GB1575265A

GB1575265A - Ceramic tubular capacitor and a method of producing the same

Info

Publication number: GB1575265A
Application number: GB920278A
Authority: GB
Original assignee: KESTAFIL GmbH
Current assignee: KESTAFIL GmbH
Priority date: 1977-03-09
Filing date: 1978-03-08
Publication date: 1980-09-17
Also published as: FR2383511A1; FR2383511B3

Description

(54) CERAMIC TUBULAR CAPACITOR AND A METHOD OF PRODUCING THE SAME (71) We, KESTAFIL SPEZIALFAB RIK KERAMISCHER BAUELEMENTE GMBH., a body corporate organised under the laws of the Federal Republic of Germany, of 8300 Landshut, Ludmillastrasse 23/25, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a ceramic capacitor and has particular reference to a ceramic capacitor with through-going passages having metallized inner and outer surfaces.

The problem underlying the present invention is above all that of providing a ceramic tubular capacitor of the kind previously defined which, for its size, has signific- antly increased capacitance in comparison with previously known or proposed solutions, but which can nevertheless be manufactured with simple means by mass production methods.

According to the present invention there is provided a capacitor comprising a ceramic body with two passages extending through the body, the two passages being separated by a web and the surfaces of the passages each having respective metallized coverings electrically insulated from each other, there being further provided two terminal mem hers each terminal member being electrically connected to the metallized covering in a respective one of said passages and wherein at least one metallized covering is provided on the outer surface of the ceramic body and an electrical connection is provided between said at least one metallized covering and the metallized covering on the surface of one of said passages.

By cutting a ceramic body which is obtained by extrusion into pieces of a determined length it is possible to obtain, in a particularly simple manner, by series production methods, capacitor sections which, after suitable metallizing, already have a capacitance of a determined magnitude and which can then be accurately adjusted within close tolerances, for example by sandblasting the metal covering provided on the outer surface.

A first aspect of the invention thus consists in providing an electrically conductive connection of a definite type between an outer metallized covering and one of the inner metallized coverings, since in this manner the internal series connection which would otherwise occur is eliminated and thus a substantial increase in capacitance is achieved.

The electrically conductive connection preferably consists of at least one metallized bridge which at least substantially fills a notch provided in the end face of the ceramic tube.

The grinding of a notch of this kind in the end face of the tubular body entails very little expense, but after metallizing and surface grinding of the end faces of the tubular body will necessarily produce the capacitance increasing electrical connection between one of the two inner metallized coverings and the outer metallized covering.

In an embodiment of the invention which is characterized by a particularly distinct increase of total capacitance the outer covering is divided into two partial coverings, each of the latter being connected by an electrically conductive connection to a respective one of the two inner coverings.

In this manner optimum use is made of the available inner and outer surfaces of the tubular body provided with a central web, and the total capacitance yield resulting from the connection in parallel of three individual capacitances is maximized.

It is expedient for the outer metallized covering to be subdivided into two partial coverings by two separating regions extend ing at least substantially along a generatrix of the tubular body.

These separating regions may for example be obtained by sandblasting, grinding, or by removing by means of laser beams and metal applied, and it is also possible for these separating regions to be kept free by suitable masking, for example by means of lacquer, before the tubular body is metallized.

The metallized notches are preferably situated in the region where the web and tubular body meet, and they may lie diametrically opposite one another or be disposed at least substantially on a diameter of the tubular body. For manufacturing reasons it is advantageous for the metallized notches to be disposed parallel to one another.

This special arrangement of the metal bridges permits utilisation of the strength which, among other features, is provided by the middle web, so that the grinding of the notches can be effected without problems.

An advantageous process for the production of a ceramic tubular capacitor according to the invention is characterized in that, before the ceramic body is metallized a notch extending from the outer surface of the body to one of the two inner walls is provided on at least one end face of the body, and that, after metallizing of the body, the metal covering is superficially removed on the end faces, thus producing metallized notches as desired.

