Technology of fine pitch interconnect with lead-free solder joint has been developed to enhance the performance of flip-chip high density packages. This study presents an investigation of solder bump forming behavior by means of CFD simulation analysis. The flow motion of molten solder is analyzed with 3D model we developed, and the simulation result is validated with the experiment. Moreover, the investigation of factors affecting solder bridging across adjacent pads is also performed. It is revealed that wettability between liquid solder and organic insulator, which is represented as contact angle in the calculation has large effect on the solder bridging phenomena. The simulation result suggests that worsening the wettability of the insulator can reduce the occurrence of bridging.