A Novel Submodeling Scheme on Thermal Cycle Test for CMOS Image Sensor

A novel submodel scheme based on St. Venant´s principle has been developed to evaluate the reliability thermal cycle test (TCT) for CMOS image sensor (CIS). The region of interested in board level CIS package is lead-free paste, which is the peak stressed area to predict fatigue life. A solid finite element model of CIS using ANSYS codes is developed to predict the thermal strain distributions. The predicted thermal-induced displacements were found to be very good agreement with the Moire interferometer experimental in-plane u and v deformations. The developed finite element model is then applied to investigate the reliability of the JEDEC standard JESD22-A104 TCT. In order to save computational time and produce satisfactory results in the coarse region of interest, an independent more finely meshed so-called submodel scheme based on cut-boundary displacement method is generated. The mesh density for different area ratio of submodel/global model was verified and the results were found to be good agreement with previous researches. The modified Coffin-Manson equation is applied to evaluate the predicted fatigue life of SnAgCu pastes. A series of comprehensive parametric studies were conducted in this paper