Airtight terminal

Abstract

The airtight terminal according to the present disclosure comprises: a columnar or cylindrical first continuity member; a first insulating member that has a through-hole in which a part of the first continuity member is positioned, and that is positioned along the axial direction of the first continuity member; a first annular member that is positioned on the outer circumferential surface of the first continuity member; a cylindrical second continuity member that is positioned on the outer circumference of the first insulating member; and an insulating layer that is positioned at a portion facing the first insulating member and the first continuity member. The first insulating member includes a first annular insulating portion, and a second annular insulating portion having an outer diameter larger than that of the first annular insulating portion. The first annular insulating portion is positioned at least on one axial-direction side of the second annular insulating portion. The first annular member is joined to the end surface of the first annular insulating portion, and the second continuity member is joined to the outer peripheral surface of the second annular insulating portion. The insulating layer includes a first insulating layer located at a portion facing the first annular insulating portion and the first continuity member, and a second insulating layer located at a portion facing the second annular insulating portion and the first continuity member. The radial-direction thickness of the first insulating layer is smaller than the radial-direction thickness of the second insulating layer.

Description

Airtight terminal

[0001] The present disclosure relates to a hermetic terminal used in vacuum equipment, nuclear equipment, equipment that operates at extremely low temperatures in the presence of liquid hydrogen or the like (for example, a flow meter for cryogenic liquids), and the like.

[0002] Conventionally, as an airtight terminal, for example, an insulated coaxial vacuum terminal as described in Patent Document 1 is known, which comprises a metal round bar-shaped pin, a first ceramic cylindrical body having a through hole for inserting the pin, a first metal cylindrical body fitted around the outer periphery of the first ceramic cylindrical body, a second ceramic cylindrical body fitted around the outer periphery of the first metal cylindrical body, and a second metal cylindrical body fitted around the outer periphery of the second ceramic cylindrical body.

[0003] Special Publication No. 55-2065

[0004] The airtight terminal of the present disclosure includes a columnar or tubular first conductive member, a first insulating member having a through hole through which a portion of the first conductive member is located and positioned along the axial direction of the first conductive member, a first annular member positioned on the outer peripheral surface of the first conductive member, a tubular second conductive member positioned on the outer periphery of the first insulating member, and an insulating layer positioned at a portion where the first insulating member and the first conductive member face each other. The first insulating member includes a first annular insulating portion and a second annular insulating portion having an outer diameter larger than that of the first annular insulating portion. The first annular insulating portion is positioned at least on one axial side of the second annular insulating portion. The first annular member is bonded to an end face of the first annular insulating portion, and the second conductive member is bonded to the outer peripheral surface of the second annular insulating portion. The insulating layer includes a first insulating layer positioned at a portion where the first annular insulating portion and the first conductive member face each other, and a second insulating layer positioned at a portion where the second annular insulating portion and the first conductive member face each other. The radial thickness of the first insulating layer is smaller than the radial thickness of the second insulating layer.

[0005] Fig. 2A is a cross-sectional view showing a hermetic terminal according to an embodiment of the present disclosure. Fig. 2B is an enlarged cross-sectional view of a portion A of the hermetic terminal shown in Fig. 1. Fig. 2C is a partially enlarged cross-sectional view of the hermetic terminal not having a first insulating layer shown in Fig. 2A. Fig. 2D is a cross-sectional view showing another embodiment of the hermetic terminal shown in Fig. 1. Fig. 2E is a cross-sectional view showing yet another embodiment of the hermetic terminal shown in Fig. 1. Fig. 2F is a cross-sectional view showing a hermetic terminal according to another embodiment of the present disclosure. Fig. 2G is a cross-sectional view showing a hermetic terminal according to yet another embodiment of the present disclosure.

[0006] Conventional airtight terminals such as those described in Patent Document 1 do not have impedance matching in the high frequency band, particularly in the GHz band or higher, and therefore do not have good transmission characteristics for high frequency signals. ＯＵＴ and the input impedance R of the circuit (load side) to which the voltage is input ＩＮ This means that the output impedance R ＯＵＴ and input impedance R ＩＮ By making these two terminals the same, it is possible to maximize the power transmitted by the circuit that outputs the voltage, thereby improving the transmission characteristics of high-frequency signals. Therefore, there is a demand for a hermetic terminal that has good transmission characteristics for high-frequency signals in the high-frequency band, particularly in the GHz band or higher.

[0007] The hermetic terminal of the present disclosure, having the above-described configuration, ensures a creepage distance between the first conductive member and the second conductive member, thereby improving insulation, and also facilitates impedance matching in the GHz band or higher, thereby improving signal transmission characteristics in the high frequency band.

