I'm using 4 layers PCB, with the following stuck-up:
Signal1 GND VCC Signal2
the GND layer flooded with GND Not all the VCC layer flooded with VCC because I needed to route some nets there
I've some free spaces on layer 2&3&4... What should I do with it?
To flood with GND any free space? or can I just leave it without flooding...
There are more nets in the VCC layer:
Generally I try to flood as much of the board as possible to ensure consistent heating over the entire board during the reflow process. Leaving large holes in the copper pours can cause some parts of the board to heat up more than others, potentially leading to warping. Additionally, large holes in the pours potentially means a longer time to etch, which may cause over-etching in the smaller areas (around traces). I recommend flooding as much as you can, even if it's just dead copper.
How to break the planes in your pcb (with signal traces) and whether layers are partially used as planes depends on the type of signals your pcb will see. Are they very high frequency? i.e. Should you be taking controlled impedance into consideration (where planes impact what type of impedance your traces will see - stripline, microstrip, etc). If low frequency traces only, and discounting power applications (where large traces/planes are used to limit the track self-heating), then you are probably fine with the current design you have.
Use ground planes if you need them as reference to signals in inner layers. Or maybe this is your way to hold high current.
But if you don't know why would you need those planes, don't use them. Pouring planes on all layers is not for free- you may experience trouble with assembly, debug, etc.
So if you know why you pay the price- go ahead, otherwise- no need.
