Study On The Fragmentation Of Infrared Focal Plane Array Detector

Infrared focal plane array detector can wildly be used in aerospace infraredremote sensing, meteorological, national defence and scientific instruments, and otherareas. But the extremely low yield under thermal shock makes large plane array infrareddetector only be used in the area of advanced military equipment, and the mostfundamental reason for this is the specific structure and low temperature workingenvironment of infrared focal plane array detector. For higher responsivity and signal tonoise ratio, at the same time in order to reduce the crosstalk, the InSb substrate isusually thinned to10μm, and resistance to deformation relatively weak. In order toobtain higher signal to noise ratio, InSb IRFPA usually operates at liquid nitrogentemperature (77K) to suppress background noise. When the temperature of InSb IRFPAdecreases from storage temperature (300K) to77K rapidly, usually there is stress/strainappearing in InSb chip due to different thermal expansion coefficient betweenneighboring components, which is the major causes of fracture in InSb chip, and the lowyield of InSb chip becames the main obstacle in series production of infrared focal planearray detectors.Relying on analysis method of convention flip chip devices reliability, forstructural analysis model of16×16InSb infrared focal plane array detector, here finiteelement analysis software ANSYS, is employed to research the impacts from bothindium bump heights, diameters and underfill material models on both Von Mises stressand its distribution appearing in InSb chip. Simulation results show that the Von Misesstress in InSb chip decreases with increased indium bump heights and increases slowlywith increased indium bump diameters. The simulation results clearly demonstrate thatunderfill models have obvious impacts on Von Mises stress. And we infer that the VonMises stress in InSb chip obtained with temperature dependent elasticity model is muchmore accuracy, and linear elastic model and viscoelastic model may overestimate the Von Mises stress in InSb chip.Using underfill temperature dependent elasticity model，here equivalent method isemployed to build structural analysis model of128×128InSb detector in order to verifythe applicability of the model, and the method of reducing Z-direction Young’s modulusof InSb chip is employed to research the impacts of process injury on InSb chipdeformation. The strain distribution and the position of the maximum value in thesimulation results are consistent with the crack origin and distribution in photograph of128×128InSb chip back deformation under thermal shock, which proved theapplicability of the model. Also simulation results show that deformation area ratio ofthe photosensitive array raised area to the mesa isolation tank depression area can beused as the basis for the InSb chip Z-direction Young’s modulus selection, here bulkmaterial Young’s modulus’s30percent is selected.In order to clarify the incentive of InSb detector deformation, here bulk materialYoung’s modulus’s30percent is selected, Based on layered structure characteristics ofInSb detector, to infer the key factors which can affect InSb chip Z-direction straindistribution. Simulation results show that interaction of Si readout circuit, underfill andindium column arrays causes deformation on Si readout circuit top surface is the mostserious, and the deformation significantly reduces after the buffer by the underfill andIndium column array, finally, the deformation reaches the minimum when it istransferred to the InSb chip top surface. So if the strain of Si readout circuit top surfacecan be reduced, will help reduce the strain on the InSb chip top surface, therebyreducing the strain concentration to reduce the fragmentation chances of the InSb chipand improve the yield of the detector.