Design method of deep hypothermia infrared focal plane flexible circuit for space navigation

Abstract

According to the design method of the deep hypothermia infrared focal plane flexible circuit for space navigation, the phosphor copper conducting medium is selected, the wiring mode is adjusted, heat exchange of the deep hypothermia imaging system flexible circuit with the large temperature difference can be effectively reduced, and the working environment of a refrigerating machine is improved. Based on material selection of phosphor copper, a traditional flexible circuit design mode is adopted, and heat exchange can be greatly reduced; a middle shielding ground layer is further optimized and removed, new wiring design is carried out on wiring, heat dissipation is further reduced by reducing the radiation area, and the system is optimized; on the basis, an outer shielding ground layer is changed into grid phosphor copper or directly removed, so that the heat exchange problem is greatly improved. According to the invention, wiring design is carried out on circuit signals of adjacent layers and the same layer, the influence of stray capacitance and signal coupling is reduced, the signal integrity is improved, and the space utilization efficiency is improved. According to the invention, a point-to-point design method is adopted, so that the reliability is enhanced.

Description

Technical Field

[0001] The invention relates to a design method of a deep low-temperature infrared focal plane flexible circuit for aerospace use, which is applied to an infrared optical low-temperature and low-noise video processing circuit. Background Art

[0002] Space infrared remote sensors have the characteristics of strong concealment, high resolution and not affected by bad weather, and they play an extremely important role in space applications. Lowering the temperature of the detector is conducive to improving the measurement accuracy of the system, obtaining a higher signal-to-noise ratio, and thus improving the imaging quality. In recent years, deep low-temperature infrared detectors have been commonly used in space infrared remote sensors.

[0003] Due to the performance limitations of devices, video processing circuits generally work independently at room temperature and are packaged separately from infrared detectors that operate at low temperatures. Mechanical refrigerators are usually used to cool space infrared remote sensing detectors to operating temperature, but a large amount of heat exchange will place a huge burden on the refrigerator. When the refrigerator cannot reach the temperature, the normal operation of the detector is affected and the imaging quality is reduced.

[0004] At present, the processing methods and ideas for the detector of deep low temperature infrared imaging system mainly include the following two: one method is to improve the working capacity of the refrigeration device. This method ensures the working temperature of the detector by increasing the cooling capacity of the refrigerator, improving the working temperature of the refrigerator, and improving the deep cold loop heat pipe. This method is accompanied by the increase of refrigerator power consumption, and lacks a fundamental treatment method for the heat dissipation of the flexible circuit. Another method is to design a highly integrated, deep low temperature monolithic analog front-end dedicated chip. Compared with the traditional analog front-end processing circuit, this chip works in the low temperature zone and is directly connected to the detector readout circuit. The advantage of this method is that it shortens the signal transmission distance and reduces transmission interference and system noise. From the perspective of heat dissipation, this output method reduces the connection signal with the video processing circuit, thereby reducing heat exchange to a certain extent. However, this method increases the power consumption of the detector end, has relatively higher requirements for refrigerator temperature control, is more difficult to design, and is still in the exploratory stage because the integrated chip design is difficult to implement. The above two methods can meet the requirements of infrared detectors working at deep low temperatures, but the effect of reducing the heat exchange of flexible circuits is not obvious. Heat exchange is proportional to the thermal conductivity, area, and temperature difference between the two sides of the material. When the detector operating temperature is low and the temperature difference with the video processing circuit is large, the heat transfer on the connection circuit cannot be ignored. Therefore, it is considered to design a low thermal conductivity aerospace infrared transfer flexible circuit that can be applied to deep low temperature detectors. The key point of this design is to reduce heat exchange while ensuring the transmission quality of the signal, reduce the influence of signal coupling, and thus improve the image quality. Summary of the invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, while reducing heat exchange, ensure the transmission quality of the signal, reduce the influence of post-signal coupling, and thus improve the image quality.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A design method for a deep low temperature infrared focal plane flexible circuit for aerospace, the flexible circuit mainly consists of a rigid area and a flexible area, and the design method includes:

