Thermal stress analysis of InSb IRPFAs assembled in Dewar

Thermal stress accumulated in InSb infrared focal plane arrays (IRFPAs) during liquid nitrogen shock tests usually gives rise to brittle fracture of InSb chips, local delamination between InSb chips and underfill. Upon the specific structure of the InSb IRFPAs installed in the Dewar, we propose the end surface circular ring fixed mode should be adopted to describe its boundary conditions instead of the well-accepted bottom surface center point fixed mode. From the created structure modeling of the InSb IRFPAs adopting the fixing modes mentioned above, we extract the thermal stresses and plot them together for easy comparison. We find that the end surface circular ring fixed mode is superior to the well-accepted bottom surface center point fixed mode in aspects of the considerable reduction of the thermal stress in the InSb chips, the moderate decrease of both the shear stress and the peeling off stress between the InSb chips and the underfill. All these findings suggest that the thermal stress of the InSb IRFPAs assembled in the Dewar is overestimated by the well-accepted bottom surface center point fixed mode and can be greatly decreased by adjusting its fixing mode.