First-principles investigation of the structural stability and electronic properties of Pd doped monoclinic Cu6Sn5 intermetallic compounds

• Published in: Materials science--Poland 2014-12, Vol.32 (4), p.592-596
• Main Authors: Shao, Wei-Quan, Lu, Wen-Cai, Chen, Sha-Ou
• Format: Article
• Language: English
• Subjects: ab-initio calculations; Chemistry and Materials Science; intermetallic compounds (IMC); Materials Science; site occupancy; thermal stability
• ISSN: 2083-1331; 2083-134X; 2083-134X
• DOI: 10.2478/s13536-014-0233-x

Tri-layer Au/Pd/Ni(P) films have been widely used as surface finish over the Cu pads in high-end packaging applications. It was found that a thin (Cu,Pd) 6 Sn 5 IMC layer was beneficial in effective reducing inter-diffusion between a Cu substrate and a solder, and therefore the growth of the IMC layer and the EM (electromigration) processes. In this study, the structural properties and phase stability of monoclinic Cu 6 Sn 5 -based structures with Pd substitutions were studied by using the first-principles method. The (Cu,Pd) 6 Sn 5 structure with the 4e site substituted by Pd has the lowest heat of formation and is the most stable among (Cu,Pd) 6 Sn 5 structures. Hybridization of Pd-d and Sn-p states is a dominant factor for stability improvement. Moreover, Pd atoms concentration corresponding to the most stable structure of (Cu,Pd) 6 Sn 5 was found to be 1.69 %, which is consistent with the experimental results.