Silver Hybrid Paste for Improvement of Radio Frequency Characteristics

Abstract

Printed electronics based on nanomaterial has been a potential alternative to conventional electronic technology and is favorable to polymer material. However, printed circuit has insufficient electrical performance and mechanical reliability. We designed two kinds of Ag hybrid pastes to overcome obstacles of printed electronics. One is Ag nanoparticle (30-50 nm) mixed with Ag nanowire (aspect ratio = 1:200). The other is Ag nanoparticle mixed with Ag flake (2.5-3.5 µm in diameter). Ag hybrid pastes were manufactured with hybrid Ag content (70 wt. %), dispersing agent (solvent: diethylenglycol), and binder (ethyl cellulose dissolved in α-terpineol). Ag hybrid paste was screen-printed on polyimide (PI) substrate and sintered at 200 °C for fabricating flexible circuit board. We simulated coplanar waveguide (CPW) pattern before measuring S-parameter with 50 Ω matching. A Network analyzer and Cascade's probe system in the frequency range from 100 MHz to 20 GHz were employed to analyze radio frequency characteristics of printed Ag circuit. In the simulation results, return loss was minimized and Insertion loss was maximized at 6.1 and 12.25 GHz (resonance frequency). S-parameter was measured prior to and after 100,000 bending cycles. Bending stress deteriorated radio frequency characteristics of printed circuit. However, hybrid Ag circuit showed diminished change of insertion loss. Improved electrical and mechanical characteristics were achieved with Ag hybrid paste. Microstructures were analyzed with field emission scanning electron microscope for identifying crack behavior of printed circuit.