Whisker Formation in Sn Coatings on Cu: Fundamental Mechanisms and Approaches to Mitigation

铜上锡镀层中晶须的形成：基本机制和缓解方法

• 批准号: 0856229
• 负责人: Eric Chason
• 金额: $ 27.04万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-01 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0856229&HistoricalAwards=false
• 关键词: Whisker; Formation; Sn; Coatings; Cu

This Award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARY:Sn-based alloy coatings have been used for many years in the manufacture of electronic components to enhance solderability and prevent corrosion. Recent environmental legislation has forced the elimination of Pb in these parts, which has enabled the re-emergence of tin whiskers, i.e. thin filaments that grow from the surface and can ultimately cause short circuits. Whisker-induced failures have been documented in numerous systems (satellites, aviation systems, medical devices, etc.) and represent a significant risk for manufacturers of high reliability systems. Despite significant research, many fundamental aspects of whisker formation are still not understood. Part of the difficulty is that multiple materials processes interact to create the whiskers (e.g. interdiffusion, phase transformations, stress generation and relaxation, etc.) so that it is difficult to identify the underlying mechanisms. Moreover, many processing variables (film thickness, grain size, plating conditions, etc.) have been shown to play a role in whisker formation. This makes it difficult to compare the results of different studies done under different conditions. The proposed research program is designed to identify the fundamental mechanisms that govern whisker formation by focusing on the several questions: 1. Which processes control stress in the Sn layer? 2. How is the stress evolution related to whisker formation? 3. What causes whiskers to nucleate at particular sites? 4. How does the addition of Pb prevent whisker formation? 5) How can we use our understanding of whisker formation to prevent their occurrence? Real-time thin film diagnostics will be used to quantify the simultaneous temporal evolution of several critical parameters such as film stress, intermetallic phase formation and whisker density, using carefully controlled samples. These kinetic studies will be complemented by electron microscopy studies to determine the underlying atomic-scale mechanisms behind these processes as well as whisker nucleation. Microstructure, film thickness, and Sn content in Pb-Sn alloys will be varied systematically to isolate and identify different kinetic processes that contribute to whisker formation. Analytical models will be used to interpret the measurements and to develop predictive capability for assessing reliability.NON-TECHNICAL SUMMARY:The formation of Sn whiskers, i.e. thin filaments of pure tin that grow from the surface of Sn-rich lead-free alloys, is a serious concern in Pb-free electronics manufacturing because they can ultimately cause short circuits in electronic components. The proposed research program is designed to identify the fundamental mechanisms that govern whisker formation by identifying the processes that control stress in Sn-rich layers in Sn-containing alloys, learning how the stress evolves and relates to whisker formation, finding out what promotes the nucleation of whiskers and why the addition of Pb prevents whisker formation. An ultimate objective is to discover how the acquired understanding of whisker formation can be used to prevent their occurrence so that new coatings and Sn-rich alloys can be prepared with predictable reliability. An informal collaboration with the EMC Corporation will broaden the knowledge of students as well as the industrial participants. These participants will expose the students to problem solving in a real-world environment, where issues such as economics can be as important as technical issues. This work will involve the education of graduate and undergraduate students in experiments and modeling of a fundamental materials problem. Involvement of under-represented minorities and women will be enhanced by recruiting and a collaboration-student exchange with the Florida State University-Florida A&M University (an HBCU) association. K-12 educational outreach will be achieved by working with teachers to develop modules on thin film stress to be used in school visit program at Brown University. These outreach activities will be leveraged through coordination with the Brown MRSEC educational programs.

该奖项由2009年美国复苏和再投资法案（公共法111-5）资助。技术总结：锡基合金涂层多年来一直用于电子元件的制造，以增强可焊性并防止腐蚀。最近的环境立法已经强制消除这些部件中的铅，这使得锡须重新出现，即从表面生长并最终导致短路的细丝。许多系统（卫星、航空系统、医疗设备等）都记录了晶须引起的故障。并且对于高可靠性系统的制造商来说代表了显著的风险。尽管有大量的研究，晶须形成的许多基本方面仍然没有被理解。部分困难在于多种材料工艺相互作用以产生晶须（例如，相互扩散、相变、应力产生和松弛等）。因此很难确定潜在的机制。此外，许多工艺变量（膜厚度、晶粒尺寸、电镀条件等）已经显示在晶须形成中起作用。这使得很难比较在不同条件下进行的不同研究的结果。建议的研究计划的目的是确定的基本机制，管理晶须形成的几个问题集中：1。哪些工艺控制Sn层中的应力？2.应力的演变与晶须的形成有什么关系？3.是什么导致晶须在特定位置成核？4.铅的加入如何防止晶须的形成？5)我们如何利用我们对晶须形成的理解来防止它们的发生？实时薄膜诊断将被用来量化的几个关键参数，如薄膜应力，金属间相的形成和晶须密度的同时时间演变，使用精心控制的样品。这些动力学研究将通过电子显微镜研究来补充，以确定这些过程以及晶须成核背后的原子尺度机制。Pb-Sn合金的微观结构、薄膜厚度和Sn含量将系统地变化，以分离和识别有助于晶须形成的不同动力学过程。分析模型将用于解释测量结果，并开发评估可靠性的预测能力。非技术总结：Sn晶须的形成，即从富含Sn的无铅合金表面生长的纯锡细丝，是无铅电子制造中的一个严重问题，因为它们最终会导致电子元件短路。拟议的研究计划的目的是确定的基本机制，管理晶须形成的过程中，控制应力在富锡层的含锡合金，学习如何应力的演变，并涉及晶须的形成，找出什么促进晶须的成核和为什么添加铅防止晶须的形成。最终目标是发现如何获得晶须形成的理解可以用来防止其发生，以便可以以可预测的可靠性制备新的涂层和富锡合金。与EMC公司的非正式合作将扩大学生和工业参与者的知识。这些参与者将让学生在现实世界的环境中解决问题，其中经济学等问题与技术问题一样重要。这项工作将涉及教育研究生和本科生在实验和建模的基本材料问题。代表性不足的少数民族和妇女的参与将通过招聘和与佛罗里达州立大学-佛罗里达A M大学（HBCU）协会的合作学生交流来加强。K-12教育推广将通过与教师合作开发薄膜压力模块来实现，这些模块将用于布朗大学的学校访问计划。这些推广活动将通过与布朗MRSEC教育计划的协调来发挥作用。