Brazing structure and vacuum capacitor

Abstract

A brazing structure of a vacuum container (1a) is provided. The vacuum container (1a) is provided with: a fixed conductor (5) on which a fixed electrode (7) is supported; a movable conductor (6) on which the movable electrode (8) is supported; a flange tube (4) joined to the movable conductor (6) so as to be coaxial with the fixed electrode (7) and the movable electrode (8); and a ceramic tube (21) disposed coaxially therewith. One end of the ceramic tube (21) is joined to the fixed conductor (5) by means of brazing, a connecting flange tube (31) is interposed therebetween, and the other end of the ceramic tube (21) is joined to the flange tube (4) by means of brazing by means of the connecting flange tube (31) not shown in the figure. The connecting flange pipe (31) is provided with a joint part that is joined to the ceramic pipe (21) by means of active metal brazing using an AgCuTi-based, AgCuInTi-based, or AgCuSnTi-based metal.

Description

Technical Field

[0001] The present invention relates to a brazed structure and a vacuum capacitor used, for example, for adjusting impedance in high-frequency devices such as high-frequency power supplies for semiconductor devices or high-power transmission circuits. Background Art

[0002] Conventionally, various vacuum capacitors have been used to adjust impedance in high-frequency devices such as high-frequency power supplies of general semiconductor devices or high-power transmission circuits.

[0003] Figure 2 A schematic cross-sectional view showing an example of a conventional vacuum capacitor (i.e., a vacuum variable capacitor). The vacuum container 1 of the vacuum capacitor includes a cylinder, which includes a ceramic tube 2, a flange tube 3, and a flange tube 4. The ceramic tube 2 is an insulator made of 90-95% alumina, and includes a first end and a second end metallized by nickel plating. The flange tube 3 and the flange tube 4 are respectively mounted on the first end and the second end of the ceramic tube 2. The cylinder of the vacuum container 1 is sealed by brazing a fixed conductor 5 and a movable conductor 6 to the first end and the second end of the cylinder, respectively.

[0004] The metallization adopts nickel plating to obtain wettability for soldering, and thereby joins the ceramic tube 2 with the fixed conductor 5 and the movable conductor 6. The wettability is based on the following physical phenomenon, which depends on the relationship between the surface tension of the molten solder, the surface tension of the ceramic tube 2, and the interfacial tension between the molten solder and the ceramic tube 2.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 4692211 Summary of the invention

[0008] As described above, the temperature of the conventional vacuum capacitor rises mainly due to the heat generated by the current-carrying part. This heat generation also occurs in the ceramic body and the nickel plating layer of the ceramic tube 2 made of 90-95% alumina and metallized by nickel plating. As described below, it has an influence particularly due to the increase of the current carried.

[0009] Each nickel plating layer at the first end and the second end of the ceramic tube 2 metallized by nickel plating is ferromagnetic, and forms a ferromagnetic magnetic circuit having a ring shape around the current path of the high-frequency current. This concentrates the magnetic flux and generates a high magnetic flux density and a high-frequency magnetic field, and thus causes the ferromagnetic magnetic circuit in the ring shape formed by nickel to heat up due to hysteresis loss and eddy current loss, and increases the temperature of the metallized part of the ceramic tube 2.

[0010] When a high-frequency voltage is applied to the vacuum capacitor, the ceramic tube 2 generates heat due to high-frequency dielectric polarization. The amount of heat generated per unit volume is proportional to the square of the field intensity, the frequency, the relative dielectric constant, and the dielectric tangent tanδ.

[0011] By increasing the high-frequency voltage applied to the vacuum capacitor, the high-frequency current in the vacuum capacitor can be increased. For example, the high-frequency voltage can be applied 100% to the fixed conductor 5 and 0% to the movable conductor 6. In this case, invisible equipotential lines can be defined, each equipotential line represents a cross section of an equipotential surface, and the potential lines are shown as 80% equipotential line 28, 60% equipotential line 26, 40% equipotential line 24, and 20% equipotential line 22. The narrower the gap between the two equipotential lines, the higher the field strength at the gap.

[0012] exist Figure 2 In the case of the biased field strength, the field strength is biased to be highly concentrated near the brazing joint between the ceramic tube 2 and the flange tube 3, and biased to be low in other parts. This concentration of field strength in a specific part causes heat to be generated in the specific part in proportion to the square of the field strength there. In the case of this biased field strength, the total heat generated in the ceramic tube due to high-frequency dielectric polarization is greater than the total heat generated in the case of the dispersed field strength.

