Crosstalk is an important part of the EMC design of a PCB. A PCB with a good EMC design must be able to avoid common-mode interference current flowing through the internal circuit of the product and directing it to the earth, low-impedance housing, or non-sensitive circuit areas of the circuit.

Thus, a crosstalk problem must be considered, that is, the common mode interference current flows through the region and the common mode current does not flow through the sensitive current region. If the crosstalk problem is not considered, there must be electric field (capacitive coupling) or magnetic field (inductive coupling) coupling between the two regions, which will eventually lead to design failure. Similarly, the EMI noise source circuit inside PCB, such as clock generating circuit, clock transmission line, switching circuit of switching power supply, high-frequency signal line, and EMI noise or common mode voltage of products must also be isolated inside the circuit to avoid coupling with peripheral circuits or cables, and eventually form radiation.