[0008] The airtight terminal of the present disclosure will be described below with reference to the drawings. However, for the sake of convenience, the drawings shown below are simplified versions of the embodiments of the present disclosure. Therefore, the airtight terminal disclosed below may include optional components not shown in the drawings. Furthermore, the dimensions of the components in the drawings do not faithfully represent the actual dimensions of the components or the dimensional ratios of the components.

[0009] FIG. 1 is a schematic cross-sectional view of an airtight terminal according to this embodiment. As shown in FIG. 1 , the airtight terminal according to this embodiment includes a columnar first conductive member 1, a first insulating member 3 having a through hole 2 through which a portion of the first conductive member 1 is located, a first annular member 4 located on the outer periphery of the first conductive member 1, and a tubular second conductive member 5 located on the outer periphery of the first insulating member 3. Cylindrical bodies 6a and 6b are joined to both axial end surfaces of the second conductive member 5. The cylindrical bodies 6a and 6b are members for mating with coaxial connectors such as SMA connectors, N connectors, and BNC connectors. The cylindrical bodies 6a and 6b may have the same structure or different structures. Providing such cylindrical bodies 6a and 6b allows for easy connection to connectors standardized by industrial standards. In other words, the cylindrical bodies 6a and 6b are not limited to simple cylindrical bodies, and may have any structure as long as they can be connected to standardized connectors.

[0010] Here, the airtight terminal of this embodiment is a coaxial terminal (hereinafter sometimes referred to as a high-frequency coaxial terminal), with the first conductive member 1 functioning as the inner conductor and the second conductive member 5 functioning as the outer conductor. The inner conductor of a coaxial line is referred to as the inner conductor, and the outer conductor is referred to as the outer conductor. The inner conductor is also called the internal conductor, and the outer conductor is also called the external conductor. The first conductive member 1 may be cylindrical. The cylindrical first conductive member 1 contributes to reducing the weight of the airtight terminal, and the larger the airtight terminal, the greater this contribution becomes. The first conductive member 1 is inserted through the through hole 2.

[0011] The first insulating member 3 has a convex shape including a first annular insulating portion 31 (hereinafter sometimes referred to as the first insulating portion 31) and a second annular insulating portion 32 (hereinafter sometimes referred to as the second insulating portion 32) having an outer diameter larger than that of the first insulating portion 31. The first insulating portion 31 and the second insulating portion 32 are located along the axial direction of the first conductive member 1. The first insulating portion 31 and the second insulating portion 32 may be formed integrally or separately, and a gap may be present between the first insulating portion 31 and the second insulating portion 32. However, the gap must be sized so as not to affect the signal transmission characteristics of the coaxial terminal in the high frequency band (hereinafter sometimes referred to as the RF (radio frequency) characteristics). Not affecting the RF characteristics means that the high frequency (radio frequency) characteristics satisfy a VSWR of 3 or less (VSWR: Voltage Standing Wave Ratio). The reason why VSWR≦3 is set is that this corresponds to the case where the output signal strength is at least half the input signal strength, even if the signal strength is attenuated. The target value of VSWR can be changed as appropriate depending on the required characteristics.

[0012] The first annular member 4 may be, for example, a flange provided on the outer peripheral surface of the first conductive member 1, or a washer located on the same outer peripheral surface. To ensure the airtightness of the airtight terminal, the first annular member 4 is joined without gaps to the end face of the first insulating portion 31 continuously in the circumferential direction of the first annular member 4. The second conductive member 5 is joined without gaps to the outer peripheral surface of the second insulating portion 32 continuously in the circumferential direction of the second conductive member 5. Being joined without gaps means that the airtightness required by, for example, a helium leak test (JIS Z 2331:2006) is satisfied.

[0013] The first conductive member 1, the first annular member 4 and the second conductive member 5 include, for example, a Fernicoid alloy, an Fe—Ni alloy, an Fe—Ni—Cr—Ti—Al alloy, an Fe—Co—Cr alloy, an Fe—Cr—Al alloy, Ti, a Ti alloy, Mo, Cu, a Cu alloy, etc.

[0014] The first insulating member 3 includes, for example, a ceramic whose main component is aluminum oxide. The main component of the ceramic refers to a component that accounts for 85% by mass or more of the total 100% by mass of the components that make up the ceramic. In addition to the main component, aluminum oxide, the ceramic may also contain at least one of silicon, calcium, and magnesium as an oxide. The main component of the ceramic can be determined by identifying the crystalline phase of the main component using an X-ray diffraction (XRD) analyzer, and then determining the content of the metal elements that make up the main component using an X-ray fluorescence analyzer (XRF) or an inductively coupled plasma (ICP) emission spectrometer (ICP), and converting the content of the main component into the content of the main component.

