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Investigation of mass transfer inside micro structures and its effect on replication accuracy in precision micro electroforming
International Journal of Machine Tools and Manufacture ( IF 14.0 ) Pub Date : 2021-03-18 , DOI: 10.1016/j.ijmachtools.2021.103717
Honggang Zhang , Nan Zhang , Fengzhou Fang

Micro electroforming is a promising electrodeposition-based precision replication technique for the fabrication of microstructured moulds. In this process, a poor mass transfer inside the micro structure with a high aspect ratio significantly affects the replication accuracy of the mould. 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. Based on the designed patterns, the effects of different flow fields (cathode rotating/jetting agitation) on the ion concentration distribution and thickness of the diffusion layer were investigated theoretically. Our simulation indicated that nickel ion transportation was determined by convection and diffusion, depending on the width and aspect ratio of the micro structure. When the aspect ratio was higher than 1, the diffusion of nickel ions dominated the mass transfer. 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 will significantly affect the replication accuracy. Star-pattern micro electroforming experiments with the hybrid agitation were conducted to validate the effect of mass transfer on the pattern replication accuracy. The results indicated that the maximum replication relative error of the height and aspect ratio was ~16% and ~10%, respectively, with a designed high aspect ratio of 2.5 at a feature width of 20 μm. Both experiments and simulations consistently indicated that the thickness of the diffusion layer determined the replication accuracy of high-aspect-ratio features, in which the limiting current density was constrained by the thickness of the diffusion layer because of the ion transportation efficiency. Hybrid agitation can effectively reduce the thickness of the diffusion layer inside high-aspect-ratio feature, thus increasing the limiting current density. This can effectively increase the replication accuracy of high-aspect-ratio micro structures using micro electroforming.



中文翻译:

微结构内部传质及其对精密微电铸中复制精度影响的研究

微电铸是一种有前途的基于电沉积的精密复制技术,用于制造微结构模具。在此过程中,具有高纵横比的微结构内部不良的质量传递会显着影响模具的复制精度。在本文中,首次提出了一种新颖的星形图案,其线宽在20-320μm范围内连续变化,对应于0.16-2.5的可变长宽比,用于评估传质能力和微结构复制精度。根据设计的模式,从理论上研究了不同流场(阴极旋转/喷射搅拌)对离子浓度分布和扩散层厚度的影响。我们的模拟表明,镍离子的输送取决于对流和扩散,具体取决于微结构的宽度和纵横比。当长径比大于1时,镍离子的扩散主导了质量传递。当应用结合阴极旋转和喷射流的混合搅拌时,与单独的旋转或喷射搅拌相比,高纵横比微结构内部的镍离子的传质使扩散层的厚度减小了50%。这将严重影响复制准确性。通过混合搅拌进行星型微电铸实验,以验证传质对图案复制精度的影响。结果表明,高度和长宽比的最大复制相对误差分别为〜16%和〜10%,设计的高长宽比为2.5且特征宽度为20μm。实验和仿真均一致地表明,扩散层的厚度决定了高纵横比特征的复制精度,其中极限电流密度由于离子传输效率而受到扩散层厚度的限制。混合搅拌可有效减小高纵横比内部扩散层的厚度,从而增加极限电流密度。这可以有效地提高使用微电铸的高纵横比微结构的复制精度。5的特征宽度为20μm。实验和仿真均一致地表明,扩散层的厚度决定了高纵横比特征的复制精度,其中极限电流密度由于离子传输效率而受到扩散层厚度的限制。混合搅拌可有效减小高纵横比内部扩散层的厚度,从而增加极限电流密度。这可以有效地提高使用微电铸的高纵横比微结构的复制精度。5的特征宽度为20μm。实验和仿真均一致地表明,扩散层的厚度决定了高纵横比特征的复制精度,其中极限电流密度由于离子传输效率而受到扩散层厚度的限制。混合搅拌可有效减小高纵横比内部扩散层的厚度,从而增加极限电流密度。这可以有效地提高使用微电铸的高纵横比微结构的复制精度。其中由于离子传输效率,极限电流密度受到扩散层厚度的限制。混合搅拌可有效减小高纵横比内部扩散层的厚度,从而增加极限电流密度。这可以有效地提高使用微电铸的高纵横比微结构的复制精度。其中由于离子传输效率,极限电流密度受到扩散层厚度的限制。混合搅拌可有效减小高纵横比内部扩散层的厚度,从而增加极限电流密度。这可以有效地提高使用微电铸的高纵横比微结构的复制精度。

更新日期:2021-03-23
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