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Experiment: Which mosfet thermal interface material is best?
Experiment: Which mosfet thermal interface material is best?
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Old 4th November 2018, 09:36 PM   #21
Eric is offline Eric  United States
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Experiment: Which mosfet thermal interface material is best?
oreo: See e) above in Methods section. Screw head both measured highest and provided best consistency.

kasey: you are quite welcome!

rookakoma: black kept the mosfet the coolest, resulting in slightly higher sink temp. This makes sense: heat from the mosfet is dissipating through the sink the best. If I had a DMM that reported temps with decimals (rather than integers), there might be more interesting things to see here.

Mark: Wow- I didn't know such a device existed! This looks like it would provide better data. Next time I place an order, I'll have to grab a few.
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Old 5th November 2018, 02:10 AM   #22
alexberg is offline alexberg
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Default Urban Legends about Thermal Interface Materials by INFINEON

As Infineon put it: there is no correlation at all between the chip temperature achieved in the test and the datasheet value given for thermal conductivity p.24 middle row
https://www.infineon.com/dgdl/Infine...43f875b52e3343
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Old 5th November 2018, 06:47 AM   #23
MEnsing is offline MEnsing
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Eric, Thank you very much for testing and sharing the results. Good to know that Aluminum Oxide Ceramic works well compared to the expensive Keratherm.
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Old 5th November 2018, 03:08 PM   #24
McQuaide is offline McQuaide  United States
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I use the 900S in my F5. SP900S-0.009-00-104 Bergquist | Fans, Thermal Management | DigiKey


Last I checked the body of the MOSFET was a couple degrees higher than the heatsink (black aluminum from the store).
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Old 7th November 2018, 06:31 AM   #25
rookakoma is offline rookakoma  Hungary
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[QUOTE=Eric;5592542]

rookakoma: black kept the mosfet the coolest, resulting in slightly higher sink temp. This makes sense: heat from the mosfet is dissipating through the sink the best. If I had a DMM that reported temps with decimals (rather than integers), there might be more interesting things to see here.


Eric, Wrong conclusion!

Better heatsink emission means better dissipation and / or better radiation.
At your experiment the dissipation factor is constant (because you used the same heatsink), so better radiation makes cooler heatsink.
1°C is not too much at heatsink... It makes 1°C cooler device (when the thermal resistance between the device and sink is constant).
The reason of the different device temperatures at your experiment is th. res. between the device and heatsink.

This conclusion based on the lows of thermodynamic.
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Old 7th November 2018, 06:43 AM   #26
Extreme_Boky is offline Extreme_Boky
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Tighten a transistor onto a heatsink, and watch that goop squirts-out... slowly -> a very very satisfying feeling indeed.
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Old 7th November 2018, 07:33 AM   #27
davidsrsb is offline davidsrsb  Malaysia
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I would have expected a good mica insulator to be better than the others, but with serious fussiness with getting a very thin paste layer. Your mica must be thick or something was not flat.
If you use so much paste that is squeezes out, you have too much and may have big trouble later as it dries out.
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Old 7th November 2018, 12:38 PM   #28
Eric is offline Eric  United States
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Experiment: Which mosfet thermal interface material is best?
rookakoma: fair enough - thank you for the additional details.

davidsrsb: it is possible that something was not flat. The mounting hole was drilled on my drillpress, so I'd expect it to be reasonably perpendicular to the surface of the sink, though it is possible that something is off. The same hole was used for all measurements, though some of the thermal interfaces were more rigid than others. If the hole is not perpendicular and this disadvantaged the mica & grease, then the AlOx performs even better than measured as it is also rigid.

One of my motivations was to actually see what happens since we all have certain expectations. I like data.
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Old 7th November 2018, 01:10 PM   #29
phase is offline phase  United States
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The silver paste (conductive metal particles) doesn’t belong in an amplifier, unless by chance electric isolation is not a factor.
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Old 12th November 2018, 07:52 PM   #30
Eric is offline Eric  United States
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Experiment: Which mosfet thermal interface material is best?
Quote:
Originally Posted by MEPER View Post
How would only thermal grease (the white stuff) compare?
Some of the comments that were posted made me wonder about about how perpendicular my hole was in the surface of my sink. I double checked my drill press - the table is as perpendicular as I can make it (I ended up not actually adjusting it). I drilled a new hole and was as careful as I could be to make sure the hole was true. I then re-ran my experiment as described in my first post. The results were the same (ambient temp may have drifted a bit, but I compensated in my table to provide the same starting point).

I added a new measurement: only thermal grease was used between the mosfet and the sink. This only works for a single channel of the MoFo amp, DON'T DO THIS WITH ANY OTHER AMP HERE - you'll create an electrical short.

I expected thermal paste alone to perform the best, but the magnitude of the difference was a bit of a surprise to me. I have attached an updated chart with the new test condition.

Finally, the thermal compound that was used for all tests is Ceramique2, Tri-Linear Thermal Compound by Arctic Silver.
Attached Images
File Type: jpg Thermal Interface.jpg (82.0 KB, 129 views)
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Last edited by Eric; 12th November 2018 at 07:59 PM.
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