Flexible printed circuit ( FPC) or Flex PCB is a printed circuit board manufactured using substrate that is naturally flexible. Flex circuits are typically manufactured using a polyimide material and one to multiple layers of copper.
A flexible printed circuit board material will bend without snapping. A flexible printed circuit board can be used as connectors, and as full circuits assembled with components. And it can hold the soldering heat .
Moreover ,it can stand way more than rigid ones with high temperature based on the used film material type.
Flexible printed circuit boards are quite different than rigid boards:
Material : Rigid boards are typically made out of FR4 (glass-epoxy compounds) while flexible circuits are made from polyimide. There are cases when rigid boards are built with polyimide, but it isn't as common.
Coverlay :Flex pcbs either have a flexible mask or coverlay while rigid boards typically just use a solder mask. When a coverlay is used, the openings are routed, or laser cut. Then an adhesive (typically 1 or 2 mils thick) is used to adhere the coverlay to the flex.
Stiffeners : Flexible printed circuit boards typically use FR4 / Al / SUS or polyimide stiffeners to stiffen specific non-flexing regions. Stiffeners are either laminated to the flex or adhered using a PSA (pressure sensitive adhesive). Rigid boards do not need stiffeners.
Permittivity : There is a wide range of relative permittivity (dielectric constants) for rigid board materials while flexible polyimide material is typically 3.4.
There are many benefits to use a flexible printed circuit board in your application:
Lightweight : Flex circuit's polyimide material is lighter than FR4.
Thin : A typical 2-layer flex can range in thickness between 4.4 and 10 mils.
Flexible : This is obvious, but with the ability to make bends, you have more freedom to decrease the overall mechanical footprint.
High Temperature : Polyimide flex materials are suited for very high temperatures compared to FR4. They are also resistant to oils, gases, and acids.