How Are Rigid Flex Circuits Different From Rigid PCBs?

Rigid Flex Circuits Different From Rigid PCBs

Rigid flex circuits are hybrid printed circuit boards that offer designers a combination of reliability, space efficiency and flexibility. They are a common choice for high-reliability, high-density applications in industries such as aerospace, automotive and medical where the need to transmit signals rapidly and reliably is paramount.

To understand how rigid flex circuits are different from traditional rigid PCBs, we must first look at the manufacturing process. Rigid flex PCBs begin with one or more single- or double-sided flex layers. The fabricator may add copper foil to the flex layer via lamination to an epoxy or acrylic adhesive, or they may start with unclad flex film and use sputtering to create a seed layer for a plating key that is then chemically deposited onto the flex. Some fabrication processes now allow adhesiveless cladding of rolled annealed copper, and these newer techniques are resulting in a lower cost of production.

The flex layers are then drilled, plated and etched in the same way that the core of a rigid PCB is fabricated. This is done in order to establish the electrical connections between the rigid and flex layers of the board. Rigid-flex boards also incorporate copper traces in the flexible substrate that are connected to a circuit pattern on both sides of the board. The traces are designed to flex during normal use, so they must be properly modeled during the design stage in order to ensure that they can handle the mechanical stress.

How Are Rigid Flex Circuits Different From Rigid PCBs?

These rigid-flex circuits eliminate the need for extra connectors and cables to interconnect each board, which speeds up assembly and cuts manufacturing costs. This also reduces overall system weight and streamlines the mounting process, allowing manufacturers to meet the demand for more compact devices with fewer components.

While the benefits of rigid flex circuits are many, they do come with some additional challenges. For example, it can be difficult to transition signal layers between rigid and flex sections of the circuit board, especially when there are multiple layers involved. This can lead to impedance mismatches, which can impact performance and cause signal degradation. Another issue is thermal management. Rigid-flex circuits require a greater amount of heat sinking than conventional rigid PCBs. This is due to the fact that there are more conductive paths and heat sources in a flexible structure. This can lead to a higher temperature rise, and the circuit board must be carefully engineered to maintain a consistent temperature throughout its operation.

In addition to the advantages discussed above, rigid-flex circuits are typically more aesthetically pleasing than traditional rigid PCBs. This can be a significant benefit in applications where aesthetics are important to the end customer. When considering the use of rigid-flex in your next project, talk to the experts at APCT. We can help you design and manufacture a custom rigid-flex circuit that will suit your unique application. Call us today for more information!