Flex PCB Trace Calculator
Polyimide | LCP | Rigid-Flex | FPC
Calculate trace width and impedance for flexible PCB designs. Polyimide-based flex circuits require different considerations than rigid FR4 boards—get the right parameters for reliable flexible electronics.
Flex PCB Materials
| Material | Dk | Df | Flexibility |
|---|---|---|---|
| Polyimide | See your laminate supplier datasheet | See your laminate supplier datasheet | Excellent |
| LCP | See your laminate supplier datasheet | See your laminate supplier datasheet | Good |
| PET | See your laminate supplier datasheet | See your laminate supplier datasheet | Moderate |
| Coverlay (PI) | See your laminate supplier datasheet | See your laminate supplier datasheet | Excellent |
Flex PCB Design Considerations
Bend Radius
Traces in bend areas experience stress. Keep traces perpendicular to the bend, use curved traces instead of angles, and follow minimum bend radius guidelines.
Trace Geometry
Use wider traces in flex areas for reliability. Avoid sharp corners—use curves. Stagger traces on different layers to reduce stress concentration.
Coverlay vs Solder Mask
Flex circuits can use polyimide coverlay. Coverlay and adhesive affect impedance; see your laminate supplier datasheet and use a model that includes these layers.
Flex vs Rigid PCB Differences
Flex PCB Characteristics
Key Differences from FR4
• Dielectric properties depend on the selected laminate
• Thinner total thickness typically
• Loss tangent depends on the selected material and frequency
• Coverlay instead of solder mask
• Adhesive layers affect impedance
Types of Flex Circuits
Single/Double Layer Flex
- • 1 or 2 copper layers
- • Most flexible option
- • Lowest cost flex type
- • Common for simple interconnects
- • Easy impedance calculation
Multi-Layer Flex
- • 3+ copper layers
- • Reduced flexibility
- • Higher density routing
- • Controlled impedance possible
- • Complex stackup design
Rigid-Flex
- • Flex + rigid sections
- • Components on rigid areas
- • Flex for interconnection
- • Eliminates connectors
- • Complex impedance design
Calculate Flex PCB Trace Dimensions
See your laminate supplier datasheet for dielectric properties. Account for coverlay and adhesive in a suitable impedance model, and confirm stackup parameters with your flex fabricator.
Flex PCB FAQ
What Dk for flex PCB calculations?
See your laminate supplier datasheet for the selected material and operating frequency. Account for coverlay and adhesive layers in an appropriate impedance model and confirm the stackup with your fabricator.
How does bending affect traces?
Bending stresses traces. Review trace geometry, routing direction, copper type, and bend radius with the fabricator for the intended static or repeated-flex use.
What copper type for flex?
Rolled annealed (RA) copper is more flexible and fatigue-resistant than electrodeposited (ED). Use RA for dynamic flex applications.
Can I do controlled impedance on flex?
Yes, but it's more challenging than rigid PCB. Work with an experienced flex fabricator. Multi-layer flex and rigid-flex are better for impedance control.
Related Tools & Resources
Trace Width Calculator
CalculatorCalculate PCB trace width for your current requirements
Controlled Impedance Stackup Calculator Guide
CalculatorChoose PCB stackup, layer, dielectric height, copper, and trace geometry for controlled impedance routing
FR4 Trace Calculator
MaterialTrace calculations for standard FR4 PCB material
Aluminum PCB Trace Width Calculator
MaterialSize traces on aluminum and metal-core PCBs for LED, power module, and heat-spreading layouts
Rogers Impedance Calculator
MaterialHigh-frequency RF calculations for Rogers materials
LED Strip PCB Current Calculator
MaterialSize copper, current, and power injection for rigid and flex LED strip boards