Parallel micro component-to-substrate assembly with controlled poses and high surface coverage

Abstract

We demonstrate a novel parallel micro assembly process based on both shape recognition and capillary-driven self-assembly in an air environment. Mechanically diced 790 µm square silicon parts with flat or step edges were used for proof-of-concept demonstrations. Each part had only one hydrophobic 790 µm × 790 µm face and its other faces were hydrophilic. On a vibrating plate, tumbling parts were captured by cavities having an opening clearance that only admitted a single part standing vertically. The trapped parts were then transferred to a substrate having an array of receptor sites covered with water droplets. The flat-edge parts attached vertically to these sites and then capillary forces from water condensate turned them to face the substrate with their 790 µm × 790 µm hydrophilic faces. The step-edge parts attached at a tilted angle due to their featured edges and then a pressing plate laid them down. This process assembled micro parts to 1000 densely packed receptor sites in about 2 min with a defect rate of ∼1%. A single batch assembly process achieved 31% surface coverage, and a second batch doubled the ratio to 62%.