Thermo-mechanical stress modelling of MOS device with electro-thermal considerations

In power electronic applications, the self-heating process of the main components impacts the electrical characteristics of the device. This power dissipation can also induce large thermal gradients which cause mechanical stresses that will reduce the operational lifetime of the device and induce premature failure. Since the electrical loading is usually a function of time, the thermal gradients change as the device is cycled. Accurate modelling of thermo-mechanical stresses must consider the electro-thermal phenomena. In addition, a particular difficulty lies in taking into account the great differences of space and time scales (dimensions of the sensitive areas, and electrical, thermal and mechanical interactions). This paper presents a global method, which couples the electrical and mechanical simulations, that helps estimate the thermo-mechanical stresses in the device. In certain cases this information can be used to redesign the chip package.