Droplet self-alignment: High-precision robotic microassembly and self-assembly

Abstract

Droplet self-alignment is a microassembly process where the surface tension of liquid aligns microparts to a substrate. Traditionally, solder has been used, but using unconventional liquids, such as water or adhesives in air, has several attractive properties. Water is compatible with most materials and processes, it is easy to achieve good droplet confinement and it evaporates quickly. Adhesives have the ability to make irreversible bonding. Nevertheless, achieving adhesive droplet self-alignment is difficult, because adhesives generally have a small surface tension. Both liquids can be adapted to low temperature processes.\nThis thesis describes water droplet self-alignment in high detail, by measuring yield, accuracy, capabilities to build complex structures, and speed of the process. Experiments have been done using an environment-controlled microassembly station and recorded using high-speed microscopy. The results show that droplet self-alignment can achieve industrially relevant performance, and the results may be used as a basis of future process design rules.\nA new, microfabricated silicon capillary gripper has been developed, which picks microparts using the surface tension of water. Pick-and-place experiments showed that microparts are self-aligned to the tool by droplet self-alignment. The developed gripper enables handling microparts accurately and delicately.\nFinally, new patterned oleophilic / oleophobic surfaces have been developed that enable self-alignment using oil-like liquids, including low-temperature curable adhesives. Self-alignment using an industrial adhesive on the patterns was demonstrated. While this surface was used for droplet self-alignment, a micropatterned oleophilic / oleophobic surface may well have other applications outside droplet self-alignment.