基于钎料液态结构演变的钎焊界面反应机理研究

In the process of electronic packaging, interfacial reaction during soldering is the basic science issue that can achieve reliable interconnect of solder joint. Since the solder is in liquid state all along during soldering, its liquid structure has strong interaction with the interfacial reaction. But the effect of flux of element from solder on interfacial reation is not included in the traditional theory of interfacial reaction. This causes the deviation between real growh behaviour of interfacial intermetallic compound (IMC) and traditional growth model. The related mechanism needs further study. Therefore, in this project, the research on mechanism of interfacial reaction during soldering is proposed based on liquid structure evolution of solder. The liquid structure of solders will be studied by using high-temperature X-ray diffraction technology, to obtain the type of ordered cluster formed from Cu, Ag, Zn and Ni in liquid solder, illustrate the change in form, size and amount of the ordered cluster with composition and temperature, and fed back the change information of flux of element from solder. By combining with the growth behaviour of interfacial IMC of the solder joint, the correlation between liquid structure evolution of solder and interfacial reaction during soldering will be clarified, and the mechanism of liquid structure of solder on the nucleation, growth and transformation of interfacial IMC will be revealed. The results of this project will greatly contribute to develop and enrich the theory of interface reaction during soldering, and provide directions for controlling the formation and growth of interfacial IMC by regulating the ordered clusters.

在电子封装技术中，钎焊界面反应是实现焊点可靠互连的基础科学问题。钎焊时钎料始终处于液相，其液态结构与界面反应存在强烈的相互作用。但传统界面反应理论忽略了液态钎料中合金元素通量对界面反应的影响，导致实际界面金属间化合物（IMC）生长行为与传统生长模型存在偏差，相关机理亟需深入研究。因此，本项目提出基于钎料液态结构演变探索钎焊界面反应机理的研究思路，主要通过高温X射线衍射技术在线研究钎焊过程中钎料的液态结构，获得Cu、Ag、Zn、Ni等主要合金元素在液态钎料中形成有序团簇的类型，明确有序团簇形成、尺寸和数量随成分和温度的变化规律，反馈液态钎料合金元素通量变化的信息，结合焊点界面IMC的生长行为，阐明钎料液态结构演变与界面反应的相关性，揭示钎料液态结构对界面IMC形核、生长和转变的作用机理。研究成果有助于丰富和发展钎焊界面反应理论，为通过调控有序团簇控制界面IMC形成与生长提供理论指导。

钎焊界面金属间化合物（IMC）的生长与演变行为是先进封装微互连制造中的关键科学问题。本项目首先利用同步辐射荧光EXAFS技术对Sn/Cu钎焊界面反应进程中液态Sn钎料中Cu原子周围近邻结构进行了原位研究，获得了液态Sn钎料的结构信息，通过对扩展边数据进行拟合分析，得到了Cu原子周围原子团簇随温度的变化规律，建立了钎料液态结构与界面IMC形核生长的相关性。同时，在钎焊反应过程中引入温度梯度，利用同步辐射原位成像技术研究了微焊点中Cu、Ni、Zn等合金元素在温度梯度作用下的热迁移规律，观测到微焊点冷、热端界面IMC的非对称生长行为和金属基体的非对称溶解行为，并通过原子扩散通量分析了热迁移对微焊点钎焊界面反应行为的影响规律，获得了界面金属间化合物的生长动力学和基体金属的溶解动力学。此外，还发现温度梯度增强了微焊点中的Cu-Ni交互作用，使得有序原子团簇的数量和尺寸增大，从而显著促进了钎焊界面IMC的形核和生长。最后，研究还发现钎料中引入Zn元素使微焊点热端界面形成稳定的Cn-Zn化合物，可显著抑制热迁移条件下冷端界面金属间化合物的过度生长并降低热端Cu基体的快速溶解。