Required For Flex Circuit PCBs
A flex circuit pcb is an electronic assembly with flexible materials designed to withstand dynamic bending and vibration. Flex PCBs are lighter, thinner and more reliable than rigid PCBs that can help to reduce design costs and enable more compact and ergonomic designs. They also provide superior thermal management, vibration resistance and improved performance.
Flex PCBs are often used in industrial equipment such as robotic arms, processing machines and bar code equipment. They can also be found in medical devices such as heart monitors and hearing aids. Consumer electronics such as smartwatches and fitness trackers use them to conform to ergonomic shapes. Automotive electronics such as infotainment systems, safety features and under-the-hood components also utilize them.
Copper is the conductive material in most flex circuit pcb and offers excellent electrical conductivity and durability for dynamic bending applications. However, copper can be prone to fatigue and work-hardening if the copper is not rolled and annealed before fabrication. Rolled and annealed copper is springier in the Z direction (the bending direction) and can handle more cycles of flexing before fatigue cracking occurs. It is important to select the appropriate copper foil grade based on your application.
What Certifications Are Required For Flex Circuit PCBs?
Stiffeners are a common material addition to flex circuits and can be added for various purposes including relief of strain, balancing weight, improving heat dissipation and adding abrasion resistance. They can be attached to the substrate using acrylic or epoxy adhesives, or they can be bonded directly with the copper. Stiffeners can be constructed of metals such as aluminum or stainless steel, or they can be made of polyimide films.
Choosing the right materials for a flex circuit requires careful consideration of all aspects of the design. For example, if the circuit will be subjected to repeated flexing, then it is critical that the layer architecture avoids stacking traces adjacent to each other. This is because if the circuits are not staggered, they can rub together and wear out over time, leading to signal interference and potentially shorting or failing. It is also advisable to limit via placement in bend areas and to add tabs or anchors to the vias, as this can prevent them from cracking.
It is also important to select the correct surface finish type. Many different types of finishes are available, and selecting the one that best suits your application can improve solderability, abrasion resistance and corrosion prevention. Lastly, the design should consider the location of any stiffeners and their impact on bending radius. Stiffeners should not be located over a bend area or a via, and it is advisable to keep the drill-to-copper distance to 8 mil or less.
When ordering a flex circuit, it is vital to choose a manufacturer that is able to produce high-quality quick-turn prototypes and production boards. It is also advisable to partner with a PCB shop that regularly produces flex and rigid-flex PCBs, as they will be familiar with the manufacturing processes and will be better able to offer advice on layouts and materials that will be optimal for your specific project.