Hybrid infrared focal plane array detector is always a heterogeneous components assembly. The thermal expansion
mismatch between the components, HgCdTe detector chip and silicon readout integrated circuit, combined with large
thermal variations (300 K-80 K), results in substantial thermal stress in the interconnection layer and large warpage of
the whole assembly. In this paper, the thermal stress distribution and warpage of the assembly are analyzed by finite
element method. The results show that the thickness of sapphire electrical lead board, Si-ROIC and GaAs substrate have
influences on the thermal stress distribution and warpage of the assembly, and the warpage is affected significantly.
Furthermore, we adopt the theoretical formula of multilayer structure to calculate the warpage of IRFPA module. The
simulation results are in good agreement with those obtained from the theory. In order to improve the reliability of the
IRFPA detector, the assembly is optimized according to the analysis result. After optimizing, the warpage of the assembly
decreases from -10.2 um to -5.5 um, the maximum Von Mises Stress in HgCdTe layer decreases by 15.5%, and the
uniformity of thermal stress distribution is improved effectively.