Rigid-Flex printed circuit boards are using a combination of flexible and rigid board that are permanently connected to one another. And they are designed in a 3D space, which also offers greater spatial efficiency.
Most rigid flex boards are composed of of multiple layers of flexible circuit substrates attached to one or more rigid boards externally and/or internally, depending upon the design of the application. The flexible substrates are with a constant state of flex and are usually formed into the flexed curve during manufacturing or installation.