In one embodiment, the channels have depths in the range of about 12.5 to 75 ??m (0.5 to 3 mils), and preferably about 25 to 50 ??m (1 to 2 mils). [0095] The conductive traces are typically formed using a conductive material 56 such as carbon (e.g., graphite), a conductive polymer, a metal or alloy (e.g., gold or gold alloy), or a metallic compound (e.g., ruthenium dioxide or titanium dioxide).