The fatigue resistance of flexible PCB (FPC) boards is a critical performance parameter, especially in applications where they are subject to repeated bending, flexing, or vibration. Fatigue failure in FPCs typically occurs due to the accumulation of mechanical stress in the conductive traces and substrate material over time, leading to cracks, delamination, or breakage. The fatigue resistance of FPCs is influenced by several factors, including the material properties of the substrate and conductive traces, the design of the circuit (e.g., trace width, thickness, and routing), and the operating conditions (e.g., temperature, humidity, and bending radius).

Substrate materials play a significant role in determining the fatigue resistance of FPCs. Polyimide (PI) is widely used as a substrate material due to its high tensile strength, excellent flexibility, and resistance to fatigue. PI substrates can withstand thousands of bending cycles without significant degradation, making them suitable for applications with frequent flexing, such as wearable devices and automotive sensors. The conductive traces in FPCs, typically made of copper, also contribute to fatigue resistance. Annealed copper, which has a softer and more ductile structure, is often used to improve the fatigue life of the traces, as it can better withstand the mechanical stress of repeated bending.

Design optimization is another key factor in enhancing the fatigue resistance of FPC boards. For example, using rounded corners on trace bends instead of sharp angles reduces stress concentration, minimizing the risk of crack formation. Additionally, incorporating flexible solder masks or cover layers can distribute mechanical stress more evenly across the FPC, reducing the strain on individual traces. Testing methods, such as cyclic bending tests, are used to evaluate the fatigue resistance of FPCs, simulating real-world operating conditions to ensure that they meet the required durability standards for their intended applications.