JPH07220984A - Solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To improve yield of a product by eliminating generation of a protrusion of solid electrolyte at a corner of a pyramidal pellet when the electrolyte is formed at the pellet. CONSTITUTION:One set of opposed side faces 10c, 10e of four side faces 10b-10e of a pyramidal pellet are formed in circular arc-like faces 12b extended toward outside with a predetermined curvature, and a crossing surface 12a between the face 12b and the other side face is also formed in a curved surface having a predetermined curvature.

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, and more particularly to a solid electrolytic capacitor having an anode sintered body having a shape in which the solid electrolyte is less likely to be damaged by thermal stress or mechanical stress. is there.

[0002]

2. Description of the Related Art A method of manufacturing a tantalum solid electrolytic capacitor will be described. First, a suitable binder is mixed with tantalum powder to form a rectangular parallelepiped or a cylinder having a predetermined size, and an anode lead is implanted. Then, it is sintered to obtain a sintered pellet of tantalum (anode sintered body).

Then, an oxide film as a dielectric is formed on the sintered pellet. Usually, this oxide film is formed by a single chemical conversion treatment using a phosphoric acid aqueous solution or a nitric acid aqueous solution, or a two-step chemical conversion treatment in which chemical conversion is performed using a nitric acid aqueous solution and then phosphoric acid aqueous solution.

Next, a solid electrolyte made of manganese dioxide is formed on the sintered pellet. That is, the same sintered pellet is immersed in an aqueous solution of manganese nitrate to impregnate it with manganese nitrate and then pulled up for thermal decomposition. The concentration of manganese nitrate is sequentially increased and this is repeated several times, and re-formation is repeated several times for the purpose of repairing the oxide film damaged by the thermal decomposition process.

After that, a carbon layer and a silver layer as a cathode conductive layer are formed on the solid electrolyte and mounted on a lead frame, and finally a resin outer package is formed by resin molding.

[0006]

By the way, this kind of sintered pellet is usually formed into a cylindrical body or a prism, but in order to cope with downsizing of equipment, the sintered pellet is changed from the cylinder to the prism. By doing so, the volume efficiency is increased.

FIG. 3 shows a sintered pellet 1 having a prismatic shape.
According to this, the area ratio in the cross section of the same sintered pellet 1 and the cylindrical sintered pellet 1A inscribed therein is 1: 0.785, which is a prismatic shape. As a result, the volume efficiency can be increased accordingly.

However, in the case of the prismatic sintered pellet 1, as shown in FIG. 4, in the step of forming the solid electrolyte 2 made of manganese dioxide around it, the protrusions 2A of manganese dioxide are formed at the corners. Is generated.

Thermal stress and mechanical stress, especially distortion due to the difference in thermal expansion from the resin exterior body, concentrates on the protrusion 2A. For this reason, the same portion is easily damaged, which causes a defective leakage current, thus lowering the yield rate.

[0010]

The present invention has been made in order to solve the above-mentioned problems, and is characterized in that it is formed by sintering valve action metal powder such as tantalum or niobium.
A solid electrolytic capacitor having an anode sintered body having an anode lead implanted on the top surface thereof, and a chemical conversion film, a solid electrolyte consisting of manganese dioxide, and a conductive layer for a cathode being sequentially formed on the anode sintered body. The anode sintered body is a quadrangular prism, and at least a pair of side surfaces facing each other among the side surfaces orthogonal to the top surface are formed into arcuate surfaces that bulge outward with a predetermined curvature.

In this case, the distance between the vertices of the arc surface is R
, The curvature of the same arc surface is 0.2R to 0.4R in a portion intersecting with another adjacent side surface (hereinafter, also simply referred to as an intersection surface), and the curvature between the intersection surfaces is 0.
It is preferably 8R or more. That is, when the curvature of the intersecting surface is 0.2R or less, manganese dioxide (solid electrolyte)
When it is formed, it is difficult to suppress the formation of the protrusions. On the other hand, when it is 0.4 R or more, the advantage of the volumetric efficiency with respect to the cylindrical body decreases. Further, when the curvature of the circular arc surface between the intersecting surfaces is 0.8R or less, the advantage of the volumetric efficiency with respect to the cylindrical body is similarly reduced. Furthermore, curved surfaces having a predetermined curvature may be formed at the corners of the top surface and side surfaces and the bottom surface and side surfaces of the above-mentioned anode sintered body.

[0012]

According to the above construction, even if the anodic sintered body has a prismatic shape, the pair of opposite side surfaces are formed into arcuate surfaces, so that the boundary portion between the arcuate surfaces and the side surfaces adjacent thereto is reduced. Since it is curved, no extreme protrusion is generated during the formation of manganese dioxide. Therefore, the yield rate of products can be improved without impairing the good volume efficiency, which is an advantage of the prismatic body.

