Electromigration-induced remarkable intermetallic compound (IMC) formation in micro joints and its prevention
Pei-Tzu Lee, Cheng‐Yu Lee, Wan‐Zhen Hsieh, Chih-Tsung Chen, Cheng–En Ho
Abstract
The electromigration reliability of Au/Pd(P)/Ni(P) surface finish in micro joints was investigated in this study. We found that the reaction of Pd(P) with molten Sn would yield a noticeable amount of (Pd,Ni)Sn4 intermetallic compound (IMC) scattering in the Sn matrix after soldering reaction. Interestingly, upon electron current stressing, (Pd,Ni)Sn4 was gradually driven to the anode interface, and a remarkable volume expansion was caused by the transition from a low Ni-containing (Pd0.22Ni0.78)Sn4 (17 μm on thickness) into a high Ni-containing (Pd0.04Ni0.96)Sn4 (56 μm on thickness) because of the substitution of Pd sublattice by a high fraction of Ni as a result of electromigration. This electromigration-induced unusual stoichiometric transition and massive IMC propagation has been rarely reported previously in the literature. The underlying mechanism associated with the electromigration phenomenon and mitigation strategies to the NiSn4 formation were proposed in this study.