Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors

Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by segfaultbuserr on Tuesday August 18, 2020 @10:22PM (#24206549)

How do you connect such an enormous chip to a circuit board? What packaging and wire bonding technologies are available? I don't think it uses a conventional package like a (Flip-Chip) BGA - the process of soldering a 65535-pin BGA, and instantly losing millions of dollars if there are defective joints is simply unimaginable. The huge chip also have a heat dissipation problem that conventional packaging is unable to solve.

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Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by aveni on Tuesday August 18, 2020 @10:29PM (#24206583)

A lot of system-related questions were answered at HotChips last year: https://www.hotchips.org/hc31/HC31_1.13_Cerebras.SeanLie.v02...

And SC19: https://secureservercdn.net/198.12.145.239/a7b.fcb.myftpuplo...

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Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by npunt on Wednesday August 19, 2020 @12:09AM (#24207068)

It's mind-boggling to consider what it takes to power and cool a 15 kilowatt 'chip'. That is a huge amount of electricity.

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Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by bleepblorp on Wednesday August 19, 2020 @03:08AM (#24207933)

For comparison's sake, 15kw is enough power to heat a house in a moderate winter climate. Getting a furnance worth of power into and out of a chip without melting it is, indeed, very impressive.

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Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by segfaultbuserr on Wednesday August 19, 2020 @04:28AM (#24208337)

15 kW is 7x more than anything that can be (legally) powered from a standard European 230 V, 10 A outlet. With a 2.3 kW wall outlet, you can already power a Bitcoin miner unit or a small IBM mainframe computer. It's indeed impressive.

Which brings us to the next topic: What does the power supply look like, and how does power delivery work? Given the huge amount of power, the PSU for the chip alone is an interesting piece of electronics. Assuming its power supply is similar to a PC or server... First, the mains power is converted to a system DC voltage such as 12 V. For a typical modern cheap and boring switched-mode power supply, the standard efficiency requirement is 80%. But in this case, it means the PSU itself will waste 3 kW of energy, this is unacceptable both from an environmental and thermal perspective. A really good supply can achieve an efficiency of 95%-98%, and this is when things get interesting, at least you'll see some expensive controller chips and high-power, high-frequency transistors in such a PSU, terms like SiC, GaN or IGBT come to mind, switching 1,250 amps on and off. And it doesn't end here, the next step is converting the 12 V system voltage to the chip's core voltage, say 1.0 V, by a Voltage Regulator Module near or on the motherboard. Now, don't even mention the technical challenge of designing a VRM. I can't even imagine how they run the huge current on the motherboard, it's 15,000 amps!

Unfortunately, there's no information about power supply and power delivery.

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Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by avianes on Wednesday August 19, 2020 @07:15AM (#24209180)

There are probably several power domains in the chip and therefore several separate power supplies, which avoids the need to manage 15kW in a single spot.

Edit: In the slides shared above [1] (page 16), it says "12x 4kW hot-swappable universal PSUs".

[1] : https://secureservercdn.net/198.12.145.239/a7b.fcb.myftpuplo...

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Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by ac29 on Wednesday August 19, 2020 @10:50PM (#24219373)

Not sure why this was downvoted - a relatively small natural gas forced air heater as is common nearly everywhere I've lived in the US is about 50,000 BTU or very nearly 15kW. Its a lot of heat.

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Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by segfaultbuserr on Tuesday August 18, 2020 @10:29PM (#24206585)

Thanks for the links!

So everything is custom-developed, including wire bonding, packaging, connectors, heat spreaders, an impressive achievement. Unfortunately it's only a three-page overview, I'd love to read more on technical details.

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Re:Cerebras Wafer Scale Engine Gen2 7nm 2.6T Transistors by ChuckMcM on Wednesday August 19, 2020 @12:30AM (#24207145)

Definitely a challenge, heat dissipation is "easier" if you can glue it to a plumbed 1/2" thick copper heat exchanger.

I had an opportunity see a laser sintered copper heat exchanger that was very very efficient. Pumping in water and pulling out steam efficient. It was pretty cool.

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