Soldering techniques for PCB modules where all pads are on bottom
Personally I would have a framed stainless-steel stencil made, apply low temperature Sn 42 Bi 58 fine 138°C solder paste (if necessary repeat to get it perfect under the microscope) and then bake the board in an inexpensive benchtop T962 SMT oven. That's not much equipment but it does cost more than zero. 

Those pads are pretty tiny, you might also want to consider having someone do it for you.