Transient thermal analysis as measurement method for IC package structural integrity
Hanß Alexander, Schmid Maximilian, Liu E, Elger Gordon†
       
Example of normalization procedure. Transient thermal curves are measured using different drive currents. 600 mA/700 mA/800 mA. The R th_el grows with increased drive current because the efficiency of the junction decreases slightly. The time-derived curves are moved up and the peaks increase due to the higher thermal load. Note that the time derived curves are not divided through the electrical load. In contrast, the R th_real, i.e., the thermal path, remains constant. This becomes visible after taking the logarithm of the time-derived curve and performing normalization. The simplest way of normalization is to divide every measured value of a measurement curve through the value at the center of the normalization area. To reduce potential errors due to noise the red and black curves are fitted on the blue curve by a least squares fit of a constant axis offset. It is readily apparent that all three curves precisely overlap; therefore the thermal path and R th_real are identical.