Guidelines of Flex Board Design

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.

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.

I-BEAM DESIGN AND STIFFENERS
I-Beam constructions occur when the inductors on both layers lie directly on top of each other, increasing the stiffness of the circuit through fold areas. A better alternative is 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 12mil to avoid stress points. Eliminating the stress points reduce the chance of traces breaking.

DESIGN TIPS TO MINIMIZE CIRCUIT COST
1.Consider how circuits will be “nested” on a panel.

2.Keep circuits small; consider using a WHERE 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.