Flexible circuit boards (PCBs) are thin, bendable electronic substrates designed to fit into compact or irregularly shaped spaces, offering versatility in device design that rigid PCBs cannot match. Constructed from polyimide (PI) or polyester films (typically 25–125 μm thick) as the base material, these boards feature thin copper traces (12–70 μm) etched into patterns, enabling electrical connectivity while maintaining flexibility.

The key advantage of flexible PCBs lies in their ability to bend, twist, or fold repeatedly without compromising performance, making them ideal for applications like smartphones (connecting displays to motherboards), wearable devices (fitness trackers, smartwatches), and automotive sensors (airbag modules, dashboard electronics). Their lightweight nature (up to 70% lighter than rigid PCBs) and reduced thickness also contribute to miniaturization, a critical trend in modern electronics.

Manufacturing processes for flexible PCBs involve laminating copper onto polyimide films, followed by photolithography to etch traces. Adhesiveless variants (using direct copper bonding) offer better thermal resistance and flexibility, suitable for high-temperature environments. Cover layers (polyimide or acrylic) protect the copper traces from moisture, dust, and mechanical damage, while stiffeners (thin metal or FR-4) may be added to areas requiring stability, such as component mounting pads.

Flexible PCBs support both through-hole and surface-mount components, though miniaturized parts are preferred to maintain flexibility. They can be single-sided, double-sided, or multi-layered, with multi-layer designs using flexible adhesives to bond layers. Testing includes flex endurance (up to 100,000 cycles), thermal cycling, and moisture resistance to ensure reliability in dynamic applications. By combining adaptability with high performance, flexible PCBs enable innovative designs in industries ranging from consumer electronics to medical devices.