Challenge
Four candidate TIMs looked similar on datasheets, and steady-state thermocouple tests could not resolve the difference between them.
Approach
Each TIM was measured on the same chip-on-board package and fixture, and the differential structure function isolated the TIM layer from the package.
Result
The TIM layer resistance ranged from 0.31 to 0.73 K/W between candidates. The team selected the lowest-Rth material and documented the test as an internal standard.