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To: tcmay who wrote (77905)	4/22/2002 1:53:48 AM
From: Mani1	Read Replies (1) \| Respond to of 275872

Re <<No, you have it backwards. >> No I don't. You misunderstood what I said. Or intentionally misinterpret it. Bigger contact area is better as heat flow is proportional to the area. But in order to get this bigger contact area, heat has to get through an extra path (die to heat slug). All things being equal, it is better to go straight from the die to the heatsink / heat spreader combo. It is not as good to go through a heat slug (such as the one intel uses and AMD plans to use with hammer) then to heatsink/heat spreader combo. That heat slug which is only a few times the size of the die is there for mechanical protection. Re <<No one is talking about adding more series links>> What? Having the heat slug on the die is a series link. Re <<To see this, switch from thinking of resistance and instead think of its inverse form, conductivity. (Or go ahead and compute the form 1/R = 1/ (1/R1 + 1/R2 + ...).)>> I know this, so should anyone who has taken heat transfer 101. Your ignorance stems from your lack of knowledge in back end packaging. Mani

To: tcmay who wrote (77905)	4/23/2002 1:22:59 AM
From: pgerassi	Read Replies (1) \| Respond to of 275872

Dear TCMay: You forget that there still exists the die to heat spreader interface. The die has not changed shape thus it still has the same resistance. The bond between the HIS and the die still incurs a thermal resistance and the design of the HIS incurs more. Then there is the thermal resistance between the HIS and the HSF. All of these resistances will add up to more than a direct die to properly designed HSF setup. You add a thermal interface of HIS to HSF which will be more than zero and the internals of the HIS will add even more. Thermal flow needs a more complex analysis like FEA because heat flows in three dimensions and at different rates depending on materials, orientation, temperatures (some materials conduct better at some temperatures than other temperatures), gas flow (typically air), humidity, geometry, etc. Most of the time, the heat flows outward in HSF in the base as a flattened spheroid (thats why they call it a heat spreader). Since any integrated heat spreader is a compromise between many factors, a direct mounted HSF will be able to beat it in both lower thermal resistance, higher heat sinking and lower die temperature differential with ambient. What an HIS does is reduce the cost of the HSF that minimally works and allow for "ham handed amateurs" to mount it. The disadvantage is that the best it can do will be less than one could do with a middle to top end HSF which usually is well designed for direct mount. To get premium performance the HIS version will cost more than the direct mount HSF for the same performance, if possible to achieve. Pete

To: tcmay who wrote (77905)	4/23/2002 6:49:48 AM
From: hmaly	Read Replies (2) \| Respond to of 275872

tcmay Re..If water is leaking from a bucket through a couple of holes, punching a new hole does not reduce the overall flow, even if the resistance of the hole is considerable. (The above equation is how we compute overall resistance given a lot of various holes and their associated resistances...) In this case, the area of the contact between die and substrate/heatsink is like the size of a hole in a bucket. Making the hole larger increases the water leakage rate.<<<<<<<<<<< I believe Mani is saying that, instead of adding another hole as you suggest; if you thicken the walls of the bucket from say 1/8 inch to 1/2 inch, you will slow down the flow. Why would a heat spreader add parallism over a heat sink?