Whats better for multilayer PCB a power or ground plane?

[taring77]

power and ground plane

If i have a multi layered PCB circuit to design,
For the power plane layer,
is it better to have a thick power Traces with poured ground or
is it better to have just a split poured power plane

 

[flatulent]

Re: Power or Ground plane?

You are generally better off making the ground more continuous and having what you can get for the power distribution.

 

[alphi]

Re: Power or Ground plane?

such as 4 layer:
use inner two layer for ground and power ,and more area is better for ground.

 

[EEHardware]

Power or Ground plane?

it is better to have just a split poured power plane:
1、Impedance control: If we want to control trace
impedance as a strategy for the control of reflections
(using proper trace termination techniques), then good,solid, continuous planes are almost always required. It is very difficult to control trace impedance without the use of planes.
2、Loop Areas: Loop area can be visualized as the
area defined by the path of the signal (traveling down a trace) and its return current. When the return signal is on the plane immediately under the trace, loop area is minimized. Since EMI is directly related to loop area, EMI is minimized when good, solid, continuous planes exist under traces.
3、Crosstalk: The two most practical ways to control
crosstalk are (a) separation between traces and (b)
closeness of the traces to their reference planes.
Crosstalk is inversely proportional to the square of the distance between the traces and their reference planes.
4、Planar Capacitance: The capacitance formed by
the proximity of two planes placed close together can be very important and beneficial in circuit decoupling at very high frequencies, where bypass capacitors and their associated mounting and lead inductance begin to have problems. And planar capacitance can be effective in controlling EMI radiations caused by both differential mode and common mode noise signals.

 

[xinxin]

Power or Ground plane?

EEHardware, good ideas , I'm also a RF engineer who designs mobile phone , Could u let me know ur more experiences about RF layout. thks!

 

[eternal_nan]

Power or Ground plane?

If I understood correctly, the OP wants to put both power and ground pours one one layer, if that is true than it is a very bad idea.

You really want to have power and ground planes on adjacent layers (use two layers at least for power and ground). Trying to cram both on one layer is a bad idea, as:
- the planar capacitance will vanish
- placement of decoupling caps will neccessarily
have a high-inductance path either to power or
ground
- Return paths for signals running over only one of
the two pours will be complicated in case they
need to make it into the other pour.
- You need to avoid or pay a lot of attention to
signals whose traces cross the power-ground
pour boundary.

Overall, I would say that if you REALLY HAVE TO only use one plane for power/ground use it as a ground plance and then route power using thick traces on signal layers, but pay a lot of attention to how you do this.

 

[taring77]

Re: Power or Ground plane?

Thanks all,
but i do not want power and ground layer in one layer. i know its best to have one of the inner layer a ground plane and the other a power plane that i understand.

a) my previous practise is pouring every layer ground plane. (L1-L4)
having a thick traces for power lines in one of the inner layer (eg L3) but still poured gnd

b) my current practise is having the L3 (power layer) poured of +5V and/or 3.3V. Split power plane is poured. So L3 totally no gnd

Which is better and why is that?

 

[pisoiu]

Re: Power or Ground plane?

B, allows a better capacitive coupling through pcb substrate, between power and ground planes (less noise, less EMI). Also a poured gnd around power lines in a inner layer means more spaces and potentially poor return paths. This means impedance discontinuities in the return paths, and this can seriously affect high speed signal traces routed above (if any).

/pisoiu

 

[amjad]

Re: Power or Ground plane?

It is better to have split power plane since in this case power get flooded so gives better connectivity