What are the advantages of laying copper on the bottom of the PCB
Do you know the advantages of laying copper on the bottom of the PCB? In the whole process of PCB design, engineers want to ignore the link of laying copper on the bottom of the PCB in order to save time. Is this right? Is it necessary for the PCB to lay copper on the bottom of the surface? What are the advantages of copper on the bottom of the PCB?
First of all, we need to be clear: copper on the bottom of the surface is beneficial and necessary for the PCB, but the copper on the whole board needs to comply with some conditions.
Advantages of paving copper on the bottom of the PCB:
1. From the emc point of view, the whole board is covered with copper on the bottom of the surface, which provides additional shielding protection and noise suppression for the inner signal, and also has a certain shielding protection for the devices and signals on the bottom of the surface.
2. From the perspective of heat dissipation, as the current PCB boards are getting higher and higher density, the BGA main chip also needs to consider heat dissipation issues more and more. The copper on the whole board improves the heat dissipation capacity of the PCB board.
3. From the perspective of process analysis, the whole board is covered with copper, so that the PCB board is evenly distributed, avoiding the bending and warping of the board during PCB processing and pressing, and avoiding the different stress caused by the PCB over reflow due to the uneven copper foil The PCB is warped and deformed.
Reminder: For two-layer boards, copper coating is necessary
On the one hand, since the two-layer board does not have a complete reference plane, the ground 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 on the bottom layer, and put the main components on the top layer and take the power and signal lines. For high-impedance circuits, analog circuits (analog-to-digital conversion circuits, switch-mode power conversion circuits), copper plating is a good practice.
The condition of copper paving on the bottom surface
Although the copper on the bottom surface is good for the PCB, it also needs to follow some conditions:
1. When laying copper, try to lay it by hand, do not cover it all at once, avoid broken copper skin, and properly add via holes to the ground plane in the copper paving area.
Reason: The surface copper-clad plane must be separated by the surface components and signal lines. If there is a poorly grounded copper foil (especially the thin and long copper), it will become an antenna and cause EMI problems. .
2. Consider the thermal balance of small packages, especially small devices, such as 0402 0603, to avoid tombstone effect.
Reason: If the whole board is covered with copper, if the component pins are fully connected with copper, the heat will be lost too quickly, and it will be difficult to desolder and rework.
3. It is best to pave the whole board continuously, and the distance from the ground to the signal needs to be controlled to avoid discontinuity in the impedance of the transmission line.
Reason: The copper skin that is too close when laying the ground will change the impedance of the microstrip transmission line, and the discontinuous copper skin will also cause a negative impact on the impedance discontinuity of the transmission line.
4. Some special situations depend on the application scenario. PCB design should not be an absolute design, it should be weighed and used in combination with the theories of all parties.
Reason: In addition to sensitive signals that need to be grounded, if there are many high-speed signal lines and components, a lot of small and long copper fragments are generated, and the wiring channels are tight, it is necessary to avoid perforating the surface copper to connect to the ground plane. The surface layer can choose not to be coated with copper. The above are the advantages of laying copper on the bottom of the PCB Manufacturer. I hope to help everyone.