Should the PCB design surface be coated with copper?

In pcb design, we often wonder whether the surface of the pcb should be covered with copper? This actually depends on the situation, first we need to understand the advantages and disadvantages of surface copper.

First let’s look at the benefits of copper coating：

1. The copper surface can provide additional shielding protection and noise suppression for the inner signal;
2. Can improve a heat dissipation capacity of pcb
3. In the PCB production process, save the amount of corrosive agent;
4. Avoid PCB warping deformation caused by PCB over reflow stress caused by copper foil imbalance

The corresponding surface coating of copper also has corresponding disadvantages:

1, the outer copper-covered plane will be separated by the surface components and signal lines fragmented, if there is a poorly grounded copper foil (especially that thin long broken copper), it will become an antenna, resulting in EMI problems;

For this kind of copper skin we can also dig through the function of the software

2.If the component pin is covered with copper and fully connected, it will cause heat loss too fast, resulting in difficulties in welding and repair welding, so we usually use the copper laying method of cross connection for the patch components

Therefore, the analysis of whether the surface is coated with copper has the following conclusions:

1, PCB design for the two layers of board, copper coating is very necessary, generally in the bottom floor, the top layer of the main device and walk the power line and signal line.
2, for high impedance circuit, analog circuit (analog-to-digital conversion circuit, switching mode power supply conversion circuit), copper coating is a good practice.
3.For multi-layer board high-speed digital circuits with complete power supply and ground plane, note that this refers to high-speed digital circuits, and copper coating in the outer layer will not bring great benefits.
4.For the use of multi-layer board digital circuit, the inner layer has a complete power supply, ground plane, copper coating in the surface can not significantly reduce crosstalk, but too close to the copper will change the impedance of the microstrip transmission line, discontinuous copper will also cause a negative impact on the transmission line impedance discontinuity.
5.For multilayer boards, where the distance between the microstrip line and the reference plane is <10mil, the return path of the signal is directly selected to the reference plane located below the signal line, rather than the surrounding copper sheet, because of its lower impedance. For double-layer plates with a distance of 60mil between the signal line and the reference plane, a complete copper wrapper along the entire signal line path can significantly reduce noise.
6.For multi-layer boards, if there are more surface devices and wiring, do not apply copper to avoid excessive broken copper. If the surface components and high-speed signals are less, the board is relatively empty, in order to PCB processing requirements, you can choose to lay copper on the surface, but pay attention to the PCB design between the copper and high-speed signal line at least 4W or more, to avoid changing the characteristic impedance of the signal line