JP2637199B2 - Method for manufacturing solid electrolytic capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a solid electrolytic capacitor having good high-temperature life performance.

[Conventional technology]

The solid electrolytic capacitor has a structure in which a semiconductor layer and a conductor layer are sequentially laminated on an anode substrate having a dielectric oxide film layer made of a valve metal such as aluminum, tantalum, and niobium. Conventionally, manganese dioxide formed mainly by thermal decomposition of manganese nitrate has been used for the semiconductor layer of this type of solid electrolytic capacitor. However, due to the high heat required during this thermal decomposition and the oxidizing action of the generated NO ₂ gas, the metal oxide film such as aluminum and tantalum, which is a dielectric, is damaged, so the withstand voltage is reduced and the leakage current is reduced. There is a major drawback such as an increase in size and deterioration of dielectric properties. Also, several steps of re-chemical formation are required.

To solve these drawbacks, a method of forming a semiconductor layer without applying high heat, that is, a method of forming a highly conductive inorganic semiconductor layer has been attempted. Examples thereof include a solid electrolytic capacitor using α-type PbO ₂ as a semiconductor layer in JP-A-62-189713, and a β-type PbO ₂ electrochemically forming a semiconductor layer in JP-A-62-185307. Solid electrolytic capacitors are known.

[Problems to be solved by the invention]

α-type PbO ₂ has good adhesion to the dielectric oxide film layer, but has the disadvantage of poor electrical conductivity, and β-type PbO ₂ has excellent electrical conductivity, but the dielectric oxide film layer Has a disadvantage that the adhesiveness to the adhesive is poor. For this reason, the solid electrolytic capacitor using the former for the semiconductor layer has poor high-frequency performance, and the solid electrolytic capacitor using the latter for the semiconductor layer cannot obtain a good high-temperature life performance.

[Means for solving the problem]

An object of the present invention is to provide a method for manufacturing a solid electrolytic capacitor which does not have the disadvantages of α-type PbO ₂ and β-type PbO ₂ as described above and has only the advantages of each.

That is, the present invention firstly forms an α-type PbO ₂ layer electrochemically on the surface of an anode substrate made of a metal having a valve action, and then electrochemically forms a β-type PbO ₂ layer to form a semiconductor layer. A method for manufacturing a solid electrolytic capacitor.

Hereinafter, the present invention will be described in detail. As the valve action metal used as the anode substrate of the solid electrolytic capacitor according to the present invention, any metal having a valve action such as, for example, aluminum, tantalum, niobium, titanium and alloys using these as a substrate can be used.

The dielectric oxide film layer provided on the surface of the valve metal may be an oxide layer of the valve metal itself provided on the surface of the valve metal, or may be another oxide layer provided on the surface of the valve metal. It may be a layer of a dielectric oxide, but is particularly preferably a layer made of an oxide of the valve metal itself.
In any case, as a method of providing the oxide layer, a conventionally known method such as an anodizing method using an electrolytic solution can be used.

The semiconductor layer formed on the dielectric oxide film layer first has an α
It is obtained by forming a type PbO ₂ layer and then laminating a β type PbO ₂ layer. As a method for forming the α-type PbO ₂ layer and the β-type PbO ₂ layer, a method of electrochemically forming each is effective. When formed by a chemical reaction, there is a disadvantage that the conductivity of the semiconductor layer is unstable because the thickness of each PbO ₂ layer is not uniform.

As a method for forming the α-type PbO ₂ layer, a method for forming the layer by performing electrolysis in a solution containing copper ions having a pH of 7.5 or more can be mentioned.

On the other hand, the method of forming the β-type PbO ₂
There is a method of forming by performing electrolysis in a solution containing copper ions. As the solution containing copper ions, for example, an aqueous solution of lead acetate, an aqueous solution of lead nitrate,
An aqueous lead citrate solution, an aqueous lead propionate solution and the like can be mentioned.

The above-described electrolysis method for forming each PbO ₂ layer is performed by using a separately prepared stainless steel with the anode substrate side as an anode.
There is a method in which an electric circuit is formed by using a metal such as aluminum as a cathode and electrolysis is performed by a known method such as a constant voltage method, a constant current method, or a combination thereof. Among them, a method of forming each PbO ₂ layer by a constant current method is particularly preferable because the thickness of the layer can be made constant.

In the present invention, a conductive layer such as a carbon paste layer and / or a silver paste is taken out of the above-described semiconductor layer by a conventionally known method, and further sealed by a conventionally known method such as a resin case to obtain a product.

