A Passivated Electrode Batch Edm Technology for Bulk Metal Transducers and Packages

Batch mode micro-electro-discharge machining ( EDM) is a lithography-compatible microfabrication method suitable for making devices from bulk metals, including stainless steel. In high-density patterns, spurious discharges through debris can cause workpiece edge rounding, fast tool wear, and mushroom-shaped metal recasting of the tool. This paper reports a Si coating technique that acts as a discharge barrier on the sidewalls of batch Cu tools to diminish these effects. Copper tools were fabricated by electroplating into 80 m tall SU-8 molds. The tools were then sputter coated with 500 Å of Ti and 1000 Å or 2000 Å of Si. The Si on the top of the tool was removed by EDM on a flat surface. As a result, discharges occurred primarily at the top of the tool during machining. This provided a 93% reduction in mean tool wear, a 78% improvement in machining depth uniformity, more vertical sidewalls, and sharper workpiece edges. These results were obtained while machining 4.5 m wide, 25 m tall, 1 mm long unreleased stainless steel beams.