[0008] The routing of the flexible circuit is made of phosphor copper material, with the composition content of 2% to 8% tin, 0.1% to 0.4% phosphorus, and the rest is copper;

[0009] The flexible area of ​​the flex circuit uses one of the following three stack-up structures:

[0010] Method 1: ground plane layer 1 - signal layer 1 - ground plane layer 2 - ground plane layer 3 - signal layer 2 - ground plane layer 4;

[0011] Method 2: ground plane layer 1 - signal layer 1 - signal layer 2 - ground plane layer 2;

[0012] Method 3: Signal layer 1-signal layer 2;

[0013] The surface layers of each place are paved with complete phosphor copper or grid phosphor copper;

[0014] Device layout is performed in the rigid area, and the layout follows the following principles:

[0015] The detector needs an external decoupling capacitor signal, and the corresponding decoupling capacitor is arranged next to the corresponding signal in the rigid area of ​​the flexible circuit connected to the detector; the temperature measurement signal lead is inserted into the binding hole and fixed with glue, and the distance between the binding hole and the lead-out interface is greater than the preset distance;

[0016] (1) The adjacent signal layers are designed for wiring as follows: For non-identical signals in stacking structure mode 2 and mode 3, the parallel transmission paths in adjacent layers do not overlap; reduce the overlap of transmission paths, and when the intersection of adjacent layer signals is unavoidable, reduce the intersection area and set the spatial angle between the two signal transmission lines to 45°~90°; for the same signal, the adjacent layer routing overlaps. In mode 1, the two signal layers in the flexible area are not adjacent, and there is no need to specially consider the above adjacent layer wiring method. (2) The same layer wiring follows the following principles: For the three stacking structures, in the rigid area of ​​the flexible circuit, the distance between the conductor and the edge is greater than the thickness of the printed circuit board; the ground signal is set as an edge protection copper wire on both sides of the flexible area of ​​the flexible circuit; the temperature measurement signal in the flexible area is arranged on the inner side close to the edge protection copper wire; the analog signal and digital signal of the entire flexible circuit are divided and arranged without crossing, and the width of each signal line is set according to the current carrying capacity requirements and derating requirements; for the wiring method without a ground plane layer in mode 3, the signal layer in the flexible area is arranged with a ground wire as a return line.

[0017] A deep low temperature infrared focal plane flexible circuit for aerospace use mainly consists of a rigid area and a flexible area, and adopts the above-mentioned design method to determine the stacking structure, device layout and wiring method.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention selects a new conductive medium through property comparison, improves the wiring method, can effectively reduce the heat exchange of the flexible circuit of the deep low temperature imaging system with large temperature difference, and improves the working environment of the refrigerator.

[0020] (2) Based on the selection of phosphor copper, the traditional flexible circuit design method can greatly reduce heat exchange. Further optimization can be carried out by removing the middle shielding layer and making a new wiring design for the routing. By reducing the radiation area, the heat dissipation can be further reduced and the system can be optimized. On this basis, the outer shielding layer can be changed to grid phosphor copper or directly removed, which will greatly improve the heat exchange problem.

[0021] (3) The present invention performs wiring design for circuit signals in adjacent layers and the same layer, thereby reducing the influence of parasitic capacitance and signal coupling, improving signal integrity, and enhancing space utilization efficiency.

[0022] (4) The present invention adopts a point-to-point design method to enhance reliability.