[Action]

The α-type PbO ₂ layer laminated on the dielectric oxide film layer formed on the surface of the valve metal anode substrate is closely adhered to the oxide film layer. And β-type Pb laminated on this α-type PbO ₂ layer
O ₂ layer has a good electrical conductivity. Accordingly, a solid electrolytic capacitor having excellent high-temperature life performance and good high-frequency performance can be obtained only by such a configuration of each layer.

〔Example〕

 Hereinafter, examples and comparative examples will be described.

Examples 1 to 3 A small 1 cm × 1 cm piece of a 10 μF / cm ² aluminum etching foil (hereinafter referred to as a chemical conversion foil) having a dielectric coating layer formed on the surface by chemical conversion treatment in an aqueous solution of ammonium adipate was used for 60 times.
A total of 20 sheets were prepared and used in each example. First
In each solution described in the table, the first stage was 0.5 mA / cm
Electrolysis at constant current of ² for 20 minutes, then 1.0 mA / cm ^{2 in the} second stage
And 80 minutes electrolysis at a constant current of each α-type PbO ₂ layer and β
A type PbO ₂ layer was formed. The structure of the PbO ₂ layer was confirmed by X-ray analysis of a sample prepared separately and subjected to the same operation.
Next, after applying and drying a commercially available silver paste on the semiconductor layer,
It was sealed with epoxy resin to produce a solid electrolytic capacitor. The thickness of the semiconductor layer of the embodiment, alpha-type PbO ₂ layers 5
The thickness of the β-type PbO ₂ layer was 8 to 15 μm.

Comparative Examples 1-3 Sixty pieces of the same chemical conversion foil as in Example 1 were prepared, and twenty pieces were used for each of the comparative examples. In Comparative Example 1, the α-type PbO ₂ layer was formed by electrolysis at a constant current of 0.5 mA / cm ² for 1 hour with the first stage solution composition of Example 2. In Comparative Example 2, the β-type PbO ₂ layer was formed by electrolysis at a constant current of 1.0 mA / cm ² for 1.2 hours using the solution composition in the second stage of Example 2. In Comparative Example 3,
2.8 mol of ammonium persulfate was added to the first stage solution of Example 1.
And 28% aqueous ammonia to maintain pH 9.2.
After reacting for an hour to form an α-type PbO ₂ layer, 2.8 mol of ammonium persulfate was further added to the second stage solution of Example 1.
The pH was adjusted to 6.0, and the mixture was reacted for 1 hour to form a β-type PbO ₂ layer.

A conductor layer was formed on the element formed up to the semiconductor layer in the same manner as in the example, and sealing was performed to produce a solid electrolytic capacitor. The thickness of the semiconductor layer was 15 in Comparative Example 1.
-25 μm, 20-50 μm in Comparative Example 2, 15-120 μm in Comparative Example 3.
μm.

Table 2 shows the performance of the solid electrolytic capacitor manufactured as described above. The average value of n = 20 points.

As is clear from Table 2, the solid electrolytic capacitor using the α-type PbO ₂ layer as the semiconductor layer (Comparative Example 1) has poor high-frequency performance, while the solid electrolytic capacitor using the β-type PbO ₂ layer as the semiconductor layer (Comparative Example 1) 2) is inferior in high-temperature life performance. In addition, a solid electrolytic capacitor in which a semiconductor layer is obtained by a chemical reaction (Comparative Example 3)
Since the thickness of the semiconductor layer is uneven, the semiconductor layer lacks stability. As a result, the high-frequency performance and the high-temperature life performance are inferior.
In contrast to these comparative examples, it can be seen that the examples satisfy both high-frequency performance and high-temperature life performance.

〔The invention's effect〕

As described above, according to the method for manufacturing a solid electrolytic capacitor of the present invention, the α-type PbO ₂ layer having excellent adhesion to the dielectric oxide film layer is used as the first layer, and the β
The PbO ₂ layer is laminated as a second layer, and the PbO ₂
Since the thickness of the layer is uniform, a solid electrolytic capacitor having good high-frequency performance and excellent high-temperature life performance can be manufactured.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-305509 (JP, A) JP-A-62-185307 (JP, A) JP-A-62-189713 (JP, A)

Claims (1)

(57) [Claims] 1. A method for manufacturing a solid electrolytic capacitor comprising a dielectric oxide film layer, a semiconductor layer, and a conductor layer sequentially formed on a surface of an anode substrate made of a metal having a valve action. Α-type PbO ₂ layer on top, then β-type
A method for manufacturing a solid electrolytic capacitor, wherein each of PbO ₂ layers is electrochemically formed to be the semiconductor layer.