JP3246540B2 - Solid electrolytic capacitors - Google Patents

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 in which a solid electrolyte is hardly 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, an appropriate binder is mixed with a tantalum powder and molded into, for example, a rectangular parallelepiped or a column having a predetermined size, and an anode lead is implanted. Then, sintering is performed to obtain a sintered pellet of tantalum (anode sintered body).

An oxide film as a dielectric is formed on the sintered pellet. Usually, this oxide film is formed by a single chemical conversion treatment with a phosphoric acid aqueous solution or a nitric acid aqueous solution, or a two-stage chemical conversion treatment in which a chemical conversion with a nitric acid aqueous solution is performed, followed by a chemical conversion with a phosphoric acid aqueous solution.

Next, a solid electrolyte composed of manganese dioxide is formed on the sintered pellet. That is, the sintered pellet is immersed in an aqueous solution of manganese nitrate to be impregnated with manganese nitrate, pulled up, and thermally decomposed. This is repeated several times while sequentially increasing the concentration of manganese nitrate, and re-chemical formation is repeated several times in order to repair 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, 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 prismatic body, but in order to cope with miniaturization of equipment, the sintered pellet is converted from the cylindrical body into a prismatic body. 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 of the cross section of the sintered pellet 1 and the cylindrical sintered pellet 1A inscribed therein is 1: 0.785, which is a prismatic shape. Thereby, the volumetric efficiency can be increased accordingly.

However, in the case of the prismatic sintered pellet 1, as shown in FIG. 4, a step 2 A of manganese dioxide is formed at the corner in the step of forming a solid electrolyte 2 made of manganese dioxide around the pellet. Generated.

[0009] Thermal stress and mechanical stress, particularly strain due to a difference in thermal expansion with the resin outer package, are concentrated on the projection 2A. For this reason, the same portion is easily damaged, causing a leakage current defect, and lowering the yield.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and its structural feature is that a valve action metal powder such as tantalum or niobium is sintered,
A solid electrolytic capacitor having an anode sintered body having an anode lead implanted on a top surface, a conversion film, a solid electrolyte made of manganese dioxide, and a cathode conductive layer formed in this order on the anode sintered body, a anode sintered body quadrangular form, of the sides perpendicular to the top surface, contact is formed in an arc face a pair of side surfaces at least opposed bulges toward the outer side
Where R is the distance between the vertices of the arc surface,
The curvature of a surface is determined by the intersection with another adjacent side surface (hereinafter,
0.2R-0.4R,
Also, the curvature between the intersecting planes is 0.8R or more.
Features.

[0011] ie, the curvature of the crossover plane below 0.2R, it is difficult to suppress the generation of the protrusion during formation of the manganese dioxide (solid electrolyte), while when the above 0.4R, volume to the cylinder Efficiency benefits are reduced. When the curvature of the arc surface between the intersecting surfaces is 0.8R or less, the advantage of the volumetric efficiency with respect to the cylindrical body similarly decreases. Further, a curved surface having a predetermined curvature may be formed at the corners between the top and side surfaces and the bottom and side surfaces of the anode sintered body.

[0012]

According to the above construction, even when the anode sintered body is prismatic, a pair of opposing side surfaces are formed in an arc surface, so that a boundary portion between the arc surface and the adjacent side surface is formed. Since the manganese dioxide is formed, no extreme projection is generated because the manganese dioxide is formed. Therefore, the product yield can be improved without impairing the volumetric efficiency, which is an advantage of the prismatic body.

[0013]

FIG. 1 shows a sintered pellet 10 according to an embodiment of the present invention. The sintered pellet 10 is formed by mixing a valve metal powder such as tantalum or niobium with an appropriate binder, molding the prism into a prismatic shape, implanting an anode lead 11 on the top surface 10a, and sintering the pellet. Is obtained by

According to the present invention, 4
At least a pair of opposing side surfaces, for example, 10c and 10e, of the one side surfaces 10b to 10e are formed as arcuate surfaces which 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 in FIG. 1. In this embodiment, the distance between the opposing side surfaces 10b and 10d and the opposing side surfaces 10b and 10d are shown. The distance between the vertices of the side surfaces 10c and 10e is equal. That is, the original shape of the sintered pellet 10 is, for example, a prism having a square R-shaped cross section with one side parallel to the top surface 10a of the side surface 10b (10d).

With the length R of one side, the side surfaces 10c and 10c
If the curvature of the arc surface of e is expressed, these side surfaces 10c, 10c
e and each intersecting surface 12 between the adjacent other side surfaces 10b and 10d
a has a curvature in the range of 0.2R to 0.4R, and has the same side face 10c, 1 located between its crossing faces 12a, 12a.
It is preferable that the curvature of the main arc surface 12b of 0e is 0.8R or more, and according to this, the flat side surfaces 10b, 1
Since the intersection between 0d and the arc-shaped side surfaces 10c and 10e is formed as a gentle curved surface, as shown by the imaginary line in FIG. It is formed with a substantially uniform thickness over the entire surface.

