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Grain refinement, surface smoothening, and compressive strength enhancement of Au films were achieved by pulse electroplating using non-toxic sulfite-based electrolyte. The estimated grain size of the Au film prepared by pulse electroplating was 10.5nm, and it was much smaller than the grain size of the Au film prepared by constant-current electroplating, which was 22.8nm. This can be attributed to the increase in the nucleation rate during the on-time period. The mechanical strength of the Au films in micro-scale was also evaluated. The pulse electroplated Au micro-pillar acquired a high compressive strength of 800MPa, and it was larger than the constant-current electroplated micro-pillar, which was 600MPa. The high strength is presumably due to the grain-boundary strengthening known as the Hall-Petch effect. The compression test also revealed that the pulse electroplated Au micro-pillar possesses better ductility and malleability than that fabricated by constant-current electroplating.

Influences of pulse plating parameters on chemical composition, grain size, morphology, and mechanical property of Au-Cu alloy films electrodeposited with an Au-rich sulfite-based electrolyte were investigated. A wide range of Cu concentration (w Cu ) varied from 3.5 to 26.7 wt% was attained in the Au-Cu films. The galvanic displacement reaction occurred during the off-time period showed great influences on the composition and the grain size. Meanwhile, surface morphology of the Au-Cu films was interrelated with the alloy composition. An increase in the pulsed current density lead to roughening of the surface, and smoothening of the surface was achieved by promoting the displacement reaction. Micro-mechanical properties of the Au-Cu films were evaluated by micro-compression tests for applications as movable micro-components in electronic devices. A pronounced high yield strength at 1.38 GPa was achieved in the Au-Cu film with the smallest grain size at ca. 4.40 nm and the w Cu at ca. 15 wt%, which is suggested to be a result of synergetic effects of grain boundary strengthening and solid solution strengthening mechanisms.

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