C5 Reflow and Flux Clean Characterization for Automotive FCBGA

This study focused on C5 leadfree solder reflow and flux clean characterization on FCBGA for automotive application. Impact of short versus long time above solder liquidus temperature (TAL) on intermetallic growth, solder ball shear strength and fracture mode were studied. A very short TAL resulted in higher solder ball shear strength and near to zero intermetallic layer formation. A very long TAL had significant thicker intermetallic growth and low shear strength. A balance TAL within flux-solder reflow profile recommendation was employed to overcome the 2 TAL extremes of poor joint and thick intermetallic layer. DI water flux clean interaction between different water pressure zones and spray type were studied. Change in wash zone water pressure impacts the pre-wash zone water pressure. Top piping pressure in each zone were set to maximum to ensure continuous water flooding on BGA side of all units while bottom piping pressure were set to values that prevented unit fly off. Spray type water reach was studied to ensure all units received water spray consistently. Drying zone temperature and conveyor speed were studied and successfully determined to ensure units received temperature above water boiling point for complete unit drying.