[0013] By replacing the ceramic tube 2 made of 90-95% alumina and having a relative dielectric constant of 8.8-9.2 and a dielectric tangent tanδ of 0.0003-0.0004 with a high-purity ceramic tube made of 99.5-99.97% alumina and having a relative dielectric constant of 9.7-10.1 and a dielectric tangent tanδ of 0.0001, the dielectric tangent tanδ is reduced, thereby reducing the heat generation. However, in the case where the field strength is highly concentrated in a specific part, the reduction in heat generation is less than the increase in heat generation. This results in the total heat generation not being reduced. In addition, the increase in high-frequency voltage further increases the total heat generation in the ceramic tube, thereby further increasing the temperature increase. In the case of dispersed field strength, in terms of the total heat generation in the ceramic tube, due to the characteristic differences between the ceramic tubes, the high-purity ceramic tube is smaller than the ceramic tube 2.

[0014] Recently, the load applied to high-frequency devices has gradually increased, the required high-frequency current flowing in the high-frequency devices has increased, and the size of the high-frequency devices has increased, while the high-frequency voltage applied to the vacuum capacitor has also increased.

[0015] Originally, as a countermeasure to the temperature rise, it was inevitable to increase the size of the energized part because the temperature rise was mainly caused by the heat caused by the increase in the energized current. In addition to this, as the heat caused in the part other than the energized part due to the strength of the magnetic field and the electric field, the ceramic tube 2 made of 90-95% alumina and metallized by nickel plating generates heat due to hysteresis loss, eddy current loss and high-frequency dielectric polarization. This has an influence particularly in the case of increasing the energized current because the energized current is increased by increasing the applied high-frequency voltage.

[0016] In view of the above, it is desirable to reduce the temperature rise of the current-carrying portion of the vacuum capacitor and to improve the high-frequency current carrying performance of the vacuum capacitor.

[0017] One aspect of the present invention is a brazing structure of a vacuum container accommodating a pair of electrodes, wherein the vacuum container includes: a first conductor supporting a first electrode of the pair of electrodes; a second conductor supporting a second electrode of the pair of electrodes; a flange pipe coaxially joined to the second conductor with the pair of electrodes; a ceramic tube coaxially arranged with the pair of electrodes; and a connecting flange pipe connecting the ceramic tube to the first conductor or the flange pipe. The connecting flange pipe includes a junction joined to the ceramic tube by brazing using an active metal of an AgCuTi-based, AgCuInTi-based, or AgCuSnTi-based metal.

[0018] According to another aspect of the present invention, the above soldering structure is further configured such that: the first electrode of the pair of electrodes is a fixed electrode fixed to the first conductor; and the second electrode of the pair of electrodes is a movable electrode configured to be movable in the axial direction of the vacuum container.

[0019] According to yet another aspect of the present invention, the brazing structure is further configured such that the connecting flange pipe includes a field-relaxing ring provided on the outside or inside of the joint portion.

[0020] According to yet another aspect of the present invention, the brazing structure is further configured such that the ceramic tube is made of ceramic composed of 99.5-99.97% alumina.

[0021] According to still another aspect of the present invention, a vacuum capacitor has the brazing structure as described above.

[0022] The above aspects of the present invention serve to reduce the temperature rise of the current-carrying portion of the vacuum capacitor and to improve the high-frequency current carrying performance of the vacuum capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1is a cross-sectional view showing the structure of a vacuum capacitor according to an embodiment of the present invention.

[0024] Figure 2 is a cross-sectional view showing the structure of a vacuum capacitor according to the prior art. DETAILED DESCRIPTION

[0025] Figure 1 A vacuum capacitor according to an embodiment of the present invention is shown. The vacuum capacitor includes a vacuum container 1a. The vacuum container 1a includes a fixed conductor 5 (i.e., a first conductor), a movable conductor 6 (i.e., a second conductor), a fixed electrode 7, a movable electrode 8, a flange tube 4, and a ceramic tube 21. The fixed conductor 5 supports the fixed electrode 7. The movable conductor 6 supports the movable electrode 8. The flange tube 4 is coaxially joined to the movable conductor 6 with the fixed electrode 7 and the movable electrode 8. The ceramic tube 21 is coaxially arranged with the flange tube 4.

[0026] The ceramic tube 21 is made of insulating high-purity alumina ceramic, wherein 99.5-99.97% of the ceramic is composed of alumina. The ceramic tube 21 includes a first end joined to the fixed conductor 5 via the connecting flange tube 31 by brazing. In addition, although omitted in the figure, the ceramic tube 21 includes a second end joined to the flange tube 4 via the connecting flange tube 31 by brazing.

[0027] The joint flange pipe 31 includes a joint portion 31 a that joins the ceramic tube 21 to the fixed conductor 5 by active metal brazing.

