Physical Properties of Paste Synthesized from Wet- and Dry-Processed Silver Powders.

This study compares the characteristics and low-temperature curing properties of pastes prepared from silver (Ag) powders synthesized by either wet powder (WP) or dry powder (DP) processing. The WP synthesis of electrode particles has the advantage of controlling the average particle size and particle size distribution but the disadvantage of producing low-purity, crystalline particles because they are synthesized through chemical reduction at less than 100 °C. Conversely, the DP synthesis of electrode particles has the advantage of producing pure, highly crystalline particles (due to synthesis at high temperatures) but the disadvantage of a high processing cost. WP and DP were used to manufacture pastes for low-temperature curing, and the physical properties of the pastes and the electrode characteristics after low-temperature curing were compared between powder types. Shear stress as a function of the shear rate shows that the WP paste is a plastic fluid, whereas the DP paste is a pseudoplastic fluid, closer to a Newtonian fluid. Screen printing the Ag pastes and curing for 30 min at 130 °C produces a nonconductive WP paste, whereas it produces a DP paste with a conductivity of 61 mΩ/sq, indicating that the highly crystalline DP paste is advantageous for low-temperature curing.

Enhanced Conductivity in Highly Stretchable Silver and Polymer Nanocomposite Conductors.

In stretchable conductors, there is a trade-off relationship between the stretchability and conductivity which makes it difficult to increase both properties simultaneously. From a practical point of view, however, high conductivity is a more important parameter for real-world applications of wearable and mobile electronics. To obtain a highly conductive stretchable conductor, we developed a stretchable conductor composed of silver (Ag) flat-type microparticles, Ag nanoparticles and a polyester binder. The printed stretchable conductor was then sintered using the intense pulse light sintering technique. The effects of different mixing ratios of Ag flat-type particles and nanoparticles on dispersibility, printability, surface properties, conductivity, and stretchability were examined. Increasing the content of Ag-flat type particles in the composite improved dispersibility, printability, and conductivity. The stretchable conductor exhibited the outstanding conductivity of 5.5×106 S/m. Increasing the Ag nanoparticles content increased the stretchability of the conductor. As the nanoparticle content increased to 30%, the stretchable conductor showed the excellent stretchability of 210%, and withstood 2,600 repeated stretching cycles at a fixed tensile strain of 50%. The conductors also exhibited superb foldability during 10,000 repeated folding tests, up to a radius of 1 mm, without any failures.

Printed Electrode for High-Performance Bow-Tie Antenna by Photonic Sintering Process.

Recently, flexible electronic device technology has evolved beyond curved devices with the development of flexible/stretchable devices that can be crumpled or stretched. Both elasticity and durability are essential for these devices, which should have high-conductivity for antennas and repeatability for sensors. In addition, electronic-skins, which can have a direct impact on the human-body, should be harmless to the human-body and should not be deformed by contact with sweat or organic matter. In this study, PDMS substrates were used to satisfy the above conditions. PDMS is used to fabricate human-friendly, flexible/stretchable substrates, and it has excellent repeat durability characteristics. To improve the adhesion of these PDMS films and electrodes, conductive paste was produced based on PDMS resins of the same properties. In addition, two types of Ag particles were selected as conductive fillers because the electrode characteristics of the antenna application requires excellent conductivity, and conductive paste were produced using flake Ag, which could affect conductivity, and Ag nanoparticles that affect stretchability and repeatability. The paste was applied using a high-efficiency printing technique. The printed electrodes were cured in a thermal oven. For higher conductivity, photonic-sintering was carried out during post-processing. As a result, 1.1117×106 (S/m) had excellent conductivity, performed well in repeated tensile-durability experiments of 30% to 100 times, and produced a bow-tie antenna for the above electrodes. As a result of tensing up to 35% through a Network-Analyzer, there was no performance change in the resonance-frequency or return-loss values, and excellent electrodes were developed that would achieve excellent performance even if they are applied in the sub-frequency area of 5G-antennas in the future.