Electromigration: Lognormal versus Weibull distribution

Lognormal and Weibull distributions are commonly used to fit experimental data from accelerated electromigration tests and to extrapolate lifetimes to use conditions. The predicted lifetimes thus obtained for use condition at low failure rates can differ by orders of magnitude. In this work, a comparison between the two distributions is conducted for both experimental and simulated electromigration lifetime data. Even though Weibull distribution fits the data better when all the data points are considered, it is not theoretically justified to use a weakest link failure distribution. i.e., Weibull, for electromigration data. When the data is separated into different modes of failure, the lognormal distribution fits the data equally well, if not, better than the Weibull distribution.