Thermal-fatigue life prediction equation for wafer-level chip scale package (WLCSP) lead-free solder joints on lead-free printed circuit board (PCB)

A new thermal-fatigue life prediction equation for a class of lead-free solder alloys, 95.5wt%Sn3.9-4.0wt%Ag0.5-0.6wt%Cu is proposed in this investigation. The test vehicle consists of a lead-free solder-bumped WLCSP, lead-free PCB, and lead-free solder paste. The coefficients of the fatigue equation presented herein are determined by best fitted with the isothermal fatigue data of the test vehicle. Failure modes and locations of the failed samples are discussed.