Reliability of SnPb and Pb-free flip-chips under different test conditions

This paper presents the results of an experimental study of the lifetime of flip-chip solder joints on low temperature cofired ceramics (LTCC) substrates. No underfill was used, thus the lifetime of the solder is separated from secondary influences such as underfill degradation or delamination. Otherwise identical test vehicles were built with SnPb37 and SnAg4Cu0.5 solder. The mean lifetimes of the SnPb37 joints were - depending on test condition and die size - between 637 and 1465 temperature cycles. The solder joints made out of SnAg₄Cu_0.5 solder showed a significantly longer lifetime. In the second part of the paper, a model for lifetime prediction of solder joints based on FEM simulation is derived from these results: By combining the experimental results with the computer simulation, it is possible to generate equations that permit the prediction of the lifetime of solder joints based on FEM simulations. They can be used to calculate the lifetime for future flip chip interconnects. The two common approaches (strain-based or energy-based) for generating such equations are compared. Both approaches were capable of describing the experimental observations.