Integrated low-loss sealing and heat-insulating transmission line

Abstract

The invention relates to the technical field of weak signal detection, and provides an integrated low-loss sealed heat-insulating transmission line, which comprises a low-temperature microstrip printed board, and glass bead insulators, a microstrip heat-insulating printed board and an MMIC chip which are arranged in bilateral symmetry by taking the low-temperature microstrip printed board as a center and are sequentially connected, the device further comprises a cold source installation part, a low-temperature circuit base plate and a low-temperature assembly vacuum sealing cavity. The 77K low-temperature end of the micro-strip heat insulation printed board, the MMIC chip and the low-temperature micro-strip printed board are arranged on the low-temperature circuit base plate; the low-temperature circuit base plate is arranged on the cold source mounting part; and all the components are integrated and sealed in a vacuum cavity by the low-temperature assembly vacuum sealing cavity and the glass bead insulator. The contradiction between the high heat insulation efficiency and the low loss characteristic of the transmission line is solved by optimizing the heat conductivity, the heat transfer path, the conduction sectional area and the like of materials, and miniaturization and integration of the low-loss heat insulation transmission line are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of weak signal detection, in particular to an integrated low-loss sealed heat-insulated transmission line. BACKGROUND

[0002] The heat-insulated transmission line in a low-temperature receiving system (such as a system used in deep space measurement and control, radio astronomy, etc.) is a key component connecting a low-temperature refrigeration unit (such as a refrigerator or a liquid helium Dewar) and a low-temperature amplifier (such as a low-noise amplifier LNA) or a receiving front end. Its core task is to efficiently transmit microwave signals while maximally inhibiting heat conduction and heat radiation from the high-temperature end (about 300K) to the low-temperature end (possibly as low as 77K or even lower), thereby maintaining the extremely low operating temperature of the low-temperature components and ensuring the high sensitivity and low noise performance of the system.

[0003] Currently, there are three main implementation paths for the heat-insulated transmission line of a low-temperature receiving system: one is to use a coaxial sealed connector and a low-temperature heat-insulated cable, and the typical categories of the low-temperature heat-insulated cable include small-diameter cables with stainless steel and nickel-copper outer conductors; for example, the Chinese utility model patent No. CN203521570U “Heat-insulated transmission line for coaxial N-type radio frequency calorimeter” discloses a heat-insulated transmission line including an inner conductor and an outer conductor, and the inner conductor is arranged inside the outer conductor, and the materials of the inner and outer conductors are both stainless steel. The second is to use a sealed waveguide and a heat-insulated waveguide assembly, and the heat-insulated waveguide assembly is mostly thin-walled stainless steel structure. The third is to use a waveguide-coaxial low-temperature probe structure, which realizes low loss and heat insulation through outer conductor heat insulation and inner conductor refrigeration. The above three methods all use long conduction heat leakage paths to achieve heat insulation, so the outer dimensions are large (the typical lengths of the cable, waveguide and probe are all more than 80mm), and they cannot be applied in high-density space, small-sized vacuum refrigeration systems; at the same time, the above three heat insulation methods exist in the form of independent assemblies, and cannot be integrated with low-temperature devices. SUMMARY

[0004] The technical problem to be solved by the present application is how to make up for the shortcomings of the prior art, and to provide a small-sized, low-loss, sealed, heat-insulated transmission line integrated with low-temperature components.

[0005] The present application solves the above technical problems by the following technical means:

[0006] The application provides an integrated low-loss sealed heat-insulated transmission line, which comprises a low-temperature microstrip printed board, a glass bead insulator arranged symmetrically left and right around the low-temperature microstrip printed board, a microstrip heat-insulated printed board and an MMIC chip connected in sequence, a cold source mounting part, a low-temperature circuit pad and a low-temperature component vacuum sealed cavity, the 77K low-temperature end of the microstrip heat-insulated printed board, the MMIC chip and the low-temperature microstrip printed board are arranged on the low-temperature circuit pad, the low-temperature circuit pad is arranged on the cold source mounting part, and the low-temperature component vacuum sealed cavity and the glass bead insulator seal all the components in the vacuum cavity.

[0007] Preferably, the glass bead insulator is welded to the low-temperature component vacuum sealed cavity by a vacuum brazing process, so as to realize the airtight internal and external connection of the transmission line, and the airtightness is better than 1x10 -10 Pa·m3 / s.

