Editor’s note: This question was asked in response to Electronics Cooling’s recent webinar by Roger Stout. To view the webinar, click here.
Question: I thought power density (W/sq.mm) went up at the rate of Moore’s Law? Are you saying it doesn’t?
Answer: Yes and no. The problem is, feature size on silicon chips keeps decreasing – that’s what Moore’s Law is all about. As feature size decreases, various other aspects of silicon technology, such as Rdson, change such that power dissipation tends to increase per sq.mm. The problem is, there are fundamental physical laws that dictate how much heat you can get out of the silicon, per sq.mm. for a given allowed temperature rise. (In fact, I’ve seen data showing that in certain high-performance computing applications, they want actually want to reduce maximum chip operating temperature, which only makes matters worse!) Free convection air cooling imposes one limit; forced air a higher limit; liquid cooling presents a higher limit; micro-channel cooling yet an even higher limit. But these are true limits, and at some point, there’s no advantage in decreasing feature size, because you’ll still have to get the heat out, so you’ll need more silicon to do it, not less. And I’ve used the surface flux density of the sun as a sort-of benchmark, but the fact is, chip technology and cooling technology is being developed today that actually surpasses the sun’s surface flux density by a factor of 5. That’s pretty amazing.
– Roger Stout
