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In a 2 layer PCB with a top layer densely populated, from an EMI & EMC point of view should the ground plane be on top, bottom or both and why?

Dealing with splits in my ground planeTraces over ground planeWhat are the advantages of having two ground pours?Plane pull-back and board keep-outVCC pour and decoupling capacitors on a dual layer boardSplitting Power Tracks/Planes into Different LayersWhich is the best way to ground the top layer copper pour on a PCB?In a 4-layer PCB, operating at a 8-16 MHz clock speed, should there be any copper pour on the top and bottom signal layers?2-layer PCB design, through hole technology and ground planeMaking 2 layer board, using ground pour when I already use ground plane?Four layer board in Altium Designer, the power and ground layer is shown without copper pourWhy are ground pours isolated from each other on the top layer?

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2

$begingroup$

Suppose I have a 2 layer PCB with the following characteristics:

• Top layer is relatively densely populated by both THT ad SMD components


• Bottom layer has very few traces

Among the following, what is the best option from a theoretical EMI & EMC point of view and why?

1. Top ground plane (copper pour)


2. Bottom ground plane (copper pour)


3. Both top and bottom ground planes with connecting vias

If you think another option not listed might be better please do propose it and explain why.

This is a theoretical question so I don't have a concrete example to show. Feel free to report some practical examples.

My guess is that option 2 would be the best since it allows for the current to choose the path of least resistance and avoid large loops, although maybe depending on the layout option 3 might also be reasonable.

pcb pcb-design ground emc

share|improve this question

asked 10 hours ago

mickkkmickkk

48433 gold badges77 silver badges2323 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  What makes you think that 1 or 2 is better than 3? Looking at return paths, option 3 is good at least as 1 and 2, since it is both of them...
  $endgroup$
  – Vladimir Cravero
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  If you turn the board upside down top becomes bottom.... what’s your question?
  $endgroup$
  – Andy aka
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @Andyaka the point is that one layer is densely populated by components and traces.. (i.e. the top one in this case, but it may be the bottom one as far as the problem is concerned).
  $endgroup$
  – mickkk
  9 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  related: Dealing with splits in my ground plane and Traces over ground plane
  $endgroup$
  – Nick Alexeev♦
  39 mins ago
  

  
  
  
  

add a comment | 

2

$begingroup$

Suppose I have a 2 layer PCB with the following characteristics:

• Top layer is relatively densely populated by both THT ad SMD components


• Bottom layer has very few traces

Among the following, what is the best option from a theoretical EMI & EMC point of view and why?

1. Top ground plane (copper pour)


2. Bottom ground plane (copper pour)


3. Both top and bottom ground planes with connecting vias

If you think another option not listed might be better please do propose it and explain why.

This is a theoretical question so I don't have a concrete example to show. Feel free to report some practical examples.

My guess is that option 2 would be the best since it allows for the current to choose the path of least resistance and avoid large loops, although maybe depending on the layout option 3 might also be reasonable.

pcb pcb-design ground emc

share|improve this question

asked 10 hours ago

mickkkmickkk

48433 gold badges77 silver badges2323 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  What makes you think that 1 or 2 is better than 3? Looking at return paths, option 3 is good at least as 1 and 2, since it is both of them...
  $endgroup$
  – Vladimir Cravero
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  If you turn the board upside down top becomes bottom.... what’s your question?
  $endgroup$
  – Andy aka
  9 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  @Andyaka the point is that one layer is densely populated by components and traces.. (i.e. the top one in this case, but it may be the bottom one as far as the problem is concerned).
  $endgroup$
  – mickkk
  9 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  related: Dealing with splits in my ground plane and Traces over ground plane
  $endgroup$
  – Nick Alexeev♦
  39 mins ago
  

  
  
  
  

add a comment | 

$begingroup$

Suppose I have a 2 layer PCB with the following characteristics:

• Top layer is relatively densely populated by both THT ad SMD components


• Bottom layer has very few traces

Among the following, what is the best option from a theoretical EMI & EMC point of view and why?

1. Top ground plane (copper pour)


2. Bottom ground plane (copper pour)


3. Both top and bottom ground planes with connecting vias

If you think another option not listed might be better please do propose it and explain why.

This is a theoretical question so I don't have a concrete example to show. Feel free to report some practical examples.

