JP2006080266A - Solid electrolytic capacitor element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor which has excellent leakage current characteristics, a high electrostatic capacity, and merits possessed by both a high-density molded element and a low-density molded element in capacitor elements which are formed by compacting and molding valve-action metal powder. <P>SOLUTION: The molded element of multilayered structure is formed by the method wherein valve-action powder is supplied by in multistages, laterally compacted and molded three times or more. A joint (internal layer) between the molded element and an anode lead wire, and the peripheral part (external layer) of the molded element are set higher in density than an intermediate layer, so that a dielectric film can be protected against damage caused by an external force applied in capacitor manufacturing processes, and the capacitor having excellent leakage current characteristics can be obtained. The intermediate layer of low density is formed between the internal layer and the external layer, so that the sintered element can be increased in surface area, and the solid electrolytic capacitor having a high electrostatic capacity can be provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an element used for a solid electrolytic capacitor and a method for manufacturing the same.

  The molded body element used in the conventional solid electrolytic capacitor has been designed so that the molding density in the molded body element is as uniform as possible during pressure molding of the valve action metal (for example, see Patent Document 1).

In addition, by forming from the vertical direction in multiple stages using an upper and lower press, the bonding density between the sintered body element after sintering and the anode lead wire is improved, and the molding density in the molded body element is made uniform. (For example, refer to Patent Document 2).
JP-A-1-181509 JP-A-6-176985

  In order to prevent the dielectric film from being damaged and the electrical characteristics of the capacitor from being deteriorated due to external force applied during the capacitor assembly process, the bonding density between the sintered body element and the anode lead wire and the sintering are increased by increasing the molding density. Although it is better to improve the body element strength, there is a problem that the surface area of the sintered body element is reduced and the capacitance is lowered.

  However, when the predetermined density is obtained by lowering the molding density and preventing the surface area of the sintered body element from decreasing, the bonding strength between the sintered body element and the anode lead wire and the firing Since the strength of the bonded element is lowered, there is a problem that it becomes weak against the external force applied in the capacitor manufacturing process.

  In addition, in order to improve the bonding force between the sintered body element and the anode lead wire and increase the surface area of the sintered body element, the method of performing the vertical direction in multiple stages with the upper and lower punches, In order to increase the volume in multiple stages, it is necessary to change the molding machine and the molding die each time the molding is performed step by step, resulting in a problem that man-hours are required.

  Due to the above-described problems, the solid electrolytic capacitor element having a high bonding force between the sintered body element and the anode lead wire and the strength of the sintered body element, no reduction in capacitance, and less man-hours, and a method for manufacturing the same Was demanded.

The present invention solves the above problems, and in a solid electrolytic capacitor element formed by pressure-molding a valve metal powder and a method for producing the same,
A solid electrolytic capacitor element and a method for manufacturing the same, characterized in that a valve-acting metal powder is pressure-molded three or more times from the lateral direction to form a molded body element having at least two different densities.

A solid electrolytic capacitor element characterized in that the molding density of the molded body layer for joining the molded body element and the anode lead wire is the same as or higher than the molding density of the outer layer of the molded body layer, and its production Is the method.
Furthermore, the molded body element has a three-layer structure of an inner layer, an intermediate layer, and an outer layer, and the density of the intermediate layer is lower than that of the inner layer and the outer layer, and a manufacturing method thereof.

  By increasing the molding density of the joint (inner layer) between the molded body element and the anode lead wire, the bonding force between the two is increased and the dielectric film damage of the joint (inner layer) due to external force applied in the capacitor manufacturing process is prevented. Therefore, increase in leakage current can be prevented.

  Moreover, since the density of the outer periphery (outer layer) of the molded body element is higher than that of the intermediate layer, the strength of the sintered body element is improved, and damage to the dielectric film due to external force during capacitor production can be prevented. Leakage current characteristics can be obtained.

  Furthermore, the surface area of the sintered body element is reduced by making the density of the intermediate layer between the joint (inner layer) of the molded body element and the anode lead wire and the outer peripheral portion (outer layer) of the molded body element lower than the inner layer and the outer layer. Therefore, a high capacitance can be obtained.

