Procedure of Failure Analysis on Commercial Available Thermoelectric Modules

In this work, the procedure of a failure analysis on commercial available thermoelectric modules (TE-M) is presented. Due to the research activities in recent years, TE-materials become excellent candidates for power generation devices (TEG) which can be used in the mid- and high-temperature range up to 500 °C on the hot side of the TE-M. Now, in order to bring TE-M from laboratory status to industrial applications, it is very important that the intrinsic positive properties of a TEG, such as no moving parts, easy scalability, etc. can be fully exploited through a high long-term stability / reliability.<br/>To quantify reliability, appropriate stress tests / reliability tests must be performed and defective modules must be analyzed for their failure mode and failure cause / failure location using non destructive (NDE) and destructive evaluation (DE) techniques. Failure analysis is a complex process of collecting and analyzing data to determine the failure mode / failure mechanism and location of the failure in a TE-M (root cause failure analysis). The results of failure analysis now allow the weaknesses of the component to be identified and help to understand the mechanisms and causes of failures, making it possible to undertake corrective measures to optimize the product and guarantee its quality and reliability. In this context, a rough distinction between so-called ‘soft’ and ‘hard’ failures is helpful. A soft failure means that the TE-M is working, but is out of specification, generally resulting in an increased internal resistance due to degeneration. A hard failure means that the TE-M is completely inoperable, i. e. no current can flow due to delamination or a gap (e. g. defective soldering or broken leg).<br/>In this work we present the applicability of the NDE methods measuring the internal resistance (for soft and hard failures), IR-thermography (for soft failures), scanning acoustic microscopy (for hard failures) and X-ray computed tomography (mainly for hard failures). After NDE, DE methods of embedding the TE-M, cutting, grinding and polishing the surface where applied, followed by the NDE analysis methods using optical microscopy, SEM and EDS to determine the location of the defect.<br/><br/><i>Acknowledgments</i><br/>This work was financially supported by the voestalpine Stahl GmbH and Energie AG Oberösterreich Umwelt Service GmbH. The authors would like to thank Peltron GmbH Peltier-Technik for supplying thermoelectric modules free of charge.