Journal of Electronic Materials ( IF 2.2 ) Pub Date : 2021-07-26 , DOI: 10.1007/s11664-021-09067-4 A. Leineweber 1 , M. Löffler 1 , S. Martin 1
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Abstract
Cu6Sn5 intermetallic occurs in the form of differently ordered phases η, η′ and η′′. In solder joints, this intermetallic can undergo changes in composition and the state of order without or while interacting with excess Cu and excess Sn in the system, potentially giving rise to detrimental changes in the mechanical properties of the solder. In order to study such processes in fundamental detail and to get more detailed information about the metastable and stable phase equilibria, model alloys consisting of Cu3Sn + Cu6Sn5 as well as Cu6Sn5 + Sn-rich melt were heat treated. Powder x-ray diffraction and scanning electron microscopy supplemented by electron backscatter diffraction were used to investigate the structural and microstructural changes. It was shown that Sn-poor η can increase its Sn content by Cu3Sn precipitation at grain boundaries or by uptake of Sn from the Sn-rich melt. From the kinetics of the former process at 513 K and the grain size of the η phase, we obtained an interdiffusion coefficient in η of (3 ± 1) × 10−16 m2 s−1. Comparison of this value with literature data implies that this value reflects pure volume (inter)diffusion, while Cu6Sn5 growth at low temperature is typically strongly influenced by grain-boundary diffusion. These investigations also confirm that η′′ forming below a composition-dependent transus temperature gradually enriches in Sn content, confirming that Sn-poor η′′ is metastable against decomposition into Cu3Sn and more Sn-rich η or (at lower temperatures) η′.
Graphic Abstract
中文翻译：
涉及 Cu6Sn5 金属间化合物的稳定和亚稳定相平衡
摘要
Cu 6 Sn 5金属间化合物以不同排列的相η、η'和η''的形式出现。在焊点中，这种金属间化合物会发生成分和有序状态的变化，而不会或同时与系统中过量的 Cu 和过量的 Sn 相互作用，这可能会导致焊料机械性能的有害变化。为了从根本上详细研究这些过程并获得有关亚稳态和稳定相平衡的更多详细信息，模型合金由 Cu 3 Sn + Cu 6 Sn 5以及 Cu 6 Sn 5 组成+ 对富锡熔体进行热处理。粉末X射线衍射和扫描电子显微镜辅以电子背散射衍射被用来研究结构和微观结构的变化。结果表明，贫锡 η 可以通过在晶界处的 Cu 3 Sn 沉淀或通过从富锡熔体中吸收 Sn来增加其 Sn 含量。从前一过程在 513 K 下的动力学和 η 相的晶粒尺寸，我们获得了 (3 ± 1) × 10 -16 m 2 s -1的互扩散系数。该值与文献数据的比较表明该值反映了纯体积（互）扩散，而 Cu 6 Sn 5低温下的生长通常受到晶界扩散的强烈影响。这些研究还证实，在与组成相关的转变温度以下形成的 η''逐渐丰富了 Sn 含量，证实了 Sn 贫乏的 η'' 对分解为 Cu 3 Sn 和更多富 Sn η 或（在较低温度下）是亚稳态的η'。
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