JPH03104207A - Etching method for electrode of electrolytic capacitor - Google Patents

Abstract

PURPOSE:To increase the area increasing rate of an electrode for an electrolytic capacitor by increasing the tunnel-like etching hole formed by first DC etching by means of second DC etching, and etching the surface by an AC current of a pulse current. CONSTITUTION:A tunnel-like etching hole is formed in a high purity aluminum electrode by first DC etching, the etched hole is enlarged by second DC etching, and an AC or pulse current is then applied thereto to electrolytically etch it. For example, the etched hole having a diameter of 1mum or less is formed by the first DC etching, and the diameter of the hole is increased to 1 to 4mum by the second DC etching. Thus, when the hole having a large average opening diameter is formed, etchant is smoothly supplied to the interior of the hole, a corrosion by the AC etching on the inner wall of the hole is conducted similarly to that on the surface to uniformly proceed the etching on the whole surface of the electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of etching an electrode for an electrolytic capacitor used in manufacturing an electrolytic capacitor.

[Conventional technology]

An electrolytic capacitor uses a so-called valve metal, such as aluminum, capable of forming an insulating oxide film as an electrode, and uses an insulating oxide film formed on the electrode surface as a dielectric. For the electrodes of this electrolytic capacitor, high-purity aluminum foil with a thickness of several tens of micrometers to more than 100 micrometers is generally used. The electrode can take various forms, but the aluminum foil cut into strips is wound into a cylindrical shape together with Sebaret paper.

In addition, in order to increase the capacitance value per unit volume of the electrolytic capacitor, the electrodes are subjected to various physical or chemical etching treatments to expand the surface area, and then a dielectric layer is applied to the surface. An insulating oxide film layer is formed.

Various types of etching processes have been used to etch these electrodes, but in recent years, electrolytic etching, which is an electrochemical process, has been mainly used because it is easy to set various conditions. There is.

In this electrolytic etching, the aluminum electrode foil to be treated is immersed in an etching solution containing halogen ions, especially chlorine ions, etc., and the aluminum electrode foil is set as one electrode, and carbon etc. are removed from the etching solution. Set a counter electrode of It is common to do this by Ru.

Furthermore, in those using alternating current or pulsed current, in addition to a method of directly feeding power to the electrode foil, a method of indirect power feeding is also used in which power is fed through an aluminum electrode foil between opposing electrodes.

By the way, among these electrolytic etching methods, etching holes that use a direct current or a pulsed current that does not reverse the potential are usually used to form etching holes vertically from the aluminum surface of the electrode, as if digging a tunnel. A new active point for starting etching appears at the bottom of the etching hole, and as etching progresses in sequence, a deep hole is formed in the direction perpendicular to the electrode surface. In addition, in etching using alternating current, the potential is reversed every half cycle, so dissolution proceeds during the period when the current flows from the aluminum of the electrode, but when the next reverse potential occurs, the dissolution of the aluminum that is etching stops. Rather, a film is formed on the surface that masks the active sites of etching. For this reason, the etching in the cycle in which the next dissolution occurs differs from etching in which the bottom surface is sequentially dug like the starting point of DC etching, and the etching starts at an arbitrary location and etching begins. It will be repeated every cycle of alternating current.

Therefore, DC etching and AC etching each exhibit a characteristic etching hole shape, as described above. Therefore, attempts are being made to combine these features to achieve higher etching efficiency. For example, as described in Japanese Patent Publication No. 31-1830, direct current etching and alternating current etching are used alternately for short periods of time, and as in Japanese Patent Publication No. 54-40379, direct current etching is performed in the first stage In the latter stage, AC etching is performed with the ratio of each amount of electricity set within a predetermined range, and in the former stage, DC etching is performed with a fixed liquid composition or under etching conditions, as in Japanese Patent Application Laid-Open No. 63-268237. Etching, followed by alternating current etching are known. Furthermore, as described in Japanese Unexamined Patent Publication No. 1-212427, there is also a method that performs stepwise direct current etching.

[Problem to be solved by the invention]

In the conventional etching method that uses a combination of DC etching and AC etching, first a tunnel-shaped etching hole is formed by direct current, and then AC etching is used to uniformly form fine particles on the electrode surface and inside the tunnel-shaped etching hole. By sequentially forming etching holes, the effective surface area per unit area can be increased.

However, in the conventional composite etching method, the average opening of the tunnel-shaped etched holes formed by the first step of DC etching is at most 0.9 μm or less. The problem is that the etching process hardly progresses on the inner wall surface of the etching hole, and only the electrode surface portion is uniformly etched by dissolution, making it impossible to obtain the desired surface enlarging effect.

