5 ms·

> If AMD/TSMC develop a way to stack chiplets in 3 dimensions, we could wind up with another huge bump in logical transistor density per socket/node. Isn't tha

by pkaye 7y ago

> If AMD/TSMC develop a way to stack chiplets in 3 dimensions, we could wind up with another huge bump in logical transistor density per socket/node. Isn't that already done for HBM (high bandwidth memory)

monocasa 7y ago
Yeah, but it'd be way more complex if you changed those chips to being regular logic, or your memory access pattern to HBM changed. GPU memory is overwhelmingly accessed as long streaming transfers, which means that the hotspots (like, literally tiny points of high temperatures) migrate around the chip which is ideal for cooling. That's why you haven't even seen HBM for general purpose CPUs yet (I guarantee you that a threadripper could consume that bandwidth under the right circumstances).
- baybal2 7y ago
  There is nothing preventing usage of the same microvias and wafer thinning for non-memory ICs.
  - monocasa 7y ago
    Sure, but the hotspots are going to be intrinsically more localized in logic chips, or even memory chips with non streaming access patterns.
    - baybal2 7y ago
      And? Semiconductor thermal engineers are paid salaries to solve exactly that.
      - monocasa 7y ago
        I mean, we've thrown tens of billions at that problem and don't have a good solution beyond "chips with consistent hot spots array their transistors on a 2D plane, and even then you have to play games with turning parts of the chip on and off to keep it from melting itself". If you've got a solution that's manufacturable, I'm all ears, and so is every fab out there.
        heartbeats 7y ago
        I am a layman here, but couldn't they just use more aggressive cooling on the outside? If the exterior were cooled to -20°C, wouldn't that keep the interior from getting too hot as well?
        baybal2 7y ago
        That's even worse, frequent thermal shocks are not good for IC longevity. ICs frequently passing zero degrees, which aren't packaged in completely water impermeable packaging like ceramics or metal are also having issues
        heartbeats 7y ago
        Sure, they'll last shorter, but at least they will work. Besides, couldn't they keep it at a stable -20 °C? > ICs frequently passing zero degrees, which aren't packaged in completely water impermeable packaging like ceramics or metal are also having issues Issues with condensation? Well, that makes sense. So why can't they be packaged in metal or ceramics?
        baybal2 7y ago
        > Well, that makes sense. So why can't they be packaged in metal or ceramics? Money > Sure, they'll last shorter, but at least they will work. Besides, couldn't they keep it at a stable -20 °C? I can't say that. I'm not a thermal engineer
        heartbeats 7y ago
        A CPU costs at least $50 already. Is it that much more expensive to package it in metal? Also, aren't they already packaged in metal? On graphics cards, the dies are directly exposed. Liquid nitrogen cooling can already get good results in overclocking, so it seems like it should work here too.

by pkaye 7y ago

monocasa 7y ago

Yeah, but it'd be way more complex if you changed those chips to being regular logic, or your memory access pattern to HBM changed. GPU memory is overwhelmingly accessed as long streaming transfers, which means that the hotspots (like, literally tiny points of high temperatures) migrate around the chip which is ideal for cooling. That's why you haven't even seen HBM for general purpose CPUs yet (I guarantee you that a threadripper could consume that bandwidth under the right circumstances).

baybal2 7y ago
There is nothing preventing usage of the same microvias and wafer thinning for non-memory ICs.
- monocasa 7y ago
  Sure, but the hotspots are going to be intrinsically more localized in logic chips, or even memory chips with non streaming access patterns.
  - baybal2 7y ago
    And? Semiconductor thermal engineers are paid salaries to solve exactly that.
    - monocasa 7y ago
      I mean, we've thrown tens of billions at that problem and don't have a good solution beyond "chips with consistent hot spots array their transistors on a 2D plane, and even then you have to play games with turning parts of the chip on and off to keep it from melting itself". If you've got a solution that's manufacturable, I'm all ears, and so is every fab out there.
      - heartbeats 7y ago
        I am a layman here, but couldn't they just use more aggressive cooling on the outside? If the exterior were cooled to -20°C, wouldn't that keep the interior from getting too hot as well?
        baybal2 7y ago
        That's even worse, frequent thermal shocks are not good for IC longevity. ICs frequently passing zero degrees, which aren't packaged in completely water impermeable packaging like ceramics or metal are also having issues
        heartbeats 7y ago
        Sure, they'll last shorter, but at least they will work. Besides, couldn't they keep it at a stable -20 °C? > ICs frequently passing zero degrees, which aren't packaged in completely water impermeable packaging like ceramics or metal are also having issues Issues with condensation? Well, that makes sense. So why can't they be packaged in metal or ceramics?
        baybal2 7y ago
        > Well, that makes sense. So why can't they be packaged in metal or ceramics? Money > Sure, they'll last shorter, but at least they will work. Besides, couldn't they keep it at a stable -20 °C? I can't say that. I'm not a thermal engineer
        heartbeats 7y ago
        A CPU costs at least $50 already. Is it that much more expensive to package it in metal? Also, aren't they already packaged in metal? On graphics cards, the dies are directly exposed. Liquid nitrogen cooling can already get good results in overclocking, so it seems like it should work here too.