A gemstone cold chain heat conduction structure and implementation method for an infrared detector dewar

Abstract

The present invention discloses a gemstone cold chain heat conduction structure and implementation method for an infrared detector dewar, including a cold platform, a cold cap, a gemstone rod, and an elastic cold chain transition block. The cold cap, the gemstone rod, and the elastic cold chain transition block are supported and clamped by a special brazing fixture, and then a gemstone cold chain is formed by vacuum brazing. The gemstone cold chain is connected to the cold platform by a threaded connection. In this structure, the cold platform is made of invar or molybdenum, the cold cap is made of kovar, and the elastic cold chain transition block is made of kovar, oxygen-free copper, or molybdenum. The gemstone cold chain described in the present invention can effectively reduce the transmission thermal resistance between the refrigerator and the cold platform and improve the heat transfer efficiency between the refrigerator and the cold platform. The structure of the present invention is simple, easy to operate, has good interchangeability, and has a high utilization rate of the refrigerator cooling capacity.

Description

Technical Field

[0001] The present invention discloses a gem cold chain heat conduction structure and an implementation method for an infrared detector dewar, belonging to the low-temperature packaging technology of infrared detectors, applicable to the heat transfer channels of fully low-temperature dewar components in cold boxes for cold optics, and can also be applicable to heat transfer parts of infrared detector packaging components for other purposes. Background Art

[0002] The dewar of the infrared detector assembly, as the main packaging form of infrared detectors, has wide applications in the fields of space astronomy, earth observation, resource environment, etc. At present, due to the expansion of the wavelength of infrared detectors and the improvement of detection sensitivity, there are more stringent requirements for the operating temperature of infrared detectors. Mechanical refrigeration is still the main refrigeration method for infrared detectors under low-temperature and cryogenic working conditions.

[0003] With the development of space infrared detection technology, the demand for high-resolution and high-sensitivity detection systems is becoming increasingly urgent. When the performance of infrared devices reaches the detection background limit, the background radiation mainly comes from the optical system of the instrument itself and its support structure, etc. The adverse effects it brings mainly include two aspects: First, the stray radiation generated by the optical and mechanical components of the optical system will reduce the signal-to-noise ratio and contrast of the system, especially in the space environment where the target signal is very weak, and the impact is more obvious. Second, for a wide-field high-sensitivity infrared optical system, due to the large field of view of the instrument and a very small F number, some cold optical lenses must be encapsulated near the detector position, otherwise the entire opto-mechanical system will be very large and complex. If we want to further improve the detection ability of the infrared system, using cryogenic refrigeration technology to cool the infrared optical components and reduce the background photon flux of the detection system and its background thermal noise is one of the most effective measures to improve the detection sensitivity. Thus, the packaging structure form of the detector cold box or Dewar of cold optics has emerged. For example, the Advanced Vertical Sounder ABS (later renamed HES - Hyperspectral Environmental Sounder) of the US GEOS-R satellite. It has short-wave, mid-wave, and long-wave infrared detectors inside. The specification is 48×22 detector elements, and the size of the detector photosensitive element is 58μm. Their cut-off wavelengths are 4.7μm, 8.5μm, and 15.1μm respectively. The working temperature of the detectors is all 65K, and its packaging form is a cold box design that uses a cold chain method for cold quantity transmission to achieve the packaging of short-wave, mid-wave, and long-wave detectors. The working temperature of the cold box and cold optics is 200K. The domestic "Fengyun-4" Interferometric Atmospheric Vertical Sounder (GIIRS) has achieved infrared Fourier transform spectroscopy measurement in the 4.44μm - 14.6μm band, with a spectral resolution of 0.625cm-1, an instantaneous field of view of 7.9°, and the entire field of view (FOV) of the detector is 108°×108°. In addition to the mid- and long-wave detectors, its Dewar assembly also encapsulates 4 lenses, with a temperature below 90K, and there are 2 lenses, 1 reflector, and 1 semi-transparent and semi-reflective mirror installed in the subsequent optical path inside the instrument. The 4 optical mirrors work at 200K. Whether it is a cold box or a Dewar, it involves the cold chain transmission problem between the refrigerator and the detector. Currently, the cold chain generally uses a flexible cold chain plus a rigid support cold chain connection method for connection, which can not only ensure efficient heat transfer but also overcome the stress caused by the shrinkage at low temperature. The flexible cold chain highlights the flexible characteristics at low temperature, while the rigid cold chain requires the highest possible thermal conductivity to achieve the purpose of reducing the heat transfer temperature difference. Summary of the Invention

