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Need help on laying PCB!

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ericmar

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basic of laying pcb

Hi,

I am designing a PCB which basically is a data acquisition system tat convert analog signals to digital signals before feeding into PC.

I am not sure if I should design a 4-layer PCB or just a double-sided layer PCB to implement ground plane and power plane for EMC. Basically, I can route all my signals on 1 layer so if I m going to design this in a 4-layer PCB, my bottom layer would then not be used at all.
Wat I planned is:
Top layer - Signal layer
Internal Plane 1 - VCC
Internal Plane 2 - GND
Bottom layer - empty

Any suggestion?

Thanks,
Eric
 

mayu_wakui

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Is the EMC requirement high? most data acquisition boards use 2 layers, with planes on bottom side..
 

ericmar

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mayu_wakui said:
Is the EMC requirement high? most data acquisition boards use 2 layers, with planes on bottom side..
The EMC requirement is not high.

If I were to lay a 2 layers PCB, which plane should be placed on bottom side for a better result? The ground plane?

Wat abt the top layer? Can place VCC plane? or manually route all the VCC tracks on the top layer?

Thanks,
Eric
 

mayu_wakui

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i would normally put my gnd on the bottom side..Vcc on top side with ample area distibution..i wouldn't call it planes..you could also stitch your gnd on the bottom to the top..mainly for protecting victim lines or isolating the aggressor lines..again, it all depends on your app..
 

ericmar

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mayu_wakui said:
i would normally put my gnd on the bottom side..Vcc on top side with ample area distibution..i wouldn't call it planes..you could also stitch your gnd on the bottom to the top..mainly for protecting victim lines or isolating the aggressor lines..again, it all depends on your app..
So is it good to have many vias connected to the GND plane on the bottom layer? Or should I try to group up the adjacent GND pads and use as few vias as possible to connect to the GND plane?

Also, I am using an AC-to-DC power supply to provide power to my board and it comes with Earth connection. Should I make few mounting holes on the board and connect the GND plane to this Earth connection through the mounting points on the chasis?
 

mayu_wakui

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rule of thumb;u need ur gnd planes as large as possible to create a high impedance return path..and of course by stitching, u could connect top to bottom gnd..vias r placed scattered through both the planes to provide short current paths..it doesn't mean that having a lot of vias to stitch is good..it's all about proper placement..

is your gnd connected to earth? since ur acdc comes wif earth, so i'm under the impression that ur pcb gnd is tied to neutral..

for protection, most guard rings are placed at the edges of the board and is connected to gnd..it also helps in esd protection..

and if ur chasis is metal, u should tie it to earth..safety first my fren..
 

ericmar

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mayu_wakui said:
rule of thumb;u need ur gnd planes as large as possible to create a high impedance return path..and of course by stitching, u could connect top to bottom gnd..vias r placed scattered through both the planes to provide short current paths..it doesn't mean that having a lot of vias to stitch is good..it's all about proper placement..

is your gnd connected to earth? since ur acdc comes wif earth, so i'm under the impression that ur pcb gnd is tied to neutral..

for protection, most guard rings are placed at the edges of the board and is connected to gnd..it also helps in esd protection..

and if ur chasis is metal, u should tie it to earth..safety first my fren..
Thank you for teaching me so much.

I am thinking of laying the whole bottom layer as the GND plane.

As for the AC-DC power supply i m using, it is an open-frame module which its Earth connection is connected to its metal frame. Its COMMON (GND) is not tied to its Earth. So r u suggesting me to tie them up together for safety reason? Meaning that PCB GND that is connected to the COMMON (GND) of the AC-DC will eventually be connected to the Earth at some points?

I dont have any guard rings on my design. Is it necessary? If it is, may I know how should i lay it?

Thanks.

Sincerely,
Eric
 

mayu_wakui

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ericmar said:
Thank you for teaching me so much.

I am thinking of laying the whole bottom layer as the GND plane.

As for the AC-DC power supply i m using, it is an open-frame module which its Earth connection is connected to its metal frame. Its COMMON (GND) is not tied to its Earth. So r u suggesting me to tie them up together for safety reason? Meaning that PCB GND that is connected to the COMMON (GND) of the AC-DC will eventually be connected to the Earth at some points?

i believe ur pcb gnd is common to acdc gnd..so do not tie earth

I dont have any guard rings on my design. Is it necessary? If it is, may I know how should i lay it?

guard ring has many functions, but in ur case..i think it's not that critical..check out:

https://www.ce-mag.com/ce-mag.com/archive/01/03/0103CE_028.html


Thanks.

Sincerely,
Eric
 

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