JPH0613271A - Manufacture of solid electrolytic capacitor - Google Patents

Abstract

PURPOSE:To stably supply a solid electrolytic capacitor of high quality, by making the inside of the cavity of a mold having a negative pressure, filling the cavity with powder, and compression molding it, when a molded object of valve action metal powder is formed. CONSTITUTION:Powder 5 is deposited in a moving hopper 8 wherein the upper end and the lower end are opened. When the hopper 8 is moved on the upper end surface of a casting mold 9 and reaches the aperture part of a cavity 7 while retaining the powder 5, a linking hole 12 is cut off by a shutter 14 and a vacuum pump 13 is operated. The shutter 14 is opened when the cavity aperture is plugged by the powder 5, the inside of the cavity is rapidly turned into the negative pressure state, and the powder 5 is sucked in the cavity. Before the cavity 7 is filled with the powder, the liking hole 12 is cut off by the shutter 14. The hopper 8 leaves from the cavity 7, and the filling is ended. A wire for an electrode is attached, and compression molding and sintering are performed. Thereby a solid electrolytic capacitor of high quality can be stably supplied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid electrolytic capacitor. More specifically, the present invention relates to a method for producing a solid electrolytic capacitor which can prevent variations in the amount and density of the raw material powder when forming a valve metal sintered body and can improve the filling speed.

[0002]

2. Description of the Related Art In the conventional method for manufacturing a solid electrolytic capacitor, when molding a valve-acting metal powder (hereinafter, simply referred to as powder), a frame of a predetermined size placed on the upper surface of a molding die 51 as shown in FIG. A predetermined amount of powder 53 is deposited in the hopper 52 (see FIG. 7A). Then, the hopper 52, the powder
While holding 53 inside thereof, the powder 53 is moved along the end surface of the molding die 51, and the powder 53 is naturally dropped into the cavity 54 while passing through the upper opening of the cavity 54 of the molding die 51 (see FIG. 7B). ). Then, as shown in FIG. 7C, for example, the powder 53 is completely filled with the cavity 54 by the lower end edge of the hopper 52 (so that the upper surface of the powder 53 is flush with the upper surface of the molding die 51).

On the other hand, in the method shown in FIG. 8, the powder 53 is deposited in the funnel-shaped hopper 61, and the valve 62 at the lower end of the hopper 61 is opened for a certain period of time, whereby a predetermined amount of the powder 53 is obtained.
Is also poured into the cavity 54 by free fall.

[0004]

However, in the above-mentioned conventional method, the powder 53 is filled into the cavity 54 of the molding die 51 by free fall, so that the filling density and the filling amount are different depending on the particle size and the wetness of the powder 53. It may vary from product to product and it takes a long time to fill. As a result, there are problems that the capacitance of the solid electrolytic capacitor varies, the quality is not stable, and the cost increases.

The present invention has been made in order to solve the above problems. The powder is forcibly filled in a short time by forcibly filling the powder in the cavity of the mold with a negative pressure. It is an object of the present invention to provide a method for producing a solid electrolytic capacitor capable of preventing fluctuations in the density, volume, etc. of a sintered body for each product.

[0006]

According to the manufacturing method of the present invention, a molded body of valve action metal powder having electrode wires protruding therefrom is sintered,
A method for producing a solid electrolytic capacitor, in which a dielectric film, a metal oxide layer, and a conductor layer are formed in that order on the outer surface thereof, wherein in forming a molded body of the valve action metal powder, in a cavity of a molding die It is characterized in that a negative pressure is applied, the powder is filled, and compression molding is performed.

Then, when the opening of the cavity of the mold is temporarily covered with the powder conveyed by the frame-shaped hopper for filling, it is preferable to start negative pressure inside the cavity. .

[0008]

In the manufacturing method of the present invention, when the powder is filled in the cavity, a negative pressure is created in the cavity, so that the powder is forcibly drawn into the cavity uniformly. That is,
The particles of the powder are forcibly filled throughout the cavity. In particular, if the opening of the cavity is covered with powder using a frame-like hopper at the start of filling, the negative pressure in the cavity effectively acts on the powder,
The powder is more evenly and strongly drawn in and filled. As a result, the filling time of the powder is greatly shortened, a sintered body with a uniform density is obtained, and stable high-quality solid electrolytic capacitors with extremely few fluctuations in the density or volume depending on the product are obtained. Can be supplied.

[0009]

EXAMPLES Next, the manufacturing method of the present invention will be described with reference to the attached surface. FIG. 1 is a process diagram showing an example of the first half of the powder forming step in the production method of the present invention, and FIGS. 2 to 3 are schematic explanations showing an example of the cavity negative pressure mechanism used in the process of FIG. FIG. 4, FIG. 4 is a process diagram showing an example of the latter half of the powder forming process in the production method of the present invention, and FIG. 5 is a process diagram showing an example of a process after forming a sintered body in the production process of the present invention. 6 is a cross-sectional view showing a state where an oxide film or the like is formed on the surface of the powder after the powder has been molded and sintered.

First, as shown in FIG. 1, the particle size is 0.03 to 0.1 m.
The metal powder 5 such as tantalum, aluminum, and niobium, which has a valve action, of about m 3 is filled in the cavity 7 of the molding die 6. First, the powder 5 moves in a cylindrical shape or a rectangular tube shape with both upper and lower ends opened. It is deposited in the hopper 8 (see FIG. 1A). The hopper 8 is arranged so as to be movable on the upper end surface of the molding die 6 (strictly speaking, on the upper end surface of a later-described middle die 9).

The molding die 6 includes a middle die 9, a lower die 10 which can slide up and down in the middle die 9, and an upper die for compressing powder (see FIG. 4).
(See (c)) 11), and the size of the cavity 7 is appropriately set according to the size of the solid electrolytic capacitor to be manufactured (hereinafter referred to as capacitor). In this embodiment, the length is about 1 mm, the width is about 1 mm, and the depth is about 1.5 mm. The upper die 11 presses the molded body to a height of about 1 mm, and the molded body is about 1 mm square. Is formed. A communication hole 12 that opens to the side of the cavity 7 is formed in the middle mold 9, and is connected to a vacuum pump 13 for creating a negative pressure inside the cavity 7. In the communication hole 12,
A shutter 14 that can block the communication between the cavity 7 and the vacuum pump 13 is provided, and a filter 15 through which the powder 5 cannot pass is provided upstream thereof.

Then, as shown in FIG. 1B, the hopper 8 holds the powder 5 and moves on the upper end surface of the middle mold 9 to reach the opening of the cavity 7. At that time, the opening of the cavity 7 is blocked for a moment by the powder 5 in the hopper 8. Before that, the vacuum pump 13 is operated while the communication hole 12 is blocked by the shutter 14 to open the cavity. If the shutter 14 is opened when the powder is blocked, the inside of the cavity 7 rapidly becomes a negative pressure, and the powder 5 is drawn into the cavity 7. The communication hole 12 is blocked by the shutter 14 before the inside of the cavity 7 is filled with powder. These operations take place in a very short time. The timing of opening and closing the shutter 14 and filling the powder 5 can be set arbitrarily, but generally the time for filling the powder 5 is about 3 seconds, and the shutter 14 starts filling (the opening of the cavity 7 is closed by the powder 5). To about 0.3 to 0.5 seconds. Further, it is preferable to change the suction speed of the powder by changing the suction force of the vacuum pump 13 or the operation time of the vacuum pump 13 before opening the shutter 14 to change the suction force. This is because the production rate of the capacitor can be increased.
According to the present invention, the time required for the filling operation (from the start of filling to the end of filling) is shortened from about 1 second in the related art to about 0.5 seconds.

Next, as shown in FIG. 1C, the hopper 8 is separated from the cavity 7 and the filling is completed. In addition,
Each of these steps can be automatically performed according to a time schedule.

In the present embodiment, the vacuum pump 13 is connected to the communication hole 12 opened on the side of the cavity 7, but the structure is not limited to this. For example, instead of the communication hole 12, as shown in FIG. 2, a communication hole 16 that opens to the bottom of the cavity 7 may be formed in the lower mold 10 and a vacuum pump 13 may be connected, as shown in FIG. The vacuum pump 13 may be connected to the communication hole 17 separately through a very narrow gap between the inner surface of the middle mold 9 and the lower mold 10. No matter which configuration is used, the communication holes 12, 16,
17 is preferably provided with a shutter 14 and a filter 15.

In the next step, the powder filled in the cavity 7 as described above is compression-molded and sintered with the electrode wire attached. The method of attaching, compressing, and sintering the wire is not particularly limited, and a suitable method including a known method can be selected.

Here, the method developed by the present inventors will be exemplified. As shown in FIG. 4 (a), a jig 18 is inserted into the powder 5 filled in the cavity 7 by the above step (FIG. 4 (b)), so that a guide hole 20 for inserting a wire 19 described later can be obtained. To form. The diameter of the portion 18 a of the jig 18 to be inserted into the powder 5 (hereinafter referred to as the insertion portion) is preferably the same as or slightly larger than the diameter of the wire 19, but may be slightly smaller. Also, the guide hole 20
The depth can be arbitrarily set according to the insertion depth of the wire 19, but it is preferable that the depth is the same as the insertion depth of the wire 19 or slightly shallower. In this embodiment, the wire insertion length is
Since it is 0.6 to 0.7 mm, it is set to 0.4 mm. Jig 18
As the material of the insertion portion 18a, diamond, cemented carbide, tungsten carbide or the like having a higher hardness and strength than the material of the wire 19 (for example, tantalum) is used.

