Conductive ink is an advanced ink which is used to draw or print circuits on various substrates that can conduct electricity and are used in printed electronics. Conductive ink printing usually uses common printing equipment i.e. a printer suitable for defining patterns on material, e.g. flexography, screen printing, gravure, offset lithography, and inkjet. They are the dominant conductive ink technologies, serving a range of markets such as photovoltaics, switching membranes, electromagnetic interference shielding etc. Conductive inks are based on the metallic nanoparticles which serve as a conduction medium for the electricity. Copper and silver nanoparticles or flakes and carbon nanotubes are currently used as conductive materials in commercially available products. There are numerous companies producing conductive ink products such as Henkel, Ink Tec, Methode Electronics, Inc., DuPont, Microcircuit Materials, Sun Chemicals, ID Tech Ex, Plextronics, Inc., Nova Centrix, etc.

Before the dawn of nanotechnology, the most conductive materials for such inks were charge transfer complexes and conductive polymers. The emerging nanotechnology has replaced these materials with metallic and carbon nanomaterials. The most important part of the electronic devices is their guided pathway structure for electricity conduction by connecting various components of the device like transistor, electronic gates etc. This pathway structure fabricated by depositing the metals by different methods like photolithography, vacuum deposition, screen printing and inkjet printing. In commercialization, there is always a gap to develop methods to make them cheaper and quick with high quality. In electronics industry, conductive inkjet printing technology with the use of inks based on metal nanoparticles, metal-organic decomposition ink is a very attractive, direct, fast, scalable and cost effective metallization technology. While none inkjet printing methods have disadvantages like high curing temperatures, difficulty in achieving fine feature size and often a non-smooth surface obtained. A major challenge in applying inkjet techniques for the deposition of functional materials is the formulation of suitable inks. Electrical resistivity is the inverse measurement of the conductor’s performance after sintering process followed by printing. Sintering is a process of joining of metal particles at a temperature below the melting point of the metal so that they can conduct electricity continually. Due to the Brownian movement, the aggregation of metal nanoparticles in the colloidal solution (ink) before printing overcome with addition of stabilizing agent by two mechanisms, electrostatic and steric. The other hurdle is oxidation of metal nanoparticles which is also tackled by the stabilizing agents (ionic or non-ionic dispersant or polymer) which reduces the oxidation rate.

Silver nanoparticles are inkjet printable, need low curing temperature, have close packing, and fine feature size and they have higher conductivity. They are prepared with a range of manufacturing techniques including chemical reduction method and evaporation-condensation etc. Copper nanoparticles are cheaper than silver having reasonable conductivity however preventing their oxidation and stabilizing the ink limit the cost reduction. Graphene has advantages of its high performance and mechanical flexibility; however, there is no obvious way to manufacture it cheaply at large scale.

The major applications of metal conducting inks are in photovoltaic cells, membrane switches, thin film transistors, electroluminescence devices, displays, automotive, rear view mirror defrosters, solid-state lighting, sensors, radio-frequency identification (RFID) antennas and most of all printed circuit boards. RFID is the transfer of data wirelessly through electromagnetic fields, for the purposes of automatically finding and tracking tags attached to objects which could contain electronically stored information used in many industries. Touch control buttons are replacing mechanical switches, in which silver inks are screen printed onto two polyester film layers separated by spacer layer, and when physically depressed, the two silver traces make a connection. Transparent conductive ink is a screen-printable, electrically conductive ink ideal for touch-screen and other applications where fine feature printing is required. In conclusion, conductive inks allow engineers to develop smaller and powerful electronics that can be manufactured in some footprints. These inks offer a more economical way to lay down modern conductive traces. The conductive inks are widely used today in varied applications and have become a necessity of the modern electronic world.

Author- Dr. Muhammad Irfan Majeed and Allah Ditta Department of Chemistry, University of Agriculture Faisalabad