[0028] Active metal brazing is performed using an active metal brazing filler metal that easily wets and spreads on the surface of the ceramic tube 21 even when the surface of the ceramic tube 21 is not metallized. For example, the active metal brazing filler metal is a non-magnetic or weakly paramagnetic metal such as AgCuTi-based metal, AgCuInTi-based metal, or AgCuSnTi-based metal.

[0029] The connecting flange pipe 31 includes an electric field relaxation ring disposed outside or inside the joint portion 31a. Figure 1 In the embodiment of the present invention, the connecting flange pipe 31 includes an atmosphere external electric field relaxation ring 31b and a vacuum internal electric field relaxation ring 31c. The atmosphere external electric field relaxation ring 31b is arranged on the outside of the joint 31a, that is, the atmosphere outside of the joint 31a. The vacuum internal electric field relaxation ring 31c is arranged on the inside of the joint 31a, that is, the vacuum side of the joint 31a.

[0030] The fixed electrode 7 is fixed to the inner surface of the fixed conductor 5 in the vacuum container 1 a , and includes a plurality of electrodes which are substantially cylindrical thin plates having different diameters and are coaxially arranged at constant intervals.

[0031] Similar to the fixed electrode 7, the movable electrode 8 includes a plurality of electrodes which are generally cylindrical thin plates having different diameters and are coaxially arranged at constant intervals. The movable electrode 8 is configured to be opposed to the fixed electrode 7 in a manner not to contact the fixed electrode 7 while reciprocating in the axial direction Y of the vacuum container 1a. The movable electrode 8 is provided on a movable support 9. The movable support 9 is made of copper and is configured to adjust the insertion degree of the movable electrode 8 in the fixed electrode 7 along the axial direction Y.

[0032] The movable support 9 includes a back surface, that is, a surface opposite to the movable electrode 8, on which a movable rod 10 is provided. The movable rod 10 is hollow, and extends in the axial direction Y of the vacuum container 1 to protrude from the movable conductor 6, and is driven by an operating rod 12. The movable rod 10 is surrounded by a bellows 14 located between the movable conductor 6 and the movable support 9, and is supported by a bearing 11 of the movable conductor 6 coaxially with the flange tube 4. The movable rod 10 has a gap between its outer peripheral surface and the bearing 11, and is in sliding contact with the bearing 11, thereby being guided in the axial direction Y of the vacuum container 1.

[0033] The operating rod 12 includes a first end and a second end, wherein the first end includes an external thread 12b, and the second end includes an operating rod head 12a. The external thread 12b is screwed into the internal thread 10a of the movable rod 10. The operating rod head 12a is linked to a driving source of a vacuum capacitor such as a motor. The operating rod 12 is supported by an operating rod support 13 in a rotatable manner.

[0034] The operating rod support 13 includes a screw retainer 13a and a thrust bearing 13b. The screw retainer 13a protrudes from the movable conductor 6 of the vacuum container 1, covers the bearing 11, and is fixed to the movable conductor 6. The thrust bearing 13b reduces the rotation torque of the operating rod 12.

[0035] The operating rod support 13 enables the movable rod 10 to be guided by the bearing 11 and move in the axial direction Y of the vacuum container 1 in response to the rotation of the operating rod 12 caused by a driving source such as a motor. This changes the facing area between the fixed electrode 7 and the movable electrode 8, thereby obtaining an arbitrary capacitance.

[0036] The bellows 14 has an accordion shape, is made of a copper alloy or a thin metal metalized by copper plating, and can extend in the axial direction Y of the vacuum container 1. The bellows 14 includes a first end engaged with the inner wall of the movable conductor 6 and a second end engaged with the movable support 9. Therefore, the bellows 14 surrounds the movable rod 10, is coaxially arranged with the flange tube 4, and establishes the airtightness of the vacuum chamber 15 with the fixed electrode 7 and the movable electrode 8. On the other hand, the vacuum container 1 includes an atmospheric chamber 16, which is formed on one side of the movable rod 10 relative to the bellows 14 and is maintained at atmospheric pressure.

[0037] The vacuum capacitor as described above is configured so that the rotation of the operating rod 12 caused by a driving source such as a motor causes the movable rod 10 to move in the axial direction of the vacuum container 1, and then changes the facing area between the fixed electrode 7 and the movable electrode 8. This enables the capacitance formed by the fixed electrode 7 and the movable electrode 8 to increase and decrease, thereby enabling the impedance to be arbitrarily adjusted.

