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To: Reseller Mike who wrote (239010)	8/17/2007 6:33:03 PM
From: j3pflynn	Respond to of 275872

RM - Your recollection and reality are correct and haven't changed.

To: Reseller Mike who wrote (239010)	8/17/2007 7:46:18 PM
From: wbmw	Read Replies (2) \| Respond to of 275872

Re: My recollection from about 20 years ago was that case temperature (Tc) is not the same as junction temperature (Tj). I've come to learn that there is an obvious difference between posts designed to chastise, or degrade another poster, and posts designed to educate. Yours is clearly not the latter. One might be inclined to ask why not follow such a statement made above, with the appropriate definition handy that would help a fellow reader to actually distinguish the difference between junction and case temperatures? It's an interesting question, and one I would love for you to answer for me some day. Has it become so easy and fashionable to attack one's character on SI that it no longer becomes profitable to educate? Rather than attempt to answer that question for you, let me take on the burden of educating, since you are either too lazy or just plain uninclined to do so. The junction is the thing that produces the heat, and therefore, junction temperature is the temperature at the heat producing element. In this case, the silicon die. The case is the surface interface material that the heat passes through on its way to reaching the ambient air. Therefore, the case temperature would be the temperature of the top of this interface material, which in this case is the heat spreader device on top of the CPU package. Tj would presumably be larger than Tc, since some of the head is presumably lost through the edges of the material, or from the resistance of the interface itself. In order to measure Tj, one would need some kind of digital sensor in the silicon of the die itself, while measuring Tc would require any kind of temperature probe attached to the IHS of any Intel or AMD CPU. It just so happens that today, both Intel and AMD standardize around Tc, so it's irrelevant to have any kind of Tc vs. Tj debate. However, for historical reference, it's worth noting that the heat spreader interface was not always present in CPUs, and due to the flip chip package, the bottom of the silicon substrate very nearly touched the top of the chip package, which would have made Tc almost exactly equivalent to Tj, anyway. With the addition of the IHS, measuring Tc is sufficient, and both Intel and AMD do the hard calculations for the thermal designer by making their specs compatible with the area of the chip facing the ambient temperature. Please, feel free to correct me on any of this, but all I ask is that if the spirit of what I said is correct, at least mention that, too, rather than derailing the entire conversation so that you can include your zinger response.