The Official Thermal Conductivity Thread!!!!!!

[Tchay]

The Official Thermal Conductivity Thread
(now nerdier than ever!!!)

I stumbled upon this set of info on Yahoo of all places:

Here are relative thermal conductivities:
Steel 43 - credit to Beta
Aluminum 237
Gold 318
Copper 401
Silver 429
Diamond 900 - 2320

Note that silver is the metal with the best thermal conductivity (also best electrical conductivity), not gold. Also, diamond is better yet by more than a factor of two and is actually used for its thermal conductivity in some very specialized applications.

This should be verified before being considered law; however, I can verify that the above statement is correct in that Silver is better than gold, copper, and aluminum. But I am not so sure about their listing for Gold. I had always believed gold was better than copper and aluminum

I think this would be a very useful thread for any modders that wish to build their own heatsinks or for beginners that want to learn. I remember back when I had no idea what heatsinks were.....I coulda used a thread like this.


Heatsink Basics

Noob Version
Heatsink means heat dissipation. For modding purposes, a heatsink will be some sort of metal plating that is tightly held to a processing chip that gets really hot. Heatsinks come in all shapes and sizes, but for portable hacks and what not, you would be looking for a "low profile heatsink". All heatsinks follow a typical format: the base and the dissipator. The base is the flat part of the heatsink that rests on the chip (there should be clay or glue in between the heatsink and the chip to allow for the best heat transferal). The "dissipator" part dissipates the heat and will either be prongs (protruding at varying lengths depending on how much surface area is need to transfer the heat) or groves (sometimes both). In some cases there will be a fan that has these groves surrounding it. The fan will then channel the heat away from the chip.

Wiki Version
http://en.wikipedia.org/wiki/Heat_sink

Modder version
- contact is important (so have clay, glue, or some paste keeping the heatsink tight to the chip)
- Smoothness is better than roughness (usually) - heat will transfer better across the heatsink if it is smooth - not to mention a fan can disperse the heat more easily. If you want to rough it up, do it along the prongs or furthest points on the heatsink.
- copper transfers heat better than aluminum
- the greater the surface area on the heatsink, the greater the heat dispersion (which is what you want)
- Fans are great for dispersing the heat that has transferred from the chip to the heatsink Fans can get rid of the heat that just sits around the heatsink. From my experience, it is better to have the fan blow into the heatsink. Then simply have a vent on the other side of the case to allow the heat to escape. Another option is to have two smaller fans - one blowing across the heatsink, and another sucking that heat outside of the case of the other side of the case.

I will add to this as everyone throws in their two cents

 

[snowpenguin]

That's it, I'm using diamond for my next N64 heatsink.

 

[βeta]

For comparison, Steel has a thermal conductivity of only 43.

 

[Mako321]

maybe microsoft should invest in diamond heatsinks, it'll probably cost less to use those than to replace the RROD'ing 360's.

 

[jleemero]

I've seen people make thermal paste using diamond dust.

It's apparently not terribly expensive, and the numbers associated with it are astounding.
(That is, the difference it makes over normal thermal paste)

The guy in the linked article took a system that idled at 57C down to 38C with nothing but a switch to the Diamond Dust thermal paste.

 

[Kyo]

I've seen people make thermal paste using diamond dust.

It's apparently not terribly expensive, and the numbers associated with it are astounding.
(That is, the difference it makes over normal thermal paste)

The guy in the linked article took a system that idled at 57C down to 38C with nothing but a switch to the Diamond Dust thermal paste.

Man, think of the results fairy dust would bring

 

[jleemero]

I don't know, cocaine's expensive.

 

[Kyo]

I don't know, cocaine's expensive.

Oh you

 

[vskid3]

Gold doesn't corrode or tarnish, that's why it is used on contacts and pins over silver. Kind of the best of all worlds.

 

[bentomo]

Gold doesn't corrode or tarnish, that's why it is used on contacts and pins over silver. Kind of the best of all worlds.