[0004] The object of the present invention is to provide a gemstone cold chain heat conduction structure and an implementation method for an infrared detector dewar, to solve the problem of efficient heat transfer at low temperatures at the cold end of the flexible cold chain of the infrared detector and the refrigerator. Through the gemstone cold chain provided by the present invention, the dewar assembly is directly coupled and installed in the cold box, greatly simplifying the design and operation process. At the same time, the coupling force between the gemstone cold chain and the cold platform is controlled by torsion, improving the reliability of the detector at low temperatures.

[0005] A gemstone cold chain heat conduction structure for an infrared detector dewar of the present invention includes a cold platform 100, a cold cap 201, a gemstone rod 202, and an elastic cold chain transition block 203.

[0006] The gemstone cold chain 200 is connected to the cold platform 100 by a thread.

[0007] The material of the cold platform 100 is invar or molybdenum, and threaded holes are machined on the cold platform 100.

[0008] The material of the cold cap 201 is kovar. The center of the cold cap 201 is a through hole, and a solder reserve groove for brazing the cold cap 201 and the gemstone rod 202 is machined at one end. The connecting thread for cooperating with the cold platform is machined after brazing.

[0009] The material of the gemstone rod 202 is sapphire. All surfaces of the gemstone rod 202 are polished. Both ends of the gemstone rod 202 are metallized according to the assembly height of the cold cap 201 and the elastic cold chain transition block 203. After metallization, nickel is electroplated, and the nickel plating thickness is 4 - 5μm. The total thickness of the metallized layer is less than 0.15mm. The metallized layer and the plating layer need to meet the brazing requirements at 850°C.

[0010] The material of the elastic cold chain transition block 203 is kovar, oxygen-free copper or molybdenum. The center of the elastic cold chain transition block 203 is a counterbore, and a solder reserve groove for brazing with the gemstone rod 202 is also machined. And the elastic cold chain transition block 203 reserves a margin for fine machining in terms of thickness and bottom area.

[0011] An implementation method for a gemstone cold chain heat conduction structure for an infrared detector dewar, the process method is as follows:

[0012] 1) Uniformly metallize and nickel-plate the gemstone rod 202;

[0013] 2) Fine-machine the apertures of the cold cap 201 and the elastic cold chain transition block 203 that cooperate with the gemstone rod 202

[0014] 3) Perform pickling, ultrasonic cleaning with deionized water, etc. on the brazing surfaces of the cold platform 100, the cold cap 201, the gemstone rod 202, and the elastic cold chain transition block 203;

[0015] 4) Fill the space between the cold cap 201 and the gem bar 202, and between the elastic cold chain transition block 203 and the gem bar 202 with silver-copper brazing filler metal. Support and clamp them with a special brazing fixture 202, and complete the forming of the gem cold chain 200 through vacuum brazing;

[0016] 5) Perform liquid nitrogen impact on the gem cold chain 200 after vacuum brazing;

[0017] 6) Machine the threads on the cold cap 201 of the gem cold chain 200 and finely machine the elastic cold chain transition block 203;

[0018] 7) Perform multi-step ultrasonic cleaning on the finely machined gem cold chain 200 to remove the residual oil and grease from processing;

[0019] 8) Install the cleaned gem cold chain 200 in cooperation with the cold platform 100.

