Life-time modeling of DBC-based MOSFET-power modules

Abstract:
Active endurance tests of Direct-bonded-copper based MOSFET power modules showed, that the aluminium bonds and the die attach are the most critical design elements regarding product reliability. In this paper well-known life-time modelling approaches for bond-lifts are enhanced by a physically motivated expression in order to model changes in geometry of the die and the bonds. Bond lifts occur due to thermo-mechanical mismatch between the bond and the surface of the semiconductor, which is driven by the temperature at this interface. It will be shown that based on the heat conduction equation a modelling of the temperature contribution caused by electric current density can be implemented. The local temperature is described in terms of the global temperature swing due to the power loss in the semiconductor and the electric current density in the FET metallization layer close to the bond land. In addition to the experimental results, we will present results from Finite-Element simulations in order to verify the findings. We will conclude this paper with an introduction how the life-time model may be used during the reliability-driven product development.