Flex Circuit Design Guide
A flex circuit allows the engineer to incorporate more components into a small footprint. This is important in reducing the overall weight of a product and making it more portable. However, there are several limitations to consider when designing a flex circuit.
One limitation is the minimum bend radius. This is usually around 10x the thickness of the flex board, but in high-end applications it may need to be pushed even further. Another limitation is the different coefficients of thermal expansion between copper and other materials used in the flex circuit stackup. Matching these CTEs is an important step in ensuring the long life of your flex PCB.
Flex circuits also tend to be less dense than rigid PCBs, especially with the addition of flex layers. This means you cannot have as many through holes, pads and stubs on the top side of your flex board. However, there are ways to increase the density of your flex PCB by using anchoring stubs, selective pad plating and reduced coverlay access openings.
In order to minimize signal interference, it is common to run both the signal and return lines on adjacent layers in a flex circuit. However, this can cause the traces to become thicker and create an I-beam effect when the flex circuit is bent. To avoid this, stagger the traces in each layer.
Limitations of Flex Circuit Design Guide
It is also important to consider the use of a selective copper plating process in your flex circuit design guide. This will reduce the amount of copper plated on the outside of the drilled hole and prevent additional stress on the trace during flexing. It is also recommended that the copper be rolled annealed, which will improve the mechanical bend reliability of the flex circuit.
The final limitations of a flex circuit are the physical and environmental conditions in which it will be used. Flex circuits should be tested before assembly to make sure they can withstand the environment in which they will be operated. These tests include vibration, temperature and humidity testing. If a flex circuit fails in an environmental condition, it should be evaluated to determine what the root cause is.
A flex circuit is a complex piece of engineering, and the EE and mechanical engineers must take into account many different factors during design. With proper planning and consideration, a flex circuit can provide a reliable connection inside the device. By following these flex circuit design tips, you can create a robust PCB that will work for your application. If you have any questions, please contact your CM’s engineering team. They can help you plan and execute your next project.
They can also ensure you meet IPC-610 standards and guidelines for the acceptable acceptance of PCB assemblies, including flex/rigid-flex boards. This will reduce your production time and error rates during assembly. They can even help you with any unforeseen problems, such as a faulty flex board. They will be able to quickly troubleshoot the problem and provide a solution.