[0020] In the above step 4), the special brazing fixture 300 is used to ensure that the vacuum brazing between the cold cap 201 and the gem bar 202 and between the elastic cold chain transition block 203 and the gem bar 202 is carried out simultaneously, and to ensure that the end face where the brazed end of the gem bar 202 and the cold cap 201 is located is higher than the end face of the cold cap 201; the special brazing fixture 300 consists of two parts: the cold cap support 301 for precise positioning between the cold cap 201 and the gem cold chain 200 and the brazing support 302 that can be used to load the brazing filler metal; the cold cap support 301 is made of graphite material, and the brazing support 302 is made of stainless steel material. After the special brazing fixture 300 supports and clamps the workpiece and places it in the high-temperature furnace, when the vacuum degree is better than 5×10 -3 Pa, start brazing heating. To ensure that the brazed parts are heated evenly and sufficiently, a suitable heating and cooling curve needs to be set. The set heating and cooling program is: 20°C to 600°C, the heating rate is 20°C / min, hold for 10 min, 600°C to 800°C, the heating rate is 10°C / min, hold time is 5 min, 800°C to 810°C, the heating rate is 10°C / min, hold time is 10 min. After heating is completed, the cooling program is: 810°C to 500°C, the cooling rate is 10°C / min, 500°C to 300°C, the cooling rate is 20°C / min, and then the workpiece cools with the furnace.

[0021] In the above step 6), the threads machined on the cold cap 201 of the gem cold chain 200 need to be matched with the threads of the cold platform 100; the elastic cold chain transition block 203 is finely machined according to the required flatness, parallelism, and the required contact area of the bottom surface for use;

[0022] In step 8), when the gem cold chain 200 is installed in cooperation with the cold platform 100, indium sheets need to be added between the contact surfaces of the gem cold chain 200 and the cold platform 100 to improve the thermal coupling efficiency, and at the same time avoid the rigid contact between the gem cold chain 200 and the cold platform 100, which increases the additional stress on the detector.

[0023] The present invention has the following advantages:

[0024] (1) The gemstone cold chain has a simple structure, high integration, and good interchangeability;

[0025] (2) The gemstone rod has a high thermal conductivity at low temperatures, which can effectively reduce the temperature difference between the elastic cold chain transition block and the cold platform, thereby improving the cold quantity transmission efficiency of the refrigerator;

[0026] (3) The present invention solves the problem of efficient heat transfer at the cold end of the flexible cold chain of the infrared detector and the refrigerator.

[0027] (4) By controlling the coupling force between the gemstone cold chain and the cold platform through torsion, the reliability of the detector at low temperatures is improved. Description of the Drawings

[0028] Figure 1 It is a heat conduction structure of a gemstone cold chain for a Dewar of an infrared detector assembly.

[0029] Figure 2 It is a sectional view of the cold platform structure.

[0030] Figure 3 It is a sectional view of the cold cap structure.

[0031] Figure 4 It is a schematic diagram of the metalization of the gemstone rod.

[0032] Figure 5 It is a sectional view of the elastic cold chain transition block structure.

[0033] Figure 6 It is a sectional view of the cold cap support structure.

[0034] Figure 7 It is a sectional view of the brazing support structure. Detailed Description of the Invention

[0035] The following further details the specific implementation manners of the present invention in conjunction with the drawings and embodiments:

[0036] Embodiment 1

[0037] A heat conduction structure of a gemstone cold chain for a Dewar of an infrared detector assembly and its implementation method according to the present invention are as shown in the attached Figure 1 figures. The cold platform 100 is made of invar material, the cold cap 201 is made of kovar material, the material of the gemstone rod 202 is sapphire, and the elastic cold chain transition block 203 is made of molybdenum material.

[0038] The cold platform 100 is machined with an M12×0.75mm threaded hole, the threaded depth is 5mm, the relief groove is 0.5×0.75mm, the bottom hole of the thread is a flat bottom hole, and the depth of the bottom hole of the thread is 6mm (as shown in the attachedFigure 2 as shown); the inner diameter of the cold cap for processing is 10 mm, the outer diameter is 14 mm, the depth of the reserved groove for brazing filler metal is 1.5 mm, and the width is 0.3 mm (as shown in the appendix Figure 3 as shown); the diameter of the mating hole between the elastic cold chain transition block 203 and the gem bar 202 is 10 mm, the depth of the reserved groove for brazing filler metal is 1 mm, and the width is 0.4 mm (as shown in the appendix Figure 5 as shown);