My guess is that option 2 would be the best since it allows for the current to choose the path of least resistance and avoid large loops, although maybe depending on the layout option 3 might also be reasonable.

pcb pcb-design ground emc

share|improve this question

asked 10 hours ago

mickkkmickkk

48433 gold badges77 silver badges2323 bronze badges

$endgroup$

share|improve this question

asked 10 hours ago

mickkkmickkk

48433 gold badges77 silver badges2323 bronze badges

share|improve this question

asked 10 hours ago

mickkkmickkk

48433 gold badges77 silver badges2323 bronze badges

asked 10 hours ago

mickkkmickkk

48433 gold badges77 silver badges2323 bronze badges

asked 10 hours ago

mickkkmickkk

48433 gold badges77 silver badges2323 bronze badges

2 Answers
2

active

oldest

votes

4

$begingroup$

You want as solid ground plane as possible, so you should have the ground on bottom and preferably have no other traces there.

For better copper balance you should also have the copper pours on the top layer to fill the empty spaces. If there isn't any better use for it, connecting the pours to the bottom ground plane with vias is a good choice. Though this has little to no effect on EMC performance.

So from your options the number 3 is the best, but if you are considering only EMC performance the option 2 is practically equally good.

Though, with this questions about 2 layer boards, I always like to remind that nowadays 4 layer boards are cheap, and using 2 layers is recommended only if you have to save every last penny, i.e. you have huge volumes. Otherwise the higher design cost of two layers will outnumber the higher production cost of 4 layers

share|improve this answer

edited 8 hours ago

answered 9 hours ago

TemeVTemeV

97311 silver badge99 bronze badges

$endgroup$

add a comment | 

1

$begingroup$

A copper pour amongst a bunch of component traces is NOT the same as a ground plane. This is because the whole point of a ground plane is to provide currents the shortest, lowest inductance (smallest loop) possible path. This does not happen in a copper pour riddled with component pads and traces since the ground/return currents must take the long route around all the interruptions.

It's just a copper pour so less etchant is required and enure more symmetrical copper balance on both sides of the board (to prevent warping) that has been connected to a fixed potential so that it doesn't float and cause EMI issues.

With this in mind:

Option 1 is not a ground plane at all.

Option 2 is a ground plane.

Option 3 is not two ground plane connected by vias. It's one copper pour on top which has been connected to a ground plane on the bottom via copper pour.

share|improve this answer

edited 9 hours ago

answered 9 hours ago

DKNguyenDKNguyen

5,79911 gold badge77 silver badges2626 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  So are you answering the OP with option 2? Your answer doesn't say...
  $endgroup$
  – TonyM
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @TonyM My point was to tell the OP the facts and have him draw his own conclusion. From an EMI/EMC point of view the difference should not matter between 2 and 3. But that doesn't mean 2 and 3 are the same in all other matters.
  $endgroup$
  – DKNguyen
  8 hours ago
  
  
  

  
  
  
  

add a comment | 

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4

$begingroup$

You want as solid ground plane as possible, so you should have the ground on bottom and preferably have no other traces there.

For better copper balance you should also have the copper pours on the top layer to fill the empty spaces. If there isn't any better use for it, connecting the pours to the bottom ground plane with vias is a good choice. Though this has little to no effect on EMC performance.

So from your options the number 3 is the best, but if you are considering only EMC performance the option 2 is practically equally good.

Though, with this questions about 2 layer boards, I always like to remind that nowadays 4 layer boards are cheap, and using 2 layers is recommended only if you have to save every last penny, i.e. you have huge volumes. Otherwise the higher design cost of two layers will outnumber the higher production cost of 4 layers

share|improve this answer

edited 8 hours ago

answered 9 hours ago

TemeVTemeV

97311 silver badge99 bronze badges

$endgroup$

add a comment | 

4

$begingroup$

You want as solid ground plane as possible, so you should have the ground on bottom and preferably have no other traces there.

For better copper balance you should also have the copper pours on the top layer to fill the empty spaces. If there isn't any better use for it, connecting the pours to the bottom ground plane with vias is a good choice. Though this has little to no effect on EMC performance.

So from your options the number 3 is the best, but if you are considering only EMC performance the option 2 is practically equally good.

Though, with this questions about 2 layer boards, I always like to remind that nowadays 4 layer boards are cheap, and using 2 layers is recommended only if you have to save every last penny, i.e. you have huge volumes. Otherwise the higher design cost of two layers will outnumber the higher production cost of 4 layers

share|improve this answer

edited 8 hours ago

answered 9 hours ago

TemeVTemeV

97311 silver badge99 bronze badges

$endgroup$

add a comment | 

$begingroup$

You want as solid ground plane as possible, so you should have the ground on bottom and preferably have no other traces there.

For better copper balance you should also have the copper pours on the top layer to fill the empty spaces. If there isn't any better use for it, connecting the pours to the bottom ground plane with vias is a good choice. Though this has little to no effect on EMC performance.

