Encapsulation of smart power electronic devices - Thermal degradation and dielectric behavior

This paper gives an overview about current processes and materials used for encapsulation of power electronics modules. The implications of the material classes on process and reliability will be discussed and special focus is put on thermal ageing of the encapsulants and the effect on dielectric strength and thus on functional reliability. Latest results of thermo-oxidation and thermo-degradation of encapsulants will be presented, showing a minor influence of oxygen compared to effects of just thermal degradation. Besides the influence of ageing on thermo-mechanical behavior of mold compounds, dielectric strength is also an essential material property and this paper will discuss also the high voltage stability of epoxy material, depending on test conditions.