[0015] The end face of the first insulating portion 31, which contains ceramic, and the first annular member 4 are joined via a first joint portion 71. Furthermore, the outer peripheral surface of the second insulating portion 32, which contains ceramic, and the second conductive member 5 are joined via a second joint portion 72. To ensure airtightness, the second joint portion 72 is formed continuously in the circumferential direction over the entire outer peripheral surface of the second insulating portion 32. However, the second joint portion 72 may also be formed continuously in the circumferential direction over a portion of the outer peripheral surface. Examples of the first joint portion 71 and the second joint portion 72 include brazed portions.

[0016] 2A, brazing can be performed using a brazing material 10 via metal layers 9a, 9b located on the first insulating portion 31 side and the second insulating portion 32 side. This ensures airtightness. The metal layers 9a, 9b include metallized layers located on the first insulating portion 31 side and the second insulating portion 32 side, and coating layers located on the metallized layers.

[0017] 2A is an enlarged view of portion A in FIG. 1 and schematically shows a first joint portion 71 and a second joint portion 72. As shown in FIG. 2A, the first joint portion 71 joins the first insulating portion 31 and the first annular member 4 by a brazing material 10 through a metal layer 9a located on the first insulating portion 31 side. The second joint portion 72 also joins the second insulating portion 32 and the second conductive member 5 by a brazing material 10 through a metal layer 9b located on the second insulating portion 32 side.

[0018] The metallization layers constituting the metal layers 9a and 9b are primarily composed of molybdenum and contain manganese. The coating layer is a layer for reducing oxidation of the metallization layers, and is primarily composed of nickel, copper, or a copper-nickel alloy, and may contain phosphorus or boron. The thickness of the metallization layer may be, for example, 10 μm to 50 μm, and the thickness of the coating layer may be, for example, 1 μm to 10 μm.

[0019] The main component of the coating layer refers to a component that accounts for 88% by mass or more of the total 100% by mass of the components that make up the coating layer. In the case of a coating layer whose main component is a copper-nickel alloy, the total content of the main component is the sum of the contents of copper and nickel. The main component of the coating layer can be determined by using an X-ray fluorescence analyzer (XRF) or an inductively coupled plasma (ICP) emission spectrometer (ICP) to determine the content of the elements that make up the main component and converting it into the content of the main component.

[0020] Brazing can be performed using a brazing filler metal 10 containing silver as a main component, such as BAg-8, BAg-8A, or BAg-8B. The main component of the brazing filler metal 10 refers to a component that accounts for 60% by mass or more of the total 100% by mass of the components that make up the brazing filler metal 10. The element content of the main component that makes up the brazing filler metal 10 can be determined using an X-ray fluorescence analyzer (XRF) or an inductively coupled plasma (ICP) emission spectrometer (ICP). The brazing filler metal 10 in the present disclosure is a brazing filler metal used for brazing as defined in JIS Z 3001-3:2008 (ISO 857-2:2005 (MOD)).

[0021] Furthermore, the end surface of the first insulating portion 31 containing ceramic may be joined to the first annular member 4 using a brazing filler metal containing an active metal instead of the brazing filler metal 10. The outer peripheral surface of the second insulating portion 32 containing ceramic may also be joined to the second conductive member 5 using a brazing filler metal containing an active metal instead of the brazing filler metal 10. This allows joining without the need for metal layers 9 a, 9 b.

[0022] In this case, the brazing filler metal 10 used contains, for example, 20% by mass to 40% by mass of copper, 1% by mass to 3% by mass of an active metal, 1.2% by mass to 6% by mass of tin or indium, and the balance being Ag. The active metal may be, for example, at least one selected from titanium, zirconium, hafnium, and niobium.

[0023] 1 , in the hermetic terminal of this embodiment, an insulating layer 8 is located at the portion where the first insulating portion 31 and the first conductive member 1 face each other. The insulating layer 8 includes a first insulating layer 8a and a second insulating layer 8b. The first insulating layer 8a has a smaller radial thickness than the second insulating layer 8b. That is, the outer diameter of the portion of the first conductive member 1 facing the first insulating portion 31 is larger than the outer diameter of the portion of the first conductive member 1 facing the second insulating portion 32.

[0024] That is, the value of the characteristic impedance of the portion where the first insulating member 3 is located is determined by the ratio between the outer diameter of the first conductive member 1 and the inner diameter of the second conductive member 5, and the thickness and relative dielectric constant of the insulating members (first insulating member 3, first insulating layer 8a, second insulating layer 8b, and insulating layer (vacuum, gas, resin, etc.) between the first insulating portion 31 and the second conductive member 5) between the outer peripheral surface of the first conductive member 1 and the inner peripheral surface of the second conductive member 5. Here, the radial thicknesses of the first insulating portion 31 and the second insulating portion 32 are different. Therefore, impedance matching can be achieved by adjusting the thicknesses of the first insulating layer 8a and the second insulating layer 8b.

