What are the advantages of PCB bottom layer of copper?

Do you know the advantages of copper bottom layer of PCB table? Engineers in the whole process of PCB design, in order to save time to ignore the table bottom of the whole board copper paving this link. Is this the right approach? Is it necessary to lay copper on the bottom of the table for PCB? What are the advantages of laying copper on the bottom of the PCB table?

First of all, we need to be clear: the bottom layer of copper is good and necessary for PCB circuit board, but the whole board copper must comply with some conditions.

PCB table bottom copper advantages:

1. From the perspective of EMC, the whole board at the bottom of the table is covered with copper, which provides extra shielding protection and noise suppression for the inner signal and the inner signal. At the same time, it also provides some shielding protection for the underlying devices and signals.

2. From the perspective of heat dissipation, since the current PCB board is more and more high-density, the BGA main chip needs to consider the heat problem more and more. The whole board copper floor improves the heat dissipation capacity of PCB board.

3. From the perspective of process analysis, the whole board is laid with copper, so that the PCB board is evenly distributed, and the PCB board can avoid bending and warping when the PCB is processed and pressed. At the same time, the PCB warping deformation caused by the different stress caused by the PCB over-reflow welding caused by the copper foil imbalance can be avoided.

Reminder: For two layers of plate, copper coating is very necessary

On the one hand, since there is no complete reference plane for the two layers, the floor can provide a return path and can also be used as a coplanar reference to achieve the purpose of impedance control. We can generally lay the ground plane at the bottom, and put the main devices and power lines and signal lines on the top. For high impedance circuit, analog circuit (analog to digital conversion circuit, switching mode power supply conversion circuit), copper coating is a good practice.

Conditions for laying copper on the bottom of the table

While the bottom layer of copper is good for printed circuit board, there are some conditions that need to be followed:

1, shop at the same time as far as possible manual shop, do not cover all at once, avoid broken copper, appropriate in the copper area to add holes to the ground plane.

Reason: The surface coppered plane will be fragmented by the surface components and signal wires. If there is poorly grounded copper foil (especially the thin long broken copper), it will become an antenna, resulting in EMI problems.

2. Consider especially the thermal balance of small devices, such as 0402 0603 and other small packages, to avoid the presence of monument effect.

Reason: If the whole plate is covered with copper and the pin of the component is fully connected, the heat will be lost too fast, resulting in difficulties in diswelding and repairing welding.

3. The whole slab paving is the best continuous paving, and the distance from the paving to the signal needs to be controlled to avoid the impedance discontinuity of the transmission line.

Reason: Copper sheets that are too close to each other when paving the floor will change the impedance of the microstrip transmission line, and discontinuous copper sheets will also cause negative impact on the impedance discontinuity of the transmission line.

4. Some special cases depend on the application scenario. PCB design does not appear absolute design, should be combined with various theories to weigh and use.

Reason: in addition to sensitive signals need to cover the ground, if the high-speed signal lines and components are more, a lot of small and long broken copper, and the wiring channel is nervous, need to try to avoid surface copper through the hole and ground plane connection, this time the surface can choose not to spread copper.