Zhang Yuanxiang, Zhang Jicheng, Wang Yong, Fang Yike
Key Laboratory of Air-Driven Equipment Technology of Zhejiang Province, Quzhou University, Quzhou 324000, China.
College of Mechanical and Electrical Engineering, China Jiliang University, Hangzhou 310018, China.
Micromachines (Basel). 2022 Jun 16;13(6):953. doi: 10.3390/mi13060953.
The development of advanced electronic devices leads to highly miniaturized interconnect circuits (ICs), which significantly increases the electromigration (EM) phenomenon of solder and circuits due to higher current density. The electromigration of solder joints under high current density has become a severe reliability concern in terms of microelectronic product reliability. The microstructure of the solder plays an important role in the electromigration induced degradation. In this study, Sn-3.0Ag-0.5Cu solder bumps with Ni/Au under bump metallization (UBM) layer were fabricated and electromigration acceleration tests were conducted under current density of 1.4 × 10 A/cm and 120 °C to investigate the effect of grain structure and Ni/Au-UBM layer on EM-induced failure. Grain structures of solder bumps were determined by utilizing the Electron Backscatter Diffraction (EBSD) technique, and single-crystal solder, single-crystal dominated solder, and polycrystalline solder are observed in different test samples. According to the Scanning Electron Microscope (SEM) images, it is observed that the Ni/Au-UBM layer of the Cu pad can inhibit atom diffusion between solder bump and Cu pad, which reduces the consumption of Cu pad but causes a large void and crack at the interface. The EM lifetime of single crystal solder bumps is lower than that of polycrystalline solder bumps when the c-axis of single crystal solder bumps is perpendicular to the electron flow direction. Additionally, the single crystal structure will increase the brittleness of the solder bump, and cracks are easily generated and expanded under the stress caused by the mismatch of thermal expansion coefficients between the solder bump and Ni/Au-UBM layer near Cu pad. Polycrystalline solder bumps with a higher misorientation angle (15-55°) have a higher atom diffusion rate, which will result in the acceleration of the EM-induced failure.
先进电子设备的发展导致互连电路（IC）高度小型化，由于电流密度更高，这显著增加了焊料和电路的电迁移（EM）现象。就微电子产品可靠性而言，高电流密度下焊点的电迁移已成为一个严重的可靠性问题。焊料的微观结构在电迁移引起的退化中起着重要作用。在本研究中，制备了在凸块下金属化（UBM）层具有Ni/Au的Sn-3.0Ag-0.5Cu焊料凸块，并在1.4×10 A/cm的电流密度和120°C下进行电迁移加速试验，以研究晶粒结构和Ni/Au-UBM层对电迁移诱导失效的影响。利用电子背散射衍射（EBSD）技术确定了焊料凸块的晶粒结构，在不同的测试样品中观察到了单晶焊料、单晶主导焊料和多晶焊料。根据扫描电子显微镜（SEM）图像，观察到Cu焊盘的Ni/Au-UBM层可以抑制焊料凸块与Cu焊盘之间的原子扩散，这减少了Cu焊盘的消耗，但在界面处产生了大的空洞和裂纹。当单晶焊料凸块的c轴垂直于电子流动方向时，单晶焊料凸块的电迁移寿命低于多晶焊料凸块。此外，单晶结构会增加焊料凸块的脆性，在焊料凸块与Cu焊盘附近的Ni/Au-UBM层之间热膨胀系数不匹配所引起的应力作用下，容易产生并扩展裂纹。取向差角较高（15 - 55°）的多晶焊料凸块具有较高的原子扩散速率，这将导致电迁移诱导失效加速。
