A plane gets called swiss cheese when antipads, the clearance holes around vias of other nets, crowd so closely that the copper between them thins out or disappears. It typically happens under BGAs and connector pin fields, where rows of antipads merge into slots. Return currents have to detour around the holes, raising inductance and crosstalk, so designers shrink antipads, stagger vias or reroute to keep copper webbing between them.
Look at layer 2 under the connector, it's swiss cheese, the return path for those pairs is gone.
Also heard as
- swiss-cheesed plane
Related terms
Ground plane
Large continuous copper area, usually a whole layer, that serves as ground and as the reference for signals.
Fanout
Short connections that bring each pin of a dense part out to a via so it can be routed on other layers.
Sliver
Very narrow strip of copper or soldermask in the artwork that can peel loose during fabrication.