Board level reliability study on three-dimensional thin stacked package

This paper discusses the optimal design for PS-etCSP to achieve reliable thermal fatigue life of solder joint. For this purpose design analysis was performed using both simulation and experimental approaches. Since reduction of warpage is most critical issue to ensure good solder joint connection for thin packages, parametric study was performed to find the optimal set of package outline dimensions using finite element method. Next to find the optimal design far solder joint reliability, 3D FEA fatigue model was established with non linear material properties of solder joint. Various factors such as ball land size, motherboard thickness and surface mounting type were studied. As a result, it is found that thin die with small size and small CTE molding compound is better for minimizing package warpage and larger opening size, thinner board and single mounting on board are good for solder joint reliability. The stack of package however has little effect on solder joint reliability. The effects of board thickness and surface mounting type (single/double) were investigated in terms of assembly stiffness and solder joint reliability. Simulation results showed good correspondence with experiment. The fatigue life and failure location predicted by simulation agreed well with experimental data. The fatigue life of optimal design was 1225 cycles for single PS-etCSP and 990 cycles for stacked PS-etCSP with single side mounting on board under the thermal cycling loading of temperature of -40°C∼125°C. Subsequently it can be concluded that optimal design of PS-etCSP can meet the requirement for most portable product applications.