I made this
to measure the thermal conductivity of a 3Gshielding gap-pad material. They spec it at 6 w/mK without any details.
I used a modified TO-220 resistor (tab cut off, thermocouple added) as the heater. A micrometer squeezed the gap-pad to tweak thickness.
I measured 2.7 w/mK at zero compression, and 5 at 50% compression. This soft stuff needs to be compressed. Between the change in conductivity and the change in thickness, the compressed thermal resistance is about 1/3 of not compressed.
I could buy one of these
but it would cost about $40K.
My machined copper parts are done, so I'll try the AlN next.
That $40K machine won't measure AlN directly. It's only spec'd up to 8 w/mK, and AlN is more like 170.