is POLYGON PLANE in PCB needed for my project ?

[hm_fa_da]

use of polygon in pcb

hi ,

i am making a payphone ,
it has both digital and analog circuits , is it good to use polygon plane in my PCB ?

and what are usages of polygon plane in PCBs , what's it's exact effect , both good and bad ?

thanks ,
hm_fa_da

 

[bone]

pcb polygon

hi ,

i am making a payphone ,
it has both digital and analog circuits , is it good to use polygon plane in my PCB ?

and what are usages of polygon plane in PCBs , what's it's exact effect , both good and bad ?

thanks ,
hm_fa_da

What i know, a polygon is a fixed copper area/shape. Commonly used to
make special pads and shapes. A area can be allot of things but i guess
there is copper you are talking about. Split/mixed area/planes is mostly
used in multilayer boards to handle power and ground.


The use of plane areas depends on the layerstack,
u need atleast 4 layers to use that in a proper way,


Thing we need to know to answer you.

How many layers are you using?
How many different power source is there in your designe. ect


The name of all this area stuff depends of
the software you are using. All vendors handle areas in there
own way.

Reg

//BoNe

 

[hm_fa_da]

polygon plane pcb

my PCB has two layers ,
i showed the polygon plane in the below pic , i think it is for reducing noise(when is connected to ground) , and i want to know if it is useful and good for my circuit ( payphone ) or not good and may make noises more and ....


thanks ,
& regards ,
hm_fa_da

 

[House_Cat]

polygon ground pcb

A polygon pour is just another way of placing copper on a printed circuit board. By itself, it has no good or bad properties.

You need to remember that every signal on a circuit board is a complete loop. For every signal trace you put on the board, there must be a complete circuit including a return path ( thus defining a signal loop ). The return path for a signal is often through the ground side of the power supply to the signal device; however, it could just as well be through the positive power supply side.

The purpose of copper flooding on a two sided board is to provide the shortest return path for each signal. You must also take care that digital and analog signals do not share the same return path. The reason is the broadband, noisy, character of the digital signal. A shared return can introduce noise into the analog circuitry from the digital circuitry. Consequently, it is sometimes prudent to split the ground and/or power areas of the copper flooding into analog and digital ground areas, and connect them at a controlled point under the most critical component.

A poorly placed polygon pour can also act as a capactive coupler for digital noise into an analog circuit, even if you keep the return paths separated. This can occur if you route a low level analog signal path close to a polygon pour that is carrying a high amplitude digital signal return (or vice-versa).

The bottom line is that you must design the circuit layout with the idea in mind of keeping digital and analog signal loops separated. You also want the signal loops to be as physically small as possible to reduce crosstalk. Finally, you want to layout the high current circuits away from the low level amplifiers. Having done all that, the polygon pours can be used to distribute both ground and power to assist in meeting the first two goals in this paragraph.

As a side note - in high frequency RF, you will sometimes see the top and bottom layers of a multilayer circuit board flooded with grounded copper polygons. The purpose of that kind of structure is to attempt to reduce radiated signals from the board to surrounding circuits and structures. It has nothing to do with the signal loops descibed earlier - those signal paths are defined with internal planes and signal trace layout on a properly engineered board. It is perhaps from that sort of RF board that the mistaken idea of copper flooding somehow reducing circuit noise gets passed along.