Effect of Thermal Aging on High Speed Ball Shear and Pull Tests of SnAgCu Lead-free Solder Balls

Solder joint reliability concerns are increasing exponentially with the continuous push for device miniaturization, and the expanded use in portable electronic products. In order to predict the solder joint reliability under drop conditions, it is important to increase the testing speed of package level test methods, such as high-speed solder ball shear and pull. Traditional ball shear and pull tests are not considered suitable for evaluation of joint reliability under drop loading, since the applied test speeds, usually lower than 5 mm/s, are well below the impact velocity applied to the solder joint in a drop test. Recently, high-speed shear and pull test equipment (Dage 4000HS) with testing speeds beyond 1,000 mm/s has become available. The present study continues the efforts reported recently and investigates the effect of thermal aging on the attachment strength and fracture energy of SnAgCu lead-free solder balls during high speed ball shear/pull tests. The ball shear test speeds ranged from 100 mm/s to 1,000 mm/s, while the ball pull test speeds ranged from 5 mm/s to 100 mm/s. The test specimens were aged at 125degC or 150degC for durations of 100, 300 and 500 hrs, with some additional samples exposed up to 1,000 hrs. Correlations were established between solder joint fracture force/energy and IMC thickness, and between fracture energy and failure mode.