JPS6048092B2 - 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 in particular to improving the characteristics and shortening the process of a solid electrolytic capacitor.
The aim is to improve the temperature and humidity dependence of capacitance, improve the frequency dependence, and shorten the process time to obtain an extremely stable solid electrolytic capacitor.

Generally, solid electrolytic capacitors are manufactured by anodizing the surface of an anode body 1 made of a film-forming metal such as tantalum, titanium, or aluminum to form a dielectric oxide film 2, as shown in FIG. A semiconducting metal oxide layer 3 of manganese dioxide is formed on the dielectric oxide film 2 by wetting the surface with pyrolysis and then coating it with carbon graphite 4 and a conductive substance 5 of silver. The finished product is either sealed in a case or coated with resin.

In FIG. 1, 6 is a solder layer and 7 is a lead wire. Hereinafter, the present invention will be explained in comparison with the problems of the conventional art.

Conventionally, after dipping into silver conductive paint and pre-drying it indoors, the silver conductive paint was dried in a hot air drying oven.
Hardening was being carried out.

However, when left to dry indoors, the environmental conditions such as temperature and humidity within the process change greatly throughout the year, resulting in variations in properties (especially t
anδ, capacitance, impedance) and the formation of the solder layer after the silver paint layer was formed as shown in FIG. In addition, in FIG. 2, A is a sectional view of a conventional element, and A is a sectional view of an element according to the present invention. For example, if you perform pre-drying during a period when relatively high temperatures and variable temperatures continue every day, such as during the rare seasons of the rainy season, the relative humidity in the air is extremely high, making it extremely difficult to set the pre-drying conditions, and the silver paint layer will deteriorate. There is a risk of absorbing moisture from the air.

In this way, the moisture adsorbed to the silver paint layer is
The moisture could not be easily removed by subsequent hot air drying, and even during inspection after the device was completed, the reliability of the inspection was sometimes lowered due to adsorption and evaporation of these moistures. It also affected the formation of the solder layer mentioned above, and often caused property deterioration and assembly failure due to solder cracking due to uncured solder. In addition, in the middle of winter when the moisture in the air is low (relative humidity is low), when pre-drying, only the surface part of the silver paint layer will harden first, and the organic solvents contained in the deeper layers will not fully evaporate and remain inside. During hot air drying in the next process, when these organic solvents evaporate due to rapid heating, the surface of the silver conductive material layer is destroyed and holes are formed.When these crater-shaped holes are formed, the silver paint layer is damaged. This results in non-uniformity, especially the loss mentioned above (Tanδ
) and frequency dependence, and during solder layer formation, solder repellency (solder does not adhere), etc. occurs. The present invention aims to eliminate the above-mentioned conventional problems and utilize infrared rays as a means for drying and curing silver conductive paint in order to obtain a stable and uniform silver paint layer.

Before specifically explaining the method of curing silver conductive paint, a brief explanation of infrared rays will be given.The wavelength of infrared rays is generally between 0.75 and 1000μ, and the coating film of commonly used paints is The constituent elements, except for special ones, are organic substances, and organic substances absorb energy in the wavelength range of 2 to 25 μ and cause molecular motion. If infrared rays in this wavelength range are emitted, this energy will be absorbed by the object with almost 100% efficiency, promoting the curing of the coating film. Infrared rays in the above waveform region are generally referred to as far infrared rays, and refer to a wavelength region of 4 to 400p. The characteristic of heating with far infrared rays is that the inside of the material is instantaneously and uniformly heated without heating the intermediate medium, so the surface of the material is not heated more than necessary and excellent physical properties are achieved. That's what you get. Other effects include a significant reduction in heat treatment time, power consumption savings, improved processing temperature accuracy, and no generation of combustion or harmful gases, so it has many unique advantages compared to other heating methods. ing. In addition, considering the improvements in the Q characteristics of the conventional solid electrolytic capacitors mentioned above, in the formation of a silver paint layer using infrared rays, the characteristics of Tan δ, capacitance, and impedance are affected by variations in the thickness of the silver paint layer and the appearance of craters. This is a dramatic improvement for reasons such as prevention of holes. The method for curing silver conductive paint using infrared rays will be described below with specific examples.

First, the infrared furnace is constructed as shown in FIG.

That is, the infrared heater section 11 is installed directly above a box 12 large enough to accommodate the electrode elements, and everything except the infrared section 13 is lined with aluminum foil. The infrared heater section 11 is
It is connected to the slider 14, and the temperature inside the furnace is controlled by adjusting the voltage. The element 15 immersed in silver conductive paint is
It is spot welded to a stainless steel ribbon, attached to the pallet 16, and placed in the position shown at the opening in Figure 3.
In this case, it is desirable to place the pallet directly under the infrared heater section. When the power is turned on, the infrared rays emitted from the infrared heater section 11 directly hit the element 15 spot-welded to the stainless steel ribbon that is the object to be irradiated, and are diffusely reflected by the aluminum foil around the furnace, causing the element 15 to be emitted from all directions. irradiation, and the element 15 is raised instantly. These conditions are shown in FIG. As shown by the solid line, the element placed in the infrared oven reached T°C in t1 minutes, but as shown by the broken line, it took T2 minutes for the element placed in the hot air circulation furnace to reach T°C. According to experiments by the inventors, when T=100, t1=0.5, T2
= 10, and it turned out that it actually rises at a speed of about 2 km. Here, an example is shown in which infrared rays are used for dry curing of a silver conductive coating.

