Inputs
- Flex thickness
- Bend radius
- Thickness multiplier
- Process margin
- Existing setback
FPC / PCB Engineering Calculator
Stiffener Setback Calculator
Estimate the minimum setback between stiffener edge and bend tangent for flex reliability review.
How to use the Stiffener Setback Calculator
A stiffener edge too close to the bend zone can concentrate stress and reduce flex life. This calculator estimates a practical setback from bend radius, flex thickness and process margin.
Stiffener setback estimate
Formula: Recommended setback = bend radius + flex thickness x multiplier + process margin
- Bend radius: planned inside bend radius.
- Flex thickness: local flex-zone thickness.
- Multiplier: user-defined thickness-based safety distance.
- Process margin: extra space for bonding, routing and assembly tolerance.
Formula Basis
- Formula basis: engineering setback rule combining bend radius, flex thickness multiplier and process margin.
- Engineering note: final setback should be confirmed with the assembly fold path, manufacturer design rules and bend testing.
Example
With 1.5 mm bend radius, 0.15 mm flex thickness, 3x multiplier and 0.5 mm process margin, recommended setback is 2.45 mm.
Outputs
- Recommended setback
- Design margin
- Pass / warning indication
Engineering Notes
- Keep stiffener edge, adhesive edge and copper transitions away from bend tangent where possible.
- Dynamic bend applications should use larger margins and cycle testing.
- Connector support may conflict with bend setback, so review assembly geometry early.
Validation Checks
- Stiffener edge distance
- Bend reliability
- Connector support
- Assembly folding path
Related Manufacturing Process
- Circuit Layout - Trace width, spacing, bend-zone routing, differential pair spacing
- Lamination - Lamination thickness, adhesive squeeze-out, registration, CTE mismatch
- Reliability Validation - Bending test, thermal shock, peel strength, solder float, ionic contamination
Related Calculators
- FPC Bend Radius Calculator - Estimate minimum bend radius and flex strain for RA or ED copper.
- FPC Neutral Axis & Bend Stress Calculator - Visualize an FPC stack-up, estimate neutral-axis location, copper strain and layer stress, and compare coverlay opening or air-gap bend zones.
FAQ
Is setback measured from the bend center?
Use a consistent definition in your drawing. This calculator treats setback as distance from the bend tangent or practical bend boundary to the stiffener edge.
Can this replace bend testing?
No. It is an early design check. Dynamic and high-reliability applications need validation testing.