A passivated electrode batch /spl mu/EDM technology for bulk metal transducers and packages

Batch mode micro-electro-discharge machining (muEDM) 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 mum tall SU-8 molds. The tools were then sputter coated with 500 Aring of Ti and 1000 Aring or 2000 Aring 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 mum wide, 25 mum tall, 1 mm long unreleased stainless steel beams