A 3D interposer (and method of making same) that includes a crystalline substrate handler having opposing first and second surfaces, with a cavity formed into the first surface. A layer of insulation material is formed on the surface of the handler that defines the cavity. The cavity is filled with a compliant dielectric material. A plurality of electrical interconnects is formed through the interposer. Each electrical interconnect includes a first hole formed through the crystalline substrate handler extending from the second surface to the cavity, a second hole formed through the compliant dielectric material so as to extend from and be aligned with the first hole, a layer of insulation material formed along a sidewall of the first hole, and conductive material extending through the first and second holes.