A method includes forming an interposer, which includes forming a rigid dielectric layer, and removing portions of the rigid dielectric layer. The method further includes bonding a package component to an interconnect structure, and bonding the interposer to the interconnect structure. A spacer in the interposer has a bottom surface contacting a top surface of the package component, and the spacer includes a feature selected from the group consisting of a metal feature, the rigid dielectric layer, and combinations thereof. A die-saw is performed on the interconnect structure.