A method of forming a package includes bonding a device die to an interposer wafer, with the interposer wafer including metal lines and vias, forming a dielectric region to encircle the device die, and forming a through-via to penetrate through the dielectric region. The through-via is electrically connected to the device die through the metal lines and the vias in the interposer wafer. The method further includes forming a polymer layer over the dielectric region, and forming an electrical connector. The electrical connector is electrically coupled to the through-via through a conductive feature in the polymer layer. The interposer wafer is sawed to separate the package from other packages.