Three-dimensional (3D) microstructure visualization of LaSn3 intermetallics in a novel Sn-rich rare-earth-containing solder
Three-dimensional (3D) microstructure visualization of LaSn3 intermetallics in a novel Sn-rich rare-earth-containing solder
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DOI：
10.1016/j.matchar.2007.10.008
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发表时间：
2008-09
影响因子：
4.7
通讯作者：
M. A. Dudek;N. Chawla
中科院分区：
文献类型：
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作者：
M. A. Dudek;N. Chawla
全球对消费电子产品中铅基焊料的环境影响和健康影响的关注导致了无铅焊料替代品的开发。富锡焊料如Sn-Ag和Sn-Ag-Cu是最有希望替代Pb-Sn焊料的无铅合金[1]。与其机械性能和可靠性相关的许多问题仍需要解决。这尤其包括它们的较高熔点和较低延展性[2，3]。焊料的较低延展性具有重要意义，因为它与机械冲击和抗跌落性直接相关[4]。最近，少量添加稀土元素（RE），如Ce和La，已被证明可以细化微观结构并改善富Sn焊料的机械响应[5-8]。由于这些三元和四元系统的复杂性，非常少的信息是在凝固过程中形成的Sn-RE金属间化合物。Dudek等人[7]结果表明，少量La添加（0.1wt.%和0.5重量%）的Sn-Ag-Cu导致形成稳定的，均匀分布的LaSn 3金属间化合物。他们表明，LaSn 3颗粒直接导致这些材料中观察到的较高延展性，通过允许微观空隙在整个焊料体积中成核（通过最小化应变局部化），并消除焊点中的应变。为了了解这些RE相如何影响焊料的物理、电学和机械行为，有必要充分表征富Sn基质内的金属间尺寸和形态。LaSn 3金属间化合物具有特征性的刻面几何形状，也被称为“中国文字”，这也在其他系统中观察到[9-12]。由于这些颗粒的复杂形态和形状，二维（2D）表示不是非常准确。为了表征LaSn 3金属间化合物的三维（3D）形态，可以使用与计算机辅助重建软件耦合的连续切片技术来可视化3D中的微观结构。这种技术越来越多地用于三维复杂微观结构的可视化[13-25]。例如，Sidhu和Chawla
Global concern over the environmental impact and health effects of Pb-based solders in consumer electronics has led to the development of Pb-free solder alternatives. Sn-rich solders such as Sn–Ag and Sn–Ag–Cu are the most promising Pb-free alloys for replacement of Pb–Sn solder [1]. Many issues relating to their mechanical properties and reliability still need to be addressed. This includes, in particular, their higher melting point and lower ductility [2, 3]. The lower ductility of the solder has important implications because it is directly related to mechanical shock and drop resistance [4]. Recently, small additions of rare-earth elements (RE), such as Ce and La, have been shown to refine the microstructures and improve the mechanical response of Sn-rich solders [5–8]. Due to the complexity of these ternary and quaternary systems, very little information is available on Sn–RE intermetallics formed during solidification. Dudek et al.[7] showed that small La additions (0.1 wt.% and 0.5 wt.%) to Sn–Ag–Cu results in the formation of a stable, homogeneously distributed LaSn3 intermetallic. They showed that the LaSn3 particles are directly responsible for the higher ductility observed in these materials, by allowing microscopic voids to nucleate throughout the solder volume (by minimizing strain localization), and homogenizing the strain in the solder joint. In order to understand how these RE phases may affect the physical, electrical, and mechanical behavior of the solders, it is necessary to adequately characterize the intermetallic size and morphology within the Sn-rich matrix. The LaSn3 intermetallics have a characteristic faceted geometry, also referred to as “Chinese scripts”, which have also been observed in other systems [9–12]. Because of the complex morphology and shape of these particles, two dimensional (2D) representation is not very accurate. In order to characterize the three-dimensional (3D) morphology of the LaSn3 intermetallics, a serial sectioning technique, coupled with computer-aided reconstruction software can be used to visualize the microstructure in 3D. This technique is increasingly being used to visualize complex microstructures in three dimensions [13–25]. For example, Sidhu and Chawla