JP2908830B2 - Manufacturing method of electrolytic capacitor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for manufacturing an electrolytic capacitor using a compact of a valve metal powder of tantalum, and more particularly to a technique for improving the composition of the valve metal powder. Related.

[Prior Art] Generally, an electrolytic capacitor is provided with a dielectric layer of an oxide film on a surface of a sintered body obtained by vacuum sintering a molded body of a valve metal powder, and a dioxide layer is formed so as to be in close contact with the dielectric layer. It has a configuration in which a manganese layer, a graphite layer, a silver paste layer, and the like are sequentially coated to form a cathode.

A specific method for manufacturing such an electrolytic capacitor will be described in detail below.

First, while embedding a metal wire of the same type as the valve metal powder having an average particle diameter of several μm, pressing the powder into a predetermined shape and dimensions to form a compact, and then forming the compact, 1 × 10 ^-4
Sintering is performed at 1600 to 1800 ° C. for 15 to 30 minutes in a vacuum of not more than mmHg to form a sintered body.

Next, the sintered body is anodized in an electrolyte such as an aqueous phosphoric acid solution to form an oxide film serving as a dielectric layer on the surface of the sintered body, thereby obtaining an anodized element.

Subsequently, the anodized element is impregnated with a manganese nitrate solution, and the impregnated manganese nitrate solution is thermally decomposed and baked to form a manganese dioxide layer on the surface of the anodized element. Thereafter, a graphite layer and a silver paste layer are sequentially formed, and an appropriate metal serving as a cathode lead wire is connected using a solder or a conductive adhesive, and reinforced with a resin or the like to complete a capacitor.

[Problems to be Solved by the Invention] However, the electrolytic capacitor manufactured by the above-described method has the following problems.

That is, an electrolytic capacitor is desired to have a high breakdown voltage and a small leakage current, but elements other than the valve action metal contained in the valve action metal powder (metals, oxygen, non-metals such as hydrogen, etc. are collectively referred to). (Referred to as impurities) is unlikely to be anodized, so that when forming an oxide film to be a dielectric layer, these impurities make it difficult to form an oxide film. As a result, the number of defective portions of the oxide film increases, and cracks occur in the oxide film due to external stress after the formation of the oxide film. Thus, there is a defect that the leakage current increases and the withstand voltage deteriorates. On the other hand, it is required to reduce the leakage current by reducing the content of impurities and prevent the withstand voltage from deteriorating.
In these respects, it is difficult to reduce the total content of impurities to such an extent that a remarkable effect can be obtained, and as a result, it was not possible to prevent an increase in leakage current or deterioration in withstand voltage.

The present invention has been proposed to solve the above-described problems of the related art, and an object of the present invention is to provide a high-quality electrolytic capacitor having a small leakage current and preventing withstand voltage deterioration. It is an object of the present invention to provide an excellent method for manufacturing an electrolytic capacitor.

[Means for Solving the Problems] For the above-described objects, the present inventors have focused on the concentrations of potassium and sodium which can be relatively adjusted among various impurities contained in the valve metal powder. Various types of electrolytic capacitors were manufactured by appropriately changing these concentrations. When comparing the characteristics of these various types of electrolytic capacitors, when the concentration of potassium is within a certain low concentration range and the concentration of potassium and sodium is not more than a certain concentration, the defect of the oxide film is reduced. As a result, it has been found that the occurrence of cracks in the oxide film can be prevented, whereby the leakage current can be remarkably reduced and the withstand voltage deterioration can be prevented. The present invention has been proposed based on such experimental results.

That is, the method of manufacturing an electrolytic capacitor according to the present invention comprises forming a valve body metal powder into a compact, sintering the compact at high temperature and high vacuum to form a sintered body, In the method of manufacturing an electrolytic capacitor for obtaining an anodized element by forming an oxide film serving as a dielectric layer on the surface thereof as an anode body, the concentration of sodium and potassium contained therein as valve action metal powder However, it is characterized in that one having a potassium concentration of only 5 to 10 ppm and a total concentration of potassium and sodium of 15 ppm or less is used.

[Operation] The operation of the present invention having the above-described configuration is as follows.

That is, as the valve metal powder, the concentration of sodium and potassium contained therein is 5 to 10 ppm only in the concentration of potassium, and the total concentration of sodium added to the powder is 15 ppm or less. Accordingly, the number of defects in the oxide film can be reduced, and the occurrence of cracks in the oxide film due to external stress after the formation of the oxide film can be prevented. Therefore, the leakage current can be significantly reduced, and the withstand voltage deterioration can be prevented.

[Examples] In order to more specifically clarify the operation and effect of the method for manufacturing an electrolytic capacitor according to the present invention, anodized elements (conventional products, lots A to A) were manufactured using tantalum powder having four types of conventional impurity concentrations. D) and 2 according to the invention
Anodizing elements (products of the present invention, lots E and F) were formed using tantalum powders having various impurity concentrations, and a leakage current test was performed.

That is, first, each of the impurities having different impurity (sodium Na, potassium K) concentrations as shown in Table 1 is used.
Using a type of tantalum powder, a weight of 1 g, a diameter of 1.0 mm, a density of 5.0 g / cm ³ and a 0.5 mm diameter tantalum wire are planted therein to form a molded body. 10 ^-6 Torr
In a vacuum at 1500 ° C. or 1600 ° C. for 30 minutes to obtain a tantalum sintered body. Then, this tantalum sintered body is
In a 90 ° C phosphoric acid electrolyte, a chemical conversion treatment is performed at a chemical conversion voltage of 100 V and a chemical conversion time of 2 hours to form an oxide film on its surface.
Then, in a phosphoric acid aqueous solution at room temperature, the measurement voltage was 70 V
Was applied, and the leakage current after 3 minutes was measured. The results shown in Table 1 and FIG. 1 were obtained. In FIG. 1, the vertical axis indicates the leakage current, and the horizontal axis indicates the sintering temperature.

