Regarding TIM "R"
I pulled some numbers out of thin air, but I don't think they are unreasonable.
Assumed:
1. Full, total contact between core and copper (k=392 W/m*°C) is 1% of total area. (total guess)
2. Remaining 99% area is average 0.1mm deep (probably less) and
3. filled totally with compound @9 W/m*°C (Probably BS)
=0.01*k copper+ 0.99*k paste= k TIM =12.83 W/m*°C
C/W = dT/Q = L/k*A = 0.0001m/12.83W/m*°C*0.0001m^2 = 0.077942 C/W
The silicon die surface itself is not included in this. It is assumed to be the core temp, which it isn't.
Making 0.08 W/m*°C too low. Probably. But I am not sure yet how to handle that. At this point it doesn't matter too much.
Quote:
Originally posted by pHaestus
Perhaps a custom wb base with the needed raised cube for this experiment would make things easier.
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That would work very well I think. It would not need to be a super high performance block. The mounting would be tricky though.
Quote:
Originally posted by pHaestus
Combine that with phenolic resin of the same size as the base of the block (but with a cutout for your cube) so that wb mounting isn't too compromised and so the insulation is good.
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What I am planning to do is pretty much as you suggest here phaestus, except that I will machine a polycarbonate (0.21 W/m*°C?) block as the support and push fit/glue the copper plug in it. The "plug" I'll mill to the same dimensions as a Barton core with height the same as the Lexan so that it remains transparent, making it easier to see. Alignment might be a little tricky so I may have the "plug" inset ~0.1mm to guide it over the CPU die.
BillA's TIM shim experiments are partly what led me to this, but I always thought that idea was missing a needed data point. Hence this way.
Any good numbers on the conductivity of ETP C110 copper?
So far I have seen: 392, 391 and 388 W/m*°C which is instantly an uncertainty of 1% How does one handle error summation? With what I work with they are added quadratically ie E tot= sqrt(E1^2+E2^2...) but that may not be applicable in this case.
Cheers
Incoherent
Edited to correct erroneous poly k
Edited again to correct C/W 0.77942