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About completing a motherboard - Issues with power supplies

mulfycrowh , 06-29-2022, 02:36 PM
Hi everyone,

Almost 2 months after having started one motherboard project, I am completing the design and I am still having some issues with the power supplies.
I have 12 layers: Bottom & Top Layers - 4 Layers dedicated to high speed signals - 4 Ground Planes - 2 Layers dedicated to power supplies.

The issues I get come from the high amount of power supplies and it is difficult to get a solution with the 2 layers dedicated to power supplies.

The attached screenshot highlights two nets I should tie together.

Any idea maybe ...
qdrives , 07-01-2022, 03:03 PM
Just my comments without any knowledge on your design.
- Component placement is key to reducing the amount of crossings. This includes power supplies.
- There is no rule that states that power may not be routed on signal layers, nor the other way around.

But for the others that my have better ideas: are the blue, cyan and green all individual (power) layers? Orange is signal layer? You mentioned only 2 power layers.
mulfycrowh , 07-02-2022, 12:15 AM
Blue is bottom layer.
I poured it with GND.
Orange is one signal layer.

I guess this is not a good idea to use one GND plane to tie these nets (red arrows) together ...
mulfycrowh , 07-02-2022, 02:35 AM
As you can see, there are a lot of vias.
Is it a problem having vias on polygon pours dedicated to power supplies ?
Now it would be very difficult to avoid them ...
qdrives , 07-02-2022, 03:27 PM
Is the Gnd plane used as a reference plane for any (power) signal?

Is it a problem having vias on polygon pours dedicated to power supplies ?
No, why would it?
Did you mean switching layers for power supplies when using polygons? Just use multiple vias. And optionally also some Gnd return companion vias. That is exactly what my proposal is the next layout. If cyan is one layer and green another, then why would the next layout not work?
robertferanec , 07-08-2022, 12:50 AM
Place the core power supplies close to the CPU and place them the way, their plane crossing will be minimum. That will help (and it is the proper way to do it). Also, have a look how they did it on the reference board, that also often helps.
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