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Old 23rd May 2014, 10:38 AM   #1
ishiru is offline ishiru  Indonesia
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Default thermalpaste choice

hello and sorry if i came into the wrong room

i need advice about thermalpaste for my finals (class A mode)

i usually used shinetsu white paste (dont know the series) but i want better thermal conductivity..

i have some deepcool Z3 leftover from my computer but they're metal oxide based..is it safe?.or i'd better use another paste?..any recommendation?

thanks!
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Old 23rd May 2014, 12:04 PM   #2
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Aluminium Oxide is a good thermal conductor and electrical insulator. I use SG502 from ACC Silicones. It doesn't drip and stays where you put it. Electrolube make HTC Plus, that is creamier and I have had good results.
If you use Silicon Pads, no compound is required, in fact if you apply heat paste, the pads will fall apart after a short time.
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Old 23rd May 2014, 01:48 PM   #3
ishiru is offline ishiru  Indonesia
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i see..how much it costs?..

i couldn't understand the specs but here's my Z3 specs :
Thermal Conductivity : >1.134W/m-K
Thermal Impedance : <0.201C-In^2/W
Dielectric Constanta : >5.1
Operating Temp : -50C~300C

is it worse or better than SG502?

HTC Plus :
Thermal Conductivity : 2.5 W/m.K
Temperature Range : -50C~130C

i guess HTC Plus better?

and i didn't use SilPad since they always break apart everytime i remove the transistors..just a mica..

thanks!

-add-

looks like there's none selling HTCP in my country .any other recommendations?..could be better if it's computer grade since it could be found easier
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Last edited by ishiru; 23rd May 2014 at 01:50 PM.
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Old 23rd May 2014, 03:06 PM   #4
AndrewT is online now AndrewT  Scotland
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the paste should be so thin that you have metal to hard surface on all the high spots between the scratches.

The paste, theoretically, is there only to fill the scratches.

Now with that paste that thin that it allows metal to hard surface contact, there is no thickness left to put into the resistance equation.
I.E. it makes almost no difference which thermal paste you use.
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Old 23rd May 2014, 03:18 PM   #5
ishiru is offline ishiru  Indonesia
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Quote:
Originally Posted by AndrewT View Post
the paste should be so thin that you have metal to hard surface on all the high spots between the scratches.

The paste, theoretically, is there only to fill the scratches.

Now with that paste that thin that it allows metal to hard surface contact, there is no thickness left to put into the resistance equation.
I.E. it makes almost no difference which thermal paste you use.
hmm..makes sense

so..the thinner is better maybe?..as long as i changed my computer's thermal paste there's 1 brand/series that has pretty thick paste (harder to apply the paste) while the other one has thinner paste (and it makes me easier to apply the paste)
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Old 23rd May 2014, 03:35 PM   #6
AndrewT is online now AndrewT  Scotland
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The purpose of the paste is to exclude air from the interface.
The biggest pockets of air are in the scratches.
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Old 23rd May 2014, 04:11 PM   #7
Pemo is offline Pemo  Mexico
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You might also try polishing the heatsink surface to mirror like finish. (And use paste of course).
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Old 23rd May 2014, 08:56 PM   #8
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This pretty much explains what AndrewT is saying:

ESP - Heatsink design and transistor mounting

Karsten
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Old 24th May 2014, 11:00 AM   #9
ishiru is offline ishiru  Indonesia
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Quote:
Originally Posted by AndrewT View Post
The purpose of the paste is to exclude air from the interface.
The biggest pockets of air are in the scratches.
ah..yes..but from my thought, the gap filler should be a good one since there's thermal resistance

Quote:
Originally Posted by Pemo View Post
You might also try polishing the heatsink surface to mirror like finish. (And use paste of course).
this reminds me when i was an overclocker

Quote:
Originally Posted by Karsten Sømand View Post
This pretty much explains what AndrewT is saying:

ESP - Heatsink design and transistor mounting

Karsten
thanks!.i'll read it

anyway, anyone knows a good replacement for mica?..like ceramic or something like that?..
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Old 24th May 2014, 11:07 AM   #10
AndrewT is online now AndrewT  Scotland
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Thin Mica is second best to the new and not yet copied Keratherm.
No other insulator can better thin mica.

Thin mica equals less than 1mil, < 1thou, < 0.025mm

Medium and thick mica can be shaved down to thin with practice.
Quote:
the gap filler should be a good one since there's thermal resistance
there should be no gap. If you were attaching the device direct to the heatsink (isolated from all other electical potentials) you would have metal to metal contact. Your clamping method should try to maximise the metal to metal contact.
Any remaining "gaps" require the air to be excluded. This is where the "filler" comes in.
The Thermal resistance of that metal to metal, no air, interface is about 0.2C/W for a To247 size.

Where you have a "hard" insulator, to give electrical isolation, you must have TWO of these interfaces. That immediately puts your Thermal resistance at > 0.2+0.2C/W.
Typically mica will give ~0.5C/W

Keratherm is a soft insulator. It is the best of all the soft insulators.
Some are so bad at Thermal Conductance that we should NEVER use them for heat transfer, but we do !
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Last edited by AndrewT; 24th May 2014 at 11:16 AM.
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