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96 DESIGN007 MAGAZINE I NOVEMBER 2020 Next-Generation Flex Circuits: Printable Is Compatible With Flexible Copper foil is the primary conductor material used in traditional flexible circuits. These thin metallic foils laminated on heat-resistant plas- tic films are called copper-clad laminates. Pho- tosensitive chemicals are coated on the copper foil, and circuit patterns are printed. Next, a process called photolithography or subtrac- tive is used, and the result is the production of electronic circuits (once unnecessary material is removed). The photolithography process is now popu- lar in the printed circuit industry, and circuit manufacturers have an etching line process in their basic manufacturing. The chemical etching is not environmentally friendly. Its by- products are considered chemical waste and require supplemental recycling; this adds cost to printed circuit products. Thick-film circuits are another option to gen- erate flexible circuits. They are created using a printing process that is very simple. Conduc- tive ink (such as silver and graphite conduc- tive powders) is printed on plastic films from a traditional screen-printing process, dried, and baked in a thermal oven. Copper-clad lami- nates are not required, so material expenses are minimized. Almost any material can be used (papers, textiles, or rubber sheets) with the flexibility from printing. Wearable and medical devices require abnor- mal performances such as stretchability, trans- parency, moisture permeability, and more. These new products and applications require the use of flexible circuits and are dependent on non-traditional electronic materials. Con- ductive inks are very compatible with these EPTE Newsletter by Dominique K. Numakura, DKN Research LLC