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How do I use power planes?

Power planes are often required for low noise requirements and consist of complete layers of copper (excluding through holes) and are normally on internal layers. For this purpose a PCB with 4 layers or more is required.

Start your project and complete your schematic design in the normal way. Ensure the nets such as VCC and GND that will be assigned for the power planes are named. The (illustrational) schematic below is used for this example.

Example_Schematic.png

Note that the top and bottom traces have their net names displayed and are named VCC and GND.

 

The next step is to "Translate to PCB" and select a technology file for 4 or more layers, here we select 2 signal plus 2 planes.

Translate_to_PCB_2_sig_2_plane.png

 

Now assign the layers. Select "Define Layers", 4 layer board and assign the Powerplane layers to VCC and GND.

Specify_layers.png

The PCB view will appear in the normal way, place your components as required. You will notice some used pads do not have air wires and a symbol showing two quadrants of a circle is present, these are the pads that require a connection to the powerplane. Through hole components such as the pad on Q1 do not have this symbols as they have a path to the required powerplane and are connected.

PCB_showing_powerplane_connections.png

 

Using the autorouter these surface mount pads will if possible automatically have a via connected by a short track to the pad and connect to the powerplane.

 

The PCB will appear as shown. The layout can now be optimised by positioning the components as required. The component plus the powerplane via's can be selected and moved as one item using a select box.

Vias_placed_to_planes_after_auto_route.png

 

The size of the via's can be changed in the Design Technology (shortcut Shift +T) on the Net Classes tab. Here we change both powerplanes from "Large Via" to "Via"

Via_size.png

 

Apply the settings. Now to update the layout, in-route the PCB and then autoroute again to use these new values.

After applying these changes and manually optimising the design we achieve the following layout.

Optimise_layout.png

 

View the powerplane.

To view a powerplane, from the menubar select View --> Powerplane --> Show and select the desired power plane.

Show_powerplane.png

 

The powerplane is then displayed and you can see the thermal relief and spoke connections. Here I have also highlighted the GND net (View --> Highlight Net) so that you can see the clearances.
Using the Interaction bar (shortcut F9) you may turn on and off other layers as required.

VCC_powerplane.png

Should you make any further changes to your PCB design you must regenerate the powerplanes (View --> Powerplane --> Regenerate ).

 

As always perform design checks and reports prior to manufacture.

 

 

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