[0023] (5) The solution of the present invention has low heat exchange, simple method, small coupling between signals, and wide application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the structural block diagram of the deep low temperature infrared imaging system;

[0025] Figure 2 This is a schematic diagram of a typical infrared focal plane flexible circuit structure;

[0026] Figure 3 It is a schematic diagram for explaining the point numbers of the point-to-point design scheme of the present invention;

[0027] Figure 4 This is a schematic diagram of the signal routing that overlaps in space between adjacent layers;

[0028] Figure 5 It is a cross-sectional view of the adjacent layer intercalation type wiring of the present invention. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] Infrared detectors in low-temperature working environments have higher sensitivity, but at present, the performance of most components and signal processing circuits decreases when working in low temperatures. In traditional infrared imaging systems, infrared detectors and video processing circuits are packaged separately. The infrared detector in deep low temperature is connected to the infrared video processing system at room temperature through an infrared focal plane flexible circuit.

[0031] For a long time, aerospace products have mostly used copper as a conductive material. However, copper has good thermal conductivity, which makes the material have certain limitations in the use of flexible circuits in deep cryogenic systems, especially when there is a large temperature difference.

[0032] The present invention proposes a design method for a deep-cryogenic infrared focal plane flexible circuit for aerospace use. The design uses new materials to greatly reduce the heat transfer radiation on the switching circuit and relieve the pressure on the refrigerator. At the same time, it takes into account the analog and digital cross-influence and signal coupling issues, and carries out a layout design for the signal of the switching circuit, which effectively improves the integrity of the signal and enhances the space utilization efficiency.

[0033] like Figure 1 The figure shows the block diagram of the deep low temperature infrared imaging system. The infrared detector works at 40K (deep low temperature environment) and is connected to the infrared video processing circuit with an operating temperature of 300K (normal temperature environment) through the focal plane flexible circuit. Through the focal plane flexible circuit, the infrared detector receives the signals required for the detector to work, mainly including: control timing signals, such as detector integration time control signal, master clock signal, gain control bit, format selection, output channel number selection bit, etc.; digital and analog power after power conversion; fixed bias voltage generated by the operational amplifier module, such as frequency modulation voltage, operational amplifier reference voltage, anti-blooming control, photovoltaic diode substrate, etc.; bias adjustable voltage generated by the DA module, such as photovoltaic diode bias, etc. At the same time, the infrared detector outputs multi-channel analog signals, digital output discrimination signals, temperature measurement signals, etc. through the focal plane flexible circuit. The multi-channel input and output signals transmitted through the focal plane flexible circuit will cause a large amount of heat exchange when using traditional copper material design, so it is necessary to select a better way to design the flexible circuit.

[0034] Based on the good conductivity of copper, copper is often used as a signal transmission material at this stage, and is pressed together with covering films, reinforcement materials, insulating materials, etc. to form a focal plane flexible circuit. Figure 2 The following is a schematic diagram of a typical infrared focal plane flexible circuit structure. A typical flexible circuit consists of two parts: a rigid area and a flexible area, both of which can contain more than one area. The rigid area is divided into two parts, namely Figure 2The middle rigid area 1, in which the connector 1 is electrically installed, the signal in the flexible circuit is connected to the detector signal through the connector on this side, and the rigid area 2, in which the connector 2 is electrically installed, and the signal is connected to the video processing circuit signal through the connector on this side. The two rigid areas realize the signal conduction between the detector and the video processing circuit through the flexible area. A small number of components can be arranged in the two rigid areas. When designing a rigid-flexible circuit board, a multi-layer printed circuit board stacking method is required. The rigid area usually uses a stacking structure of 16 layers, 14 layers, 12 layers, 10 layers, etc. It is recommended to use the center 2, 4, and 6 layers of the circuit board as the flexible layer for the flexible area stacking.

[0035] Considering the number of signals and the structure of the flexible circuit, in order to avoid the influence of coupling between signals, traditional flexible circuits usually adopt the stacking structure design of "ground plane layer 1 - signal layer 1 - ground plane layer 2 - ground plane layer 3 - signal layer 2 - ground plane layer 4" in the flexible area. This method can form an effective shield between signal layers, has strong anti-interference ability, and has few routing constraints between adjacent layers, meeting the requirements of use at room temperature. However, in the flexible circuit of the deep cryogenic system, the large area of ​​copper plating greatly increases the heat dissipation, and the disadvantages of this traditional design scheme are very prominent.

