Currently I am designing a 4-layer PCB, with the layers as follows:
- (1st layer, top) signal
- (2nd layer) ground
- (3rd layer) power
- (4th layer, bottom) signal
The clock frequency is either 8 MHz (running at 3.3V) or 16 MHz (running at 5V).
There are no active RF components on the board, just surface-mounted SPI-based devices.
The total board dimensions are ~4cm x ~3cm.
My current design has no copper pour on the signal layers, but have copper pour on the ground and power layers.
So under these circumstances, would it make any difference whether or not I have a copper pour on the top and bottom signal layers?
Best Answer
All copper on the board should be consciously designed.
I am against copper pours on principle, because they seem to cause more problems than they solve - increased stray capacitance, confusion about where return currents are flowing, unintentional coupling between signals, or creation of an antenna. It can complicate debug and modification as well.
They seem to lead to a lazy mindset, where the designer thinks 'well there's lots of copper on the board, surely the grounding will be OK now!' A copper pour is unnecessary, and insufficient to achieve a good board.
There are good reasons to use a copper pour, thermal conductivity, reducing the amount of etch solution used, improving thickness tolerance, reduction of warping, beefing up of tracks, but 'should' isn't one of them.