JPS603768B2 - Manufacturing method of solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a solid electrolytic capacitor.

In general, a solid electrolytic capacitor is a capacitor element A, which is made by press-molding metal powder with a valve action such as tantalum, niobium, or aluminum into a cylindrical shape and then solidifying it, as shown in Figures 1 and 2. A metal member having a valve action is set up in advance as an anode lead B, and a first external lead member C bent in an L shape is welded to the protruding portion of this anode lead B, and a second external lead member D is attached. Solder the electrode lead layer G formed on the surface of the capacitor element A via the oxide layer E and the semiconductor layer F, and then attach the main part including the capacitor element A with a resin stamping trowel. It is composed of

By the way, since this capacitor is formed by polymerizing the semiconductor layer F on the oxide layer E in the capacitor element A, it is said that it can operate stably at a higher voltage than a capacitor with only the oxide layer E. Has characteristics.

However, this capacitor is equivalently divided into the capacitor part due to the oxide layer and the semiconductor layer F, as shown in FIG.
It can be expressed as a series circuit with a resistance of
Even if it is possible to form a semiconductor layer F by polymerization on the oxide layer E on the inner surface of the metal layer, it is not possible to form a metal layer as the electrode lead layer G.

For this reason, in the capacitor portions formed on the outer and inner surfaces of the capacitor element A, the magnitude of the resistance equivalently connected to each of them is naturally smaller on the outer surface and larger on the inner surface. Therefore, when a DC voltage is applied to the capacitor element A through the anode lead B and the electrode lead layer G, the breakdown voltage characteristics are more likely to be impaired on the outer surface where the series resistance is small rather than on the inner surface where the series resistance is large. There is a tendency to become.

Therefore, in the past, attempts have been made to improve the breakdown voltage characteristics by increasing the resistance of the semiconductor layer F itself.
), and no satisfactory solution has yet been proposed.

In view of these points, the present invention provides a method for manufacturing a solid electrolytic capacitor that can effectively improve the withstand voltage characteristics without sacrificing the capacitor characteristics.Examples will be described below.

In FIGS. 4 and 5, reference numeral 1 denotes a capacitor element formed by pressure molding metal powder having a valve action into a desired shape. However, depending on the characteristics, the sintering operation may be omitted.

Reference numeral 2 denotes an anode lead led out from the capacitor element, and is composed of, for example, a metal part having a valve action.

The anode IJ-de 2 can be placed on the capacitor element 1 or can be welded to the outer surface. 3
1 is an oxide layer formed on the inner surface of the capacitor element 1, and is formed by chemical conversion treatment.

Reference numeral 32 denotes an oxide layer formed on the outer surface of the capacitor element, and is formed in the same manner as the oxide layer 3 on the inner surface.

The oxide layer 32 on the outer surface is formed to be thicker than the oxide layer 3 on the inner surface, preferably at least twice as thick. 4 is a semiconductor layer formed by polymerization on the oxide layers 3, 32 on the inner and outer surfaces of the capacitor element.

Reference numeral 5 denotes an electrode lead layer mainly formed on the semiconductor layer 4 on the outer surface of the capacitor element 1, and is composed of, for example, a silver paste layer superposed on a graphite layer. It can also be configured.

Reference numeral 6 denotes a first external lead portion bent into, for example, an L shape, and the bent portion 6a thereof is welded to cross the protruding portion 2a of the anode lead 2.

Reference numeral 7 denotes a second external lead portion, one end of which is soldered to the electrode lead layer 5 at the same time as the solder layer 8 is formed.

Reference numeral 9 denotes a resin material that covers the main parts including the capacitor element 1.

Next, a method for manufacturing this capacitor will be explained with reference to FIG.

