A Review of Recent Research on the Mechanical Behavior of Lead-Free Solders

Due to the restriction of lead-rich solder and the miniaturization of electronic packaging devices, lead-free solders have replaced lead-rich solders in the past decades; however, it also brings new technical problems. Reliability, fatigue, and drop resistance are of concern in the electronic industry. The paper provides a comprehensive survey of recent research on the methodologies to describe the mechanical behavior of lead-free solders. In order to understand the fundamental mechanical behavior of lead-free solders, the visco-plastic characteristics should be considered in the constitutive modeling. Under mechanical and thermal cycling, fatigue is related to the time to failure and can be predicted based on the analysis to strain, hysteresis energy, and damage accumulation. For electronic devices with potential drop impacts, drop resistance plays an essential role to assess the mechanical reliability of solder joints through experimental studies, establishing the rate-dependent material properties and proposing advanced numerical techniques to model the interconnect failure. The failure mechanisms of solder joints are complicated under coupled electrical-thermal-mechanical loadings, the increased current density can lead to electromigration around the current crowding zone. The induced void initiation and propagation have been investigated based on theoretical approaches to reveal the effects on the mechanical properties of solder joints. To elucidate the dominant mechanisms, the effects of current stressing and elevated temperature on mechanical behavior of lead-free solder have been reviewed. Potential directions for future research have been discussed.