Flexible circuits can be designed in a variety of ways, depending on the specific application. Some of the most common design options include layer count, substrate material, conductor material, surface finish, and stiffeners.

• Number of layers: FPCs can be single-sided, double-sided, or multilayer. Single-sided FPCs are the simplest and least expensive type of FPC. Double-sided FPCs have circuits on both sides of the board. Multilayer FPCs have circuits on multiple layers of the board. Multilayer FPCs are the most complex and expensive type of FPC, but they offer the greatest flexibility and routing density.
  
  
• Substrate material: The most common substrate material for FPCs is polyimide (PI). PI is a strong and flexible material that is also resistant to heat and chemicals. Other substrate materials that can be used for FPCs include polyethylene terephthalate (PET) and aramid.
  
  
• Conductor material: The most common conductor material for FPCs is copper. Copper is a good conductor of electricity and is also relatively inexpensive. Other conductor materials that can be used for FPCs include gold and nickel.
  
  
• Surface finish: The surface finish of an FPC is the protective coating that is applied to the copper conductors. The most common surface finish for FPCs is organic solderability preservative (OSP). OSP is a thin, conformal coating that protects the copper conductors from oxidation and corrosion. Other surface finishes that can be used for FPCs include electroless nickel immersion gold (ENIG) and hot air solder leveling (HASL).
  
  
• Stiffeners: Stiffeners are used to add rigidity to FPCs. Stiffeners can be made from a variety of materials, including FR4, aluminum, and stainless steel. Stiffeners are typically used in areas of the FPC that will be subjected to high stress, such as bend radii and connector locations.
  
  

• Flexibility: Flexible circuits can be bent, folded, and twisted without damaging the circuit. This makes them ideal for applications where the PCB needs to be able to move or conform to a curved surface.
  
  
• Weight savings: Flexible circuits are typically lighter than rigid PCBs, which makes them ideal for applications where weight is a factor, such as aerospace and medical devices.
  
  
• Space savings: Flexible circuits can be designed to fit into complex or confined spaces. This makes them ideal for applications where space is limited.
  
  
• Durability: Flexible circuits are typically very durable and can withstand repeated bending and flexing. This makes them ideal for applications where the PCB will be subjected to harsh conditions.
  
  

Flexible circuits can be used in a variety of applications, such as factory automation equipment, robotics, and sensors. They are also used in many aerospace and defense applications.