EMI behavior of copper areas on outer layers of PCBs

In the design of multilayer printed circuit boards (PCBs), it is common that copper areas are introduced on the outer layers of the PCB as shown. There are different reasons for the use of these “area-fills”. Two of them are: an enhanced EMC-performance due to a reduced crosstalk, and secondly, to gain a uniformly coverage of the layer with copper to avoid an underetching of the traces. Nevertheless, PCB designers should consider that these area-fills have the potential to create serious EMC hazards. For a better understanding of these copper areas, several test structures were examined using a full wave field solver. Depending on the geometry, different resonating structures can be detected and explained. From these results, design guidelines are derived