A microelectronic unit is provided in which front and rear surfaces of a semiconductor element may define a thin region which has a first thickness and a thicker region having a thickness at least about twice the first thickness. A semiconductor device may be present at the front surface, with a plurality of first conductive contacts at the front surface connected to the device. A plurality of conductive vias may extend from the rear surface through the thin region of the semiconductor element to the first conductive contacts. A plurality of second conductive contacts can be exposed at an exterior of the semiconductor element. A plurality of conductive traces may connect the second conductive contacts to the conductive vias.