  Further, since the molding is performed from the horizontal direction with the left and right punches of the same molding machine, it is not necessary to change the molding machine and the molding die each time the molding is performed step by step, and the man-hours can be reduced as compared with the molding in the vertical direction.

Next, a method for manufacturing a solid electrolytic capacitor element according to the present invention will be described.
The metal element powder is supplied in multiple stages to the mold at the time of molding, and the molded body element has a multilayer structure by performing pressure molding three times from the lateral direction.
First, as the inner layer, the joint between the molded body element and the anode lead wire is molded at a high density.
Next, a layer having a molding density lower than that of the inner layer is formed as the intermediate layer.
Finally, a high-density molded layer is formed as the outer layer.

[Example]
As shown in FIGS. 1 and 2, a concave cross-section mold having a groove width of 4.0 mm and a depth of 5.0 mm separated by left and right punches is filled with 28 mg of niobium powder, and an anode lead wire is supplied together with the upper mold as shown in FIG. Then, an inner layer having an inner layer molding density of 3.57 g / cm ³ of 4.0 mm × 5.0 mm × 0.4 mm as shown in FIG.
Next, 76 mg of niobium powder is additionally supplied as shown in FIG. 5, and an intermediate layer having an intermediate layer molding density of 2.71 g / cm ³ is formed by pressing from the lateral direction as shown in FIG. A molded body element 2 of 0 mm × 1.8 mm was obtained.
Further, 14 mg of niobium powder is additionally supplied as shown in FIG. 7, and an outer layer having an outer layer molding density of 3.50 g / cm ³ is formed by pressing from the lateral direction as shown in FIG. The molded body element 3 was 4.0 mm × 5.0 mm × 2.0 mm.
The molded body element 3 was heat-treated at 1300 ° C. for 20 minutes in a vacuum of 1.33 × 10 ⁻³ Pa to obtain a sintered body element. This sintered body element was anodized while being held in 0.1% phosphoric acid at 30 V for 2 hours to form a dielectric oxide film.

(Comparative Example 1)
As shown in FIGS. 1 and 2, the concave cross-section mold is filled with 108 mg of niobium powder, and the anode lead wire is supplied together with the upper mold as shown in FIG. A molded body element in which the entire size of × 5.0 mm × 2.0 mm was reduced to a molding density of 2.71 g / cm ³ was formed. The other production conditions were the same as in the example.

(Comparative Example 2)
As shown in FIGS. 1 and 2, the supply amount of niobium powder into the concave cross-section mold is 140 mg, and the anode lead wire is supplied together with the upper mold as shown in FIG. A compact element of 4.0 mm × 5.0 mm × 2.0 mm, which was molded as a whole with a molding density of 3.51 g / cm ³ , was formed. The other production conditions were the same as in the example.

(Comparative Example 3)
As shown in FIGS. 1 and 2, a concave cross-sectional mold having a groove width of 4.0 mm and a depth of 5.0 mm separated by left and right punches is filled with 28 mg of niobium powder, and the anode lead wire is used together with the upper mold as shown in FIG. As shown in FIG. 4, pressure was applied from the lateral direction to form a high-density inner layer having a molding density of 3.57 g / cm ³ of 4.0 mm × 5.0 mm × 0.4 mm.
Next, 86 mg of niobium powder is additionally supplied as shown in FIG. 5 and pressed from the lateral direction as shown in FIG. 6 to form a low-density outer layer with a molding density of 2.69 g / cm ³ , as shown in FIG. A molded element of 4.0 mm × 5.0 mm × 2.0 mm having a two-layer structure was formed. The other production conditions were the same as in the example.

  About the sintered compact element of an Example and Comparative Examples 1-3, the joining strength with an anode wire and the breaking strength of a sintered compact element were measured, respectively, and it was set as wire tensile strength and element strength.

  Next, after forming a dielectric oxide film on the sintered body, a voltage of 21 V was applied in a 10% phosphoric acid aqueous solution and charged for 2 minutes, and then the leakage current was measured to obtain LC in liquid. LC was converted to a value per 1 μF · V. The measurement results are shown in Table 1.

