Rigid-flex bend radius calculator
Minimum bend radius from your flex stack-up, checked against IPC-2223 outer-fibre strain limits. A bend radius that fails is a scrapped panel, not a rework.
Minimum bend radius
—mm
Ratio to thickness: —
Confirm against your fabricator's capability before layout. This is the calculation; they hold the process.
The formula
IPC-2223 expresses bend capability as outer-fibre strain:
strain (%) = [ c / (2r + h) ] × 100
where c is the copper thickness, h the total flex
thickness and r the inside bend radius. Rearranged for the minimum
radius at a given strain limit:
r_min = c / (2 · strain_limit) − h / 2Strain limits
| Construction | Static bend | Dynamic bend |
|---|---|---|
| Single-sided | 16% | 0.3% |
| Double-sided | 10% | 0.3% |
| Multilayer | 5% | not recommended |
The calculator also reports the simple ratio of radius to thickness, because that is the number most fabricators quote back at you — commonly 6:1 for single-sided static, 12:1 for double-sided, and 100:1 or more for anything dynamic.
What the calculation does not tell you
- Copper type. Rolled-annealed copper has grain structure aligned for bending; electrodeposited copper cracks far sooner. For any dynamic bend, specify RA.
- Trace direction. Copper should run perpendicular to the bend axis. Traces crossing a bend at an angle concentrate strain.
- Stress concentrators. Vias, pads, sharp corners and abrupt width changes belong outside the bend zone entirely.
- Stiffener placement. The transition from stiffened to unstiffened is where cracks start. It needs a defined keep-out.
- Assembly. A radius that is fine in theory is useless if a human cannot fold the assembly into the enclosure in the right order.
Related: rigid-flex PCB design · PCB design services · trace width calculator
Designing a flex that has to survive assembly?
Bend zones, stiffener transitions and fold order are where rigid-flex designs get scrapped. Send us the mechanical constraint and we'll tell you whether it is buildable.