Some Pros and Cons about PCB Copper Pour
Copper pour is an important part of PCB design. Whether it is made by Chinese PCB design software or some foreign Protel, PowerPCB provides intelligent copper pour function. Then how can we make copper pour? I will share some experience with you here, and I hope it will benefit you.
The copper pour is to use the idle space on the PCB as the reference surface, and then filled with solid copper, which is also called copper filling.The significance of copper coating is to reduce the ground impedance, improve the anti-interference ability, reduce the pressure drop and improve the power efficiency, connect with the ground wire, and also reduce the area of the loop. Also for PCB welding as far as possible without deformation, most PCB manufacturers will also require PCB designers filled copper wire or grid in the PCB free area, if the improper processing of copper, the copper is “The loss outweighs the gain., whether the advantages outweigh the disadvantages” or “more harm than good?
We all know that in case of high frequency, capacitance wiring on printed circuit board will play a role, when the noise frequencies greater than the length of the corresponding wavelength 1/20, will produce the antenna effect and noise will be emitted outside through wiring, if there are bad grounding copper clad in PCB, copper became the spread tool of noise. Therefore, in the high frequency circuit, do not think a place connects ground, this is the ground ,the space is less than λ/20, placed via on the wiring , ground plane and multilayer board “well grounded”. If copper pour is properly treated, the copper cladding can not only increase the current, but also play a double role in shielding interference.
Copper pour generally has two basic ways, that is large area of copper clad and grid copper. It is often asked that large area copper pour is good or grid pour copper is good. This is not a good generalization. Why? The large area of copper pour, with the double effect of increasing current and shielding, but if welding, the plate may be warped up, and even bubble. Therefore, a large area of copper will also open several grooves to relieve blister of copper foil. The pure grid copper pour is mainly shielding effect, and the effect of increasing current is reduced. From the point of view of heat dissipation, the grid is beneficial (it reduces the heating surface of copper) and acts as a certain electromagnetic shielding.However, it is necessary to point out that the grid is composed of alternating direction line, we know that for the circuit, walk the line width of the operating frequency for the circuit board is its “electric length” (digital frequency corresponding to the actual size divided by the working frequency can be specific to the relevant books). When the working frequency is not very high, the function of the grid can not be very obvious. Once the length of the electric power matches with the working frequency, it will be very bad. You will find that the circuit is not working at all, and the signal of the jamming system is being launched everywhere.So for the people who use the grid, the individual proposal is based on the design of the circuit board work and choose not to hold a thing. Therefore, the high frequency circuit has a high demand for multipurpose grid, and the low frequency circuit has a full current of copper with large current.
In order to achieve the desired effect, we need to pay attention to the following questions:
1.If PCB is more SGND, AGND, GND, etc., will be based on the PCB plate in different position, with the main “place” as reference to independent copper, analog ground and digital ground to separate copper from the few words, while copper before power connection the first phase should be bold: 5.0V, 3.3V and so on, as a result, on the formation of a number of different shapes of structure deformation.
2.For different single point connections, the practice is connected by 0 ohm resistors or magnetic beads or inductors.
3.Copper pour in the vicinity of the crystal oscillator, the crystal oscillator in the circuit is a high frequency emission source. The method is to cover the copper with the crystal oscillator, and then separate the shell of the crystal oscillator from the ground.
4.The problem of a solitary island (dead zone), if it is very large, it’s easy to define a via in a field.
5.When starting layout, the ground should be treated equally. When the line is taken, the ground wire should go well. It can not rely on copper overlaying to eliminate the unconnected ground pins by adding vias. This effect is not good.
6.It is best not to have a sharp angle on the board (“=180 degrees”), because from the point of view of electromagnetics, this constitutes a launching antenna! It is only big or small for others that have some influence, and it is recommended to use the edges of the arc.
7.Do not pour copper at the middle layer of the multi-layer plate in free area. Because it’s hard to make this copper “good ground”.
8.The metal in the equipment, such as metal radiator and metal reinforcing bar, must be “good grounding”.
9.The heat dissipating metal block of the three terminal regulator must be well grounded. The grounding isolation zone near the crystal oscillator must be well grounded.
In conclusion, if the grounding problem is handled well, the copper pour on the PCB will be more effective than the disadvantages. It can reduce the backflow area of the signal line and reduce the electromagnetic interference of the signal.