Aluminum Oxide Thermal Pads

[DrGonz78]

So I have a quick question regarding themal pads for transistors. I usually use mica and grease but this time I had to order aluminum oxide thermal pads for insulators. My question is whether or not people put grease on these pads? My first thought is that you do not, but I better ask to make sure. Thanks.

[tedmich]

its almost always either or not and, the newer pads are often phase-change material and need to melt into the interface to work, the paste will just mess with this. The pads are commonly used for pre-applied material on the chip or heatsink as they can be done with machines and last during shipment, where the pastes need a guy to fingerpaint during assembly. That said the CPU guys love their fancy pastes but the pads are plenty good enough for most applications.

[Jazz P Bass]

[QUOTE=tedmich;347789 That said the CPU guys love their fancy pastes but the pads are plenty good enough for most applications.[/QUOTE]

Yeah, and they love their whetstones, too.

[R.G.]

I think the OP may have been asking about AlOx solid pads. If so, yes, you grease both sides. Grease is an attempt to fill up the surface irregularities with something that's lower thermal resistance than the air it would otherwise be.

If you have isolated heat sinks, you can use the no-insulator phase change stuff. Great thermal conduction, but no electrical insulation.

I am **very** fond of the silicon rubber insulators. No grease needed as the rubber conforms into the hills and valleys and they get very close to mica-and-grease conductivity.

By the way, if you do mica and grease, use a razor blade as a grease spreader (like a trowel to smooth it) to get the thinnest possible even layer. You only need a few thousandths of an inch of goo.

[Jazz P Bass]

By the way, if you do mica and grease, use a razor blade as a grease spreader (like a trowel to smooth it) to get the thinnest possible even layer. You only need a few thousandths of an inch of goo.

HAH.
#1 to that.

I get a kick out of manufacturers that assemble transistors with half a tube of the stuff.

Here is a good comparison chart of the different types of pads.

Link: http://www.mecint.co.uk/sitedocument...rmancedata.pdf

[DrGonz78]

Here is an example of the pad in question. 4180G Aavid Thermalloy | Mouser

The reason I ask is because I have seen it both ways. Mostly, I have not seen many of these insulators coupled with thermal compound grease.

[R.G.]

It's a solid (i.e., not flexible rubber) insulator. Use grease. Use very, very little grease, as the smoothness specs are good, so the hills and valleys you're filling up are on the semiconductor.