[0039] Apply molybdenum-manganese paste metallization treatment to the part of the processed gem bar 202 (diameter 10 mm, height 44 mm) that is brazed in cooperation with the cold cap 201 and the elastic cold chain transition block 203. The required metallization thickness is 15 - 30 μm. Metallize both ends of the gem bar 202, and the metallization heights are 3 mm and 8 mm respectively (as shown in the appendix Figure 4 as shown), and then electroplate nickel on the gem bar 202 after molybdenum-manganese metallization, and the nickel layer thickness is 4 - 5 μm; precisely machine the hole diameters of the cold cap 201 and the elastic cold chain transition block 203 that cooperate with the gem bar 202 according to the metallization thickness of the gem bar 202 to ensure that the fit clearance is 0.03 - 0.05 mm; pickle and ultrasonically clean the gem bar 202, the cold platform 100, the cold cap 201 and the elastic cold chain transition block 203 with alcohol to remove the grease and debris remaining on the surface of the parts; install the gem bar 202, the cold cap 201 and the elastic cold chain transition block 203 with a special brazing fixture so that the mating surfaces of the gem bar 202 and the elastic cold chain transition block 203 are closely fitted, and use a special brazing fixture 300 for clamping so that the upper end surface of the cold cap 201 is 2 mm lower than the end surface of the gem bar 202. Add silver-copper brazing filler metal to the two reserved grooves for brazing filler metal of the cold cap 201 and the elastic cold chain transition block 203, and put it into a vacuum brazing furnace. When the vacuum degree is better than 5×10 -3Perform heating brazing on Pa. Set the heating and cooling program as follows: from 20°C to 600°C, the heating rate is 20°C / min, hold for 10 min; from 600°C to 800°C, the heating rate is 10°C / min, hold for 5 min; from 800°C to 810°C, the heating rate is 10°C / min, hold for 10 min. After heating is completed, the cooling program is: from 810°C to 500°C, the cooling rate is 10°C / min; from 500°C to 300°C, the cooling rate is 20°C / min, and then the workpiece is cooled with the furnace; after brazing is completed, immerse the integrated gemstone cold chain 200 completely into liquid nitrogen for about 5 minutes, take it out, keep it at room temperature for more than 5 minutes, repeat 5 times. When there are no cracks at the brazing joint of the gemstone cold chain 200 observed under a microscope, it is qualified; machine an external thread of M12×0.75 on the outer diameter of the cold cap 201 on the brazed integrated gemstone cold chain 200, and precisely machine the bottom surface of the elastic cold chain transition block 203 into a 25×25 mm square, chamfer the right-angle position with a fillet radius of 3 mm, then machine 4 M2 through screw holes on the bottom surface, the center distance between adjacent two screw holes is 19 mm, and the center connection line between adjacent two screw holes is parallel to the corresponding side of the 25×25 mm square (as shown in the attachment Figure 5 ); perform pickling and alcohol ultrasonic cleaning on the precisely machined gemstone cold chain 200 to remove the grease and debris remaining on the part surface during processing; according to the diameter of the gemstone rod 202, use a laser to cut indium sheets with a diameter of 10 mm and a thickness of 0.1 mm. Dip a lint-free cloth in an appropriate amount of alcohol and wipe the slag remaining on the edge of the indium sheet after laser cutting until the edge of the indium sheet restores the luster of the indium sheet body, then rinse it with alcohol and set it aside for use; wipe the contact surface between the gemstone cold chain 200 and the cold platform 100 with alcohol, attach the indium sheet to the contact surface of the gemstone cold chain 200, and then connect the gemstone cold chain 200 with the indium sheet and the cold platform 100 together by threading, and apply an appropriate amount of alcohol glue on the thread to prevent loosening.

