Probably nobody tried... spot weld ICs heatsinks to PCB copper.. using solder mask around as soldering boundary and vias to help escape solder pase to the back of pcb, so we should get soldered ICs heatsink, but without need to heat whole element-just heatsink, while solder pase resistance is higher than pure copper, so it should melt first and when we do it with high spot welder currents ICs heatsink shouldn't have enougth time to absorb too much heat.
This PCB is designed to do this trick (need to remove solder mask manually in this prototype), but unsure, what could be thickness of solder mask?
I'd like use solder mask around heatsink as a small gap where solder paste only will conduct high spot weld current, so it is critical to do not have any comtact between copper PCb tracks/heatsink pads and ICs heatsink, because of PCB copper will disapear and we'll smell vaporized copper in the air, I guess
NOTE: Of course, I've welding helmet, so no worry about flying crap around during this experiment
BTW: Text on pads was made intentionally, to... mark diodes cathode and I know it might be issue with some maufacturers, but I hope they will be able manufacture this without any text layers, since everything will be later immersed in epoxy, so no need to read/write anything, but pure copper and solder mask...