electrochemical method is not so different from that of the present invention, but the contact portion between the dielectric oxide film layer and the lead dioxide layer is small and the capacitance is extremely high. It is a low value. Also, the ESR was inferior to that of the examples of the present invention.

【The invention's effect】

As described above, according to the present invention, in the method for manufacturing a solid electrolytic capacitor, the lead dioxide layer, which is a solid electrolyte, is bonded well to the cathode extraction layer, and the electrical characteristics such as loss and ESR are excellent. In addition, since peeling between the solid electrolyte layer and the cathode extraction layer is unlikely to occur during long-term use, stable characteristics can be maintained for a long time and reliability can be improved. Further, the solid electrolyte layer can be formed in a short time, and the manufacturing process can be simplified and made more efficient.

[Brief description of drawings]

The drawings are explanatory views schematically showing the structure of each layer of the solid electrolytic capacitor manufactured by the present invention. 1 ... Valve metal anode 2 ... Dielectric oxide film layer 3 ... First lead dioxide layer 4 ... Second lead dioxide layer 5 ... Conductive carbon layer 6 ... Silver paste layer 7,8 ... Lead line

Claims (1)

[Claims] 1. A first lead dioxide layer is formed by a chemical means on the upper surface of the dielectric oxide film layer of a valve metal anode having a dielectric oxide film layer formed on the surface thereof, and the first dioxide film is formed. A method of manufacturing a solid electrolytic capacitor, wherein a second lead dioxide layer is formed on the upper surface of a lead layer by electrochemical means.