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Abstract

template require homogenous deposition conditions, which can be complex to monitor. In 2D LIGA, a majority of challenges were addressed and simulated. Griffiths et al. [9][10][11] pioneered LIGA simulation and focused on transport limitations occurring in templates. Nilson and Griffiths [12] added a detailed description of natural convection in templates and Chen and Evans [13] optimized moving boundaries in finite element method (FEM) simulation for electrodeposition. Tsai et al. [14] discussed ion concentration gradients in high aspect ratio with a tertiary current distribution model. Pulsed electrodeposition, a frequently used technique to improve homogeneity of the deposits, was used and modeled by Yeh et al. [15] Similar to the 2D LIGA process, 3D LIGA was used to create complex structures. However, previous work was mainly focused on material properties of these structures, not on the study and description of the electrodeposition into the complex 3D templates. In addition to the already existing difficulties in 2D LIGA, deposition in 3D templates offers multiple additional challenges. Large changes of the active area in vertical direction, bottleneck features within the templates, lateral diffusion and migration of the electrolyte constituents have to be considered. [16] Furthermore, 3D templates can shield and deflect electrolyte current density vectors inducing changes in local current density.To understand the aforementioned challenges, this work exploits 3D nanocrystalline nickel electrodeposition simulation built upon the previously mentioned 2D electrodeposition simulation studies. The simulation is verified by nickel electrodeposition from a nickel sulfamate electrolyte [17][18][19] into 3D microprinted electrode arrays. Nickel is a suitable material for electrodeposition as it is thoroughly researched as well as simulated. Nickel sulfamate electrolytes produce low internal stress deposits, crucial for 3D microstructures. Nickel sulfamate can also be used for pulsed electrodeposition, involving long, low current pulses, another instrumental technique to ensure good filling ratio. [18] To display the potential of the process, we present a new variant of a 3D LIGA process using negative-tone photoresist for the creation of electrodeposition templates and the subsequent stripping of the tone resist. Negative-tone photoresist exhibits very high chemical resistance compared to positive tone resist used mainly so far. [3,7] Negative tone resist offers higher resolution enabling the creation of better-defined templates and increases the possible height of the templates. [20] Furthermore, negative-tone Electrodeposition in combination with templates created by two-photon lithography is used to fabricate dense metallic 3D microcomponents. Nanocrystalline nickel microcomponents deposited from nickel sulfamate electrolyte in 3D templates are presented. Using 3D electrodeposition simulation, different template designs for a bridge-like microcomponent are investigated. The influence of the template design on cur...