Abstract: Based on viscoplastic model,the reliability of indium sphere soldered joint in infrared focal plane array detector was analyzed by finite element method.Simulation results show that the maximum equivalent stress appears on the contact area between InSb chip and indium sphere,which is located in the corner of indium sphere array and far away from the symmetric center of the detector.When the infrared detector was loaded periodically with temperature cycles,the maximal stress also varied periodically.As the temperature decreases from the room temperature to 77 K,the maximal stress increases rapidly to the maximum value,and during the holding time,the stress relaxation phenomena appears,and as the temperature increases,the maximal stress reduces sharply.As the diameter of the indium sphere increases,the maximum stress varies irregularly,while the plastic energy analysis results show that as the diameters of indium sphere increase,its plastic work decreases,and its plastic energy accumulation also reduces,which indicates that the structure with larger diameter has the higher fatigue reliability.It is noticed that when the diameter of the indium solder is set to be 30 μm,the stress distribution on all the contacting areas is uniform and concentrated,and the stress is the lowest.