SuperiorDrop test performance of BGA assembly using SAC105Ti solder spheres - virtual fracture analysis

Assembled BGA/CSP devices with SnAgCu (SAC) solder joints are vulnerable when dropped due to the fragility of solder joints. Although reducing the Ag content of SAC alloy does help, the crack resistance when dropped is still considerably poorer than the eutectic SnPb system. Therefore a new alloy with improved drop test performance is greatly desired. In this work, SAC105 doped with Ti (SAC105Ti) as a BGA/CSP sphere was studied for its drop test reliability. Four different solder combinations were evaluated: 1) SnPb solder paste with SnPb balls, 2) SnPb solder paste with SAC105Ti balls, 3) SAC305 solder paste with SAC105Ti balls, and 4) SAC305 solder paste with SAC105 balls. The number of completely fractured interconnects was counted for each type of component after a total of 100 drops. The cell with the fewest number of fractured joints was the pure SnPb cell, followed closely by SAC305 solder paste/SAC105Ti ball, then SAC305 solder paste/ SAC105 ball and lastly SnPb solder paste/SAC105Ti ball. This trend is consistent with the trend observed by measuring the electrical resistance. The combination of SAC305 solder paste with SAC105Ti balls was the best solder joint structure tested in terms of the lowest number of partial interconnect fractures and outperformed the other three combinations.