[0008] Further, the glass bead insulator is respectively provided with a transmission line input port and a transmission line output port, which are used for adapting a radio frequency connector.

[0009] Preferably, the transmission line input and output ports adopt a plug-in interface design and adapt to multiple types of plug-in coaxial radio frequency connector sockets.

[0010] Preferably, the 300K temperature zone end face of the back face of the microstrip heat-insulated printed board and the 77K temperature zone end face of the back face are respectively bonded to the printed board welding end face of the low-temperature component vacuum sealed cavity and the upper surface of the low-temperature circuit pad by conductive silver paste, the printed board welding end face of the low-temperature component vacuum sealed cavity and the upper surface of the low-temperature circuit pad are on the same horizontal plane, and the height difference is within ±0.05mm.

[0011] Preferably, the microstrip heat-insulated printed board is composed of a front circuit layer, a microstrip heat-insulated printed board dielectric substrate and a back circuit layer, electric signals are low-loss transmitted from the signal transmission port of the front circuit layer to a signal transmission strip line with a width of 0.25mm and a thickness of a copper layer plated with gold within 5μm, the back circuit layer is a defective ground circuit which is composed of a microstrip heat-insulated printed board defective ground structure DGS-metal ground layer strip line, a microstrip heat-insulated printed board defective ground structure DGS-blank defect pattern and the remaining ground metal layer to form a complete defective ground transmission circuit structure, wherein the ground layers are all copper layers plated with gold within 5μm, the line width of the microstrip heat-insulated printed board defective ground structure DGS-metal ground layer strip line is 1.5 times more than the transmission microstrip line width of the front circuit layer, the line length is more than 12mm, and the line length is located directly below the line width.

[0012] Preferably, the microstrip heat-insulated printed board dielectric substrate adopts 0.1mm thick polyimide material, the substrate width is 3mm, and the total length is within 20mm.

[0013] Preferably, the low-temperature microstrip printed board is welded on the low-temperature circuit pad plate by low-temperature solder; the MMIC chip is adhered to the low-temperature circuit pad plate by conductive silver adhesive; and the interconnection between the MMIC chip and the low-temperature microstrip printed board and the microstrip heat-insulating printed board is realized by gold wire bonding to achieve signal interconnection.

[0014] Preferably, the low-temperature assembly vacuum sealed cavity (5) is made of Kovar alloy 4J29 and is subjected to surface polishing treatment.

[0015] Preferably, the mounting contact surface between the low-temperature circuit pad plate and the cold source mounting part is tightly attached by 0.1 mm thick indium sheet or soft-glow gold material, and is fastened by screw pressure bonding.

[0016] The present application has the following advantages:

[0017] (1) The present application uses glass bead insulator and microstrip heat-insulating printed board as core functional elements of transmission line, and encapsulates and integrates main functional parts of MMIC chip, low-temperature microstrip printed board, low-temperature assembly vacuum sealed cavity, low-temperature circuit pad plate and other low-temperature assemblies, to realize integrated low-temperature integration of low-temperature assembly and low-loss heat-insulating transmission line and low-loss heat-insulating transmission from 300K to 77K. The contradiction between high heat-insulating efficiency and low-loss characteristic of transmission line is solved by optimizing material thermal conductivity, heat transfer path and conduction cross-sectional area, so that the low-temperature assembly can be integrated, low-loss heat-insulating transmission from 77K to 300K in small space size is realized, and the low-loss heat-insulating transmission line is miniaturized and integrated.

[0018] (2) The present application uses polyimide material as dielectric substrate material of microstrip heat-insulating printed board, which has the characteristics of small dielectric loss, low thermal conductivity and high material flexibility, and is used as substrate material of heat-insulating band line in 300K-77K temperature range, which can effectively reduce substrate heat leakage, and can better adapt to deformation stress generated by high temperature gradient at both ends of transmission line, two fixed end faces and cold source micro-vibration interconnection and conduction, to improve the reliability of heat-insulating transmission line.

[0019] (3) The present application uses glass insulator to realize airtight interconnection between the inside and outside of the transmission line, and the insulator probe interface can be adapted to multiple types of plug-in coaxial RF connector sockets, which are suitable for the working frequency band corresponding to the designed heat-insulating transmission line in the DC-18GHz range. At the same time, compared with the conventional coaxial sealed wall connector, the plug-in coaxial RF connector socket realizes external protection for the glass insulator, and the external interface can be directly replaced after damage, which improves the convenience of low-temperature assembly interface maintenance and reduces maintenance cost, and eliminates the technical risk of damaging the whole vacuum assembly for maintenance and replacement after the interface is damaged due to the overall welding sealing of the conventional coaxial sealed wall connector, and the increase of maintenance cost.

