A fracture mechanics approach to thermal fatigue life prediction of solder joints

A life prediction approach for solder joints under thermal fatigue, based on fracture mechanics and assuming that the thermal fatigue crack propagation in solder joints is primarily controlled by the C* and the J Integrals, is presented. The approach is applied to model experiments in which surface mounted electronic components were mounted on substrates with eutectic Pb/Sn solder joints and subjected to thermal cycling. The constitutive equation used for eutectic solder takes into account elasticity, time-independent plasticity, and power law secondary creep. Shear stress, strain components, and crack growth history in the solder joint are solved numerically by the Runge-Kutta method. The results are compared with both experimental data and predictions based on a modified Manson-Coffin equation. Good agreement is found between the present results and the experimental data, while the Manson-Coffin predictions are inconsistent with either the present ones or the experimental data. Examples illustrate how to apply the approach in order to design accelerated thermal cycling tests