纳米复合无铅钎料焊点可靠性及界面生长动力学机理研究

The growth mechanism of nanocomposite of lead-free solder is a key problem to be solved in electronic packaging field. Through the experimental and thermodynamic calculation, the project investigates the wettability law of nanocomposite of lead-free solder and reveals the mechanism of nanoparticles on wettability of nanocomposite of lead-free solder. Scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD) and other analysis methods are applied to observe the change rules of interface morphology, phase structure, formation of void and microstructural evolution. Alloying effect and Ostwald ripening theory are used to study the characteristic of interfacial microstructure, diffusion mechanism is applied to research the cause of Krikendall holes’ formation. Combined the theory of adsorption and heterogeneous nucleation, we reveal the growth mechanism of interface from both atomic and microcosmic scale. According to interfacial morphological characteristics, we estabilish the growth kinetics curve of intermetallic compound (IMC) layer. With the aid of Fick diffusion law, we research both the atomic interdiffusion between solder and pad and grain boundary diffusion. Based on the diffusion, the growth kinetics of IMC is proposed in order to control the thickness of IMC effectively. Most important of all, it can improve the reliability of solder joints of nanocomposite of lead-free solder reinforced with nanoparticles. The research will not only deepen the understanding of the mechanism and kinetics of interface growth, but also provide theoretical basis for promoting the development of lead-free solder. Moreover, it can provide a strong guarantee for the rapid development of electronic information industry.

纳米复合无铅钎料的生长机理是电子封装行业亟待解决的关键问题。本项目通过实验和热力学计算，探索纳米复合无铅钎料的润湿性规律，揭示纳米颗粒对复合钎料润湿性的作用机理。利用SEM、EDX、XRD等多种分析手段，分析纳米复合无铅钎料的界面形态、相结构、界面孔洞的形成及组织演化规律，利用合金化效应及Ostwald熟化理论研究界面组织结构的变化特征。运用扩散机制研究孔洞的形成内因。结合吸附理论、非均质形核理论等从原子尺度及微观尺度揭示界面的生长机理。根据界面形态特征，建立金属间化合物（IMC）层厚度生长动力学曲线，运用Fick扩散定律研究钎料和基板原子的互扩散以及晶界处的扩散，揭示纳米复合无铅钎料IMC生长动力学过程，以期有效控制界面IMC层厚度，提高焊点的可靠性。本项研究不仅会加深界面生长的机理和动力学的理解，而且对促进无铅钎料的开发提供理论依据，并且为电子信息产业的快速发展做好坚实后盾。

无铅钎料焊点的可靠性问题可直接导致电子元器件失效，是制约电子器件应用的关键问题之一。本项目针对焊点可靠性问题，制备了不同含量的ZnO纳米复合Sn-3.0Ag-0.5Cu无铅钎料，从润湿性、熔化特性、IMC生长行为、力学性能等方面对可靠性进行分析，旨在提高焊点的可靠性，探明ZnO纳米复合无铅钎料的润湿机制，揭示焊点界面IMC层的生长机理。. 添加ZnO纳米颗粒（0-2.0wt%）后，钎料的润湿性显著提高，随着ZnO颗粒含量的增加，润湿性能降低。ZnO纳米颗粒的最佳添加量为0.5wt%，ZnO纳米颗粒的添加对熔化特性影响不明显。. 对不同含量的ZnO纳米复合SAC305钎料进行高温存储研究，结果表明，添加ZnO纳米颗粒后，界面IMC层比较平整，IMC层厚度减小，且界面Kirkendall空洞减少。IMC层的厚度和Cu6Sn5颗粒的尺寸随着ZnO含量的增加而增大，表明ZnO纳米颗粒的添加有效抑制了IMC的生长。结合润湿性和力学性能分析，ZnO纳米颗粒的最佳添加量为0.5wt%。. IMC层的厚度和IMC颗粒的尺寸随着存储时间的延长而增大，表明IMC在存储过程中发生了粗化。通过分析，揭示了IMC既纵向生长又横向生长，纵向生长由体扩散控制，Cu6Sn5颗粒的横向生长由晶界扩散控制，Cu6Sn5颗粒的横向生长方程为d=1.70t^0.38。.ZnO纳米颗粒的作用机理体现在两方面：一、纳米颗粒的吸附原理，ZnO颗粒作为吸附质被吸附在金属间化合物颗粒表面来降低其表面能，提高润湿性，抑制界面IMC层生长；二、ZnO颗粒的阻碍扩散作用，纳米复合钎料的结合能比SAC305高，界面IMC的生长需要克服其高能障即激活能Q，因而抑制了界面IMC的生长，即激活能Q决定着IMC的生长速率。纳米复合钎料的优良表现推进无铅钎料进入纳米时代，纳米复合钎料的研究不仅推进和丰富了纳米钎料的理论发展，而且促进了电子封装领域纳米复合钎料的工业应用。