[0020] (4) The application adopts defect ground structure (DGS) design, extremely narrow transmission microstrip line design, plating thinning design and other means to optimize heat transfer path and conduction cross-sectional area, so that the heat insulation transmission line realizes low-loss heat insulation transmission efficiency of 300K-77K in a small space size range; compared with conventional means, the transmission line size is reduced by more than 70%, and the heat insulation efficiency is improved by more than 50% (the conventional means is a typical heat leakage of about 0.1-0.15W of a stainless steel heat insulation cable with a line diameter of 2.2mm and a length of 100mm; the typical thickness of the copper plating layer of the printed board is generally 18um), further improving the integration and miniaturization integration capability of the space cryogenic assembly. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 An integrated structure diagram of an integrated low-loss sealed heat insulation transmission line according to an embodiment of the application is shown in FIG. 1.

[0022] Figure 2 A front circuit structure diagram of a microstrip heat insulation printed board according to an embodiment of the application is shown in FIG. 2.

[0023] Figure 3 A back circuit structure diagram of a microstrip heat insulation printed board according to an embodiment of the application is shown in FIG. 3.

[0024] The drawings show: 1, a glass bead insulator; 2, a microstrip heat insulation printed board; 3, an MMIC chip; 4, a low-temperature microstrip printed board; 5, a low-temperature assembly vacuum sealed cavity; 6, a low-temperature circuit pad; 7, a cold source mounting part; 8, a microstrip heat insulation printed board dielectric substrate; 9, a microstrip heat insulation printed board defect ground structure DGS-metal ground layer strip line; 10, a microstrip heat insulation printed board defect ground structure DGS-blank defect pattern; J1, a transmission line input port; J2, a transmission line output port; J3, a front circuit layer signal transmission head port; J4, a front circuit layer signal transmission tail port; J5, a 300K temperature zone end face of the back of the microstrip heat insulation printed board; J6, a 77K temperature zone end face of the back of the microstrip heat insulation printed board. DETAILED DESCRIPTION

[0025] To make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described below in detail with reference to the embodiments of the application. Obviously, the described embodiments are some embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0026] Embodiment 1

[0027] This embodiment provides an integrated low-loss sealed heat insulation transmission line, and an integrated structure thereof is shown in FIG. 1. Figure 1As shown, it comprises a low-temperature microstrip printed board 4, a glass bead insulator 1, a microstrip heat-insulating printed board 2 and an MMIC chip 3 which are symmetrically arranged around the low-temperature microstrip printed board 4 and are connected in sequence, a cold source mounting part 7, a low-temperature circuit base plate 6 and a low-temperature component vacuum sealing cavity 5; the 77K low-temperature end of the microstrip heat-insulating printed board 2, the MMIC chip 3 and the low-temperature microstrip printed board 4 are arranged on the low-temperature circuit base plate 6; the low-temperature circuit base plate 6 is arranged on the cold source mounting part 7; and the low-temperature component vacuum sealing cavity 5 and the glass bead insulator 1 seal all the above components in the vacuum cavity. The MMIC chip 3 is a monolithic microwave integrated circuit, which is a prior art. The cold source mounting part 7 is provided with a conventional refrigeration means, such as a Stirling refrigerator or other prior art, which will not be described in detail in the present embodiment.

[0028] The glass bead insulator 1 is welded to the low-temperature component vacuum sealing cavity by a vacuum brazing process, so as to realize the airtight internal and external connection of the transmission line. The overall airtightness of the glass bead insulator 1 and the weld after welding is better than 1x10 -10 Pa·m3 / sHe.

[0029] The glass bead insulator 1 is provided with a transmission line input port J1 and a transmission line output port J2, respectively, for adapting a radio frequency connector. After the electric signal passes through the input port J1 of the integrated low-loss sealed heat-insulating transmission line of the present embodiment, the signal has completed low-loss heat-insulating transmission and signal amplification after passing through the microstrip heat-insulating printed board 2 and the MMIC chip 3, and the signal output by the output port J2 can be directly used as the signal input of the subsequent device, that is, the heat-insulating transmission line of the present embodiment is an integrated structure.