If the curvature of the intersecting surface 12a is 0.2R or less, it is difficult to suppress the formation of projections when manganese dioxide (solid electrolyte) is formed. The advantage of is reduced.

In this embodiment, four side surfaces 10b to 10b
e, the main part of the pair of opposed side surfaces 10c and 10e is formed as an arc surface having a curvature of 0.8R or more, so that the intersection 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 a matter of course that a curved surface having a predetermined curvature may be provided also at a corner between the bottom surface 10f facing the top surface 10a and each of the side surfaces 10b to 10e.

In this case, the curvature can be set based on the preferable range (0.2R to 0.4R) described above. In the present invention, the cross section of the sintered pellet 10 is not necessarily limited to a regular square, but may be a rectangular shape having a long side and a short side. Is set arbitrarily.

Example 1 Pellet size width 0.9 ×
Tantalum sintered pellets with a pair of side surfaces opposing each other with a vertical width of 0.9 × height of 1.0 (mm) and an arc surface with a curvature of 0.8R and an intersection surface with the other side surface with an arc surface of 0.2R. 0.0
An oxide film was formed by applying a DC voltage of 25 V in a 5% phosphoric acid aqueous solution.

Next, the tantalum sintered pellet was immersed in an aqueous solution of manganese nitrate to be impregnated with manganese nitrate, pulled up and thermally decomposed to form a solid electrolyte made of manganese dioxide on the tantalum sintered pellet.

In this case, the concentration of manganese nitrate is 20%,
The thermal decomposition was repeated 10 times with increasing sequentially to 40%, 70%, and 100%, and the re-chemical formation was repeated 5 times with a phosphoric acid aqueous 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 the solid electrolyte, and after attaching to a lead frame, a resin outer package is formed by a resin molding method, and the product size is 3.2 × 1.6. × 1.6 (mm) and rated 6.3V
3.3 μF tantalum solid electrolytic capacitor
This was produced.

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

Further, 20 products were randomly picked up, and the following electrical measurements were made on them. As a result, the capacitance at 120 Hz was 3.09 μF at the maximum, 2.94 μF at the minimum, and 3.03 μF on average. 120H
The tan δ at z was 1.9% at the maximum, 1.4% at the minimum, and 1.6% on average. The impedance at 100 KHz was 0.7 Ω at the maximum, 0.4 Ω at the minimum, and 0.6 Ω on average. The maximum leakage current (LC) is 0.01
4 μA, minimum 0.008 μA, average value 0.010 μA.

<Conventional Example 1> Tantalum sintered pellets of the same pellet size and prismatic shape as in Example 1 were used, and the same number of tantalum solid electrolytic capacitors of the same size and rating as in Example 1 were used. Produced.

In this case, the product yield rate is 94.0%.
And the tangent (tan) of the leakage current (LC) defect and the loss angle
δ) The characteristic failure rate including both failures was 3.0%.
And the defect by other causes was 3.0%.

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

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

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

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

Tables 1 and 2 show the measurement results of Example 1 and Conventional Examples 1 and 2 for easy comparison.

[0033]

[Table 1]

[0034]

[Table 2]

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

[0036]

As described above, according to the present invention,
Of the four side surfaces of the quadrangular prism sintered pellets, and inflated arcuate surface towards the pair of side surfaces, at least facing the outer side, its
Let R be the distance between the vertices of the arc surface of
With a curvature of 0.2R to 0.4R,
Also, the curvature between the intersecting surfaces should be 0.8R or more.
By the, when forming the solid electrolyte consisting of manganese dioxide around the sintered pellets can be formed with a substantially uniform thickness of the solid electrolyte, including the corner portion
You .

As a result, even if the sintered pellets are prismatic, the solid electrolyte is not likely to be damaged by thermal stress or mechanical stress, and the yield of the product is greatly improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a sintered pellet used for a solid electrolytic capacitor of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG. 1;

FIG. 3 is an explanatory diagram for explaining the volume efficiency of prisms and cylinders.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Sintered pellet 10a Top surface 10b-10e Side surface 10f Bottom surface 11 Anode lead 12a Crossing surface 12b Arc surface

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-172340 (JP, U) JP-A-2-88229 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01G 9/052

Claims (2)

(57) [Claims] An anode sintered body obtained by sintering a valve metal powder such as tantalum or niobium and having an anode lead implanted on a top surface thereof, wherein the anode sintered body is provided with a chemical conversion film and manganese dioxide. in the solid electrolyte and a solid electrolytic capacitor formed by sequentially forming a cathode conductive layer made of, a the anode sintered body is quadrangular form, of the sides perpendicular to the top surface, a pair of side surfaces of at least facing It is formed in an arc surface bulging toward the outer side, to the distance between the apexes of the arcuate surface and R
The curvature of the arc surface, the intersection with the other adjacent side
0.2R to 0.4R on the surface, and between the intersections
Characterized by having a curvature of 0.8R or more.
Capacitors. 2. A top surface, side surfaces and a bottom surface of the anode sintered body.
A curved surface with a predetermined curvature is also formed at the corner between
The solid electrolytic capacitor according to claim 1, wherein: