Electromigration Mechanism of Indium-44Tin-6Zinc Alloy

Abstract

In-Sn alloys have great potential in high-power semiconductor packaging, but their applications are constrained by electromigration. The electromigration mechanism of a In-44Sn-6Zn alloy was studied with the current density at a direct current of 1.0 × 103A/cm2. The results indicated that the alloy exhibited an obvious phase separation under the influence of electron wind force. The β phase (In3Sn) was enriched at the cathode side and the γ phase (InSn4) was enriched at the anode side, while the zinc (Zn) phase had no obvious migration tendency. The migration of indium (In) and tin (Sn) atoms caused lattice distortion and the change rate of unit cell volume at the anode side was about twice as high as that of the cathode side. The primary Zn phase tended to migrate along the phase boundary and its size decreased with the process of diffusion. The mutual transformation between γ and β phases was carried out in a manner similar to the spinodal decomposition and the process of transformation accompanied by the solid solution or precipitation of Zn. After electromigration, the structure of the alloy was more uniform. The average area of the β phase at the cathode side was about 64% of the original size and that at the anode side was about 31% from the initial size. The resistance of the alloy increased 4% and the microhardness of the two poles were both increased by about 30%.