Can Flexible Printed Circuit Boards Be Folded Or Cruced?

Flexible Printed Circuit Boards

A flexible printed circuit board (PCB) can be folded or creased but they should never be twisted or crushed. This will cause the copper to crack or break, and may also damage other components. A good fabrication partner will help you develop a robust folding and assembly process for your flex circuits. Clearly documenting this process and providing step by step instructions will minimize assembly risks. This will also allow you to communicate with your assembly team on the best way to fold the flex section and how to align it and secure it.

flex circuit boards can be single or multi-layered and are generally made with a flexible base material such as polyimide (Kapton), polyester (PET), polyamide or fluoropolymers (PTFE). These films are bonded together with an adhesive film and then a thin layer of conductive copper foil is laminated onto this for the conductors. A dielectric coverlay is then deposited over the copper foil to provide insulation and protection for the conductors and plated through-holes.

The IPC 2223 flex design standard allows for most 1 and 2-layer designs to be folded and hard creased without significant loss of performance. However, this requires that the bending radius is well within the allowed range and that the design be constructed using an appropriate material choice.

Can Flexible Printed Circuit Boards Be Folded Or Cruced?

For example, a rigid-flex PCB is a woven fiberglass impregnated in epoxy resin and it’s stiffer than an organic flex PCB but it’s able to withstand some dynamic bending and movement. It also provides good flex life.

To achieve a higher level of flexibility, a more expensive option is to use a flex-copper construction that has an un-bonded air gap between the layers. This configuration is used when a high-density, high-speed design requires a greater level of flexability and reliability than can be achieved with the standard IPC 2223 design rules.

For flex circuits that will be subject to repeated bending or movement, it’s necessary to select the proper copper material and consider the grain direction of the copper. Rolled annealed (RA) copper is a better choice than electro-deposited copper for dynamic flex applications because it has an elongated grain structure and can stretch more before fatigue cracking occurs.

To reduce stress and avoid copper fatigue during bending, the layout should be designed to keep the conductors away from the edges of the flex. It’s also recommended that a staggered arrangement of the traces in multi-layered flex circuits be used to reduce the stress on the overlapping copper regions and thereby improve conductor lifespan. Finally, the placement of plated through-holes and other components should be carefully considered to prevent them from being a source of stress during the flexing process. Lastly, any service loops or other length extensions of the flex PCB should be clearly marked on the circuit boards and documented in the fabrication drawings. This will make it easier to identify them when the flex is inspected or repaired.