Analysis of Structural Stress in 8􀀁8 InSb Array Detector

Abstract

Based on viscoplastic Anand's model, structural stress of 8� 8 InSb array detector dependent on indium bump sizes is systemically researched by finite element method. For the detector with underfill, simulation results show that as the diameters of indium bump decrease from 36μm to 20μm in step of 2μm, the maximum stress existing in InSb chip first reduces sharply, then increases flatly, and reaches minimum with indium bump diameter 32μm. When the height of indium bump increases from 9μm to 21μ m in step of 6μm, the maximal stress in InSb chip first reduces sharply from 800MPa to 500MPa, then almost remains constant. This phenomenon is contrary to the detector without underfill, where the stress is smaller with lower indium height. In the whole device, the maximal Von Mises stress appears in the InSb chip with 10μm, and the minimal Von Mises stress appears in the indium bump array with 16MPa, almost 1/10 of that in underfill encapsulate, where the stress is180MPa. It is noticed that when the Von Mises stress reaches minimum with some selected indium bump dimensions, its stress distribution is uniform and concentrated at all contacting areas, this is favorable to reduce the crack happening in InSb chip, and improve the yield.