Three-dimensional microstructure characterization of Ag3Sn intermetallics in Sn-rich solder by serial sectioning
Three-dimensional microstructure characterization of Ag3Sn intermetallics in Sn-rich solder by serial sectioning
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DOI：
10.1016/j.matchar.2004.04.010
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发表时间：
2004-06
影响因子：
4.7
通讯作者：
R. Sidhu;N. Chawla
中科院分区：
文献类型：
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作者：
R. Sidhu;N. Chawla
对电子封装中使用的Pb-Sn焊料的环境和健康危害的日益关注促使人们需要无铅焊料替代品[1-3]。共晶Sn-3.5 Ag焊料系统是替代Pb-Sn焊料的潜在候选者，原因有几个，包括优异的机械性能、与Pb-Sn系统相比改进的耐高温性以及与其他无铅焊料替代品相比的成本效益[1-8]。在Sn-3.5 Ag焊料系统中，凝固时，共晶显微组织由两相组成：富Sn基质和由于Sn和Ag之间的反应而形成的Ag 3Sn金属间化合物[6-8]。最近，Ochoa et al. [7，8]已经确定冷却速率对金属间尺寸和形态具有显著影响。在相对较快的冷却速率（24 μ C/s）下，观察到球形Ag 3Sn颗粒的精细分布。然而，在较慢的冷却速率（0.08 μ C/s），金属间化合物具有针状形态。因此，要了解焊料的物理、电学和机械性能，就必须准确地表征富锡基体中金属间化合物的尺寸、分布、形态和取向。传统的金相技术依赖于二维（2D）图像，如光学和/或扫描电子显微镜照片，用于表示材料的微观结构。球形显微结构特征的尺寸和纵横比可以通过2D圆充分表征[9]。然而，在针的情况下，垂直于针的主轴的2D截面可能显著低估针的尺寸和纵横比。显然，三维（3D）可视化的技术是需要准确表征的非球形功能，如Ag 3Sn针在锡矩阵。利用计算机辅助重建和可视化的2D显微结构图像的连续切片越来越多地用作显微结构的3D可视化技术[9-21]。Yamaguchi等[18]利用3D重建技术来量化致病酵母细胞，并揭示它们在冷冻前后的形态变化。在钢中，Yokomizo et al. [14]研究了在Fe-0.1C-1.5Mn钢合金中形成的晶内铁素体和夹杂物的3D分布、形态和形核位置。该技术也已用于复合材料，其中Wunsch et al. [10]使用连续切片来可视化和模拟SiC颗粒在Al基体中的微观结构。在这项研究中，我们已经使用了一个连续切片技术来表征的Sn-3.5 Ag焊料的微观结构。研究了Ag_3Sn金属间化合物的尺寸和长径比。
Increasing concerns over the environmental and health hazards of Pb–Sn solders, used in electronic packaging, have prompted the need for Pb-free solder alternatives [1–3]. The eutectic Sn–3.5 Ag solder system is a potential candidate for replacement of Pb–Sn solder for several reasons, including excellent mechanical properties, improved high temperature resistance compared with the Pb–Sn system, and cost effectiveness when compared with other Pb-free solder alternatives [1–8]. In the Sn–3.5 Ag solder system, upon solidification, the eutectic microstructure consists of two phases: a Sn-rich matrix and Ag3Sn intermetallics that form due to the reaction between Sn and Ag [6–8]. Recently, Ochoa et al.[7, 8] have determined that cooling rate has a significant effect on intermetallic size and morphology. At relatively fast cooling rates (24 jC/s), a fine distribution of spherical Ag3Sn particles was observed. At slower cooling rates (0.08 jC/s), however, the intermetallic had a needlelike morphology. Thus, to understand the physical, electrical, and mechanical properties of the solder, it is necessary to accurately characterize the intermetallic size, distribution, morphology, and orientation within the Sn-rich matrix.Traditional metallographic techniques rely on twodimensional (2D) images, such as optical and/or scanning electron micrographs, for representing the microstructure of a material. The size and aspect ratio of spherical microstructural features can be characterized adequately by 2D circles [9]. In the case of needles, however, a 2D section perpendicular to the major axis of the needle can significantly underestimate the size and aspect ratio of the needle. Clearly, a technique for three-dimensional (3D) visualization is required for accurate characterization of nonspherical features, such as Ag3Sn needles in a Sn matrix. Serial sectioning of 2D microstructural images with computer-aided reconstruction and visualization has increasingly been used as a technique for 3D visualization of microstructures [9–21]. Yamaguchi et al.[18] utilized a 3D reconstruction technique to quantify pathogenic yeast cells and reveal variations in their morphology before and after freezing. In steels, Yokomizo et al.[14] studied the 3D distribution, morphology, and nucleation sites of intragranular ferrite and inclusions formed in an Fe–0.1 C–1.5 Mn steel alloy. The technique has also been utilized in composites, wherein Wunsch et al.[10] used serial sectioning to visualize and model the microstructure of SiC particles in an Al matrix. In this study, we have used a serial sectioning technique to characterize the microstructure of a Sn–3.5 Ag solder. The size and aspect ratio of the Ag3Sn intermetallic within the Sn-