Try fitting a traditional printed circuit board inside a smartwatch. Or getting one to survive the constant opening and closing of a laptop hinge. It’s not happening. Rigid PCBs have served us well for decades, but they hit a wall when you need circuits that actually bend, twist, or fit into tight spaces.

That’s the whole point of flexible printed circuit boards (flex PCBs). They’re exactly what they sound like—circuit boards you can bend. But there’s a lot more to them than just being bendy versions of regular PCBs. The materials are different, the design rules change completely, and if you don’t know what you’re doing, you’ll end up with circuits that crack, connections that fail, or costs that spiral out of control.

This guide covers what you actually need to know if you’re working with flex PCBs. We’ll start with the basics—what they are, how they work, and when you should use them instead of

 rigid boards. Then we’ll get into the details: materials, design rules, manufacturing, costs, and the mistakes people make (so you don’t have to).

If you’re designing your first flex circuit, trying to decide between flex and rigid for a project, or just want to understand why your phone’s display connector looks the way it does, you’re in the right place.