With increasing demands for more economic routes to the manufacture of electronic devices incorporating polymer- based printed circuit boards (PCBs), various techniques for the fabrication of microelectronic devices, including screen printing, nano-imprinting, inkjet printing, and direct printing, are generating increasing interest. Among these methods, inkjet printing is considered to be an economical and highly functional technology for the microscale patterning of metallic traces in microelectronic devices. Conventional lithographic processes are well developed but include multiple steps that are time consuming, uneconomical, and not versatile towards corrective repatterning However, the employment of inkjet printing can solve many of the problems in a facile and effective manner. The inkjet printing method allows for the patterning of conductive traces onto a substrate in one step, therefore reducing the time, cost, and space consumed and the toxic waste created during the manufacturing process. Nanomaterials are considered to be highly useful for application of materials through inkjet printing technology based on size-dependent mesoscopic properties such as enhanced dispersibility, melting point depression below that of the same bulk material based on more significant surface energy instability, and greater compatibility with various chemical and physical environments due more significant effects from interchangeable surface coatings. Inkjet printing technology employing conductive silver inks has been developed recently in order to manufacture low-cost disposable electronics, such as smart packaging, RF-ID tags, and digital calendars. However, silver as a conductive material has problems due to ion migration at relatively high-temperature and humidity conditions as well as cost-benefit issues compared to copper, which is significantly less expensive for virtually identical bulk conductivities. In this research, a large-scale (5 l), high-throughput (0.2 M) process for the synthesis of copper nanoparticles was developed using a modified polyol process that includes chemical reduction and hot addition. Furthermore, these copper nanoparticles were dispersed into an ether-based solvent, patterned onto various substrates through inkjet printing, and then converted into conductive metallic traces through a relatively low-temperature, reductive sintering process. The results are optimistic, however, there are some disadvantages of copper which must be overcome are that the copper ion is not easily reduced under mild reaction conditions and copper nanoparticles tend to be easily oxidized in air under ambient atmospheric conditions in comparison to noble metals like gold and silver.
To read more: Lee, Youngil; Choi, Jun-rak. “Large-scale synthesis of copper nanoparticles by chemically controlled reduction for applications of inket-printed electronics” Nanotechnology. 19(2008).