Modelling the fatigue life of solder joints for surface mount resistors

This paper discusses the results from a modelling study that is being undertaken to compliment a large-scale experimental programme currently underway at the National Physical Laboratory. One aspect of this programme is to investigate the effect of different thermal cycles on both tin-lead and lead-free solder joints for surface mount resistor components. Detailed data gained from this part of the experimental programme is providing the opportunity to ensure that the models used are robust and appropriate for further in-depth cost-effective modelling studies on the behaviour, and possible failure, of such materials during thermal cycling. The paper primarily focuses on the modelling techniques and methodologies adopted to predict the response of solder materials to different thermal cycles. Three-dimensional models have been assembled to fully characterise the changing stress and strain profiles in the resistor component throughout a thermal cycle. The paper provides results from this modelling study that detail the reliability of tin-lead solder joints associated with four different thermal cycles. The modelling results appear to show that a large decrease in time per cycle, while keeping the thermal range constant, does not dramatically affect cycles to failure.