[0036] The present invention uses phosphor copper material, the basic components of which are: 2% to 8% tin, 0.1% to 0.4% phosphorus, and the rest is copper. The material has good ductility and fatigue resistance, and its reliability is higher than that of general copper alloy products. At the same time, phosphor copper has good electrical conductivity, lower thermal conductivity than copper, less heat dissipation, and higher corrosion resistance, fatigue resistance, and better wear resistance, and is a better alternative material.

[0037] Table 1 below compares the thermal conductivity of copper and phosphor copper in a certain ratio. Heat transfer is proportional to the thermal conductivity of the material and the temperature difference on both sides. This is why the influence of heat transfer cannot be ignored when the temperature difference between the infrared detector and the infrared video processing system is large. Taking the ambient temperature of 80K as an example, it can be seen from Table 1 that when the heat dissipation temperature difference is the same, the heat transfer of copper is 24 times that of phosphor copper, and at 20K, the ratio reaches 110 times. As the ambient temperature decreases, this gap will continue to increase.

[0038] Table 1 Thermal conductivity of copper and phosphor copper

[0039]

[0040] Table 2 shows the resistance comparison of copper and phosphor copper at room temperature and low temperature. The length of flexible circuit is generally about 0.1m-0.3m. The increase of transmission line impedance mainly affects the signal with large current on the line. For example, the voltage drop of analog power signal line changes greatly with the increase of impedance. In view of such influence, this design adopts the method of parallel impedance reduction, which will be introduced in the adjacent layer wiring design later.

[0041] Table 2 Conductivity of copper and phosphor copper

[0042]

[0043] Materials with similarly low thermal conductivity, such as nickel-chromium and manganese-copper alloys, have thermal conductivity slightly lower than that of phosphor copper, but at the same order of magnitude, their resistivity at low temperatures is 5-10 times that of phosphor copper with the same diameter. In comprehensive comparison, phosphor copper has better performance. In summary, phosphor copper is selected as the conductive material for flexible circuits. On the basis of meeting the requirements of signal transmission, it can significantly reduce heat transfer, and is a better material choice in flexible circuits in deep cryogenic systems.

[0044] For infrared imaging systems working in deep low temperature environments, only the conductive medium in the flexible circuit is improved, phosphor copper is selected as a new material for the switching circuit, and the traditional "ground plane layer 1 - signal layer 1 - ground plane layer 2 - ground plane layer 3 - signal layer 2 - ground plane layer 4" stacking structure and layout routing method is adopted, the heat transfer on the flexible circuit can be reduced to a few tenths.

[0045] In view of the large amount of heat dissipation problems caused by the large-area copper plating of flexible circuits in traditional design methods, the present invention also provides two flexible area laminated structure solutions to reduce the impact caused by it.

[0046] The first solution (method 2) is to remove the two middle ground plane layers and only retain the ground plane layer outside the flexible area, that is, the stacked structure is "ground plane layer 1-signal layer 1-signal layer 2-ground plane layer 2", and avoid the influence of signal crosstalk through the routing design of the two signal adjacent layers and the same layer. In this solution, the two ground plane layers can be directly paved with complete phosphor copper, or grid phosphor copper can be laid. Directly laying complete phosphor copper can minimize the interference effect of external signals of the flexible circuit on the signals in the switching circuit. This method combines the advantages of traditional design methods. A diamond grid is used when laying the grid phosphor copper. This solution can further reduce heat dissipation and shield most interference signals at the same time.

