[Albigger]

Originally Posted by bigben2k

Keep it simple.

Agreed. This has gotten very big very fast.

pH: answered my questions, thanks. IF you want to explore the IHS to CPU joint:

Originally Posted by pHaestus

The dT CPU-water is the same for the same wb at the same flow rate and at the same vcore/FSB/multi on multiple chips. Since I did the calibration of the whole soldered up system described before.

This is good info, shows consistency and that in fact, on bare die cpus the heat output may actually be fairly consistent.

And YES if CPU temps go down then C/W would decrease. How much though? Is this a constant change (an offset) for all wbs, or do some cool the IHS or die area in a way that makes them particularly affected by the change? THIS is a good question I think.

IF you think its a good question (and many others here do also) then may be worth exploring. The decrease in C/W, in general, has no reason to be a constant offset. Issues:
1) The internal geometries of the waterblock probably has an optimum C/W for a specific heating area (die size) - the effect may not be too large (for example on pin-array blocks) but may be more pronounced on concentrated cooling blocks. This (in my mind) can never be generalized as an offset, only found by a) testing each waterblock on different die sizes / die sims or b) computational fluid dynamics / other modeling
2) The IHS joint, IF variable, will introduce varying amounts of resistance to the heat path, thus on different processors the heat will diffuse more than others in the IHS, and present a larger effecting heating area to the waterblock on some cpus, and of course it will diffuse large heat flux gradients and appear a more uniform distribution.
3) the IHS joint degrades over time. I don't find this particularly interesting, and would think you would have to pick one cpu and test with one standard block over multiple heat and mounting cycles.

My take is that 1) is probably negligible for 'small' changes in die area (wrt the original die size) and can probably be logically estimated once we have some examples. I would much like to characterize 2). IF it is found that the IHS joint IS consistent, then the modeling (I believe) can portray it as just an offset (temperature) from the core. IF it is found not consistent, the best we can do is provide an 'average' offset with statistics (requires testing more cpus).

Sorry for the long-windedness. pH if you are serious about characterizing the IHS joint as I said earlier, I THINK it would be enough that if you saw uniform temp drops (NOT WITH EVERY BLOCK) but with the same block on multiple cpus after removing the IHS then you could say it is consistent. If you want to be more thorough grooving the IHS is an option and then provides a verification method.
Scenario:
1) IHS is constant/consistent. calibrated Thermocouple in grooved IHS is a constant offset (on all cpus with same cooling method) from calibrated thermocouple soldered to cpu pins. When removing IHS the temperature drop associated with a specific waterblock is the same across all cpus.
2) variable IHS - neither dT(IHS topside - core) or the temp. drop across cpus is consistent.

I may be able to groove the IHS top if you need, if this is the route you decide to go with (but would have to know the requirements before I could say for sure).