Effects of joule heating on the electromigration properties of eutectic SnBi solder joints

Electromigration could induce the movement of atoms/ions towards the direction of electron flow in pure metal line in chips. However, in the eutectic SnBi solder joints, the constituted elements are Sn and Bi. Due to the different drift velocity of Bi atoms and Sn atoms under high current density, the electromigration properties of eutectic SnBi are unique. With a current density of 104A/cm2 and the Joule heating effect, the temperature of solder joints increased from 25 to 50C, and the Bi-rich phases grew bigger during current stressing due to the high ambient temperature (49C). In addition, Bi atoms initially arrived at the anode side and eventually formed a barrier layer to inhibit the movement of Sn atoms towards the anode side. Sn-rich phase bulged, and a valley formed along the interface at cathode side.