Four layer circuit boards have the usual two external surfaces and two additional internal copper surfaces. You can design and order four layer boards in Pad2Pad. For example you might want to use a four layer board to improve capacitive coupling between Power and Ground and to reduce the size of a circuit board since less space will be taken by power and ground traces.

alt To design a four-layer circuit board:
  1. Choose Job | Settings
  2. Choose Specifications
  3. Select Number of Layers | 4 Layers.
  4. Click OK.
  5. To connect a multi-layer pad pad or a via to an internal layer of a 4-layer board, select the pad or via in the workspace and set the property bar Net property to Power or Ground. (You can also do net assignment in Nets | Edit Nets.)

Four layer circuit boards provide two extra solid internal copper layers. By default internal layers are connected to Power and Ground nets but you can change that assignment in the Edit Nets Dialog.

Pad2pad uses the following pattern to connect a multilayer pad to an internal layer when the "Thermal" connection type is selected for the pad (this is default setting):

four-layer-pcb-1

, when the "Solid" connection type is selected for the pad:

four-layer-pcb-1

and the following pattern when not connected to an internal layer:

four-layer-pcb-2

alt To indicate for a pad whether to use solid connection:
  1. Click a pad.
  2. On the property bar click the Additional properties alt button.
  3. Below "Connection to inner layer planes" choose "Solid"*.
  4. Click OK.
* The option is not available if it's not a 4-layer board or if the pad net property is not  Power or Ground.

The width of the clearance around vias and holes can be specified at Job | Settings | Specifications | Width of clearance around vias and holes.

To view the internal layers, select View | Layers... Set checkmark next to "1st inner" and "2nd inner" to open a four-layer view and see  the inner layers.  Use the Job | Analyze command to find partial net errors where a multi-layer-pad that should be connected to an inner plane is not connected. Use the X button in the upper right corner to close the four-layer view or just close the layer dialog.