After immersing the device in a bath of silver conductive paint, gently lift it out and leave it in a clean environment in a wind-free place for 5 minutes. When the silver conductive paint loses some fluidity, it is heated in an infrared furnace. Put it in. In this case, compared to conventionally used hot air circulation type furnaces, the cost can be lowered, and depending on the shape of the element,
A temperature range of ~150°C is appropriate, and the infrared radiation time is short, so that drying and curing of the silver paint layer can be completed with 5 to 1 powder. In addition, the wavelength range of infrared rays is 4 to 50
The far infrared range of μ was appropriate. When the manufacturing method according to the present invention is used, significant effects can be obtained particularly on loss, frequency characteristics, impedance characteristics, and soldering characteristics. These reasons are as follows. The equivalent circuit of a solid electrolytic capacitor is shown in FIG. In the figure, L is equivalent series inductance, Req is equivalent series resistance, and C is capacitance. Furthermore, Reqs is composed of the following elements. (H′. o = Nini ≠ = Column resistance and R.

is broken down into the following components: R″o: Distributed constant related to resistance, which changes depending on specific resistance of manganese dioxide, pore shape, etc. Rex:
The resistance of the manganese dioxide on the outer surface, the contact resistance of the manganese dioxide/graphite/silver conductive paste/solder layer, etc., and the specific resistance of the material, i.e., and the loss of the capacitor (Tan δ) are expressed as:

However, ω=2π8f=frequency. Therefore, when a silver paint layer is produced by the method of the present invention, the above-mentioned R. Among the constituents of ReO, the contact resistance and material resistance of ReO are significantly reduced. This is thought to be because the silver paint layer not only does not contain water or organic solvents immediately after production, but also because the silver paint layer is formed extremely uniformly from the deep layer to the surface. Next, as a specific example of the present invention, a case where the present invention is used in a tantalum solid electrolytic capacitor will be described. Note that anodic oxidation (chemical conversion) was performed under the conditions shown in the following table. Then, specific gravity 1.35
(30°C) and impregnated with manganese nitrate aqueous solution at a temperature of 30°C.
Thermal decomposition is carried out in a hot air circulation furnace at 0°C for 1 hour and 15 minutes.

This operation of impregnation and thermal decomposition is carried out several times in combination with reconstitution as appropriate, and then a carphone layer with a specific gravity of 1.05 (25°C) is provided, and this is dipped in silver paint with a dilution rate of 50% by weight. After pulling it up and leaving it indoors (normal temperature and humidity) for 5 minutes in a place where it is not exposed to wind,
The following table shows a comparison between the elements subjected to one-powder treatment in an infrared furnace set to C and the cathode-treated elements treated by the conventional method (hot air circulation furnace treatment). In addition, in the above table, the O mark indicates good quality, the × mark indicates poor quality, and the Δ mark indicates an intermediate value.

FIG. 6 shows the characteristics when the method of the present invention is used.

FIG. 6A shows the loss (Tanδ) characteristics of the solid tantalum electrolytic capacitor obtained by the manufacturing method according to the present invention,
The same is the impedance characteristic. The aforementioned Re, . ，
It can be seen that the portion a, which is considered to be the pure resistance value, has become considerably lower due to the reduction in . Further, C is the leakage current of the element when the relative humidity %RH at a temperature of 55 DEG C. is changed from 50% RH to 90% RH. As is clear from the above results, according to the manufacturing method of the present invention, it is possible to reduce loss of solid electrolytic capacitors, improve frequency characteristics, improve solderability, and significantly shorten process time. This is of great industrial value.

[Brief explanation of the drawing]

Figure 1 A, A, and C are a perspective view of an anode body constituting a solid electrolytic capacitor according to the present invention, a sectional view of the element, and an enlarged sectional view of the same essential parts, and Figure 2 A is an anode body soldered to a light silver paint layer. An enlarged cross-sectional view of the main parts of the conventional element and an enlarged cross-sectional view of the main parts of the element according to the method of the present invention, Figure 3A shows a perspective view and internal configuration diagram of the infrared furnace, and Figure 4 shows the hot air of the infrared furnace. Figure 5 is an equivalent circuit diagram of a solid electrolytic capacitor; Figure 6 shows the loss characteristics and impedance characteristics of the capacitor according to the present invention and the conventional capacitor;
FIG. 4 is a comparison diagram of leakage current characteristics. 1... Anode body, 2... Dielectric oxide film, 3... Manganese dioxide layer (semiconductor metal oxide layer)
, 4... Carbon layer (carbon graphite), 5... Silver paint layer, 6... Solder layer, 7... Lead wire, 11... ... Infrared heater section, 12 ... Box, 13 ...
Infrared section, 15...element.

Claims (1)

[Claims] 1 A film-forming metal is used as an anode body, a dielectric oxide film is formed on its surface, and a manganese dioxide layer,
In a method for manufacturing a solid electrolytic capacitor in which an element is constructed by sequentially laminating a carbon layer and a silver paint layer, after forming a carbon layer, 4 to 5 layers of silver paint are applied.
A method for manufacturing a solid electrolytic capacitor, which comprises drying and curing with far infrared rays having a wavelength of 0μ to form a silver paint layer.