GOALI: Creep and Microstructural Coarsening of Lead-Free Solders in Micro-Electronic Packaging Applications

该项目由材料研究司和数学和物理科学局多学科活动办公室支持，旨在研究电子封装用无铅焊料的极限热循环、蠕变和微观结构不稳定性，特别是倒装芯片(FC)和球栅阵列(BGA)封装。该项目是海军研究生院(NPS)和英特尔(亚利桑那州钱德勒)之间高度利用的合作研究计划。该方案的目标是：(1)设计一种基于印模蠕变方法的FC和BGA焊球的快速蠕变表征方法；(2)建立一个统一的蠕变模型，该模型考虑了相粗化的影响，适用于两种典型的微结构类型的无铅焊料；(3)生成属于这些微结构类型的两种选定的无铅合金焊点的全面蠕变和粗化动力学数据；以及(4)为微观结构尺度和成分伪影(与将微小焊料附着到其他材料上)在热机械循环(TMC)期间蠕变行为演变中的作用提供基本的力学见解。该项目的一个主要目标是直接测量连接到衬底上的单个焊球的蠕变响应，而不是对凸起阵列和散装材料进行标准测试。这项研究将有助于理解蠕变动力学在(A)微观结构尺度上的基本唯象依赖性，以及(B)与过程-历史相关的接头成分变化。这些目标是通过系统地改变材料和工艺参数来实现的。这项工作建立了包括微结构粗化效应在内的封闭形式的统一蠕变定律，这些定律可以并入焊点可靠性评估的有限元模型中。单个焊料凸点的压痕蠕变是一项具有挑战性的科学工作，该项目的成功完成将直接影响半导体电子封装技术在预测性工程过程中的应用。这项工作是多学科的，影响到材料科学和力学的实验方面，以及涉及微结构和有限元方面的预测建模工作。该项目利用了学术机构(NPS)和工业同行(Intel/Chandler)可用的专业知识和实验设施。此外，还寻求与摩托罗拉的专家进行合作。这一目标计划的独特之处包括英特尔PI在学术机构所花费的时间。研究院(NPS)的人员(PI、博士后研究员和研究生)计划在工业实验室(Intel/Chandler)进行研究，而英特尔在此期间为博士后研究员提供支持。该计划的教育和技术影响被评为一流的。该计划是NPS和英特尔之间的密切合作，与摩托罗拉的人员进行二次互动，有助于深入了解微电子封装中无铅焊料的寿命限制方面。该项目对微电子工业具有实际意义，同时解决了基本的科学问题。这项研究将(A)开发测试方法和模型，以改进当前的可靠性工程实践，并(B)生成对该行业具有战略重要性的两种无铅焊料的动力学数据。大学人员与行业同行的合作为学生提供了一个重要的机会。

This project, which is supported by the Division of Materials Research and the Office of Multidisciplinary Activities in the Directorate for Mathematical and Physical Sciences, aims to investigate the life limiting thermal cycling, creep and microstructural instability of lead-free solders for electronic packaging with special reference to flip-chip (FC) and ball-grid array (BGA) packages. The project is a highly leveraged collaborative program of research between Naval Postgraduate School (NPS) and Intel (Chandler, AZ). The objectives of this GOALI proposal are to (1) devise a methodology for rapid creep characterization of FC and BGA solder balls with minimal sample preparation, based on the impression creep approach; (2) develop a unified creep model incorporating the effect of phase coarsening applicable to lead-free solders of 2 representative microstructural types; (3) generate comprehensive creep and coarsening kinetics data for solder joints of 2 selected lead-free alloys belonging to these microstructural types; and (4) provide fundamental mechanistic insight into the roles of microstructural scale and compositional artifacts (associated with attaching tiny volumes of solder to other materials) on the evolution of creep behavior during thermo-mechanical cycling (TMC). A major goal of the project is to directly measure the creep response of individual solder balls joined to a substrate, in lieu of the standard tests on bump arrays and bulk materials. The study will lead to an understanding of the fundamental phenomenological dependence of creep kinetics on the (a) microstructural scale, and (b) process-history dependent compositional variations of the joints. These goals are achieved by a systematic variation of material and process parameters. The work constitutes developing closed-form unified creep laws including microstructural coarsening effects, which may be incorporated into finite element models for solder-joint reliability assessment. The impression creep of single solder bumps is a challenging scientific effort and the successful completion of the project will have direct impact on semiconductor electronic packaging technology in predictive engineering processes. The work is multidisciplinary with impact on experimental aspects in materials sciences and mechanics, as well as predictive modeling efforts involving microstructural as well as finite element aspects. The project takes advantage of the expertise and experimental facilities available at the academic institution (NPS) as well as industrial counterpart (Intel/Chandler). In addition, collaboration with experts at Motorola is pursued. The unique aspect of this GOALI program includes the time spent by the Intel PI at the academic institution. The personnel (PI, post-doctoral fellow and graduate students) from the academic institute (NPS) plan to perform studies at the industrial laboratory (Intel/Chandler) while Intel supports the post-doctoral fellow during that time. The educational and technological impacts of the program are rated superior.The program is a close collaboration between NPS and Intel with secondary interactions with personnel at Motorola with implications to developing a thorough understanding of the life-limiting aspects of lead-free solders in microelectronic packaging. The project has practical importance to the microelectronic industry while addresses basic scientific issues. The study will (a) develop testing methodologies and models for improving current reliability engineering practices, and (b) generate kinetics data for two lead-free solders of strategic importance to the industry. The collaboration of the university personnel with industrial counterparts provides a significant opportunity for students.