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