A package includes a first package including a device die, a molding compound molding the device die therein, a through-via penetrating through the molding compound, and a first plurality of Redistribution Lines (RDLs) and a second plurality of RDLs on opposite sides of the molding compound. The through-via electrically couples one of the first plurality of RDLs to one of the second plurality of RDLs. The package further includes a second package bonded to the first package, a spacer disposed in a gap between the first package and the second package, and a first electrical connector and a second electrical connector on opposite sides of the spacer. The first electrical connector and the second electrically couple the first package to the second package. The spacer is spaced apart from the first electrical connector and the second electrical connector.