[0038] In response to the high-frequency voltage being applied to the vacuum container 1a, a high-frequency current flows from the fixed conductor 51 to the fixed electrode 7, flows to the capacitance adjustable according to the cross area between the fixed electrode 7 and the movable electrode 8 facing each other, and flows to the movable support 9, the bellows 14, and the movable conductor 6. Thus, the vacuum container 1a is energized.

[0039] When a 100% high frequency voltage is applied to the fixed conductor 51 and a 0% high frequency voltage is applied to the movable conductor 6 , invisible equipotential lines are generated, which are shown as 80% equipotential line 218 , 60% equipotential line 216 , 40% equipotential line 214 , and 20% equipotential line 212 in the figure.

[0040] The above embodiment is configured to join the fixed conductor 5 and the ceramic tube 21 via the joint flange tube 31 by active metal brazing using non-magnetic or weakly paramagnetic metals such as AgCuTi-based, AgCuInTi-based or AgCuSnTi-based metals. This makes the hysteresis loss and eddy current loss of the embodiment smaller than the case of conventional nickel plating using ferromagnetic materials.

[0041] The connecting flange pipe 31 includes an electric field relaxation ring arranged on the outside and / or inside of the joint 31a. This sets the equipotential lines, especially the 80% equipotential line 218, away from the brazed joint and relaxes and disperses the field strength over the entire ceramic. This helps to reduce the total heat generation of the energized part of the vacuum capacitor and lower the temperature of the energized part. In particular, the relaxation and dispersion of the field strength occurs in the high heat generation part of the ceramic tube 2 that is likely to experience the square of the field strength, reducing the total heat generation of the ceramic tube 2 and suppressing the temperature rise of the energized part.

[0042] The active metal brazing filler metal according to the present embodiment not only reduces the heat generation due to hysteresis loss and eddy current loss, but also has better wettability on the ceramic tube 21 made of 99.5-99.97% alumina than that of 90-95% alumina. This improves brazing and improves the vacuum reliability of the vacuum container 1a.

[0043] The configuration of the connecting flange tube 31 including both or one of the atmospheric external electric field relaxation ring 31b and the vacuum internal electric field relaxation ring 31c is combined with the configuration of the ceramic tube 21 having a high relative dielectric constant, thereby presenting a synergistic effect: the equipotential lines are greatly changed and dispersed, and the field intensity is further dispersed. This reduces the heat generated due to the high-frequency dielectric polarization of the ceramic tube 21, and further reduces the heat generated due to the low dielectric tangent tanδ. This significantly reduces the total heat generation and suppresses the temperature rise compared to the case where one of the above configurations is adopted alone.

[0044] Conventional temperature rise countermeasures mainly target the heat generated by the increase in the current, which inevitably leads to an increase in the size of the current-carrying part. According to the vacuum capacitor of this embodiment, the total heat generation is reduced by the temperature rise countermeasures targeting the intensity of the magnetic field and electric field in the ceramic tube 2. This helps to improve the high-frequency current carrying performance of the vacuum capacitor while avoiding an increase in size.

[0045] Furthermore, the brazing structure according to the present invention is not limited to applications Figure 1 The vacuum variable capacitor may also be applied to a vacuum fixed capacitor including a vacuum container accommodating a pair of electrodes.

Claims

1. A brazing structure, a brazing structure of a vacuum container (1a) accommodating a pair of electrodes (7, 8), characterized in that: The vacuum container (1a) comprises: A first conductor (5) supporting a first electrode of the pair of electrodes (7, 8); a second conductor (6) supporting the second electrode of the pair of electrodes (7, 8); A flange pipe (4) coaxially joined to the second conductor (6) with the pair of electrodes (7, 8); a ceramic tube (21) disposed coaxially with the pair of electrodes (7, 8); and connecting the flange tube (31) to connect the ceramic tube (21) to the first conductor (5) or the flange tube (4), The connecting flange pipe (31) includes a joint portion (31a) joined to the ceramic pipe (21) by active metal brazing using AgCuTi-based, AgCuInTi-based or AgCuSnTi-based metal.

2. The brazing structure according to claim 1, wherein: The first electrode of the pair of electrodes (7, 8) is a fixed electrode (7) fixed to the first conductor (5), The second electrode of the pair of electrodes (7, 8) is a movable conductor (6) configured to be movable along the axial direction (Y) of the vacuum container (1a).

3. The brazing structure according to claim 1 or 2, wherein: The connecting flange pipe (31) includes an electric field relaxation ring (31b, 31c) arranged on the outside or inside of the joint (31a).

4. The brazing structure according to claim 1 or 2, wherein: The ceramic tube (21) is made of ceramic containing 99.5-99.97% alumina.

5. A vacuum capacitor having the brazing structure according to claim 1.

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