Study on Electrocrystallization of Pulse Micro-electroforming in UV-LIGA

UV-LIGA is one of the main fabrication technology in MEMS and micro-electroforming is a key procedure in UV-LIGA. Microstructures with small grains, high density and high aspect ratio can be obtained easily by pulse current micro-electroforming than by direct current micro-electroforming. In this study, the relationship between overpotential and time is established by multi-current step method under various pulse current parameters. It is shown that overpotential is the primary kinetics factor that induces electro-deposition on the cathode. On basis of adsorptive layer theory, the concept of positive metal atom in intermediate state is used to analyse the crystal seed production and nucleation. A related model of crystal nucleus formation is set up. The results are also shown that intermediate metal atoms can grow into crystal seeds under certain conditions, and crystal seeds can grow into crystal nuclei. The change trend of nucleus size in the course of crystal growth is forecasted. The crystal grain diameter of Ni microstructure in micro-electroforming experiment is about 8 r_crit, where r_crit is the critical radius of nuclei.