Inspection Solution for 2μm RDL from Wafer-Level to Panel-Level Fan-out Process

Abstract

In the advanced packaging industry, both fan-out wafer-level packaging (FOWLP) and fan-out panel-level packaging (FOPLP) have grown quickly in recent years since they are compatible with largescale, low-cost manufacturing and are key enablers for ultra-thin and high-density packages. However, the commercialization of the fan-out process continues to face technical challenges with the rapid adoption of finer pitch and width of the Cu redistribution layer (RDL) in die-first or die-last integration approaches. AOI has been widely used in the advanced packaging industry as a major tool for defect inspection during various process steps. The conventional bright field and dark field imaging techniques suffer from a high nuisance rate for RDL inspection; in many cases, the RDL metal grain size could be larger than the defect of interest, and the interferences from underneath the pattern, such as bottom RDL layers or molding compounds, can increase the difficulties of defect detection. In this paper, we present Onto Innovation’s innovative fluorescence technology to enhance contrasts between organic material, such as polyimide, or photoresists and metals that enable fine-pitch RDL inspection with increased accuracy by eliminating nuisance defects. By using powerful fluorescence technology, in conjunction with higher resolution, high-definition inspection (HDI) technology, fine-pitch RDL defect inspections on both wafer-level and panel-level packaging were studied and shown to enable accelerated development cycles in the R&D stage, as well enable rapid yield enhancements in the HVM environment.