thermal conductivity and thermal resistivity of heatsink pads

[Jamie Morken]

Hi,

I am comparing some heatsink pads, some specify thermal conductivity and
some specify thermal resistivity, how do I convert from one spec to the
other to see which pad has better thermal heat transfer?

I like to use thermal resistivity, ie 0.2celcius/watt for an SP2000 pad,
digikey part# BER202-ND, also 3.5W/m-K is specified as the thermal
conductivity for this part.

the K-10 Sil Pad has 0.41celcius/watt thermal resistivity, and 1.3W/m-K
thermal conductivity, digikey part# BER114-ND.

How do these parts compare to Aavid aluminum oxide insulators, with a
thermal conductivity of 15.06W/m-K, mouser part#: 532-4170

Also Aavid Thermasil III, with a thermal conductivity of 0.92W/m-K,
mouser part#: 532-53-77-4ACG

I think the thermal conductivity is a material spec, while the thermal
resistivity depends on the size of the component (thermal transfer cross
section area) is this correct?

Also the aluminum oxide seems to be by far the best insulating material
for highest heat transfer, do these need to be used with silicone
heatgrease?

cheers,
Jamie

 

[RoyLFuchs]

Actually, diamond is the best insulating material for highest heat
transfer.

Except that the discussion is about commercially available product
mediums, not what one finds in the CRC Handbook.

Show me where Digi-Key (or anyone else) sells diamond transfer
plates... That's what I thought.

 

[Bill Sloman]

Except that the discussion is about commercially available product
mediums, not what one finds in the CRC Handbook.

Show me where Digi-Key (or anyone else) sells diamond transfer
plates... That's what I thought.

That's not how you get a diamond insulating layer - you can vapour-deposit a
diamond film from a suitable plasma, but you have to talk to specialists
about getting the sort of layer you want on one of the surfaces you need to
insulate.

I've never had it done, but one of my ex-employers got quite excited about
it a few years ago.

 

[RoyLFuchs]

That's not how you get a diamond insulating layer - you can vapour-deposit a
diamond film from a suitable plasma, but you have to talk to specialists
about getting the sort of layer you want on one of the surfaces you need to
insulate.

I've never had it done, but one of my ex-employers got quite excited about
it a few years ago.

Again, unless you have space contracts or the like, I am quite sure
that such a process is not cheap.

Hard anodization on Aluminum is a very good electrical insulator, and
it too is coupled directly to the underlying Aluminum strata.