Ultra-Thin FO Package-on-Package for Mobile Application

Abstract

Today, Package on Package is a major trend of three-dimensional fabrication for processors and high-performance memory applications in portable applications. Package-on-Package has the benefit of a mini packaging size with multi-functionality by stacking two different packs. However, an ordinary Printed circuit board substrate Package on Package has a weak point to meet the now low profile necessary of high-performance in the thin portable application. To overcome this weak point, the package has been introduced to the market by Fan Out Wafer Level, and this structure of the package allows I/O to be within the device surface and expand through the combination of form so that they can be accommodated more FOWLP. Ultra-thin Fan-out PoP was developed using RDL-first process flow. The developed Fan-out PoP has a package size of 15 x 15 mm2 and thickness of 800 µm, and it consists of three embedded chips. The bottom package consists of a 10 x 10 mm2 processor chip assembled to under bump metallization (UBM) of the bottom RDL layers. Vertical wire-bonds are integrated into the bottom package to act as vertical through mold interconnect (TMI) to the top RDL layers. The top package consist of two 7 x 11 mm2 silicon chips assembled laterally 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 an integrated 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 associated with conventional Mold-first process. The ultra-thin Fan-out PoP samples pass the reliability include the MST level 3, drop impact test and the Thermal Cycling. It also provides good thermal performance on packaging level and system level applied in mobile device.