Void regions on top and bottom layer under USB and Ethernet sockets.

[Guest]

In the attached picture, you can see that under the USB and Ethernet sockets on the bottom and top layer are empty? (the board is 4 layer and the 2nd layer is GND and 3rd layer VCC, both are extended under the sockets )
anyone knows why?

[robertferanec]

This can for example help with ESD. Usually, in these cases the GND shield is not directly connected to board GND.

For example, if you would place connector very close to board GND (e.g. if you place connector shield on the top of board GND plane), then this separation (basically, there would be only a thin layer of solder mask separating shield from board GND plane) would not help for ESD protection (spark could simply jump between shield and board GND). If you remove the grounds in area under connector, you have better control how possible ESD will be travelling and discharged.

[Guest]

Thanks Robert,
Just as a question, Is there any standard regarding to these rules. Because I am faced with a new approach that I've never seen before.
till now, I know we should not extend the ground under isolation components, Transformer and high-speed sockets.

[robertferanec]

I have not seen any special documents about it - learned same way as you - noticed that in some designs and read explanation in design guides.