First, as shown in FIG.
Apply negative polarity DC voltage. Then, an oxide layer 3 as a dielectric layer is formed on the inner and outer surfaces of the capacitor element 1. Next, as shown in Figure b, the capacitor element is melted (melting point: 69-70℃).
It is immersed in electrically insulating stearic acid 11' to thoroughly impregnate the inside, and then pulled out. Then, as shown in FIG. 3c, the stearic acid coating 11 deposited on the outer surface of the capacitor element is removed using ethanol. In addition, it can also be removed by immersing it in hot water at 100° C. for a very short time. Next, as shown in FIG. 4D, the capacitor element 1 is immersed in a chemical conversion liquid 10, and treated in the same manner as the chemical conversion treatment shown in FIG. Note that the formation voltage is set to, for example, 2 to 3 times or more that in the case of a in the figure. Through this chemical conversion treatment, the oxide layer 3 on the outer surface of the capacitor element 1 further grows to become an oxide layer 32 that is thicker than the oxide layer 3. Note that the thickness of the oxide layer 3 is preferably at least twice that of the oxide layer 3. Next, as shown in Figure e, the condenser element is placed in a high temperature atmosphere furnace of, for example, 260 to 300 qO, and the stearic acid impregnated inside is removed. After sufficient removal, the capacitor element 1 is immersed in a chemical conversion solution 10' as shown in FIG. Thereafter, the solid electrolytic capacitor shown in FIG. 4 is obtained by a conventional method. In this way, the oxide layer 3 on the outer surface of the capacitor element 1
Since the thickness of the oxide layer 2 is set to be thicker than the thickness of the oxide layer 3 on the inner surface, the breakdown voltage characteristics can be sufficiently improved even if the series resistance due to the semiconductor layer 4 superposed on the oxide layer is small. In particular, since the oxide layer 32 is formed by impregnating the inside of the capacitor element I with stearic acid, a thick oxide layer 32 can be easily formed on the outer surface of the capacitor element 1.

Furthermore, since it is necessary to heat the capacitor element 1 to around 300° C. to remove stearic acid from the capacitor element 1, an annealing effect can be expected.

Furthermore, since there is no need to increase the resistance of the semiconductor layer formed on the oxide layer 32, the loss angle characteristics are not adversely affected.

In this regard, the present inventor used the method shown in FIG.
The formation voltage of 15 to 20V, the formation voltage of d of the same figure is 60V.
After setting each of these, we manufactured an OFIOI capacitor and measured its characteristics, and the results shown in the table below were obtained.

As is clear from the table above, the product of the present invention can increase the withstand voltage to about 15 times that of the conventional product, but the capacitance is slightly reduced due to the thicker oxide layer 32. There is no practical problem.

Normally, the rated voltage of an OFIOI capacitor is 3.15V, but in the product of the present invention, the withstand voltage is improved by about twice, so it is also possible to use it with a rated voltage of 6V class, for example. Furthermore, since the breakdown voltage is close to the formation voltage shown in FIG. 6a, the ratio of the formation voltage to the rated voltage, that is, the formation magnification, can be made small, so metal powder with a small CV value can be used and costs can be reduced. Note that the present invention is not limited to the above-mentioned embodiments; for example, the oxide layer on the outer surface of the capacitor element may be formed after forming the oxide layer on the inner surface, or may be formed before the oxide layer is formed on the inner surface. can.

In addition to being removed by heating, stearic acid can also be removed chemically. As described above, according to the present invention, withstand voltage characteristics can be effectively improved without sacrificing capacitor characteristics.

Brief Description of the Drawings Figure 1 is a front sectional view of the conventional example, Figure 2 is an enlarged sectional view of the x section in Figure 1, Figure 3 is an equivalent circuit diagram, and Figure 4 is a solid electrolytic capacitor according to the present invention. 5 is a front cross-sectional view showing Y in FIG. 4.
FIG. 6 is a front sectional view for explaining the method of the present invention.

In the figure, 1 is a capacitor element, 31 and 32 are oxide layers, 4 is a semiconductor layer, and 11' is stearic acid. Juice na figure 3 figure Juice 2 figure O4 figure Otaku figure 6 figure

Claims (1)

[Claims] 1 A process of forming an oxide layer on the inner and outer surfaces of the capacitor element by immersing the capacitor element, which is made by pressure-molding metal powder that requires valve action into a desired shape, in a chemical solution and chemically treating it, and forming the capacitor element. A step of immersing it in molten stearic acid to impregnate the inside,
After pulling the capacitor element from the stearic acid, there is a process to remove the stearic acid adhering to the outer surface of the capacitor element, and a chemical conversion treatment by immersing it in a chemical solution with only the inside of the capacitor element impregnated with stearic acid. and a step of removing stearic acid impregnated inside the capacitor element after the chemical conversion treatment. A method for manufacturing a solid electrolytic capacitor characterized by forming a thicker oxide layer.