单晶UBM在电子封装微互连中的研究进展

Research progress of single crystal UBM in electronic packaging micro-interconnects

摘要:

3D封装是未来电子封装制造技术领域的重要发展方向,3D封装中微凸点的尺寸将急剧降低,此时,芯片凸点下金属层(UBM)可能仅包含几个甚至单个晶粒。因此,UBM的晶体取向对界面金属间化合物(IMC)的形核和生长过程将具有显著影响,而界面IMC的特性会直接影响到凸点微/纳尺度互连的可靠性。因此,以单晶作为UBM研究界面物质的传输与IMC的生长规律,具有重要的理论和应用价值。本文对近年来以单晶Cu、Ni和Ag作为UBM焊点的界面反应进行综合分析,总结了单晶UBM上特殊形貌IMC晶粒的形成条件、界面IMC与单晶基体的位向关系、IMC的生长动力学过程、柯肯达尔空洞的形成规律、单晶UBM上IMC的晶体取向调控方法及晶体取向对无铅焊点力学性能和可靠性的影响,为评价单晶UBM凸点的力学性能和可靠性及提供指导。

Abstract:

With the development of electronic packaging and manufacturing technology to high performance and miniaturization, 3D (three dimensional) packaging is an important development direction in the field of future electronic packaging and manufacturing technology. 3D packaging with high-density and high-reliability is the key technology for the transformation and upgrading of the IC (integrated circuit) industry. 3D packaging will reduce the size of chip bump interconnection interface to the sub-micron or nano level, making the size of the UBM (under-bump metallization) pad rapidly decreasing and may contain only a few or even a single grain. The roof-type Cu₆Sn₅ grain formed by the interfacial reactions on single crystals (001) Cu and (111) Cu shows preferred orientation, resulting in different electrical properties, strength and hardness. Therefore, the crystal orientation of the UBM will have a significant effect on the nucleation and growth process of IMCs (interfacial intermetallic compounds), and the properties of interfacial IMCs will directly affect the reliability of bumps in the micro/nano-scale interconnects. Therefore, using single crystal as UBM to study the transport of interfacial materials and the growth pattern of IMCs has important theoretical and application values. In this paper, the interfacial reaction of solder joints with single crystal Cu, Ni and Ag in recent years is comprehensively analyzed, and the formation conditions of IMC grains with special morphology on single crystal UBM, the orientation relationship between IMC and single crystal substrate, the growth kinetic process of IMC, the formation law of kirkendall voids, the crystal orientation control method of IMC on single crystal UBM, and the influence of crystal orientation on the mechanical properties and reliability of lead-free solder joints are summarized. It provides guidance for evaluating the mechanical properties and reliability of single crystal UBM.