Possible reason for Ivy Bridge heat problem explained

It has been pretty much confirmed, even by Intel, that Ivy Bridge runs a whole lot hotter than Sandy Bridge when overclocked and it appears that the reason for it was hiding under the Integrated Heat Spreader all along. It appears that Intel decided to use TIM paste rather than fluxless solder which is a much better heat conductor.

As there has always been a possibility that some Ivy Bridge CPU would die during testing, it was only a matter of time before someone took the IHS off just to have some fun and see the CPU die in its glory. The heat problem was usually attributed to either the fact that power density is greater on Ivy Bridge or to problems that Intel has with 22nm tri-gate manufacturing process.

According to a post over at Overclockers.com, the first reason is only partly true as although the power density is indeed greater it can't explain a difference of up to 20°C when overclocked Ivy Bridge and Sandy Bridge are compared. Although, there is also a minor possibility that second reason has something to do with it as Ivy Bridge certainly has a lower overclocking potential, but mostly due to heat, as some reviewers were even scared to push it beyond 4.5GHz.

Apparently, Intel decided to use TIM paste between the CPU die and IHS which results in lower heat conductivity or simply the IHS actually becomes a heat barrier rather than the heat spreader. Of course, the TIM paste usage might only be limited to engineering samples sent to reviewers, and Intel is still to give any official details regarding this issue, but for now it is quite possible that this could be Ivy Bridge's main problem, or should we say, its Cougar Point.

As briefly noted by Overclockers.com, the same issue was with Intel's E6xxx and E4xxx CPU lines and probably some others in past. Unfortunately, it looks like all is not well in Ivy Bridge world, and to make things worse we heard a few other things but we'll leave that for another article.

You can check out the Overclockers.com post here and you can check out Intel Ivy Bridge 3570K IHS removal video below.

Ivy Bridge Temperatures – It’s Gettin’ Hot in Here

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Why is Ivy Bridge so hot? Ask that question in any forum currently, and you are likely to receive one of two different popular (but not entirely correct) answers that everyone has been parroting:

“Power density is greater on Ivy Bridge than Sandy Bridge”
“Intel has problems with tri-gate/22nm”
The first answer is correct, but wrong at the same time – power density is greater, but it isn’t what is causing temperatures to be as much as 20 °C higher on Ivy Bridge compared to Sandy Bridge when overclocked. The second answer is jumping to conclusions without sufficient evidence. If you aren’t in the loop, there’s evidence of a considerable temperature difference nearly everywhere you look – we confirmed it by mirroring settings in our Ivy Bridge review, and we have read similar reports in solid testing at Anandtech as well as from other sites.

Intel is using TIM paste between the Integrated Heat Spreader (IHS) and the CPU die on Ivy Bridge chips, instead of fluxless solder.

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How does TIM paste generally compare with fluxless solder for conducting heat? Heat conductivity can be measured in watts per meter Kelvin. To be technically exact, we would need to know exactly what Intel is using for TIM paste/solder. When I went to Intel and asked, their polite answer may not surprise you – “Secret sauce”! Given that, we can use some rough approximations. A solder attach could have a heat conductivity in the range of 80 W/mK. A TIM paste could have a heat conductivity in the range of 5 W/mK. That’s your problem right there! Note that these values are not exact, as we don’t know the exact heat conductivity of Intel’s “Secret sauce”. However, these are values representative of solder or TIM paste, and there is a giant gap between how TIM paste and solder perform in regards to conducting heat. They are in different leagues.

Demonstrating the Problem

Most importantly here, if Intel is using TIM paste between the IHS and CPU die, the IHS effectively becomes a heat barrier rather than a heat spreader. Here is a rough diagram of the current heat transfer on Ivy Bridge:

CPU Die -> 5 W/mK TIM -> IHS -> 5 W/mK TIM -> Heatsink

It would be far more beneficial for temperatures to take a more direct route such as:

CPU Die -> 5 W/mK TIM -> Heatsink

Extra heat interfaces are a bad thing, especially when they have relatively low thermal conductivity. On a fundamental level, it doesn’t make much sense to do things this way from the perspective of optimal cooling. However, it could make sense from a die-protection standpoint.

In contrast, a fluxless solder attach like that described in Intel patents was invented for the specific purpose of quickly and effectively radiating heat away from the CPU die. In this situation with a solder that can conduct heat in the range of 80 W/mK and in light of tighter and tighter power densities as Intel continues to shrink its processor die, you can start to see on a fundamental level how quickly getting the heat from a very small area to a slightly larger area may be helped by the design of a soldered IHS. This still leaves the problem of a 5 W/mK TIM paste interface between IHS and heatsink, but before you get there you have a high conductivity solder attach between die and IHS that radiates the die heat to a larger area.

From the comments at the Fudzilla article:

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Paste is an interesting theory but my sense is that the root cause is that IvyB is not running at the target ~0.8V announced by Intel. Since voltage for IvyB remains
about the same than for SandyB at ~1.0V and C is higher for trigate IvyB, it is
no surprise that IvyB has a higher power ( P ~ CV^2)

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So maybe it is a problem only for the overclockers.....

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