Reliability of power electronics/modules in electric cars

Canary structures based on SMD devices with reduced solder widths for PHM

© Fraunhofer ENAS
Geometry models of SMD resistors with reduced solder width.
© Fraunhofer ENAS
Distribution of accumulated creep energy density during passive thermal cycling.

Canary structures being used as early warning indicators represent an important tool for condition and health monitoring of electronic components and systems in the context of Prognostics and Health Management (PHM). For this purpose, printed circuit boards with canary structures based on SMD 2512 ceramic chip resistors with reduced solder pad sizes (20 % and 80 %) were studied within the European project EVC1000.

Focus of these investigations was set on thermo-mechanical and mechanical stresses caused by thermal cycling as well as by vibrational loads. They included temperature-dependent out-of-plane and in-plane deformation measurements, end-of-life stress tests as well as finite element simulations. Based on these studies, a fundamental understanding of the lifetime in dependency of the solder pad geometry is now available. In the next step, this can be employed in order to further develop the methodology for implementing such canary structures into different applications. As example case, health monitoring of a dual inverter electronic control unit (ECU) boards for electrical powertrain applications is currently being investigated.