Gap pad W/m.K (thermal conductivity)

[cupoftea]

Hi,
We have a piece of gap pad 2.5mm thick to get heat from case top of SOT223 to metal enclosure.
The gap pad has thermal conductivity of 1 W/m.k
Aluminium has 247 W/m.K.

So basically, we can say that our Thermal resistance across the gap pad, will be 247 times worse than what it would be if the gap pad was of aluminium.
Would you agree?

 

[dick_freebird]

You can do better with gap pads, the 1W/mK is pretty lame.
But if you must have voltage standoff then you are looking at
either a silicone (maybe loaded) or the aluminum nitride slabs
(not compliant, but 100W/mK). Graphite seems semi-decent
too but won't stand off anything. Maybe you get as thin a soft
piece for both faces crush-fit, and mostly AlN slab, if you need
voltage (if no voltage, then use the damn aluminum if you're
too cheap for copper).

 

[cupoftea]

Hi,
Thanks, and we have 1W of dissipation per SOT223 transistor.....the area of gap pad on it is approx 1.5cm^2. The distance is 2.5mm

so taking 1 W.m/m^2.K

.that means we get 16.7 kelvin drop across the gap pad. Would you agree?

 

[FvM]

I wonder how you arrive at 1.5 cm^2, SOT223 case top is less than 0.25 cm^2.

Form factor 16.7 is correct.