JPH04177812A - Method of forming electrolytic layer of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To make a uniform electrolytic layer with a constant thickness at the surface of an electrode body by making the air flow in from below a porous plate thereby dispersing the silicon dioxide particles laid uniformly on the porous plate so as to make the surface of an capacitor element adsorb them. CONSTITUTION:A capacitor element 8, where a dielectric oxide film is made at the surface of a tantalum porous body, is impregnated with manganese nitrate solution, and this capacitor element 8 is placed in an adsorbing bath 1. The air compressed with a compressor 6 is dried with an air drier or a heater 1, and is guided into the adsorbing bath 1 from below a porous plate 2, whereby the silicon dioxide particles 4 laid uniformly on the porous plate 2 are dispersed in atmosphere so as to make the surface of the capacitor element adsorb the silicon dioxide particles. Subsequently, the thermal decomposition of the manganese nitrate solution is performed to form an electrolytic layer. Hereby, a uniform electrolytic layer can be made easily with a constant thickness at the surface of the electrode body.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of forming an electrolyte layer of a solid electrolytic capacitor that protects a dielectric layer.

Conventional technology Conventional solid electrolytic capacitors are made using valve metal powders such as tantalum, aluminum, niobium, and titanium.
A dielectric oxide film, a manganese dioxide layer, a carbon layer, and a silver paint layer are sequentially formed on the surface of the capacitor element, which has been pressure-formed and sintered with a lead wire made of a metal having a valve action. It was constructed by leading out external lead wires and covering the main part including the capacitor element with an exterior resin.

The first method for forming the manganese dioxide layer in this fixed electrolytic capacitor is to impregnate the electrode body in a low concentration manganese nitrate solution with low specific gravity, and then repeat the operation several times to thermally decompose it at an appropriate temperature. The interior is filled with manganese dioxide, then impregnated with a highly concentrated manganese nitrate solution with a high specific gravity, and the process of thermal decomposition at an appropriate temperature is repeated several times to form a manganese dioxide layer on the surface. Ta. In addition, the second method, similar to the first method, impregnates the electrode body in a low concentration manganese nitrate solution with low specific gravity,
Then, after repeating the operation of thermal decomposition at an appropriate temperature several times to fill the interior with manganese dioxide, it is impregnated with a liquid in which silicon dioxide powder particles are dispersed in a manganese nitrate solution, and thermal decomposition is performed at an appropriate temperature. This process was repeated several times to form a manganese dioxide layer on the surface.

Problems to be Solved by the Invention However, these methods have the following problems. That is, in the first method, in order to form a necessary and sufficient thickness of the manganese dioxide layer, the impregnation step with the manganese nitrate solution and the thermal decomposition step are repeated many times, which increases the cost. There was a problem in that it was difficult to obtain a uniform manganese dioxide layer on the surface. In addition, in order to form the necessary and sufficiently thick manganese dioxide layer with a small number of thermal decomposition cycles, it was necessary to use a highly concentrated manganese nitrate solution with a high specific gravity; Since the manganese nitrate solution is highly hygroscopic, it is extremely difficult to adjust and manage its concentration.

Although the second method has the advantage of reducing the number of repetitions of the manganese nitrate impregnation step and the thermal decomposition step, it is difficult to keep the silicon dioxide powder particles in the solution uniformly dispersed, and the immersion method Therefore, it is difficult to deposit the manganese dioxide layer on the surface as a uniform dispersion, resulting in a non-uniform manganese dioxide layer.

The present invention has been made to solve these problems, and provides a method for forming an electrolyte layer of a solid electrolytic capacitor that can form a very uniform electrolyte layer with a constant thickness on the surface of an electrode body. The purpose is to provide

Means for Solving the Problems In order to solve the above problems, the method for forming an electrolyte layer of a solid electrolytic capacitor of the present invention includes, as a first means, an anode lead made of a valve metal in a porous body made of a valve metal. At the same time, a capacitor element is constructed by impregnating an electrode body formed by forming a dielectric oxide film on the surface of the porous body with a manganese nitrate solution. Silicon powder particles are laid down, air is introduced from below the porous plate to disperse the silicon dioxide powder particles in an atmosphere, and the silicon dioxide powder particles are placed on the surface of the capacitor element placed in this atmosphere. The manganese nitrate solution is adsorbed, and then the manganese nitrate solution is thermally decomposed to form an electrolyte layer.

In addition, in recent years, valve action metal powder, which is the main material of solid electrolytic capacitors, has been becoming finer. However, as this valve action metal powder becomes finer, the ability to draw out the capacity tends to deteriorate. When an electrolyte layer is formed by the method described above, the second method is to impregnate an electrode body formed by forming a dielectric oxide film on the surface of a porous body made of a valve metal with a manganese nitrate solution. The process of thermal decomposition is then repeated several times to use a capacitor element whose interior is filled with manganese dioxide.

