CSP solder ball reliability

The solder joint reliability for Chip Scale Package(CSP) as assembled on Print Circuit Board(PCB) is believed to be poorer than that for QFP. The main cause of this poor reliability is the in mismatch Coefficient Thermal Expansion(CTE) mismatch between CSP and PCB. With a view to implement CSP into practical board assembly without underfill, we performaed experimental study and FEM analysis about solder joint reliability for three different CSPs, among which two were ceramic fine-pitched ball grid array(C-FBGA) and remaining one was plastic(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-alpha) and P-FBGA, whereas difference between them was observed in the case of C-FBGA(Al2O3). Among three CSPs, P-FBGA turned out to have excellent solder fatigue life and resultantly we have the prospect it can be implemented in board assembly without underfill.