Aducm350 thermal resistance help

Dear experts,

I checked the data sheet and it says 35*C/w As the thermal resistance of the chip. I'm sorry but I have no clue what it means and I was wondering if you could please tell me the threshold temperatures and the time duration within which this chip can be soldered properly on a PCB. I'm pretty new to the bga soldering and if you could point me in the right direction, any documents or theory I need to study specific to this bga package

PS - not sure if this is relevant, but I'm using 2 layer PCB board. Datasheet says " a device soldered in a circuit board for surface-mount packages; assumes use of a JEDEC 4-layer board. " Does my 2 layer PCB would make any difference?

Regards