Flex Circuits Be Folded Or Cruced
A common question is “Can flex circuits be folded or creased?” The answer to this is yes, but it depends on a number of design and construction parameters. For example, the thickness of the conductive copper layer can be critical to how much a flex circuit can flex, as well as the type of copper used and the thickness of the insulator. In addition, the operating environment needs to be considered. If the flex circuit will only be bending occasionally, then a thinner conductive layer and a less complex stack up is recommended to minimize stress on the material. In contrast, if the flex circuit will be bending continuously (dynamic flex) then a thicker conductive layer and a more complex stack up is required to ensure that the material can sustain repeated dynamic bending without delamination or cracking.
To maximize the flexibility of a flex circuit it is important to optimize the copper thickness and insulator materials, while still meeting electrical requirements. It is also essential to use a high quality flex core. A good flex core is made of polyimide with a buried or plated copper layer. For higher layers, a flex core with an Un-bonded Air Gap construction is preferred as it will give a much greater degree of flexibility due to the fact that the copper layers are not bonded together at each segment.
When a flex circuit is bent, the inner copper layer tends to compress and the outer layers tend to extend. This can cause the copper to fatigue and break. To prevent this, a minimum bend radius should be determined and set early in the design process. A flex circuit with a tight bend radius is more likely to suffer damage and should not be used in dynamic applications.
Can Flex Circuits Be Folded Or Cruced?
Traces and pads should be kept away from the flex circuits bending regions as this will make the traces more difficult to route, especially if the conductor is terminated in these areas. The flex circuit is typically manufactured from a thin polyimide film that is more difficult to process than rigid boards. Pad fillets can be added to improve etch yield and material strength, but they should not be utilized near a bending region.
Flex circuits also offer greater design freedom compared to rigid PCBs. Designers can create intricate, three-dimensional layouts that conform to the specific requirements of the device or application, optimizing space utilization and performance. This flexibility in design facilitates the integration of electronics into unconventional shapes and structures, enabling innovative product designs that were once deemed impractical or impossible.
It is also important to define the flex circuits folding zones in the layout and ensure that they meet industry standard guidelines. This will help to avoid issues with alignment and component interference when the flex circuit is being bent or flexed. In addition, it is a good idea to create a folding test prototype and physically fold and unfold the flex circuit to identify any unforeseen issues with the design or fabrication. In addition, if possible, additional layers of flexible materials or reinforcement should be used in the fold areas to distribute stresses and provide mechanical support.
