Post processing of microstructures by PDMS spray deposition

A method of depositing polydimethylsiloxane (PDMS) onto microfabricated surfaces by spray coating is presented. Low-viscosity PDMS combinations suitable for spraying are developed by mixing Dow Corning Sylgard 184 with 200 Fluid 20 cSt, and also by dilution with hexane. Spray coating is carried out on rotating substrates using blank Si wafers. Film quality is characterised with mechanical and optical profilometry and process parameters are optimised to yield micron-scale thickness with low surface roughness. High gas pressures and substrate motion improve the quality of sprayed films. The coating process is extended to microstructures formed by lithography and etching of silicon, and it is found that heating to accelerate cross-linking improves conformal coverage. The material can be used in many applications requiring spin coated or cast PDMS. Spray coated PDMS can be used as an adhesion layer and construction of microfluidic channels is demonstrated by plasma activated bonding. The coatings can also adsorb alkanethiols and micro contact printing is demonstrated using embossed, spray coated PDMS and using spray coated etched stamps.