[0040] Tests have shown that in a 77K liquid nitrogen test Dewar environment, in the case of the cold loss caused by the gemstone cold chain 200 itself, for the thermal conduction structure of the gemstone cold chain 200 and the cold platform 100 integrated with the elastic cold chain transition block 203 made of molybdenum material, the surface temperature of the cold platform 100 is about 79.3K (the temperature measuring diode passes a 0.1 mA bias current and the voltage is 1.02952V), and the bottom surface temperature of the elastic cold chain transition block 203 is about 78.9K (the temperature measuring diode passes a 0.1 mA bias current and the voltage is 1.03013V), and the temperature difference is about 0.4K. Heat the cold platform 100 by attaching a heating sheet. When the heating power is about 550 mW, the surface temperature of the cold platform 100 is about 80.7K (the temperature measuring diode passes a 0.1 mA bias current and the voltage is 1.02725V), and the bottom surface temperature of the elastic cold chain transition block 203 is about 79.2K (the temperature measuring diode passes a 0.1 mA bias current and the voltage is 1.02964V), and the temperature difference is about 1.5K.

[0041] Example 2

[0042] The same structure, assembly method, and component cleaning method as in Example 1 are adopted. The materials of the cold platform 100, cold cap 201, and gem bar 202 are the same as those in Example 1. The difference is that the elastic cold chain transition block 203 is integrally brazed and assembled using oxygen-free copper material.

[0043] Tests have shown that in a 77K liquid nitrogen test Dewar environment, in the case of cold loss caused by the cold chain itself, the thermal conduction structure of the gem cold chain 200 and the cold platform 100 integrated with the elastic cold chain transition block 203 made of oxygen-free copper material has a temperature of approximately 79.2K on the upper surface of the cold platform 100 (the temperature measuring diode passes a bias current of 0.1mA and the voltage is 1.02974V), and the temperature of the bottom surface of the elastic cold chain transition block 203 is approximately 78.9K (the temperature measuring diode passes a bias current of 0.1mA and the voltage is 1.03024V), with a temperature difference of approximately 0.3K. When a heating sheet is attached to the cold platform 100 for heating, when the heating power is approximately 550mW, the temperature of the upper surface of the cold platform 100 is approximately 80.3K (the temperature measuring diode passes a bias current of 0.1mA and the voltage is 1.02789V), and the temperature of the bottom surface of the elastic cold chain transition block 203 is approximately 79.1K (the temperature measuring diode passes a bias current of 0.1mA and the voltage is 1.02982V), with a temperature difference of approximately 1.2K.

[0044] Example 3

[0045] The same structure, assembly method, and component cleaning method as in Example 1 are adopted. The materials of the cold platform 100, cold cap 201, and gem bar 202 are the same as those in Example 1. The difference is that the elastic cold chain transition block 203 is integrally brazed and assembled using kovar material.

[0046] Tests have shown that in a 77K liquid nitrogen test Dewar environment, in the case of cold loss caused by the cold chain itself, the thermal conduction structure of the gem cold chain 200 and the cold platform 100 integrated with the elastic cold chain transition block 203 made of kovar material has a temperature of approximately 79.6K on the upper surface of the cold platform 100 (the temperature measuring diode passes a bias current of 0.1mA and the voltage is 1.02903V), and the temperature of the bottom surface of the elastic cold chain transition block 203 is approximately 78.8K (the temperature measuring diode passes a bias current of 0.1mA and the voltage is 1.03035V), with a temperature difference of approximately 0.8K. When a heating sheet is attached to the cold platform 100 for heating, when the heating power is approximately 550mW, the temperature of the upper surface of the cold platform 100 is approximately 93.5K (the temperature measuring diode passes a bias current of 0.1mA and the voltage is 1.00507V), and the temperature of the bottom surface of the elastic cold chain transition block 203 is approximately 79.5K (the temperature measuring diode passes a bias current of 0.1mA and the voltage is 1.02918V), with a temperature difference of approximately 4K.

