Bump non-wet issue in large-die flip chip package with eutectic Sn/Pb solder bump and SOP substrate pad

This paper describes a study on non-wet issue encountered in flip chip assembly process of high-density flip chip ball grid array (FCBGA) packages with eutectic Sn/Pb solder interconnects. A nonwet occurrence is more obvious in large-die flip chip (die size >16mm) with high I/O counts (>1000). Thermal-mechanical mismatch between die and substrate shows a role in affecting soldering condition of the die solder bump and substrate SOP. Positive evaluation results, involving: 1) new flux material with increased percentage of solid content or modified activator and 2) plasma treatment on substrate prior to FC assembly, indicate that a more effective approach is needed to improve bump solderability in large die flip chip devices