Tin pest in lead-free solders

Considers the effect of low temperatures on the characteristics of lead-free alloys based upon tin, which is the most popular basis for the new alloys

Effect of Hold Time on Low Cycle Fatigue Life of Micro Solder Joint

Effect of holding time and temperature on the fatigue life of micro Sn-Ag-Cu solder joint has been studied with waveform of triangle and trapezoid wave at 298K and 398K. Both the microstructural coarsening and the crack propagation occurred simultaneously and therefore the cyclic load decreased rapidly in the trapezoidal wave at 398K compared with the other conditions. Therefore, under the condition of waveform that includes holding time at high temperature, it is necessary to define fatigue life by considering crack length, although the load drop life definition is typically employed for the low cycle fatigue evaluation. The fatigue life of Sn-Ag-Cu micro solder joints is not strongly affected by temperature and holding time when the crack length is considered to define fatigue life. This is different form the trends in large scale bulk specimen and is attributed to the peculiar microstructure of the Sn-Ag-Cu. [doi:10.2320/matertrans.MF200852

InterPack2003-35165 ISOTHERMAL SHEAR FATIGUE LIFE OF Sn-xAg-0.5Cu FLIP CHIP INTERCONNECTS

ABSTRACT The mechanical shear fatigue test has been performed to look for the effect of silver content on the fatigue properties of Sn-xAg-0.5Cu (x=1, 2, 3 and 4) flip chip interconnections. As the strength of the solder alloy increases with increasing silver content, the increase in silver content results in preventing a shear plastic deformation of solder bump. Therefore, the flip chip joints made using higher silver content solder such as 3 and 4Ag exhibit longer fatigue life, if the same levels of displacement is applied. The fatigue ductility of the solder decreases with increasing the silver content. Therefore, the fatigue endurance of the 1Ag solder itself is superior to other solders in high plastic strain regime, even though the strength of the solder is the lowest in the solders tested. Based on this study, the 3Ag solder might exhibit good fatigue performance for all condition, and the 1Ag solder is optimum for severe strain condition

Tin pest in Sn-0.5 wt.% Cu lead-free solder

Tin pest (the product of the allotropic transformation of β-tin into α-tin at temperatures below 286 K) has been observed in a Sn-0.5 wt.% Cu solder alloy. Some 40 percent of the specimen surface was transformed into gray tin after aging at 255K for 1.5 years, and after 1.8 years, the proportion increased to about 70 percent. The degree of transformation in work-hardened areas is much higher than in other areas, suggesting residual stress might provide an additional driving force for the transformation into α-tin. The allotropic change results in a 26 percent increase in volume, and cracks are initiated to accommodate the changes in volume. Results indicate that tin pest could lead to total disintegration of micro-electronic solder joints. The tin-copper eutectic system may become a prominent lead-free solder, and tin pest could have major ramifications on service lifetime of electronic assemblies