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Design Considerations Unique to Flex PCBs

Unique to Flex PCBs

PCBWay can do some electrical test on your flex pcb. This can help you find some issues during manufacturing such as short circuit, cut in a trace etc. This option will increase the cost.

A flex circuit is a circuit board that has the ability to bend or curve to allow it to fit in a specific area of a device. While a rigid circuit board is designed for one position only, a flex circuit can move back and forth, which means the design needs to reflect this movement. In addition, a flex circuit is often exposed to harsh environments, so the components need to be able to withstand this abuse. To avoid stress fractures, a flexible circuit’s copper traces should be spread out as much as possible and the board should have rounded edges.

Manufacturability considerations are also unique to flex pcb. It’s important that the board layout is optimized for streamlined fabrication processes and that detailed flexibility analysis is performed. This ensures that the flexible portions of the circuit will be able to sustain repetitive bending cycles while maintaining structural integrity over its operational lifespan.

It’s also important to consider how the flex circuit will be mounted in its final application. Will it be glued to a surface or attached with an adhesive? If so, it’s crucial that a pressure-sensitive adhesive (PSA) is used. This type of adhesive is extremely adaptable, easy to use, and can be applied with minimal effort. In addition, it’s environmentally friendly and offers high bond strength.

Design Considerations Unique to Flex PCBs

Flex circuits have different requirements than traditional rigid boards, including signal transmission, impedance control, and electromagnetic interference (EMI) mitigation. To minimize signal attenuation and loss, the substrate material’s dielectric constant and loss tangent need to be low. Additionally, the copper trace widths and spacing need to be appropriate for the speed of the signal. It is also best to route high-speed signals as differential pairs to reduce crosstalk and interference.

A flex circuit’s plated through-holes are connected with copper pads called annular rings. These connections are generally stronger in flex circuits than standard through-hole connections because they are bonded to the substrate rather than the connecting copper traces. However, it’s still recommended that the annular ring be as large as possible to prevent stress concentration spots.

Conductors ought to be run perpendicular to the overall bend of the flex circuit, which helps to eliminate stress points that can cause copper trace breakage. In addition, a curved shape instead of a sharp angle increases longevity. Lastly, use hatched polygons for pads instead of solid polygons to make them more durable in a flex circuit.

It’s also a good idea to use the largest possible pad size and to connect plated through-holes with fillets, which are extensions of the copper pad that help strengthen the connection. In addition, a flex circuit’s vias should be surrounded by an annular ring that is at least 8 mils in diameter to prevent stresses and cracking. Finally, keep the area around the bend free of discontinuities like vias, cut-outs, slits, and holes. This will help to reduce stress and cracking that can lead to malfunctions and failures.

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