Effects of Ge addition on the growth of interfacial Ni₃Sn₄ IMC in the Sn58Bi/Ni solder joint: First-principles and Experimental Investigations

Interfacial intermetallic compound (IMC) is an important interconnection medium in soldering, and its brittleness makes it the most failure-prone region in soldered joints, Therefore, the growth and evolution of interfacial IMCs has been a focus of attention in electronic packaging. The conventional Cu-Sn system gradually generates Cu3Sn. The resulting Kirkendall voids affect the reliability of solder joints during service. An effective way to alleviate such a situation is to add Ni as a diffusion barrier layer. Therefore, it is necessary to study the reaction between Sn-based solder and Ni substrate and the growth of intermetallic compounds at the interface, which are crucial for design the bonding material composition and optimize the bonding parameters during the bonding process.In high-density packaging, the choice of solder needs to meet the requirements of multi-level interconnections. Sn58Bi solder alloy with its excellent properties has become a promising low-temperature solder in the field of high-density gradient packaging.Therefore, this paper investigated the evolution of interfacial IMC at the Sn58Bi/Ni solder joint and researched the effect of Ge element on the growth of interfacial IMC. Besides, the diffusion rates of Sn, Ni and Ge atoms in Ni-Sn IMC were calculated using density functional theory (DFT). The effect of Ge element addition on the composition and structure of Ni-Sn-based IMCs interconnected with Sn58Bi/Ni substrates was researched. The results show that the addition of Ge element promotes the IMC growth, and the growth pattern obtained from DFT was verified by the reflowing experiments. A reliable calculation model to predict the thickness of interfacial IMC was proposed.