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

该项目由数学和物理科学理事会材料研究部和多学科活动办公室支持，旨在研究电子封装无铅焊料的寿命限制热循环、蠕变和微观结构不稳定性，特别涉及倒装芯片（FC）和球栅阵列（BGA）封装。该项目是海军研究生院（NPS）和英特尔（钱德勒，AZ）之间的一个高度杠杆化的合作研究项目。本GOALI提案的目标是：(1)设计一种基于印象蠕变方法的FC和BGA焊料球快速蠕变表征方法，只需最少的样品制备；(2)建立了统一的含相粗化效应的适用于2种具有代表性的组织类型无铅焊料的蠕变模型；(3)对这两种组织类型的无铅合金的焊点进行了全面的蠕变和粗化动力学分析；(4)对微观结构尺度和成分伪影（与将微小体积的焊料附着到其他材料上有关）在热-机械循环（TMC）期间蠕变行为演变中的作用提供基本的机制见解。该项目的一个主要目标是直接测量连接到基板上的单个焊料球的蠕变响应，而不是对凹凸阵列和大块材料进行标准测试。该研究将导致对蠕变动力学在(a)微观结构尺度上的基本现象学依赖性的理解，以及(b)依赖于过程历史的节理成分变化。这些目标是通过材料和工艺参数的系统变化来实现的。该工作建立了包含微观组织粗化效应的封闭统一蠕变规律，可用于焊接接头可靠性评估的有限元模型。单焊点凹痕蠕变是一项具有挑战性的科学研究，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工程过程中的应用。这项工作是多学科的，影响材料科学和力学的实验方面，以及涉及微观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）以及工业对手（英特尔/钱德勒）的专业知识和实验设施。此外，还将与摩托罗拉的专家进行合作。这个GOALI项目的独特之处包括英特尔PI在学术机构花费的时间。学术研究所（NPS）人员（PI，博士后和研究生）计划在工业实验室（英特尔/钱德勒）进行研究，英特尔在此期间支持博士后。该计划的教育和技术影响被评为优越。该项目是NPS和英特尔之间的密切合作，并与摩托罗拉人员进行了二次互动，旨在全面了解微电子封装中无铅焊料的寿命限制方面。该项目在解决基础科学问题的同时，对微电子工业具有实际意义。该研究将(a)开发测试方法和模型，以改善当前的可靠性工程实践，以及(b)生成对行业具有战略重要性的两种无铅焊料的动力学数据。大学人员与工业同行的合作为学生提供了重要的机会。

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.