US Patent 7851269 Method of stiffening coreless package substrate

Embodiments of the present invention relate to a method of stiffening a semiconductor coreless package substrate to improve rigidity and resistance against warpage. An embodiment of the method comprises disposing a sacrificial mask on a plurality of contact pads on a second level interconnect (package-to-board interconnect) side of a coreless package substrate, forming a molded stiffener around the sacrificial mask without increasing the effective thickness of the substrate, and removing the sacrificial mask to form a plurality of cavities in the molded stiffener corresponding to the contact pads. Embodiments also include plating the surface of the contact pads and the sidewalls of the cavities in the molded cavities with an electrically conductive material.