Big thick copper plane for distribution of 1V5 node which delivers 175A?

[treez]

Hello,
For a 1.6mm thick PCB of size 30cm * 20cm, what is the thickest copper that we can have all over one side?...4oz?
This plane distributes 175A to an array of 162 processors.

..i mean, should we really be "latticing" the copper, instead of having thick solid copper layer over the entire back and top surfaces (ground and power)?

Ditto the ground plane for this power plane.

 

[D.A.(Tony)Stewart]

I would suggest busbars instead.

 

[treez]

Thanks, due to warping of the PCB with thick uniform (non latticed) copper all over it?

 

[FvM]

You didn't tell about the wiring topology details, but in most cases, "latticing" will considerably increase the effective resistance. So it's most likely not appropriate.

I presume that you have reasons to use PCB wiring instead of bus bars. To prevent warping, you'll use an symmetrical stackup. Instead of a single very thick plane, you'll better use a sandwich of multiple planes.

 

[treez]

..thanks, so it will warp unless we have both top and botom completely covered in copper?
We cannot have bus bars, because this 1v5 plane supplies 162 processors, its a very distributed load, so we cant bus-bar to all of them...we need the big copper plane.

 

[FvM]

so it will warp unless we have both top and bottom completely covered in copper?

Not necessarily. The overall distribution of large copper features matters, not only the plane continuity.

 

[Dan Mills]

Wurth have an interesting approach involving embedding a heavy copper wire in an otherwise light copper board, might be worth a look.

Personally I would be very tempted to split the load across several point of load regulators, distributing that sort of power at 12V and then doing 4 * 50A (or even 8 * 25A) sync bucks seems likely to be less annoying then doing a single 175A plane that size.

Regards, Dan.

 

[treez]

thanks,

Personally I would be very tempted to split the load across several point of load regulators, distributing that sort of power at 12V and then doing 4 * 50A (or even 8 * 25A) sync bucks seems likely to be less annoying then doing a single 175A plane that size.

...this was suggested, but the response was that the individual nodes of each separate 1V5 regulator would be awkward to route over the PCB and keep separate.

 

[asdf44]

You can add a lot of 2oz layers without causing problems for most manufacturing processes (and may give you more options in terms of managing the distribution and voltage drop). Top layers can often be 3oz. I've found additional layers to be preferable over exotic thicknesses.

The distributed nature of the load means that 175A isn't going everywhere which makes things easier. The problem may be the source of the power. Connectors, bus bars or wires might help to provide bulk distribution to a couple initial points on the board.

 

[treez]

Thanks, one bad thing is that due to a BGA processor on the reverse of the board, we have to use 1oz copper max.....is it possible to have a pcb that has 1oz copper on the back, and say 4 oz copper on the top?

 

[FvM]

Combination of different copper weights are generally possible, with the restrictions imposed by the sequential PCB layer manufacturing. You should either learn more about the PCB manufacturing process to plan feasible stackups yourself or discuss the details with a PCB maker.

Please consider what's been said before about stackup symmetry and power plane sandwiches as possible solution for high current.

 

[D.A.(Tony)Stewart]

I have seen multicore CPU designs with 50 layer boards with daisy-chain water cooling. circa mid-80's on mainframes. ($$$) also with PCB fab and gold plating done inhouse at a Sperry plant we closed with 200K square ft in TriCity Tenn. USA. Too expensive.

You can consider a 2oz multilayer track + pwr plane for low inductance and Vcc-Gnd high capacitance, using thinnest high quality substrate. .... but for low conductance use copper tubing conduit to also supply water cooling.This will be high inductance but shunted by power/ground plane to provide low ripple. Compute all impedances and load regulation ripple.

cheapest and best cooling solution if done right with a grid manifold.

 

[marce]

I have done boards with 4 and 6oz inner layers... as long as the stack up mirrors around the centre there should be no problems, you cannot create an unbalanced stack without possible issues....

 

[ads-ee]

..thanks, so it will warp unless we have both top and botom completely covered in copper?
We cannot have bus bars, because this 1v5 plane supplies 162 processors, its a very distributed load, so we cant bus-bar to all of them...we need the big copper plane.

I really don't understand why bus bars are a no go. You don't need 162 bus bars, you need maybe 4-5 across the entire board and uniformly distribute the connections over the length of the board. This would avoid having to use really thick copper planes and all the cost associated with that. Just evenly distribute the connections from the bus bars to the PCB over the entire length and the distribution of the power should be pretty uniform over the entire board, with little voltage sag.

I don't see using a 50 layer board like someone else mentioned as very cost effective compared to using the bus bars.

 

[treez]

I have done boards with 4 and 6oz inner layers... as long as the stack up mirrors around the centre there should be no problems, you cannot create an unbalanced stack without possible issues....

Thanks, So we can have 4oz copper inner layers and 1oz copper outer layers, as long as its symetrical?

 

[ads-ee]

Here is a pretty interesting article on heavy copper traces with a nice table on the current carrying capacity of the board.