βSn组织和晶粒取向对焊锡接头可靠性影响机理研究进展

Research Progress on the Influence Mechanisms ofβSn Structure and Grain Orientation on the Reliabilities of Solder Joints

焊锡接头是集成电路中整合连接不同电子元器件的关键部位,在高电流密度、高低温循环、机械加载等恶劣服役条件下,会发生电迁移、热循环和机械疲劳等失效。由于单个焊锡接头仅包含少数取向随机的βSn晶粒且βSn具有严重的各向异性,焊锡接头的三类主要失效均受到βSn组织和晶粒取向的强烈影响。本文基于βSn的各向异性物理特性,深入分析了焊锡接头的电迁移、热循环及机械剪切疲劳失效机理,总结了βSn组织和晶粒取向影响各类失效的规律,明确了当βSn晶粒的c轴平行于电流方向时,焊锡接头的抗电迁移性能最差,而抗热循环性能最佳;但部分研究表明当βSn晶粒c轴垂直于基板时,焊锡接头的抗热循环性能较差;βSn组织和晶粒取向对焊锡接头抗机械剪切疲劳性能影响的研究较少,但已有的研究也表明两者之间存在较强关联。鉴于βSn组织和晶粒取向对焊锡接头可靠性的强烈影响,本文还梳理了近年来在焊锡接头βSn组织和晶粒取向调控方面的研究进展,包括利用异质形核剂、多晶及单晶Co基板、磁场及温度梯度等多种调控方法。最后,本文讨论了未来进一步提高焊锡接头可靠性的研究方向。

Electronic solder joints that interconnect different components are the key parts in integrated circuits.Since solder joints service with high current density,thermal cycling,and mechanical loading,they commonly suffer from electromigration,thermomechanical fatigue,and mechanical fatigue.A typical solder joint usually contains fewβSn grains with random orientations,which causes that the three main reliabilities of solder joints are heavily influenced byβSn structure and grain orientation,consideringβSn is physically anisotropic.This paper bases on the key physical properties ofβSn,analyzes the failure mechanisms of electromigration,thermomechanical fatigue,and mechanical fatigue of solder joints,summarizes the effects ofβSn structure and grain orientation on these failures,confirms that when the c-axis ofβSn is parallel to the current direction,the solder joints have the worst resistance to electromigration but the best thermal cycling performance;however,some studies have shown that whenβSn c-axis is perpendicular to the substrate,the solder joints exhibit poor thermomechanical performance;there are few studies on the influence ofβSn structure and grain orientations on the mechanical shear fatigue resistance of solder joints,but some published studies indicated that there is a strong correlation between them.In view of the strong influence ofβSn structure and grain orientations on the reliabilities of solder joints,this paper also outlines the research progresses on controllingβSn structure and grain orientations,including using heterogeneous nucleating agents,polycrystalline and single-crystal Cobalt substrates,magnetic fields,and temperature gradients.Finally,this paper discusses the required future researches for improving the reliabilities of solder joints.