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106 DESIGN007 MAGAZINE I JANUARY 2022 Calling Out Materials for Flex Circuits and Getting it Right An excerpt from e Printed Circuit Designer's Guide to... Flex and Rigid-Flex Fundamentals by Anaya Vardya, American Standard Circuits. Only a limited number of material types are used in flex circuit manufacturing; however, materials and material callouts are the source of many phone calls between designers and fabricators, mostly for the purpose of seeking clarification. e following are some of the top recurring issues. Missing Dielectric Material Callouts Flexible and rigid-flex circuits are manufac- tured using numerous types of materials to meet a wide array of cost targets and perfor- mance requirements, both physical and elec- trical. Because of this variety, relative to the prospective concerns related to each choice, it is vitally important that the designer provide detailed information about the dielectric mate- rials to be used. It is recommended that design- ers educate themselves about the choices avail- able in terms of cost and performance. e Internet is packed with easily tapped informa- tion about flexible circuit materials and how they might be used. e PCB fabricator can also help with this topic. e basic flex mate- rial types are: • Adhesiveless materials, which have no acrylic bonding the copper to the polyimide dielectric • Adhesive materials, which have acrylic bonding the copper to the polyimide dielectric • Flame retardant and non-flame retardant laminates, coverlayers, and bond plys