Low temperature processing of copper conductive ink for printed electronics applications

Abstract

Silver conductive ink is widely used to form conductive electrode in printed electronics applications. However, rapid rise in silver price is driving the need for alternative conductive ink that is significantly more cost-effective [1]. Copper based conductive ink is a promising alternative due to inherently lower material cost compared with silver conductive ink. In addition, copper conductive ink will provide solderable printed interconnects unlike those using silver conductive ink [2]. A key limitation of copper based conductive ink is inherently higher electrical resistivity compared with silver conductive ink. This study focuses on large area screen printing, low temperature ink curing and electrical characterization. The selected copper conductive ink has a metal loading of 65wt.%, and viscosity range of 25,000 to 35,000 cps. Two test vehicles on Polyethylene Terephthalate (PET) substrate were used for performance characterization: 1) printed conductive circuit 2) printed frequency selective electromagnetic interference (EMI) shield. By optimising key screen printing parameters including screen mesh size, printing speed and squeegee pressure, a minimum printed line width of 100µm was achieved for a printed area of 500mm × 500mm. A low curing temperature of 60°C was achieved by optimising air-flow rate and curing profile. Good printing uniformity was achieved, translating to a 10% tolerance for measured electrical resistance in printed conductive circuit. High-frequency characterization was also performed on printed frequency selective EMI shield. A shielding effectiveness of 24 dB was achieved at the tuned rejection frequency of 1.8 GHz for a narrow band topology. The shielding performance is comparable with that of printed frequency selective EMI shield using silver conductive ink.