  Further, manganese dioxide was formed as a solid electrolyte layer on the element after the dielectric oxide film was formed, and a graphite layer and a cathode silver layer were formed thereon. An anode lead wire was welded to the anode frame, and the cathode was bonded to the cathode frame with adhesive silver, and then packaged with a resin to produce a niobium capacitor. The leakage current after charging for 1 minute by applying a voltage of 6.3 V and the electrostatic capacity at a bias voltage of 1.5 V were measured, and LC and Cap were respectively assembled. LC was converted to a value per 1 μF · V, and Cap was converted to a value per 1 g. The measurement results are shown in Table 2.

  As is clear from Table 1, the following effects were obtained in the examples. First, by making the inner layer high in density, wire tensile strength and element strength were improved, and the same strength as that of a sintered body element obtained by molding the entire Comparative Example 2 at high density was obtained.

  In addition, regarding the leakage current characteristics, the LC in the liquid after the anodic oxidation was not different between the example and the comparative examples 1 to 3, whereas as apparent from Table 2, the LC after the capacitor assembly was The result that the example was the best was obtained.

  Furthermore, regarding the capacitance, the Example was able to obtain a high Cap that is close to a sintered body element obtained by molding the entire Comparative Example 1 at a low density.

  In addition, since the examples are formed from the horizontal direction, the number of man-hours can be reduced as compared with the vertical direction in which the molding machine and the mold need to be changed every time the molding is performed in stages.

Here, in the three-layer structure molded body element of the example, either the inner layer or the outer layer may have a higher density, or both may have the same density.
In the above embodiment, niobium is used as the valve metal, but the same effect can be obtained by using tantalum.

FIG. 3 is a state diagram of a first stage of powder supply when forming a molded body element according to an embodiment of the present invention. FIG. 2 is a perspective view of a molding stage of the molded body element shown in FIG. 1. FIG. 3 is a perspective view of an anode lead wire embedding stage of the molded body element shown in FIG. 2. FIG. 2 is a state diagram after a first pressurization step of the molded body element shown in FIG. 1. FIG. 5 is a state diagram of a second stage of powder supply after molding the molded body element shown in FIG. 4. FIG. 6 is a state diagram after a second pressure stage of the molded body element shown in FIG. 5. FIG. 7 is a state diagram of a third stage of powder supply after molding the molded body element shown in FIG. 6. FIG. 8 is a state diagram after a third stage of pressurization of the molded body element shown in FIG. 7. It is a cross-sectional perspective view of the molded body element of the three-layer structure formed by the Example of this invention. It is a cross-sectional perspective view of a molded body element obtained by low-density molding of the entire element of Comparative Example 1 at a molding density of 2.71 g / cm ³ . FIG. 5 is a cross-sectional perspective view of a molded body element obtained by high-density molding of the entire element of Comparative Example 2 at a molding density of 3.51 g / cm ³ . FIG. 5 is a cross-sectional perspective view of a molded body element having a two-layer structure in which the inner layer of Comparative Example 3 is molded at a high density of a molding density of 3.57 g / cm ³ and the outer layer is molded at a low density of a molding density of 2.69 g / cm ³ . It is a cross-sectional perspective view of the molded body element of the 3 layer structure shape | molded from the vertical direction of Unexamined-Japanese-Patent No. 6-176985.

Explanation of symbols

1 Concave section mold 2 Powder feeder 1
3 Horizontal punch 4 Valve action metal powder 5 Upper die 6 Anode lead wire 7 High density molding layer 1
8 Powder feeder 2
9 Low density molding layer 10 High density molding layer 2
11 High density molded layer 3

Claims (3)

In a solid electrolytic capacitor element formed by pressure molding a valve action metal powder and a manufacturing method thereof,
A solid electrolytic capacitor element and a method for producing the same, characterized in that a valve-acting metal powder is pressure-molded three or more times from the lateral direction to form a molded body element having at least two different densities.   A solid electrolytic capacitor element characterized by having a molding density of a molded body layer for joining the molded body element according to claim 1 and an anode lead wire equal to or higher than a molding density of an outer layer of the molded body layer, and Production method.   2. The solid electrolytic capacitor element according to claim 1, wherein the molded body element has a three-layer structure of an inner layer, an intermediate layer, and an outer layer, and the density of the intermediate layer is lower than that of the inner layer and the outer layer.

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