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Via's and drill holes connect to ground plane different

StefanTh

Hi

 

If I have a 4 layer pcb with one layer for GND and connect vias to the GND plane it all looks fine, like this

 

image

 

 

The GND plane "connect to the via all the way around

 

 

however, when I connect the GND pin of the power supply connector to the GND plane the connections is not done "all the way around" but with 4 smaller stripes of copper, like this (lower green circle)

 

image

 

 

 

Why do it does that ?

Will it be connected all the way around in the production ?

 

The reason I am asking is that this will be the weak chain in how much current can be passed via the GND plane,

It is not the width of the wires between components in Top/Bottom layer but it is these 4 small wires and their thickness that decide it.

 

Even if I choose 140 um copper in all layers, calculate the maximum current along the normal Via's circumference and the width of the wires in top/bottom layers it is still these 4 wires that limit the current.

 

Regards

  • On 29/10/12 07:17, Stefan Olsson wrote:

    Hi

     

    If I have a 4 layer pcb with one layer for GND and connect vias to the GND plane it all looks fine, like this

     

       Image:CopperVia.png

     

    >

    The GND plane "connect to the via all the way around

     

    >

    however, when I connect the GND pin of the power supply connector to the GND plane the connections is not done "all the way around" but with 4 smaller stripes of copper, like this (lower green circle)

     

      Image:CopperDrill.png

     

    >

     

    Why do it does that ?

     

    Because it's what you want it to do! The via is just part of the PCB,

    but the hole for a connector is going to be soldered to. If it were

    connected all round it would conduct heat away and make the soldering

    difficult.

     

    Will it be connected all the way around in the production ?

     

    No. For the reason above.

     

     

    The reason I am asking is that this will be the weak chain in how much current can be passed via the GND plane,

     

    Not really, because the connections are too short to really matter, but

    you can make (at least one of) them larger either by routing a thick

    track before filling or setting the flood width wider (or possibly

    changing thermal settings).

     

    It is not the width of the wires between components in Top/Bottom layer but it is these 4 small wires and their thickness that decide it.

     

    Even if I choose 140 um copper in all layers, calculate the maximum current along the normal Via's circumference and the width of the wires in top/bottom layers it is still these 4 wires that limit the current.

     

    Well, the standard formula you're using is intended for tracks, meaning

    at least a quarter inch of length. These thermal breaks are too short

    for the formula to apply. But you can adjust the widths anyway.

     

    Cheers,

    Rob