Toward a multi-physical approach to connection ageing in power modules

Generally, studies on ageing of power module have very often sought to write phenomenological laws able to give an estimate of their lifespan. These laws, identified experimentally, are empirical functions of the characteristic electrical loads that the component must withstand. As an alternative, this paper presents a first attempt of numerical approach for wire bond ageing in semiconductor power modules that takes account for the different multi-physical coupling mechanisms that occur during the component life. The electro-thermal and thermo-mechanical interactions are physically described and numerically modeled. The calculations show important viscoplastic strains in the connection zones and bonding wires from the first loading cycles. A quasi-cyclic stabilization of the mechanical and thermal states is observed at more than a hundred cycles (viscoplastic shakedown). The creep-fatigue damage mechanisms become then preponderant inducing mechanical-electrical couplings.