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.