[0030] The transmission line input and output ports adopt a plug-in interface design, which is suitable for multiple types of plug-in coaxial radio frequency connector sockets. It is suitable for the working frequency band corresponding to the designed heat-insulating transmission line in the DC-18GHz range. At the same time, compared with the conventional coaxial sealed wall connector, the plug-in coaxial radio frequency connector socket realizes external protection of the glass insulator. After the external interface is damaged, it can be directly replaced, which improves the convenience of low-temperature component interface maintenance and reduces the maintenance cost, and eliminates the technical risk of damaging the interface after the overall welding sealing of the conventional coaxial sealed wall connector and the increase of maintenance cost caused thereby.

[0031] The 300K temperature zone end face J5 on the back of the microstrip heat-insulating printed board 2 and the 77K temperature zone end face J6 on the back are respectively bonded to the printed board welding end face of the low-temperature component vacuum sealing cavity 5 and the upper surface of the low-temperature circuit base plate 6 by conductive silver paste; the printed board welding end face of the low-temperature component vacuum sealing cavity 5 and the upper surface of the low-temperature circuit base plate 6 are on the same horizontal plane, and the height difference is within ±0.05mm.

[0032] AsFigure 2 and Figure 3 As shown in the figure, the microstrip heat insulation printed board 2 is composed of a front circuit layer, a microstrip heat insulation printed board medium substrate 8, and a back circuit layer; the electrical signal is transmitted from the front circuit layer signal transmission head port J3 to the front circuit layer signal transmission tail port J4 with low loss, the signal transmission band line width is 0.25 mm, and the thickness is within 5 μm with a gold-plated copper layer; the back circuit layer is a defective ground circuit, which is composed of a microstrip heat insulation printed board defective ground structure DGS-metal ground layer band line 9, a microstrip heat insulation printed board defective ground structure DGS-blank defect pattern 10, and the remaining ground metal layer to form a complete defective ground transmission circuit structure, wherein the ground layer is within 5 μm with a gold-plated copper layer; the line width of the microstrip heat insulation printed board defective ground structure DGS-metal ground layer band line 9 is 1.5 times or more of the transmission microstrip line width of the front circuit layer, and the line length is 12 mm or more and located directly below. By using the above defective ground design, extremely narrow transmission microstrip line design, and plating thinning design means to optimize the heat transfer path and conduction cross-sectional area, the low-loss heat insulation transmission in the temperature range of 300K-77K with small time and space size, and the transmission line uses a microstrip interface, which is convenient for the integration of low-temperature components.

[0033] The microstrip heat insulation printed board medium substrate 8 uses 0.1 mm thick polyimide material, the substrate width is 3 mm, and the total length is within 20 mm. The polyimide material has the characteristics of small dielectric loss, low thermal conductivity, and high material flexibility, and is used as the substrate material of the heat insulation band line in the temperature range of 300K-77K, which can effectively reduce the substrate heat leakage, and the material flexibility can better adapt to the deformation stress generated by the high temperature gradient at both ends of the transmission line, the two fixed end faces, and the micro-vibration interconnection of the cold source, and improve the reliability of the heat insulation transmission line.

[0034] The low-temperature microstrip printed board 4 is welded on the low-temperature circuit pad plate 6 by low-temperature solder; the MMIC chip 3 is adhered to the low-temperature circuit pad plate 6 by conductive silver glue; the interconnection between the MMIC chip 3, the low-temperature microstrip printed board 4, and the microstrip heat insulation printed board 2 is realized by gold wire bonding to realize signal interconnection.

[0035] The low-temperature component vacuum sealed cavity 5 uses Kovar alloy 4J29, the surface should be polished, the cavity surface should be kept clean and the welding position should be free of scratches before welding, and the probe of the glass bead insulator 1 should not be short-circuited after passing through the low-temperature component vacuum sealed cavity 5 welding hole. The thermal expansion curve of the Kovar alloy 4J29 is highly consistent with the specific glass or ceramic in a wide temperature range, which ensures that no cracks are generated after sealing, and in this embodiment, the use of the glass bead insulator 1 can improve the air tightness of the vacuum cavity.

[0036] The low-temperature circuit base plate 6 and the mounting contact surface between the cold source mounting part 7 are tightly attached by 0.1 mm thick indium or soft gold material, and are fastened by screw pressure connection.

