JPS6036090B2 - 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, and specifically to a method for thermally decomposing an element soaked with manganese nitrate to complete a semiconductor layer.

In the manufacturing process of solid electrolytic capacitors, a metal with a valve action such as aluminum, tantalum, niobium, zircon, or titanium is used as an anode body, and this is connected to the anode IJ-domain of a suitable metal conductor.
By joining this lead to the mounting bar, a large number of anode bodies are supported on the bar, and in this state, a protective coating is applied to the joint of each anode body with the anode cord to prevent short circuit failure. Then, the surface of the anode body is expanded by etching, etc., and then an oxide layer is formed on the anode body by anodizing treatment, and a semiconductor layer of manganese dioxide is formed on this by, for example, soaking in a manganese nitrate solution and thermal decomposition treatment. Then, a carbon layer is formed on this by immersion in a carbon suspension and heat treatment, and then a cathode layer of silver or other material is formed on this to form a capacitor element.A cathode lead is soldered to this element, and then molded. An exterior coating such as resin is applied.

In such a manufacturing method, the following method has been proposed as one method for impregnating the surface oxidized layer of the anode body with a manganese nitrate solution and thermally decomposing it.

That is, the capacitor element, which has been immersed in manganese nitrate, is immersed in molten metal, specifically solder, at the bottom of the element (on the opposite side of the leads) (specifically, the capacitor element is simply brought into contact with the surface tension of the solder). degree), the impregnated manganese nitrate is thermally decomposed by soldering heat to form a semiconductor layer of manganese dioxide.
This semiconductor formation is called a chemical conversion treatment, and this chemical conversion treatment is repeated an appropriate number of times. However, this thermal decomposition method has the disadvantage that the leakage current of the capacitor increases. In order to study this problem, the present inventor investigated the temperature distribution of the element during thermal decomposition over time.

FIG. 1 is an explanatory diagram showing the relationship between the element and solder during thermal decomposition, and the temperature heated by soldering heat at each of the bottom part c, middle part b, and top part a of the element changes over time. It changes as shown in the graph of FIG. In FIG. 1, 1 is a lead, 2 is an anode oxide layer containing manganese nitrate, and 3 is a solder layer. As is clear from the graph, the heating temperature decreases significantly as the distance from the location near the soldering temperature increases.

Therefore, it was determined that such a temperature difference between the upper and lower sides applies mechanical stress to the chemical layer (semiconductor layer) of the element, resulting in distortion of the chemical layer and an increase in leakage current. Therefore, with the above recognition in mind, the present inventor attempted measures to reduce the temperature difference between the upper and lower sides, and as a result, completed the effective thermal decomposition method of the present invention in which the leakage current can be suppressed to a small level.

FIG. 3 is a graph showing the relationship between the countermeasures attempted by the inventor and the resulting leakage current.

In this case, in the pyrolysis step shown in Figure 1, the entire solder is placed in a furnace, and the temperature around the solder is changed from room temperature to a high temperature exceeding the solder's temperature (approximately 400 oo). Each element was brought into contact with a solder bath under an atmosphere at each temperature.

As a result of measuring the leakage current of the samples at each ambient temperature, the curve characteristics shown in FIG. 2 were revealed. As is clear from this graph, it was confirmed that the leakage current is at its minimum when the ambient temperature is 200 to 500 degrees Celsius, which is close to the solder bath temperature. A leakage current of about this minimum value is sufficiently permissible in practice. Therefore, it is clear that it is most effective to keep the atmosphere at a temperature similar to that of the soldering temperature. Although the above experimental example relates to the thermal decomposition of manganese nitrate, it is of course also effective to apply to the thermal decomposition of lead nitrate, etc.

Moreover, the heating source is not limited to solder, and may of course be other molten metal.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the thermal decomposition process under room temperature atmosphere, Figure 2
The figure is a graph showing temperature changes over time at locations a, b, and c shown in FIG. 1, and FIG. 3 is a graph showing leakage current when the process shown in FIG. 1 is performed in atmospheres at various temperatures. In the figure, 1 is a lead, 2 is an element, and 3 is a solder bath. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A method for manufacturing a solid electrolytic capacitor comprising the step of bringing the bottom of the element into contact with a molten metal bath and forming a semiconductor layer on the element by thermal decomposition; temperature close to that of the molten metal bath,
A method for manufacturing a solid electrolytic capacitor, characterized in that the manufacturing method is carried out in an atmosphere of 200°C to 500°C.