Preparation of monosized copper micro particles by pulsated orifice ejection method

A pulsated orifice ejection method (POEM) has attained mass-production of monosized spherical micro particles of solder. In this method, the micro droplet melts are emitted from a small orifice by applying both mechanical pulses and constant gas pressure to the melt. This paper reports further development of this method for alternative monosized copper spherical particles with a size in the order of 100 mu m. The possibility of the droplet formation was strongly determined by the wettability of orifice material to the melt. Droplets of molten copper could be stably formed at a particularly high contact angle. Using an orifice with the low wettability, monosized copper particles are obtained in a wide range of process parameters such as the rod displacement and gas pressure. Their particle size was also clarified to vary with changes in the two parameters. Especially, the gas pressure may linearly control the particle size from 75 to 120 mu m, which is equivalent to 75 to 120% of the orifice diameter. All monosized particles produced by the POEM have an excellent mono-dispersivity less than 2.0 in standard deviation.