Quote:
Originally posted by Cathar
Actually not my testing but by way of BillA. Bill had forwarded me a very interesting graph once that plotted the thermal junction difference betwen various points using thermal sensors placed at different levels between the heat source and the water coolant.
Roughly speaking it was showing around a 0.08 to 0.10 C/W for the thermal interface junction (when using goop) for a 100mm^2 heat die.
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I doubt that numbers for several reasons: First lets make some calculation with AS3 specs.
Quote:
Thermal conductivity: >9.0 W/mK (Hot Wire Method Per MIL-C-47113)
Thermal Resistance: <0.004°C-in²/Watt (0.001 inch layer)
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For an 1cm2 die and 80W load that gives 2ºC temp drop. The big variable here is layer thickness; it can be even lower on a good base and high pressure.
Then there are some specific issues with BillA tests: The CPU die simulator that he have used for all his WB tests can not measure just the [block + tim] C/W; it measures [Block + tim + temp gradient to the probe location on the simulator] C/W. That's why he have a fixed 0.1 C/W added to each block own termal resistance; most of it comes fron the probe positioning, and a small part from the tim.
The cause of this is what I consider a wrong decision on the design of bill's simulator: He placed the probe some milimeters lower than the surface, and on one side. While all recomendations are to place the probe at the center and as close to the surface as possible.
Sorry if this is threadjacking, just wanted to make clear that one of the suposed advantages of direct die is not as big as the mith says.