Embodiments disclosed herein include composite dies and methods of forming such composite dies. In an embodiment, a composite die comprises a base substrate, a first die over the base substrate, and a second die over the base substrate and adjacent to the first die. In an embodiment an underfill layer is between the first die and the base substrate, between the second die and the base substrate, and between the first die and the second die. In an embodiment, a trench into the underfill layer is between the first die and the second die. In an embodiment the composite die further comprises, a mold layer over the first die and the second die, wherein the mold layer fills the trench.