A fan-out package includes a redistribution structure having redistribution-side bonding structures, a plurality of semiconductor dies including a respective set of die-side bonding structures that is attached to a respective subset of the redistribution-side bonding structures through a respective set of solder material portions, and an underfill material portion laterally surrounding the redistribution-side bonding structures and the die-side bonding structures of the plurality of semiconductor dies. A subset of the redistribution-side bonding structures is not bonded to any of the die-side bonding structures of the plurality of semiconductor dies and is laterally surrounded by the underfill material portion, and is used to provide uniform distribution of the underfill material during formation of the underfill material portion.