[0025] The end of the second insulating layer 8b is preferably located at the same position as the opposing end of the first insulating member 3, or closer to the first insulating member 3 than the opposing end to the extent that it does not affect the RF characteristics (VSWR≦3). This ensures that the first conductive member 1 always comes into contact with the first insulating member 3 inside the through hole 2, ensuring a creepage distance and maintaining the insulation of the airtight terminal.

[0026] Instead of changing the outer diameter of the first conductive member 1, the first insulating layer 8a and the second insulating layer 8b can also be formed by making the inner diameter of the first insulating member 3 larger than the outer diameter of the first conductive member 1 and making the inner diameter of the first insulating portion 31 smaller than the inner diameter of the second insulating portion 32.

[0027] Examples of the first insulating layer 8a and the second insulating layer 8b include vacuum, gas, or resin having a lower dielectric constant than the first insulating member 3. Examples of the gas include air, oxygen, nitrogen, hydrogen, helium, and sulfur hexafluoride. Examples of the resin include epoxy resin, silicone resin, urethane resin, fluororesin (such as Teflon (registered trademark)), and liquid crystal polymer.

[0028] The first insulating member 3 has a convex shape including a first insulating portion 31 and a second insulating portion 32, and is joined to the first conductive member 1 and the second conductive member 5 by a first joint portion 71 and a second joint portion 72. Therefore, as shown in Fig. 2A, the creepage distance, which is the shortest distance separating the first conductive member 1 and the second conductive member 5 along the surface of the first insulating member 3, is long due to the convex shape of the first insulating member 3.

[0029] In other words, the starting point of the creepage distance on the first conductive member 1 side is end L1 of the metal layer 9a electrically connected to the first conductive member 1 via the brazing filler metal 10, which is closest to the second conductive member 5. The starting point of the creepage distance on the second conductive member 5 side is end L2, which is closest to the first conductive member 1 and where the second conductive member 5 and the second insulating portion 32 come into contact. End L2 is closest to the first conductive member 1 side when the edge of the surface of the second insulating portion 32 facing the first insulating portion 31 comes into contact with the inner circumferential surface of the second conductive member 5, regardless of the position of the second joint portion 72. Therefore, when the first insulating member 3 has a convex shape, the length from end L1 to the surface (end L2) of the second insulating portion 32 is longer than the creepage distance (L11-L21) when the first insulating member 3 does not have a convex shape, ensuring a long creepage distance. This ensures the insulation required for an airtight terminal.

[0030] If the first insulating layer 8a is a vacuum or gas, a gap is formed by the first insulating layer 8a below the first insulating portion 31. Therefore, as shown in Fig. 2A, in the first joint portion 71, fillets 11 and 12 are formed at both ends of the brazing material 10 that brazes the end face of the first insulating portion 31 to the first annular member 4. In particular, the gap in the first insulating layer 8a forms a stable fillet 12 below the brazing material 10. If the first insulating layer 8a is a resin, the resin is filled in after brazing, forming the fillet 12.

[0031] 2B is a partially enlarged cross-sectional view showing a hermetic terminal without the first insulating layer 8a. In FIG. 2B, the central conductive member 100 and insulating member 130 are in close contact with each other (although for ease of explanation, the figure shows a gap between them). As a result, the brazing material 10 penetrates and accumulates between the conductive member 100 and insulating member 130. As a result, the insulating member 130 may crack due to localized stress concentration caused by the expansion of the brazing material 10.

[0032] In contrast, in the present embodiment, when a gap is formed by the first insulating layer 8a below the first insulating portion 31, a fillet 12 is formed between the first insulating portion 31 and the first conductive member 1. As a result, the brazing material 10 does not accumulate, and there is no risk of the insulating member 130 cracking due to local stress concentration. Furthermore, in the airtight terminal shown in FIG. 2B , strict dimensional control is required to ensure close contact between the conductive member 100 and the insulating member 130. However, when the first insulating layer 8a (gap) is present as shown in FIG. 2A , strict dimensional control is not required, and manufacturing is easy.

[0033] 1 , the second conductive member 5 includes a first cylindrical portion 51 and a second cylindrical portion 52. The inner diameter of the first cylindrical portion 51 is larger than the inner diameter of the second cylindrical portion 52, and the first cylindrical portion 51 is joined to the outer peripheral surface of the second insulating portion 32 via a second joint portion 72. That is, the inner diameter of the second cylindrical portion 52 is smaller than the outer diameter of the second insulating portion 32, which is the maximum outer diameter of the first insulating member 3, and therefore forms a step.

[0034] This allows the characteristic impedance to be matched to the difference between the dielectric constant of the first insulating member 3 and the dielectric constant of the space (in gas or vacuum) in the signal transmission characteristics of the high-frequency band of the airtight terminal, which is a high-frequency coaxial terminal. Matching of the characteristic impedance means that the value of the characteristic impedance is within the range (VSWR≦3) that does not affect the RF characteristics, as described above. Furthermore, the second cylindrical portion 52 of the second conductive member 5 and the first insulating member 3 do not necessarily need to be in contact with each other, and may be spaced apart within the range (VSWR≦3) that does not affect the RF characteristics.