[0037] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An integrated, low-loss, sealed, and heat-insulated transmission line, characterized in that, It includes a low-temperature microstrip printed circuit board (4) and glass bead insulators (1), microstrip thermal insulation printed circuit board (2) and MMIC chip (3) arranged symmetrically on the left and right sides of it and connected in sequence; it also includes a cold source mounting part (7), a low-temperature circuit pad (6) and a low-temperature component vacuum sealing cavity (5); the 77K low-temperature end of the microstrip thermal insulation printed circuit board (2), the MMIC chip (3) and the low-temperature microstrip printed circuit board (4) are set on the low-temperature circuit pad (6); the low-temperature circuit pad (6) is set on the cold source mounting part (7); the low-temperature component vacuum sealing cavity (5) and the glass bead insulators (1) integrate and seal all the above components in the vacuum cavity.

2. The integrated low-loss sealed and heat-insulated transmission line according to claim 1, characterized in that, The glass bead insulator (1) is welded to the vacuum-sealed cavity of the low-temperature component using a vacuum brazing process, achieving airtight interconnection of the transmission line inside and out, with an airtightness better than 1×10⁻⁶. -10 Pa·m3 / s (He).

3. The integrated low-loss sealed and heat-insulated transmission line according to claim 1, characterized in that, The glass bead insulator (1) is provided with a transmission line input port (J1) and a transmission line output port (J2) for use as an adapter for radio frequency connectors.

4. The integrated low-loss sealed and heat-insulated transmission line according to claim 3, characterized in that, The input and output ports of the transmission line adopt a pluggable interface design, which is compatible with various types of pluggable coaxial RF connector sockets.

5. The integrated low-loss sealed and heat-insulated transmission line according to claim 1, characterized in that, The 300K temperature zone end face (J5) and the 77K temperature zone end face (J6) on the back of the microstrip thermal insulation printed circuit board (2) are respectively bonded to the printed circuit board welding end face of the low-temperature component vacuum sealing cavity (5) and the upper surface of the low-temperature circuit pad (6) using conductive silver paste; the printed circuit board welding end face of the low-temperature component vacuum sealing cavity (5) and the upper surface of the low-temperature circuit pad (6) are on the same horizontal plane, with a height difference within ±0.05mm.

6. The integrated low-loss sealed and heat-insulated transmission line according to claim 1, characterized in that, The microstrip thermally insulated printed circuit board (2) consists of a front circuit layer, a microstrip thermally insulated printed circuit board dielectric substrate (8), and a back circuit layer. The electrical signal is transmitted from the front circuit layer signal transmission first port (J3) to the front circuit layer signal transmission tail port (J4) with low loss. The signal transmission line width is 0.25 mm and the thickness is less than 5 μm with copper plating and gold plating. The back circuit layer is a defect ground circuit, which consists of the microstrip thermally insulated printed circuit board defect ground structure DGS-metal ground layer strip (9), the microstrip thermally insulated printed circuit board defect ground structure DGS-blank defect pattern (10), and other ground metal layers to form a complete defect ground transmission circuit structure. The ground layers are all less than 5 μm with copper plating and gold plating. The line width of the microstrip thermally insulated printed circuit board defect ground structure DGS-metal ground layer strip (9) is more than 1.5 times the line width of the front circuit layer transmission microstrip, the line length is more than 12 mm, and it is located directly below it.

7. The integrated low-loss sealed and heat-insulated transmission line according to claim 6, characterized in that, The microstrip thermally insulated printed circuit board substrate (8) is made of 0.1mm thick polyimide material, with a substrate width of 3mm and a total length of no more than 20mm.

8. The integrated low-loss sealed and heat-insulated transmission line according to claim 1, characterized in that, The low-temperature microstrip printed circuit board (4) is soldered onto the low-temperature circuit pad (6) using low-temperature solder; the MMIC chip (3) is bonded to the low-temperature circuit pad (6) using conductive silver paste; the interconnection between the MMIC chip (3) and the low-temperature microstrip printed circuit board (4) and the microstrip thermal insulation printed circuit board (2) is achieved by gold wire bonding.

9. The integrated low-loss sealed and heat-insulated transmission line according to claim 1, characterized in that, The vacuum-sealed cavity (5) of the cryogenic component is made of Kovar 4J29 alloy and has been polished.

10. An integrated low-loss sealed and heat-insulated transmission line according to claim 1, characterized in that, The low-temperature circuit pad (6) and the cold source mounting part (7) are closely fitted with a 0.1mm thick indium sheet or soft gold material and are fastened by screws.

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