Flexibility Play in Rigid Flex Circuits
A rigid flex circuit is a combination of a traditional rigid PCB and a flexible circuit. It is often used in a variety of applications to reduce weight and space constraints while providing the functionality required by the circuit. Regardless of the application, it is important to understand what role flexibility plays in rigid flex circuits so that the appropriate design considerations are taken into account.
Flexibility in a physical sense is characterized by the ability to assume positions that would otherwise be unachievable or difficult to maintain through natural means. This flexibility is largely a result of the body’s soft connective tissue. While it can be augmented through exercise, the physical structure of the joints limits the amount of flexibility that is possible. The bones themselves also impose some limitations on the extent to which a joint can be bent. This is especially true of knees, which are often the site of injury in athletes due to their inherent vulnerability to bending and twisting forces.
When it comes to PCBs, the flexibility of a circuit is dependent on the thickness and material properties of the substrate as well as the design of the trace pattern. Thicker substrates will provide a greater level of stability to the flexible portion of the circuit, while smaller trace patterns can be more easily formed to conform to the shape of the rigid section. Using a rigid-flex PCB assembly method can help to ensure that the flexible portions of a circuit are properly formed for the most reliable operation.
What Role Does Flexibility Play in Rigid Flex Circuits?
The flexibility of a rigid-flex circuit is also determined by the number and layers of copper within the flex and the rigid sections. Keeping the layer-count down is crucial, as more copper layers will make a flex less flexible. Generally speaking, a high-speed or other controlled impedance traces should be routed through a mesh layer rather than a solid copper plane in the flex section as it is less likely to fail when flexed.
Depending on the specific use case, it may be necessary to add additional features to rigid-flex circuits. For example, a EMI shield can be added to some parts of the rigid-flex PCB to prevent Electromagnetic interference (EMI) from damaging other components in the system. The addition of adhesive pads can be useful in some cases to keep the flex PCB in place once it is mounted.
If cost is a major concern, it is worth pointing out that high-quality rigid flex PCBs are a much better long-term investment than cheaper alternatives, which will likely cut corners in manufacturing that can lead to thermal problems, electrical performance issues and mechanical failures over time. The best way to avoid these issues is by working closely with a trusted CM.
To learn more about the role of flexibility in rigid-flex circuits, please contact the PCBWay team. Our experts are happy to review your design for pliability and suggest ways to optimize it. We can even conduct a comprehensive electrical test on your finished rigid-flex PCB to make sure everything was done right and that you are getting the most out of it!