Copper pouring, also known as copper filling, refers to using solid copper to fill the unused space on a circuit board as a reference plane. These copper areas are also called copper pours.
Functions of Copper Pouring
The main functions of copper pouring are:
- Reduce ground impedance and improve anti-interference capability;
- Lower voltage drop and enhance power supply efficiency;
- Connect to the ground to minimize the loop area.
To prevent PCB deformation during soldering, most PCB manufacturers require designers to fill empty areas of the PCB with solid copper or grid-shaped ground. However, improper copper pouring can do more harm than good—so is copper pouring "more beneficial than harmful" or vice versa?
It is well known that distributed capacitance of PCB traces plays a role at high frequencies. When the trace length exceeds 1/20 of the wavelength corresponding to the noise frequency, the antenna effect occurs, and noise will radiate outward through the traces. If there is improperly grounded copper pouring on the PCB, the copper pour will become a tool for spreading noise.
Therefore, in high-frequency circuits, never assume that a ground connection at a certain point makes it a "proper ground". It is essential to drill vias along the traces at intervals less than λ/20 to achieve "reliable grounding" with the ground plane of multi-layer boards. When copper pouring is properly handled, it not only increases current capacity but also provides shielding against interference—serving a dual purpose.
Two Forms of Copper Pouring
Copper pouring generally has two basic forms: large-area solid copper pouring and grid copper pouring. A common question is: which is better, large-area solid copper or grid copper? There is no one-size-fits-all answer.
1. Large-Area Solid Copper Pouring
Large-area solid copper pouring offers both the dual advantages of increasing current capacity and shielding. However, during wave soldering, large-area solid copper can cause the board to warp or even blister due to uneven heating. Therefore, several slots are usually cut in large-area solid copper pours to alleviate copper foil blistering.
2. Grid Copper Pouring
Pure grid copper pouring mainly serves a shielding function, with its current-carrying capacity significantly reduced. From a heat dissipation perspective, the grid design is beneficial (it reduces the heated area of copper) while still providing a certain degree of electromagnetic shielding—this is particularly useful in touch circuits and similar applications.
It should be noted that the grid is composed of crisscrossing traces. For circuits, the width of traces has a corresponding "electrical length" relative to the operating frequency of the circuit board (calculated by dividing the actual size by the digital frequency corresponding to the operating frequency; refer to relevant books for details).
At low operating frequencies, the effect of grid traces may not be obvious. However, once the electrical length matches the operating frequency, serious problems will arise—the circuit will fail to work normally, with interference signals radiating everywhere that disrupt the system.
Recommendation for Selection
Choose the appropriate copper pouring form based on the operating conditions of the designed circuit board:
- Grid copper pouring is preferred for high-frequency circuits with high anti-interference requirements;
- Large-area solid copper pouring is commonly used for low-frequency circuits or circuits requiring large current capacity.
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