温度梯度对微尺度焊点液-固界面反应与凝固行为的影响及调控机制

The size of solder joints in advanced packaging is continuously downsizing. In the processes of soldering and thermocompression bonding, a certain temperature gradient may form in micro solder joints due to small temperature fluctuation and directional energy transmission. This can result in an obvious thermomigration (TM) of atoms, which significantly affects the growth of intermetallic compound (IMC) at liquid-solid interface. Moreover, our latest research results showed that a temperature gradient during soldering can induce a preferred orientation of Sn-based solder after solidification. However, the mechanism is not clear yet. In this project, the growth and evolution of interfacial IMC and the dissolution of under bump metallization (UBM) in micro solder joints (<100μm) under temperature gradient will be in situ observed by using synchrotron radiation real-time imaging technology. The law and influence factors of TM of atoms during soldering will be revealed. The theoretical model of interfacial IMC growth under temperature gradient will be established. At the same time, the solidification of micro solder joint will be controlled by regulating atom diffusion using temperature gradient. Combining with microstructure analysis after soldering, the formation mechanism of Sn grains with specific orientation will be clarified and the growth model of Sn grains under temperature gradient will be established. Based on the above research results, new interconnection technology will be developed to control the liquid-solid interfacial reaction and solidification of micro solder joints by using temperature gradient. Finally, the project will provide theoretical and practical guidance for high reliable interconnection of micro solder joints in advanced packaging.

先进封装互连焊点尺寸的持续减小，导致钎焊和热压键合工艺中温度微小波动和能量定向传输都会使微焊点内产生一定的温度梯度，引发原子发生明显的热迁移行为，显著影响液-固界面金属间化合物（IMC）生长；此外，申请人最新研究发现，钎焊时温度梯度还会诱导Sn钎料凝固组织具有明显的择优取向特征，以上相关机制还不清楚。本项目拟利用同步辐射实时成像技术原位观测温度梯度下微尺度焊点（<100μm）液-固界面IMC生长、演变及基体溶解行为，揭示钎焊过程中原子热迁移的规律和影响、控制因素，建立温度梯度下液-固界面IMC生长理论模型；同时，探索利用温度梯度控制原子扩散对微焊点凝固行为进行调控，结合焊后显微组织分析，阐明特定取向Sn晶粒的形成机制，建立温度梯度下Sn晶粒择优生长模型。在此基础上，开发利用温度梯度调控微尺度焊点液-固界面反应与凝固行为的新技术，为实现先进封装微尺度焊点的高可靠互连提供理论和实践指导。

先进封装互连焊点尺寸持续减小，导致钎焊和热压键合工艺中温度微小波动和能量定向传输都会使微焊点内产生一定的温度梯度，引发原子发生明显的热迁移行为，显著影响微焊点液-固界面金属间化合物（IMC）生长及焊后晶粒特征。本项目在钎焊时引用温度梯度，结合同步辐射实时成像技术及微结构与晶体取向分析技术，系统研究了钎焊过程中微焊点金属原子热迁移行为及驱动力、液-固界面反应行为及IMC生长动力学、温度梯度对界面IMC晶粒与Sn晶粒取向的影响及调控。主要研究成果如下：1）基于Cu原子扩散通量关系建立温度梯度下微焊点液-固界面Cu6Sn5生长理论模型，实现界面Cu6Sn5生长与溶解动力学及热端界面Cu6Sn5临界厚度的准确预测；2）发现添加Zn元素可有效抑制热端Cu基体的溶解和冷端界面IMC的生长，阐明热端界面Cu-Zn IMC层脱落的机制，揭示出添加Zn元素提高焊点液-固热迁移抗力的机理；3）发现温度梯度下冷端界面Cu6Sn5晶粒在单晶(111)Cu上可持续外延生长，不仅棱晶状形貌得到保持还具有强烈的织构特征，提出温度梯度下制备择优取向全IMC微焊点的方法；4）揭示出微焊点在温度梯度下凝固形成强烈织构特征Sn晶粒的机制，建立Sn晶粒c轴与温度梯度方向之间的角度关系，为微焊点Sn晶粒取向调控提供新思路。上述研究成果可为实现先进封装微尺度焊点的高可靠互连提供理论和实践指导。共发表学术论文32篇，其中在Appl. Phys. Lett.、J Alloys Compd、Mater. Res. Bull.、Mater. Chem. Phys.等期刊上发表SCI论文24篇，在ECTC等国际学术会议上发表EI论文8篇；授权中国发明专利9项；培养博士研究生毕业2名，硕士研究生毕业4人。