Patterning of fine particles by means of supercritical CO₂

Abstract

A new method for positioning fine particles on surfaces has been developed. Supercritical CO₂-assisted printing (SCAP) was utilized to spray and deposit the prepared particles on solid substrates. By means of masks, regular arrays of the particles were successfully created in designed patterns. Typical size of the particles employed was in the range of submicrometers to micrometers. Supercritical CO₂ (sc-CO₂) acted as an effective dispersion and transportation medium in this process. Good dispersion state of the particles was achieved by stirring in sc-CO₂. Fabrications of fine patterns of solder particles and other ceramic powders on smooth plates were demonstrated. Under optimum operation conditions, fine structures of 30 μm in width can be formed in a minimal pitch of 60 μm. Ultra high yield of the patterning was obtained since the deposition rate could be as high as 100 μm per second. Main factors affecting the process were discussed. The research results indicate that the SCAP is a potential approach to the organization of fine particles into microstructures. Hopefully, it may find wide industrial applications where lithography is needed, such as solder printing in surface mounting technology for higher density electronics and thick film fabrication for miniature systems.