Quantitative reliability estimation of surface mount solder joints for reflow optimization

A novel method of reliability analysis on the thermal fatigue failure of surface mount solder joints, based on the heating factor Q_η, is introduced, by which quantitative reliability estimation and prediction of solder joints suffering from cyclic thermal shock can be carried out. Based on the published data of thermal fatigue lifetime, two explicit functions are deduced in a unified form, which reveal the effect of the heating factor on the MTTF and reliability of solder joints intuitionistically. Numerical analysis and calculation are performed. The results show that the MTTF of solder joints firstly decreases quickly with an increment of Q_η and then slowly approximates to a constant value when Q_η≥1500s°C. The reliability of solder joints R(t) against thermal shock cycle t degrades in an analogical fashion for different heating factors, and the larger the heating factor, the less thermal shock cycles that the solder joints can endure. The presented method provides a useful and applicable way for computer-based online solutions to achieve numerical calculation and control for quantitative reliability estimation during reflow process optimization.