Methodology for Reliability Evaluation of Power Modules

This paper describes the methodology for reliability evaluation of power semiconductor devices. When they are used in power systems, they are subjected to thermal cycles caused by power fluctuations. In such circumstances, power modules break down because of wire-liftoff in wire-bond and solder crack in dye-bond induced by thermal fatigue. In most papers concerning power electronics, such thermal fatigue life Nf has been related with temperature range ΔT together with the mean temperature Tm during cycling. The Nf -ΔT relation depends on the dimensions of power modules, even if they are made of the same materials. On the other hand, the Manson-Coffin rule correlating Nf with inelastic strain range Δεin or inelastic strain energy density ΔWin is independent of the dimensions of power modules. This paper presents how to obtain the Manson-Coffin rule from thermal fatigue experiments of power modules. In addition to the mechanical reliability problems described above, the present paper describes the importance of an electrical reliability problem of power devices, in which the electronic performance of semiconductor power devices is adversely affected by the action of stress.