Micro-electroforming under periodic vacuum-degassing and temperature-gradient conditions

Pinhole defects in deposits are one of the problems which have not yet been solved fundamentally when micro-electroforming of nickel into high-aspect-ratio (HAR) micro-moulds. To reduce the voids of micro-electroformed parts, a new micro-electroforming technique carried out under periodic vacuum-degassing and temperature-difference conditions was introduced in this paper. The effect of vertical temperature gradient between the bath electrolyte (low temperature) and the electrodeposition surfaces (high temperature) on the existing natural convection motion within the HAR micro-trenches was analyzed numerically, and the mechanism of vacuum degassing was also introduced. To investigate the feasibility of the exploited technique, a series of experiments were performed using special equipment developed by the authors, followed by an evaluation of the surface morphology of nickel micro-electroforms. Experimental results showed that, when comparing with the conventional electroforming practices, a significant reduction in pinhole defects of the samples electroformed by the novel process was obtained. The combined electrodeposition conditions with periodic vacuum degassing (20 kPa) and vertical temperature gradient (25 °C/65 °C) between the bath electrolyte and the electrodeposition surfaces help to reduce the formation of gas bubbles as well as to speed up the elimination of the dissolved gas during the micro-electroforming of nickel.