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Why some PCB has copper circles on top and bottom layer?

Lucast85

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Hi everyone,

in these days I've looked for the Tesla Model 3 BMS and, like some other PCBs, I see the board has some dot/circle of copper on top layer.
model-3-battery-pack-bms.jpg
What is the purpose of this solution? It was designed to distribuite the copper on outer layer of the board and avoid copper plating issues (over/under plating)? Why circles and why not copper areas?

Thanks ;)
 

FvM

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These patterns are for so called "copper balancing" purposes, to achieve more uniform etching and additive copper deposition during PCB manufacturing. You see that copper balancing is blocked in some regions to guarantee creepage distance for high voltage potentials.
 

maqbool_sid

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These patterns are for so called "copper balancing" purposes, to achieve more uniform etching and additive copper deposition during PCB manufacturing. You see that copper balancing is blocked in some regions to guarantee creepage distance for high voltage potentials.
Is there any software to analyse or calculate the copper balancing ?
 

marce

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Either use proper copper pours or don't let the manufacturer do that... These days it is not required, can cause issues, it is unconnected copper after all. We never allow it on the actual PCB, it can be used on the Panel borders, but never on the actual PCB circuit.
 

FvM

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Don't agree. Some major PCB manufacturers are requesting copper balacing patterns, for what reason ever. If you have special requirements, e.g. on creepage distances, as seen in the above HV board, you'll want to generate teh copper balacing in your PCB design. Tools like Mentor Expedition are supporting it well.
 

marce

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You don't have to agree, we never ever use it and it isn't necessary, if you design the boards correctly.
 

WangJingjie

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PCB design need calculate copper area normally to protect the circle line.
 

reza147

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Hello.
I understood your question this way, what are all those holes (VIAs) for!

In designing to transfer heat out of the board, the use of VIAs is very good. Circuits that have a lot of heat.
It is also very good to use a large number of VIAs to match the ground between the layers. Circuits that consume a lot of power.
It is also very good to use a VIA to remove noise and prevent noise interference on the board. Ground VIA. Almost all circuits.
It is also very good to use VIAs to prevent the noise produced by an element. Ground VIA. Some special circuits.
S.Rezapoor
 

marce

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Well spotted, my old eyes didn't notice that the copper dots do look to have vias in them, in this case to avoid floating copper dots. Interesting, I wonder why they diden't use a 0V copper pour.
Despite what others say, we have had problems with sensitive boards (analogue and microwave) when manufacturers have added copper balancing without asking.
 

FvM

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I'm not sure if the copper dot's in post #1 are vias, the photo isn't sharp enough to see it clearly. But there are definitely copper balancing patterns on inner layers, e.g. near the upper left PCB corner.

Here's an example of copper balancing (also called copper thieving) on outer layers

1597566013052.png
 
Last edited:

marce

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I thought that it looked like a via in the middle, thanks for the enlarged view, possible an artefact of the photo, only got basic windows stuff on this laptop.
 

FvM

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My photo is from a different PCA, it doesn't say anything about the Tesla PCA, except that people use isolated copper balacing patterns in some situations.
 

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