In addition, as the ability to extract the capacitance becomes worse, the tangent value of the loss angle (tan δ) becomes larger. In order to solve these problems, the present invention provides a valve metal After impregnating the electrode body, which is made by forming a dielectric oxide film on the surface of a porous body with a manganese nitrate solution, the process of thermal decomposition is repeated several times to pre-fill the inside with manganese dioxide. Subsequently, the electrode body is impregnated with a manganese nitrate solution, and the silicon dioxide powder particles spread uniformly on the porous plate are dispersed in the atmosphere by flowing air from below the porous plate. a step of adsorbing silicon dioxide powder particles onto the surface of the capacitor element placed in this atmosphere, then thermally decomposing the manganese nitrate solution, and then subsequently impregnating the manganese nitrate solution and thermally decomposing it. This process is repeated several times to form an electrolyte layer.

Effect: According to the method for forming an electrolyte layer of a solid electrolytic capacitor of the present invention described above, a very uniform electrolyte layer with a constant thickness can be extremely easily formed on the surface of an electrode body, and as a result, the process can be easily performed. Since troubles can be largely eliminated, productivity can be improved. Furthermore, since an electrolyte layer of a required thickness can be formed with a small number of thermal decomposition cycles, the process can be shortened.

And when forming an electrolyte layer, compared to the past,
Since an electrolyte layer of the required thickness can be formed using a manganese nitrate solution with a low concentration (low specific gravity), concentration control of the manganese nitrate solution becomes very easy.

Furthermore, as mentioned above, it is possible to form an extremely uniform electrolyte layer with a constant thickness on the surface of the electrode body, which not only improves process yield but also improves short-circuit failure rates in high-temperature load tests and moisture resistance tests. The short-circuit failure rate of solid electrolytic capacitors can be improved, and the variation in withstand voltage can also be reduced, resulting in a significant improvement in the quality of solid electrolytic capacitors.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the structure of a silicon dioxide powder particle adsorption device used in the method for forming an electrolyte layer of a solid electrolytic capacitor according to an embodiment of the present invention. 1 is an adsorption tank; A porous plate 2 is attached to the porous plate 2, and a plurality of electrostatic charging electrodes 3 are attached to the porous plate 2.

The tip of this electrostatic charging electrode 3 is positioned above the porous plate 2. Further, silicon dioxide powder particles having a particle size of 7 μm to 40 μm are uniformly spread on the porous plate 2, and a high voltage is applied to this electrostatic charging electrode 3 from a high voltage generator 5. ing. Furthermore, a compressor 6 and an air dryer or heater 7 are provided outside the adsorption tank 1, and the air compressed by the compressor 6 is dried by the air dryer or heater 7, and this dried air is adsorbed! I am trying to install it within 1.

The capacitor element 8 placed in the adsorption tank 1 is a porous body made of tantalum, which is a valve metal. This electrode body is connected to a stainless steel plate 10 at the anode lead wire 9, and a voltage of 115V is applied by anodizing method using a boat. A voltage is applied to form a dielectric oxide film on the surface of the tantalum porous body.

Then, the capacitor element 8, which is an electrode body in which the dielectric oxide film is formed on the surface of a porous body, is immersed in a manganese nitrate solution having a specific gravity of 1.30 using a general method to impregnate it, and the surface is also impregnated with the manganese nitrate solution. After sufficiently adhering the liquid, the process of thermally decomposing the manganese nitrate solution for 5 minutes in an electric furnace at 250°C was repeated three times to fill the interior with manganese dioxide.

After repeating the above thermal decomposition treatment three times, the capacitor element 8 was then immersed in a manganese nitrate solution with a specific gravity of 1.40 and pulled out.
was installed in the adsorption tank 1.

In this state, the air compressed by the compressor 6 is dried by an air dryer or heater 7, and the dried air is introduced into the adsorption tank 1 from below the porous plate 2. The introduced compressed air causes the silicon dioxide powder particles 4 evenly spread on the porous plate 2 to move into the adsorption tank 1.
will be dispersed into the atmosphere. In this case, a high voltage generator 5 generates a corona discharge with an output of 70 kV at the tips of the plurality of electrostatic charging electrodes 3 attached to the porous plate 2 to generate static electricity, and charge the silicon dioxide powder particles 4. When given, the silicon dioxide powder particles 4 repel each other, so that the above-described dispersion of the silicon dioxide powder particles 4 is performed more evenly.

