JP2004146850A - Electrolytic capacitor and electrode for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for an electrolytic capacitor whose apparent surface area is large, and through which a heavy-current can flow, and which is excellent in high frequency characteristic. <P>SOLUTION: In an electrode 4 for an electrolytic capacitor made by furnishing a compact 1 made of valve metal powder with a reed made of valve metal, the reed at least contacting with the compact 1 is formed in a foil shape and thickness of foil 2 is set to 200μm or less. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an electrode for an electrolytic capacitor in which a valve metal lead is attached to a valve metal powder compact.

Generally, an electrolytic capacitor element used on the secondary side of a power supply smoothing circuit or around a CPU of a personal computer is required to be compatible with high frequencies and to allow a large current to flow.

FIG. 6 shows a conventional electrode for an electrolytic capacitor. A lead wire 3 made of a valve metal is implanted on a molded body 1 made of a metal powder having a valve action such as tantalum, aluminum, titanium, or niobium to form an electrode 4 for an electrolytic capacitor.

化 The formed body 1 of the electrode 4 for the electrolytic capacitor is subjected to chemical conversion to form a dielectric oxide film, and a solid electrolyte layer and a cathode electrode layer are formed on the oxide film. Then, an external anode terminal is joined to the lead wire 3 as an anode, and an external cathode terminal is joined to the cathode electrode layer. The electrolytic capacitor element is molded by covering the entire anode with an epoxy powder resin or the like. can get.

In order to allow a large current to flow through such an electrolytic capacitor element, it is necessary to increase the bonding area (hereinafter, referred to as “apparent surface area”) between the lead wire 3 and the valve metal powder constituting the compact 1. Therefore, various methods for increasing the apparent surface area have been conventionally proposed.

For example, Japanese Utility Model Laid-Open No. 57-138330 proposes a method of thinly flattening a portion of the lead wire 3 embedded in the molded body 1. Further, Japanese Utility Model Application Laid-Open No. 58-187136 discloses a method of not only simply flattening the lead wire 3 but also increasing the apparent surface area by limiting the embedded length and the degree of flatness. Japanese Utility Model Application Laid-Open No. 58-187129 also discloses a method in which the embedded portion of the lead wire 3 is similarly formed in a flat shape and its thickness is defined.
Japanese Utility Model Publication No. 57-138330 JP-A-58-187136 JP-A-58-187129

However, in the above-mentioned conventional electrolytic capacitor element, although the lead wire 3 is flattened to increase the apparent surface area, the flattening of the lead wire 3 is limited by problems such as strength and the like. As a result, there is a problem that ultra-thin high-density mounting cannot be realized.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 63-283012 proposes a method in which a lead wire 3 is welded to a side surface of a molded body 1 and then formed into a flat shape. There is a problem that the process is complicated.

Further, although the above-mentioned electrolytic capacitor elements have an increased apparent surface area, there is a problem that none of them has an apparent surface area sufficient to flow a large current.
The present invention solves the above-mentioned problems, and provides an electrode for an electrolytic capacitor having a large apparent surface area, allowing a large current to flow, and having excellent high-frequency characteristics.

The electrode for an electrolytic capacitor of the present invention is characterized in that the shape of the anode lead has a special configuration.
According to the present invention, it is possible to provide an electrode for an electrolytic capacitor having a large apparent surface area, allowing a large current to flow, and having excellent high frequency characteristics.

The electrolytic capacitor according to claim 1 of the present invention has an anode body in which a foil as a lead made of valve metal is attached to a molded body of valve metal powder, a dielectric oxide film formed on the surface of pores of the anode body, An electrolytic capacitor including a solid electrolyte formed in contact with an oxide film and used at a high frequency of 100 kHz or more, wherein the lead foil has a substantially constant width, a portion embedded in the molded body, A part is buried in the molded body so that a foil width of a part not buried in the molded body is substantially the same, and a thickness of the lead foil is 100 μm or less.

The electrode for an electrolytic capacitor according to claim 2 of the present invention is an electrode for an electrolytic capacitor in which a foil as a lead made of a valve metal is attached to a molded body of valve metal powder, and the lead foil has a width of the molded body. The width is substantially constant at 0.17 or more with respect to the width, and a part of the molded body is so formed that the foil width of the part embedded in the molded body and the part not embedded in the molded body are substantially the same. And the lead foil has a thickness of 100 μm or less.

