Flex Circuit PCBs Be Folded
A flex circuit PCB is similar to a rigid printed circuit board but is flexible. It consists of a metal layer of conductors, typically copper, that is bonded to a dielectric layer of polyimide or other material. The thickness of the dielectric and copper can vary. The traces are etched in as many layers as the design requires. The layers are then bonded together using an adhesive, or in some cases heat sealed. The end of the flex is terminated to a connector, or in some cases with a stiffener.
The most common reason to use a flex circuit pcb is for weight reduction. The circuits are much thinner and lighter than their rigid counterparts, which can significantly reduce the overall product weight. The smaller thickness also helps with heat dissipation, making flex circuits suitable for high-temperature applications.
When designing a flex circuit, it is important to consider the bending radius. The bending radius is the amount of curvature that can be sustained by the flex circuit without cracking, delamination or excessive stress that could cause a failure. Using the PCB design software to calculate the bend radius can help ensure that the design will meet industry standards for fabrication and assembly.
Can Flex Circuit PCBs Be Folded?
To maximize flex life, it is a good idea to choose rolled annealed copper (RA copper) for the circuit traces. This type of copper has an elongated grain structure that can withstand more stressing than electro deposited copper. It is also a good idea to place the flex circuits so that the copper grain direction is perpendicular to the bending point.
Other design considerations for flex circuits include the choice of coatings. Tin and soft gold are popular choices for soldering, but a hard gold coating can be used for more demanding applications. Since flex materials are prone to more movement and contraction during manufacturing, the drill-to-copper distance should be larger to avoid stress on the copper. Using pad-only plating, in which copper is deposited only on the pads/vias, is also an option. This can allow for higher etch yields with small traces, but it may require more processing steps and increase the cost.
Finally, it is a good idea to test a prototype of the flex circuit to see how well it folds and how easy it is to assemble. In addition to ensuring that the flex will work properly, it can help to identify any unforeseen problems, such as a sharp corner or edge that could create stress points. It is also a good idea to add reinforcement in the folded areas to distribute stress and provide mechanical support.
Another consideration is the method of attaching any folded sections to the remainder of the flex circuit. This can be accomplished with epoxy, acrylic or hot-melt glue. However, these liquids can be difficult to work with and require special handling for maximum safety and quality. Additionally, they can be slow to cure which will affect the production schedule.
