Effect of microstructure design on reliability of FBGA lead-free solder joints

In this paper, the fine pitch ball grid array (FBGA) assembly with lead free solder was tested under thermal cycling condition. Finite element modeling and simulation was conducted. The microstructure designs of via in pad of substrate and through hole (via) in PCB under the solder joint were simulated. The solder mask definition (SMD) and non-solder mask definition (NSMD) on PCB board side was also simulated. The global-local modeling technique was implemented in FE simulation for FBGA assembly. Based on global model result, the critical solder joint location was detected and then the fine meshed local model was created for critical solder joint including the detailed microstructure design. Fatigue life prediction of solder joint was carried out based on FE simulation results. Some summaries can be made from FE simulation results. Through hole in PCB changes the failure site from package side solder joint interface to board side solder joint interface. For the case of solder joint with SMD on PCB side, through hole in PCB reduces the solder joint fatigue life significantly. Via in pad of substrate slightly reduces the solder joint fatigue life.