An embodiment package includes a first fan-out tier, fan-out redistribution layers (RDLs) over the first fan-out tier, and a second fan-out tier over the fan-out RDLs. The first fan-out tier includes one or more first device dies and a first molding compound extending along sidewalls of the one or more first device dies. The second fan-out tier includes one or more second device dies bonded to fan-out RDLs, a dummy die bonded to the fan-out RDLs, and a second molding compound extending along sidewalls of the one or more second device dies and the dummy die. The fan-out RDLs electrically connects the one or more first device dies to the one or more second device dies, and the dummy die is substantially free of any active devices.