JPS63146423A - Solid electrolytic capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a solid electrolytic capacitor, and more specifically, to a solid electrolytic capacitor having a partially reinforced dielectric oxide film.

2. Description of the Related Art A conventional solid electrolytic capacitor is constructed as shown in FIG. That is, a capacitor element is made by implanting a metal lead having a valve action into a metal powder having a valve action, such as tantalum, aluminum, niobium, titanium, etc., press-forming it, and sintering the capacitor element. , after sequentially forming the carbon layer 3 and the silver paint layer 4, the first external lead 6 is welded to the lead of the capacitor element, and the second external lead is led out from the silver paint layer by soldering or conductive adhesive. However, the main parts including the capacitor element are covered with an exterior resin 6.

By the way, the anodic oxide film 1 formed on the surface of the capacitor element is formed by immersing the capacitor element in a phosphoric acid aqueous solution, applying a predetermined DC voltage corresponding to the rated working voltage for a long time with the capacitor element as the positive electrode and the phosphoric acid aqueous solution as the negative electrode. Since the element is held and formed by anodic oxidation, a dielectric oxide film is formed almost uniformly on the inner and outer surfaces of the element. A semiconductor layer, which is a solid electrolyte, is formed on the surface of the anodic oxide film, and the semiconductor layer can have the electrical resistance characteristics of a capacitor due to its ability to repair the oxide film and its self-insulating ability.

Problems to be Solved by the Invention However, this anodic oxide film does not allow the semiconductor layer formed on its surface to impregnate the capacitor element with semiconductor liquid and thermally decompose it at a high temperature of 200°C or higher. Because it is formed through a process of repeating ~10 times and physically removing the excess portion of the semiconductor that has finally precipitated, it is particularly noticeable on the surface of the outer layer of the capacitor element.
In addition to deteriorating and reducing the withstand voltage, it is also susceptible to physical stress during the subsequent assembly process, and furthermore, in various environmental tests of finished products, it does not directly receive physical stress due to expansion and contraction of the exterior resin 6 and semiconductor layer 2. Therefore, most of the deterioration of leakage current characteristics and occurrence of short circuit failures occur in the anodic oxide film on the outer surface of the capacitor element. This element can be equivalently represented as a series circuit consisting of a capacitor formed by the dielectric film 1 and an external resistor of the semiconductor layer 2, as shown in FIG. 6, for example.
Due to the difference in the thickness of the semiconductor layer, in the capacitor section composed of the element top surface section 7, side surface section 8, and bottom surface section 9, the size of the resistors that are equivalently connected to each other is naturally small in the top surface section 7. It becomes larger at the side surface portion 8 and the lower surface portion 9.

Therefore, when a DC voltage is applied to the capacitor element through the anode lead silver paint layer, the breakdown voltage characteristics are degraded not at the side surface portion 8 and bottom surface portion 9 where the series resistance is large, but rather at the top surface portion T where the series resistance is small. It had an easy-to-understand drawback.

In addition, the upper surface part 7 is easily subjected to physical stress in the subsequent assembly process, and furthermore, in various environmental tests of products coated with exterior resin, it is easy to directly receive physical stress due to expansion and contraction of the exterior resin, so leakage occurs. The drawback is that deterioration of current characteristics and occurrence of short circuit failures are concentrated in the dielectric film on the top surface of the capacitor element.

The present invention is intended to solve these problems, and aims to improve voltage resistance and physical stress resistance.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention has a structure in which the dielectric film of the weak portion of the capacitor element is locally thickened.

Effect With the above configuration, the withstand voltage of the fragile portion of the capacitor element can be increased, and the withstand voltage characteristics of the solid electrolytic capacitor can be improved.

In addition, the physical stress resistance of the fragile portion of the capacitor element is increased, the short-circuit failure rate in the assembly process can be reduced, and reliability can be improved in various environmental tests.

Example Embodiments of the present invention will be described below with reference to the accompanying drawings.

Figure 1 shows a sintered body of metal powders such as tantalum, titanium, niobium, and aluminum that have valve action, and has a diameter of 2.3 rta.
n X l 3. It is cylindrical in shape.

10 is an anode IJ − of 0.3 mmφ implanted in the sintered body.
It is made of the same metal member as the sintered body. A mask member 13 having the same diameter as shown in FIG. 2 is inserted into this capacitor element.

