3 ms·

The bigger the chip, the worse the yield.

by azinman2 8mo ago

moralestapia 8mo ago
This comment doesn't make sense.
- DocJade 8mo ago
  Bigger chip = more surface area = higher chance for somewhere in the chip to have a manufacturing defect Yields on silicon are great, but not perfect
  - moralestapia 8mo ago
    Does that mean smaller chips are made from smaller wafers?
    - Sohcahtoa82 8mo ago
      Nope. They use the same size wafers and then just put more chips on a wafer.
      - moralestapia 8mo ago
        So, does a wafer with a huge chip has more defects per area than a wafer with 100s of small chips?
        dgfl 8mo ago
        There’s an expected amount of defects per wafer. If a chip has a defect, then it is lost (simplification). A wafer with 100 chips may lose 10 to defects, giving a yield of 90%. The same wafer but with 1000 smaller chips would still have lost only 10 of them, giving 99% yield.
        moralestapia 8mo ago
        As another comment referenced in this thread states, Cerebras seems to have solved by making their big chip a lot of much smaller cores that can be disposed of if they have errors.
        dgfl 8mo ago
        Indeed, the original comment you replied to actually made no sense in this case. But there seemed to be some confusion in the thread, so I tried to clear that up. I hope I’ll get to talk with one of the cerebras engineers one day, that chip is really one of a kind.
        moralestapia 8mo ago
        Yes, amazing tech. You should join their Discord, it's pretty active these days!
    - wat10000 8mo ago
      They can be made from large wafers. A defect typically breaks whatever chip it's on, so one defect on a large wafer filled with many small chips will still just break one chip of the many on the wafer. If your chips are bigger, one defect still takes out a chip, but now you've lost more of the wafer area because the chip is bigger. So you get a super-linear scaling of loss from defects as the chips get bigger. With careful design, you can tolerate some defects. A multi-core CPU might have the ability to disable a core that's affected by a defect, and then it can be sold as a different SKU with a lower core count. Cerebras uses an extreme version of this, where the wafer is divided up into about a million cores, and a routing system that can bypass defective cores. They have a nice article about it here: https://www.cerebras.ai/blog/100x-defect-tolerance-how-cerebras-solved-the-yield-problem https://www.cerebras.ai/blog/100x-defect-tolerance-how-cereb...
- azinman2 8mo ago
  Sure it does. If it’s many small dies on a wafer, then imperfections don’t ruin the entire batch; you just bin those components. If the entire wafer is a single die, you have much less tolerance for errors.
  - dekhn 8mo ago
    Although, IIUC, Cerebras expects some amount of imperfection and can adjust the hardware (or maybe the software) to avoid those components after they're detected. https://www.cerebras.ai/blog/100x-defect-tolerance-how-cerebras-solved-the-yield-problem https://www.cerebras.ai/blog/100x-defect-tolerance-how-cereb...
  - pertymcpert 8mo ago
    You can just do dynamic binning.
- Sohcahtoa82 8mo ago
  One wafer will turn into multiple chips. Defects are best measured on a per-wafer basis, not per-chip. So if if your chips are huge and you can only put 4 chips on a wafer, 1 defect can cut your yield by 25%. If they're smaller and you fit 100 chips on a wafer, then 1 defect on the wafer is only cutting yield by 1%. Of course, there's more to this when you start reading about "binning", fusing off cores, etc. There's plenty of information out there about how CPU manufacturing works, why defects happen, and how they're handled. Suffice to say, the comment makes perfect sense.
  - snovv_crash 8mo ago
    That's why you typically fuse off defective sub-units and just have a slightly slower chip. GPU and CPU manufacturers have done this for at least 15 years now, that I'm aware of.
- louiereederson 8mo ago
  You say this with such confidence and then ask if smaller chips require smaller wafers.
speedgoose 8mo ago
I suggest to read their website, they explain pretty well how they manage good yield. Though I’m not an expert in this field. I does make sense and I would be surprised if they were caught lying.
thunderbird120 8mo ago
Cerebras has effectively 100% yield on these chips. They have an internal structure made by just repeating the same small modular units over and over again. This means they can just fuse off the broken bits without affecting overall function. It's not like it is with a CPU.
- moregrist 8mo ago
  I think what you’re saying is that every wafer is usable, but won’t have the same performance characteristics, depending on how many bits are broken. Doesn’t that just bucket wafers based on performance? Which effectively gives a yield to each bucket.

