Simulation of stress concentrations in wire-bonds using a novel strain gradient theory

Fatigue failure of wire-bonds is one of the key factors limiting the lifetime of power electronic devices. In IGBT (insulated gate bipolar transistor) modules, wire-bonds are exposed to repeated temperature changes leading to thermo-mechanical stresses in the constituent materials. Due to the geometry, stress concentrations arise at the interfaces of aluminum wires and silicon chips. In the framework of classical continuum mechanics, these stress concentrations show the characteristics of stress singularities. Nevertheless, IGBT modules reach lifetimes of about 30 years under service conditions. Therefore, it seems that classical continuum mechanics exaggerates the stress concentrations occurring at the material transitions. Hence, it is the subject of the present investigation to calculate more realistic stress distributions using a novel strain gradient theory.