Author Topic: Running tacks in gound plain layer  (Read 517 times)

0 Members and 1 Guest are viewing this topic.

Offline Ray Hall

  • Contributor
  • Posts: 7
  • Country: au
Running tacks in gound plain layer
« on: June 11, 2018, 09:47:04 pm »
Hello,

I am making a PCB for testing automotive electronic controllers. The PCB is four layer (Top, GND, Power,Bottom). I need to run sixteen more tracks and cannot find the room to do this on the top or bottom layers. I am thinking of running them on the ground plain layer. The signals are 0 to 5 volt and 0 to 14 volts.

Is this okay to do,  or should I run them in the power plain ?

Ray.
 

Offline BocaDev

  • Contributor
  • Posts: 42
  • Country: us
Re: Running tacks in gound plain layer
« Reply #1 on: June 11, 2018, 10:04:04 pm »
If I were you, I would never touch the ground plane. Take the power plane and run a split plane with power in one and signals you need to connect in the other.
 

Offline Aspin

  • Contributor
  • Posts: 6
  • Country: au
Re: Running tacks in gound plain layer
« Reply #2 on: June 12, 2018, 02:35:49 am »
If I were you, I would never touch the ground plane. Take the power plane and run a split plane with power in one and signals you need to connect in the other.
Yes this is What I would Advise.
Noting which ever plane you Choose try to keep it to a minimum and be aware or return/supply current paths and do not cut them with these traces.
 

Offline Ray Hall

  • Contributor
  • Posts: 7
  • Country: au
Re: Running tacks in gound plain layer
« Reply #3 on: June 12, 2018, 04:15:32 am »
Thank you for your replies. I will split the power plane and keep it way from vital power supply areas.

Ray.
 

Offline ejeffrey

  • Super Contributor
  • ***
  • Posts: 2003
  • Country: us
Re: Running tacks in gound plain layer
« Reply #4 on: June 12, 2018, 05:29:22 am »
Keep in mind that at AC, ground and power planes are equivalent.  If you have any high speed signals on the bottom their return current will travel in the "power" plane, not the "ground" plane.  If those signals pass over a cut in the power plane, they will see a large inductance due to the return path disruption.  This will cause stray coupling, noise, and signal reflections.

The normal reason to split power planes is because you have multiple supplies.  If one region of your PCB is running on 3.3 V and another on 2.5 V, you would divide the power plane and try to avoid having any signals run over the gap.  Since you are doing this because you are running out of routing space, chances are you will have signals crossing the gap.  Try to keep that to low-speed, non critical signals and add supply stitching capacitors across the gap to allow a path for return currents.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf