Method of producing an anode for a capacitor

Details Method of producing an anode for a capacitor Method of producing an anode for a capacitor

2002-02-20

2004-03-02

Jenkins, Daniel J. (Department: 1742)

Powder metallurgy processes

Powder metallurgy processes with heating or sintering

Making composite or hollow article

C419S007000

Reexamination Certificate

active

06699431

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method of producing an anode for a capacitor.
In its preferred implementation, the capacitor is a chip capacitor. However, the present invention can also readily be applied to other capacitors, such as for example, capacitors without housings. A capacitor without a housing is of low structural height and is integrated, for example, in a hybrid circuit. However, the following text assumes that the capacitor according to the invention is a chip capacitor.
Chip capacitors, in particular tantalum chip capacitors, are distinguished by a high volume-specific capacitance-voltage product, also known as the “CV product.” This means that in these capacitors the value of the volume-related product of capacitance and voltage which can be applied to the capacitor is particularly high. Further advantageous properties of chip capacitors include a stable thermal behavior and frequency response, a low residual current and a small loss factor.
Due to these excellent properties, in particular tantalum chip capacitors are used for numerous applications in a very wide range of fields. New applications, demanding conditions of use and an increasing tendency toward miniaturization in electronics mean that the demands imposed on chip capacitors are becoming ever greater.
A pertinent prior art assembly is illustrated in
FIGS. 24-26
.
FIG. 24
shows a diagrammatic section through the structure of a conventional tantalum chip capacitor.
FIG. 25
shows a side view of the anode body of that chip capacitor, and
FIG. 26
is a plan view of the anode body.
The prior art chip capacitor comprises an anode body
1
, a dielectric
2
, and a layered cathode
3
, which form an actual capacitor element.
In addition, there is a housing
4
which is responsible for important protective functions for the capacitor element.
A tantalum wire
5
, which in the interior of the housing
4
is connected to a first metal connector
6
. The wire
5
leads to the capacitor element comprising the anode body
1
, the dielectric
2
, and the layered cathode
3
. By means of a conductive adhesive
8
, the layered cathode
3
is connected to a second metal connector
7
. The second metal connector
7
, similarly to the metal connector
6
, leads out of the housing
4
.
Chip capacitors of this nature are produced in different sizes of housing
4
, usually with standardized basic surface area dimensions and structural heights. Consequently, if a higher CV product is to be achieved, the volume taken up by the capacitor element or the anode body
1
contained therein must be increased.
Owing to the use of the tantalum wire
5
in the anode body
1
(in this respect see, in particular,
FIGS. 25 and 26
) as the anode-side conductor, the utilization of the housing can scarcely be increased further. This is because the free end of the tantalum wire
5
is welded to the metal connector
6
which, in the finished chip capacitor, is intended to provide electrical connection to an electronic circuit on a printed-circuit board, together with the other metal connector. In a design of this nature, the distance between the capacitor element and the housing wall is particularly great especially on the positive side. The distance between the positive metal connector
6
and the capacitor element or the anode body
1
, which is formed by the tantalum wire
5
, can scarcely be reduced further, for manufacturing reasons. In other words, the volume of the housing is only insufficiently utilized in the prior art chip capacitor.
East German Patent DD 215 420 discloses a tantalum chip capacitor in which an anode conductor is embedded in a two-part anode body produced by extrusion. That anode body and anode conductor preassembly is then sintered. The use of two pre-extruded partial anode bodies has the drawback that it is impossible to achieve an exact form fit between the anode body and the anode conductor, owing to manufacturing tolerances. Consequently, the electrical contact between the anode body and the anode conductor is impaired.
German published patent application DE 36 34 103 A1 discloses a tantalum capacitor in which a tantalum powder is pressed around a wire anode conductor. That capacitor has the drawback of a small contact area between the wire anode conductor and the anode body. The result is an increased resistance in the capacitor which may have an adverse effect on the electrical characteristics of the capacitor. This is an undesirable effect.
U.S. Pat. No. 3,903,589 discloses a tantalum capacitor, the anode of which is produced by immersing the anode conductor in a dispersion containing metal powder. When the anode conductor is pulled out of the dispersion, a drop remains hanging from the anode conductor, which is then dried and sintered. That tantalum capacitor has the drawback that the anode body cannot be produced with a defined geometry. Because of the absence of an optimized anode geometry and the broad tolerances, that prior art capacitor is subject to poor volume utilization.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method of producing an anode for a capacitor which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which has a large contact area between the anode conductor and the anode body, the anode body of which is of fixedly predetermined shape, and in which there is good electrical contact between the anode body and the anode conductor.
With the above and other objects in view there is provided, in accordance with the invention, an anode for an electrolytic capacitor, comprising:
a flat anode conductor; and
an anode body of a continuously deformable material molded onto the anode conductor and solidified into a fixedly predetermined shape.
In other words, the anode has an anode body of fixedly predetermined shape and a flat anode conductor. The anode body is molded onto the anode conductor from a continuously deformable material which can be solidified.
There is also provided, in accordance with the invention, a capacitor, comprising:
the anode according to the above summary, wherein a second end segment of the anode conductor is shaped into a first terminal connector;
a dielectric enclosing the anode body; and
a layered cathode disposed on the dielectric and connected to a second terminal connector.
In other words, the anode body of the capacitor is surrounded by a dielectric, and a layered cathode is provided on the dielectric. A further end section of the anode conductor is shaped into a first terminal connector and the layered cathode is connected to a second terminal connector.
The anode according to the invention has the advantage that as a result of the entire anode body being molded onto the anode conductor in the form of a continuously deformable material, it is possible to form a homogeneous anode body which exhibits a good form fit with the anode conductor and good electrical contact with the anode conductor.
Furthermore, the anode according to the invention has the advantage that, as a result of the anode body being shaped with the aid of a continuously deformable material, it is possible to achieve any desired shape with the aid of suitable molds which are removed before or after solidification of the anode body. The material from which the anode body is formed may, for example, be a paste containing metal powder, a green film produced from the paste, or a suitable metal powder itself.
Due to the flat design of the anode conductor which is sintered into the anode body made from sintered tantalum powder, for example, a larger contact area between anode conductor and anode body is achieved compared with a sintered-in tantalum wire of the same cross-sectional area. The number of powder particles which are in contact with the surface of the anode conductor is increased, and consequently the mean length of the current paths between the dielectric and the anode conductor, which comprise tantalum particles which have been sintered together, is

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