Measuring partial thermal resistances in a heat-flow path

The paper presents techniques of measuring partial steady state thermal resistance values in a heat flow path with the help of thermal transient measurements and the subsequent numerical evaluation. The method is based on the further evaluation of the structure functions of the heat flow path. After presenting the theoretical background of the evaluation two different practical examples are presented to demonstrate the use of the method. The first example presents a series of experiments on how to use the method to detect die attach and/or soldering failures in packaged devices. The second example demonstrates that the method can be applied to measure the very small R_th values of thin conducting layers. Various practical solutions are discussed and demonstrated by simulations. The chances and the limits of the methodology are discussed in detail in the conclusion section.