design considerations for rigid flex
Providing a unique combination of rigidity and flexibility, rigid flex PCBs are ideal for applications where the circuitry requires stability while still allowing for movement or folding. Common uses for rigid flex include wearable electronics, medical devices and aerospace systems, in addition to automotive and industrial robotics. Rigid flex offers the durability, thermal stability and flexibility required for these critical applications, as well as the ability to reduce weight, save space and withstand harsh environments and high temperatures.
While the benefits of using rigid flex are clear, some designers may find themselves unsure of how to approach designing a rigid-flex circuit board. This type of PCB can be quite complex, with both rigid and flexible sections interconnected by plated through holes (PTH) and mounting components. The PTH on the rigid section provide electrical connections between both the rigid and flexible sections of the circuit board, while the mounting components allow for a finished product that is able to bend and fold.
The design of a rigid-flex circuit board starts with the creation of a layered stack diagram that includes all the necessary information. This includes the layer stackup for each rigid-flex section, the traces and vias for each flex-area and the final through-plated holes on the rigid sections. The design of the rigid-flex sections must be carefully considered to ensure mechanical integrity and a safe operating environment for the end product.
What are the design considerations for rigid flex?
One of the most important considerations for creating a rigid-flex circuit board is selecting a suitable material for both the rigid and flexible portions of the circuit board. Manufacturers typically choose FR4 for the rigid portion of the circuit, as it provides excellent insulation and resistance to heat, static, and moisture. For the flex-area, a popular choice is polyimide or Kapton film – a robust thermoset with low CTE and Dk values that make it a good option for vibrations and temperature variations.
Trace routing is also an essential factor for the design of a rigid-flex circuit board. It’s vital to use a grid-based design and minimize sharp corners, as they can increase stress on the flex area. Rigid-flex circuit boards should also be designed with adequate clearance between traces to avoid short circuits. Finally, the placement of heat-generating components and thermal vias must be carefully considered to promote efficient heat dissipation and prevent damage to the flex-area during bending or folding.
Rigid-flex circuits are redefining the possibilities in electronics design, offering unmatched versatility and reliability. As technology evolves and devices become increasingly compact and complex, rigid-flex PCBs provide an elegant solution to meet the growing demand for miniaturization, performance, and durability. This blend of rigid and flexible materials supports creative engineering solutions across various industries.
Once a rigid-flex circuit board design is complete, it must be analyzed and tested to ensure the resulting prototype meets its intended design requirements. This is particularly important for critical applications like medical equipment and aerospace equipment, where any failures could have serious consequences. Using a quality PCB manufacturer that provides rigorous testing and reliability testing is key to ensuring that the final product is able to withstand the expected environmental conditions, mechanical stress, and other risks.