[0013]

EXAMPLE FIG. 1 shows a sintered pellet 10 according to an example of the present invention. The sintered pellets 10 are formed by mixing a valve action metal powder such as tantalum or niobium with an appropriate binder to form a prismatic shape, implanting the anode lead 11 on the top surface 10a, and then sintering. Is obtained by

According to the present invention, 4 which is orthogonal to the top surface 10a
Of the two side surfaces 10b to 10e, at least a pair of opposing side surfaces, for example, 10c and 10e are formed into arcuate surfaces that bulge outward with a predetermined curvature. The other side surfaces 10b and 10d are flat surfaces.

FIG. 2 shows a cross section of the sintered pellet 10 taken along the line AA of FIG. 1, and in this embodiment, the distance between the opposite side surfaces 10b and 10d and the opposite side surfaces 10b and 10d. The distances between the vertices of the side surfaces 10c and 10e are equal. That is, the original shape of the sintered pellet 10 is, for example, a prismatic body having a regular square cross section with one side length R parallel to the top surface 10a of the side surface 10b (10d).

With the length R of this side, the side surfaces 10c and 10
When the curvature of the arc surface of e is expressed, these side surfaces 10c, 10
Crossing surfaces 12 between the e and the other side surfaces 10b and 10d adjacent to each other
The curvature of a is in the range of 0.2R to 0.4R, and the side surfaces 10c, 1 located between the intersecting surfaces 12a, 12a.
The curvature of the main arcuate surface 12b of 0e is preferably 0.8 R or more, and the flat side surfaces 10b, 1
Since the intersection of 0d and the side surfaces 10c, 10e having an arc shape is a gently curved surface, the solid electrolyte 2 made of manganese dioxide is formed around the sintered pellet 10 as shown by an imaginary line in FIG. The entire surface is formed with a substantially uniform thickness.

When the curvature of the intersecting surface 12a is 0.2R or less, it is difficult to suppress the formation of protrusions when manganese dioxide (solid electrolyte) is formed. On the other hand, when it is 0.4R or more, the volumetric efficiency of the cylindrical body is increased. The benefits of are less.

In this embodiment, four side surfaces 10b-10b are provided.
Although a main portion of the pair of facing side surfaces 10c and 10e of e is an arc surface having a curvature of 0.8R or more, the intersecting surface 12a between the side surfaces is a curved surface of 0.2 to 0.4R. In addition to this, the top surface 10a and each side surface 10b to 10e
It is needless to say that curved surfaces having a predetermined curvature may be provided also at the corners between them and the corners between the bottom surface 10f and the respective side surfaces 10b to 10e that face the top surface 10a.

The curvature in that case can be set with reference to the above-mentioned preferable range (0.2R to 0.4R). In the present invention, the cross section of the sintered pellet 10 is not necessarily limited to a regular square, and may be a rectangular shape having long sides and short sides. Is arbitrarily set.

Example 1 Pellet size width 0.9 ×
A tantalum sintered pellet in which a pair of side surfaces having a vertical width of 0.9 and a height of 1.0 (mm) are arc surfaces having a curvature of 0.8R, and intersecting surfaces with other side surfaces are arc surfaces having a radius of 0.2R. To 0.0
A DC voltage of 25 V was applied in a 5% phosphoric acid aqueous solution to form an oxide film.

Next, the same tantalum sintered pellet was immersed in an aqueous solution of manganese nitrate to impregnate it with manganese nitrate, and was pulled up for thermal decomposition to form a solid electrolyte of manganese dioxide on the same tantalum sintered pellet.

In this case, the concentration of manganese nitrate is 20%,
The thermal decomposition was repeated 10 times by sequentially increasing it to 40%, 70%, and 100%, and re-formation was repeated 5 times with an aqueous phosphoric acid solution for the purpose of repairing the oxide film damaged by the thermal decomposition step.

Thereafter, a carbon layer and a silver layer are sequentially formed on this solid electrolyte, and after being attached to a lead frame, a resin exterior body is formed by a resin molding method, and the product size is 3.2 × 1.6. × 1.6 (mm) rating 6.3V
3μF tantalum solid electrolytic capacitor 30000
Individually made.

According to this, the product yield rate is 98.0.
%, Leakage current (LC) failure and loss angle tangent (ta
The characteristic defect rate including both of nδ) defects was 1.0%. The defects due to other causes were 1.0%.

Twenty products were randomly picked up, and the following electrical measurements were carried out for these. As a result, the maximum electrostatic capacity at 120 Hz was 3.09 μF, the minimum was 2.94 μF, and the average value was 3.03 μF. 120H
The maximum tan δ at z was 1.9%, the minimum was 1.4%, and the average value was 1.6%. The maximum impedance at 100 KHz was 0.7Ω, the minimum was 0.4Ω, and the average value was 0.6Ω. The maximum leakage current (LC) is 0.01
The value was 4 μA, the minimum value was 0.008 μA, and the average value was 0.010 μA.

