Abstract
We have studied electrochemical pulse etching of NiTi shape memory alloy (SMA) sheet for a micromachining application. The effects of pattern width, etching depth and pulse duty ratio on etch rate and side etching have been studied in comparison with DC etching. Etch factor (=etching depth/side etching width) tended to be lower at narrow and deep etched grooves in the case of the DC etching, however, the factor was not influenced by the pattern width in the case of the pulse etching. The etch factor of the pulse etching increased with increasing the etched depth, contrary to the DC etching, because reaction products could be diffused out of the etched groove while the pulse voltage was turned off. The pulse etching is more suitable for narrow and deep micromachining than the DC etching. When the pulse duty ratio was below 50%, the etching rate was proportional to the duty ratio, therefore, the etch rate could be controlled by the duty ratio. When the duty ratio was over 50%, the etch rate did not increase any more, because the diffusion of the reaction products was not sufficient and the electrolytic current decayed during the ON-time of the pulse. In the decayed current region, mirror-like flat etched surface was obtained because of the electrolytic polishing effect. Through etching could be carried out successfully by using a dummy Ni layer on the backside of the sheet; therefore, micro actuators could be fabricated from an SMA sheet by using the electrochemical pulse etching.
