Characteristic study of anand and modified anand creep models for area array type WLCSP

WLCSP is one of the fastest growing segments in semiconductor packaging industry due to the rapid advances in integrated circuit (IC) fabrication, small form factor, and low cost. The WLCSP may not achieve prescribed solder joint reliability requirements due to current trend of large die WLCSP development, the ball fatigue reliability risk becomes more critical and challenging due to larger stress concentration caused by mismatch of coefficient of thermal expansion (CTE) in between silicon and PCB[1]. Accelerated thermal cycling (ATC) has been widely used in industry for microelectronic reliability lifetime assessment. In recent decades, as the rapid development of computing performance and simulation technique, the numerical approach is more and more frequently adopted by designers and is believed to have its potential on tackling the issues related to electronic packages in the future. In this research work, the solder joint creep behavior on WLCSP under thermal cycling loading will be studied in Finite Element Modelling with the help of Two Creep Models namely Anand Model and Modified Anand Model. This study will make use of a large die, 14mm × 14mm full array WLCSP with 0.4mm ball pitch, 0.25mm ball size and 96.5Sn-3.5Ag ball material, as test vehicle and apply JEDEC thermal cycling profile from -40 °C to 125 °C with 10 minutes of dwell time and ramp rate of 16.5°C per minute to validate the simulation results. Later, a new creep model called Modified Anand Model will be used, by which further the testing time of the thermal cycling can be reduced. The creep strain of solders under both the models have been analyzed for a better understanding of the creep behavior of lead-free solder ball of WLCSP during thermal cycling loading. The simulation result shows there exists a variation in the creep strain between the models under the thermal cycling. The Outcome reveals that different Anand Model Parameters leads to the significant change in variation of creep strain. Using a Modified Anand Model to calculate the package fatigue lifetime, and prediction has been further validated by simulation results. The preliminary study provides a permissible variation to that of the WLCSP creep analysis. The finding of new creep model has recommended implementing the same with different solder materials and also to various electronic packages.