what is the difference between layer thickness in regular digital boards and RF board

I'm asking this because some RF expert I've talked to asked this in a lecture I attended to, and didn't give the answer...
I guess there is a difference, but what is it?
In the case where the first layer is component side (what we call CS) and the second layer is GND. In RF designs, the layers should be closer or farther apart than a digital regular boards?
Thx,
Tom

The layer spacing tollerance might be tighter. But as long as you know the spacing you can adjust your trace widths for whatever it is. Hi Q RF PCBs tend to be thin overall as the Hi Q RF materials are pricy and the RF boards I design don't usually have more than 4 layers. But the spacing of my 4 RF layers is not noticably different than the spacing of a thicker digital 8 or 12 layer PCB. Depending on what you mean by RF the actual frequency range may be the same.

In both "digital" and RF boards, you need to be concerned with signal integrity as signals traverse your PCB. In both cases (especially very fast digital signals, read: high frequency content), you need to design your PCB traces to act as transmission lines. These can be coplanar, microstrip, stripline, etc. The thickness of the dielectric layers is dependent upon the characteristic impedance of your transmission lines and the relative permittivity of the dielectric material. The answer to your question is "it depends". It depends on what you are trying to accomplish, and what board materials you are using.

Ok,
thank you all for clearing this point for me.