Wafer-level chip-scale package lead-free solder fatigue: A critical review

•Solder reliability of WLCSP due to fatigue is a significant concern.•Trends in solder technology for WLCSP to address fatigue failure were presented.•Prediction models and design guidelines for solder fatigue were discussed.•Three main challenges were identified for WLCSP reliability on solder joints.•Fatigue models are cost-effective means to evaluate WLCSP solder joint reliability.