Flex and Rigid-Flex boards

Please keep in mind the following Design-Rules for your Flex- or Rigid-Flex circuit boards

For designers of flexible circuit boards we recommend the IPC-2223 Guideline / Design guidelines for flexible circuit boards, which is available from the IPC online store or in German, from the FED website.

Calculation of the bending radius

The minimum bending radius r results from the factor 6 to 25 (depending on the number of layers or application) multiplied by h, the overall height of the flexible part.

rigid-flex board bending radius

Example:
2 layers flexible PCB; overall height of flexible part: 300µm
minimum bending radius r = 10 x 300µm = 3000µm = 3mm

Flexible PCB for dynamic installation; overall height of flexible part: 400µm
minimum bending radius r = 25 x 400µm = 10000µm = 10mm

Design of bending areas

Design of bending areasDivide wide conductor traces into narrower conductor traces in the bending area.

Flixible PCB bending area 1

Fill open regions in the bending area with blind conductors.

Flexible circuit board bending area 2

Ensure a perpendicular path of the conductor traces to the bending axis. Avoid pads plated-through holes in the bending area.

FPB bending area 3

The bending area may be optimized depending on the application.

Flex PCB frequently or durable bending

Dynamic bending:
spontaneous and frequent bending
Optimization for dynamic bending:

  • drill holes or slots
  • copper edges at the bending location
  • copper stiffeners as bending aids

Durable bending:
single occurrence bending, such as for a bending tool
Optimization for durable bends:

  • drill holes or slots
  • Contour narrowing
  • Stabilization through more copper

For 2 or more flex layers, please ensure an alternating arrangement of the conductor traces on the front and back sides of the flexible portion.

2 layer flexible circuit board conductors

Use curves instead of corners in the conductor trace path.

FPC curves