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Flex PCB Design Guidelines: Annular Ring | Gold Phoenix PCB

Time: 2018-10-26 03:10:11

Guidelines of Flex Board Design

This Gold Phoenix PCB Knowledge Center article covers essential design guidelines for flexible printed circuit boards, including conductor annular ring filleting, tie-downs, radiused traces, I-beam construction, stiffener design and cost optimization tips.

Conductor Annular Ring Design and Filleting

All pads, on both through-hole and surface mounted pads, should be filleted to reduce stress points. This helps eliminate breaking during flexing.

Conductor annular ring filleting example

Tie-Downs and Radiused Traces

Tie-downs are captured by the coverlay to anchor the copper to prevent separation between the copper and the base material. Radiused traces help to reduce breaking during folding and bending.

Tie-downs and radiused traces example

I-Beam Design and Stiffeners

I-Beam constructions occur when the conductors on both layers lie directly on top of each other, increasing the stiffness of the circuit through fold areas. A better alternative is to stagger conductors, alternating their location to retain the maximum flexibility of the circuit.

Stiffeners Design Reference

Stiffener and coverlay termination line should overlap a minimum of 12 mil to avoid stress points. Eliminating the stress points reduces the chance of traces breaking.

Stiffener and coverlay termination overlap reference

Design Tips to Minimize Circuit Cost

1. Consider how circuits will be “nested” on a panel.

Circuit nesting on panel example

2. Keep circuits small; consider using a set of smaller circuits instead of one large circuit.

3. Follow recommended tolerances whenever possible.

4. Design unbonded areas only where they are absolutely necessary.

5. If circuits have only a few layers, using stiffeners can be far less expensive than a rigid-flex circuit.

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