<Prior art example 1> Using tantalum sintered pellets having the same pellet size and prismatic shape as in the above-mentioned Example 1, the same number and the same number of tantalum solid electrolytic capacitors having the same size and rating as in the above-mentioned Example 1 are used. It was made.

In this case, the product yield rate is 94.0%.
, The leakage current (LC) defect and the loss angle tangent (tan
δ) The characteristic defect rate including both defects was 3.0%.
The defects due to other causes were 3.0%.

Further, as in Example 1, 20 products were picked up at random and the following electrical measurements were carried out. As a result, the maximum capacitance at 120 Hz is 3.38 μF, the minimum is 3.28 μF, and the average value is 3.32 μF.
Met. The maximum tan δ at 120 Hz was 3.5%, the minimum was 1.7%, and the average value was 2.5%. 100 KHz
The maximum impedance was 2.3Ω, the minimum was 0.8Ω, and the average value was 1.0Ω. Regarding the leakage current (LC), the maximum value was 0.015 μA, the minimum value was 0.010 μA, and the average value was 0.012 μA.

<Conventional example 2> Diameter 0.9 mm, axial length 1.0
The same number of tantalum solid electrolytic capacitors having the same rating were produced in the same manner as in Example 1 using the columnar sintered tantalum pellets having a diameter of mm.

In this case, the product yield rate is 94.0%.
, The leakage current (LC) defect and the loss angle tangent (tan
δ) The characteristic defect rate including both defects was 5.0%.
The defects due to other causes were 1.0%.

In the same manner as in Example 1, 20 products were randomly picked up and the following electrical measurement was carried out. As a result, the maximum capacitance at 120 Hz is 2.53 μF, the minimum is 2.40 μF, and the average is 2.45 μF.
Met. The maximum tan δ at 120 Hz was 4.0%, the minimum was 2.5%, and the average value was 3.0%. 100 KHz
The impedance at that time was 3.5Ω at maximum, 1.5Ω at minimum, and 2.0Ω on average. Regarding the leakage current (LC), the maximum value was 0.016 μA, the minimum value was 0.010 μA, and the average value was 0.013 μA.

In order to facilitate comparison, the measurement results of Example 1 and Conventional Examples 1 and 2 are shown in Tables 1 and 2.

[0033]

[Table 1]

[0034]

[Table 2]

As can be seen from this table, according to the present invention, the processing defect rate and the characteristic defect rate, particularly the leakage current value and the tan.
The δ value is greatly improved, and the product yield rate is dramatically improved.

[0036]

As described above, according to the present invention,
Of the four side surfaces of the quadrangular prism-shaped sintered pellet, at least a pair of side surfaces facing each other are formed into arc surfaces that bulge outward with a predetermined curvature, and the intersection surface of the arc surface and the other side surface has a predetermined curvature. Due to the curved surface, when the solid electrolyte made of manganese dioxide is formed around the sintered pellet, the solid electrolyte is formed with a substantially uniform thickness including the corners.

As a result, even in the case of prismatic sintered pellets, there is no risk of damage to the solid electrolyte due to thermal stress or mechanical stress, and the yield rate of products is greatly improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a sintered pellet used in a solid electrolytic capacitor of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram for explaining the volume efficiency of prismatic pellets and cylindrical pellets.

FIG. 4 is a cross-sectional view for explaining a state in which a solid electrolyte is formed on a conventional prismatic pellet.

[Explanation of symbols]

 10 Sintered Pellet 10a Top Surface 10b to 10e Side Surface 10f Bottom Surface 11 Anode Lead 12a Crossing Surface 12b Arc Surface

Claims (3)

[Claims] 1. An anode sintered body made by sintering valve action metal powder such as tantalum or niobium, and having anode leads implanted on the top surface, and a chemical conversion film, manganese dioxide on the anode sintered body. In a solid electrolytic capacitor formed by sequentially forming a solid electrolyte and a conductive layer for a cathode made of, the anode sintered body is a quadrangular prism, among the side surfaces orthogonal to the top surface, at least a pair of opposing side surfaces is A solid electrolytic capacitor, which is formed on an arc surface that bulges outward with a predetermined curvature. 2. When the distance between the vertices of the arcuate surface is R, the curvature of the arcuate surface is 0.2R to 0.4R at the intersecting surface with another adjacent side surface, and the intersecting surface thereof. The solid electrolytic capacitor according to claim 1, wherein the curvature between them is 0.8 R or more. 3. The solid electrolytic capacitor according to claim 1, wherein curved surfaces having a predetermined curvature are also formed at the corners of the top surface and side surfaces and the bottom surface and side surfaces of the anode sintered body.