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Comment by mrtksn | Hacker News Reader

Not exactly a wafer but once I tried to create a very powerful LED bulb by combining LEDs of multiple 10W LED bulbs close together and yep, it got very hard to cool it down. I wasn't expecting to get that hot but later once I gave it some thought, I said silly me of course it would be hard to cool it down. When you put together multiple elements that heat-up, the radiator-to-heater ratio quickly deteriorates.

And now when I've red the title, the heat was the first thing that came to my mind.

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I built a 4096-pixel LED array (64x64 addressable pixels) that, when lit fully up used something like a kilowatt. However it was about 4 feet by 4 feet with spacing between each pixel and could run just fine without overheating.

These days I'm working on a PCB with many LEDs on it and heat management is much more challenging; I ended up designing the board so that the LEDs sit on thermal rectangles with through-holes (vias) that connect it to a massive ground plane (in this case it's "thermal ground" not just electric ground), as described in the datasheet for my LED chip. Each LED is 3W so it can get hot really quickly, but as long as the board is adequately coupled to a larger heat sink, it can run at fairly high power. Thermal coupling is harder than I expected! I have learned you can melt solder with a hot LED(!).

Also, it helps to run LEDs at a lower-than-max power; you get most of the light but less of the heat. Keeping LEDs in their happy zone prolongs their life signficantly.

Thanks for the tip

If there's serious work that can't be effectively done any other way then complex and esoteric cooling setups to overcome those challenges are fine to design and use.

Not sure what needs 1600 cores in one 'chip' but it's probably fairly impressive.

You can’t call it a chip anymore as it’s not cut into chips. More a slice.. perhaps they’ll put it in a 19” pizza box.

Pizza Computing

Sure, at some point solving the cooling becomes the path with least resistance. It's just surprisingly hard if you have to account in the reliability and dimensions - so it depends on the application.

I haven’t done the math - why wouldn’t something as ‘simple’ as a die diameter solid copper slug work?

Easy to drill for water cooling, and at these scales pretty cheap.

Or are we talking just getting the heat out to whatever heat management device is attached without burning something in the chip itself?

In my understanding, normally you have a tiny chip that is inside a larger package and then you can attach that packaged chip to something that takes away the heat. So the ratio of cooling element(package + heat remover) to heating element(the IC) is pretty large. Also, the speed of removing heat from the silicon IC is limited to the heat conductivity of the silicon itself and the materials used to make the package. The silicon itself is not where the heating happens but on the "etched/printed" features on top of the silicon.

Therefore, the amount of heat by heating elements(the tiny wires over the wafer) grow faster than the heat dissipation capacity, which rises the temperature until the unit breaks.

Notice that when the heating elements are close together you lose the horizontal heat gradient advantage since that grows by the perimeter when the heat generating elements grow by the area.

Which means you have to get creative, add moving parts or use more exotic materials, which makes the thing significantly more expensive and less reliable as more things to break are added.

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