Creep-fatigue life evaluation of Sn-3.5Ag lead-free solder at low temperatures

摘要

This paper describes creep-fatigue lives of Sn-3.5Ag lead-free solder at low temperatures. Since solders have lower melting temperature and electronic devices are often used at low temperature environment, it is effective for improving the fatigue life evaluating precision of solder joints to make clear the mechanical properties and creep-fatigue properties of solders at low temperatures. Cyclic push-pull fatigue tests with various strain waveforms were conducted at 253K and 273K to examine influence of strain rate and testing temperature on fatigue life of Sn-3.5Ag lead-free solder. Creep-fatigue lives under unsymmetrical full reversed strain waveform were smaller than that of symmetrical waveform at low temperatures. An application of five kinds of creep-fatigue life evaluation parameters for electronic materials at low temperatures was also discussed. They are Linear Damage Rule, Frequency Modified Fatigue Life, Ductility Exhaustion Model, Strain Range Partitioning method and Grain Boundary Sliding Model. Grain Boundary Sliding Model, which has been proposed as a fatigue life evaluation parameter for Pb-content solders and lead-free solders at high temperatures, was a suitable parameter for the correlation of creep-fatigue lives of Sn-3.5Ag lead-free solder at low temperatures. Grain Boundary Sliding Model parameter predicted almost all of the experimental lifetimes within a small scatter conservatively.