Package-on-package system with internal stacking module interposer

A package-on-package system includes: forming a first integrated circuit package including second top electrical contacts and first external electrical contacts on opposite sides thereof; forming an internal stacking module interposer including first top electrical contacts and base electrical connectors on opposite sides thereof; attaching the internal stacking module interposer to the first integrated circuit package with the first top electrical contacts connected to the second top electrical contacts; and molding a package encapsulant over the first integrated circuit package and around the internal stacking module interposer leaving a package encapsulant cavity for attaching a stacked package to the base electrical connectors.