It is particularly advantageous to utilize an extruded tubular body, which has projections extending along its outer wall, and for these projections to be ground away after metallizing so as to form separating regions sub- dividing the metallized covering on the outer surface.

In addition to the very considerable advantage of increased capacitance provided by the invention, it must be referred to as a particular advantage that with one basic dimension it is possible to produce various alternative capacitances with simple means, while retaining the same manufacturing equipment. If in addition the ceramic material is varied while the same dimensions are retained, very economical production of a complete capacitance series will be possible without the need for conversion of the production line.

It is a particular advantage that the web not only increases strength but also additionally permits the fastening of the terminal members in a particularly satisfactory and novel manner forming a second aspect of the present invention.

According to this second aspect of the invention there is provided a capacitor comprising a ceramic body with two passages extending through the body, the two pas sages being separated by a web and the sur faces of the passages each having metallized coverings electrically insulated from each other, there being further provided two terminal members, each terminal member being located in a respective one of said passages by contact with opposing sides thereof.

The terminal members are preferably cranked adjoining the point where they pass out of the ceramic body in such a manner that their free ends extend at least substantially parallel to the axis of the ceramic body.

In this way, while caps or wires bent in a complicated manner are avoided, capacitors are obtained which are particularly suitable for binding.

The tubular body may be made of high dielectric-constant or low dielectric-constant material, but is preferably made of semiconductor ceramic material.

The invention is described more fully below by way of example only and with reference to the drawings, in which: Figure 1 is a diagrammatical view of axial section of one form of construction of a tubular capacitor; Figure 2 is a sectional view on the line X-X' in Figure 1; Figure 3 shows the electrical equivalent circuit diagram of the capacitor of Figure 1; Figure 4 is a diagrammatical view in axial section of another form of construction of a tubular capacitor; Figure 5 is an end view of the capacitor shown in Figure 4; Figure 6 shows a diagrammatical end view of an alternative form of a tubular capacitor to an enlarged scale; Figure 7 shows the electrical equivalent circuit diagram of the tubular capacitor of Figure 4; Figure 8 shows on a larger scale a diagrammatical end view of another form of construction of a ceramic tubular capacitor;; Figure 9 shows the electrical equivalent circuit diagram of the tubular capacitor according to Figure 8, and Figure 10 & 11 show once again an enlarged scale, end views of two additional forms of construction of ceramic tubular capacitors, before their final completion.

Figure 1 shows a ceramic body in the form of a tubular element 1 produced by extrusion and cut to length in the required manner. The ceramic body has two through-going passages 8, 9 which are separated by a central web 2. The outer surface of the tubular element 1 has a metallized covering 3 on its outer surface, hereinafter referred to as the "outer covering", and the surfaces of the passages 8, 9 Iying between the central web 2 and the inner wall of the tubular element are also provided with respective metallized coverings 4, 5 hereinafter referred to as the "inner coverings".

The end faces 6, 7 of the tubular element 1 are not metallized.

As shown in Figure 1, especially in con junction with Figure 2, terminal members in the form of connecting wires 10,11 are fastened in the passages 8, 9 between the central web 2 and the wall of the tube. The diameter of the connecting wires 10, 11 is preferably so selected that it substantially corresponds to or is slightly smaller than the maximum distance between the middle web 2 and the inner wall of the tube, in order to ensure the preferably used clamping action by which the terminal members are located in their respective passages by contact with opposing sides thereof.

In the region where they pass out of the tubular element 1 each of the terminal members 10, 11 has a cranked portion 12, 13 which is so selected that the free ends 14, 15 of the terminal members are substantially coaxial to the axis of the tubular element, so that binding of capacitors produced in this manner is possible without problems.

Figure 3 shows the electrical equivalent circuit diagram of the tubular capacitor shown in Figure 1 and 2. From this equivalent circuit diagram it can be seen that the provision of a central web in the tubular element, in conjuction with the metallizing selected, results in an increase in capacitance.

