面向高密度互连的Sn单晶粒微凸点热疲劳微观行为研究

In order to response to the challenge of ever-growing I/O density, the Pb-free solder bumps continue to shrink in volume for the high density solder interconnects. Finally, the solder bulk layer would only contain one Sn grain due to the solder bump volume shrinkage. Herein, this kind of solder bumps is called Sn single grain micron solder bumps. However, due to the lack of grain boundary coordination in the deformation, Sn single grain micron solder bumps would show much different microscopic behaviors in thermal fatigue, compared with the solder bumps containing limited or multiple grains. Therefore, it becomes a new research field in the reliability of high density solder interconnects. In present project, the Sn single grain micron solder bumps array with a 30×30μm pitch will be used as the research subject. EBSD,SEM and C-SAM are applied to study the microscopic behaviors of the research subjects.The aims of the present project are to reveal the microstructural evolution rule, deformation mechanism and failure modes of the Sn single grain solder bump during the thermal fatigue process, to establish the relationship model of faluire cycles and shear strain range, and to establish the weibull model of the accumulated failure proportion and thermal cycles. The proposal will explore a new research space for the reliability assessment of high density solder interconnects. And it is much valuable in the academic study and practical application.

为了应对芯片I/O密度日益攀升的挑战，在高密度互连结构中，无铅微凸点的体积不断缩小，并最终形成焊料层中仅含一个Sn晶粒的微凸点。在本项目中，将该类微凸点称之为Sn单晶粒微凸点。由于缺少晶界的变形协调作用，Sn单晶粒微凸点的热疲劳微观行为将会与多晶粒体系或有限个数晶粒体系的微凸点存在很大差异，因而，成为高密度互连可靠性研究的新领域。本项目将以30×30μm的Sn单晶粒微凸点阵列为研究对象，采用电子背散射衍射分析技术(EBSD)、电子扫描显微镜(SEM)及超声波扫描显微镜(C-SAM)等微观分析方法，揭示Sn单晶粒微凸点在热疲劳过程中的微观组织演变规律、热疲劳变形机制和热疲劳失效模式；建立Sn单晶粒微凸点阵列的失效周期-剪切应变范围关系模型，及其累积失效率-循环周次Weibull模型。本课题将为高密度互连焊点的可靠性评估研究拓展一个新领域，具有较高的学术研究价值和实际应用价值。

为了应对芯片I/O密度日益攀升的挑战，在高密度互连结构中，无铅微凸点的体积不断缩小，并最终形成焊料层中仅含一个Sn晶粒的微凸点，称之为Sn单晶粒微凸点。本项目研究了Sn单晶粒微凸点的形成条件、微观组织结构、各向异性力学特性、蠕变力学性能和断裂失效机制。获得了Sn单晶粒剪切应变速率敏感度指数m=0.1和蠕变速率敏感度指数m=0.0848两个关键力学参数；研究发现由于单晶粒各向异性和缺乏晶界变形协调，Sn单晶粒微凸点的微观力学行为与多晶粒体系存在很大差异。本项目的研究成果为高密度互连焊点的可靠性评估提供了重要的技术支持。