Rigid-Flex printed wiring are hybrid constructions consisting of rigid and flexible substrates that are laminated together into a single structure and then sequentially electrically interconnected using plated through-holes (see Figure above). Unlike multilayer flex, the use of plated through-holes is typically a requirement for rigid flex products. Over the years, rigid-flex printed wiring have enjoyed tremendous popularity among military product designers. In more recent years the technology has made inroads into the commercial world.
Rigid-Flex circuit construction is known as a Type 4 circuit as defined by IPC-2223 and should not be confused with a flexible circuit with a rigid stiffener attached (or rigidized flex). Flex circuits with stiffener constructions are simply flex circuits to which a stiffener is attached to support the weight of the electronic components locally. A rigidized or stiffened flex circuit can have one or more conductor layers. Although the two terms sound similar, they represent products that are quite different.
Rigid-flex printed boards are often considered a specialty product for low volume applications because of manufacturing challenges. Rigid-Flex circuits are often used when components are mounted on both sides of the rigid section. Rigid-Flex is more costly than alternative flex designs so ideal applications require maximum usage of three dimensional space. Rigid-Flex is often used in designs that can allow higher costs. Applications include medical, aerospace and military.