The embodiment shown in Figures 4 and 5 differs from the form of construction of a tubular capacitor described above in that the series connection of partial capacitances, which can be seen in the equivalent circuit diagram in Figure 3, is avoided owing to the fact that only the end face 7 of the tubular element is ground bare so that it is not metallized, whereas the end face 6 is metallized on part of the surface as shown by the reference 16. This partially metallized end face 6 thus forms an electrical connection connecting the outer covering 3 to one of the inner coverings, namely the inner covering 5. Thus simply because only a part of the end surface 6 is ground away another increase of capacitance yield is achieved.

The two embodiments described have the common feature that, particularly when ceramic semiconductor material is used for the tubular body, it is possible, without using caps or complicated bending of the connecting wires, to obtain a tubular capacitor which meets with all the requirements for problemless series production. This is above all due to the presence of the central web 2, which is obtained during the extrusion and which has a multiple function inasmuch as, in addition to increasing the total strength, it permits increased capacity and in addition ensures particularly advantageous mechanical fastening and holding of the connecting wires.

Figure 6 shows a tubular element 1 which has a middle web 2 and which was produced by extrusion and cut to length in the required manner. The tubular element may consist of high dielectric-constant and low dielectricconstant materials, although it is preferred to use a semiconductor ceramic material.

The outer surface of the tubular element 1 is provided with a metallized covering 3 and the surfaces of the passages situated between the central web and the inner wall of the tubular element are likewise provided with metallized coverings 4, 5.

The end faces of the tubular element are free from metallized coverings except at a notch 7 as will be later described.

The inner spaces 8, 9 serve to receive the connecting wires (not shown in the drawing), which are preferably fixed in position in the passages between the central web and the inner wall of the capacitor, as explained with reference to Figure 1 to 5. The connecting wires are expediently taken axially out of the tubular body, for which purpose they may be slightly cranked directly after passing out of the tubular body.

In the region of the transition from the middle web 2 into the cylindrical tubular body 1 an electrical connection is provided in the form of a metallized notch 7, which electrically connects the inner covering 4 directly to the outer covering 3. This metal bridge 7 is preferably obtained by providing in the end face of the tubular body a notch in which metal will be deposited during metallizing of the tubular body and will not be removed when the end surface is superficially ground bare, thus making the electrically conductive connection between the outer covering 3 and the inner covering 4.

Through this electrically conductive connection the internal series connection of partial capacitances, which would otherwise exist, is eliminated and a substantial increase in capacitance is achieved.

Figure 7 shows the equivalent circuit diagram of the tubular capacitor according to Figure 6, and this equivalent circuit diagram clearly shows that, because of the connection between the inner covering 4 and the outer covering 3, there is no longer an internal connection in series. The portion of the equivalent circuit diagram shown in broken lines with the partial capacity formed between the coverings 3 and 4 is electrically ineffective and is shown in the equivalent circuit diagram only to make clearer the effect of the use of the electrically conductive connection 7.

The tubular capacitor shown diagrammatically in an end view in Figure 8 differs from that shown in Figure 7 in that two metallized notches 10, 11 disposed diametrically opposite one another are provided, and that the metallized covering on the outer surface of the cermaic body is divided into first and second metallized coverings 12, 13 which are separated from one another by separating strips 14, 15.

The metallized notch 11 constitutes an electrically conductive connection between the inner covering 4 and the outer covering 13, while the metallized notch 11 makes an electrically conductive connection between the inner covering 5 and the outer covering 12. Each of the two inner coverings 4, 5 is thus associated with a respective outer covering lying on the opposite side of the separating web 2.

The separating regions 14, 15 can for example be produced by longitudinal grinding, but it is also possible without difficulty for these separating strips to be obtained by sandblasting or by burning-off by means of a laser. However, it is also possible for strips of lacquer to be applied before metallizing in order to mask the ceramic material, these strips being removed after metallizing and thus at the same time forming the necessary separating regions between the metallized outer coverings.

