Methods and apparatus for flip chip substrates with guard rings. An embodiment comprises a substrate core with a die attach region for attaching an integrated circuit die; at least one dielectric layer overlying a die side surface of the substrate core; and at least one guard ring formed adjacent a corner of the substrate core, the at least one guard ring comprising: a first trace overlying the dielectric layer having rectangular portions extending in two directions from the corner of the substrate core and in parallel to the edges of the substrate core; a second trace underlying the dielectric layer; and at least one via extending through the dielectric layer and coupling the first and second traces; wherein the first trace, the at least one via, and the second trace form a vertical via stack. Methods for forming the flip chip substrates with the guard rings are disclosed.