Electromigration induced Kirkendall void growth in Sn-3.5Ag/Cu solder joints

Abstract

Effects of electric current flow on the Kirkendall void formation at solder joints were investigated using Sn-3.5Ag/Cu joints specially designed to have localized nucleation of Kirkendall voids at the Cu3Sn/Cu interface. Under the current density of 1 x 10(4) A/cm(2), kinetics of Kirkendall void growth and intermetallic compound thickening were affected by the electromigration (EM), and both showed the polarity effect. Cu6Sn5 showed a strong susceptibility to the polarity effect, while Cu3Sn did not. The electromigration force induced additional tensile (or compressive) stress at the cathode (or anode), which accelerated (or decelerated) the void growth. From the measurements of the fraction of void at the Cu3Sn/Cu interface on SEM micrographs and analysis of the kinetics of void growth, the magnitude of the local stress induced by EM was estimated to be 9 MPa at the anode and -7 MPa at the cathode.