Heat sinks: Deciphering thermal pad specifications

[cvanc]

I have always been unclear about the ratings of thermal pads, can I enlist the braintrust for some clarity?  When you see specifications like this:

Thermal Resistivity   0.35°C/W   
-or-
Thermal Conductivity   1.0 W/m-K

...Is a high number or a low number 'better'?  And by better I mean more heat is passed through the pad to the heat sink.

Here's an example that I'm currently working on.  I'll attach a Digi-Key sorted list, I hope it comes through OK.  Which of these products is the best performer in terms of helping heat move away from my silicon?

https://www.digikey.com/products/en/fans-thermal-management/thermal-pads-sheets/218?FV=188006f%2C8dc02a5%2Cffe000da%2C24c00a1%2C24c0015%2C24c0263%2C24c0265&mnonly=0&ColumnSort=-677&page=1&stock=1&pbfree=0&rohs=0&cad=0&datasheet=0&nstock=0&photo=0&nonrohs=0&newproducts=0&quantity=&ptm=0&fid=0&pageSize=25

Thanks!

[T3sl4co1l]

Lower resistance, higher conductivity.

1 W/m/K is pretty typical for such materials, with much better (10+) available if you're willing to also pay for it.

To do it for any device, use:
Rth = thickness / sigma / area
Thickness is the compressed figure (the gooier materials compress and squeeze a lot, which BTW, beware of that when it comes to screw torque), and area is the area of the device backside (not the full area of the insulator, unless you're using a heat spreader to cover it too).  Sigma is the conductivity.

If you're using units of whatever, just plug this into Google and it'll convert everything for you.

The technically-correct answer to your question is the solid pyrolytic graphite, or copper or aluminum heat spreader, but I'm guessing you actually want an electrical insulator, too.

Tim