"Investigation of mass transfer inside micro structures and its effect on replication accuracy in precision micro electroforming" by Honggang Zhang was accepted for publication as full paper in <International Journal of Machine Tools and Manufacture>
In this paper, a novel star pattern with a continuously changing line width in the range of 20–320 μm, corresponding to a variable aspect ratio of 0.16–2.5, was firstly proposed for the assessment of mass transfer capability and microstructural replication accuracy. Our results indicated that nickel ion transportation was determined by convection and diffusion, depending on the width and aspect ratio of the micro structure. When a hybrid agitation combining cathode rotating and jetting flow was applied, the mass transfer of nickel ions inside a high-aspect-ratio micro structure achieved a 50% decrease in the thickness of the diffusion layer compared with individual rotating or jetting agitation. This can effectively increase the replication accuracy of high-aspect-ratio micro structures using micro electroforming. This study revealed that the thickness of the diffusion layer in micro electroforming was critical for determining the ion transportation efficiency, and thus the replication accuracy of a high-aspect-ratio micro structure with a narrow entrance. Effective agitation of electroforming equipment and appropriate design of micro structures are critical for high-precision fabrication based on micro electroforming.