A package includes a first package component having a top surface, a second package component bonded to the top surface of the first package component, and a plurality of electrical connectors at the top surface of the first package component. A molding material is over the first package component and molding the second package component therein. The molding material includes a first portion overlapping the second package component, wherein the first portion includes a first top surface, and a second portion encircling the first portion and molding bottom portions of the plurality of electrical connectors therein. The second portion has a second top surface lower than the first top surface.