In addition, when direct current etching is performed in stages, there is an advantage that the tunnel-shaped etching holes formed in the previous etching process are enlarged by the subsequent direct current etching, but this alone is not sufficient to enlarge the surface. I can't.

Therefore, a first object of the present invention is to provide an etching method for an electrode for an electrolytic capacitor, which increases the area enlargement ratio by combining stepwise direct current etching and alternating current etching.

In addition, this invention provides an electrode for electrolytic capacitors that achieves an appropriate and efficient area expansion ratio by setting the size of the etching hole that should be controlled in the initial stage of DC etching and the expansion ratio of the etching hole in the next stage of DC etching. A second purpose is to provide an etching method.

A third object of the present invention is to provide an etching method for an electrode for an electrolytic capacitor in which the area expansion ratio is increased by changing the form of stepwise DC etching.

[Means to solve the problem]

In this invention, a tunnel-shaped etching hole is formed by direct current etching in the initial stage, and the diameter of the opening is enlarged by direct current etching in the next stage. This is based on the knowledge that etching is performed uniformly on the inner wall surface of the hole.

(Claim 1) That is, in order to achieve the first object, the method of etching an electrode for an electrolytic capacitor of the present invention forms a tunnel-shaped etching hole in a high-purity aluminum electrode by first direct current etching (first step). The etching hole is then enlarged by second DC etching (second step), and then electrolytic etching is performed by applying alternating current or pulsed current.

(Claim 2) Furthermore, in order to achieve the second object, the method for etching an electrode for an electrolytic capacitor of the present invention forms an etching hole having a diameter of less than 1 μm in a high-purity aluminum electrode by first direct current etching. Then, the diameter of the etching hole is enlarged to 1 μm to 4 μm by second DC etching.

(Claim 3) In order to achieve the third purpose, the first and second
The DC etching is characterized by being a DC etching under different conditions.

(Claim 4) Furthermore, in order to achieve the third object, the second DC etching is characterized in that it is a chemical etching.

[For production]

(Claim 1) With the above structure, a tunnel-shaped etching hole progresses by the first DC etching. A second DC etching process is performed on the electrode in which the etching hole is formed, thereby enlarging the opening diameter of the etching hole.

When a tunnel-shaped etching hole with a large average opening diameter is formed by this process, the etching solution can be smoothly supplied to the inside of the etching hole, and the corrosion effect caused by AC etching on the inner wall of the etching hole is also prevented from occurring on the surface. Etching is performed in the same manner, and etching progresses uniformly over the entire surface of the electrode. For this reason, the inside of the tunnel-shaped etched hole, which conventionally remained as an unetched portion, is also enlarged, so that the surface area per unit volume of the electrode becomes larger.

(Claim 2) Then, when a tunnel-shaped etching hole of less than 1 μm is formed in the first DC etching and the opening diameter of the etching hole is expanded to 1 to 4 μm in the second DC etching, an alternating current or a pulse current is generated. Etching processing is performed effectively, and efficient surface enlargement is achieved. By the way, the optimum average opening diameter varies somewhat depending on the etching conditions in the later stage, but normally, if it is 1 μm or less, the etching inside the tunnel-shaped etching hole will be difficult, regardless of the etching conditions in the later stage. Etching progresses slowly and only on the surface, so
Although the dissolution of aluminum increases, no effective improvement in the etching ratio can be expected.

On the other hand, when the average opening diameter increases to 4 μm or more, the opening diameter is large enough for subsequent alternating current or pulse etching, so that etching progresses inside the tunnel-shaped etching hole without any problem. However, even if the aperture diameter is increased further, there is not much difference in improving the etching magnification.In fact, the etching process that enlarges the aperture diameter increases the amount of argonium dissolved, which increases the etching process time and increases the etching magnification. This is not preferable because it causes problems such as a decrease in the mechanical strength of the foil.

〔Example〕

Hereinafter, this invention will be explained in detail based on examples.

In the following examples, as a common condition, a high purity aluminum foil with a purity of 99.99% and a thickness of 100 μm is used as the aluminum foil to be treated.

Example 1 First step: DC etching In this DC etching, the aluminum foil was placed in a 5wt% hydrochloric acid solution at a temperature of 85°C and a current density of 300mA.
Etching was performed under etching conditions of /c4 and 115 coulombs of electricity.

Second Process: Direct Current Etching This etching also uses the direct current electrolytic etching method, and the etching conditions are a temperature of 90°C, a current density of 300 mA/aa, and an amount of electricity of 10 to 25 coulombs in a 5% sulfuric acid solution. A shown in Table 1 by changing the value of electricity among the conditions
Etching was performed under the four conditions of -D, so that etching with different opening diameters could be achieved. Also shown in the same table is the case where the second step is not performed, that is, only the first step is performed.

