I'm working on a design of a 4-layer PCB. The stackup is like this:
- Top: signal
- Inner 1: power distribution traces and copper fill (VCC) in some areas
- Inner 2: signal
- Bottom: ground plane
There is a lot of unused space on the signal layers. I'm tempted to fill this to give the board fab a break. But, should I leave these unconnected? Or connect them to ground? Or should I just not fill these spaces?