Self-assembly of micro-parts using electrostatic forces and surface tension

Abstract

This investigation regards self-assembly of parts by means of electrostatic forces and surface tension. Self-assembly is a rather novel technology to assemble and align small parts on a substrate without the help of additional machinery. Mainly, the state-of-the-art technologies for self-assembly rely on fundamental physical principles, such as surface tenisons, electrostatic forces or gravitational force. Future perspectives are integration of photonic devices and assembly of electronic micro-systems. The present publication discusses two different concepts. One has been described in the literature by third parties and involves the alignment of parts by utilising the surface tensions of small adhesive pads, which are selectively coated on hydrophobic alignment structures. Especially, how the layout of such alignment structures and their dimensions affect the process flow have been considered in the present investigation. The second concept is a novel approach to accomplish self-alignment of micro-structures with electrostatic attraction. Several complementary and electrically conductive micro-structured patterns serve as binding sites for the alignment in this approach. Since the fluidic medium is an adhesive in the presented experimental work it is conceivable to permanently bound the part to the substrate when the alignment has been accomplished. Firstly, modelling and computations have revealed the magnitude of the alignment forces, acting on parts, for these approaches. Secondly, self-assembly experiments have demonstrated their feasibility. For processes that utilise electrostatic forces the experimental work with a variety of binding sites with different shapes and sizes has revealed promising results. Parts, comprising 4.5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> structured square-shaped binding sites with a size of 10times10 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , were successfully self-aligned in experiments. Furthermore, parts with alignment structures with a size of 1000 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a surface area ratio of the alignment structures to the entire part of about 2% could be aligned successfully. The fact that only a small area of the part has to be covered with alignment structures is unique in comparison to related research. Finally, modelling and computations have approved that electrostatic forces can be considerably stronger than surface-tension-driven forces.