PCB Design and Assembly Techniques Vary For Flexible Circuit Board
When you design a flexible circuit board, you must consider the material, fabrication, assembly and packaging processes. These vary considerably from traditional PCBs. Flexible circuits need to be able to endure significant stress, as well as the mechanical shocks of being bent and folded. This is a challenge to meet with the best possible results. To ensure you get the most durable and reliable product, be sure to follow the guidelines set forth by your flexible PCB manufacturer.
Like traditional pcb design and assembly, flexible circuit boards start with copper clad polyimide. This material is highly conductive and can be purchased either fully or partially annealed. Both forms have good flex properties. The annealing process helps reduce cracking and improves the ability to withstand repeated bending cycles. The next step in the process involves photo-imaging and development. The resulting images are used to etch the boards, which produces the final circuit board. The etched circuit boards are then baked to remove moisture and prepare them for the coverlay station.
The assembly process of a flexible circuit differs from that of traditional PCBs, as the finished products will usually include more complex wiring, connectors, and sensors than rigid-board assemblies. This means the assembling steps are more time-consuming and labor intensive. You will also need to use more adhesives than traditional PCBs. These include acrylic, epoxy, and pressure-sensitive adhesives (PSA).
How Do PCB Design and Assembly Techniques Vary For Flexible Circuit Boards?
Another important difference between flex and traditional PCBs is that there are special considerations for routing traces near bend areas. These locations can be subject to stress fractures, so the traces must be routed perpendicular to the bend line. This will protect the holes from damage. Also, be careful when stacking layers. Attempting to overlap them with traces will add stiffness and may create problems during bending.
In addition, you will want to avoid using vias in the areas of a flex circuit that will be subject to bends. If you must use them, then the plated stubs should be extended with solder fillets to help prevent peeling from flex circuit movement. You should also make sure to use teardrop shaped vias, which lessen the likelihood of stress concentration spots. Finally, make sure to give via annular rings the largest size possible.
As a result of these differences, you should only work with a reputable flexible PCB manufacturer. These experts should be able to assist you with the design, manufacture, and assembly of your product. They should also be able to offer you flexible PCB prototypes for testing and evaluation.
Flex circuits are a great option for integrating form and function into your electronic product design. By combining multiple circuits into one, they can save space and weight. In addition, they can help you reduce the number of assembly steps needed, which will in turn lower your production cost. However, as with any type of electronics manufacturing, there are some risks involved. In particular, you should be aware of the differences between pcb design and assembly and flexible pcb design to ensure your product is successful.