Influence of the electrode distance and metal ion concentration on the resulting structure in electrochemical micromachining with structured counter electrodes

In this contribution a novel approach to Electrochemical Micro Machining (EMM), utilizing a structured counter-electrode with an integrated microfluidic channel, is presented. The process is capable of transferring numerous structures in parallel. The structure was defined by SU-8 photoresist. A 20μm high fluidic channel from the same material simultaneously acting as a spacer was applied on top of the electrode. During the structuring process, 3M NaNO3 was pumped through the channel and the applied current density was 100 A/cm2. Since the current density is significantly higher than in previous works, it can be assumed that the faradic component of material removal predominates the non-faradic part due to the double layer. A FEM simulation using COMSOL Multiphysics shows the dependence of the material removal rate to the concentration of Fe3+ ions. The influence of different process parameters on the etch profile and the spatial resolution is investigated in theory and in practical tests. Computational and experimental results show a removal rate of 7.5μm/As to 8.5μm/As (As=Ampere seconds) which is in accordance to the theoretical value of 7.7μm/As calculated with Faraday's first law for Fe3+ ions.

•We use a structured cathode with an integrated microfluidic channel.•The working distance is 20μm.•The process is simulated with COMSOL Multiphysics.•Experiments are conducted at a current density of 100 A/cm2.•At high current densities the effect of non-faradic components can be neglected.