Post History

**Flex with stiffeners**

The main purpose of flex with stiffeners is to be able to place SMT components onto the flex board.  Without a stiffener a flex has a somewhat undetermined shape, and pick&place would miss the pads.  The components can be placed only on one side of the stiffener.  The amount of components on such assemblies tends to be small.  Typically they're cables-like with few component: connectors, LEDs, sensors.

Historically flex with stiffeners appeared well before flex-rigid.

By the way, it’s also possible to have metal stiffeners which can conduct heat.

**Flex-rigid**

Consider the flex-rigid as rigid PCBs which can bend in some places.  It's a rigid PCB first.  All of the technology available for rigid PCBs is also available for flex-rigid (microvias etc).  Components can be mounted on both sides.  Flex-rigid is used when space is very constrained.  Often the rigid sections are larger than the flex section.