Improvement of drop reliability in OSP/Cu pad finished packages

This study investigated the improvement of drop reliability of OSP (organic solderability preservatives) pad finished packages having half etched solder ball pads. Besides the effect of the Cu pad etching depth, effects of other factors such as solder composition or reflow peak temperature on drop reliability were examined by the bending impact test and drop test. The bending impact test results showed that the increase of etching depth at the solder ball pad increased the drop reliability because of the fracture mode transition from solder/pad interface failure to solder bulk failure, but that the increase of reflow peak temperature decreased the drop reliability. The drop test results showed that the increase of the etching depth at the solder ball pad increased the drop reliability without the fracture mode transition, and that the change of the solder composition from Sn3.0Ag0.5Cu to Sn1.2Ag0.5Cu0.05Ni increased the drop reliability and shifted the fracture mode from interface failure to the bulk failure. The optimal conditions for the drop reliability improvement are presented in terms of the etching depth at the solder ball pad, the reflow peak temperature, and the solder composition.