In general we want as soft a bend as possible to extend the life of our flex material. This software bend translates to a larger
bend radius. As your radius gets smaller, the bend gets tighter and the copper in the flex material is more prone to break over
repeated bending. We therefore want to have a radius no smaller than a certain amount. This is called the minimum bend
radius. That minimum bend is:
Bend radius calculation
i. Calculation of a recommended/minimum bend radius
Number of Layers (Copper)
Recommended Bend Radius (Go no smaller than this
radius to avoid bend damage) mils
1- to 2- layer flex PCB Thickness of Flex Material × 10
3-layer flex PCB Thickness of Flex Material × (15-20)
Multi-layer (4 or more) flex PCB Thickness of Flex Material × (25-30)
Source: MadPCB.com
Material Considerations
Copper Type and Grain Orientation: Rolled annealed copper (RA copper) is commonly used for flex PCBs due to its improved
ductility for bending applications.
Layer Count: The number of layers in a dynamic flex board is limited to minimize stress on the copper circuits. A single-layer
construction is ideal, placing the copper trace close to the neutral bend axis (the area with minimal tension or compression
during flexing). Two-layer boards are acceptable with a thin adhesive-less core to maintain minimal distance between the
circuits and the neutral bend axis.
11 www.cadence.com
Rigid Flex Design Guide
