An IC package and methods for making the same are described. The IC package includes a die and a heat sink that is attached to the back surface of the die with a thermal interface material layer. The heat sink includes a base and a partition. The partition extends around the periphery of the base and is offset from the outer edge of the base such that a ledge region is formed that surrounds the periphery of the base. The inner surfaces of the partition define an inner region that includes heat dissipation structures. A molding material encapsulates at least portions of the die and the ledge region around the periphery of the heat sink while leaving the inner region of the heat sink unencapsulated by molding material and exposed. The molding material covering the ledge region provides a locking feature that secures the heat sink in the package.