A microelectronic assembly can include a microelectronic device (310) having device contacts (312) exposed at a surface (328) thereof and an interconnection element having element contacts (340) and having a face adjacent to the microelectronic device. Conductive elements (365), e.g., wirebonds connect the device contacts with the element contacts and have portions extending in runs above the surface of the microelectronic device. A conductive layer (360) has a conductive surface (375) disposed at at least a substantially uniform distance above or below the plurality of the runs of the conductive elements. In some cases, the conductive material (360) can have first and second dimensions (326, 336) in first and second horizontal directions which are smaller than first and second corresponding dimensions (324, 334) of the microelectronic device. The conductive material (360) is connectable to a source of reference potential so as to achieve a desired impedance for the conductive elements.