Die backside stress modification by coating of Si3N4 or AlN layers

The ability to improve the mechanical properties of a microelectronic package, including reducing the thermal-mechanical stress and increasing the die breaking strength is a long-sought goal in electrical assembly and packaging technology. Failure modes related with die backside stress caused by warpage or cosmetic defects may occur without a well control of die-backside stress. In this study, the modifications of die backside stress by coating of a thin layer of AlN or Si₃N₄ have been investigated. The simulation through the Finite Element Method (FEM) indicated that the stress distribution can be modified after coating and it is strongly related to the thickness of the coated layer, as the stress of die backside surface reduces. Die breaking strength has been measured by 3 point bending test and the measurement results are compared between samples with and without coatings. It is demonstrated that the die breaking strength is related with the thickness and the surface roughness of the coating layer of AlN or Si₃N₄. Improvement in the die breaking strength can be realized when the thickness and surface roughness are both optimized. The results suggested the additional coating of the die backside may be a feasible way to improve the mechanical properties of the electronic packages.