A substantially uniform layer of a metal is electroplated onto a work piece having a seed layer thereon. This is accomplished by employing a “high resistance ionic current source,” which solves the terminal problem by placing a highly resistive membrane (e.g., a microporous ceramic or fretted glass element) in close proximity to the wafer, thereby swamping the system's resistance. The membrane thereby approximates a constant current source. By keeping the wafer close to the membrane surface, the ionic resistance from the top of the membrane to the surface is much less than the ionic path resistance to the wafer edge, substantially compensating for the sheet resistance in the thin metal film and directing additional current over the center and middle of the wafer.