Low Cost, High Reliability WLCSP for Higher Pin Counts

Abstract

The proliferation of Wafer Level Chip Scale Packages (WLCSPs) in portable handheld products has occurred due to the minimalist form factor, high reliability and low cost packaging that they afford. As the demand for WLCSPs has grown exponentially in recent years, the industry has also been coping concurrently with the technical challenges associated with increasing array sizes and more demanding end user reliability requirements. Since handsets are inherently prone to being dropped, they are particularly susceptible to this type of component failure though striking a proper balance of mechanical robustness and thermal cycling performance has remained an ongoing industry goal. Similar to other packages, WLCSPs have transitioned over the past decade from lead-based solder alloys to Lead Free (LF) solders. LF solder connections are especially susceptible to brittle fracture and can result in variations in drop test performance from one bump structure to the next. This paper will provide an overview of process and material add-on strategies that have been shown to considerably improve mechanical robustness for bump structures or bumping applications that are inherently less robust than others. Such supplemental improvements can result in passing Board Level Reliability qualification requirements which may otherwise be elusive or have limited levels of reliability reproducibility.