Development of FO-WLP Package-on-Package using RDL-first Integration Flow

In this paper, a fan-out package-on-package (PoP) was developed using RDL-first integration flow. The developed fan-out PoP has package size of 15 × 15 mm
²
and consists of three silicon chips. The bottom package consists of a 10 ×; 10 mm
²
silicon flip-chip assembled to under bump metallization (UBM) of the bottom redistribution layers (RDL). Vertical wire-bonds are integrated into the bottom package to act as vertical through mold interconnects (TMI) to the top RDL layers. The top package consist of two 7 × 11 mm
²
silicon chips attached directly on top of the bottom package and connected to the top RDL layer with low-loop wire-bonds. The top chips were encapsulated in epoxy mold compound to form to the bottom package forming a seamless Fan-out PoP. RDL-first integration flow was used to fabricate the fan-out package whereby RDL, molding and chips assembly processes were performed on a carrier wafer to overcome warpage and other issues associated with conventional Mold-first process.