In RF Design Basics there is an explanation about the purpose of a golden ring around the PCB edge and around some parts (functional blocks) within the PCB. However, I want to know what is the purpose of the golden area surrounding the RF traces, like in the Lime Microsystems board below. I suppose it is, again, used as a shield, but does it have to be golden in this case when it is not intended for shell mounting  ? Will the masked (painted) copper with the proper via stitching around do the same thing  ? And, is there some rule that defines the width of the surrounding area that have to be golden  ?

Thank you much for your time,

Igor

In the answers to my previous question "RF Design Basics", there are explanations about the purpose of a golden ring around the PCB edge and around some parts (functional blocks) within the PCB. 

However, I want to know: What is the purpose of the golden area surrounding the RF traces, like in the Lime Microsystems board below? I suppose it is, again, used as a shield, but does it have to be golden in this case when it is not intended for shell mounting? Will the masked (painted) copper with the proper via stitching around do the same thing? And, is there some rule that defines the width of the surrounding area that have to be golden?