Effects of Grain Orientation on Cu6Sn5 Growth Behavior in Cu6Sn5-Reinforced Composite Solder Joints During Electromigration

Electromigration is a major reliability problem in composite solder joints. Due to the anisotropy of the β -Sn crystal structure, the Sn grain orientations present in the solder matrix dominate the principal failure mechanism in solder joints under electric current stressing. In this work, the Cu 6 Sn 5 growth behavior in Cu 6 Sn 5 -reinforced composite solder joints with three different Sn grain orientations was investigated at current density of 10 4  A/cm 2 at room temperature. Micron-sized Cu particles were added to Sn-3.5Ag solder at 2% volume fraction using an in situ method. After current stressing for 528 h, the polarity effect in the composite solder joint was greatest for an angle ( θ ) between the c -axis and electron flow direction of 30°, resulting in higher growth rate of Cu 6 Sn 5 in the solder matrix compared with composite solder joints with θ of 60° or 90°. There were no noticeable changes in the composite solder joint with θ of 90°. The growth behavior of Cu 6 Sn 5 , Cu atomic motion, and Cu diffusivity in the composite solder joints with different Sn grain orientations were analyzed in detail.