Flex PCB Design Guidelines for Manufacturing

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Flex PCBs are the go-to choice for manufacturers due to their longevity and ability to absorb shocks and vibrations. However, their design must be optimized before being deployed for devices such as hearing aids and fitness trackers. But there are a few flex PCB design guidelines that should be followed.


Identify the Electronic Applications of the FLEX PCB


Before you start designing the flexible circuit board, make sure you know what the PCB will be used for. Also, try to figure out how many times the flexible PCB will bend. If the PCB is bent too often, the copper may stretch and crack. This can render the board useless.

Decide if the board is static or dynamic. A static board can only flex less than 100 times during its lifetime before it breaks. Ideally, these boards should only bend during installation. By contrast, a dynamic board can be regularly flexed and twisted without damaging the copper. Common applications for dynamic flex PCBs include printers and fitness trackers.


Best Practices for Designing FLEX pcb Bend Areas


Use the following tips when designing bend areas:
● Define the flex and rigid regions
● Calculate the bend radius
● Increase flexibility by adding slots and cut-outs when designing bend areas
● Avoid creating sharp 90 degree bends because they can damage the circuit
● Use conductors smaller than ten mils with a neutral bend axis because they are better suited to working with compression than stretching
● Avoid through-holes or plated thru-hole in areas near bend
● Conductors running through the bend should be located perpendicular to them
● Staggered configurations should be used in multi-layer circuits to maximize their effectiveness


Identify the Most Appropriate Flex pcb Materials


The two most popular materials for a flex pcb are:


Adhesive-based materials - These cores utilize a layer of flexible adhesive, which bond under heat and pressure to each copper layer.
Adhesive-less materials - These cores have copper directly applied to them without adhesives.

Adhesives with rigid cores develop cracks in the copper plating via holes because they soften over time. Consequently, this is why it is important to utilize teardrops and anchors in your circuit design when using adhesive-based cores.


Tips for Flex pcb Trace Routing


It is recommended to use a much larger bend radius with curves instead of sharp angles to improve the durability of the board. Curved traces are much more reliable than angled traces. This is especially true for multi-layer PCBs that should be designed using stagger traces instead of stacked ones.

The latter can reduce the reliability of the circuit and increase the likelihood of the erosion of copper around the bend radius. The stress will be evenly displaced during the bend and improve its reliability by staggering the conductors.

The signals trace should be at right angles to the overall bend.


Use the Most Appropriate flex PCB Stack-up


Stackup refers to how the copper and insulators are arranged on a PCB before the final layout of the board is designed. It is recommended to have an in-person meeting with the vendor to understand flex PCB capabilities and design guidelines properly.


Choose the Right Manufacturer


Every manufacturer has its own design rules. This will affect things such as line spacing and circuit density. It is recommended to contact your manufacturer to identify the most suitable materials for the application and environment in which the flex PCB can operate. Flex materials are very durable, but flex laminates may not be ideal for certain applications.

Make sure the PCB manufacturer produces circuit boards regularly. This is because practice makes perfect. Also, interview them to learn more about the flex circuit boards, including the materials they work with, the surface finishes, and other questions.


Using Annual Rungs in Flex pcb Design


Annular rings are used to facilitate a high-quality connection between the copper trace and a via. It facilitates a connection between leads or wires to electronic components. However, annual rings in flex multi-layers can be compromised where tight hole to pad ratios are required. This is why designers should allow for some misregistration between the drilled hole and internal pads when designing flex PCB boards.


Use Flex PCB Stiffeners


Stiffeners are used to make parts of the board more stable so that it is easier to solder components and interconnect to the stiffer parts of the board. PCB stiffeners are mostly used to provide mechanical support to specific areas of the board. It can increase durability, rigidity, and thickness.

Stiffeners should be used if components are placed close to a flex area. The most popular stiffeners are FR4 and Kapton materials attached to the pressure-sensitive adhesive and thermally cured acrylic.


Strategically Placing Vias in a Flex pcb Design


Vias are more likely to be displaced from flex layers. You can reduce this risk by using the following tips:
• Make larger annular rings
• Create teardrop-shaped vias because they can lower the stress that the components on the PCB board are subjected to
• Prevent peeling by using anchor spurs
• Place vias at a distance of 30 mils from the flex interface


Get Acquainted with the Basics of Flex pcb Drawing


Designers should know the basics of flex drawing for successfully drawing a flexible PCB. The requirements for flex drawing are as follows:
● Stack-up construction
● Layer order
● Dimensional drawing
● Flex PCXB materials
● Specifications
● Bend radius for flexibility
● Plating requirements
● Marking requirements
● Testing requirements


Testing instead of Prototyping


Prototyping effectively identifies areas that require attention. For instance, you should revisit the board and change some of the dimensions. However, this can be an extensive process of trial and error. A better idea is to make paper doll models to ensure you get the design right the first time.


Wrapping Up
Feel free to contact the experts at Hemeixin for consultation and quotes. They provide various services such as PCB assembly, circuit design, PCB technology, and much more. As one of the leading manufacturers of PCB, Hemeixin can help you achieve your goals. Call them today and discuss your goals.

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