The bigger the chip, the worse the yield.

moralestapia 8mo ago

This comment doesn't make sense.

DocJade 8mo ago
Bigger chip = more surface area = higher chance for somewhere in the chip to have a manufacturing defect Yields on silicon are great, but not perfect
- moralestapia 8mo ago
  Does that mean smaller chips are made from smaller wafers?
  - Sohcahtoa82 8mo ago
    Nope. They use the same size wafers and then just put more chips on a wafer.
    - moralestapia 8mo ago
      So, does a wafer with a huge chip has more defects per area than a wafer with 100s of small chips?
      - dgfl 8mo ago
        There’s an expected amount of defects per wafer. If a chip has a defect, then it is lost (simplification). A wafer with 100 chips may lose 10 to defects, giving a yield of 90%. The same wafer but with 1000 smaller chips would still have lost only 10 of them, giving 99% yield.
        moralestapia 8mo ago
        As another comment referenced in this thread states, Cerebras seems to have solved by making their big chip a lot of much smaller cores that can be disposed of if they have errors.
        dgfl 8mo ago
        Indeed, the original comment you replied to actually made no sense in this case. But there seemed to be some confusion in the thread, so I tried to clear that up. I hope I’ll get to talk with one of the cerebras engineers one day, that chip is really one of a kind.
        moralestapia 8mo ago
        Yes, amazing tech. You should join their Discord, it's pretty active these days!
  - wat10000 8mo ago
    They can be made from large wafers. A defect typically breaks whatever chip it's on, so one defect on a large wafer filled with many small chips will still just break one chip of the many on the wafer. If your chips are bigger, one defect still takes out a chip, but now you've lost more of the wafer area because the chip is bigger. So you get a super-linear scaling of loss from defects as the chips get bigger. With careful design, you can tolerate some defects. A multi-core CPU might have the ability to disable a core that's affected by a defect, and then it can be sold as a different SKU with a lower core count. Cerebras uses an extreme version of this, where the wafer is divided up into about a million cores, and a routing system that can bypass defective cores. They have a nice article about it here: https://www.cerebras.ai/blog/100x-defect-tolerance-how-cerebras-solved-the-yield-problem https://www.cerebras.ai/blog/100x-defect-tolerance-how-cereb...
azinman2 8mo ago
Sure it does. If it’s many small dies on a wafer, then imperfections don’t ruin the entire batch; you just bin those components. If the entire wafer is a single die, you have much less tolerance for errors.
- dekhn 8mo ago
  Although, IIUC, Cerebras expects some amount of imperfection and can adjust the hardware (or maybe the software) to avoid those components after they're detected. https://www.cerebras.ai/blog/100x-defect-tolerance-how-cerebras-solved-the-yield-problem https://www.cerebras.ai/blog/100x-defect-tolerance-how-cereb...
- pertymcpert 8mo ago
  You can just do dynamic binning.
Sohcahtoa82 8mo ago
One wafer will turn into multiple chips. Defects are best measured on a per-wafer basis, not per-chip. So if if your chips are huge and you can only put 4 chips on a wafer, 1 defect can cut your yield by 25%. If they're smaller and you fit 100 chips on a wafer, then 1 defect on the wafer is only cutting yield by 1%. Of course, there's more to this when you start reading about "binning", fusing off cores, etc. There's plenty of information out there about how CPU manufacturing works, why defects happen, and how they're handled. Suffice to say, the comment makes perfect sense.
- snovv_crash 8mo ago
  That's why you typically fuse off defective sub-units and just have a slightly slower chip. GPU and CPU manufacturers have done this for at least 15 years now, that I'm aware of.
louiereederson 8mo ago
You say this with such confidence and then ask if smaller chips require smaller wafers.

speedgoose 8mo ago

I suggest to read their website, they explain pretty well how they manage good yield. Though I’m not an expert in this field. I does make sense and I would be surprised if they were caught lying.

thunderbird120 8mo ago

Cerebras has effectively 100% yield on these chips. They have an internal structure made by just repeating the same small modular units over and over again. This means they can just fuse off the broken bits without affecting overall function. It's not like it is with a CPU.

moregrist 8mo ago
I think what you’re saying is that every wafer is usable, but won’t have the same performance characteristics, depending on how many bits are broken. Doesn’t that just bucket wafers based on performance? Which effectively gives a yield to each bucket.