Three-dimensional microstructures fabricated by multi-step electrochemical aluminum-foil etching

Abstract

We present a fabrication process for three-dimensional (3D) microstructures using multi-step electrochemical etching of metal foils. The conventional electroplating process for 3D metallic microstructures is complex, expensive, and time-consuming. In this thesis, we propose a multi-step electrochemical metal foil etching process which offers advantages of simple, cost-effective, and fast process with uniform and well-controlled material property. In this study, we performed single-step electrochemical etching of 2D cantilever array and multi-step electrochemical etching of 3D micro probe array using aluminum-foils of 4.5cm × 7cm × 0.2mm. We decided the electrochemical etching potential of 15 V and the electrolyte temperature of 10 °C through preliminary electrochemical etching experiments. In the electrochemical etching of 2D cantilever array, the average depth etch rate and the average bias etch rate were measured as 1.50 ± 0.10 μm/min, and 0.77 ± 0.03 μm/min, respectively. Based on single-step etching results, we designed and fabricated 3D micro probe array for two-step electrochemical etching. After the first electrochemical etch step for the tip formation, we performed the second electrochemical etch step for the cantilever fabrication. The fabricated probe array showed the height and lateral dimension errors of 15.5 ± 5.8 % and 3.3 ± 0.9 %, respectively. The surface roughness was improved from 154.7 ± 52.7 nm on the bare aluminum-foil to 37.4 ± 9.6nm on the fabricated micro probe array. In this thesis, we proposed and demonstrated the multi-step electrochemical aluminum-foil etching process for a simple, cost-effective, and timesaving 3D metallic microstructure fabrication applicable to semiconductor probe cards, micro cantilever sensors, and biological electrode arrays.