[0047] The second solution (method three) is to remove the four layers of ground plane in the middle and on both sides, and only keep the two signal layers in the flexible area, that is, the stacking structure is "signal layer 1-signal layer 2". When the peripheral signal interference is small, or the interference to the flexible circuit is reduced by technical means such as shielding layer, this technical solution is the best, which can minimize the heat dissipation area and reduce heat dissipation. Reducing the number of layers in the flexible area also makes it softer, with a smaller bending radius, and easier to install on non-planar surfaces.

[0048] The components of the flexible circuit are laid out and designed in the rigid area. Common components include connectors, resistors, and capacitors. The layout design follows the following principles: (1) The distance between components and holes and the structural frame around the circuit board should be greater than 2mm; the minimum distance between the edges of mechanical mounting holes should be greater than the thickness of the printed circuit board; wiring in the middle layer is prohibited if the diameter of the component mounting hole is expanded beyond 2mm; wiring is prohibited if the diameter of the screw head or gasket on the top and bottom layers is expanded beyond 2mm. (2) The spacing between the non-metallic bodies of components should be no less than 0.13mm, and the spacing between metal shells should be no less than 1.6mm. (3) For signals that require external decoupling capacitors, such as op amp reference voltage, since their proximity can achieve better results, they are placed in the circuit layout stage according to the flexible circuit structure. Figure 2 Medium rigidity zone 1, close to the corresponding signal position. (4) For the temperature measurement signal, a C55 wire is used to directly lead out from the transfer circuit to the refrigeration control machine. In order to improve the vibration resistance of the lead-out signal line, in addition to the conventional glue-sealing measures, a non-metallic binding hole is set at the interface lead-out position. Considering the requirements of the wire bending radius, the binding hole is greater than 5mm away from the lead-out interface. In actual use, the welded lead wire is inserted into the binding hole and fixed with glue, which can offset the force of the welding point and improve the reliability of the temperature measurement system.

[0049] In the signal transmission of the entire flexible circuit, the present invention adopts a point-to-point connection method, that is, a signal on the connector on the detector side of the flexible circuit is directly connected to a signal on the connector on the corresponding video processing circuit side. Figure 3 For example, the MC signal of the detector side connector CN1 pin 3 is directly connected to the MC signal of the infrared video processor side connector CN2 pin 1; the VDDO signal of CN1 pin 10 is connected to the VDDO signal of CN2 pin 31; the VDDO signal of CN1 pin 15 is connected to the VDDO signal of CN2 pin 35. When a signal has multiple lead-out points, they are connected separately by routing to enhance reliability.

[0050] The design requirements for single-layer wiring of the signal layer are as follows: (1) Copper foil can be laid in the rigid area. The top and bottom layers of the rigid area are within 2mm of the structure around the board edge, and the inner layer is set as a prohibited wiring area within 1.25mm from the board edge. (2) Edge protection copper wires are set in the flexible area to reduce the tearing of the flexible area caused by external stress. The width of the protection copper wire is not less than 40mil, parallel to the edge of the flexible area, and connected to the ground signal. At the same time, the 2mm range of the edge of the flexible area should be set as a prohibited wiring area. (3) In order to reduce the coupling effect of the temperature measurement signal on other working signals of the detector, in the flexible area, the temperature measurement signal is laid out at the adjacent position on the inside of the protection copper wire, and is kept 3 times the line width away from other inner signals. (4) The analog signals and digital signals of the entire flexible circuit are divided and wired without crossing. (5) In order to reduce crosstalk between lines of the same layer signal, the line spacing follows the "3W rule". If 98% of the electric fields do not interfere with each other, a spacing of 10W is used. (6) Set the width of each signal line according to the current carrying capacity requirements and derating requirements. The current of power signals, ground signals, and some bias signals is relatively large. In order to reduce the impedance voltage drop on the line, the signal line width is increased on the basis that the spatial distribution of the flexible area meets the requirements during wiring. (7) For the stacked structure without a ground plane layer in Scheme 2 (Method 3), in order to ensure the return flow capacity of the signal, the ground wire of each layer should be laid nearby as the return line. Considering the number of signals, the structure of the flexible area, and the signal characteristics, a ground wire is laid as the return line for every 2 to 3 signals.

