| The ultra-large scale linear infrared focal plane detector assembly has important applications in the fields of the meteorology,resource,environment,and astronomy in recent years.The infrared detectors usually need to work at low temperature below100K because of limited by background noise suppression.With the increasing demand of system application requirements for large field of view,high spatial resolution and high time resolution,the development of the single detector module scale can't meet the design index requirements,and several or even dozens of detector modules are needed to be integrated in the dewar assembly,the problems about thermal matching of detector modules,the heat transfer and lightweight of the dewar assembly are prominent.It is of great significance to develop the next-generation infrared focal plane technology by developing the integrated packaging technology for ultra-large scale linear infrared focal plane detector to solve the key packaging technologies such as high temperature cycle reliability,high temperature uniformity and lightweight.The low-temperature packaging of the ultra-large scale linear infrared focal plane detector assembled by 20 modules is taken as the research object,through the combination of finite element simulation analysis,structural design and iterative optimization,and experimental verification,it focuses on solving the problem of thermal adaptation between the detectors and cold platform,low thermal stress and high reliability coupling with the long cold platform and cryocooler,lightweight design and preparation of the ultra-large scale dewar,the main research contents and innovative achievements are as follows:The long cold platform structure was innovatively designed,which was composed of the multiple"Z"-shaped sub-substrates and TC4 aid-plate with the working temperature below 100K for the principle that the ultra-large scale linear infrared focal plane detector assembly was expandable,repairable,and convenient for testing.Each sub-substrate was three-dimensional adjustable and integrated with 4?8detectors.The structure and support of long cold platform were optimized by the finite element software,and the influences of support distribution,support material and support wall thickness on the mechanical vibration and heat conductive loss of long cold platform were analyzed according to the requirements of resistance vibration and low heat conductive loss.The results show that the TC4 support with wall thickness of 0.3mm and three-point staggered distribution has high resistance to mechanical vibration;the first modal frequency of the long cold platform is 356Hz,the maximum amplification factor of Y-direction Sine vibration is 1.46;When the number of detector modules is expanded from 20 to 100,the first modal frequency and Y-direction amplification of the long cold platform are basically stable while the support density remains unchanged,which verifies the scalability of the long linear dewar cold platform and staggered support distribution structure.The thermal analysis model of the package structure of the detector sub-module was established,and the influences of different thickness and different material substrate on the detector modules thermal stress and low-temperature deformation were clarified according to the design index requirements of the higher temperature uniformity,lower packaging stress and low-temperature deformation of the long cold platform.The results show that among the metal substrates,the Kovar substrate package has the smallest thermal stress and the best comprehensive index;When the thickness of the Kovar substrate is 6mm and the thickness of the Invar balance layer is0.5mm,the thermal stress of the Ga As substrate is less than 20MPa.The finite element thermal simulation of the long cold platform composed of five"Z"-shaped Kovar sub-substrates with thickness of 6mm and TC4 aid-plate shows that the maximum low-temperature deformation of the Hg Cd Te epitaxial layer on all detector modules isħ12.5?m,and the maximum thermal stress of Ga As substrate is 25.3 MPa,and it has good resistance to low-temperature deformation.According to the characteristics of the single-point cold source transmission structure between the long cold platform by multiple sub-substrates butting and the cryocooler,the indirect coupling of multiple flexible thermal links,indirect coupling of double flexible thermal links and direct coupling of single three-dimensional flexible thermal link were compared,and the influence of three structures on the temperature uniformity of long cold platform and the temperature difference between the cold platform and the single cold source was clarified,in the aspect of temperature difference control,the minimum temperature difference between the the cold platform and the single cold source is 4.64K by using three-dimensional flexible thermal link structure;in terms of temperature uniformity control,when the 5W detector Joule heat is loaded,the results of temperature uniformity by using the dual flexible thermal links structure and three-dimension flexible thermal link structure areħ0.26K andħ0.22K respectively;in terms of flexibility,the thermal simulation analysis of the long cold platform integrated with three-dimensional flexible thermal link shows that the low-temperature deformation of the Hg Cd Te epitaxial layer on all the detector modules isħ12.34?m,the thermal stress of Ga As substrate is about 25.9 MPa,and the flexibility of thermal link is excellent.The integrated design method was proposed,which combined topology optimization,lightweight material application,multi-component high hermetical welding structure and process design for the requirements of lightweight application of ultra-large scale linear infrared focal plane dewar.The silver copper solder was used to connect TC4 window base with Kovar parts by multiple brazing.The contact between Ti and Fe was restrained by nickel plating on Kovar and TC4 brazed specimens.The EDS and XRD results show that there are no brittle intermetallic compounds such as Ti Fe and Ti Fe2 in the brazing seam,and the average tensile strength reached 505.8MPa;The leakage rate of the optical window assembly is better than 4.8×10-11Torr.l/s.The optimized weight of the dewar is 9.82kg,and the reduction rate is 57.3%.The thermal characteristics test system of ultra-large scale linear infrared focal plane dewar was built,the evaluation tests of temperature field and low temperature flatness of dewar cold platform were realized,and the mechanical and thermal environment test verifications of dewar assembly were completed.The measured results show that the temperature uniformity of 20 detector modules butted on the long cold platform is 95ħ0.26K,the temperature difference between the long cold platform and the cold finger of the coaxial pulse tube cryocooler coupling surface is4.67K,the low temperature flatness of the long cold platform is 26.4?m,and the total weight of the dewar is 9.86Kg,the first response frequency of the long cold platform coupled with the axial tube crycooler is 341.99Hz at the random sweep vibration test,which is consistent with the design results;and the total leakage rate of the dewar is4.2×10-12Torr.l/s,and the dewar assembly has passed the random vibration test with total root mean square of 6.8 grms.Therefore,the research of this topic has important reference significance for the following engineering preparation of the ultra-large scale infrared focal plane detector dewar assembly. |
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