Structural model of InSb IRFPAs including underfill curing process

Abstract

InSb infrared focal plane array(IRFPA) detector, active in 3-5 m range, has been widely used in military fields. Higher fracture probability appearing in InSb infrared focal plane arrays(IRFPAs) subjected to thermal shock test, restricts its final yield. In order to analyze and optimize the structure of InSb IRFPAs, it is necessary to create the three-dimensional structural model of InSb IRFPAs, which is employed to estimate its strain distribution appearing in the different fabricating processes. In this paper, the curing model of underfill is described by its volume contraction percentage combined with the elastic modulus of the completely cured underfill. Thus, both the von Mises stress and the Z-components of strain accumulated in the curing process of underfill are calculated. When InSb IRFPAs is naturally cooled to room temperature from the curing temperature of underfill, the Z-component of strain distribution appearing on the top surface of InSb IRFPAs is obtained with our structural model, which is identical to the deformation distribution on the top surface of InSb IRFPAs measured at room temperature. In the following thermal shock simulation, we find that the maximal von Mises stress appears at 100 K and the maximal Z-component of strain appears at 150 K, these two temperature points are located in the second half of the thermal shock process, these results indicate that the fracture of InSb chip happens more easily in liquid nitrogen shock test. This inference is consistent with the fact appearing in liquid nitrogen shock test. All these findings suggest that the proposed model is suitable to estimate the deformation distribution of InSb IRFPAs and its changing rule in its different fabricating stages.