Package-on-Package (PoP) structures and methods of forming the same are disclosed. In some embodiments, a method of forming a PoP structure may include: placing a device die having a plurality of metal posts over a release layer, wherein the release layer is over a first carrier; forming a plurality of through-assembly vias (TAVs) over the release layer; forming a dam member between the device die and the plurality of TAVs; molding the device die, the dam member, and the plurality of TAVs in a molding compound; and grinding the molding compound to expose ends of the plurality of metal posts and ends of the plurality of TAVs, wherein a top surface of the molding compound is substantially level with the exposed ends of the plurality of metal posts and exposed ends of the plurality of TAVs.