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Technology Stocks : Advanced Micro Devices - Moderated (AMD)
AMD 259.65+2.3%3:59 PM EST
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To: tcmay who wrote (77905)4/23/2002 1:22:59 AM
From: pgerassiRead Replies (1) 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
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