Figure 9 shows the equivalent circuit diagram of the tubular capacitor of Figure 8, and in this diagram it can be seen that because of the steps taken the partial capacitances obtained between the inner coverings 4 and 5, the inner covering 4 and the outer covering 12, and between the inner covering 5 and the outer covering 13 are connected in parallel, so that the best possible capacitance yield is obtained.

Figure 10 shows an end view of a tubular capacitor according to the embodiment shown in Figure 8, but before its final completion.

In this figure it can be seen that projections 16 and 17 project from the outer surface of the tubular body, directly adjacent the metallized notches 10 and 11, these projections being produced during the extrusion of the tubular body.

During the metallizing operation these projections 16, 17 are likewise covered with a layer of metal. If these projections are completely, or optionally only partly, ground away, it is possible in a simple manner to obtain the necessary separating strips between the outer coverings 12 and 13. This grinding operation may advantageously also be used at the same time to effect the adjustment of the individual capacitor to a determined final value.

The embodiment shown in Figure 11 differs from that shown in Figure 10 essentially only in that the projections 16 and 17 lie on a common diameter of the tubular body aligned with the central web. Thus the metal bridges 18, 19 are disposed at an angle to the middle web 2, but extend parallel to one another, i.e. lie along a pair of parallel lines.

WHAT WE CLAIM IS: 1. A capacitor comprising a ceramic body with two passages extending through the body, the two passages being separated by a web and the surfaces of the passages each having respective metallized coverings electrically insulated from each other there being further provided two terminal members, each terminal member being electrically connected to the metallized covering in a respective one of said passages and wherein at least one metallized covering is provided on the outer surface of the ceramic body and an electrical connection is provided between said at least one metallized covering and the metallized covering on the surface of one of said passages.

2. A capacitor according to claim 1 and wherein the metallized covering is separated into two parts to define first and second metallized coverings on the outer surface of the ceramic body there being a second electrical connection between said second metallized covering and the metallized covering on the surface of the other of said passages.

3. A capacitor according to either of claims 1 or 2 and in which the or each electrical connection is provided by a or a respective partially metallized end face of the ceramic body.

4. A capacitor according to either of claims 1 or 2 and in which the, or each, electrical connection is provided by a, or a respective, metallized notch in the end face of the ceramic body.

5. A capacitor according to claim 2 and in which said metallized coverings on the outer surfaces of the ceramic body are electrically insulated from each other by ceramic projections formed on the ceramic body.

6. A capacitor according to claim 4 and in which two said notches are provided each metallized notch serving to connect the metallized covering of the surface of one of the passages with the metallized covering on the outer surface of the ceramic body which lies adjacent the other of the passages.

7. A capacitor according to either of claims 4 or 6 and in which two said notches are provided the notches lying along adjacent parallel lines on the end face of the ceramic body.

8. A capacitor according to any one of claims 1 to 7 in which said ceramic body is tubular.

9. A capacitor according to any one of claims 1 to 8 in which said ceramic body is made of semiconductor ceramic material.

10. A capacitor according to any one of claims 1 to 9, in which said metallized coverings are made of a metal capable of forming boundary layers.