[0035] The convex first insulating member 3 may have curved corners R on its surface as long as the curved corners do not affect the RF characteristics (VSWR≦3). This makes it easier to manufacture the first insulating member 3 and also reduces stress concentration at the corners R due to external forces and thermal stress.

[0036] To find the optimal value for the average radius of curvature of the corner R, a simulation can be performed. For example, the simulation can be performed using software such as "Feko" manufactured by Altair, which analyzes the VSWR (Voltage Standing Wave Ratio) against frequency using the finite element method (FEM). The value of the radius of curvature of the corner R can be determined so as to match the characteristic impedance without affecting the RF characteristics.

[0037] An alternative embodiment to the embodiment shown in Fig. 1 is shown in Fig. 3. In Fig. 3, the same components as those in the previously described embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in Fig. 3, the second conductive member 5 includes a first cylindrical portion 51, a second cylindrical portion 52, and a third cylindrical portion 53 located between the first cylindrical portion 51 and the second cylindrical portion 52. The inner diameter of the third cylindrical portion 53 is smaller than the inner diameter of the first cylindrical portion 51, and the inner diameter of the second cylindrical portion 52 is smaller than the inner diameter of the third cylindrical portion 53.

[0038] Therefore, the radial length of the end face of the second insulating portion 32 in the first insulating member 3 that contacts the gap formed by the third cylindrical portion 53 is longer by a length h than the radial length of the end face of the second insulating portion 32 in the first insulating member 3 that contacts the gap formed by the second cylindrical portion 52 in the first insulating member 3 shown in FIG. 1 . In other words, the radial length of the end face of the second insulating portion 32 that contacts the second conductive member 5 is shorter by a length h than the radial length of the end face of the second insulating portion 32 in the first insulating member 3 that contacts the second conductive member 5 in the first insulating member 3 shown in FIG. 1 . As a result, the RF characteristics of the high-frequency coaxial terminal can be improved by matching the characteristic impedance while increasing the creepage distance of the first insulating member 3, thereby improving the insulation of the hermetic terminal. The rest of the configuration is the same as the embodiment shown in FIG. 1 .

[0039] The voids may be filled with, for example, a vacuum or a gas (e.g., air, oxygen, nitrogen, hydrogen, helium, sulfur hexafluoride, etc.) having a lower dielectric constant than the first insulating member 3. Alternatively, the voids may be filled with a resin (e.g., epoxy resin, silicone resin, urethane resin, fluororesin (e.g., Teflon (registered trademark)), liquid crystal polymer, etc.). The voids or the resin used to fill the voids may be made of the same material as the first insulating layer 8a and the second insulating layer 8b. Using the same material facilitates the manufacturing process and is effective in terms of manufacturing costs.

[0040] To find the optimal value for the depth d of the third cylindrical portion 53, a simulation similar to that described above can be performed. The VSWR (Voltage Standing Wave Ratio) versus frequency can be analyzed using the finite element method (FEM) with Altair's "Feko." The value of the depth d can be determined so as to match the characteristic impedance without affecting the RF characteristics. However, to ensure insulation between the end face of the second insulating portion 32 and the second cylindrical portion 52 via the gap, the minimum value of the depth d should be set to 0.1 mm or more.

[0041] Fig. 4 shows another embodiment of the embodiment shown in Fig. 1. In Fig. 4, the same components as those in the previous embodiment are given the same reference numerals, and detailed description thereof will be omitted. As shown in Fig. 4, the second conductive member 5 includes a fourth cylindrical portion 54 in addition to a first cylindrical portion 51 and a second cylindrical portion 52. The fourth cylindrical portion 54 is located at a position where the first insulating member 3 is not located in the axial direction. The inner diameter D of the fourth cylindrical portion 54 is ４１ and the outer diameter D of the first conductive member 1 facing the fourth cylindrical portion 54 ４ Relative to D ４ / D ４１ is the inner diameter D of the second cylindrical portion 52 ２１ and the outer diameter D of the first conductive member 1 facing the second cylindrical portion 52 ２ Relative to D ２ / D ２１ However, the above ratio D ４ / D ４１ and D ２ / D ２１ As described above, the values ​​may be different within a range that does not affect the RF characteristics. The rest is the same as the embodiment shown in FIG.

[0042] As described above, in yet another embodiment, even if the dielectric constant of the first insulating member 3 differs from the dielectric constant of the space, impedance matching can be maintained at each of the first cylindrical portion 51, the second cylindrical portion 52, and the fourth cylindrical portion 54 in the RF characteristics of the high-frequency coaxial terminal, thereby improving the RF characteristics.

