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To: tcmay who wrote (78044)	4/23/2002 1:59:35 PM
From: pgerassi	Read Replies (1) \| Respond to of 275872

Dear TCMay: Your bench analogy is ok except for the fact that if the metal plate was a lead plate 3" thick and the bench was a solid block of copper, the man would be warmer on the lead plate than he would be directly on the bench. Why would a HIS made out of a material be any better than a heat sink with a base plate made of that very same metal? You have two interfaces with the HIS/HSF, but only one with the HSF alone. The die to HSF interface will be no less conductive than the same die to any HIS and sometimes could be better. The HIS/HSF interface however will be of higher resistance than the internal metal of the HSF, no matter what you do. To understand this is simple. Take two identical blocks of metal. Cut one at 1cm into one side all the way across the face. Take the best thermal compound and layer it between the pieces you cut. Now check the thermal resistance of the two. Given the same external dimensions, the uncut one will have lower thermal resistance than the cut one. Now take it one step further, cut the thin piece to 2cm square and use that. Now the cut one has even higher resistance than it had before. That is more like the situation. The HIS does not spread the heat any more than the HSF base plate and most of the time spreads it less, mostly because the HSF base plate is bigger than the HIS in area. Pete

To: tcmay who wrote (78044)	4/23/2002 9:58:57 PM
From: hmaly	Read Replies (1) \| Respond to of 275872

tcmay re...Looking at several designs, including the URL I gave, and also Intel's PIII/P4 descriptions, it's clear that heat spreaders and slugs are used to make contact to the rest of the package. Obviously so, but it bears repeating.<<< I tried but the URL didn't pop up, so I didn't read it. To increase the heat flow, the man places a 1-foot by 6-foot metal plate on the bench and then sits down on that. The metal plate is an excellent lateral (and isotropic) conductor of heat. Being that it makes contact with the wooden bench over much more area than the man's butt, it drains heat out of the man with amazing efficiency.<<<<< Perhaps I am thinking wrong. When we are talking metal spreaders, what kind of metal are we talking about? I always assumed they were simple iron, but then your analogy about the wooden bench would be ass backwards, (pun intended), as the aluminum or copper heat sinks would be more conductive than a metal spreader. I am probably out of my league here, as most of my knowledge here is from car radiators. Yes your parallelism is important, as a bigger radiator can disperse more heat, but Mani's point is also important, as I know the thinner the wall, the better the conductivity between air and coolant. I will try your URL again to see if I can bone up on the subject. Thanks.