The average opening diameter of the etching obtained as a result was as follows. The etching opening diameter was measured by taking an enlarged electron micrograph of the etched electrode foil surface, measuring the diameters of the etching holes present in a certain area, and finding the average. This measurement method is common to all of the following examples.

(Margins below this page) Table 1 The results are shown in Table 2.

Table 2 3rd step: AC etching AC etching was performed for each of the examples 1-0 to 1-D in Table 1 under the following common conditions.

Etching conditions were in a solution containing 5 wt% hydrochloric acid at a temperature of 50°C.
, the current density is 500 mA/c and the amount of electricity is 50 coulombs.

After this etching has been completed, after washing with water,
After an oxidation film was formed at a constant current of 00 mA, it was washed with water again, dried, and cut into a certain area (10 cm4) to measure the capacitance. Conclusion Example 2 First step: DC etching This DC etching was carried out under the same conditions as in Example 1.

Second step: Chemical etching A chemical etching method was used in this step. In this etching, 50%
Aluminum foil was immersed for 400 seconds, and etching was performed under the four conditions A to D shown in Table 3 by varying the processing time to achieve etching with different opening diameters. did. Also, this second
The same table also shows the case where no step was performed, that is, only the first step was performed.

(Margin below this page) Table 3 3rd step: AC etching For each example of l-O to 1-D in Table 1,
Etching was performed under the same conditions as the AC etching in the third step of Example 1.

After this etching was completed, after washing with water, an oxide film was formed under the same conditions as in Example 1, and the capacitance was measured. The results are shown in Table 4.

Table 4 Example 3 1st step: DC etching The etching conditions are the same as in Example 1.

Second step: DC etching The etching conditions in this step are also the same as in Example 1. Therefore, the average opening diameter of the foil at the end of the second step is the same as shown in Table 1.

Third step: Pulse etching The foils obtained in each of Examples 1-0 to 1-D in Table 1 were subjected to pulse etching under the following common conditions.

The etching conditions were an aqueous solution containing 25 wt % of common salt, a temperature of 75° C., a current density of IA/c1a, and an amount of electricity of 25 coulombs.

After this etching was completed, after washing with water, an oxide film was formed under the same conditions as in Example 1, and the capacitance was measured. The results are shown in Table 5.

(Margins below this page) As is clear from the experimental results in Table 5 and above, when we measured the capacitance of aluminum foil etched under each condition of this example, we found that the tunnel-shaped capacitance of this invention was It has been found that the capacitance per unit area can be increased by the process of enlarging the opening diameter of the etching hole, that is, the process performed in the second step.

In addition, as for the appropriate size range of the aperture diameter, as can be seen from each example, the lower limit needs to exceed 1 μm,
On the other hand, if the upper limit exceeds 4 μm, the increase in capacitance will hardly change or will tend to decrease, and problems such as a longer etching time and an increased amount of dissolved aluminum will occur. From this, it can be seen that the optimum average opening diameter is in the range of 1 μm to 4 μm.

〔Effect of the invention〕

As described above, according to the present invention, the following effects can be obtained.

(a) The tunnel-shaped etching hole formed by the first DC etching is enlarged by the second DC etching, and then the etching process is performed using alternating current or pulsed current, so that the etching process is performed effectively. By using such electrodes for electrolytic capacitors, it is possible to increase the capacitance per unit volume of electrolytic capacitors, which in turn allows for miniaturization of electrolytic capacitors. , it is possible to increase the capacity.

(b) Form an etching hole with an opening diameter of less than 1 μm in the first DC etching, expand the hole diameter to 1 μm to 4 μm in the second DC etching, and then perform etching treatment using alternating current or pulsed current. Since etching is performed efficiently, an electrode with a high area enlargement ratio can be manufactured.

(C) There is a degree of freedom in changing the processing conditions of the first and second DC etching, and by changing the processing conditions, it is possible to produce an electrode for an electrolytic capacitor with a high area expansion ratio.

Claims (4)

[Claims] 1. A tunnel-shaped etching hole is formed in the high-purity aluminum electrode by first direct current etching, then the etched hole is enlarged by second direct current etching, and then alternating current or pulsed current is applied to electrolyze the hole. A method for etching an electrode for an electrolytic capacitor, the method comprising etching. 2. forming the etching hole having a diameter of less than 1 μm in the high-purity aluminum electrode by the first DC etching, and then expanding the diameter of the etching hole from 1 μm to 4 μm by the second DC etching. The method of etching an electrode for an electrolytic capacitor according to claim 1. 3. Claim 1, wherein the first and second DC etchings are DC etchings under different conditions.
The method of etching an electrode for an electrolytic capacitor as described. 4. 2. The method of etching an electrode for an electrolytic capacitor according to claim 1, wherein the second DC etching is chemical etching.