Signal lines are common choice for ESD protection because they are internally connected to sensitive ICs, and because they often have exposed connectors. Signal degradation can become an issue when ESD protection diodes are applied to a signal pin, especially on high speed data lines. Looking at the insertion loss table on this slide, a 5pF diode will introduce an unacceptable amount of insertion loss at gigabit speed. For signal lines such as USB3 that can operate over 5GHz speeds, a terminal capacitance of 0.3pF is suitable. Even lower capacitance diodes, such as 0.1pF, are recommended if the PCB traces are long and prone to loss, or if the user is working with a very high frequency.