The impedance of a complete plane is low, but it does exist. If you use leads instead of planes, the impedance on the path will be higher. In addition, the pins and pads themselves also have parasitic inductance, and the transient current flowing in this path will inevitably generate a voltage drop, so the voltage at the power supply pin of the load chip will fluctuate with the change of the transient current, which is the impedance generation. power supply noise. In the power path, the voltage rail at the power pin of the load chip is collapsed, and in the ground path, the potential at the ground pin of the load chip is different from the reference ground potential (note that this is different from the ground bounce, which refers to the internal reference of the chip). The jump of ground potential relative to the board-level reference ground potential)