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Study of Nucleation and Solidification of Sn-based Lead-Free Solders

锡基无铅焊料的成核与凝固研究

基本信息

批准号：
1857803
负责人：
金额：
--
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-1857803
关键词：
Study Nucleation Solidification Sn based

项目摘要

The aims of the project are to study and understand the nucleation of BSn in lead free solders and the influence on the nucleation undercooling of reaction layers and phases present in solder joints. Microstructures of solders will also be studied with the aim of developing an understanding of the influence of BSn undercooling on the resulting solidification microstructures in solder joints. Nucleation of BSn in lead-free solder joints commonly exhibits large undercooling of the solid from liquid. Undercooling values of as large as 80K can be obtained in high purity samples, whereas adding certain alloying elements like Ti, Ni, and Co can reduce the nucleation undercooling of BSn to around 10-5K. The nucleation undercooling of BSn, due to the small size of each solder joint, has huge influence on the final properties of the joint, and the solidification microstructure of them. Better in-service lifetimes can be linked to the prevalence of certain microstructures that are determined by the nucleation undercooling of BSn. The approach used here is to combine differential scanning calorimetry (DSC) with novel analytical microscopy techniques (3D imaging of microstructure linked with crystallographic measurements) to extract new insights into microstructure formation in solder joints. The research has the potential to improve the reliability of electronics through controlling solder joint microstructures.The project aims to answer the following questions:-Nucleation of BSn in the presence of Ni3Sn4 intermetallic compound (IMC)Ni3Sn4 is a common IMC present as a reaction layer between Sn and Ni substrates, its effect on nucleation undercooling is known, however the mechanism of BSn nucleation on Ni3Sn4 IMC particles is not known. Electron Backscatter Diffraction (EBSD) study of BSn solidified on Ni joints, and Ni3Sn4 primary IMC crystals will reveal if this nucleation catalysis can be explained crystallorgaphically through an orientation relationship (OR), or any other mechanism.Nucleation of BSn can be studied with the aid of a Differential Scanning Calorimeter (DSC) to observe how the undercooling changes with varying processing parameters, which will be linked to the morphology and features of the Ni3Sn4 reaction layer. The above research will be used, along with past research on nucleation of BSn on Cu6Sn4, to explain why BSn solidifies with a lower undercooling on Ni substrates than on Cu substrates, both of which are used in industry.- Influence of BSn microstructure on the nucleation intercoolingMicrostructures of Sn-3Ag-0.5Cu (SAC305) solder alloy will be studied at different nucleation undercooling values to report the relationship in great detail. The use of optical microscopy combined with EBSD and Focused Ion Beam (FIB) milling on SAC305 samples will reveal the 3D microstructure of the various solidification morphologies.The morphologies will be used to better understand the nucleation and growth of BSn from liquid, and hopefully allow better control of BSn microstructures in industrial electronic joints. - Nucleation kinetics of BSnDSC studies of BSn nucleation in various solder alloys, and solder joints can be used to develop a quantitative framework on BSn nucleation, which will hopefully be useful in quickly assessing the mechanism of nucleation on different alloys.The research will aim to apply theoretical nucleation models to real industrial systems, with the aim of developing the framework.

该项目的目的是研究和了解BSn在无铅焊料中的成核以及焊点中存在的反应层和相对成核过冷的影响。还将研究焊料的显微组织，目的是了解BSn过冷对焊点凝固显微组织的影响。无铅焊点中BSn的成核通常表现为固体与液体的过冷。高纯度样品的过冷度可达80K，而添加Ti、Ni、Co等合金元素可使BSn的过冷度降至10-5K左右。由于每个焊点的尺寸较小，BSn的形核过冷对焊点的最终性能及其凝固组织有很大的影响。较长的使用寿命可能与某些显微组织的流行有关，这些组织是由BSn的成核过冷决定的。这里使用的方法是将差示扫描量热法（DSC）与新型分析显微镜技术（与晶体学测量相关联的微观结构的3D成像）相结合，以提取对焊点微观结构形成的新见解。该研究具有通过控制焊点微结构来提高电子产品可靠性的潜力。- Ni3Sn4金属间化合物（IMC）存在下BSn的成核Ni3Sn4是一种常见的IMC，作为Sn和Ni衬底之间的反应层，其对成核过冷的影响是已知的，但BSn在Ni3Sn4 IMC颗粒上的成核机制尚不清楚。电子背散射衍射（EBSD）研究BSn在Ni接头和Ni3Sn4原生IMC晶体上的凝固，将揭示这种成核催化是否可以通过取向关系（OR）或任何其他机制来解释。利用差示扫描量热仪（DSC）可以研究BSn的成核，观察过冷度随工艺参数的变化，这与Ni3Sn4反应层的形貌和特征有关。上述研究将与过去对BSn在Cu6Sn4上成核的研究一起用于解释为什么BSn在Ni衬底上的过冷度比在Cu衬底上的过冷度低，这两种材料都用于工业。研究Sn-3Ag-0.5Cu （SAC305）钎料合金在不同成核过冷值下的显微组织，详细报告两者之间的关系。利用光学显微镜结合EBSD和聚焦离子束（FIB）铣削技术对SAC305样品进行了三维显微分析，揭示了不同凝固形态的微观结构。这些形貌将用于更好地了解BSn在液体中的形核和生长，并有望更好地控制工业电子接头中BSn的微观结构。BSnDSC研究BSn在各种钎料合金和焊点中的成核动力学，可用于建立BSn成核的定量框架，有望有助于快速评估不同合金的成核机制。研究的目的是将理论成核模型应用于实际工业系统，目的是开发框架。