Analysis on Structural Stress of 64 × 64 InSb IRFPAs with Temperature Dependent Elastic Underfill

To improve the reliability of InSb IRFPAs, underfill has usually been filled between InSb chip and Si ROIC. Around the glass transition temperature, underfill shows viscoelasticity, yet, far below it, which shows apparently temperature dependent mechanical properties. Basing on the temperature dependent elastic model of underfill, firstly a small format array of 8×8 elements InSb IRFPAs is investigated by changing indium bump diameters and heights; simulated results show that the maximum stress in InSb chip has nothing to do with underfill height and is dependent on indium bump diameter; the varying tendency is just like the horizontally extended letter U. When indium bump diameter is set to 24 μm with height 21  μm, the maximal stress in InSb chip reaches minimum. To learn the stress in 64×64 elements in short time, with the above optimal structure, InSb IRFPAs array scale is doubled once again from 8×8 to 64×64 elements. Simulation results show that the stress maximum in InSb chip is strongly determined by arrays format and increases with array scale; yet, the stress maximum in Si ROIC almost keeps constant and is independent on array sizes; besides, the largest stress locates in InSb chip, and the stress distribution in InSb chip is uniform