Further, according to the above method, even when a large number of capacitor elements 8 are installed in the atmosphere inside the adsorption tank 1, the silicon dioxide powder particles 4 are scattered along the lines of electric force, so that the side, top, and bottom surfaces of the capacitor elements 8 are The silicon dioxide powder particles 4 are uniformly adsorbed. Due to this electrostatic adsorption, a thickness of 5.5 mm is applied to the surface of the dielectric oxide film of the capacitor element 8.
A silicon dioxide powder particle layer of 0.011 m to 70 μm is formed.

The electrostatic charge on the silicon dioxide powder particles 4 described above is 1
0kV or higher is required.

Furthermore, the air flowing in from below the porous plate 2 has a temperature of 20
If air is introduced at a temperature of 4 vol. Temperature is 20℃ or higher and humidity is 4volX
Dry air below LO is desirable.

Furthermore, the tips of the plurality of electrostatic charging electrodes 3 attached to the porous plate 2 are located above the porous plate 2 in the above embodiment, but are located inside the porous plate 2 or It may also be located below the porous plate 2.

As described above, corona discharge is caused by the high voltage generator 5 to generate static electricity at the tip of the electrostatic charging electrode 3, and when the silicon dioxide powder particles are charged with the static electricity, the silicon dioxide powder particles is negatively charged, and when the silicon dioxide powder particles approach the grounded capacitor element 8, the silicon dioxide powder particles are attracted to the surface of the capacitor element 8. This adsorption takes place evenly in the form that the charged silicon dioxide powder particles are attracted to the shaded areas and wrap around them.

Thereafter, the manganese nitrate solution was thermally decomposed in an electric furnace at 250° C. for 5 minutes. Due to the action of the manganese dioxide produced by this thermal decomposition as a binder, the silicon dioxide powder particles on the surface of the capacitor element 8 are bonded to the capacitor element 8.
At the same time as the particles come into close contact with the surface of the particles, bonding between each particle takes place.

After this thermal decomposition, the silicon dioxide powder particles adsorbed on the anode lead wire 9 and the stainless steel plate 10 connected thereto were removed by pouring water on them.

Subsequently, the capacitor element 8 is
The electrolyte layer was formed by repeating twice the process of immersing in the manganese nitrate solution of No. 5 to impregnate it and thermally decomposing the manganese nitrate solution for 5 minutes in an electric furnace at 250°C.

Subsequently, a colloidal carbon layer and a silver paint layer which will become a cathode conductive layer are sequentially laminated thereon, and the anode terminal is connected to the anode lead wire 9, and the cathode terminal is connected to the silver paint layer. By applying resin exterior, 35
A solid electrolytic capacitor with a voltage of 6.8 μF was completed.

Its characteristics remain as shown in Tables 1 and 2. For comparison, the characteristics of a capacitor manufactured by the second method described in the conventional technique are also shown.

Table 1 Relationship between process defect rate and withstand voltage (blank below) Table 2 Number of short circuit failures in high temperature load tests and failures in moisture resistance tests (r/n r: number of failures, n: number of tests) As is clear from Tables 1 and 2, according to the method for forming the electrolyte layer of the solid electrolytic capacitor in one embodiment of the present invention,
In addition to improving process yield, it is possible to improve the short-circuit failure rate in high-temperature load tests and the failure rate in moisture resistance tests, and it is also possible to reduce variations in withstand voltage, which cannot be achieved with conventional methods. It is possible to improve the quality of the product.

Further, the thickness of the silicon dioxide powder particle layer adsorbed onto the surface of the capacitor element 8 can be adjusted by changing the dispersion time of the silicon dioxide powder particles, charging voltage, etc. If the particle size of silicon dioxide powder particles is too small, the voids between the particles will be small, and during thermal decomposition, they will be easily pushed up by steam and nitrogen oxide gas generated during boiling (as a result, the condenser Since the electrolyte layer uniformly formed on the surface of the element 8 is destroyed, the average particle size is preferably 7 μm or more. On the other hand, if the particle size is too large, the particles become heavy and uniform adsorption becomes difficult.
It was experimentally confirmed that a thickness of 40 μm or less is desirable.

In the above embodiment, the anode lead wire 9 and the porous body constituting the capacitor element 8 are made of tantalum, which is a valve metal. However, they may be made of a valve metal such as aluminum or titanium. It goes without saying that it is okay to do so.

Effects of the Invention As described above, according to the method for forming an electrolyte layer of a solid electrolytic capacitor of the present invention, a very uniform electrolyte layer with a constant thickness can be extremely easily formed on the surface of an electrode body. , process troubles can be largely eliminated,
As a result, productivity can be improved.

Furthermore, since an electrolytic layer of manganese dioxide or the like having a required thickness can be formed with a small number of thermal decomposition cycles, the process can be shortened.

