A structure for a core layer of a substrate and a method for fabricating a core layer of a substrate are disclosed. The core layer comprises a molding compound encapsulating a die or a plurality of dies, a dielectric layer on the surfaces of the molding compound, and a conductive layer on top of the dielectric layer. A through hole is formed through the dielectric layer and the molding compound, which may be filled with a metal plate. A laser via is formed similarly. Build-up layers may be assembled next to the core layer to form the substrate, which can be used to package dies.