It is apparent from Table 1 and FIG. 1 that there is a correlation between the sodium and potassium concentrations and the leakage current, and in particular, according to the present invention, the potassium concentration alone is 5 to 5.
The products E and F of the present invention, in which the total concentration of sodium added to 10 ppm and sodium added thereto is 15 ppm or less, have significantly reduced leakage current compared to the conventional products A to D whose total concentration exceeds 15 ppm. . In particular, in the low-temperature sintering (1500 ° C. sintering) products, the leakage currents of the conventional products A to D are all much larger than 10 μA / g, while the products E and F of the present invention are extremely large.
Only a small leakage current of 4.3 to 6.1 μA / g occurs.
These results demonstrate the effect of the present invention by using a valve metal powder having a potassium concentration of 5 to 10 ppm and a total concentration of sodium added to 15 ppm or less.

Also, the CV product of tantalum powder for capacitors is 12000 CV /
g of tantalum powder, two kinds of tantalum powder having a total concentration of sodium and potassium of 31 ppm (conventional impurity concentration) and 13 ppm (impurity concentration according to the present invention) are used to form an anodized element, and then the cathode layer is formed. A solid electrolytic capacitor formed using conventional tantalum powder (conventional product)
And a solid electrolytic capacitor (product of the present invention) using the tantalum powder according to the present invention was manufactured as follows.

First, using the above two types of tantalum powder, form into a square shape with a thickness of 1.5 mm, a height of 3.5 mm, and a width of 2.0 mm. Was implanted into a molded body, and the molded body was 1 × 10 ⁻⁶ Torr
Vacuum sintering was performed at 1550 ° C. for 30 minutes in the vacuum. Subsequently, the sintered body is subjected to a chemical conversion treatment in a phosphoric acid aqueous solution at 60 ° C. for a chemical conversion voltage of 70 V and a chemical formation time of 3 hours to form an oxide film on its surface. Thereafter, a manganese dioxide layer, a graphite layer, and a silver paste layer are sequentially formed, a nickel-white lead frame is used as a cathode lead, the cathode is connected by spot welding, and the cathode is connected by a conductive adhesive. A solid electrolytic capacitor (conventional product) using a tantalum powder with a total concentration of sodium and potassium of 31 ppm, and a solid electrolytic capacitor using a tantalum powder with a total concentration of 31 ppm. The capacitor (product of the present invention) was completed.

After subjecting these solid electrolytic capacitors to heat treatment at 270 ° C. for 10 seconds as a heat treatment, for each sample, the capacitance change rate (%) at 120 Hz, the loss tangent (%) at 1 kHz, and the leakage current ( μA), and the change over time of each characteristic was examined. As a result, the results shown in FIG. 2 (product of the present invention) and FIG. 3 (conventional product) were obtained. The contents and test conditions of each sample in this measurement test are as shown in Table 2 below.

According to Table 2 and FIGS. 2 and 3, the product of the present invention in which the concentration of potassium alone is 5 to 10 ppm and the total concentration of sodium added to this is 15 ppm or less, the total concentration of these exceeds 15 ppm It is clear that the leakage current is significantly reduced as compared with the conventional product, and the effect of the present invention is also demonstrated here.

Although not shown in the table, when the withstand voltage deterioration of the product of the present invention was examined, only a slight deterioration that was almost insignificant as compared with the conventional product was confirmed.

By the way, the present invention is not limited to the above-mentioned embodiment, and the contents of sodium and potassium can be appropriately changed according to the description in the claims, and the same effects can be obtained in that case. Further, the shape and rating of the capacitor to which the present invention is applied can be appropriately selected.

[Effects of the Invention] As described above, in the method for manufacturing an electrolytic capacitor of the present invention, attention is paid to the concentration of sodium and potassium, and only by adjusting the concentration to a constant concentration, the defective portion of the oxide film can be easily and reliably formed. To provide a high quality electrolytic capacitor that can significantly reduce the leakage current and prevent the withstand voltage from deteriorating compared to the conventional type because it can reduce the occurrence of cracks in the oxide film due to external stress after the oxide film is formed. can do.

[Brief description of the drawings]

FIG. 1 shows anodizing elements A to D formed using conventional tantalum powder and anodizing elements E, E formed using tantalum powder according to the method for manufacturing an electrolytic capacitor of the present invention.
2A and 2B are graphs showing leakage current (μA / g) with respect to the sintering temperature of each of the devices A to F. FIGS. 2 and 3 show solid electrolytic capacitors (tantalum powders) manufactured using tantalum powder according to the method of the present invention. FIG. 2 is a graph showing changes over time in characteristics of a solid electrolytic capacitor (FIG. 3) manufactured by using a conventional tantalum powder. FIG.
The capacitance change rate (%) at z, (B) shows the tangent (%) of the loss angle at 1 kHz, and (C) shows the leakage current (μA).

Claims (1)

(57) [Claims] 1. A valve body metal powder is formed into a compact, and the compact is sintered at a high temperature and a high vacuum to form a sintered body. In the method for producing an electrolytic capacitor for obtaining an anodized element by forming an oxide film serving as a dielectric layer thereon, the concentration of sodium and potassium contained therein as the valve metal powder is only the concentration of potassium. 5-10
A method for producing an electrolytic capacitor, characterized in that the concentration is 15 ppm or less and the total concentration of potassium and sodium is 15 ppm or less.