Abstract
Power modules composed of semiconductor dice, thermal interface layers, and cooling mounts can be characterized by thermal transient testing at their actual position (in situ). This paper demonstrates that transient testing enables tracking of changes in material quality and structural details on the raw heating or cooling curves. Higher precision can be achieved with the structure function technique where absolute and partial thermal resistance and capacitance values can be used for unambiguous identification of structural elements in a heat conducting path. Measurement techniques are presented to characterize the self-heating of a die and heat transfer between dice. Change of the thermal interface material layers in assembly during test sequences is also highlighted by the structure function concept. The power distribution between dice and wiring is analyzed by the newly introduced “accordion” principle.
Highlights
With the growing level of power density in up-to-date power devices and assemblies, it has become essential to support their manufacturing with testing tools enabling one to check the integrity of the realized appliances
Higher precision can be achieved with the structure function technique where absolute and partial thermal resistance and capacitance values can be used for unambiguous identification of structural elements in a heat conducting path
Recognizing that the thermal transient testing always provides information about the whole heat conducting path from a heat source towards the measurement environment, in this paper we systematically follow the possibilities for analyzing complex structures built from power electronics devices, thermal interface materials, and cooling mounts
Summary
With the growing level of power density in up-to-date power devices and assemblies, it has become essential to support their manufacturing with testing tools enabling one to check the integrity of the realized appliances. The well-established framework of thermal measurement standards [4,5,6], helps in planning the structural analysis process as well These standards represent the condensed knowledge of many decades regarding the selection of assemblies, thermal boundary, electrical excitation, data acquisition, and the interpretation of the measured results. It has to be noted that thermal testing has become more important in achieving reliable operation over a long lifetime, the construction of complete appliances often overlooks thermal testability aspects These tests often need a workaround for accessing devices that are relevant for their power consumption or can be used as sensing points. These examples allow us to demonstrate how the difficulties in the thermal transient evaluation of these devices can be overcome.
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