About Stackup and Return Path

[batistalex]

Hi guys, I don't know if this is a really newbie question, but while I was working in a new project this question came up to my mind.

A have a board of 4 layers in the following order:
Layer 1- signal
Layer 2 - Power
Layer 3 - GND
Layer 4 - signal

It seems a good stackup, but my question is the following: The return path for layer 1 is compromised? Because although I have a GND plane, the power plane is between the signal and GND plane. What is the influence of this power plane in the return path?


Thanks in advance!

[Paul van Avesaath]

Try and put components top only maybe decoupling bottom, change L2 and L3 so it is TOP, GND, PWR, BOT

for most designs you do not need to worry about this . only if you are going highspeed it will matter

[robertferanec]

Paul van Avesaath mentioned, it depends on what you are designing. If you need controlled impedance, then you may want to use at least 6 layer stackup. Use 4 layer stackup for simple boards with short tracks like short USB or short ethernet and route these tracks on neighbor layer from GND. Sometimes even power plane is a good reference plane, but depends on your circuit and on power plane design. If you have a solid GND plane, current return path may be ok, but other parameters for example impedance / emci / emi may be influenced.

[batistalex]

Thanks for your tips guys. It really helped!