Wafer bumping: fine-pitch and lead-free solder
Wafer-level packaging (WLP) that uses both lead-free and fine-pitch solder captures a very small niche of the global WLP demand. But demand for lead-free solder is ramping up across a variety of markets, and fine-pitch bumping is available for high-volume deployment if the need/cost ratio is justified.
LaBennett, R., & Yeh, S. (2005). Wafer bumping: fine-pitch and lead-free solder. Semiconductor International, 28(4), SP11-18.