Which Arctic thermal paste for heatsinking emmiters?

well I got to admit I am perplexed. I have searched bothe the Alumina, Ceramique and Silver specs andd got nowhere. This is why:

A. Alumina - Thermal conductivity: >4.0 W/mK (Hot Wire Method Per MIL-C-47113)
A. Silver - Thermal Conductance: >350,000W/m2 °C (0.001 inch layer)
A. Ceramique - Thermal Conductance: >200,000W/m2.°C (0.001 inch layer)

Now what is mK? a mispell of m2???? In this case Alumina really sucks!

I think the Arctic Silver is the best, but I tried some of the DX thermal glue- and it's not bad! One step-dries fast. I just did a seoul Led on an Amuminum heatsink- drawing 1.2 amps.. Ran it five minutes with no sign of overheating. The Seoul led's are easy to overheat too. THey turn blue is about 15 seconds!
http://www.dealextreme.com/details.dx/sku.4579

Silver is the best but it conducts don't use it unless you have an isolated heatsink(ie. anodized)
I use AS Alumina Epoxy its the best option we have. The epoxy keeps the emitter in one place so unless you have some other way of restraining the led don't use the cheaper thermal compound.

My personal choice is to solder the Cree LED directly to the heatsink, I think the thermal conductivity is much greater there (not that I have done it, but I have a mod planned that will require the bond and heat transfer.

65535 said:

My personal choice is to solder the Cree LED directly to the heatsink, I think the thermal conductivity is much greater there (not that I have done it, but I have a mod planned that will require the bond and heat transfer.

Click to expand...

I've done that with a cree on a sandwich shoppe MCPCB 650.

Not too easy as my heat was coming from an electric stove top and the heatsink was on a cookie sheet. I held the solder tothe heatsink and as soon as I got the solder to flow on the pad I shut off the heat and positioned the cree on it. I then removed the whole sheet to the cold sink.
TIP: the heatsink liked to move under the cree when I was trying to get it centered right. Lock it down to something heavier, a screw to a chunk of steel. Not too much mass as you'll need to cool it quickly.

Well I have my 50 watt soldering iron so I don't foresee any problems.

For applications when the unit is a start and it's screwed down I would use arctic Silver, for adhesive I would use their Adhesive.

as a side note has anyone tried inserting a THIN leaf of solder under the Cree emitter and then heating both?

I did make that kind of leaf/strip by putting ALOT of solder on the iron tip then throwing (ejaculating should be a better word) it on a smooth surface.

nein166 said:

Silver is the best but it conducts don't use it unless you have an isolated heatsink(ie. anodized)
I use AS Alumina Epoxy its the best option we have. The epoxy keeps the emitter in one place so unless you have some other way of restraining the led don't use the cheaper thermal compound.

Click to expand...

hmm that perplexes me...the AS site says silver is non-conductive...
Not Electrically Conductive:
Arctic Silver 5 was formulated to conduct heat, not electricity.

But I think it can be used unde a Cree Star can't it?

kosPap said:

Now what is mK? a mispell of m2???? In this case Alumina really sucks!

Click to expand...

No, an abbreviation of metre Kelvin. ie the unit is Watts per meter Kelvin, which is the standard unit for thermal conductivity. The other two units have simply been converted to something which may (or may not) be more useful to you. To convert that to the same units, simply divide by 0.0000254 (which is 0.001 inches in m) - which gives ~160,000 W/m2 C.

BTW arctic silver isn't actually electrically conductive, so there is no difference using that to using alumina from that perspective. However if you use the normal method of pressing the LED down against the heatsink you will almost certainly get a direct electrical path by direct contact - the only way to avoid this is to build up a thin layer of thermal epoxy first (which won't help the heat transfer).

I've been a Overclocker for years, so i have used all of the Arctic silver products for PC applications for as long as they have been available.

Arctic Silver Paste- is very messy to use and is annoying to cleanup, AS5 should not be electrically conductive, but some of the older versions are slightly conductive. I generally avoid AS. The stuff gets everywhere..

Arctic Silver Ceramique Paste - is quite thick, can be a bit difficult to spread thinly, but its not that bad, it stays put. it almost matches AS5 in perfomance. clean up is easy with an alcohol swab. I use this most often if i can mechanically secure (screw it down)the LED or Heatsink.

Arctic silver Alumina epoxy - not as thermally conductive as either of the above, but its more than adequate for an LED, I would not use it to secure a Chipset, a CPU, GPU heatsink. I have used it for video RamSinks, Mesfets, and LEDs.

Both of the pastes can deal with large amounts of heat, the Pentium 4 Dual cores for example were rated at 130W of heat. And the Power LEDs we use produce like 5W.

-ex

kosPap said:

hmm that perplexes me...the AS site says silver is non-conductive...
Not Electrically Conductive:
Arctic Silver 5 was formulated to conduct heat, not electricity.

But I think it can be used unde a Cree Star can't it?

Click to expand...

Oh yeah my bad memory, its capacative. Perfect under a star but overkill as the star is the weak point in heat transfer equation.

nein166 said:

overkill as the star is the weak point in heat transfer equation.

Click to expand...

Certainly not with a well designed star such as comes on an SSC P4 from the factory, it's not.