Evaluation of Thermal Resistance of TIMs in Functional Packages Using a Thermal Transient Method

Two different functional die packages were characterized by measuring thermal transients and interpreting the evaluated structure functions. The objective was to find out the total junction to ambient resistance of the package and also the thermal interface resistance between the die and heat spreader .Three different tests were conducted on each package-natural convection test, natural convection with a passive heat sink, forced convection test with a big active heat sink. The measured thermal transient response of the package was converted into structure functions and the thermal interface resistance was extracted from it. The natural convection test was used to evaluate theta-ja values for the package .However the forced convection tests with bigger heats sinks made the flow essentially one dimensional and made the structure functions accurate and easier to interpret and gave reliable values of the thermal interface material layers. The structure functions obtained were compared with the analytical empirical calculations made to calculate the resistances and capacitances and were reasonably closer to each other.