The Thermal-stress Coupling Analysis Of Infrared Focal Plane Array Detector

In the monochromatic medium-wave infrared region (wavelength3~5μm), theInSb detector has a higher quantum efficiency and response uniformity, excellentresolution. So the detector has been widely applied in various fields, such as aviationand astronavigation, national defense, meteorology and so on. The structure of InSbdetector is a flip-chip structure, which is usually fabricated by flip chip bondingtechnology. When the detector is going to work, its temperature necessary rapidlyreduced from300K to77K by refrigeration equipment. In this thermal shock process,the thin InSb chip is fracture due to its peculiar structure and low-temperatureenvironment. The fracture of InSb chip has seriously affected the applicability ofdetector, and has become the most important issue needed to solve in themanufacturing process of the InSb detector.To clarify the mechanism of fracture in the thermal shock of detector, the modelof128×128InSb detector as the study object was established in this paper. With thehelp of the finite element software ANSYS, the thermal-stress coupling of InSbdetector was studied. Thermal-stress coupling analysis requires two steps. First, Inorder to obtain the temperature distribution of detector, we simulated the coolingprocess of detector. Second, based on the temperature distribution of thermal analysis,the thermal-stress coupling analysis was performed. The stress and its distribution onthe detector chip in thermal shock were studied, and the fracture reason of InSb chipwas studied too.The results of thermal-stress coupling analysis showed: due to the effect of non-uniform temperature field and the difference in coefficient of linear expansion ofmaterials, the Von Mises stress of InSb chip increased rapidly within a short time, itwill bring a severe impact to the reliability of InSb chip. Compared the stress with thestress form the analysis which did not consider interaction of heat and stress, the stressand its distribution of thermal-stress coupling manner can truly reflect the variation of stress on InSb chip, and the analysis which did not consider interaction of heat andstress will underestimate the impact of stress which increase rapidly. The stressdistribution of thermal-stress coupling analysis can furnish a useful reference to reducefragmentation of InSb chip in manufacture of detectors. Furthermore, by changing thethermal conductivity of underfill, the relationship between the material parameters andthe stress trends of InSb chip was investigated.