Flex PCB Designing Useful Tips - JLCPCB

Flexible printed circuit boards, or Flex PCBs, are thin, lightweight printed circuit boards that can be bent, folded, and twisted to fit into any shape or size without damaging the electrical connections on the board. Flex PCBs are becoming increasingly popular in various industries, such as aerospace, automotive, medical devices, and consumer electronics. In this article, we will discuss what to consider while designing a Flexible PCB for effective product development.

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Considerations for Designing Flex PCBs

Designing a Flex PCB requires careful consideration of several factors, such as the material selection, circuit layout, and component placement.

The first step in manufacturing Flex PCBs is designing the circuit. Designers use Computer-Aided Design (CAD) software to create a layout that specifies the location of components, traces, vias, and other features on the board, including the PCB Layers stackup which has to be carefully set based on the manufacturer's requirements. Following are some tips to consider while designing a Flex PCB:

• Determine the type of flexible PCB: There are several types of flexible PCBs, including single-sided, double-sided, and multilayer flexible PCBs. It's important to determine the appropriate type of flexible PCB for your application based on factors such as complexity, space limitations, and flexibility requirements.
• Minimize the number of layers: Flex PCBs are typically thinner than rigid PCBs, so it's important to minimize the number of layers to avoid excessive thickness. It's also important to keep in mind that each layer adds complexity and cost to the manufacturing process.
• Allow for sufficient bend radius: Flex PCBs are designed to bend or flex to a certain degree, so it's important to allow for sufficient bend radius to avoid damaging the board. The bend radius should be calculated based on the thickness of the board and the type of material used. Some ECAD tools allow automatic measurement of bend radius based on your design and manufacturer specifications. The thickness of the board is also controlled by the number of design layers and at this level, you can calculate the smallest bend radius based on the PCB layers as follows:

When the minimum Bend Radius is not respected, then the produced flex PCB could show compression of the inner flex layer when the board is bend.

• Minimize the use of vias: Vias can add complexity to the manufacturing process and may cause reliability issues. It's important to minimize the use of vias and to use blind or buried vias where possible.
• Use appropriate materials: The choice of materials is critical to the performance of a flexible PCB. Materials such as polyimide and copper are commonly used for flexible PCBs because they are strong, flexible, and have good thermal and electrical properties.
• Place components carefully: Components should be placed on the flexible PCB in a way that allows for flexibility and bending. It's important to avoid placing components in areas that will be subject to excessive stress or strain.
• Use appropriate trace widths and Staggered traces: Trace widths should be chosen carefully to avoid excessive resistance and to allow for sufficient current carrying capacity. Narrower traces can be used on flexible PCBs because the board material is thinner than rigid PCBs, but care should be taken to avoid excessively narrow traces. Avoid drawing stacked traces for double-sided and multi-layer PCBs because such will increase stress resulting in copper circuit thinning at the bend, use staggered traces instead.

• Curved traces and Copper corners: curved traces are necessary for flex PCBs to accommodate the bending and flexing of the circuit without causing stress on the traces. If a trace is too straight or angular, it can crack or break when the PCB flexes. Curved traces allow the PCB to flex smoothly without damaging the trace. Therefore, it is essential to design the curved traces with appropriate radii and spacing to ensure they can withstand the intended flexing and bending.

Copper corners, on the other hand, are necessary to avoid stress concentration on the PCB. When the PCB bends, the corners of the copper traces or pads can experience a significant amount of stress. This can lead to cracking or breaking of the copper, which can result in a failure of the circuit. Copper corners, which are essentially rounded edges, help to distribute the stress evenly across the copper, reducing the likelihood of damage or failure.

• Consider the environment: It's important to consider the operating environment of the flexible PCB when designing it. Factors such as temperature, humidity, and vibration can all affect the performance of the board.
• Component Placement: The placement of components on the Flex PCB should be carefully considered to avoid stress on the board. Components should be placed in areas that are not subjected to bending or twisting.

A good PCB design needs to be made of good materials to achieve the best performance. JLCPCB connects with top raw material suppliers worldwide to provide high-quality true A-grade boards for all kinds of PCB. Meanwhile, JLCPCB has five self-owned intelligent production bases. Due to the large-scale effect on production, JLCPCB is able to minimize production costs and give back profits to our customers as much as possible so that let prices no longer be an obstacle to hardware innovation. Moreover, JLCPCB offers up to $54 registered coupons for every new user. Sign up and upload your Gerber files here and start ordering premium flex PCBs.