Thermal Characterization of Electronic Packages Using the Nyquist Plot of the Thermal Impedance

It will be shown in this contribution that if the thermal impedance Z_th(jw)of an electronic package is represented in a Nyquist plot, the curve obtained can be fitted very well to a combination of a few (n) circles, n varying between 2 and a maximum of 5. For each of these circles, it is sufficient to know the radius and the coordinates of the center point or just three parameters. With 3n parameters the entire behavior of the impedance can be represented and consequently, the dynamic behavior as well.