I haven't looked at the flux-less bonding patents mentioned in the article, so I'm not sure just how difficult it would be to create that bond without flux, but otherwise it shouldn't be that difficult in principle to spread a thin layer of solder paste, then attach the heatsink and heat them to reflow and form the bond. That's basically how the QFN[1] and other 'no-leads' ICs are mounted.
There are 2 big problems though: You've got a huge overhang area, so if you do use flux, it's not going to be able to escape, and will stay as voids in the joint. But if you don't, you'll have to find some other way to replicate the cleaning and oxide stripping behaviour in order to get the solder to bond properly. Chemical cleaning and then storage/soldering in an inert atmosphere might help, but I don't know.
Secondly, and perhaps more importantly, it's really quite hard to reflow (heat to melting point) the solder layer attached to your big heatsink, without bringing the whole assembly up to that temperature (what with the whole point of the heatsink being to get heat away from there as fast as possible). And if you do that, even if you don't fry the chip straight away, you've now got all that thermal energy stored in the large mass of the heatsink to dissipate. And it has to be done relatively evenly to avoid mechanical stress on the joint due to material expansion/contraction.
Actually yeah, having thought it through, it is going to be pretty tricky :)
Comments
I haven't looked at the flux-less bonding patents mentioned in the article, so I'm not sure just how difficult it would be to create that bond without flux, but otherwise it shouldn't be that difficult in principle to spread a thin layer of solder paste, then attach the heatsink and heat them to reflow and form the bond. That's basically how the QFN[1] and other 'no-leads' ICs are mounted.
There are 2 big problems though: You've got a huge overhang area, so if you do use flux, it's not going to be able to escape, and will stay as voids in the joint. But if you don't, you'll have to find some other way to replicate the cleaning and oxide stripping behaviour in order to get the solder to bond properly. Chemical cleaning and then storage/soldering in an inert atmosphere might help, but I don't know.
Secondly, and perhaps more importantly, it's really quite hard to reflow (heat to melting point) the solder layer attached to your big heatsink, without bringing the whole assembly up to that temperature (what with the whole point of the heatsink being to get heat away from there as fast as possible). And if you do that, even if you don't fry the chip straight away, you've now got all that thermal energy stored in the large mass of the heatsink to dissipate. And it has to be done relatively evenly to avoid mechanical stress on the joint due to material expansion/contraction.
Actually yeah, having thought it through, it is going to be pretty tricky :)
[1] https://en.wikipedia.org/wiki/Quad-flat_no-leads_package