14 is an insertion hole. This is immersed in a chemical conversion tank containing a low water content organic solvent as a chemical conversion liquid, and by a general anodic oxidation method, an extremely thick dielectric film can be formed only on the upper surface of the element.

As shown in FIG. 3, a mask member 13 is inserted into the sintered body 12 to block the electric current, and at the same time, since the low water content organic chemical liquid 16 used has a small amount of hydroxide ions, the hydroxide ions are easily exposed to chemical formation. The hydroxide ions that form the film on the mask part no longer exist. For this,
The low water content organic chemical liquid 15 has the ability to chemically form only the exposed surface of the element other than the mask member 13, and forms a dielectric film locally as shown in FIG. 1 without chemically progressing to other element parts. 11 can be formed.

Examples of organic solvents include ethylene glycol, γ-butyrolactone, methoxyethanol, glycerin, polyethylene glycol, and polycarbonate.

Dimethylformamide etc. are used.

Next, a specific example will be described in comparison with a conventional example. The following chemical solution was used as an example.

Table 1 Use chemical liquid masked capacitor element with phosphoric acid 0.1!1
120 V/in 1o1/l r-butyrolactone solution
The dielectric film on the upper surface of the capacitor element shown in FIG. 1 is formed by increasing the pressure by 1 hour and holding it for 8 oV1o. After washing with water, continue with o, 1 mol/l! The pressure was raised to 12 oV/Hr in an ice-water solution of phosphoric acid and maintained at 65 V for 2 hours to form a dielectric film on the side surfaces, bottom surface, and inside of the element.

For comparison, the conventionally used 0.1 mo71/l! J
In an aqueous solution of J, the pressure was increased to 120 V/Hr, and the pressure was increased to 5
An element is used in which a uniform dielectric film is formed on the upper surface, side surfaces, lower surface, and inside of the element by holding the element for 5V for 2 hours.

After this, a semiconductor layer, a carbon layer, and a silver paint layer are formed on the surface of the dielectric film, and then the external cathode lead is soldered, the external anode lead is resistance welded, and then an exterior resin is applied to complete the product.

Table 2 shows the short-circuit failure rate, capacity characteristics, and withstand voltage characteristics of the product.

Table 2: Short-circuit failure rate, capacitance characteristics, withstand voltage characteristics The short-circuit failure rate of the extreme chemical product in which the dielectric film of the capacitor element fragile portion of the present invention is locally thickened is reduced. Also,
Although the capacity is the same, the breakdown voltage characteristics are improved.

From this, it was confirmed that the short-circuit failure rate and withstand voltage characteristics were improved.

This product was subjected to a 90% humidity resistance life test at 85° C. for 100 hours. The results are shown in Figure 4.

After the test, the leakage current value of the conventional product increased, but the chemically formed product of the present invention showed almost no deterioration in leakage current characteristics. From this, it was confirmed that the reliability of the moisture resistance life test was improved.

Effects of the Invention As in the present invention, a solid electrolytic capacitor in which the dielectric film in the fragile part of the capacitor element is locally thickened has a higher product quality than a conventional solid electrolytic capacitor in which the dielectric film is uniformly formed using an aqueous phosphoric acid solution. The defective rate has decreased and the voltage resistance characteristics have improved.

Furthermore, the reliability when subjected to a moisture resistance life test is improved, and the practical effects thereof are extremely significant.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a capacitor element according to the present invention;
FIG. 2 is a perspective view of a mask member for realizing the present invention;
Fig. 3 is an explanatory diagram showing the chemical formation to realize the present invention, Fig. 4 is a characteristic diagram showing the characteristics of the product of the present invention, Fig. 6 is a cross-sectional view of a conventional solid electrolytic capacitor, and Fig. 6 is a general FIG. 2 is an explanatory diagram showing an equal number of capacitors and a series circuit. 1o... Anode lead, 11... Dielectric film, 12... Sintered body, 13... Mask member. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
rM Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (4)

[Claims] (1) A solid electrolytic capacitor with a locally thick dielectric film. (2) The solid electrolytic capacitor according to claim 1, wherein the portion where the dielectric film is thick is the upper surface of the element and the portion where current is concentrated. (3) The solid electrolytic capacitor according to claim 2, wherein the dielectric film is formed by anodization in a low water content organic chemical solution. (4) The solid according to claim 3, wherein the organic solvent is one or a mixed solvent of two or more of ethylene glycol, γ-butyrolactone, methoxyethanol, glycerin, polyethylene glycol, polycarbonate, and dimethylformamide. Electrolytic capacitor.