[0043] The fourth cylindrical portion 54 may be made of the same or a different conductive material as the second conductive member 5. A different conductive material may be a combination of different conductive materials listed as the materials of the second conductive member 5, or may be a material such as SUS. The conductive material should be selected so as not to affect the RF characteristics. Therefore, the fourth cylindrical portion 54 may be formed integrally with the second conductive member 5 or may be formed separately from the second conductive member 5, and as described above, there may be a gap between the fourth cylindrical portion 54 and the second conductive member 5 as long as it does not affect the RF characteristics.

[0044] When the fourth cylindrical portion 54 is formed integrally with the second conductive member 5, the first cylindrical portion 51, the second cylindrical portion 52, and the fourth cylindrical portion 54 formed integrally with the second conductive member 5 may be divided in the axial direction and joined by brazing or the like. Note that, in yet another embodiment shown in Fig. 4, an airtight terminal is shown that does not have the third cylindrical portion 53 shown in Fig. 3, but it goes without saying that the third cylindrical portion 53 may be included.

[0045] Fig. 5 shows a hermetic terminal according to another embodiment of the present disclosure. As shown in Fig. 5, this hermetic terminal has a first insulating member 30 in a form in which first insulating portions 310a, 310b are located on both sides of a second insulating portion 320, i.e., a form in which convex portions are provided on both sides.

[0046] The first insulating portions 310a, 310b and the second insulating portion 320 have through holes 20 in which a portion of the first conductive member 18 is located, and are positioned along the axial direction of the first conductive member 18. The first conductive member 18 also has two first annular members 4a, 4b located on its outer circumferential surface, and these first annular members 4a, 4b are joined to the end faces of the first insulating portions 310a, 310b, respectively, by brazing or the like.

[0047] Furthermore, a cylindrical second conductive member 50 is located on the outer periphery of the first insulating member 30 and is joined to the outer circumferential surface of the second insulating portion 320. An insulating layer 80 is located in the portion where the first insulating member 30 faces the first conductive member 18. The insulating layer 80 includes first insulating layers 80a, 80b in the portion where the first insulating portions 310a, 310b face the first conductive member 18, and a second insulating layer 80c in the portion where the second insulating portion 320 faces the first conductive member 18. The first insulating layers 80a, 80b have a smaller radial thickness than the second insulating layer 80c.

[0048] The other features are the same as those of the above-described embodiment, and therefore detailed description thereof will be omitted. Note that the first insulating portions 310a and 310b do not need to be the same in size and shape, and may be different in size and shape.

[0049] Fig. 6 shows a hermetic terminal according to yet another embodiment of the present disclosure. In Fig. 6, components identical to those in the previously described embodiment are designated by the same reference numerals, and detailed descriptions thereof will be omitted. As shown in Fig. 6, the hermetic terminal according to this embodiment has a triple coaxial structure including a ring-shaped second insulating member 14 on the outer peripheral surface of the second conductive member 5, which has a gap 13 in which at least a portion of the second conductive member 5 is located, and a third conductive member 15 positioned on the outer periphery of the second insulating member 14. Cylindrical connector portions 17a and 17b are attached to both ends of the third conductive member 15, respectively, for mating with other components (not shown).

[0050] A third conductive member 15, insulated from the second conductive member 5 by the second insulating member 14, is provided on the outer periphery of the second conductive member 5 so as to cover at least the entire second conductive member 5. This eliminates the effect of external electromagnetic waves on the signal transmitted by the first conductive member 1 and the second conductive member 5, thereby reducing the noise level of the transmitted signal. That is, the third conductive member 15 functions as a shielding member and therefore entirely covers the first insulating member 3 and the second insulating member 14 in the longitudinal direction (the axial direction of the first conductive member 1). Furthermore, since the third conductive member 15 functions as a shielding member and is not related to the RF characteristics of the high-frequency coaxial terminal, there are no particular limitations on its shape, and it may be, for example, a cylindrical shape with a polygonal cross section.

[0051] The third conductive member 15 may be made of a conductive material that is the same as or different from the first conductive member 1 and the second conductive member 5. The different conductive material may be a combination of different conductive materials from those listed as the materials of the second conductive member 5, or may be a material such as SUS. The conductive material may be selected so as not to affect the RF characteristics.

[0052] The second insulating member 14 is bonded to the outer peripheral surface of the second conductive member 5 and the inner peripheral surface of the third conductive member 15, respectively. The bonded position between the outer peripheral surface of the first insulating member 3 and the inner peripheral surface of the second conductive member 5 is axially offset from the bonded position between the outer peripheral surface of the second conductive member 5 and the inner peripheral surface of the second insulating member 14, and they do not overlap (i.e., the second bonded portion 72 and the third bonded portion 73, described below). This reduces excessive stress on the second conductive member 5 during brazing of the airtight terminal or in high-temperature and low-temperature (including cryogenic) usage environments, which is effective in reducing cracks.

