Bending the rules: How to design smarter with rigid-flex PCBs

In a season three of the Printed Circuit Podcast, host Steph Chavez welcomed industry expert Tara Dunn, Director of Training and Education at SMTA, for a deep dive into the evolving world of rigid-flex PCB design. Dunn, whose career spans fabrication, supplier representation, and content creation—including her long-running Flex007 column—brought grounded insights into a technology many designers still consider “black magic.”

“Rigid-Flex is one of those technologies that feels familiar—but it’s just different enough to trip people up,” Dunn said. And when not approached intentionally, those trips can turn into costly falls.

Dunn’s unconventional entry into the industry—starting in HR and accounting at a flex circuit manufacturer—turned out to be a blessing. Early on, she was asked to work the production floor to better understand what she was budgeting for. “I went through drilling, imaging, wet processing, final inspection—the whole line,” she recalled. “That foundation gave me more than just technical knowledge. It helped me speak the same language as fabricators.”

That language, she says, is what many designers still haven’t learned.

Chavez agreed, sharing that early in his career, flex design felt mysterious. “It was black magic,” he said. “People stuck with connectors rather than diving into the unknowns of rigid-flex.”

Why collaboration beats guesswork

As designs get denser and systems shrink, the case for rigid-flex strengthens. But so does the need for upfront collaboration. From adhesive vs. adhesive-less polyimide to coverlay handling, Dunn emphasized that many manufacturing quirks are invisible from the CAD screen.

“You’re running ultra-thin materials through equipment built for rigid boards,” she said. “That means taping leaderboards, managing scrap risk, avoiding key features near panel edges—it’s a completely different game.”

And then there’s coverlay. “Most people assume there’s a photo-imageable version, like in rigid boards,” she said. “But for higher copper weights or flex counts, you’re drilling round holes over square pads. That’s a specialized—and delicate—process.”

Chavez’s advice? “Get your butt on the fab floor. The things you’ll learn by seeing it live will change how you design.”

When rigid-flex wins and what it costs

“There’s a tipping point,” Dunn explained. “If space, weight, or performance is a concern, rigid-flex almost always wins. But people get hung up comparing raw fabrication costs.”

Instead of comparing just the board + connector price to the rigid-flex cost, she urges engineers to think holistically: multiple POs, higher assembly yield loss, longer cycle times, and supply chain complexity. “With rigid-flex, you issue one PO, inspect one item, and install one assembly,” she said. “That’s powerful.”

Rigid-flex in PCB also eliminates bulky connectors, a benefit familiar to Chavez from his aerospace background. “I’m holding a board in my hand where Rigid-Flex enabled a miniaturized system,” he said. “No connectors. Less weight. Better thermal performance.”

The most common PCB design mistake? Dunn was blunt: “Designing a flex that doesn’t flex.”

From improper bend radii to ignoring pad anchoring and stiffener needs, she’s seen it all. “Dynamic vs. static flex makes a difference. And if you design flex like it’s rigid, you’re in for trouble.”

Chavez added that advanced 3D modeling helps, but nothing beats clear communication: “Show your supplier the real-world application, the physical envelope, how the board bends, and where it connects.”

Learning the PCB rigid-flex way: the education curve

Dunn’s first piece of advice: Be intentional. “There’s no shortage of resources,” she said. “SMTA, PCEA, IPC, webinars, eBooks, LinkedIn columns, podcasts. But make sure the source is trusted and vetted.”

She warns against relying too heavily on random YouTube videos or unverified blog posts. “If you’re getting advice, make sure it’s from someone who’s actually built a board.”

Chavez echoed the sentiment. “Authors of these eBooks and columns are approachable. Add them to your network. Reach out. You’ll be surprised who responds.”

Dunn also recommends using industry-vetted resources like Flex007, iConnect eBooks, and manufacturer websites from leaders like NCAB, TTM, and Sanmina.

Dunn closed with reassuring words for engineers just beginning their Rigid-Flex journey.

“Everyone is on a learning curve,” she said. “Even people with 30 years in the industry are now learning Ultra HDI, MSAP, additive processes. It’s okay to make mistakes—as long as you learn and keep iterating.”

Chavez nodded in agreement: “Rigid-flex isn’t just about passing DRC. It’s about passing HASS, HALT, and the shake-and-bake of real-world Mil-Aero environments. That’s where design for manufacturability really gets tested.”

Conclusion

Rigid-flex PCB design may still feel like magic to some, but as Dunn and Chavez made clear, success lies in education, collaboration, and intention.

From material stackups to supply chain planning, from coverlay cutouts to eliminating costly connectors, rigid-flex PCB design represents both a challenge and a competitive edge. The engineers who lean in, learn fast, and collaborate early will be the ones to unlock its full potential.

Learn more expert advice on rigid-flex and flexible circuit design, and listen to the Printed Circuit Podcast.