Techniques for mounting a semiconductor chip in a circuit board assembly includes using different buildup materials on opposite sides of a core to optimize stress in the first level interconnect structure (between the chip and core) and/or the second level interconnect structure (between the core and circuit board). The core can be, for example, ceramic, glass, or glass cloth-reinforced epoxy. In one example, the first side of the core has one or more layers of conductive material within a first buildup structure comprising a first buildup material. The second side of the substrate has one or more layers of conductive material within a second buildup structure comprising a second buildup material different from the first buildup material. In another example, an outermost layer of the second buildup structure is a ductile material that functions to decouple stress in the interconnect between the substrate and a circuit board.