Why you so care about internal IC design? I think that if manufacturer declares some operational and absolute maximum ratings you should trust them.
What about power of 20 dBm... Thats only 100 mW, every cell phone can transmit even more. And take a look at cell phone design, it's rather midget.
By the way, as the second poster said, if 1 A current is not a problem for 35 um thick and 1 mm wide wire, so your 4 um is enough to pass 100 mA with the same 1 mm width. By the way, if you have 100 mW power, 100 mA current corresponds to 1 V voltage supply. For greater voltage your current will be less I think.