JPH08203784A - Solid electrolytic capacitor - Google Patents

Abstract

PURPOSE: To attain high capacity and good humidity resistance load characteristic by making impregnation rate of a semiconductor layer to an etching fine hole in a solid electrolytic capacitor at least a specified value. CONSTITUTION: In a solid electrolytic capacitor which is formed by forming a dielectric oxide film layer, a semiconductor layer comprised of lead dioxide and lead sulfate and a conductor layer one by one on a surface of an anode substrate comprised of a valve action metallic foil which is etched to,a depth of 30μm or more, impregnation rate of a semiconductor layer to an etching fine hole is at least 85% in conversion value of electric capacity. Thereby, a solid electrolytic capacitor which has large capacity per unit volume, can resist a humidity resistant load test and has good characteristic can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor. More specifically, the present invention relates to a solid electrolytic capacitor having high capacity and good moisture resistance load characteristics.

[0002]

2. Description of the Related Art Generally, a solid electrolytic capacitor element has an oxide film layer formed on an anode substrate made of etched valve metal foil, and a semiconductor layer is formed on the outer surface of the dielectric oxide film layer as a counter electrode. Further, in order to reduce the contact resistance, a conductor layer is formed with a conductive paste or the like. The solid electrolytic capacitor element thus manufactured is sealed with an epoxy resin or the like and used as a solid electrolytic capacitor. As the semiconductor layer, a semiconductor layer made of lead dioxide and lead sulfate has been proposed to improve the high frequency performance of the produced solid electrolytic capacitor because of its high electric conductivity (JP-A-63-47917). ).

In general, passive components such as capacitors are always mounted on a large number of electronic devices, and therefore reliability is considered to be particularly important. As a measure to measure such reliability, high temperature load test, moisture resistance load test,
There are many test items such as a temperature cycle test, and only capacitors that can pass such test items will be offered to the market.

[0004]

On the other hand, in recent years, as electronic devices have become lighter, thinner, shorter, and smaller, a compact and high-capacity capacitor is required. To obtain such a capacitor, a valve action metal foil that is generally used is required. It is said that it is necessary to increase the etching pore depth to 30 μm or more to increase the surface area of the valve action metal foil itself. However, when such a valve-action metal foil is used and a semiconductor layer made of lead dioxide and lead sulfate having high conductivity is provided as a semiconductor layer, it is one of the reliability tests of the produced solid electrolytic capacitor. There is a problem that the tan δ value in the moisture resistance load test greatly increases.

[0005]

The present invention has been made to solve the above-mentioned problems, and its gist is to provide a depth 3
In the solid electrolytic capacitor, a dielectric oxide film layer, a semiconductor layer made of lead dioxide and lead sulfate, and a conductor layer are sequentially formed on the surface of an anode substrate made of a valve action metal foil that is etched to a thickness of 0 μm or more, The solid electrolytic capacitor has a rate of impregnation into the etching pores of the semiconductor layer of 85% or more in terms of electric capacitance.

The solid electrolytic capacitor of the present invention will be described below. Examples of the valve action metal used as the anode of the solid electrolytic capacitor of the present invention include aluminum,
Any metal foil having a valve action such as tantalum, niobium, titanium and alloys having these as substrates can be used.

The valve metal foil used in the present invention usually has etching pores having an average diameter of about 0.1 to 0.5 μm on its front and back surfaces. The etching pores have no orientation, but the entire etching pores are present,
That is, the etched portion has a thickness of 30 μm or more in the thickness direction of the valve action metal foil (in the present invention, the etching depth is defined by the distance in the thickness direction of the valve action metal foil). When the etching depth is less than 30 μm,
The capacity per unit volume becomes small, and it becomes difficult to obtain the intended light, thin, short and small solid electrolytic capacitor. The method of providing such etching pores is usually obtained by a known AC electrolysis method or the like.

In the present invention, the dielectric oxide film layer is formed along the entire surface of the etching pores. The dielectric oxide film layer may be an oxide layer of the anode substrate itself formed on the surface of the anode substrate, or a layer made of another dielectric oxide provided on the surface of the anode substrate. Although it may be present, it is particularly preferably a layer made of an oxide of the anode substrate itself. In any of the above cases, as a method for forming the dielectric oxide film layer, a known method such as an anodization method using an electrolytic solution can be used.

Next, a semiconductor layer made of lead dioxide and lead sulfate is formed on the surface of the dielectric oxide film layer. The semiconductor layer composed of lead dioxide and lead sulfate is formed, for example, from a reaction mother liquor containing persulfate ions and lead ions (for example, JP-A-63-47917). In the present invention, the semiconductor layer is etched. It is important that the rate of impregnation in the pores is 85% or more in terms of electric capacity. If the impregnation rate is less than 85%, the solid electrolytic capacitor produced will have a ta in a moisture resistance load test, which is one of the reliability tests.
The value of n δ becomes large and it cannot be put to practical use. The above-mentioned impregnation rate is determined by immersing the electrolytic solution in the etching pores and measuring the capacity of the valve action metal foil at a frequency of 1 kHz, and setting the value as 100%, it is a ratio with the capacity value when the semiconductor is impregnated. Expressed. As a method for increasing the impregnation rate of the semiconductor layer to 85% or more, for example, a valve action metal foil having a dielectric oxide film in the reaction mother liquor described above (hereinafter referred to as a chemical conversion foil).
Is immersed for several tens of minutes, then raised to a temperature of about 60 ° C., left for 30 minutes, then pulled up and washed with water, and a reaction mother liquor having an ion concentration lower than that of the first reaction mother liquor at about 60 ° C. for 30 minutes There is a method in which the process of leaving it up, washing with water and drying is repeated several times. The composition of lead dioxide and lead sulfate in the semiconductor layer is measured by infrared spectroscopic analysis of a semiconductor powder separately prepared by the same method. The lead ion species and persulfate ion species to be used, each concentration, reaction time The amount of lead dioxide is usually 98% to 40% by weight, and the balance is lead sulfate.

