Low-height sharp edged patterns for capillary self-alignment assisted hybrid microassembly

This paper studies the hybrid microassembly of 300 mu m (L) x300 mu m (W) x30 mu m (H) microchips on sharp edged patterns with different edge heights. Hybrid microassembly combines the robotic pick-and-place technique and the droplet based surface tension driven self-assembly technique, where the robotic pick-and-place handling tool is used for coarse positioning and the droplet self-assembly technique is used for high-accuracy self-alignment. Spreading of the liquid outside the pattern leads to failure in self-alignment. Sharp edge on a solid surface is known for enabling contact line pinning according to Gibbs inequalities, which prohibits spreading of the liquid. Topological patterns featured with the sharp edge can be used as the receptor site for surface tension driven self-alignment. However, it is unclear how high the sharp edged pattern should be to achieve successful self-alignment in hybrid microassembly. In this paper, sharp edged topological patterns with five different edge heights: 70 nm, 140 nm, 280 nm, 540 nm and 1,050 nm, have been fabricated and tested with water to investigate the influence of the edge height on the hybrid microassembly. The experimental results indicate the edge height affects both the contact line pinning and the self-alignment process. Water droplet can successfully pin at the edge of patterns higher than 280 nm. Self-alignment can reach 100 % success rate on the patterns with edge height of 1 mu m when the initial placement error is below 150 mu m.