Process enabling highly accurate die position for fan-out package applications

Abstract

A new process that can improve die shift issue in process utilising back-sided under bump metallurgy (UBM) via a self-alignment effect for fan-out package applications is proposed. The die and the pad of the substrate are spontaneously aligned and the degree of accuracy is very high after reflow. For the experiment, two kinds of UBM pads were prepared on glass dies and the SAC305 solder was formed on the copper pads of an frame retardent (FR)-based substrate. The die shift value was from 20 to 50 mu m after pick-and-placement. After reflow, the maximum die shift value was < 1 mu m. An initially misaligned die with a large shift was aligned with a high degree of accuracy during reflow due to the surface tension of the molten solder. The proposed process improves the die shift issue in the fabrication of fan-out wafer-level packaging and the active die embedded substrate.