[0051] When making flexible circuits, multiple layers of signals are laminated. Figure 4 This kind of wiring method with vertical overlap in space has a small signal spacing after the two layers are pressed together. The magnetic field coupling between the signals at the same position in adjacent layers cannot be ignored, which will affect the integrity of the signal. The spatial layout of adjacent signal layers is designed: (1) The parallel transmission paths of non-identical signals in adjacent layers do not overlap (this overlap includes complete overlap and partial parallel overlap). According to the wiring requirements of the "3W rule" mentioned above, there is a 2W spacing between signal lines for laying signal lines in adjacent layers, that is, non-identical signals in adjacent layers follow the "photographic" insertion method, such as Figure 5 As shown, the electromagnetic field interference caused by the overlap of signals in adjacent layers is reduced, especially high-speed signals should follow this wiring method. (2) When routing adjacent layers of non-identical signals, the crossing of transmission paths should be reduced. When the crossing of adjacent layer signals is unavoidable, the spatial angle between the two signal transmission lines is set to 45°~90° to reduce the crossing area, thereby reducing the coupling effect. (3) The routing of adjacent layers of the same signal overlaps. This method can effectively improve the space utilization rate. At the same time, it can reduce the line impedance by increasing the number of routing layers, thereby reducing the voltage drop between two points. It has a significant effect on the analog power supply and analog ground with larger current mentioned above. For example, the maximum current of a general analog power supply is between tens of milliamperes and one or two hundred milliamperes. After design optimization, the line impedance is about 10 -1The output voltage drop to the detector side is reduced by the order of Ω, which reduces the loss and ensures that the voltage working range is met. (4) When the width of the same signal line changes, the part with reduced line width is layered and overlapped in space. The distance between the connector pins welded on the rigid area is small, and the signal line with large current is large, which often makes it difficult to meet the direct connection requirements. Directly reducing the line width cannot meet the current carrying requirements and is not conducive to signal integrity. In response to this phenomenon, the design method of overlapping adjacent layer routing is also adopted. Vias are drilled in the rigid area, and the signal from the flexible area to the rigid area via hole is routed as a thick signal line according to the current carrying capacity requirements. From the via hole to the rigid area connector pin part, multi-layer routing is changed to meet the signal continuity. For example, the signal line with a line width of 30mil in the flexible area is divided into three 10mil signal lines of different layers after passing through the hole in the rigid area, and connected to the same signal pin of the connector through the spatial overlap position.

[0052] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

[0053] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A design method for a deep low temperature infrared focal plane flexible circuit for aerospace, wherein the flexible circuit is mainly composed of a rigid area and a flexible area, and is characterized in that: Design methods include: The routing of the flexible circuit is made of phosphor copper material, with the composition content of 2% to 8% tin, 0.1% to 0.4% phosphorus, and the rest is copper; The flexible area of ​​the flex circuit uses one of the following three stack-up structures: Method 1: ground plane layer 1 - signal layer 1 - ground plane layer 2 - ground plane layer 3 - signal layer 2 - ground plane layer 4; Method 2: ground plane layer 1 - signal layer 1 - signal layer 2 - ground plane layer 2; Method 3: Signal layer 1-signal layer 2; The surface layers of each place are paved with complete phosphor copper or grid phosphor copper; Device layout is performed in the rigid area, and the layout follows the following principles: The detector needs an external decoupling capacitor signal, and the corresponding decoupling capacitor is arranged next to the corresponding signal in the rigid area of ​​the flexible circuit connected to the detector; the temperature measurement signal lead is inserted into the binding hole and fixed with glue, and the distance between the binding hole and the lead-out interface is greater than the preset distance; (1) The adjacent signal layers are designed for wiring as follows: For non-identical signals in stacking structure mode 2 and mode 3, the parallel transmission paths in adjacent layers do not overlap; to reduce the overlap of transmission paths, when the intersection of adjacent layer signals is unavoidable, reduce the intersection area and set the spatial angle between the two signal transmission lines to 45°~90°; for the same signal, the adjacent layer routing overlaps; in mode 1, the two signal layers in the flexible area are not adjacent, and the above adjacent layer wiring method is not required; (2) The same layer wiring follows the following principles: for the three stacking structures, in the rigid area of ​​the flexible circuit, the distance between the conductor and the edge is greater than the thickness of the printed circuit board; the ground signal is set as an edge protection copper wire on both sides of the flexible area of ​​the flexible circuit; the temperature measurement signal in the flexible area is arranged on the inner side close to the edge protection copper wire; the analog signal and digital signal of the entire flexible circuit are divided into partitions and arranged without crossing, and the width of each signal line is set according to the current carrying capacity requirement and the derating requirement; for the wiring method without a ground plane layer in mode 3, the signal layer in the flexible area is arranged with a ground wire as a return line.

