Where components are attached or where the flexible circuit board is to be bent as it attaches to non-flexing circuits,
stiffeners are required.This prevents damage to both the connections and the Flex PCB.
Flexible PCBs, by their nature, are made to odd shapes; they aren’t a convenient rectangle.
After the Flex PCB is manufactured,it has to be routed, or skived, to shape it to fit. To make sure that the edges of the circuit traces are not going to be damaged in the process of routing, care must be taken in the layout and design stages to keep the circuit traces back from the edge.
When there will be continuous or dynamic flexing of the circuit material, special considerations are needed. On multi-layered Flex PCBs, this includes taking into account the number of layers while making sure that the conductors will not be fatigued when the PCB is flexed.