So from your options the number 3 is the best, but if you are considering only EMC performance the option 2 is practically equally good.

Though, with this questions about 2 layer boards, I always like to remind that nowadays 4 layer boards are cheap, and using 2 layers is recommended only if you have to save every last penny, i.e. you have huge volumes. Otherwise the higher design cost of two layers will outnumber the higher production cost of 4 layers

share|improve this answer

edited 8 hours ago

answered 9 hours ago

TemeVTemeV

97311 silver badge99 bronze badges

$endgroup$

share|improve this answer

edited 8 hours ago

answered 9 hours ago

TemeVTemeV

97311 silver badge99 bronze badges

answered 9 hours ago

TemeVTemeV

97311 silver badge99 bronze badges

answered 9 hours ago

TemeVTemeV

97311 silver badge99 bronze badges

1

$begingroup$

A copper pour amongst a bunch of component traces is NOT the same as a ground plane. This is because the whole point of a ground plane is to provide currents the shortest, lowest inductance (smallest loop) possible path. This does not happen in a copper pour riddled with component pads and traces since the ground/return currents must take the long route around all the interruptions.

It's just a copper pour so less etchant is required and enure more symmetrical copper balance on both sides of the board (to prevent warping) that has been connected to a fixed potential so that it doesn't float and cause EMI issues.

With this in mind:

Option 1 is not a ground plane at all.

Option 2 is a ground plane.

Option 3 is not two ground plane connected by vias. It's one copper pour on top which has been connected to a ground plane on the bottom via copper pour.

share|improve this answer

edited 9 hours ago

answered 9 hours ago

DKNguyenDKNguyen

5,79911 gold badge77 silver badges2626 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  So are you answering the OP with option 2? Your answer doesn't say...
  $endgroup$
  – TonyM
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @TonyM My point was to tell the OP the facts and have him draw his own conclusion. From an EMI/EMC point of view the difference should not matter between 2 and 3. But that doesn't mean 2 and 3 are the same in all other matters.
  $endgroup$
  – DKNguyen
  8 hours ago
  
  
  

  
  
  
  

add a comment | 

1

$begingroup$

A copper pour amongst a bunch of component traces is NOT the same as a ground plane. This is because the whole point of a ground plane is to provide currents the shortest, lowest inductance (smallest loop) possible path. This does not happen in a copper pour riddled with component pads and traces since the ground/return currents must take the long route around all the interruptions.

It's just a copper pour so less etchant is required and enure more symmetrical copper balance on both sides of the board (to prevent warping) that has been connected to a fixed potential so that it doesn't float and cause EMI issues.

With this in mind:

Option 1 is not a ground plane at all.

Option 2 is a ground plane.

Option 3 is not two ground plane connected by vias. It's one copper pour on top which has been connected to a ground plane on the bottom via copper pour.

share|improve this answer

edited 9 hours ago

answered 9 hours ago

DKNguyenDKNguyen

5,79911 gold badge77 silver badges2626 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  So are you answering the OP with option 2? Your answer doesn't say...
  $endgroup$
  – TonyM
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @TonyM My point was to tell the OP the facts and have him draw his own conclusion. From an EMI/EMC point of view the difference should not matter between 2 and 3. But that doesn't mean 2 and 3 are the same in all other matters.
  $endgroup$
  – DKNguyen
  8 hours ago
  
  
  

  
  
  
  

add a comment | 

$begingroup$

A copper pour amongst a bunch of component traces is NOT the same as a ground plane. This is because the whole point of a ground plane is to provide currents the shortest, lowest inductance (smallest loop) possible path. This does not happen in a copper pour riddled with component pads and traces since the ground/return currents must take the long route around all the interruptions.

It's just a copper pour so less etchant is required and enure more symmetrical copper balance on both sides of the board (to prevent warping) that has been connected to a fixed potential so that it doesn't float and cause EMI issues.

With this in mind:

Option 1 is not a ground plane at all.

Option 2 is a ground plane.

Option 3 is not two ground plane connected by vias. It's one copper pour on top which has been connected to a ground plane on the bottom via copper pour.

share|improve this answer

edited 9 hours ago

answered 9 hours ago

DKNguyenDKNguyen

5,79911 gold badge77 silver badges2626 bronze badges

$endgroup$

share|improve this answer

edited 9 hours ago

answered 9 hours ago

DKNguyenDKNguyen

5,79911 gold badge77 silver badges2626 bronze badges

answered 9 hours ago

DKNguyenDKNguyen

5,79911 gold badge77 silver badges2626 bronze badges

answered 9 hours ago

DKNguyenDKNguyen

5,79911 gold badge77 silver badges2626 bronze badges