Characterizations of ball impact responses of wafer-level chip-scale packages

We present in this paper ball impact test results conducted on package-level 95.5Sn–4Ag–0.5Cu solder joints of a wafer-level chip-scale package, under an impact velocity of 1.4 m/s. Scanning electron microscopy was employed to investigate intermetallic morphologies and fractographs around the under bump metallurgy before and after the ball impact test, respectively. An explicit three-dimensional finite element analysis was also conducted and the comparison between computed and measured impact force profiles are presented. The comparison indicates that when material properties and strengths are apppropriately and reasonably selected, the finite element analysis is capable of capturing relevant ball impact test (BIT)-induced transient structural responses of the solder joint prior to the initiation of fracturing.