Formation of Intermetallic Compounds Between Liquid Sn and Various CuNix Metallizations

Vesa Vuorinen*, Hao Yu, Tomi Laurila, Jorma Kivilahti

*Corresponding author for this work

    Research output: Contribution to journalArticleScientificpeer-review

    72 Citations (Scopus)


    Interfacial reactions between liquid Sn and various Cu-Ni alloy metallizations as well as the subsequent phase transformations during the cooling were investigated with an emphasis on the microstructures of the reaction zones. It was found that the extent of the microstructurally complex reaction layer (during reflow at 240°C) does not depend linearly on the Ni content of the alloy metallization. On the contrary, when Cu is alloyed with Ni, the rate of thickness change of the total reaction layer first increases and reaches a maximum at a composition of about 10 at.% Ni. The reaction layer is composed of a relatively uniform continuous (Cu,Ni) 6Sn 5 reaction layer (a uniphase layer) next to the NiCu metallizations and is followed by the two-phase solidification structures between the single-phase layer and Sn matrix. The thickness of the two-phase layer, where the intermetallic tubes and fibers have grown from the continuous interfacial (Cu,Ni) 6Sn 5 layer, varies with the Ni-to-Cu ratio of the alloy metallization. In order to explain the formation mechanism of the reaction layers and their observed kinetics, the phase equilibria in the Sn-rich side of the SnCuNi system at 240°C were evaluated thermodynamically utilizing the available data, and the results of the Sn/Cu x Ni 1-x diffusion couple experiments. With the help of the assessed data, one can also evaluate the minimum Cu content of Sn-(Ag)-Cu solder, at which (Ni,Cu) 3Sn 4 transforms into (Cu,Ni) 6Sn 5, as a function of temperature and the composition of the liquid solders.

    Original languageEnglish
    Pages (from-to)792-805
    Number of pages14
    JournalJournal of Electronic Materials
    Issue number6
    Publication statusPublished - Jun 2008
    MoE publication typeA1 Journal article-refereed


    • intermetallic formation
    • kinetics
    • metastable solubility
    • phase diagram
    • reliability
    • soldering, lead-free
    • solidification

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