CSP solder ball reliability

The solder joint reliability for Chip Scale Package (CSP) as assembled on Printed Circuit Board (PCB) is believed to be poorer than that for QFP. The main cause of this poor reliability is the Coefficient of Thermal Expansion (CTE) mismatch between CSP and PCB. With a view to implement CSP into practical board assembly without underfill, we performed experimental study and FEM analysis of solder joint reliability for three different CSPs, among which two were ceramic fine-pitched ball grid arrays (C-FBGAs) and one plastic package (P-FBGA). We found that solder ball life predictions from the FEM analysis coupled with Coffin-Manson's equation were in good agreement with results from reliability experiments for C-FBGA (high-a) and P-FBGA, whereas difference between them was observed in the case of C-FBGA (Al/sub 2/O/sub 3/). Among three CSPs, P-FBGA turned out to have excellent solder fatigue life and there is the prospect it can be implemented in board assembly without underfill.