The advent of new emerging technologies in materials deposition during recent years, along with new experimental tools, as well as substantial progress in high performance computing, have resulted in a growing research thrust directed to understanding of the nature of the high speed two-phase flows in micro-scale. In this paper two types of so-called “direct write” deposition techniques used for printed electronics applications will be discussed from theoretical and experimental viewpoints.
Aerosol Beam Direct-Write. It is shown that under proper conditions an aerosol flow through micro-capillary reveals new manifestation of microfluidics: the Saffman force acting on aerosol particles in gas flowing through a micro-capillary becomes significant thereby causing noticeable migration of particles toward the center line of the capillary. This finding opens up new opportunities for aerosol focusing, which is in stark contrast to the classical aerodynamic focusing methodologies. The lines deposited by this method are shown to exhibit widths of 5 micrometers – superior to ink-jet.
Cold Spray Direct-Write. The basic principle of the cold spray process is the following. A high velocity gas jet is used to accelerate solid particles and spray them onto a substrate. The kinetic energy of the particles helps these particles to plastically deform on impact and form splats, which bond together to produce coatings. The speed of solid particles in cold spray process is much higher than speeds of aerosol particles in aerosol beam deposition process. Cold spray is a relatively young process and still considerable efforts are needed to understand and control the process, as well as develop methods to focus the beam of solid particles in a similar way it is done for aerosol beam direct-write.
This material is based on research sponsored by the Department of Energy under DOE-FC36-08GO88160, Defense Microelectronics Activity (DMEA) under agreement H94003-09-2-0905, North Dakota EPSCoR and National Science Foundation grant number EPS-0814442.