The electrode for an electrolytic capacitor according to claim 3 of the present invention is the electrode for an electrolytic capacitor according to claim 2, wherein the surface of the valve metal foil has irregularities, and the surface area of the contact portion of the foil with the molded body has the irregular surface. The irregularities are formed so as to be at least twice as large as the surface area of the contact portion with the molded body.

電解 An electrolytic capacitor electrode according to a fourth aspect of the present invention is characterized in that, in the second or third aspect, the valve metal foil has a through hole.

According to the electrode for an electrolytic capacitor of the present invention, by setting the shape of the lead to a foil and setting the thickness to 200 μm or less, the bonding area between the lead of the valve metal powder and the lead constituting the molded body increases. An electrode for an electrolytic capacitor having reduced resistance, reduced equivalent series resistance, excellent high-frequency characteristics, and capable of flowing a large ripple current is obtained.

In addition, by increasing the bonding area between the lead and the molded body, the adhesive strength between the lead and the molded body can be improved.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.
Note that components similar to those in FIG. 1 showing the above-described conventional example are denoted by the same reference numerals.

(Embodiment 1)
1 to 3 show an electrode for an electrolytic capacitor according to (first embodiment) of the present invention. The electrode for an electrolytic capacitor shown in FIG. 1 has substantially the same configuration as that of FIG. 6 showing the above-mentioned conventional example, but in this (Embodiment 1), the lead wire 3 which was conventionally linear is viewed as a foil. The difference is that the hanging surface area is increased.

Specifically, tantalum powder is used as a valve metal, and the tantalum powder is formed and processed together with the foil 2 made of tantalum to form an electrode 4 for an electrolytic capacitor by vacuum sintering.
Then, after forming an oxide film and an electrolyte layer on the electrode 4 for an electrolytic capacitor in the same manner as in the conventional example, a cathode extraction electrode is provided. Thereafter, an external anode terminal is joined to the foil 2 serving as an anode, an external cathode terminal is joined to the cathode electrode layer, and molded to cover the entire anode with an epoxy-based powder resin or the like, thereby forming an electrolytic capacitor element.

Thus, by making the shape of the anode lead into a foil 2 instead of a line, the contact area, that is, the apparent surface area, of the tantalum fine powder as the anode and the lead is increased, and the obtained electrolytic capacitor element has an equivalent series resistance. Is reduced and the high frequency characteristics are excellent.

Further, by using the foil 2, the apparent surface area can be increased, and the buried volume, which is a loss in capacitance, can be reduced, so that the capacitance can be increased.
Further, in order to increase the apparent surface area, not only the thickness, width and embedding length of the foil 2 are adjusted, but the surface of the foil 2 may be increased by polishing or electrical etching.

In addition, since the thinner molded body 1 can be produced by using the foil 2, the electrode 4 for the electrolytic capacitor is inevitably thinner, and a small and large-capacity electrolytic capacitor element can be obtained.
Hereinafter, a specific example of this (Embodiment 1) will be described. The following Examples 1 to 5 and Comparative Example 1 were performed in order to examine the relationship between the apparent surface area, the equivalent series resistance, and the ripple heating temperature.

Example 1
Using a 40000 μF · V / g tantalum powder as a valve metal, the tantalum powder was formed into a size of 1.7 mm × 3.5 mm × 6.4 mm to obtain a formed body 1.

The foil 2 was also made of tantalum and had a thickness of 200 μm and a width of 0.3 mm. The depth of the embedding part in the molded body 1 was 4 mm. Thus, an electrode 4 for an electrolytic capacitor was obtained.

(5) Then, in order to evaluate as an electrolytic capacitor element, the molded body 1 of the electrode 4 for an electrolytic capacitor was formed in a phosphoric acid solution at 85 ° C. at an applied voltage of 30 V to form an oxide film. Further, after forming manganese dioxide as an electrolyte, a cathode extraction electrode composed of a carbon layer and a silver conductive resin layer was provided.

Thereafter, an external anode terminal was joined to the foil 2, an external cathode terminal was joined to the cathode extraction electrode, and molded with a resin to produce an electrolytic capacitor element. Using this electrolytic capacitor element, an equivalent series resistance of 100 kHz and a ripple heat generation temperature were measured.

