Saturday, May 12, 2012

Ivy Bridge's high temps mystery now solved

Remember how Ivy Bridge became quite a bit hotter than Sandy Bridge? I thought this was very strange since Intel's new transistors should in theory have had much better efficiency and heat output. Well, a while ago someone on Overclockers.com's forums posted an image of an Ivy Bridge processor without the IHS (integrated heatspreader) and found out that Intel is not using their normal "fluxless die-to-heat spreader" setup, but are using regular thermal paste.
How big is the difference between regular paste and the fluxless soldering method? Overclockers.com says the thermal paste is roughly 1/16 as efficient at transferring heat from the actual CPU to the IHS.


A Japanese site actually removed the ISH and replaced the Intel stock paste with Freeze Extreme and Liquid Pro and did a few tests. The results are confirm that the poor choice of thermal paste is behind the heat issue. Here are the results but please remember that the fluxless soldering would have yielded even lower temps.
At 4.6GHz and a core voltage of 1.2V, the stock processor reached 84 degrees C. With Freeze Extreme it reached 69 degrees and with Liquid Pro it only reached 64 degrees. That's a 23% drop in temps, from simply changing thermal paste.

So yeah, the mystery is solved but replaced with a new question. Why the hell did Intel decide to go with regular thermal paste instead of the soldering? I can't imaging it being that much cheaper, and it performs much worse.
Anyway, Intel might actually change back to fluxless soldering in later revisions of the chip, but as for now the poor heat performance is linked to the thermal interface the use between the die and the heatspreader.


Edit: I should probably say that while it is possible to do what the Japanese guys did with their Ivy Bridge chip (remove the heatspreader, apply new thermal paste and then reapply the heatsink again), it is NOT recommended because you can very easily break the CPU, and it will void your warranty.
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2 comments:

  1. AnonymousMay 12, 2012 at 3:31 AM

    I still agree I find it odd that Intel would choose to go with thermal paste as opposed to a heatspreader, we discussed it some time ago and its quite obviously the same release chips (as they'd send "good" chips to benchmarkers)

    Who knows, perhaps the next hot mod to do will be retrofitting a heatspreader onto these, I think they'd get very nice temperatures then.

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    1. LAwLzMay 12, 2012 at 6:32 AM

      Well it still has a heatspreader, it's just that the material between the die and heatspreader is different. From what I understand, the heatsink was pretty much "soldered" straight to the die before which means that the heat was transfered directly into the heatspreader. With Ivy Bridge Intel is instead connecting the die and heat spreader with some rather cheap and generic looking thermal paste (instead of direct contact).

      Ivy Bridge:
      CPU Die -> thermal paste -> heatspreader -> thermal paste -> CPU cooler

      Sandy Bridge:
      CPU Die/heatspreader (direct contact) -> Thermal paste -> CPU cooler

      Each jump reduces thermal conductivity, so you want as few as possible.

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