1. What Is Copper Pouring?
So‑called copper pouring means using the unused space on the PCB as a reference plane and filling it with solid copper – these copper areas are also called copper pours.
The purpose of copper pouring is to reduce ground impedance and improve noise immunity; to reduce voltage drop and improve power efficiency; and, when connected to ground, to reduce loop area.
Also, to minimise board warping during soldering, most PCB manufacturers require designers to fill empty areas with copper or a hatched ground grid. If copper pouring is not handled properly, the drawbacks may outweigh the benefits. So, is copper pouring "more beneficial than harmful" or vice versa?
As we all know, at high frequencies, the distributed capacitance of traces on a PCB becomes significant. When the trace length exceeds 1/20 of the wavelength corresponding to the noise frequency, the trace can act as an antenna, radiating noise. If there is a poorly grounded copper pour on the PCB, it becomes a tool for propagating noise.
Therefore, in high‑frequency circuits, do not assume that simply connecting a ground point somewhere makes it a "ground plane". Vias must be placed at intervals of less than λ/20 to provide a "good ground" connection to the multilayer board's ground plane. When copper pouring is handled correctly, it not only increases current‑carrying capacity but also provides shielding against interference.
2. Two Forms of Copper Pouring
There are generally two basic ways to pour copper: solid copper pour and hatched (grid) copper pour. People often ask whether solid copper pour or grid copper pour is better – but it is not a simple choice.
Why? Solid copper pour offers both increased current capacity and shielding, but during wave soldering, the board may warp or even blister. Therefore, solid copper pours typically have slots cut into them to relieve stress and reduce blistering.
A pure grid copper pour is mainly for shielding; its current‑carrying capacity is reduced. From a thermal perspective, the grid has advantages (it reduces the heated copper area) while still providing some electromagnetic shielding. This is especially relevant in circuits such as touch‑sensing applications (see figure below). It should be noted that a grid is composed of traces running in alternating directions. As we know, for a circuit, the trace width has a corresponding "electrical length" (actual dimension divided by the digital frequency – see relevant literature).
When the operating frequency is not very high, the grid effect may not be obvious. But once the electrical length matches the operating frequency, problems arise – the circuit may not work properly and may radiate interfering signals everywhere.
My advice is to choose based on the specific circuit board application, rather than sticking rigidly to one approach. High‑frequency circuits with strict anti‑interference requirements often use grids, while low‑frequency circuits with high currents typically use solid copper pours.
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