Fatigue life prediction of Sn3.9Ag0.6Cu-soldered joints in WLCSP device

Based on creep model,the fatigue life of Sn3.9Ag0.6Cu-soldered joints in WLCSP device is predicted using finite element method.It is found that the stress concentrates on the top surface of the outermost soldered joints,and this location could be the origin of micro-crack,which is in well agreement with the experimental results.After the stress-strain analysis,the accumulated increase of creep strain and creep strain energy density was found in the soldered joints,respectively.Two life prediction equations,comparing with the experimental results,were employed to analyze the fatigue life of SnAgCusoldered joints under thermal cycling test.It is seen that the calculated life with creep strain energy based fatigue life prediction equation coincides well with that of the experimental data,and the life calculated by creep strain based equation is significantly higher than that of the experimental result,therefore,the creep strain equation needs to be further studied.