usb wifi distance to Main board question...

Dear all:
How about min distance between USB Wifi dongle and Main board in PCB design?
usb wifi is parallel above Main board.

I can't find this in web, someone told me 10mm, is it correct?

Thanks,

10mm should be fine..

Dear vfone:
1. What's the min distance?
2. Have any material or equation?

Thanks,