The Combined Effect of Mechanical Package Stress and Humidity on Chip Corrosion Probability

Microelectronic components used in automotive applications have to meet very strict reliability requirements. In addition to the mechanical or thermomechanical stresses resulting from manufacturing and application conditions, also chemical processes have to be considered if the systems are exposed to harsh environmental conditions. In these cases, mechanical stresses do not only determine the risk of deformation-induced failure and cracking but can also affect the diffusion kinetics of any chemical species, e.g. humidity and corrosive compounds. This paper addresses chip-package interaction effects that determine the probability of chip damage by corrosion. The effects of mechanical stress resulting from both the package and from additional external loading on humidity diffusion kinetics, and finally on the resulting failure probability were investigated using finite element analysis (FEA). The simulation results were compared to the experimentally determined failure risk. Further the derived numerical results showed a distinct correlation with the experimentally detected failure risks provoked by different accelerated reliability tests. To validate the correlation between stress-supported diffusion and the occurrence of corrosive failures, a specific dedicated experimental test setup was created. The results showed a very good correlation of corrosive failure modes in the active die structures to the mechanical stresses at the critical regions determined from the accompanying FEA package simulation. In addition, scanning electron microscope investigations revealed that the corrosive chip damage started at locations that were also in accordance with the simulation results.