Actually it's because it's a soft metal. When you have a plug that's not plugged in it can get dirty or oxidize. But when you plug a gold cord into a plug, the plug scrapes away the old dirty gold exposing a good contact.

And yes, also because it's a very good conductor.

 

[hailrazer]

Gold doesn't corrode or tarnish, that's why it is used on contacts and pins over silver. Kind of the best of all worlds.

Actually it's because it's a soft metal. When you have a plug that's not plugged in it can get dirty or oxidize. But when you plug a gold cord into a plug, the plug scrapes away the old dirty gold exposing a good contact.

And yes, also because it's a very good conductor.

No not really.

Gold resists corrosion and tarnishing better than most metals. Also it is a better conductor of electricity because of it's free electron concentration.

Soft metal has nothing to do with it.

 

[Kyo]

I always thought they used it because it was so much more bling

(I will stop being useless now)

 

[samjc3]

(I will stop being useless now)

no you wont

also, i think im going to do this whole "diamond heat paste thing" on a certain dreamcast i shall soon have. should help with thinness. (better heat transfer = smaller heatsink, yes?)

 

[Tchay]

also, i think im going to do this whole "diamond heat paste thing" on a certain dreamcast i shall soon have. should help with thinness. (better heat transfer = smaller heatsink, yes?)

Yes, the diamond paste is a great idea. I also found some special diamond pads that are intended to go in between your heatsink and the chip. The paste sounds better tbh.

Also, I am thinking about looking around for silver sheets (for a custom made heatsink). Maybe thats a dumb idea, don't really know. Now, if silver is too expensive to get cut outs of, then maybe i could find a copper/silver compound and buy that instead. What do you guys think?

 

[zeturi]

Copper is excellent for cooling. Unless you want no fans, I don't think silver is necessary. It would likely be very expensive. Just use copper ram sinks. If you get some that have fins or pins that stick out, even better.

 

[Tchay]

Copper is excellent for cooling. Unless you want no fans, I don't think silver is necessary. It would likely be very expensive. Just use copper ram sinks. If you get some that have fins or pins that stick out, even better.

I will only be able to use a sheet of copper or silver for one of my upcoming portables - so no room for fins.

Copper cutouts may work but I doubt it. Unless I welded a heat pipe with fins to the sheets of copper (which I am considering but would rather not do).

 

[XCVG]

The thermal conductivity of copper is better than aluminum, but the thermal dissipation of aluminum is better than copper IIRC.

 

[daftmike]

Heat-sink design is notoriously complicated, you can go over the theory until you're blue in the face and still not come up with anything satisfactory, for portables it's pretty much guesswork anyway because there're so many unknown variables.

On paper, copper is better than aluminium in every way, but sometimes alu is a better choice because it's 1/3 the weight of copper and can be anodised to make it a better radiator of heat, which is sometimes good for low-airflow set-ups.
Silver is even better than copper, but not by much and a 100x150x2mm silver sheet would easily cost $400+.

The important thing to look for in a heat-sink is the thermal resistivity in °C/W, it means the rise in temp per Watt, the lower the better.

A simplified example; an n64 uses ~6W, the cpu, ram and rcp each use ~2W* and they should be kept below ~85°C*.
The ambient temp inside a case might be 50°C*. There's a thermal junction between the chip and the outside of the package, for the QFP-120 it's 5°C/W, this means inside the chip will be 5°C hotter than the surface for every Watt it uses.
So the heat-sink can't get hotter than ~25°C above ambient, therefore you need heat-sinks with ~12.5°C/W*
(*= approx)

Because we don't know all the specs for sure, it's really little more than a good guess, and you're better off just trying out a heat-sink that looks right and testing to see if it gets too hot.
Something like this http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230447544695 is fine and probably around 4°C/W, stick a fan near it and it should be good for anything <wii, likewise for a decent sized copper or alu plate.

 

[Tchay]

My God, Daftmike has graced this thread with his almighty wisdom. So it is written, so it shall be done

 

[βeta]

Favorite user award goes to DaftMike.