Abstract: Aiming at the problem of mass-transport limitation in the electroforming of microstructures with high-aspect-ratio (HAR), two kinds of numerical models of mass-transport (1-D diffusion model and 2-D diffusion-convection model) are developed. Distribution of flow field and ion-concentration field inside the micro-trench and their effect on mass transport efficiency governed by diffusion, forced convection-diffusion, and complex convection (forced convection and nature convection)-diffusion, respectively, are simulated and analyzed by using Matlab toolbox and Fluent 6.2 fluid simulation software, followed by some experiments to validate the numerical analysis results. The results indicate that diffusion-transport or forced convection transport outside the cavity does well only under the conditions of smaller HAR value (<2) and lower current density (<2 A/dm2); one or more vortex cells that occupy the whole cavity space can be formed in the cavity (aspect ratio = 5) when the natural convection inside the cavity is strengthened and collaborated with the forced convection outside the cavity. The vortex flow rate is about 1/20 ~ 1/2 of the forced convection flow rate, which results in a remarkably better transport efficiency; and experimental results agree well with numerical analysis results.

Key words: Convection-diffusion transport, High-aspect-ratio, Micro electroforming, Microstructure