Brittle Failure Mechanism of SnAgCu and SnPb Solder Balls during High Speed Ball Shear and Cold Ball Pull Tests

This study investigated brittle solder joint failure mechanisms during high-speed solder ball shear and pull testing. BGA package samples with different solder alloys (Sn4.0%Ag0.5%Cu and Sn37%Pb) were fabricated and a series of solder ball shear and pull tests were conducted at various testing speeds. The ball shear test speeds ranged from 10 mm/s to 3000 mm/s, while the ball pull test speeds ranged from 5 mm/s to 500 mm/s. Following high-speed shear/pull testing, the brittle fracture surfaces of the solder balls and corresponding pad were inspected using SEM/EDX. The results describe an increased incidence of brittle interfacial fracture for SnAgCu solder compared to SnPb solder. Microstructure analysis of brittle solder joint fracture surfaces appears an effective method to aid correlation between board level drop test and high-speed solder ball shear/pull tests.