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

该项目得到了材料研究司和数学与物理科学理事会多学科活动办公室的支持，旨在研究电子封装用无铅焊料的寿命限制热循环、蠕变和微观结构不稳定性，特别是倒装芯片（FC）和球栅阵列（BGA）封装。该项目是海军研究生院（MIT）和英特尔（钱德勒，亚利桑那州）之间的一个高度杠杆化的合作研究计划。本GOALI提案的目标是：（1）基于压痕蠕变方法，设计一种用于FC和BGA焊料球的快速蠕变表征的方法，只需最少的样品制备;（2）开发一种统一的蠕变模型，该模型包含适用于两种代表性微观结构类型的无铅焊料的相粗化效应;（3）获得了属于这些微观组织类型的两种无铅合金焊点的蠕变和粗化动力学数据;和（4）提供微观结构规模和成分人工制品的作用的基本机制的见解（与将微小体积的焊料附着到其他材料相关联）对热机械循环（TMC）期间蠕变行为的演变的影响。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球的蠕变响应，以代替对凸块阵列和散装材料的标准测试。这项研究将导致对蠕变动力学的基本现象学依赖的理解（a）微观结构尺度，和（B）工艺历史依赖的组成变化的关节。这些目标是通过材料和工艺参数的系统变化来实现的。这项工作包括开发封闭形式的统一蠕变规律，包括微观结构粗化的影响，这可能会被纳入到焊点可靠性评估的有限元模型。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对预测工程过程中的半导体电子封装技术产生直接影响。这项工作是多学科的，对材料科学和力学的实验方面有影响，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（英特尔）和工业界对应机构（英特尔/钱德勒）现有的专门知识和实验设施。此外，还与摩托罗拉的专家进行了合作。该GOALI计划的独特之处包括英特尔PI在学术机构花费的时间。 学术研究所的人员（PI、博士后研究员和研究生）计划在工业实验室（英特尔/钱德勒）进行研究，同时英特尔在此期间支持博士后研究员。该计划的教育和技术影响被评为上级。该计划是英特尔和英特尔之间的密切合作，并与摩托罗拉的人员进行了二次互动，以深入了解微电子封装中无铅焊料的寿命限制方面。该项目在解决基本科学问题的同时，对微电子工业具有实际重要性。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，（B）生成两个无铅焊料的动力学数据的战略重要性，以行业。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.