The effects of solder volume and Cu concentration on the consumption rate of Cu pad during reflow soldering

The combined effect of solder volume and Cu concentration in solder on the Cu consumption rate is of significant practical importance but has never been satisfactorily addressed in literature so far. In this study, lead-free solder balls of different volumes (400, 500, 760 and 960 μm in diameter) and different Cu concentrations (Sn3AgxCu with x = 0, 0.3, 0.5, and 0.7 wt.%) were reflowed over Cu soldering pads in order to resolve this issue. The data obtained afforded the establishment of an empirical equation that could predict the Cu consumption during reflow. Such consumption rate information is crucial for designing the Cu conduction traces with minimum but reliable dimensions. Both the solder volume and the Cu concentration had marked effects on the morphology of the reaction product. Rationalizations for the effects on the consumption rate and the morphology are presented.