Improving Receptor Surface Functionality Using Microchannels For Microchip Assembly Applications

Abstract

The accurate and repeatable manipulation of microchips is a critical challenge in advanced microchip pickand-place applications. Droplet-based manipulation offers a promising alternative to conventional mechanical handling methods due to its low mechanical stress and inherent self-alignment capabilities. However, insufficient control over droplet wetting and spreading on the receptor surface limits placement precision. This study investigates whether microchannels integrated into receptor surfaces can be used to control microdroplet behaviour and enhance droplet spreading in microchip pick-and-place systems. An experimental approach was adopted combining theoretical modelling, femtosecond laser fabrication, structural characterisation, and droplet impact experiments. The governing physical mechanism was analysed using the Gibbs criterion for contact-line pinning and depinning. Microchannels were fabricated in glass using femtosecond laser micromachining, and their geometry and roughness were validated using Keyence optical microscopy. Droplet impact experiments were conducted while systematically varying impact velocity, droplet volume, channel spacing, channel width, and droplet placement. Results demonstrate that impact velocity is the dominant parameter governing channel filling. Increasing the velocity from 0.2 m/s to 0.6 m/s consistently transitions the system from a non-filling regime to full channel filling. Channel spacing strongly influences capillary penetration, while droplet volume and channel width show limited independent effects within the tested ranges. Two operational regimes were identified: Configuration A (filled channels), which stabilises spreading through capillary-driven transport and improves repeatability, and Configuration B (non-filled channels), which promotes anisotropic and directional surface spreading. Additionally, pre-filled channels significantly enhance axial spreading while maintaining transverse confinement, resulting in the strongest directional control. It is concluded that microchannel integration does not inherently increase surface spreading in all cases, but provides a robust mechanism to actively steer, stabilise, and control droplet behaviour. Microchannels therefore represent a viable and versatile design strategy for improving controllability and precision in droplet-assisted microchip pick-and-place applications.