Ball impact responses and failure analysis of wafer-level chip-scale packages

The ball impact test (BIT) was developed based on the demand of a package-level measure of the board-level reliability of solder joints in the sense that it leads to brittle intermetallic fracturing, similar to that from a board-level drop test. The BIT itself stands alone as a unique and novel test methodology in characterizing strengths of solder joints under a high-speed shearing load. In this work, we present BIT 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 BIT, respectively. The explicit three-dimensional finite element analysis was also conducted and the comparison between computed and measured impact force profiles were presented.