What is dead copper (PCB island)?

Should dead copper (or "copper islands") be removed in PCB design? This question often sparks debate among engineers and designers. On one side, some argue that removing these copper islands is essential. Their reasoning typically includes three main points: first, copper islands can lead to Electromagnetic Interference (EMI) issues; second, they might amplify susceptibility to external interference; third, they are often seen as unused space that doesn't contribute to functionality.

On the other hand, others advocate for keeping them. Their arguments usually revolve around two key ideas: first, having too many blank areas on the board can negatively impact the board's structural integrity, potentially leading to uneven warping or bending; second, copper islands, when properly grounded, can offer mechanical support and stability to the PCB.

Personally, I lean towards removing dead copper islands whenever possible. These isolated copper patches can act as unintentional antennas, amplifying surrounding radiation if not properly managed. This can introduce unwanted electromagnetic interference (EMI) into nearby circuits or even the board itself. For example, if a copper island isn't well-grounded, it may inadvertently capture and transmit noise, which could interfere with signal integrity.

That said, there are cases where certain small copper islands might be worth preserving. If you decide to keep them, ensure they are adequately connected to the ground plane via vias or ground holes. This connection helps turn the island into a shield, reducing the risk of EMI while still maintaining structural benefits.

In high-frequency designs, the situation becomes more complex. At higher frequencies, the distributed capacitance of traces can create an antenna-like effect, especially when the trace length exceeds 1/20th of the wavelength of the noise frequency. In such scenarios, copper islands without proper grounding can inadvertently propagate noise, acting as unintended conductors. Therefore, it’s crucial to ensure that any copper layer is effectively grounded to the ground plane in multi-layer boards. Properly handled, copper cladding can serve a dual purpose: enhancing current flow and providing interference shielding.

Another practical benefit of retaining copper islands is their potential to reduce PCB deformation. Copper adds weight and rigidity to the board, which can help counteract issues like warping during manufacturing or prolonged use. By strategically placing ground holes and ensuring good connectivity, you can maintain both structural integrity and electrical performance.

In conclusion, while dead copper islands can be useful under specific circumstances, they generally pose more risks than benefits in most PCB designs. Removing them is often the safer choice, provided you carefully manage critical areas where copper islands might provide mechanical advantages or necessary shielding. Balancing these considerations is key to designing efficient and reliable PCBs.