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Old 10-04-2012, 12:43 PM   #566
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Default Proof that the benefit from Delidding is entirely due to reducing the CPU-to-IHS gap

OK I just couldn't let this go, it bothered me that we had not definitively determined whether or not the benefits observed in delidding these Ivy Bridge CPU's came from replacing the Intel stock CPU TIM with something superior or if it came from reducing the gap between the IHS and the CPU (reducing the thickness of the CPU TIM).

After failing to nail the gap height correctly using metal shims and thick paper shims (I used 0.203 mm metal shim stock and then 32lb paper), I decided to try again with the paper shim method only I used a thinner paper (20lb).

In an uncompressed state the paper measures 0.09mm thick with my digital calipers.

I cut out a shim using the IHS as a template. Here it is before I put the IHS onto it:

I used NT-H1 for the CPU thermal paste, I also used NT-H1 for the HSF mounting TIM.

When I was done with my tests I removed the H100, cleaned up the TIM on the IHS surface and measured the thickness of the entire CPU package with IHS to see how close the paper shim came to the original stock thickness.

Original Stock Thickness (before delidding, contains the IHS adhesive and Intel stock CPU TIM):

And the measured thickness after replacing the stock CPU TIM with NT-H1 and using the 20lb paper shim under the IHS:

They are identical! So we know the gap between the CPU and the IHS must be the same in both test conditions, meaning the differences (if any) in operating temperatures will be entirely due to thermal conductivity differences in the CPU TIM (Intel stock vs. NT-H1).

And the results?

^ Compare all the "a" cases to the "b" cases, the only functional differences in these two test conditions is the CPU TIM. Notice that the Intel stock CPU TIM outperforms the NT-H1 replacement TIM once the CPU-to-IHS gap is identical

(all the "b" cases are ~2-3C warmer than the "a" cases)

And if we remove the paper shim and drop that IHS down onto the CPU (not perfectly zero of course, there is still some NT-H1 CPU TIM there after all) reducing the gap to as close to zero as possible then we get the "c" cases...and the temperatures show the expected fantastic drops we have all come to expect from delidding our Ivy Bridge chips.

Conclusion: The Intel stock CPU TIM is not the reason Ivy Bridge's run hot, and replacing the Intel stock CPU TIM is not the reason a delidded Ivy Bridge runs so much cooler - the benefits of delidding are entirely due to the resultant reduction in gap height between the CPU silicon die and the underside of the IHS.
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