Nucleation and Location of Kirkendall Voids at the Tin-Based Solder/Copper Joint: A Review

Void nucleation is a critical issue in wetting because it negatively impacts the solder joint and diminishes its electrical and mechanical properties. Generally, the Kirkendall effect (unbalanced diffusion) and Kirkendall voids (KVs) are developed due to dissimilar diffusivities of species (Cu and Sn) in a diffusion process. However, voids are also nucleated in the supersaturating condition, creating an additional position at or inside the "Kirkendall voids" interface. Various factors (surface modification, reinforcement of fourth elements, substrate type, and impurities) and the environment also support the nucleation of voids. Many researchers have discussed that KVs are nucleated into to intermetallic compounds layers. Reviewing the significant parameters for developing the KV in solid-liquid and solid-solid conditions is essential. Hence, in this review, the potential process of development of the KVs, concepts of thermodynamics, chemical reactions, and growth kinetics are developed. The position and reduction of KVs nucleation are also explained in this paper.