Microelectronic elements with post-assembly planarization

A microelectronic unit, comprising:

• a carrier structure having a front surface, a rear surface remote from the front surface, and a recess having an opening at the front surface and an inner surface located below the front surface of the carrier structure, the carrier structure including at least one of semiconductor material or glass;
• a microelectronic element having a bottom surface adjacent the inner surface, a top surface remote from the bottom surface, and a plurality of contacts at the top surface, the microelectronic element having edge surfaces adjacent lateral edge surfaces of the recess;
• terminals electrically connected with the contacts of the microelectronic element, the terminals being electrically insulated from the carrier structure;
• a dielectric region contacting at least the top surface and the edge surfaces of the microelectronic element and extending between the lateral edge surfaces of the recess and the edge surfaces of the microelectronic element, the dielectric region having a planar surface located coplanar with or above the front surface of the carrier structure, wherein the terminals are exposed at the surface of the dielectric region for interconnection with an external element;
• and
• a plurality of conductive vias extending from the planar surface through the dielectric region between the lateral edge surfaces of the recess and the edge surfaces of the microelectronic element to the rear surface.