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For the long wavelength infrared detection, HgCdTe (MCT) photoconductive devices are selected as the core of
next-generation meteorological because of its mature fabrication technique and stable performance. During the assembly
process, an innovative multilayer ceramic board providing mechanical support is designed as the electrical
interconnection between MCT chips and external circuits for cryogenic application. Furthermore, due to its brittleness,
long linear MCT device is normally glued to sapphire substrates on the multilayer ceramic board with cryogenic glue.
Thus, it can be seen clearly that the assembly structure is a multilayer configuration which comprises various kinds of
materials, including ceramic broad, sapphire, MCT and glues. As a result, the difference in Thermal Expansion
Coefficient (TEC) between the layers could create the potential to introduce thermal stress at working environmental
temperature (approximately 70K), which could result in device performance degradation, even die crack.
This article analyzes the thermal stress between long linear MCT devices and a multilayer ceramic board by using Finite
Element Method (FEM). According to analysis results, two factors are revealed as the most significant causes for
introducing thermal stress: one is the sapphire substrate thickness; the other is the parameters of various materials, for
instance Yong's modulus and TEC. Since the structure of MCT detector is determined by system requirements and is
under the limitation of manufacture technology, this article reveals two effective approaches to reduce the unavoidable
thermal stress: first, choosing the appropriate thickness of ceramic board which is made by Al2O3; second, adding another
metal cushion Invar. With the above considerations, the distribution of thermal stress is simulated using FEM under
different parameter conditions. Based on the results of simulations, an optimal design of package structure which could
improve the reliability of linear MCT with minimum thermal stress is demonstrated.
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