Rigid-flex PCB technology removes connectors, reduces weight, and improves reliability in automotive sensors, medical imaging, aerospace guidance, and compact industrial equipment. But the technology introduces a signal-integrity challenge that rigid boards do not face to the same degree. A trace that measures 50 Ω single-ended in a rigid section can easily shift to 60 Ω or 70 Ω in the flexible section because dielectric thickness, copper type, and reference-plane geometry change. The result is reflections, jitter, higher bit error rates, and intermittent failures that only appear in the field. This guide to Impedance Control in Rigid Flex PCB: Design, Stack-up & Manufacturing Rules explains the design, material, and production disciplines…