A via stub is the unused, plated portion of a via barrel that extends beyond the signal layers it is intended to connect. The unused segment behaves like an open-circuited transmission-line stub, introducing reflections, increased capacitance, and insertion loss. The reflections caused by the stub can interfere constructively or destructively with the main signal, leading to data errors or reduced eye opening. As a PCB designer, you should aim to eliminate via stubs to maintain signal integri...
