About where to connect ground planes...

[Franco]

Hi guys, I have a question for the routing experts.

I have a 4 layers board, in which I dedicated one internal layer (the
upper one) to a ground plane, and another internal layer (the bottom
one) for power (5V, 3v3 and some other lines are routed in this
layer).

I have some empty space at the top layer (external) and I want to fill
that space with grounded copper. The question is: Where should I
GROUND that copper? at several points (e.g. vias)? or just at one
point (e.g. one and jus one via)?

I am worried about the little ground loops that can be created between
two vias connected to two ground planes.

Best Regards...

Franco.

 

[David L. Jones]

Hi guys, I have a question for the routing experts.

I have a 4 layers board, in which I dedicated one internal layer (the
upper one) to a ground plane, and another internal layer (the bottom
one) for power (5V, 3v3 and some other lines are routed in this
layer).

I have some empty space at the top layer (external) and I want to fill
that space with grounded copper. The question is: Where should I
GROUND that copper? at several points (e.g. vias)? or just at one
point (e.g. one and jus one via)?

I am worried about the little ground loops that can be created between
two vias connected to two ground planes.

Technically, it depends on the design.
But don't be concerned, unless you are on the bleeding edge of the
performance envelope (i.e. approaching GHz), this usually won't be
something that will make make a difference.
Generally speaking, the more vias the better.

Dave.

 

[Jon Slaughter]

Hi guys, I have a question for the routing experts.

I have a 4 layers board, in which I dedicated one internal layer (the
upper one) to a ground plane, and another internal layer (the bottom
one) for power (5V, 3v3 and some other lines are routed in this
layer).

I have some empty space at the top layer (external) and I want to fill
that space with grounded copper. The question is: Where should I
GROUND that copper? at several points (e.g. vias)? or just at one
point (e.g. one and jus one via)?

What would be the point of that? The whole point of vais is to provide the
shortest route to ground and also to make it easier to route. If you use a
star ground like method I would imagine the ground plane would be somewhat
useles? I'm sure its better than nothing but I'm guessing that its
effectiveness is drastically weakend.

I am worried about the little ground loops that can be created between
two vias connected to two ground planes.

I have no idea. I imagine its not that big a deal because high performance
PCB's have many vias. Chances are you solve more problems than you create if
you use many vias rather than trying to minimize them.

 

[[email protected]]

Hi guys, I have a question for the routing experts.

I have a 4 layers board, in which I dedicated one internal layer (the
upper one) to a ground plane, and another internal layer (the bottom
one) for power (5V, 3v3 and some other lines are routed in this
layer).

I have some empty space at the top layer (external) and I want to fill
that space with grounded copper. The question is: Where should I
GROUND that copper? at several points (e.g. vias)? or just at one
point (e.g. one and jus one via)?

I am worried about the little ground loops that can be created between
two vias connected to two ground planes.

Best Regards...

Franco.

What type of application will this board be used in? Will it be
exposed to heat, moisture, etc... If so, think carefully about
flooding top and bottom layers with ground plane. Dendretic growth
could kill an otherwise good product.

Gerb

 

[Franco]

What would be the point of that? The whole point of vais is to provide the
shortest route to ground and also to make it easier to route. If you use a
star ground like method I would imagine the ground plane would be somewhat
useles? I'm sure its better than nothing but I'm guessing that its
effectiveness is drastically weakend.

The vias are already connected to the ground panel which is an
internal layer.
That is the point indeed. I don t want to "reconnect" them to a
"redundant"
ground panel, placed at the top of the board (many little ground
loops).

 

[John Larkin]

Hi guys, I have a question for the routing experts.

I have a 4 layers board, in which I dedicated one internal layer (the
upper one) to a ground plane, and another internal layer (the bottom
one) for power (5V, 3v3 and some other lines are routed in this
layer).

I have some empty space at the top layer (external) and I want to fill
that space with grounded copper. The question is: Where should I
GROUND that copper? at several points (e.g. vias)? or just at one
point (e.g. one and jus one via)?

Unless you're doing something specific like coplanar waveguide,
additional topside ground pours probably have no effect.

I am worried about the little ground loops that can be created between
two vias connected to two ground planes.

If two points are already connected by a sheet of copper, more copper
won't do much. "Ground loops" is a pretty fuzzy concept in this
context.

If you're trying to reduce the sheet resistance of the internal ground
plane for some reason, use lots of vias.

John

 

[Rich Grise]

The vias are already connected to the ground panel which is an internal
layer.
That is the point indeed. I don t want to "reconnect" them to a
"redundant"
ground panel, placed at the top of the board (many little ground loops).

It should do no harm - just FYI, that's not where "ground loops" come
from.

Cheers!
Rich

 

[Franco]

It should do no harm - just FYI, that's not where "ground loops" come
from.

Cheers!
Rich

Thanks for the quotation.

Cheers...

Franco.