It’s a PCB design question for the ages: Should I use a multi-board system with standard cables and connectors, or should I use a rigid-flex PCB? Just like many complex questions in electronics design, the answer is a firm “it depends.” Rigid-flex PCBs have found a home in aerospace, medical, and military applications, and they are unlikely to disappear from the electronics landscape in the future.
Although the advantages of rigid-flex PCBs in certain devices are undeniable, designers can receive some of these same benefits from non-planar PCBs. Additive manufacturing has a unique role to play in prototyping and producing these devices, and working with the right additive system allows designers to create non-planar electronics with many of the same advantages of rigid-flex PCBs.
Digital cameras are just one example of devices that can benefit from the advantages of rigid-flex PCBs.
Advantages of Rigid-flex PCBs
Rigid-flex PCBs integrate a flexible polyimide or another polymer ribbon into two or more rigid PCB substrates. In effect, the ribbon appears as part of the layer stack in the rigid boards. Flex PCBs are closely related in that they do not contain rigid portions at the ends of the flex ribbon. Compared to a planar rigid PCB, this architecture provides some unique advantages.
Flexibility in Folding or Moving Packaging
The flexible ribbon in a rigid-flex PCB naturally moves and folds with its packaging while still maintaining an electrical connection between the rigid ends of a board. Some examples include laptop screens, old clamshell cell phones, televisions, and printers. Products that contain a laterally moving element, such as a DVD drive or some industrial equipment, can maintain electrical connections during motion without placing stress on connectors or solder joints.
Fewer Limits on Form Factor
The foldable nature of a flex ribbon allows rigid portions of a rigid-flex board to be installed and mounted at odd angles in unique packaging. The limitation on the rigid boards themselves is that they must be machinable using standard processes, which limits their geometry to standard shapes.
The ability to bend and fold with the device allows a rigid-flex board to be installed in a tighter space than a set of rigid boards connected with cables. Any cable on a PCB requires a connector, and the connector can take up significant space inside the package. Cables themselves can also be bulky and include unused conductors. Replacing these elements with an embedded flex ribbon gives designers more freedom to adjust a rigid-flex board to its enclosure.
Durability and Reliability
Despite their flexibility, rigid-flex PCBs do not rely on solder joints and interconnects to provide an electrical connection between the rigid boards. This reduces the number of potential failure points. Compared to FR4 or other rigid substrates, the flex ribbon can also withstand higher temperatures without damaging the conductors on the flex ribbon. This makes rigid-flex boards ideal for aerospace applications and in environments with extreme temperatures.
Copper traces on a polyimide flex ribbon
Reduced Reliance on Connectors
In a multi-board system, your device won’t get anywhere without connectors and cables to send power and signals between boards. Rigid-flex PCBs eliminate this need for connectors and cables, which simplifies the design, eliminates some components, and reduces the number of required assembly steps. This can lead to a net cost reduction for each board, as well as a better end-product.
The use of a polyimide ribbon provides another benefit in that ground and power planes in a PCB can be embedded inside the flex ribbon and extended between rigid boards. This eliminates the grounding schemes required in rigid multi-board systems. Signals that are sent across the flex ribbon can be referenced to the ground plane, ensuring that return signals have the smallest possible loop area. This provides better immunity to EMI than you’ll find in some rigid multi-board systems.
The Transition to Non-Planar PCBs with Additive Manufacturing
Rigid-flex PCBs are something of a non-planar multi-board system. The relaxed restrictions on form factor and the ability to design around arbitrary packaging make rigid-flex PCBs an attractive option for use in many electronic devices. Many of the advantages discussed above can also be gained through the use of non-planar PCBs.
Non-planar PCBs are a unique type of electronic device that is less limited by form factor, similar to a rigid-flex board. As rigid-flex devices can be extremely difficult and costly to fabricate with traditional PCB manufacturing processes, an additive manufacturing system that is tailored to electronics such as PCBs could simplify some of the same design goals. The layer-by-layer printing process naturally lends itself to the fabrication of non-planar circuits or PCBs with a wide range of shapes, geometries, and sizes.
As non-planar circuits can be fabricated with a unique form factor and 3D shape, they can also be installed in tight spaces and in enclosures with an odd shape where a flex ribbon may not be necessary. In some static packages, eliminating the flex ribbon could allow the designer to save space while still including the required functionality.
Non-planar circuits provide other benefits that do not apply to rigid or rigid-flex PCBs. For example, the layer-by-layer printing process may allow components to be embedded in a non-planar board with less cost and difficulty compared to a PCB on FR4 or another rigid substrate. Conductive elements like antennas or RF amplifiers can be placed directly on, or inside a non-planar PCB, allowing designers and engineers to experiment with unique components and topologies.
As the world of PCB design continues to evolve, you’ll need the capabilities to keep up with new design and manufacturing methods. DragonFly Pro is an award-winning precision additive manufacturing system built specifically for rapid prototyping and PCB production. Your project might be able to benefit from the advantages of rigid-flex PCBs by leveraging additive manufacturing to print non-planar electronics with a unique form factor. Read a case study or contact us today to learn more about DragonFly Pro.