Next, a conductor layer is formed on the above-mentioned semiconductor layer. The conductor layer is formed by using one or more conventionally known conductive pastes such as carbon paste and silver paste. The solid electrolytic element having the conductor layer formed as described above is sealed by a sealing agent such as an epoxy resin by transfer molding and is put to practical use.

[0011]

The solid electrolytic capacitor element has a structure in which the etching pores of the chemical conversion foil are impregnated with the semiconductor. However, since the impregnation rate is not 100%, the portion where the semiconductor layer does not cover the dielectric oxide film layer. Exists. On the other hand, in the moisture resistance load test, it is considered that the moisture in the test environment attacks the oxide film not covered with the semiconductor layer and the valve metal itself to cause a chemical reaction to change the material structure. Therefore, by increasing the impregnation rate of this semiconductor layer, the invasion of this kind of moisture can be mitigated.

[0012]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples below.

Examples 1 to 6 Aluminum valve metal foils having the etching pore depths shown in Table 1 were formed in an aqueous solution of ammonium adipate to form a dielectric oxide film layer. Table 1 shows the capacities of small pieces 2 mm × 2 mm having the dielectric oxide film layer in the ammonium adipate electrolyte.

Next, 20 pieces of 2 mm × 3.5 mm pieces of valve metal foil each having the above-mentioned dielectric oxide film layer were prepared, and the lower portion of the pieces, 2 mm × 2 mm, was separately prepared. It is immersed for 30 minutes in a mixed solution of a hydrate 2.4 mol / liter aqueous solution and an ammonium persulfate 4 mol / liter aqueous solution, and then left at 60 ° C. for 30 minutes, then pulled up, washed with water and dried, and then again lead acetate trihydrate. The mixture was allowed to stand for 30 minutes at 60 ° C. in a mixed solution of an aqueous solution of 1.8 mol / liter of a Japanese product and an aqueous solution of 2 mol / liter of ammonium persulfate, and then it was pulled up, washed with water and dried. Further, such an operation was repeated twice to form a semiconductor layer composed of 54 wt% lead dioxide and 46 wt% lead sulfate. Then, a carbon paste and a silver paste are sequentially laminated on the semiconductor layer to form a conductor layer, and then a cathode lead is formed on the conductor layer side with the silver paste, and the upper part of the piece is 2 mm ×
After taking out the anode lead by welding to the 1.5 mm part,
A solid electrolytic capacitor was produced by sealing with an epoxy resin.

(Comparative Examples 1 to 4) Small pieces 2 in Examples 1 to 6
mm × 2 mm portion is immersed in a mixed solution of a lead acetate trihydrate 2.4 mol / liter aqueous solution and ammonium persulfate 4 mol / liter aqueous solution, reacted at 60 ° C. for 1 hour, then pulled up, washed with water and dried. Example 1 except that was repeated 3 times
A solid electrolytic capacitor was produced in the same manner as in steps # 6 to # 6.

As an average impregnation rate and electric performance value of 20 points of the solid electrolytic capacitors thus obtained, and as a humidity resistance load characteristic, the capacitor of each example was applied with a voltage of 6 V in a constant humidity chamber of 85 ° C. and 85% RH. The tan δ value after standing for 100 hours is shown in Table 2. As described above, the tan δ value after the test as the moisture resistance load characteristic is smaller in the example in which the impregnation rate is 85% as compared with the comparative example, and it is understood that each step is excellent.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

Industrial Applicability The dielectric oxide film layer and the semiconductor layer composed of lead dioxide and lead sulfate are sequentially formed on the surface of the anode substrate composed of the valve metal foil which is etched to a depth of 30 μm or more, and the semiconductor layer is formed as described above. A solid electrolytic capacitor in which the etching pores are impregnated with 85% or more in terms of electric capacity has a large capacity per unit volume and can withstand a humidity resistance load test, and thus can be a good solid electrolytic capacitor.

Claims (1)

[Claims] 1. A dielectric oxide film layer, a semiconductor layer made of lead dioxide and lead sulfate, and a conductor layer are sequentially formed on the surface of an anode substrate made of a valve metal foil which is etched to a depth of 30 μm or more. In the solid electrolytic capacitor
The solid electrolytic capacitor, wherein the impregnation rate of the etching pores of the semiconductor layer is 85% or more in terms of electric capacitance.