Then, as shown in FIGS. 4 (c) and 4 (d), the powder 5 is compressed by pressing the upper mold 11 having the central portion thereof penetrated by the wire 19 into the cavity 7. The wire 19 is held so as to slightly project from the lower end surface of the upper mold 11, and the projecting portion is smoothly inserted into the guide hole 20 and fixed in the powder 5 by the compression of the powder 5.

Thereafter, as shown in FIG. 4E, the holding of the wire 19 is released, and the upper mold 11 is removed while leaving the wire 19 at that position. Then, the molded body is taken out of the molding die and heated to about 1400 ° C. to form the tantalum sintered body 21 with the wire 19 (FIG. 4 (f)).

The step after sintering, that is, the step of manufacturing a capacitor using the sintered body with wire 21 formed as described above is not particularly limited, and any suitable method including well-known ones can be adopted. Good.

An example of the manufacturing method will be described with reference to FIG. As shown in FIG. 5B, a tantalum pentoxide (Ta ₂ O ₅ ) layer 22 is formed on the surface of each powder of the tantalum sintered body 21 and a part of the surface of the wire 19. Then, the tantalum sintered body 21 is impregnated with an aqueous solution of manganese nitrate and thermally decomposed (FIG. 5).
As a result of (c)), as shown in the sectional view of the tantalum powder 5 in FIG. 6, the first manganese dioxide layer 23 is formed on the tantalum pentoxide layer 22 on the powder surface. Further, FIG. 5 (d)
A second manganese dioxide layer around the sintered body, as shown in FIG.
24 are formed. Next, as shown in FIG. 5E, the conductive paste 25 is applied to a part of the wire 19 to electrically connect the wire 19 and the second manganese dioxide layer 24. Then, as shown in (f) of FIG. 5, the wire 19 is made positive and the tank 27 of the electrolytic solution 26 is made negative to carry out electrolytic oxidative polymerization, thereby forming a polypyrrole layer 28 as shown in (g) of FIG. Form. After the formation of the polypyrrole layer 28 is completed, the conductive paste 25 is removed as shown in FIG. The conductive paste 25 can be removed by a conventionally known process such as removal with plasma or peeling with tweezers. Next, as shown in (i) of FIG. 5, a graphite layer 29 is formed and a silver paste is applied to form a silver layer 30. The metal layer of these exteriors can be formed according to a method conventionally known as a method for producing a solid electrolytic capacitor. The other electrode of the electrolytic capacitor is taken out from this silver layer.

The solid electrolytic capacitor is completed as described above. A protective film is formed on the surface of the silver layer 30 if necessary.

[0022]

According to the present invention, the powder can be forcibly and uniformly filled into the cavity of the molding die, so that the filling speed can be shortened and a sintered body having a uniform density can be obtained. Depending on the product, it is possible to stably supply high-quality solid electrolytic capacitors with extremely low fluctuations in density and volume.

[Brief description of drawings]

FIG. 1 is a process drawing showing an example of the first half of a powder molding process in a manufacturing method of the present invention.

FIG. 2 is a schematic explanatory view showing an example of a negative pressure mechanism for a cavity used in the step of FIG.

FIG. 3 is a schematic explanatory view showing another embodiment of the cavity negative pressure mechanism used in the step of FIG.

FIG. 4 is a process drawing showing an example of the latter half of the powder molding process in the manufacturing method of the present invention.

FIG. 5 is a process drawing showing an example of a manufacturing process of a solid electrolytic capacitor after forming a sintered body in the manufacturing method of the present invention.

FIG. 6 is a cross-sectional view showing a state in which an oxide film or the like is formed by a treatment after sintering of the powder used in FIG.

FIG. 7 is a process drawing showing an example of a powder molding process in a conventional manufacturing method.

FIG. 8 is a process drawing showing another example of the powder molding process in the conventional manufacturing method.

[Explanation of symbols]

 5 Powder 6 Mold 7 Cavity 8 Hopper 13 Vacuum Pump 21 Sintered Body 22 Tantalum Pentoxide Layer 23 First Manganese Dioxide Layer 24 Second Manganese Dioxide Layer 30 Silver Layer

Claims (2)

[Claims] 1. A solid electrolysis device comprising a molded body of valve action metal powder having electrode wires protruding from the sintered body, and a dielectric film, a metal oxide layer and a conductor layer formed on the outer surface of the compact in this order. A method of manufacturing a capacitor, wherein, when forming a molded body of the valve action metal powder, the powder is filled after making a negative pressure in a cavity of a molding die,
A method for producing a solid electrolytic capacitor, which comprises compression molding. 2. A negative pressure is applied to the inside of the cavity when the powder conveyed by the frame-shaped hopper temporarily covers the opening of the cavity of the mold for filling. The method for producing a solid electrolytic capacitor according to claim 1.