A system in package structure and method of fabrication using wafer reconstitution are described. In an embodiment a 3D system includes a mid-layer interposer a first package level underneath the mid-layer interposer and a second package level over the mid-layer interposer. Second package level components can be bonded to the mid-layer interposer with metal-metal bonds and optionally dielectric-dielectric bonds, while the first package level components can be bonded to the mid-layer interposer with dielectric-dielectric and optionally metal-metal bonds.