The takeaway I got from this article is that if I use solder to attach my heatsink to the spreader on my Core i5 2500K instead of thermal paste, I could get a big jump in heat conductivity. Now if only I had the tools to create a solder point that large...
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 :)
The '>20 W/mK' claimed by this method, while a lot better than the 5 W/mK of regular TIM, is still a fair way off the 80 W/mK that the article claimed for a soldered solution.
Does anyone know if any commercial CPUs have been packaged factory fused to a heatsink?
There are 200W Power 7 CPUs, and they don't have to worry about aftermarket cooling like high end x86 CPU manufacturers do. It seems like it could really make sense there.
Because a solder layer would have much higher thermal transfer rate per area than thermal paste. And the IHS is bigger than the die, resulting in better cooling (because there is more 'bandwidth' (=area) at the point where TIM is used).. which was pretty much explained in the article.
The heat sink could easily replace the role of the heat spreader if it was soldered on. It's much bigger. I could definitely see processors moving to an integrated and standardized heat sink.
That doesn't make sense - TIM is used to fill the gaps where the copper and silicon don't have direct contact (that's why you use as little of it as possible), not as a heatspreader itself. A direct heatsink-silicon contact will almost always be better for thermal conductivity...
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The takeaway I got from this article is that if I use solder to attach my heatsink to the spreader on my Core i5 2500K instead of thermal paste, I could get a big jump in heat conductivity. Now if only I had the tools to create a solder point that large...
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
Thankfully, someone already sells that. http://indigo-xtreme.com/
The '>20 W/mK' claimed by this method, while a lot better than the 5 W/mK of regular TIM, is still a fair way off the 80 W/mK that the article claimed for a soldered solution.
Does anyone know if any commercial CPUs have been packaged factory fused to a heatsink?
There are 200W Power 7 CPUs, and they don't have to worry about aftermarket cooling like high end x86 CPU manufacturers do. It seems like it could really make sense there.
Why do that when you can take the IHS off and attach the heatsink directly to the silicon? You know, like everyone does on their laptops...
Because a solder layer would have much higher thermal transfer rate per area than thermal paste. And the IHS is bigger than the die, resulting in better cooling (because there is more 'bandwidth' (=area) at the point where TIM is used).. which was pretty much explained in the article.
The heat sink could easily replace the role of the heat spreader if it was soldered on. It's much bigger. I could definitely see processors moving to an integrated and standardized heat sink.
That doesn't make sense - TIM is used to fill the gaps where the copper and silicon don't have direct contact (that's why you use as little of it as possible), not as a heatspreader itself. A direct heatsink-silicon contact will almost always be better for thermal conductivity...