Atomic insights into the ordered solid solutions of Ni and Au in η-Cu6Sn5. (1st February 2022)

• Record Type: Journal Article
• Authors: Yang, Wenhui; Tran, Xuan Quy; Yamamoto, Tomokazu; Aso, Kohei; Somidin, Flora; Tan, Xin Fu; Kawami, Youichirou; Nogita, Kazuhiro; Matsumura, Syo
• Is Part Of: Acta materialia. Volume 224(2022)
• Publication Date: 2022-02-01
• Subjects: η-Cu6Sn5 -- Structural modulation -- Long-range ordering -- Atomic-resolution XEDS mapping -- Poisson NLPCA; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2021.117513
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: The Cu6 Sn5 intermetallic, which commonly forms at the solder interconnects, is a critical component contributing to the reliability of today's electronic products. It has been established that the structural control of its hexagonal η -Cu6 Sn5 polymorph can be achieved over a wide temperature range of service conditions via chemical doping with Ni or Au, effectively suppressing the undesirable hexagonal to monoclinic ( ƞ → ƞ′ ) phase transition at 186 °C and its associated volume change. In this study, we further investigate the effects of Ni (26.5 at%) and Au (9 at%), with high doping/alloying contents, on the atomic-scale structure of η -Cu6 Sn5 using a suite of microscopy techniques including atomic-resolution imaging, chemical mapping, electron diffraction, and in-situ heating, coupled with advanced data informatics. Our study reveals that while Ni occupancy takes place in both the Cu1 and Cu2 sites of η -Cu6 Sn5 in substantial amounts, Au is mostly substituted at the Cu1 sites of η -Cu6 Sn5 . Most interestingly, characteristic occupational modulations of the Cu6 Sn5 structure arise with each type of dopants: a three-fold ordered structure for Ni accompanied by a displacive modulation of the constituent atoms, but a two-fold layer-like structure for Au. Moreover, with a high content of Ni, the unit cell of η -Cu6 Sn5 is found to contract along its hexagonal ah axis relative to the Ni-dilute case, but anisotropically expands the ch axis in a bimodal fashion; in contrast, the effect of Au appears to be of an isotropically expanding nature. Graphical abstract: Image, graphical abstract .