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In-situ measurement of wirebond strain in electrically active power semiconductors

Thermal-mechanical displacement/strain in power semiconductor devices is investigated using electronic speckle pattern interferometry (ESPI). Validated models for thermal-mechanical strain are key to improving reliability of power electronics modules. ESPI is a non-contact optical technique capable of providing surface displacement measurements with sub-micron resolution. The significant contribution of this paper is a methodology by which wirebond displacement/strain can be measured in an active device. Simultaneous in- and out-of-plane measurements are combined to accurately measure the displacement field across the wirebond interface, while decoupling thermal-mechanical deformation not related to wirebond strain (such as base plate thermal expansion). Experimental results verify the electrical-loss-driven thermal-mechanical displacement/strain in an electrically active discrete IGBT switching at 5 kHz.