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Flex PCB Conductor Width Guidelines

The conductor width in a flex PCB (flexible printed circuit board) is a critical design parameter that depends on several factors including current-carrying requirements, impedance control, manufacturing tolerances, and space constraints.

Key Factors Affecting Conductor Width in Flex PCBs:

1: Current Capacity
Wider traces are needed for higher currents.IPC-2223 and IPC-2152 standards provide guidance.As a rule of thumb:1 oz copper (35µm) ~10 mils width for ~1 amp in flex PCB (open air or mildly enclosed).

2: Bend Radius and Flexibility
Narrower and rounded traces improve flex durability.Traces should follow the bend direction (longitudinal) and avoid sharp corners.Avoid 90° angles; use teardrops and curved corners.

3: Impedance Control
For high-speed signals, controlled impedance requires precise trace width and spacing relative to dielectric thickness.Common for differential pairs (USB, HDMI, etc.)

3: Manufacturing Limitations
Typical minimum conductor width for flex PCBs:Standard processes ~4-6 mils (0.1-0.15mm)Advanced processes: down to ~2 mils (0.05 mm) or lessMinimum spacing is usually in the same range

Copper Thickness

Current (A)

Trace Width (mil)
(external layer)

0.5 oz (17.5µm)

0.5

~5-6 mil

1 oz (35µm)

1

~10-12 mil

2 oz (70µm)

2

~20-25 mil

Conductor Width vs. Copper Thickness & Current (Simplified Table)

2: Best Practices Summary in Flex PCB Trace Design:
Use wider traces when possible to improve durability.Stagger traces across layers to avoid stress concentration.Avoid vias in flexing areas.Use coverlayer instead of solder mask for better flexibility.For dynamic flexing, keep copper thickness low and traces narrow and rounded.

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