Ensuring Reliable Products with New Rigid-Flex Design Rules

摘要

For years flex and rigid-flex typically showed up in products as a flexible cable between two rigid boards. The past five to seven years have brought tighter space constraints and miniaturization challenges. Designers must now place components on the flexible circuit, using it like a rigid substrate. Using both the rigid and the flexible areas for components, while possible, introduces new design constraints that require more advanced PCB design strategies (FIGURE 1). Rigid and flex PCBs often use different materials, and the rigid section usually has more layers than the flex portion. Many advanced fabricators can support these designs with more than two flex layers. To ensure flex circuits with additional layers work well in all conditions, stiffeners that bring rigidity to these PCBs are placed near components or connector areas or on the opposite side. Stiffeners are made of materials such as stainless steel or aluminum, with the addition of dielectric material like a polyimide buildup. Smaller enclosures often require the flexible portion to be bent or folded.