[0053] Specifically, the second annular member 16 is located on the outer peripheral surface of the second conductive member 5. The outer peripheral surface of the first insulating member 3 and the inner peripheral surface of the second conductive member 5 are joined by a second joint 72, and a flat surface of the second annular member 16 facing the second insulating member 14 and an end face of the second insulating member 14 facing the flat surface of the second annular member 16 are joined by a third joint 73. In this manner, the surface joined by the second joint 72 and the surface joined by the third joint 73 are perpendicular to each other. As a result, stress applied to the second joint 72 and the third joint 73 can be further reduced.

[0054] The second annular member 16 may be formed of a flange provided on the outer peripheral surface of the second conductive member 5, or may be formed of a washer located on the same outer peripheral surface. The inner peripheral surface of the third conductive member 15 is joined to the outer peripheral surface of the second insulating member 14 by a fourth joint 74.

[0055] The third joint 73 can be formed by brazing or the like as described above. That is, the flat surface of the second annular member 16 and the end face of the second insulating member 14 are joined with a brazing material, and the brazing material forms a fillet as described with reference to FIGS. 1 and 2A , and the brazing material also flows onto the outer circumferential surface of the second conductive member 5. To achieve this, it is preferable to form a gap 13 between the outer circumferential surface of the second conductive member 5 and the second insulating member 14. The gap may be formed by at least partially increasing the inner diameter of the second insulating member 14 or by at least partially decreasing the outer diameter of the second conductive member 5.

[0056] The first insulating member 3 and the second insulating member 14 are preferably positioned so as to overlap at least partially in the radial direction, which makes it possible to shorten the axial length of the first conductive member 1 of the airtight terminal, thereby contributing to miniaturization of the airtight terminal.

[0057] The embodiments of the present disclosure have been described above. However, the invention according to the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the present disclosure as shown in (1) to (10) below.

[0058] (1) The airtight terminal of the present disclosure includes a columnar or tubular first conductive member, a first insulating member having a through hole through which a portion of the first conductive member is located and positioned along the axial direction of the first conductive member, a first annular member positioned on the outer peripheral surface of the first conductive member, a tubular second conductive member positioned on the outer periphery of the first insulating member, and an insulating layer positioned at a portion where the first insulating member and the first conductive member face each other. The first insulating member includes a first annular insulating portion and a second annular insulating portion having an outer diameter larger than that of the first annular insulating portion. The first annular insulating portion is positioned at least on one axial side of the second annular insulating portion. The first annular member is bonded to an end face of the first annular insulating portion, and the second conductive member is bonded to the outer peripheral surface of the second annular insulating portion. The insulating layer includes a first insulating layer positioned at a portion where the first annular insulating portion and the first conductive member face each other, and a second insulating layer positioned at a portion where the second annular insulating portion and the first conductive member face each other. The radial thickness of the first insulating layer is smaller than the radial thickness of the second insulating layer. (2) In the hermetic terminal described in (1) above, the first insulating layer and the second insulating layer are vacuum, gas, or resin. (3) In the hermetic terminal described in (1) or (2) above, the second conductive member includes a first cylindrical portion and a second cylindrical portion. The inner diameter of the first cylindrical portion is larger than the inner diameter of the second cylindrical portion, and the first cylindrical portion is joined to the outer peripheral surface of the second annular insulating portion. (4) In the hermetic terminal described in (3) above, the second conductive member includes a first cylindrical portion, a second cylindrical portion, and a third cylindrical portion located between the first and second cylindrical portions. The inner diameter of the third cylindrical portion is smaller than the inner diameter of the first cylindrical portion, and the inner diameter of the second cylindrical portion is smaller than the inner diameter of the third cylindrical portion. (5) In the airtight terminal described in (3) or (4) above, the second conductive member has a fourth cylindrical portion, and the fourth cylindrical portion is located at a position where the first insulating member is not located. (6) In the airtight terminal described in (5) above, ４１ and the outer diameter D of the first conductive member facing the fourth cylindrical portion ４ Relative to D ４ / D ４１ is the inner diameter D of the second cylindrical portion ２１ and the outer diameter D of the first conductive member facing the second cylindrical portion ２ Relative to D ２ / D ２１(7) The hermetic terminal according to any one of (1) to (6) above includes a second insulating member having an annular shape on the outer peripheral surface of the second conductive member, the second insulating member having a through hole through which at least a portion of the second conductive member is positioned, and a third conductive member positioned on the outer periphery of the second insulating member. (8) The hermetic terminal according to (7) above includes the second insulating member bonded to the outer peripheral surface of the second conductive member and the inner peripheral surface of the third conductive member, respectively. The joint position between the outer peripheral surface of the first insulating member and the inner peripheral surface of the second conductive member does not axially overlap with the joint position between the second conductive member and the second insulating member. (9) The hermetic terminal according to (7) or (8) above includes the second annular member positioned on the outer peripheral surface of the second conductive member. The outer peripheral surface of the first insulating member is bonded to the inner peripheral surface of the second conductive member, and the second annular member is bonded to an end face of the second insulating member. (10) In the hermetic terminal described in (8) or (9) above, the first insulating member and the second insulating member are positioned so as to overlap each other at least partially in the radial direction.

