Investigation of thermomechanical fatigue (TMF) behavior in tin-silver-based solder joints

Currently, there are two major driving forces for considering alternative materials to lead based products, specifically interconnections, in electronics applications, including the impending legislation or regulations which may tax, restrict, or eliminate the use of lead, and the trend toward advanced interconnection technology, which may challenge the limits of present soldering technology. The reliability of solder joints is a concern because fracture failures in solder joints accounts for 70% of failures in electronic components. Lead-free solders are being investigated as replacements for lead solders currently used in electronics.; Solder joints experience thermomechanical fatigue, i.e. interaction of fatigue and creep, during thermal cycling due to temperature fluctuation in service conditions. Incorporation of allying addition has been pursued to improve the mechanical and particularly thermomechanical behavior of solders, and their service temperature capability. Several service parameters, such as temperature extremes encountered, dwell times at these temperatures, and the ramp-rates representing the rate at which the temperature changes, were carried out to investigate the roles of these parameters.; Sn-Ag based solder joints that experienced a long dwell time at the high temperature extreme exhibited less surface damage accumulation and loss of residual shear strength than that of solder joints that experienced a long dwell time at the low temperature extreme. In particular, quaternary solder joints that containing small amounts of Cu and Ni in Sn-Ag solder were significantly improved the TMF behaviors during TMF with a long dwell time at the high temperature extreme.; Faster ramp rate during heating segment of TMF cycles caused highly localized surface damage in eutectic Sn-3.5Ag and Sn-4Ag-0.5Cu solder joints that resulted significant deterioration in residual shear strength in these solder joints. No significant surface damage and drop in residual strength were found in quaternary solder joints with faster heating rate during TMF.; A crack initiated and propagated along Sn-Sn grain boundaries by grain boundary sliding. There was significant residual stress within the solder joint causing more damage during TMF. Addition of small amounts of Cu and Ni into Sn-Ag solder resulted in better TMF performance under TMF with a long dwell time at the high temperature extreme due to presence in fine, hard, and sub-micron sized IMC precipitates that can retard Sn-Sn grain boundary sliding.