Ripple heating temperature was measured as follows. That is, a voltage obtained by superimposing a bias on a 100 kHz sine wave is applied as a ripple to the external anode and external cathode terminals of the electrolytic capacitor element. As for the ripple current, the output of the amplifier was adjusted so that 1000 mAP-P would flow through the electrolytic capacitor element, and the ripple heat generation temperature was measured.

Table 1 shows the equivalent series resistance and the ripple heat generation temperature of the obtained electrolytic capacitor element.

Examples 2 to 5
In order to examine the influence of the apparent surface area on the electrolytic capacitor element, the thickness and width of the foil 2 were changed as shown in Table 1 while the embedding depth of the foil 2 in the compact 1 was fixed at 4 mm. The volume of the lead portion embedded in the molded body 1 was set to be substantially the same as that of the first embodiment.

And otherwise, an electrolytic capacitor element was prepared in the same manner as in Example 1 described above, and the equivalent series resistance and the ripple heating temperature of the electrolytic capacitor element were measured. Table 1 shows the obtained measurement results.

Comparative Example 1
Unlike the above Examples 1 to 5, a lead wire 3 having a circular cross section and a diameter of 280 μm was used as a lead.

The depth of the embedded portion of the lead wire 3 was set to 4 mm, and the capacitance of the obtained electrode was set to be substantially equal to those in Examples 1 to 5 described above.
Comparing Example 1 with Comparative Example 5, both have substantially the same apparent surface area of the anode lead, and thus have the same equivalent series resistance and the same ripple heating temperature. However, as shown in Examples 2 to 5, as the thickness of the foil 2 was made smaller than 200 μm, the width of the foil 2 was increased, and the apparent surface area was increased, the tantalum fine powder as the anode and the lead were increased. Since the area of contact with the capacitor increases, the resulting electrolytic capacitor element has a reduced equivalent series resistance and excellent high-frequency characteristics.

Further, since the temperature rise of the ripple heat can be reduced, an excellent electrolytic capacitor element having an increased allowable ripple current in the same temperature rise range can be obtained.
In the above (Embodiment 1), the foil 2 as the anode lead is embedded in the inside of the molded body 1 as shown in FIG. 1, but the present invention is not limited to this, and the lead wire 3 may be used. If the apparent surface area is larger than the case, the foil 2 is attached to the surface of the molded body 1 as shown in FIG. 2, or the foil 2 is embedded in the molded body 1 as shown in FIG. Is also good.

When the surface of the foil 2 is polished or electronically etched to form irregularities to increase the apparent surface area, as apparent from the above Examples 1 to 5, the foil 2 before the irregularities are formed is formed. When the irregularities are formed so as to be at least twice the apparent surface area of the above, it is more effective to reduce the equivalent series resistance value and the ripple heat generation temperature.

Further, as is clear from Examples 1 to 5 and Comparative Example 1, a larger effect was obtained when the thickness of the foil 2 was 100 μm or less.
(Embodiment 2)
In Examples 1 to 5 and Comparative Example 1 in the above (Embodiment 1), the effects of the apparent surface area on the equivalent series resistance and the ripple heat generation temperature were examined. In Examples 6 to 8 and Comparative Example 2, the effect of the apparent surface area on the high-frequency characteristics was examined.

Examples 6 to 8
The foil 2 having a thickness of 50 μm was used, and the width and the burial depth in the molded body 1 were changed as shown in Table 2 so that the volume of the buried portion was the same. Otherwise, an electrolytic capacitor element was manufactured in the same manner as in Example 1 above.

FIG. 4 shows changes in the impedance of the obtained electrolytic capacitor element in the range of 100 Hz to 40 MHz.
Comparative Example 2
Using the same lead wire 3 as in Comparative Example 1, the lead wire 3 was embedded in the molded body 1 so as to obtain approximately the same capacity as in Examples 6 to 8 described above. Otherwise, an electrolytic capacitor element was manufactured in the same manner as in Example 1.

FIG. 4 shows changes in the impedance of the obtained electrolytic capacitor element in the range of 100 Hz to 40 MHz.
As shown in FIG. 4, there is no difference between the impedances of Examples 6 to 8 and Comparative Example 2 between 100 Hz and 300,000 Hz, but in the high frequency region exceeding 300,000 Hz, Examples 6 to 8 are compared. The impedance was smaller than in Example 2, and good high frequency characteristics were obtained.

This is because the anode lead of each of Examples 6 to 8 is not a lead wire 3 having a circular cross section but a foil 2 having a rectangular cross section, and thus has a large cross-sectional area and a low equivalent series resistance at a resonance frequency. It is considered that the wide equivalent width resulted in low equivalent series induction.