2. The method for designing a deep cryogenic infrared focal plane flexible circuit for aerospace use according to claim 1, characterized in that: When laying out devices in the rigid area, the following principles must be followed: The distance between components and holes and the structural frame around the circuit board is greater than 2mm; the prohibited wiring area in the middle layer of the component mounting hole is designed to expand 2mm outward from the hole diameter; the prohibited wiring area on the top and bottom layers expands 2mm outward on the diameter of the screw head or gasket; the minimum distance between the edges of the mechanical mounting holes is greater than the thickness of the printed circuit board; the spacing between the non-metallic bodies of components is not less than 0.13mm, and the spacing between metal shells is not less than 1.6mm.

3. The method for designing a deep cryogenic infrared focal plane flexible circuit for aerospace use according to claim 1, characterized in that: The top and bottom layers of the rigid area are set as the prohibited wiring area within 2mm from the surrounding structures of the board edge, and the inner layer is set as the prohibited wiring area within 1.25mm from the board edge.

4. The method for designing a deep cryogenic infrared focal plane flexible circuit for aerospace use according to claim 1, characterized in that: The same layer wiring also follows the following principles: the width of the protective copper wire is not less than 40 mils, it is parallel to the edge of the flexible area, and is connected to the ground signal.

5. The method for designing a deep cryogenic infrared focal plane flexible circuit for aerospace use according to claim 1, characterized in that: The same-layer wiring also follows the following principles: the 2mm range at the edge of the flexible area should be set as a prohibited wiring area.

6. The method for designing a deep cryogenic infrared focal plane flexible circuit for aerospace use according to claim 1, characterized in that: The wiring on the same layer also follows the following principles: In the flexible area, the temperature measurement signal is placed adjacent to the inner side of the protective copper wire, and is kept 3 times the line width away from other inner signals.

7. The method for designing a deep cryogenic infrared focal plane flexible circuit for aerospace use according to claim 1, characterized in that: The same layer wiring also follows the following principle: the analog signal and digital signal partition wiring of the entire flexible circuit do not cross.

8. The method for designing a deep cryogenic infrared focal plane flexible circuit for aerospace use according to claim 1, characterized in that: The same-layer wiring also follows the following principles: In order to reduce crosstalk between lines of the same-layer signal, the line spacing follows the 3W rule.

9. The method for designing a deep cryogenic infrared focal plane flexible circuit for aerospace use according to claim 1, characterized in that: For method three, in order to ensure the return capacity of the signal, a ground wire should be laid nearby the signal on each layer as a return line; and a ground wire should be laid as a return line every 2 to 3 signals.

10. A deep cryogenic infrared focal plane flexible circuit for aerospace use, characterized in that: It is mainly composed of a rigid area and a flexible area, and adopts the design method described in any one of claims 1 to 9 to determine the stacking structure, device layout and wiring method.

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