Insights into correlation between board-level drop reliability and package-level ball impact test characteristics

The ball impact test (BIT) is developed based on the demand of a package-level measure for the board-level drop reliability of solder joints in the sense that it leads to fracturing of solder joints around the intermetallics, similar to that from a board-level drop test. In this paper, both board-level drop test and package-level ball impact test are examined numerically for solder joints of different Sn-Ag-Cu compositions. We propose a stress-based drop reliability index that involves the strength of intermetallics and the maximum interfacial normal stress the solder joints have experienced during the drop impact process. Correlations between the drop reliability index and BIT characteristics are found to be dependent on solder compositions. However, the correlations appear to be universal, i.e., independent of solder compositions, when certain constant multipliers are introduced.