Spinach-based photo-catalyst for selective plating on polyimide-based substrates for micro-patterning circuitry

This work demonstrates the suitability of spinach extract as a bio-catalyser for the photo-catalysed synthesis of silver nanoparticles on polyimide and polyetherimide, and their suitability as a seed-layer for the formation of conductive micro-track after plating. The study reveals that the extract can accelerate the reaction rates of the photo-patterning process by an order of magnitude, when applied on materials for flexible electronics and 3D printing. The two main components of the extract that can act as photo-catalysers - chlorophylls and plasmatic salts - have been individually studied by energy-dispersive X-rays, UV/VIS spectroscopy and X-ray Diffraction. A simple and well-defined method for extraction of chlorophyll-A (Ch-A) from fresh spinach at 120 ± 20 mg/L, has been developed. The study reveals that the main component enhancing photoreduction rates is due to the ionic salts present in the extract. The spinach extract has been demonstrated to be a valid catalyser to achieve highly conductive, selective electroless copper plating of track features, of thickness 0.5 ± 0.2 µm and conductivity (0.7 ± 0.2) ×107 S/m. 10 µm wide tracks are obtained, and the copper plating withstands the adhesion test. Demonstration of selective, ionic-liquid immersion plating of silver onto electroless copper, highlights a high quality metal protective layer finishing process desirable for reduced waste and toxicity.