A first-principles computation-driven mechanism study on the solders dilute doping effects to η’-Cu₆Sn₅ growth kinetics

Abstract: The effects of Ni, Co, In and Zn dilute doping on the Cu₆Sn₅ IMC growth during the interfacial Cu/Sn reactions have been systematically investigated with both experimental approach and the first-principles computational method. The experimental results indicated that Ni and Co doping would promote Cu₆Sn₅ growth, whereas adding In and Zn would inhibit its growth kinetics. Moreover, with a heavier doping concentration, the effects of promoting or inhibiting IMC growth become more prominent. In order to fully understand the effect of doping elements on the growth kinetics of Cu₆Sn₅ IMC, the first-principles computational method was used in modeling the crystallographic channeling effects within the η’-Cu₆Sn₅ IMC. The first-principles calculated results demonstrated that Cu was the main diffusing element within Cu₆Sn₅, which preferred to diffuse along [ 2 , 0 , 1 ¯ ] direction. Importantly, if one or two atoms in Cu₆Sn₅ crystal were substituted by Ni, Co, In, or Zn, respectively, Ni and Co would prefer to occupy the Cu site. This would further reduce the atomic diffusion energy of Cu along [ 2 , 0 , 1 ¯ ] direction, resulting in promoting the Cu₆Sn₅ IMC growth kinetics. In contrast, In and Zn would prefer to occupy Sn site, which showed the opposite effects on both the atomic diffusion energy of Cu along [ 2 , 0 , 1 ¯ ] direction and the associated Cu₆Sn₅ IMC growth kinetics. Therefore, based on the first-principles computation, an alternative insight has been provided in understanding the dilute doping effects on Cu₆Sn₅ growth with certain alloying elements, where the promoting and inhibiting behaviors can be clearly illuminated within one theoretical framework. Graphical abstract: [Figure not available: see fulltext.]