Capillary Self-Alignment of Microchips on Soft Substrates

Abstract

Soft micro devices and stretchable electronics have attracted great interest for their potential applications in sensory skins and wearable bio-integrated devices. One of the most important steps in building printed circuits is the alignment of assembled micro objects. Previously, the capillary self-alignment of microchips driven by surface tension effects has been shown to be able to achieve high-throughput and high-precision in the integration of micro parts on rigid hydrophilic/superhydrophobic patterned surfaces. In this paper, the self-alignment of microchips on a patterned soft and stretchable substrate, which consists of hydrophilic pads surrounded by a superhydrophobic polydimethylsiloxane (PDMS) background, is demonstrated for the first time. A simple process has been developed for making superhydrophobic soft surface by replicating nanostructures of black silicon onto a PDMS surface. Different kinds of PDMS have been investigated, and the parameters for fabricating superhydrophobic PDMS have been optimized. A self-alignment strategy has been proposed that can result in reliable self-alignment on a soft PDMS substrate. Our results show that capillary self-alignment has great potential for building soft printed circuits.

Mapping microscale wetting variations on biological and synthetic water-repellent surfaces

“…Polydimethylsiloxane (PDMS) replica of silicon nanograss was fabricated as described in literature 36 . Cryogenic deep reactive ion etching was used to fabricate the silicon nanograss master on a 100 mm silicon wafer.…”

Surface tension-driven self-alignment

“…Furthermore, assembly of thin, fragile and flexible components is already being tackled through the technique, as well as self-alignment on soft substrates. 174 In contrast to its statics, the dynamics of capillary selfalignment is not yet fully captured within a theoretical model. Besides open theoretical questions, further challenges for surface tension-driven self-alignment include mastering the handling of small liquid volumes: how to controllably and reliably deliver very small amounts of liquids, and how to engineer reliable surface tension applications despite intrinsic variations of liquid volume due to evaporation, spreading and contact angle hysteresis.…”

Fabrication of a Waterborne Durable Superhydrophobic Material Functioning in Air and under Oil

“…These effects were captured in Video S1 (Supporting Information). Being dispersed in water, functionalized clay sheets sit readily on hydrophilic fibers and get coated efficiently all over the surface of cylindrical fibers by strong capillary action and large surface tension force . The extent of water repelling property of the material on fibrous soft surfaces was revealed from the unstable, frictionless movement of water drops on modified paper, demonstrated in Figure S1 and Video S2 (Supporting Information).…”

“…Being dispersed in water, these chemically modified clay sheets sit on fibrous materials efficiently through surface tension forces or strong capillary action and coat it efficiently without affecting the mechanical flexibility of the substrate. This was demonstrated with a coated filter paper (Whatman 44) shown in Figure A.…”

“…Interestingly, the coated thin film functions equally well at both air–solid and oil–solid interfaces, which is due to the controlled surface energy obtained by the incorporated chemical functionalities and hydrophobic effect‐induced enhanced surface roughness during the slow evaporation of water from the coating material. Moreover, surface tension‐induced better and effective binding capability of the clay sheets with soft and fibrous substrates makes it possible to design a flexible waterproof paper, a promising materials platform for paper‐based technologies …”