11. A capacitor comprising a ceramic body with two passages extending through the body, the two passages being separated by a web and the surfaces of the passages each having respective metallized coverings electrically insulated from each other, there being further provided two terminal members, each terminal member being located in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. electrically conductive connection between the inner covering 4 and the outer covering 13, while the metallized notch 11 makes an electrically conductive connection between the inner covering 5 and the outer covering 12. Each of the two inner coverings 4, 5 is thus associated with a respective outer covering lying on the opposite side of the separating web 2. The separating regions 14, 15 can for example be produced by longitudinal grinding, but it is also possible without difficulty for these separating strips to be obtained by sandblasting or by burning-off by means of a laser. However, it is also possible for strips of lacquer to be applied before metallizing in order to mask the ceramic material, these strips being removed after metallizing and thus at the same time forming the necessary separating regions between the metallized outer coverings. Figure 9 shows the equivalent circuit diagram of the tubular capacitor of Figure 8, and in this diagram it can be seen that because of the steps taken the partial capacitances obtained between the inner coverings 4 and 5, the inner covering 4 and the outer covering 12, and between the inner covering 5 and the outer covering 13 are connected in parallel, so that the best possible capacitance yield is obtained. Figure 10 shows an end view of a tubular capacitor according to the embodiment shown in Figure 8, but before its final completion. In this figure it can be seen that projections 16 and 17 project from the outer surface of the tubular body, directly adjacent the metallized notches 10 and 11, these projections being produced during the extrusion of the tubular body. During the metallizing operation these projections 16, 17 are likewise covered with a layer of metal. If these projections are completely, or optionally only partly, ground away, it is possible in a simple manner to obtain the necessary separating strips between the outer coverings 12 and 13. This grinding operation may advantageously also be used at the same time to effect the adjustment of the individual capacitor to a determined final value. The embodiment shown in Figure 11 differs from that shown in Figure 10 essentially only in that the projections 16 and 17 lie on a common diameter of the tubular body aligned with the central web. Thus the metal bridges 18, 19 are disposed at an angle to the middle web 2, but extend parallel to one another, i.e. lie along a pair of parallel lines. WHAT WE CLAIM IS:

1. A capacitor comprising a ceramic body with two passages extending through the body, the two passages being separated by a web and the surfaces of the passages each having respective metallized coverings electrically insulated from each other there being further provided two terminal members, each terminal member being electrically connected to the metallized covering in a respective one of said passages and wherein at least one metallized covering is provided on the outer surface of the ceramic body and an electrical connection is provided between said at least one metallized covering and the metallized covering on the surface of one of said passages.

a respective one of said passages by contact with opposing sides thereof.

12. A capacitor according to claim 11 in which said body is a hollow tubular extrusion.

13. A capacitor according to claim 12, wherein the terminal members are cranked adjoining the point where they pass out of the tubular extrusion so that the free ends of the terminal members extend at least substantially parallel to the axis of the tubular extrusion.

14. A capacitor according to either of preceding claims 12 or 13 wherein the cross sectional dimensions of the terminal members respectively correspond at least substantially to the maximum distance between the web and the inner wall of the tube facing the web.

15. A capacitor according to one of preceding claims 12, 13 or 14 and wherein the wall thickness of the web is substantially equal to the wall thickness of the tube.

16. A capacitor according to any one of preceding claims 11 or 14 and further comprising at least one metallized covering on the external surface of said ceramic body, the, or each, metallized covering being electrically connected with one of the metallized coverings on the surface of one of the passages via a respective electrical connection.

17. A capacitor according to claim 16 and in which the or each said electrical connection comprises a partially metallized end face of the cermaic body.

18. A capacitor according to claim 16, wherein the or each electrical connection comprises a metallized notch extending through the end face of the ceramic body.

19. A capacitor according to claim 16, wherein the outer surface of the ceramic body is proved with first and second metallized coverings separated by two separating regions extending along respective generatrices of the tubular body.

20. A capacitor according to any one of preceding claims 16 to 19, wherein the or each said electrical connection is disposed in a region where the web and the outer body meet.

21. A tubular capacitor according to claim 18, wherein the or each metallized notch lies at least substantially on a diameter of the tubular body.

22. A tubular capacitor according to claim 18, wherein two metallized notches are provided and are arranged to lie on two parallel lines.

23. A capacitor according to claim 19, wherein the ceramic body has projections extending along its outer surface defining the two said separating regions.

24. A capacitor according to any one of preceding claims 1 to 15 wherein end faces ?f the ceramic body and of the web are not metallized.

25. A capacitor according to any one of preceding claims 11 to 24, wherein the ceramic body consists of semiconductor ceramic material.

26. A capacitor according to any one of preceding claims 11 to 25, wherein the metallized coverings consist of metals forming barrier layers.

27. A capacitor substantially as herein described and illustrated with reference to Figures 1 to 5 of the accompanying drawings.

28. A capacitor substantially as herein described and illustrated with reference to Figures 6 to 11 of the accompanying drawings.