I am working on a PCB design (power monitoring board) in which we have a high current power rail. The power monitoring board is delivering power to front end sensors through cables. The input and output currents are the same, the input and output voltages are also almost same, except few mV drop across the shunt resistor.
On the power monitoring board, we only have voltage and current monitoring circuits. I am using 35 um thick copper layers.
In the PCB stack-up, I define 3 x planes for power rail, this supply goes to front end sensors through cables and 1 x plane for return or ground. Two additional layers for routing other signals. This means in 6 layer stack-up, I have 3 x power planes and 1 x ground or return path plane. I am not sure if this is enough or should I have 2 x power and 2 x ground ?
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Questions:
Why do you think you wanted 3 PWR plane layers?
Are components on 1 side or both sides?
What is your definition of “high current”?
Without any knowledge of your exact circuit or requirements, I normally would assume this stackup;
L1 - components and signals
L2 - GND
L3 - PWRa
L4-PWRb
L5 -GND
L6 - components and signals
For high current requirements, you might choose to have components and PWR on outside layers and signals on L3 and L4. It all depends on what your circuit looks like and performance requirements of the PWR nets.
The current requirement is 12 A and the voltage is 5 V.
I think I should have two power planes and two ground planes. These will be located in four internal layers L2 to L5.
Two power planes and two ground planes are enough to carry/deliver 12 A current ?
How about using 70 um thick copper layers for power and ground planes ? Would they have lower resistance and voltage drop and higher current carrying capacity compared to 35 um thick copper layers ?
I would expect that 2 PWR and 2 GND layers will work for 12A assuming the copper area is wide enough. Going to 2 oz copper will allow lower overall resistance and better heat control although you may not need to increase the coper thickness in this case. In the end, it always comes back to the design, how it is routed and how tight that the currents need to pass through.
Note that increasing copper thickness will have some effect on minimum trace width/clearances due to the copper etch/plating process limitations.
In some cases it might be practical to go 4 layers with both inner layers at 2oz thickness. This might be a lower cost solution over 6 layer stackup. You will need to verify that with the fabricator if cost is a serious consideration. Just keep in mind that any routing on bottom layer will be referenced to PWR layer instead of GND layer.
Another idea is if the outside layers are not too busy, you can also add parallel PWR/GND copper there to increase copper in the high current paths.
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