Influence of contact geometry variations on the lifetime distribution of IC packages during electromigration testing

Two main trends in IC packaging are the progress in integration on package level (e.g. System in Package) and the use of ICs under harsh environmental conditions e.g. in sensors for intelligent actuators. The second task often requires very low failure rates below 1ppm. To clarify the reasons for the existing lifetime distribution during reliability tests, the influence of geometry variations on the lifetime of solder joints is investigated. The dimensions of 339 solder contacts for Package-on-Package systems were measured. The resulting mean values and the standard deviations were used to design a FEM model of Package-on-Package solder joints. The FEM model was used for the simulation of electromigration reliability tests. The mass flux and the mass flux divergences due to electromigration were investigated. As a range of variation, three standard deviations were chosen, so that 99.73% of all possible solder contacts will be covered by this investigation. Finally, the simulation results of the parameter study were compared with the results of the physical electromigration lifetime tests.