Drop Shock Performance of SAC-Bi Compared to SnPb

Lead free soldering has become mainstream since the Restriction of Hazardous Substances (RoHS) Directive. Solders have come a long way from the traditional SnPb (Tin-Lead) to lead-free alloys doped with elements such as Bismuth (Bi), Antimony (Sb), Nickel (Ni), etc. Following the transition from ductile lead-based alloys to strong but brittle lead-free solder alloys, the board-level drop test has become a vital reliability evaluation criterion for electronic packages. In this paper, a drop shock reliability comparison was made between SAC305, SAC-Bi, and SnPb. The tested component was a 0.8mm pitch, 15mm body CABGA208. The test vehicle has an Organic Surface Protection (OSP) surface finish and a matching solder sphere with paste alloys. Ten test boards were subjected to drop test, with a peak acceleration of 1500G and 0.5ms pulse duration per JEDEC drop test condition B. After the drop test, a Weibull analysis was performed to study the drop shock reliability for each alloy. Microstructure analysis was also performed to determine the failure mode and the failure location on the board. It was observed that SAC-3.3Bi has the highest drop shock reliability among all the alloys, followed by SAC305, while Sn63Pb37 had the lowest drop shock reliability.