Claims

1. A gemstone cold chain heat conduction structure for an infrared detector dewar, comprising a cold platform (100), a cold cap (201), a gemstone rod (202), and an elastic cold chain transition block (203). Characterized in that: The gemstone cold chain (200) is threadedly connected to the cold platform (100); The material of the cold platform (100) is invar or molybdenum, and threaded holes are machined on the cold platform (100); The material of the cold cap (201) is kovar, the center of the cold cap (201) is a through hole, and a solder reserve groove for brazing the cold cap (201) and the gemstone rod (202) is machined at one end, and the connecting thread for mating with the cold platform is machined after brazing; The material of the gemstone rod (202) is sapphire, all surfaces of the gemstone rod (202) are polished, and both ends of the gemstone rod (202) are metallized according to the assembly height of the cold cap (201) and the elastic cold chain transition block (203), and nickel is electroplated after metallization; The material of the elastic cold chain transition block (203) is kovar, oxygen-free copper or molybdenum; the center of the elastic cold chain transition block (203) is a counterbore, and a solder reserve groove for brazing with the gemstone rod (202) is also machined, and the elastic cold chain transition block (203) reserves a margin for fine machining in terms of thickness and bottom area.

2. A method for realizing the gemstone cold chain heat conduction structure for an infrared detector dewar according to claim 1, Characterized in that The method is as follows: 1) Uniformly metallize and nickel-plate the gemstone rod (202), and control the total thickness of the metal layer to be less than 0.15 mm; 2) Fine-machine the apertures of the cold cap (201) and the elastic cold chain transition block (203) that cooperate with the gemstone rod (202); 3) Pickle and ultrasonically clean the brazing surfaces of the cold platform (100), the cold cap (201), the gemstone rod (202), and the elastic cold chain transition block (203) with deionized water; 4) Fill silver-copper solder between the cold cap (201) and the gemstone rod (202) and between the elastic cold chain transition block (203) and the gemstone rod (202), support and clamp with a special brazing fixture (300), and complete the forming of the gemstone cold chain (200) through vacuum brazing; 5) Perform liquid nitrogen impact on the gemstone cold chain (200) after vacuum brazing; 6) Machine the threads of the cold cap (201) on the gemstone cold chain (200) and fine-machine the elastic cold chain transition block (203); 7) Perform multi-step ultrasonic cleaning on the fine-machined gemstone cold chain (200) to remove the residual oil and grease from processing; 8) Assemble and install the cleaned gemstone cold chain (200) in cooperation with the cold platform (100).

3. A method for realizing the gemstone cold chain heat conduction structure for an infrared detector assembly dewar according to claim 2, Characterized in that, In step 4), the special brazing fixture (300) is used to ensure simultaneous vacuum brazing between the cold cap (201) and the gem bar (202) and between the elastic cold chain transition block (203) and the gem bar (202), and to ensure that the end face of the brazed end of the gem bar (202) and the cold cap (201) is higher than the end face of the cold cap (201); the special brazing fixture (300) consists of two parts: the cold cap support (301) for precise positioning between the cold cap (201) and the gem cold chain (200) and the brazing support (302) that can be used to load the brazing filler metal; the cold cap support (301) is made of graphite material, the brazing support (302) is made of stainless steel material, and after the special brazing fixture (300) is supported and clamped, it is placed in a high-temperature furnace. When the vacuum degree is better than 5×10 -3 Pa, start brazing heating, set the temperature control program for brazing, and set the brazing flow point temperature to 810±5°C.

4. A method for realizing the gemstone cold chain heat conduction structure for an infrared detector assembly dewar according to claim 2, Characterized in that, In step 6), the threading of the cold cap (201) on the gemstone cold chain (200) needs to be thread-matched with the cold platform (100); the elastic cold chain transition block (203) is finely processed according to the flatness, parallelism required for use, and the required contact area of the bottom surface.

5. The implementation method of a gemstone cold chain heat conduction structure for an infrared detector assembly dewar according to claim 2, characterized in that, In step 8), when the gemstone cold chain (200) is installed in cooperation with the cold platform, indium sheets need to be added between the contact surfaces of the gemstone cold chain (200) and the cold platform (100) to improve the thermal coupling efficiency, and at the same time, the rigid contact between the gemstone cold chain (200) and the cold platform (100) is avoided to increase the additional stress on the detector.

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