电子封装用Au-20Sn钎料研究进展

Research Progress of Au-20Sn Solder for Electronic Packaging

Au-20Sn钎料具有优异的综合性能且适用于无钎剂钎焊,在微电子器件和光电子器件封装领域占据重要地位。近年来,国内外学者对金锡钎料的研究工作不断深入,金锡钎料制备工艺及焊点可靠性研究已成为电子封装领域的研究热点。然而,Au-20Sn钎料在发展和应用过程中仍受到以下问题的严重制约:第一,Au-20Sn钎料铸态组织中由于存在脆性金属间化合物(IMC),难以采用常规方法加工成形;第二,钎料中贵金属金含量太高(约为80%),导致钎料价格昂贵;第三,Au-20Sn钎料在制造过程中难免会存在夹杂物,影响钎料的使用性能和连接质量;第四,有关Au-20Sn钎料的焊点可靠性研究尚未见系统报道。Au-20Sn钎料铸态组织粗大,IMC分布不均匀,导致合金脆性较大,难以通过传统铸造轧制工艺制备出符合使用要求的Au-20Sn钎料。因此,研究者们不断优化Au-20Sn钎料的制备方法,采用熔铸增韧等工艺有效控制了Au-20Sn钎料制备过程中脆性IMC的形成和分布,大幅提高了Au-20Sn钎料的使用性能。在高可靠性电子封装及芯片封装中,电子元器件通常使用镀层提高可焊性。铜(Cu)、镍(Ni)、金(Au)是电子封装中常用的基板材料和表面金属化层,Au-20Sn钎料与镀层金属形成的焊点界面IMC是实现可靠性连接的基础。目前,有关Au-20Sn钎料与不同镀层金属之间相互作用的研究主要集中在钎焊过程中焊点界面IMC的演变及时效过程中焊点可靠性的影响机制。除了对Au-20Sn钎料制备工艺进行优化和探索不同界面反应外,不少研究者尝试对焊点钎着率和钎缝气密性等可靠性问题进行研究。通过不断优化钎焊工艺参数,制定合理的工艺规范,采用焊点钎着率和钎缝气密性作为评价大功率电子及光电子器件性能及其稳定运行的重要指标。本文重点介绍并分析了Au-20Sn钎料的优点以及其制备的难点,阐述了Au-20Sn钎料在无钎剂封装焊点钎着率和钎缝气密性等可靠性的研究进展,详细讨论了Au-20Sn钎料与不同镀层的界面反应问题,探讨了Au-20Sn钎料研发、制备和应用过程中存在的问题及解决措施,从而为Au-20Sn钎料的生产与应用提供理论指导。

Au-20Sn solder occupies an important position in the microelectronic devices and optoelectronic devices packaging industries due to its excellent comprehensive properties and fluxless packing.In recent years,the research of Au-Sn solder have been focusing on the preparation technology and the reliability of solder joints,which are the hot topic in the field of electronic packaging.However,there are some problems in the development and application of Au-20Sn solder.Firstly,it is difficult to process by conventional me-thod because of the brittle intermetallic compounds in the coarse as-cast microstructure of Au-Sn solder.Secondly,the higher gold content always results in high costs of the solder.Thirdly,the inclusion is unavoidable during the manufacturing process.At last,the reliability of solder joints has not been reported systematically.The coarse as-cast microstructure and inhomogeneous distribution of intermetallic compounds(IMCs)can lead to the brittleness of the solder,which is difficult to prepare Au-Sn solder by traditional casting and rolling process.Therefore,researchers continue to optimize the preparation methods of Au-Sn solder,and use casting toughening and other processes to effectively control the formation and distribution of brittle IMCs in the preparation process,greatly improving the performance of Au-Sn solder.In high reliability electronic packaging and chip packaging industries,the coatings usually can be used to improve the weldability of electronic components.Cu,Ni and Au are commonly used as substrate materials and surface metallization layers in electronic packaging.The IMCs formed between Au-Sn solder and coated metal are the basis for reliable bonding.At present,the research on the interaction between Au-Sn solder and different coated metals are mainly focused on the evolution of IMCs at the interface during soldering and the influence mechanism of solder joint reliability during aging.In addition to optimizing the preparation process and exploring different interfacial reactions of Au-Sn solder,many researchers have attempted to study the reliability of solder joints such as soldering rates and sealing properties.By continuously optimizing the soldering parameters and formulating reasonable process specifications,the soldering rates and sealing properties are used as important indexes to evaluate the performance and stable operation of high power electronic and optoelectronic devices.This paper focuses on analysing the advantages and the difficulties in preparation technology of Au-20Sn solder,and describes the research progress of the reliability of Au-20Sn solder joints in fluxless packaging such as soldering rates and sealing properties.In addition,the interface reactions of Au-20Sn solder and various coating metals are discussed in details.At the same time,some suggestions are put forward which maybe solve the issues mentioned above,which may provide theory guide for the Au-20Sn solder.