(Embodiment 3)
FIG. 5 shows (Embodiment 3) of the present invention.
Although the configuration is substantially the same as that of the electrode 4 for an electrolytic capacitor shown in FIG. 1 in the above (Embodiment 1), in this (Embodiment 3) a plurality of through holes 5 is provided.

By providing the through-holes 5 in the foil 2 in this way, even when the apparent surface area is almost the same, the force of the compact 1 to shrink when the compact 1 and the foil 2 are vacuum-sintered (arrow A) And direction B), the joining area becomes large, and a high strength electrolytic capacitor element with low equivalent series resistance can be obtained.

Hereinafter, a specific example of this (Embodiment 3) will be described.
Example 9
Foil 2 having a thickness of 50 μm, a width of 1.2 mm and an embedding depth of 4 mm was provided with 20 through-holes having a diameter of 0.2 mm. Otherwise, an electrolytic capacitor element was manufactured in the same manner as in Example 1.

Table 3 shows the equivalent series resistance at 100 kHz of the obtained electrolytic capacitor element and the intensity ratio when Comparative Example 3 and Example 9 were compared.

Comparative Example 3
A foil 2 having a thickness of 50 μm, a width of 1.2 mm, and an embedding depth of 4 mm without a through hole 5 was used. Otherwise, an electrolytic capacitor element was manufactured in the same manner as in Example 1.

Table 3 shows the equivalent series resistance and strength ratio at 100 kHz of the obtained electrolytic capacitor element.
Although Example 9 and Comparative Example 3 have almost the same apparent surface area, Example 9 is such that the foil 2 is more susceptible to the force of contraction of the compact 1 during vacuum sintering, Since the area was increased, a low equivalent series resistance was obtained, and a high strength product was obtained.

In the above (Embodiment 3), a plurality of through holes 5 are provided in the foil 2, but the present invention is not limited to this, and the foil 2 is provided as described in the above (Embodiment 1). May be formed on the surface of the film 2 by etching or the like, and a plurality of through holes 5 may be formed in the foil 2 having the unevenness.

Further, in the above (Embodiment 1) to (Embodiment 3), tantalum is used as the valve metal, but the present invention is not limited to this, and the same applies even if a valve metal other than tantalum is used. The effect is obtained.

Perspective view showing a configuration of an electrode for an electrolytic capacitor in (Embodiment 1). Perspective view showing a configuration of another electrode for an electrolytic capacitor in (Embodiment 1). Perspective view showing a configuration of another electrode for an electrolytic capacitor in (Embodiment 1). Graph showing frequency characteristics of impedance in (Embodiment 2) Sectional view showing a configuration of an electrode for an electrolytic capacitor in (Embodiment 3). Perspective view showing the configuration of a conventional electrode for an electrolytic capacitor

Explanation of reference numerals

REFERENCE SIGNS LIST 1 molded body 2 foil 3 lead wire 4 electrode for electrolytic capacitor 5 through hole

Claims (4)

An anode body in which a foil as a lead made of valve metal is attached to a molded body of valve metal powder, a dielectric oxide film formed on the pore surface of the anode body, and a solid electrolyte formed in contact with the oxide film. , An electrolytic capacitor used at a high frequency of 100 kHz or more,
The lead foil has a substantially constant width, and a part of the molded body is formed such that a portion embedded in the molded body and a part not embedded in the molded body have substantially the same foil width. An electrolytic capacitor embedded therein, wherein the thickness of the lead foil is 100 μm or less. An electrode for an electrolytic capacitor in which a foil as a lead made of a valve metal is attached to a molded body of a valve metal powder,
The lead foil has a width substantially equal to or greater than 0.17 with respect to the width of the molded body, and a portion embedded in the molded body and a part not embedded in the molded body have substantially the same foil width. The electrode for an electrolytic capacitor in which a part is embedded in the molded body and the thickness of the lead foil is 100 μm or less. Irregularities are formed on the surface of the valve metal foil, and the irregularities are adjusted so that the surface area of the contact portion of the foil with the molded body is at least twice as large as the surface area of the contact portion of the foil with no irregularities. The electrode for an electrolytic capacitor according to claim 2, which is formed. 4. The electrode for an electrolytic capacitor according to claim 2, wherein the valve metal foil has a through hole.

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