And when forming an electrolyte layer, compared to the past,
Since an electrolyte layer of the required thickness can be formed using a manganese nitrate solution with a low concentration (low specific gravity), concentration control of the manganese nitrate solution becomes very easy.

Furthermore, as mentioned above, it is possible to form an extremely uniform electrolyte layer with a constant thickness on the surface of the electrode body, which not only improves process yield but also improves short-circuit failure rates in high-temperature load tests and moisture resistance tests. The short-circuit failure rate of solid electrolytic capacitors can be improved, and the variation in withstand voltage can also be reduced, thereby significantly improving the quality of solid electrolytic capacitors.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of a silicon dioxide powder particle adsorption device used in a method for forming an electrolyte layer of a solid electrolytic capacitor in an embodiment of the present invention. 1... Adsorption tank, 2... Porous plate, 3.
...Electrostatic charging bridge, 4...Silicon dioxide powder particles, 5...High voltage generator, 6...
... Compressor, 7 ... Air dryer or heater, 8 ... Capacitor element, 9
...Anode lead wire, 10...Stainless steel plate.

Claims (9)

[Claims] (1) An anode lead wire made of a valve metal is implanted in a porous body made of a valve metal, and an electrode body formed by forming a dielectric oxide film on the surface of the porous body is impregnated with a manganese nitrate solution. On the other hand, silicon dioxide powder particles are spread uniformly on a porous plate, and air is introduced from below the porous plate to disperse the silicon dioxide powder particles in the atmosphere. A solid electrolytic capacitor comprising the steps of adsorbing silicon dioxide powder particles onto the surface of the capacitor element placed in this atmosphere, and subsequently thermally decomposing a manganese nitrate solution to form an electrolyte layer. A method for forming an electrolyte layer. (2) An anode lead wire made of a valve metal is implanted in a porous body made of a valve metal, and an electrode body formed by forming a dielectric oxide film on the surface of the porous body is impregnated with a manganese nitrate solution. After that, the thermal decomposition process is repeated several times to pre-fill the interior with manganese dioxide, and then the capacitor element is constructed by impregnating with manganese nitrate solution. silicon dioxide powder particles are placed on the porous plate, air is introduced from below the porous plate to disperse the silicon dioxide powder particles in the atmosphere, and the silicon dioxide powder is applied to the surface of the capacitor element placed in this atmosphere. A method for forming an electrolyte layer of a solid electrolytic capacitor, comprising the steps of adsorbing particles and subsequently thermally decomposing a manganese nitrate solution to form an electrolyte layer. (3) An anode lead wire made of a valve metal is implanted in a porous body made of a valve metal, and an electrode body formed by forming a dielectric oxide film on the surface of the porous body is impregnated with a manganese nitrate solution. After that, the thermal decomposition process is repeated several times to pre-fill the interior with manganese dioxide, and then the capacitor element is constructed by impregnating with manganese nitrate solution. silicon dioxide powder particles are placed on the porous plate, air is introduced from below the porous plate to disperse the silicon dioxide powder particles in the atmosphere, and the silicon dioxide powder is applied to the surface of the capacitor element placed in this atmosphere. It is characterized by having a step of adsorbing particles, then thermally decomposing a manganese nitrate solution, and then repeating the steps of impregnating with a manganese nitrate solution and thermally decomposing several times to form an electrolyte layer. Method of forming electrolyte layer of solid electrolytic capacitor. (4) Formation of the electrolyte layer of the solid electrolytic capacitor according to any one of claims 1, 2, and 3, wherein the silicon dioxide powder particles are charged with static electricity, and the silicon dioxide powder particles are adsorbed to the surface of the capacitor element by the static electricity. Method. (5) As a means for electrostatically charging the silicon dioxide powder particles, the tip of an electrostatic charging electrode is positioned above the porous plate, in the porous plate, or below the porous plate, and the electrostatic charging electrode 5. The method for forming an electrolyte layer of a solid electrolytic capacitor according to claim 4, wherein the silicon dioxide powder particles are charged with static electricity. (6) Claim 4: The electrostatic charging voltage is 10 kV or more.
A method for forming an electrolyte layer of the solid electrolytic capacitor described above. (7) The temperature of the air flowing in from below the porous plate is 20℃
The method for forming an electrolyte layer of a solid electrolytic capacitor according to any one of claims 1, 2, and 3, which is the above. (8) The air flowing from below the porous plate has a humidity of 4 vol.
4. The method for forming an electrolyte layer of a solid electrolytic capacitor according to claim 1, wherein the dry air has a concentration of %H_2O or less. (9) The method for forming an electrolyte layer of a solid electrolytic capacitor according to any one of claims 1, 2, and 3, wherein the powder particle size of the silicon dioxide used is 7 μm or more and 40 μm or less.