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Flex-Circuit Design Guide

Document source : www.alflex.nl

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Design differences flex-circuit vs. hardboards

Designing a flex-circuit is only one step away from
designing a hardboard. The most important design
difference to keep in mind is the three-dimensionality of
a flex-circuit. Creative bending and flexing can save
space and layers. Other important differences:

Flex-circuits both require and permit looser tolerances
than hardboards.

Because arms can flex, design them slightly longer
than required.

Design Tips to Minimize Circuit Cost

Always consider how circuits will be `nested' on a
panel.

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

Follow recommended tolerances whenever possible.

Design unbonded areas only where they are
necessary.

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

Specify 0.001" of adhesive on the cover material per 1
oz. of copper (including plated copper).

Building circuits with exposed pads and no cover
layers is sometimes less expensive.

Step-by-step approach to designing a flex-circuit

1. Read the available literature that is applicable for the

circuit you desire. If the circuit is intended for a
military/aerospace application, review IPC-6013 and
IPC-2223 or MIL-P-50884. Copies are available from
Minco.
Applicable sections in this design guide:

Manufacturing of a Flex-Circuit

Reference Documents

2. Define the circuit parameters according to the

package that uses the circuit. It may be helpful to
cut out a paper template to represent the actual
circuit. Experiment with bending and forming the
template in order to achieve maximum efficiency.
Design a circuit for maximum `nesting' in order to fit
as many circuits as possible on a panel.
Applicable sections in this design guide:

Design Differences: Flex-Circuit vs. Hardboard

How to Improve Flexibility and Bend Radius

3. Determine the wiring locations and the conductor

paths. This step will determine the number of
conductor layers.
Applicable sections in this design guide:

Circuit Types

Minco Circuit Codes

Cost Impact of Layer Count

Special Considerations for Rigid-Flex

4. Calculate the conductor width and spacing according

to the current capacity and voltage.
Applicable sections in this design guide:

Tolerances

Nomograph