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DECEMBER 2022 I DESIGN007 MAGAZINE 73 New wave printing technologies: • Inkjet printing • R2R photolithographic • Plasma printing • Direct laser imaging or ablation Of these enabling technologies, screen print- Base Materials and Inks Printed electronics uses flexible sub- strates, which lowers production cost and allows fabrication of mechani- cally flexible circuits. While inkjet and screen printing typically imprint rigid substrates like glass and silicon, mass printing methods almost exclusively use flexible foil and paper. Additional substrate alternatives include polyeth- ylene terephthalate (PET), a common choice due to its low cost and higher temperature stability; polyethylene naphthalate (PEN); polyether ether ketone (PEEK), a colorless organic polymer thermoplastic used in engi- neering applications; and polyimide (PI) foil. Paper's low cost and manifold applications make it an attractive substrate, but its rough- ness and absorbency make it problematic for electronics. Low roughness and suitable wet- tability, which can be tuned pre-treatment (coating, corona), are important criteria for substrates (Table 2). Organic and inorganic materials are both used for printed electronics. Ink materials must be available in liquid form for solution, dispersion, or suspension. ey must function as conductors, semiconductors, dielectrics, or insulators. Material costs must be appropriate for the application. Most of the attention given to materials has appropriately centered on conductive inks, especially silver. Silver is the most conduc- tive commonly used metal for making circuit conductors. Membrane switch circuits, which operate at relatively high voltages and low cur- rents, have been printed onto polyester base materials using silver inks for more than a few decades. e challenge has been getting these circuits to have the bulk conductivity associ- ated with copper. Common inks have con- ductivities that hover around 10% of copper and are not generally suitable for higher per- formance applications that operate at lower voltages or may require more power. Several ing has been around the longest and is still widely used in production today. Membrane switch technology, part of the printed elec- tronics family, heavily relies on screen printing to make products. Technical details are shown in Table 1 for speed, resolution, film thickness, and ink viscosity. Table 1: Popular printing methods for printed electronics and their technical attributes 2 Table 2: Base materials for printed electronics and their suitability 2