polygon pour purpose question in PCB

[yefj]

Hello, in PCB there is polygon pour where whe have some shapes inside and gnd net defined it.
As i see it GND is a flat whole surface plane?
Why theu define GND wich is not a flat surface?
maybe i didnt understand properly the polygon pour purpose on GND?
Thanks.

 

[barry]

I’m not sure what you mean by a ”flat surface”. But the reason for polygon pour is the same as it would be for a plane layer: low impedance path, heat dissipation, shielding. For example, if you have a device with high power dissipation, you could put a polygon pour under it to help pull heat away from it.

 

[KlausST]

Hi,

My opinion:
Copper pour to generate low impedance GND ... means you need to understand
* high frequency current flow
* impedance calculations of traces
* understand that current flows in loops, not straight from A to B.
...and so on. I find it rather difficult and it took a lot of time for me to design "copper pour" properly.

If you are not familiar with this all, I recommend to use one solid layer for GND and nothing else. This is simple and effective.

Klaus

 

[FvM]

A layout tool provides different design options to the developer, it doesn't define their purpose or a strict scheme how to use it. Tutorials or example designs may however give an idea.

I read the question quite general, where to use copper pours and what's their specific advantage?

I'd ask in return, what kind of design are you going to make, analog or digital, high speed, high current, RF, how many layers?

 

[yefj]

Hello ,So current goes in loops.I know the term of return path in signal integrity as shown below.
i am used only to ground plane and traces above the substrate.
pour is surrounding the signal traces with VIA fence and planes as shown below?
is this poligon pour ?surrounding the trace as shown below.?

 

[FvM]

Polygone pour addresses how the copper feature is drawn, not its electrical function. Post #5 shows a trace with screening ground respectively a coplanar microstrip. The ground  can be drawn as copper pour.

 

[PCB Designers]

Hello, in PCB there is polygon pour where whe have some shapes inside and gnd net defined it.
As i see it GND is a flat whole surface plane?
Why theu define GND wich is not a flat surface?
maybe i didnt understand properly the polygon pour purpose on GND?
Thanks.


View attachment 184506

Dear Friend,

Copper pouring is performed for following purposes:

1-Grounding on two-layer PCBs: In this case, both layers are usually signal layers and there is no Reference Place, therefore ground pours can be very helpful for efficient routing by providing a central ground.
2-EMI shielding: In order to reduce noise, proper analysis is performed and based on results, suggested Power Planes are used between layers, in order to reduce noise in the PCB.
3-Heat Sink: These planes are used with VIAs, known as "thermal vias" for to remove the excess heat from the board.
4-Copper Balance: PCB ground pours can also be done by manufacturer during PCB fab by balancing the amount of copper of both sides of the board. This reduces the possibility that warping may occur during re-flow process. In this case,cross-hatching may be a better alternative to solid copper ground pours.
5-High current paths: It can be good to add surface ground pours to provide a short return path for high current devices; such as switching devices and converters, instead of running long and thick traces to a ground plane.

The above mentioned points are detailed topics themselves. You may discuss any or all in detail.

You were asking about difference between solid (flat) and hatched (non solid) Ground planes. Solid Ground Planes are good for signal health but solid planes make PCBs more rigid/less flexible.

The hatch ground provides wider, more manufacturable dimensions while retaining the flexibility of the circuit and assembly. It should be noted that cross-hatching reduces the amount of copper under a transmission line, which decreases the capacitance and raises its impedance. Using a hatch ground provides structural support needed for a dynamic or static flex ribbon without increasing the rigidity of the copper layer. on a two-sided flexible circuit. The layer can still be used for controlled impedance routing creating undesired rigidity, or the ribbon can be permanently deformed.

I hope it answers the question.

Regards,
PCB Designers