Flexible circuits use polyimide films and other foldable substrates to meet the requirements of complex electronic manufacturing applications. They are designed to address problems of space and weight that cannot be resolved with traditional wiring methods and rigid printed circuit boards (PCBs). Flexible circuits such as microelectronic connectors are often designed for specialized configurations and demanding environments. Typically, a flex circuit is made of a flexible, polymer film that is laminated to a thin sheet of copper which is etched to produce a circuit pattern. These patterns can be created on one or both sides of the polymer film. Most microelectronic interconnections use plated through-holes. Often, a polymer overcoat is added to provide electrical insulation and prevent the ingress of dust, dirt, and other contaminants.

Flexible circuits are designed and manufactured in accordance with guidelines such as IPC-221 and IPC-223, standards from the Institute for Printed Circuits (IPC). Flex circuits can be single-sided, double-sided, multilayer, or rigid-flex multilayer. All of these constructions may use stiffeners, plated through-holes, and blind or buried vias. Specifications for flex circuits include copper conductors, substrate material, cover plating options, and circuit protection. Copper conductor specifications consist of thickness range, minimum conductor width, conductor-width tolerance, minimum space between conductors, conductor sidewall angle, and hardness. Substrates include proprietary materials such as Kapton (DuPont) and Apical (Kaneka), as well as liquid crystal polymer (LCP). Typically, substrate thickness is measured in terms of microns. Plating materials such as gold and electroplated nickel carry specifications for purity, thickness, and thickness tolerance. Registration tolerance, thickness range, temperature resistance, pencil hardness, and minimum bending radius are common protection options for flexible circuits.

Flexible circuits are used in many different industries and applications. Some products are designed for medical, military, or aerospace applications. Others are designed for telecommunications systems or the automotive industry. Applications for flex circuits include car radios, cassette players, electronic control systems, hard disk drives, printers, optoelectronics, switching systems, industrial controls, and medical devices such as heart pacemakers and hearing aids. As a rule, flexible circuits such as microelectronic connectors are reliable, compact, and durable. They also provide an extremely high cycle life. Well-designed microelectronic connectors outperform conventional connection technologies such as bent metal, wire mesh, and pin-and-socket.