Yield Comparison of Die-first Face-Down and Die-last Fan-out Wafer Level Packaging

This analysis focuses on two of the primary variations of fan-out wafer level packaging: die-first packaging in which the die are placed face down, and die-last packaging. These two technologies share many of the same activities, but those activities occur in a different order. One key factor setting these two process flows apart is yield. Even with the assumption that the same level of defects are introduced in each process flow, the resulting total yield differs. This paper analyzes the impact of defects on the die-first and die-last processes. Each process is evaluated separately, then the two processes are directly compared across a range of designs, defect density assumptions, and incoming die cost assumptions. The cost of the processing, cost of the incoming die, and the cost of processing and die lost to scrap are included.