[0059] REFERENCE SIGNS LIST 1, 18 First conductive member 2, 20 Through hole 3 First insulating member 31, 310a, 310b First insulating portion (first annular insulating portion) 32, 320 Second insulating portion (second annular insulating portion) 4, 4a, 4b First annular member 5 Second conductive member 51 First cylindrical portion 52 Second cylindrical portion 53 Third cylindrical portion 54 Fourth cylindrical portion 6a, 6b Cylinder 71 First joint portion 72 Second joint portion 73 Third joint portion 74 Fourth joint portion 8, 80 Insulating layer 8a, 80a, 80b First insulating layer 8b, 80c Second insulating layer 9a, 9b Metal layer 10 Brazing material 11, 12 Fillet 13 Gap 14 Second insulating member 15 Third conductive member 16 Second annular member 17 Connector portion 100 Conductive member 130 Insulating member

Claims

1. A conductive member having a columnar or cylindrical shape; a first insulating member having a through hole inside which a portion of the first conductive member is located and positioned along the axial direction of the first conductive member; a first annular member positioned on the outer circumferential surface of the first conductive member; a cylindrical second conductive member positioned on the outer periphery of the first insulating member; and an insulating layer positioned at a portion where the first insulating member and the first conductive member face each other, wherein the first insulating member includes a first annular insulating portion and a second annular insulating portion having an outer diameter larger than that of the first annular insulating portion, the first annular insulating portion is positioned at least on one side of the second annular insulating portion in the axial direction, the first annular member is joined to an end face of the first annular insulating portion, and the second conductive member is joined to the outer circumferential surface of the second annular insulating portion, and the insulating layer includes a first insulating layer positioned at a portion where the first annular insulating portion and the first conductive member face each other, and a second insulating layer positioned at a portion where the second annular insulating portion and the first conductive member face each other, A hermetic terminal, wherein a radial thickness of the first insulating layer is smaller than a radial thickness of the second insulating layer.

2. The hermetic terminal according to claim 1, wherein the first insulating layer and the second insulating layer are vacuum, gas, or resin.

3. An airtight terminal as described in claim 1 or 2, wherein the second conductive member includes a first cylindrical portion and a second cylindrical portion, the inner diameter of the first cylindrical portion is larger than the inner diameter of the second cylindrical portion, and the first cylindrical portion is joined to the outer peripheral surface of the second annular insulating portion.

4. An airtight terminal as described in claim 3, wherein the second conductive member includes the first cylindrical portion, the second cylindrical portion, and a third cylindrical portion located between the first cylindrical portion and the second cylindrical portion, and the inner diameter of the third cylindrical portion is smaller than the inner diameter of the first cylindrical portion, and the inner diameter of the second cylindrical portion is smaller than the inner diameter of the third cylindrical portion.

5. The airtight terminal according to claim 3 or 4, wherein the second conductive member has a fourth cylindrical portion, and the fourth cylindrical portion is located at a position where the first insulating member is not located.

6. Inner diameter D of the fourth cylindrical portion ４１ and an outer diameter D of the first conductive member facing the fourth cylindrical portion. ４ Relative to D ４ / D ４１ is the inner diameter D of the second cylindrical portion ２１ and an outer diameter D of the first conductive member facing the second cylindrical portion. ２ Relative to D ２ / D ２１ 6. The hermetic terminal of claim 5, wherein the hermetic terminal is equal to 7. A hermetic terminal as described in any one of claims 1 to 6, comprising: an annular second insulating member having a through hole on the outer peripheral surface of the second conductive member through which at least a portion of the second conductive member is positioned; and a third conductive member positioned on the outer periphery of the second insulating member.

8. An airtight terminal as described in claim 7, wherein the second insulating member is bonded to the outer peripheral surface of the second conductive member and the inner peripheral surface of the third conductive member, respectively, and the bonding position between the outer peripheral surface of the first insulating member and the inner peripheral surface of the second conductive member does not overlap in the axial direction with the bonding position between the second conductive member and the second insulating member.

9. An airtight terminal as described in claim 7 or 8, wherein a second annular member is positioned on the outer peripheral surface of the second conductive member, the outer peripheral surface of the first insulating member and the inner peripheral surface of the second conductive member are joined, and the second annular member and the end face of the second insulating member are joined.

10. The airtight terminal according to claim 8 or 9, wherein the first insulating member and the second insulating member are positioned so as to overlap each other at least partially in the radial direction.

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