First, the reasons for laying copper:

1. EMC, for a large area of ground or power copper, will play a shielding role, some special, such as PGND play a role of protection.

2. PCB craft requirements in Flexible PCB manufacturer, generally in order to ensure the plating effect, or the laminate is not deformed, laying copper for the PCB layer with less wiring.

3. Signal integrity requirements, giving the high frequency digital signal a complete return path and reducing the wiring of the DC network. Of course, there are heat dissipation, special device installation requires laying copper and so on.

Second, the advantage of copper:

The advantage of laying copper is to reduce the ground line impedance (the so-called anti-interference is also caused by a large part of the ground line impedance reduction). There are a lot of spike currents in the digital circuit. Therefore, it is more necessary to reduce the ground line impedance. It is generally considered that Circuits composed entirely of digital devices should be grounded over a large area, and for analog circuits, the ground wire loop formed by copper laying may cause electromagnetic coupling interference than it is worth (except for high frequency circuits). Therefore, it is not a circuit that has to be laid copper (BTW: mesh copper is better than the whole block in performance )

Third, the significance of laying copper:

1. The copper is connected to the ground wire to reduce the loop area.

2. Large area of copper laying is equivalent to lowering the resistance of the ground wire and reducing the voltage drop. From these two points, whether it is digital ground or analog ground, copper should be laid to increase the anti-interference ability. At the time of high frequency, the digital ground and the analog ground should be separated to lay copper, and then connected by a single point. The single point can be wound around a magnetic ring by a few turns and then connected. However, if the frequency is not too high, or the working conditions of the instrument are not bad, it can be relatively relaxed. The crystal oscillator can be counted as a high-frequency source in the circuit. You can place copper around and ground the crystal oscillator shell, which is better.